hydrogen thesis

8/14/2019 Hydrogen Thesis

1/92

STUDIES ON HYDROGEN CHEMISORPTION ON TITANIUM NANO

POWDER

Dissertation submitted to

KANCHI MAMUNIAR CENTRE !OR POST GRADUATE STUDIES

"AUTONOMOUS#

PUDUCHERRY$%&' &&(

In Partia) !u)*i))ment o* t+e Re,uirements

!or t+e a-ard o* t+e de.ree o*

MASTER O! PHI/OSOPHY

IN

PHYSICS

01

K2SUSAINATHAN

"Re.ister No3 454%4&6#

Under t+e .uidan7e o*

Dr2 RAMADASS8 M2 S728 P+2 D2

(Research guide and Supervisor)

DEPARTMENT O! PHYSICS

KANCHI MAMUNIAR CENTRE !OR POST GRADUATE STUDIES

"AUTONOMOUS#

PUDUCHERRY$%&'&&(

1| P a g e


2/92

Dr 2RAMADASS8 M2S728 2P+2D8

Asso7iate 9ro*essor8

De9artment o* 9+1si7s8

K2 M2 C2 P2 G2 Studies "Autonomous#8

Pudu7+err1 $ %&' &&(2

0ONA!IDE CERTI!ICATE

This is to certify that the dissertation titled :STUDIES ON HYDROGEN

CHEMISORPTION ON TITANIUM NANO POWDER submitted to KANCHI

MAMUNIAR CENTRE !OR POST GRADUATE STUDIES "AUTONOMOUS#8

PUDUCHERRYis a bonafide research work carried out by Mr2 K2 SUSAINATHAN "Re.ister

No3 454%4&6# for the award of the degree of MASTER O! PHI/OSOPHY IN PHYSICS

under my guidance and supervision during the requisite period. This work is original and entirely

carried out by the candidate for the fulfillment of the project work. I also certify that this research

work has neither formed the basis for the award of any other Degree, Diploma, ellowship or

any other similar titles of the any university or institution.

This is also to certify that the dissertation represents the independent work of the candidate.

Dr2 RAGURAMAN Dr2 RAMADASS

!ead and "ssociate professor "ssociate professor

DIRECTOR

P)a7e3 Pudu7+err1

Date3

2| P a g e

DEPARMENT O! PHYSICS8

KANCHI MAMUNIAR CENTRE !OR POST

GRAGDUATE STUDIES8

"AUTONOMOUS#8

PUDUCHERRY$ %&' &&(2


3/92

Shri. C. Ramesh., Place : Kalpakkam

Materials Chemistry Division, Date :

Chemistry Group, Inira

Ganhi Centre !or "tomic Research,

Kalpakkam#$%&'%(.

)*+"ID- C-RIIC"-

This is to certify that the project work titled /S0DI-S *+ 12DR*G-+

C1-MIS*RPI*+ *+ I"+I0M +"+* P*3D-R4 submitted to the K"+C1I

M"M0+I5"R C-+R- *R P*S GR"D0"- S0DI-S 6"0*+*M*0S7 for

the award of the degree of Master o! Philosophy is a bonafide record of theresearch work done byMr. K. S0S"I+"1"+, Re8. +o. ('($(%9, Department of

Physics, Kanchi Mamuniar !entre "or Post #raduate $tudies, Puducherry%&'('')

under my guidance and superision at the M"-RI"S C1-MISR2 DI5ISI*+,

C1-MISR2 GR*0P, I+DIR" G"+D1I C-+R- "*R "*MIC R-S-"RC1,

K"P"KK"M# $%&'%( during the period "ebruary 2'1* to +ugust 2'1*

Mr. C. R"M-S1

Scienti!ic *!!icer;G

*| P a g e


4/92

Mr2 K2SUSAINATHAN8

M2 P+i) Resear7+ S7+o)ar8

De9artment o* 9+1si7s8

K2 M2 C2 P2 G2 Studies "Autonomous#8

/a-s9et8

Pudu7+err1$ %&'&&(2

DEC/ARATION

I hereby declare that the dissertation titled :STUDIES ON HYDROGEN

CHEMISORPTION ON TITANIUM NANO POWDER; is a record of project work

done by me for the degree of Master o* P+i)oso9+1 in 9+1si7s under the guidance of Dr2

RAMADASS, Asso7iate Pro*essor8 Kan7+i Mamuni


5/92

"ckno


6/92

. wish to record my deep sence of gratitude and sincerethanks to my research guide shri C.Ramesh scientific officermaterial chemistry section, chemistry group .#!+0 kalpakkam,for his unstinted inspiration, inaluable guidance, encouragement,

keen interest, good wishes and aluable suggestions throughoutmy entire research tenure . am also grateful to him for criticallyreiewing this thesis

.t gies me immense pleasure to acknowledge to myresearch co%guide shri +.muru8asan, scientific officer, materialscience section, and chemistry group .#!+0 kalpakkam, for

critically ealuating my research actiities time to time and alsofor proiding the laboratory computational facilities and seeralaluable suggestions for completion of this work

. e/press my sincere thanks to Mr > Mrs. Mathan,Chanra mo8an, Shamima 1ussian ,helping me for recordingthe ? @ray i!!racto8ram, )- sur!ace area measurement ,S-M ima8e and many useful suggestions pertinent to thisdissertation

. would like to carry my thanks to my professor Dr. Guptha,Dr. Rama=ramam an Dr. Meenakshi Associate Professor,

Department of Physics, K.M.P.C.P.S, Pondicherry gien mea support

.t is a great pleasure to acknowledge my ab matesMr."!iAith !orhelping me and proiding kind supports andencouragement during my research work . am also thanks to allmy chemistry ivision collea8ues an sta!! mem=ersfortheir support at different times

ast but not least . want to say thanks to my friends Mr.$amilselvam, Mani%andanstand with me at all the cases andthanks for their loingness

&| P a g e


7/92

"inally, . am e/tremely thanks to all those people who werethe pillar of support to me

*RG"+IS"I*+ * 1- DISS-R"I*+

C1"P-R#I

.3T04D5!T.43

This chapter contains the basic information about hydrogen demand,hydrogen economy, hydrogen production methods, hydrogen storagemethods and hydrogen storage target which forms an aim of research in myproject

C1"P-R#II

iterature revie2produced for later

use, to transport stored hydrogen from the point of production to the point of

use, and to charge and discharge hydrogen coneniently from the storage

container according to need

.* >ydrogen Production Methods

Many production processes for hydrogen e/ist The hydrogen can be

produced from the fossil fuels ?eg, steam reforming of natural gas or other

light hydrocarbons, gasification of coal and other heay hydrocarbons@ or

water ?electrolysis of water, direct and indirect thermochemical

decomposition, and processes drien directly by sunlight %photo catalytic

route@ +lthough haing so many choices of resources sounds complicated,

but indeed it is a great adantage, because no one region or country has to

be dependent on one resource to produce hydrogen and whicheer

resources are suitable enironmentally and economically can be used .n an

1*| P a g e


14/92

eneloping country like .ndia, by means of hydrogen economy, we can hae

decentrali8ed energy, as many remote areas are not haing access to

electricity?12@

Presently, the commerciali8ed hydrogen production processes aremostly fossil fuel based, like, steam methane reformation, partial o/idation

of methane, auto%thermal reforming and coal gasification E the cheapest and

largest being generated by steam%methane reformation Though all these

processes generates !42, !42 generated from the reformation process is

highly concentrated, therefore the recoery is much cheaper than the diluted

e/haust gas of the fossil fuel :ut the main adantages of hydrogen economy

comes if hydrogen is e/tracted from water, using !42%free primary sources ofenergy such as solar energy, wind energy, or nuclear energy?1*, 1-@ The

different production methods of hydrogen from water are described in the

following section

1-| P a g e


15/92

$a#le'( Different hydrogen production methods, *here hydrogen is

produced from *ater

1(| P a g e

Method Process "eed $tock ;nergy ;mission

Thermal

$team0eformation

3atural#as

>igh temperaturesteam

!arbonse7uestration canmitigate its small

emission

!oal #asification

!oal,:iomas

s

$team and o/ygenat hightemperature pressure

$mall emission!arbon$e7uestration canmitigate it

Pyrolysis:iomas

s

Moderately highTemperaturesteam

$mall emission!arbonse7uestration canmitigate it

Thermochemical=ater $plitting

=ater=aste heat fromhigh temperaturenuclear reactor

3o ;mission

;lectrochemical

;lectrolysis =ater

;lectricity from

wind, solar, hydro,nuclear

3o emission

Photoelectrochemical

=ater;lectricity fromdirect sunlight

3o emission

:iological

Photo biological=ater

+lgaeDirect $unlight 3o emission

+naerobic:iomas

s>igh temperature

heat$mall emission

"ermentatieMicro organism

:iomass

>igh temperatureheat

$mall emission


16/92

.*1 >ydrogen production from water

>ydrogen generation from water can be depicted by the following

e7uation

1(* E 1( F ';( *(

The reaction is highly endothermic '! ( )*+ %mole- at )/0 %1, and for direct

thermolysis of water, a very high temperature is required '2)344 561. The energy required to

split water can be provided by a primary energy source, like, solar, wind, nuclear heat or by a

secondary energy source like electricity or a combination of these sources using a chemical

process. 7o, a large collection of diverse processes are involved for hydrogen generation from

water and some of which are listed in Table. 8one of the above processes e9cept electrolysis

has been commerciali:ed and although electrolysis is an established process, cost of hydrogen

production is very high. 7o, efforts are being taken to improve efficiency and to minimi:e cost of

these processes to make them commercially viable. Thus, $;D on various aspects like material

development, catalyst development, reactor design etc. has to be carried out

.-Hydrogen storage methods

.n principle, hydrogen can #e stored either in a physical form

+gas or liuid- or chemical form '(&). he methods #eing used to store

hydrogen are discussed #elo1.

I.;.( 8i0uid hydrogen storage 'Cryostorage)

i7uid hydrogen storage is currently the bulk hydrogen storagemedium of choice and has a ery impressie safety record 5nfortunately,

the energy re7uirements o+ li0ue+action are high, typically /%9 o+ the

hydrogen*s heating value. 8i0uid hydrogen 1ill remain the main techni0ue o+

#ul2 and stationary hydrogen storage +or the +oreseea#le +uture '(:).

1&| P a g e


17/92

The hydrogen can also be stored as a li7uid in a cryogenic tank at

ambient pressure and low temperature ?%2(2oc). Hydrogen stored as a li0uid

has a relatively high volumetric density ' +irst, the li0ue+action process is costly. 6econd, small scale

li0uid hydrogen production is impractical. hirdly, lo1 volume

distri#utiondispensing o+ li0uid hydrogen are e-pensive '(igh pressure gas

cylinders can store hydrogen at a pressure of 2' MPa and storage is een

possible up%to pressure of )'MPa in newly deeloped light weight composite

cylinders where the hydrogen olumetric density can reach -'KgFm* $ince

the hydrogen graimetric density is low, there are also problem in holding

the high pressure, especially in the regions with high population density

!ompressed gaseous hydrogencontainers consisting o+ /;.& mpa '&%%% psi)

'/;$ atmospheres) gaseous hydrogen in metal or plastic lined car#on +i#re

1ound pressure vessels o++er advantages +or storage. 6implicity o+ design

and use, high hydrogen +raction, rapid re+ueling capa#ility, e-cellent

dormancy characteristics, minimal in+rastructure impact, high sa+ety due toinherent strength o+ the pressure vessel, and little to no development ris2

are evident advantages. he disadvantages are system volume, use o+ high

pressure, integrating the automotive designer etc. Compressed gas storage

is supporta#le #y small3scale hydrogen production +acilities as 1ell as large

scale hydrogen production +acilities. hus a possi#le hydrogen in+rastructure

transition path1ay e-ists. ?or these reasons, room temperature compressed

gas storage is vie1ed as the most appropriate +uel storage system +or 45M

+uel cell vehicles '(7).

.-./ 4hysical storage on high sur+ace area materials

16| P a g e


18/92

@ased on 1ea2 van der aals interaction #et1een gas molecules andsolids, hydrogen molecule can #e reversi#ly stored on high sur+ace area

materials such as car#on #ased materials, zeolits structures, and metal

organic +rame1or2 materials, respectively. Ho1ever, the amount o+

hydrogen that can #e adsor#ed on porous materials at am#ient temperature

and high pressure are much lo1er '%.&1t 9). he advantage o+ the sor#ed

materials lies in their ready reversi#ility. his is also their largest

disadvantage. Ho1ever, as they contain hydrogen #y means o+ 1ea2

4hysisorption +orces 'Bander aals), lo1 temperatures '3(:%C) and high

pressures are re0uired +or signi+icant adsorption '().

.-.; Metal Hydride storage method

Metal hydrides can be subdiided into two categoriesG low dissociation

temperature hydrides and high dissociation temperature hydrides The low

temperature hydrides suffer +rom lo1 H$ +raction ' $9). he high

temperature hydrides re0uire a heat source to generate the hightemperature o+ dissociation ' /%%!C). @oth systems o++er +airly dense H$

storage and good sa+ety characteristics. Indeed it is the #ad characteristics

o+ dissociation 'high temperature, high energy input) that create the good

sa+ety characteristics 'no or slo1 H$ release in a crash). ?or vehicular

hydrogen storage, metal hydrides are either too heavy or their operating

re0uirements are poorly matched to 45M vehicle systems. ithout a

dramatic #rea2through achieving high 1eight +raction, lo1 temperature, lo1dissociation energy, and +ast charge time, metal hydrides 1ill not #e an

e++ective storage medium +or 45M +uel cell vehicles. ?or stationary storage,

the 1eight o+ metal hydride system is not an adverse +actor. Conse0uently,

their attri#utes o+ high volumetric storage density and sta#ility ma2e them

0uite attractive. Improving resistance to gaseous contaminants and

1)| P a g e


19/92

increasing system cycle li+e remain as o#stacles to #e overcome. It stores

hydrogen #y chemically #onding the hydrogen to metal or metalloid

elements and alloys '+ig;). Hydrides are uni0ue #ecause some can a#sor#

hydrogen at or #elo1 atmospheric pressure, then release the hydrogen at

signi+icantly higher pressure 1hen heated and there is a 1ide operating

range o+ temperatures and pressures depending on the metal and alloy

chosen. 5ach metal and alloy has di++erent per+ormance characteristics, such

as cycle li+e and heat o+ reaction '$%).

&igure( Schematic o! a Metal 1yrie # hyro8en is inserte in =etydrogen storage target

The current goal is to deelop an effectie on%board hydrogen storage

system for mobile applications .n order for hydrogen powered ehicles to be

competitie with comparable ehicles in the market place, the on%board

hydrogen storage system needs compact, light, safe and affordable

containment and should coer a driing range of -'' km ) kg of hydrogen is

needed for the combustion engine ersion in comparison to - kg hydrogen

for an electric car with a fuel cell +t room temperature and atmospheric

pressure, -kg of hydrogen gas occupies a olume of -(m*, which is hardly a

practical solution for a ehicle ?21@ >igh%pressure hydrogen cylinder,

li7uefied hydrogen tank, and solid metal hydride are possible options $olid

metal hydride has the largest olumetric density, and therefore is now

1


20/92

considered a more safe and effectie way to handle hydrogen than

compressed gas and li7uid hydrogen The hydride offers olumetric

hydrogen densities substantially greater than that of compressed gas and is

comparable to or e/ceeding that of li7uid hydrogen >igh pressure

containment essels or cryogenic tanks ?1@ are not re7uired for solid metal

hydride storage

&igure/( $he gravimetric storage capacities of hydrogen in different form

.n 2''< the 5$ Department of energy ?5$ D4;@ updated the hydrogen

storage system performance targets for light duty ehicles ?22, 2*@ The

following criteria for the hydrogen storage technology suitable for

transportation were setG

>igh >2storage capacity ?((wtA> for system@

Moderate operation temperature for hydrogen release and uptake,

ideally between &'%12''!

"aorable kinetics for hydrogen absorptionFdesorption

2'| P a g e


21/92

ow cost

ow to/icity and non e/plosie

The 5$ D4; hydrogen storage system targets help guide researchers

by defining system re7uirements in order to achiee commercially iable

hydrogen storage capacity, reaction enthalpy, and reaction kinetics for

efficient storage for mobile application ?fig -@

!onsidering these facts, the hydrogen storage using metal hydride is

the best method

'.$ Research aim an scope

Present fossil fuel based energy system has drawbacks of polluting

enironment by releasing green house gases .n the recent past, 0 D on

fuel cell based energy system are gaining momentum like in the areas of

catalysts, proton conductors and hydrogen storage materials .n sodium

cooled fast reactors, large 7uantities of hydrogen are released during arious

processes There is need to find suitable hydrogen storage material fortrapping the hydrogen released from such processes +lthough there are so

many substantial research and deelopment actiity in the field of hydrogen

storage materials, none of the materials studied to date has demonstrated

sufficient hydrogen storage capacity or efficiency at the re7uired operating

temperature range There is still considerable opportunity for study of new

materials or material systems that could fulfill all the re7uirements for

efficient hydrogen storage for mobile applications =ith regards to thee/isting materials or material systems research is still needed to improe the

chemisorptionFdesorption performance and understand the mechanisms of

chemisorption and desorption reactions with or without effectie catalyst

doping Therefore the research interest is turned to the light metal titanium

due to its high olumetric and graimetric storage capacity >oweer, use of

21| P a g e


22/92

this metal for hydrogen storage is challenging because the stability of a

metal hydride must lie within a specific range for the

chemisorptionFdesorption boundary at pressure and temperature that is

usable in practical application

The primary aim of this research is to promote the light metal such as

titanium for hydrogen storage The e/periment is done using TPD04

instrument for hydrogen uptakeFrelease studies The samples were

characteri8ed by 90D for structural information, $;M for morphology and

:;T for surface area measurement

Chapter#II

22| P a g e


23/92

iterature revieigh enthalpyG ('KjFmolQ>%)''KjFmol

+dsorption takes place only in a Monolayer

>igh temperature

Type of interactionG strongB coalent bond between adsorbate and

surface

>igh actiation energy

.ncrease in electron density in the adsorbent%adsorbate inter+ace.

Reversi#le only at high temperature.

Due to specificity, the nature of chemisorption can greatly differ from

system to

$ystem depending on the chemical identity and the surface structure

.N1-#as%surface !hemisorptions

.N1-1 +dsorption Kinetics

+s an instance of adsorption, chemisorption follows the adsorption

process The first stage is for the adsorbate particle to come into contact

with the surface The particle needs to be trapped onto the surface by not

*(| P a g e


36/92

possessing enough energy to leae the gas%surface potential well .f it

elastically collides with the surface, then it would return to the bulk gas .f it

loses enough momentum through an inelastic collision, then it Csticks onto

the surface, forming a precursor state bonded to the surface by weak forces,

similar to Physisorption The particle diffuses on the surface until it finds a

deep chemisorption potential well Then it reacts with the surface or simply

desorbs after attaining enough energy ?*(@.

he reaction 1ith the sur+ace is dependent on the chemical species involved.

Applying Gi##s +ree energy e0uation +or reactions>

G=H-TS

#eneral thermodynamics states that for spontaneous reactions, the change

in free energy should be negatie $ince a free particle is restrained to a

sur+ace, and unless the sur+ace atom is highly mo#ile, entropy is lo1ered.

his means that the enthalpy term must #e negative, implying an

e-othermic reaction

I5.'..( Moelin8

"or e/perimental setupo+ chemisorptions, the amount o+

adsorption o+ a particular system is 0uanti+ied #y a stic2ing pro#a#ility value.

Ho1ever, chemisorptions are very di++icult to theorize. A multidimensional

potential energy sur+ace '456) derived +rom e++ective medium theory is used

to descri#e the e++ect o+ the sur+ace on a#sorption, #ut only certain parts o+

it are used depending on 1hat is to #e studied. here e-ist several models to

descri#e sur+ace reactions> the 8angmuir3Hinshel1ood mechanism in 1hich

#oth reacting species are adsor#ed, and the 5ley3Rideal mechanism in 1hich

one is adsor#ed and the other reacts 1ith it. Real systems have many

irregularities, ma2ing theoretical calculations more di++icult '/$)

*&| P a g e


37/92

$olid surfaces are not necessarily at e7uilibrium

They may be perturbed and irregular.

Distri#ution o+ adsorption energies and odd adsorption sites.

@onds +ormed #et1een the adsor#ate.

!ompared to Physisorption where adsorbates are simply sitting on the

surface, the adsorbates can change the surface, along with its structure The

structure can go through rela/ation, where the first few layers change inter

planar distances 1ithout changing the sur+ace structure, or reconstruction

1here the sur+ace structure is changed.

I5.'..& Dissociation Chemisorption:

+ particular brand of gas%surface chemisorption is the dissociation

of diatomic gas molecules, such as hydrogen, o/ygen, and nitrogen 4ne

model used to describe the process is precursor%mediation The absorbed

molecule is adsorbed onto a surface into a precursor state The molecule

then diffuses across the surface to the chemisorption sites'/:). hey #rea2

the molecular #ond in +avor o+ ne1 #onds to the sur+ace. he energy toovercome the activation potential o+ dissociation usually comes +rom the

translational energy and vi#rational energy. 5-ample is the hydrogen and

copper system, one that has #een studied many times over. It has a large

activation energy o+ ./& 3 .7& eB. he vi#rational e-citation o+ the hydrogen

molecule promotes dissociation on lo1 inde- sur+aces o+ copper

.N2 Physisorption

The fundamental interacting force of Physisorption is caused by an

der =aals force ;en though the interaction energy is ery weak ?R1'E1''

*6| P a g e


38/92

meN@, Physisorptionplays an important role in nature. ?or instance, the van

der aals attraction #et1een sur+aces and +oot3hairs o+ gec2os provides the

remar2a#le a#ility to clim# up vertical 1alls. Ban der aals +orces originate

+rom the interactions #et1een induced, permanent or transient electric

dipoles.

In comparison 1ith chemisorptions, in 1hich the electronic structure o+

#onding atoms or molecules is changed and covalent or ionic #onds +orm,

4hysisorption, generally spea2ing, can only #e o#served in the environment

o+ lo1 temperature 'thermal energy at room temperature L$: meB) and in

the a#sence o+ the relatively strong chemisorptions. In practice, the

categorization o+ a particular adsorption as 4hysisorption or chemisorptionsdepends principally on the #inding energy o+ the adsor#ate to the su#strate

'/


39/92

&igure


40/92

gas pressure and usually decreases 1ith increasing temperature. In the

case o+ systems sho1ing hysteresis the e0uili#rium may #e metasta#le.

"nder appropriate conditions o+ pressure and temperature, molecules

+rom the gas phase can #e adsor#ed in e-cess o+ those in direct contact

1ith the sur+ace.

N;9P;0.M;3T+ T;!>3.S5;$

N1 .3T04D5!T.43 T4 TPD04?&H, %7.

6emperature Pro8ramme Desorption; Reuction;*Biation7

The characteri:ation of solids, intended as knowledge of chemical-physical properties,

structure, surface activity etc, is e9tremely important, particularly in the field of catalytic systems.

The major application of the surface actiity is related to the catalysis field.

The metal supported catalysts are used in most manufacturing processes of different industries, from the

petrochemical field to fine chemistry, from the pharmaceutical field to the food industry. In general they

are capable of optimi:ing the yield of a reaction by increasing its kinetics or allowing the use of less

drastic conditions for its occurrence and thus reducing the manufacturing cost.

-'| P a g e


41/92

&igure=( $PDR5 ''>> $hermo model system.

The solid catalysts act by providing specific sites for the adsorption of molecules

reacting on the surface, loosening their links and making the reaction easier. In some instances they can

react selectively by inhibiting the reaction towards undesired products. @nce the reaction is over,

desorption of products from the catalyst surface makes the sites available for another reaction. In most

cases, the activity of a supported catalyst is proportional to the metal area, and the activity of this area is a

function of the si:e of the metal particles deposited on the inert support. To quantitatively assess the metal

surface accessible to the adsorbed molecules, a few analytical methods are available and the use of which

depends on the nature of the application of the catalyst under test.

Two analytical methods for the chemisorption of gases are available to calculate the metal surface area of

a catalystA

The static volumetric method

The in-flow methods applied with the TBD$@.

N.'.'. Principles an Methos The analytical methods available with the TBDC$C@ 44 allow the determination of the

gas quantity '!), @), 6@, etc.1 chemically adsorbed from the surface of a solid sample with the choice of

-1| P a g e


42/92

appropriate e9perimental conditions 'temperatures, pretreatments, etc.1. They also allow the

determination of the type and number of the active sites, the evaluation of different thermodynamic and

kinetic parameters and the quantitative assessment of the reactivity of the systems towards all gases.

inally it is possible to perform very precise quantitative measurements of the acid and basic properties of

the systems under test.

N.'.(. In#lo< Metho This analytical method adopts conditions of atmospheric pressure, using gas flows

'inert or reactive1.The in-flow systems provide the advantage of being rapid and sensitive, and they do not

need calibrations concerning instrumental dead volumes and also reduce the problem of weakly adsorbed

gas. " qualitative description of the tests available with the in-flow instrument TBDC$C@ 44 is reported

hereunder.

N.'.&. PD 6emperature Pro8ramme Desorption7

The TBD analysis allows defining the strength, the number and the type of active sites

available on the surface of a catalyst by the determination of the quantity of gas desorbed from the

catalyst submitted to a linear temperature ramp. "fter degassing, reducing or otherwise pretreating the

sample to be analy:ed in order to eliminate contaminants, such as water naturally adsorbed on the sample

surface, a constant flow of properly chosen reactive gas is conveyed onto the sample to allow the reaction

between the sample active sites and the reactive gas according to a known stoichiometry.4nce the chemisorptions of the reactive gas is over, desorption is performed by linearly

increasing the sample temperature. The catalyst is placed into a reactor crossed by a flow of inert gas

'nitrogen, helium, argon1, which acts as carrier gas for the molecules of reactive gas desorbing from the

sample.

=hen the temperature at which heat e/ceeds the energy of actiation

of the gas%solid system is reached, the link between the atoms of adsorbate

and adsorbent is broken, and the phenomenon of programmed thermal

desorption takes place The desorbed molecules are dragged by the carrier gas as far as a thermal conductivity

detector 'T6D1, which measures the difference of concentration of the desorbed gas versus a reference

flow. =here necessary, a mass spectrometer can also be connected for a precise assessment of the nature

of the desorbed species.

-2| P a g e


43/92

The volume of the desorbed species, which can be calculated by appropriate

calibrations of the instrument, together with the knowledge of the stoichiometric factor of the chemical

reaction and the desorption temperature, allow to calculate the number and the strength of the active site.

N.'.. PR 6emperature Pro8ramme Reuction7

The TB$ analysis allows determination of the number and quantity of the reducible

species present in the sample and the temperature at which the reduction itself takes place as a function of

the flow conditions, the percentage of reactive gas, the quantity of sample and the speed of the

temperature increase.

The gas used for this type of analysis is a mi9ture of reactive gas with an inert

gas, as hydrogen in argon or nitrogen at 3 or 4. #enerally the sample is previously o9idi:ed or

pretreated to eliminate possible contaminants and completely o9idi:e the metal portion of the catalyst."lso for this type of analysis, the sample is submitted to a linear increase of temperature and to a constant

flow of the gas mi9ture. The reaction generally starts at room temperature, but at an e9tremely low rate,

therefore negligible.

"t a certain temperature, the reaction rate becomes considerable and the hydrogen

consumption can be monitored through the T6D detector. The signal integration allows calculation of the

quantity of hydrogen consumed and therefore the number of reacting sites. The TB$ analysis also allows

checking the presence of different states of o9idation of the contained metals.

N.'.. P* 6emperature Pro8ramme *Biation7

The TB@ analysis allows evaluation of the temperature range in which a sample undergoes

o9idation due to an o9idi:ing agent contained in a gas mi9ture such as @ )C!e 3 that is flown inside the

reactor containing the sample. In this case, too, the sample is pretreated and the metal o9ides are

previously reduced with pure hydrogen before they are submitted to the gas mi9ture flow and to the linear

temperature ramp to record the o9ygen consumption.

N.'.$. emperature Pro8ramme Reaction

Eesides mi9tures of hydrogen and o9ygen in inert gases, the use of other reactive gases of

acidic or basic type is possible for the assessment of the basic and acidic sites present in a solid. In

general, the analyses in programmed temperature ramp provide spectra where the temperature is

put in relation to the intensity of the signal, which on its turn is proportional to the adsorbed or

-*| P a g e


44/92

desorbed gas. The e9act amount of gas involved in the process is determined by means of

appropriate calibrations.

N.'.9. Pulse Chemisorption

This type of analysis is performed under isothermal condition. " suitable sampling

system injects known constant amounts of reactive gas 'e.g., hydrogen or o9ygen1 and they come in

contact with the sample surface sites accessible to the gas molecules. The active surface coming in

contact with the reactive gas chemisorbs a certain quantity there-of, until complete saturation of the sites.

The total amount of chemisorbed gas is calculated by difference between the area of the peaks recorded at

the end analysis 'saturated sample1 and the areas of the peaks recorded at the beginning of the analysis'when the chemisorption occurs and the sample is not yet saturated1. It has to be stressed that this type of

analysis is e9tremely quick and reproducible.

N.'.J. Pretreatment o! Samples Eefore being submitted to any of the described analyses, the samples must be properly

pretreated to obtain easily interpretable results.

The sample used must generally hae a weight ranging from '''( g to 1g,

according to the characteristics of the sample itself .t usually consists of

powders, pellets or balls of solid material containing a certain percentage of

metal or Cactie phase deposited on an inert support ?eg, alumina, silica,

etc@ The pretreatment is performed to remoe contaminants ?eg, carbon

compounds@ or adsorbed gases that may contribute to errors in the analytical results, as

for instance water. These substances are generally removed by submitting the sample to a gas flow

'reactive or inert1 and to a temperature increase leading to desorption and removal of the undesiredsubstances.

N.'.H "pplications The samples that can be characteri:ed belong to the following applicative fieldsA

--| P a g e


45/92

>eterogeneous catalysis

Metal corrosion

Measurement of the acidity and basicity of surfaces

0educibility ?o/idability@ of materials

The instrument used for measuring the !hemisorption surface area is TPD04

Thermo Modal 11'' and is shown in the following fig istory and deelopment of 90D

9%ray photon is a form of electromagnetic radiation production

following the ejection of an orbital electron and subse7uent transition of

atomic orbital electron from states to high to low energy. hen

monochromatic #eam o+ ray photons +all onto a specimen, three #asic

phenomena may result, namely a#sorption, scatter 'or) +luorescence. he

scattered photons may undergo su#se0uent inter+erance leading in turn to

the generation o+ di++raction ma-ima. hese three #asic phenomena +orm

the #ases o+ three important -3ray methods, the a#sorption techni0ue, 1hichis the #asis o+ radiographic analysis, the scattering e++ect, 1hich is the #asis

o+ R? 6pectrometry and 3ray di++ratction studies +or determining lattice

parameters.

The /%ray was discoered by =ilhelm 0oentgen in 1)


46/92

&igure'>( A Simple 3?ray image

.n 1


47/92

introduced the no1 +amous @ragg e0uation +n@ )d SinB), 1hich descri#es

the condition +or di++raction to occur in terms o+ the 1avelength o+ the 3ray

radiation 'O), the interplanar 'PdQ) spacing*s o+ the crystal, and the angle o+

incidence o+ the radiation 1ith respect to the crystal planes '). ?ather and

son @ragg shared the No#el 4rize in 4hysics +or their contri#utions to this

ne1 +ield, 1hich #ecame 2no1n as -3ray crystallography ';$).

N22 The ;lectromagnetic $pectrum, generation of 9%rays, and the :raggsU ;7uation

Nature o+ 3rays> 3rays can #e thought o+ as 1aves 1ith

1avelengths on the order o+ %.( S to (% S. 6horter the 1avelength, the more

energetic the 1ave. @ecause o+ the relatively short 1avelengths o+

electromagnetic radiation in the 3ray region, 3rays are high energy 1aves

and are much more penetrating compared to "B, visi#le, IR, or radio 1aves.

he conversion #et1een energy, +re0uency, and 1avelength is the 1ell3

2no1n de@roglie relationship> h hcE@, 1here is the +re0uency,h

is 4lanc2*s constant ':.:$ - (%3/; Ts), c is the speed o+ light '$.7 -

(%7msec), and@is the 1avelength o+ the radiation ';/).

N2* #eneration of 9 rays

=hen electrons strike a metal anode with sufficient energy, 9%rays

are produced This process is typically accomplished using a sealed /%ray

tube, which consists of a metal target ?often copper metal@ and a tungsten

metal filament, which can be heated by passing a current through it

?typically 1'%1( m+@, resulting in the Cboiling off of electrons from the hot

tungsten metal surface These Chot electrons are accelerated from the

-6| P a g e


48/92

tungsten filament ?negatie bias@ to the metal target ?positie bias@ by an

applied oltage ?typically 1(%*' kiloolts@ The collision between these

energetic electrons and electrons in the target atoms results in electron from

target atoms being e/cited out of their core%leel orbitals, placing the atom

in a short%lied e/cited state The atom returns to its ground state by haing

electrons from lower binding energy leels ?ie leels further from the

nucleus@ making transitions to the empty core leels

&igure''( characteristic emission spectra of the target material

he di++erence in energy #et1een these lo1er and

higher #inding energy levels is radiated in the +orm o+ 3rays. his

process results in the production o+ characteristic 3rays in +ig ($ 'i.e. 3

rays 1hose energies are uni0ue to the target metal due to the 0uantized

nature o+ the electron energy levels o+ each atom and the uni0ue

energies o+ these energy levels) UCu =('8/ to = electronic transition> 5 7%; 5

7%&.$ eB, O (./$(< S)V. hus 3rays provide a convenient means o+

determining 1hat elements are present in a sample #ecause o+ the

uni0ue 1avelengths produced #y each uni0ue element. A lo1er energy

-)| P a g e


49/92

process that involves the interaction o+ electrons 1ith the nucleus o+ an

atom in the target metal produces a continuum o+ lo1er intensity 3

radiation over a #road energy range 2no1n as @remstrahllung ';;). As

the voltage on an 3ray tu#e is increased, the characteristic line spectra

o+ the target element are superimposed upon the continuous spectrum

'at right).

&igure')( "eneration of 3?rays

N2- 9%ray diffraction

Crystals are ordered 1ith three3dimensional arrangements o+

atoms 1ith characteristic periodicities. As the spacing #et1een atoms is on

the same order as 3ray 1avelengths '(3/ S), crystals can di++ract the

radiation 1hen the di++racted #eams are in3phase. he @ragg e0uation is

given as n@ )dsinB. ?or a given 1avelength 'O), di++raction can only

occur at a certain angle ') +or a given d3spacing.

-


50/92

.t should be taken into account that if only two planes of atoms were

diffracting, as sho1n in the +ig(/,

then the transition +rom

constructive to destructive

inter+erence 1ould #e gradual as

the angle is varied. Ho1ever,

since many atomic planes are

inter+ering in real materials, very

sharp pea2s surrounded #y

mostly destructive inter+erence result ';;)

&igure'( 3 ray Diffraction

N2( $ingle !rystal ?aue@ Diffraction

aue Diffraction is one of the oldest,

common 9%ray techni7ues + single crystal of the

material is irradiated with a beam of 9%rays The

diffracted beams produce spots on photographic

film + series of diffraction spots surround the

central point o+ the #eam, corresponding to

di++raction +rom a given series o+ atomic planes

'+ig(;).

&igure'/( lauediffraction pattern

he position o+ the #eam depends on the @ragg di++raction angle,

1hich is determined #y the 1avelength o+ the 3rays and the periodic

spacing o+ the crystal planes o+ atoms 'interplanar spacing ';&).

The symmetry of the diffraction pattern shows the symmetry of the

crystal 9%rays are used to study the crystal structure of materials "or

e/ample, the 9%ray diffraction spectra can be used to identify a material

('| P a g e


51/92

&igure'7( Modern Automated 3?ray Diffractometer

N2& Powder Diffraction

+ powder is used to ensure completely random crystal orientation to

get diffraction from all possible planes The diffraction pattern can be

recorded on a flat photographic film or on a !0T ?cathode ray tube@ =hen

the incident beam satisfies the :ragg condition, a set of planes forms acone of diffracted radiation at an angle to the sample $ince the cone of

9%rays intersects the flat photographic filmstrip in two arcs e7ually spaced

from the direct 9%ray beam, two cured lines will be recorded on the

photographic film The distance of the lines from the center can be used to

determine the angle, which can then be used to determine the inter%

planarXdU spacing ?-&@3ray po1der di++ractometers record all re+lections

using a scintillation detector 'in counts per second o+ 3rays).

he pattern o+ di++racted 3rays is uni0ue +or a particular structure

type and can #e used as a P+ingerprintQ to identi+y the structure type.

Di++erent minerals have di++erent structure types, thus 3ray di++raction is

an ideal tool +or identi+ying di++erent minerals.

(1| P a g e


52/92

&igure'8( $*o 3?ray diffraction patterns produced on photographic film using theDe#ye?Scherrer po*der cameras on the 3?ray diffraction generator.

&igure';( 3?ray diffraction pattern for a po*dersample +aCl-

The diffraction pattern of an unknown sample is measured and is comparedwith already known standards ?Y!PD$ cards@ to identify ithe po


53/92

N26 $cherrer e7uation

The $cherrer method predicts the si8e of crystallites, instead of the

si8e of particle arge particles might contain seeral crystallites >oweer, it

is common that nanometer%si8ed particle contains only one crystallite

Therefore, the si8e of crystallites in nanometer%si8ed Particle as predicted by

the $cherrer relation also indirectly figures out the si8e of particle itself

;/periments proed that the smaller the crystallite si8e, broader the

diffraction peak Nery large crystal with a single orientation produces

diffraction peaks which are nearly ertical line in shape 4n the other hand,

small crystal produces ery wide peak Therefore, the width of the diffraction

peaks gies information on the crystal si8es ?-(@

t thickness of crystallite

/%ray waelength

) "=>M ?full width at half ma/@ or integral breadth

N) :ragg +ngle

N2) +pplication?-6@

6dentificationG The most common use o+ po1der 'polycrystalline) di++raction

is chemical analysis. his can include phase identi+ication 'searchmatch),

(*| P a g e

hickness, t O %.H ; 6)cos N)7


54/92

investigation o+ highlo1 emperature phases, solid solutions and

determinations o+ unit cell parameters o+ ne1 materials.

Polymer crystalline(+ polymer can be considered partly crystalline and

partly amorphous The crystalline domains act as a reinforcing grid, like the

iron framework in concrete, and improe the performance oer a widerange

o+ temperature. Ho1ever, too much crystalinity causes #rittleness. he

crystalline parts give sharp narro1 di++raction pea2s and the amorphous

component gives a very #road pea2 'halo). he ratio #et1een these

Intensities can #e used to calculate the amount o+ crystalline in the material.

N* $!+33.3# ;;!T043 M.!04$!4PZ ?$;M@

N*1 =hat is $canning ;lectron Microscopy ?$;M@ The scanning electron microscope ?$;M@ uses a focused beam ofhigh%energy electrons to generate a ariety of signals at the surface of solid

specimens The signals that derie from electron% sample interactions reeal

information about the sample including e/ternal morphology ?te/ture),

chemical composition, crystalline structure and orientation o+ materials

ma2ing up the sample. In most applications, data are collected over a

selected area o+ the sur+ace o+ the sample, and a $3dimensional image isgenerated that displays spatial variations in these properties. Areas ranging

+rom appro-imately ( cm to & microns in 1idth can #e imaged in a scanning

mode using conventional 65M techni0ues 'magni+ication ranging +rom $% to

appro-imately /%,%%%, spatial resolution o+ &% to (%% nm). he 65M is also

capa#le o+ per+orming analyses o+ selected point locations on the sample

(-| P a g e


55/92

this approach is especially use+ul in 0ualitatively or semi30uantitatively

determining chemical compositions 'using 5D6), crystalline structure, and

crystal orientations 'using 5@6D). he design and +unction o+ the 65M is very

similar to the 54MA and considera#le overlap in capa#ilities e-ists #et1een

the t1o instruments ';7).

N*2 "undamental Principles of $canning ;lectronMicroscopy ?$;M@

Accelerated electrons in an 65M carry signi+icant amounts o+

2inetic energy and this energy is dissipated as a variety o+ signals produced

#y electron3sample interaction 1hen the incident electrons are decelerated

in the solid sample. hese signals include secondary electrons 'that produce

65M images), #ac2scattered electrons '@65), di++racted #ac2scattered

electrons '5@6D that are used to determine crystal structures and

orientations o+ minerals), photons 'characteristic 3rays that are used +or

elemental analysis and continuum 3rays), visi#le light

'cathodoluminescence33C8), and heat. 6econdary electrons and

#ac2scattered electrons are commonly used +or imaging samples> secondary

electrons are most valua#le +or sho1ing morphology and topography onsamples and #ac2scattered electrons are most valua#le +or illustrating

contrasts in composition in multiphase samples 'i.e. +or rapid phase

discrimination). 3ray generation is produced #y inelastic collisions o+ the

incident electrons 1ith electrons in discrete or#ital 'shells) o+ atoms in the

sample. As the e-cited electrons return to lo1er energy states, they yield 3

rays that are o+ a +i-ed 1avelength 'that is related to the di++erence in

energy levels o+ electrons in di++erent shells +or a given element) ';:). hus,characteristic 3rays are produced +or each element in a mineral that is

Ke-citedK #y the electron #eam. 65M analysis is considered to #e Knon3

destructiveK that is, -3rays generated #y electron interactions do not lead to

volume loss o+ the sample, so it is possi#le to analyze the same materials

repeatedly.

((| P a g e


56/92

N** $canning ;lectron Microscopy ?$;[email protected] % >ow Does .t =ork[

&igure'


57/92

Nibration%free floor

0oom free of ambient magnetic and electric fields

65Ms al1ays have at least one detector 'usually a secondary

electron detector), and most have additional detectors. he speci+ic

capa#ilities o+ a particular instrument are critically dependent on 1hich

detectors it accommodates.

The $;M is an instrument that produces a largely magnified image by

using electrons instead of light to form an image + beam of electrons is

produced at the top of the microscope by an electron gun The electron

beam follows a ertical path through the microscope, which is held within aacuum The beam traels through electromagnetic fields and lenses, which

focus the beam down toward the sample ?-ow is a sample prepared

:ecause the $;M utili8es acuum conditions and uses electrons to

form an image, special preparations must be done to the sample +ll water

(6| P a g e


58/92

must be remoed from the samples because the water would apori8e in the

acuum +ll metals are conductie and re7uire no preparation before being

used +ll non%metals need to be made conductie by coering the sample

with a thin layer of conductie material This is done by using a deice called

a \sputter coater\

N*( $trengths and imitations of $canning ;lectronMicroscopy ?$;M@[?('@

...*(1 $trengths

here is argua#ly no other instrument 1ith the #readth o+

applications in the study o+ solid materials that compares 1ith the 65M. he65M is critical in all +ields that re0uire characterization o+ solid materials.

hile this contri#ution is most concerned 1ith geological applications, it is

important to note that these applications are a very small su#set o+ the

scienti+ic and industrial applications that e-ist +or this instrumentation. Most

65MEs are comparatively easy to operate, 1ith user3+riendly KintuitiveK

inter+aces. Many applications re0uire minimal sample preparation. ?or many

applications, data ac0uisition is rapid 'less than & minutesimage +or 65I,

@65, spot 5D6 analyses.) Modern 65Ms generate data in digital +ormats,

1hich are highly porta#le.

...*(2 imitations

6amples must #e solid and they must +it into the microscope

cham#er. Ma-imum size in horizontal dimensions is usually on the order o+

(% cm vertical dimensions are generally much more limited and rarely

e-ceed ;% mm. ?or most instruments samples must #e sta#le in a vacuum

on the order o+ (%3& 3 (%3:torr. 6amples li2ely to outgas at lo1 pressures

'roc2s saturated 1ith hydrocar#ons, K1etK samples such as coal, organic

materials or s1elling clays, and samples li2ely to decrepitate at lo1

pressure) are unsuita#le +or e-amination in conventional 65MEs. Ho1ever,

()| P a g e


59/92

Klo1 vacuumK and KenvironmentalK 65Ms also e-ist, and many o+ these types

o+ samples can #e success+ully e-amined in these specialized instruments.

5D6 detectors on 65MEs cannot detect very light elements 'H, He, and 8i),

and many instruments cannot detect elements 1ith atomic num#ers less

than (( 'Na). Most 65Ms use a solid state 3ray detector '5D6), and 1hile

these detectors are very +ast and easy to utilize, they have relatively poor

energy resolution and sensitivity to elements present in lo1 a#undances

1hen compared to 1avelength dispersive 3ray detectors 'D6) on most

electron pro#e micro analyzers '54MA). An electrically conductive coating

must #e applied to electrically insulating samples +or study in conventional

65MEs, unless the instrument is capa#le o+ operation in a lo1 vacuum mode.

N- :;T ?:runauer, ;mmett and Teller@%$urface areaDetermination

N-1 .ntroduction The surface of a material is the diiding line between a solid and

its surroundings, namely li7uid, gas or another solid =e can anticipate

therefore, that the amount of surface, or surface area, is an important factorin the behaior of a solid $urface area affects, for e/ample, dissolution rates

of pharmaceuticals, the actiity of an industrial catalyst, how fast cement

hydrates, adsorption capacity of air and water purifiers, and the processing

of most powders and porous materials =heneer solid matter is diided into

smaller particles new surfaces are created thereby increasing the surface

area $imilarly, when pores are created within the particle interior ?by

dissolution, decomposition or some other physical or chemical means@ the

surface area is also increased ?(1@

N-2 +ssumptions of :;T ;7uation

The :;T .sotherm ?named for its inentors, :runauer, ;mmett, and

Teller@ allows nitrogen molecules to adsorb on each site

The assumptions used to derie the :;T isotherm are

(


60/92

1 #aseous molecules behae ideally

2 Multiple nitrogen molecules can be adsorbed to each site

* ;ach adsorbed molecule proides a site for the adsorption of the molecule

in the layer aboe it

- +ll sites on the surface are e7uialent

( 3o adsorbate % adsorbate interactions

& +n adsorbed molecule is immobile

6 3itrogen in the second and higher layers is assumed to be li7uid like

N1* #as $orption

The true surface area, including surface irregularities and poreinteriors, cannot be calculated from particle si8e information, but is rather

determined at the atomic leel by the adsorption o+ nonreactive, or inert gas

The amount adsorbed, letUs call it, is a function not only of the total amount

of e/posed surface, but also ?i@ temperature, ?ii@ gas pressure and ?iii@ the

strength of interaction between gas and solid $ince most gases and solids

interact weakly, the surface must be cooled substantially in order to cause

measurable amounts of adsorption E enough to coer the entire surface +sthe gas pressure is increased, more gas molecules gets adsorbed on the

surface ?in a non%linear way@ :ut, adsorption of a cold gas does not stop

when it has coered the surface in a complete layer one molecule thick ?letUs

call the theoretical monolayer amount of gas 5m@] +s the relatie pressure is

increased, e/cess gas is adsorbed to form PmultilayersQ.$o, gas adsorption %

as a function of pressure % does not follow a simple relationship, and we must

use an appropriate mathematical model to calculate the surface area =e

use the :;T e7uation ?(2@

';5 6Po; P7#'Q O 6C#'7 6Po; P7 ; 5m C F'; 5m C

=here

&'| P a g e


61/92

N% Nolume of gas adsorbed,

P% ;7uilibrium pressure of adsorbent,

Po% saturation apour pressure,

Nm% monolayer olume of adsorbant,

!%:;T constant

N-- .sotherm types ?(*@

&igure'=( types of isotherm

$ype 6

Pores are typically microspores with the e/posed surface residing almost

e/clusiely inside the microspores, which once filled with adsorbateB leae

little or no e/ternal surface for further adsorption

$ype 66

&1| P a g e


62/92

Most fre7uently found when adsorption occurs on nonporous powders or

powders with diameters e/ceeding microspores .nflection point occurs near

the completion of the first adsorbed monolayer

$ype 666

.sotherm characteri8ed by heat of adsorption lesser than the heat of

li7uefaction of adsorbate +dsorption proceeds as the adsorbate interaction

with an adsorbed layer is greater than the interaction with the adsorbent

surface

$ype 6V

4ccur on porous adsorbents with pores in the range of 1( E 1''nm +t

higher pressures the slope shows increased uptake of adsorbate as pores

become filled, inflection point typically occurs near completion of the first

monolayer

$ype V

+re obsered where there is small adsorbate absorbent interaction potentials

?similar to type

...@, and are also associated with pores in the 1( E1''nm range

N-( Principles of Measurement

The gas most commonly used is nitrogen "irstly, it is readily

aailable in high purity $econdly, the most appropriate coolant, li7uid

nitrogen, is also readily aailable Thirdly, the interaction of nitrogen with

most solid surfaces is relatiely strong astly, there is wide acceptance ofthe cross3sectional area .n the classical manometric techni7ue, relatie

pressures less than unity are achieed by creating conditions of partial

acuum ?absolute pressures of pure nitrogen below atmospheric pressure@

>igh%precision and accurate pressure transducers monitor those pressure

&2| P a g e


63/92

changes ?in a fi/ed and known olume@ due to the adsorption process. This

method is easily automated and the amount of gas adsorbed is made at a

number different relatie pressures 5sually, the analy8er obtains at least

three data points in the relatie pressure range between ''2( torr and '*'

torr ;/perimentally measured data are recorded as pairs of aluesG the

amount of gas adsorbed ?Bads@ and the corresponding relatie pressure

?44o@ + plot of these data is called an isotherm The :;T analyser used in

the present study is shown in "ig2'

&igure)>( :$? sorptomotic?'==>

N-& Principles of !alculation

The computer program takes oer and a least%s7uares linear

regression is used to fit the best straight line through a trans+ormed data set

consisting of the following pairs of aluesG

';5as6P%;P7#'Q and P;Po The monolayer capacity, 5m, is calculated

from the slope, S, and the intercept, i, of the straight line,

S+C?'-EVmC

&*| P a g e


64/92

i'EVmC

$oling for 5m,

5mO';6sFi7

3ow we need the number of molecules in the monolayer, and we get

from that the number of moles Yust diide 5mby the molar olume ?M5) for

the number of moles Multiply number of moles by +ogadroUs number to

arrie at the number of molecules coering the surface in a layer one

molecule thick .f we know how much area one molecule occupies, the total

area is one simple multiplication of number of molecules with cross sectional

area of a molecule Different gas molecules hae different si8es and occupy

different areas =e call that area the Ccross3sectional area?(*@ Therefore,

the total surface area, St,is then calculated from

StO5m"v"m;M5

=here "v is +ogadroUs number, "m is the cross%sectional

area,M5#molar olume of the sample and 5m%3umber of moles ?The surfacearea community@ takes a pragmatic approach, and assumes it to be 1&2

s7uare angstroms ?'1&2 nm2@ on all surfaces +ll surface area results are

finally reported normali8ed by sample weight, or mass, as s7uare meter pergram, written m2Fg or m2g%1

&-| P a g e


65/92

N.;9P;0.M;3T+

N.1 !haracteri8ation of !hemisorption ?TPD04@G

TPD04 e7uipment ?Thermo Modal 11''@ was used for the

characteri8ation of chemisorption surface area of the hydrogen storage

material, namely Ti and is shown in the figure ?1*@

TPD04 11'' is the single instrument in which one can do temperature

programmed desorption ?TPD@, reduction ?TP0@ and o/idation ?TP4@ and

pulse !hemisorption using a range of pure gas and mi/tures .t can perform

the actiation of one material in one reactor while analy8ing another on the

same instrument The instrument comes as standard with two electrically

heated oens TPD04 11'' is an automatic surface area characteri8ation

unit with good sensitiity

This instrument was used for the characteri8ation of titanium

powder by purging the probe gas such as hydrogen carried by carrier gassuch as argon to the reactor The chemisorption of hydrogen by the titanium

sample was carried out by temperature programmed reduction ?TP0@ and

temperature programmed desorption ?TPD@ During the TP0 process, some

of the supplyied hydrogen gets chemisorbed on the sample used for analysis

?Ti@ and the remaining gas will pass into the T!D producing the signal Thus

&(| P a g e


66/92

the chemisorption of hydrogen is monitored online by logging the T!D signal

The 7uantity of >2chemisorbed is obtained by the integration of TP0 and

TPD cures Prior to the analysis, the T!D signal was calibrated by injection

of known mass of hydrogen The reactor essel used in the e/periements is

made up of twin 7uart8 tubes in inner and outer configuration $ample gas

enters through outer tube and then enters into the inner tube through

bottom hole and passes oer sample and then reaches the T!D detector

&igure )'( Schematic representation of Pulse Chemisorption in $PDR5

:efore doing the e/periment, the reactor essels were washed

with soap solution and dried in acuum oen for an hour to remoe any

contamination of the sample Pure titanium powder was placed between

glass wool in the inner tube of reactor Then the reactor was fitted into the

instrument The sample was pretreated by flushing with 5>P argon at room

temperature for some time and then heated to 12('! to remoe any olatile

materials and moisture present in the sample +fter completing the

pretreatment, the sample was processed for analysis mode TP0 and TPD

&&| P a g e


67/92

analysis for the >2chemisorption was carried out as function of temperature

from -''o! to &''o! >eating rates is 2'o!Fmin to optimi8e the heating

parameters at which net hydrogen uptake efficiency was ma/imum .n TP0

in analysis mode, hydrogen gas from hydrogen generator was purged at

constant flow rate through the reactor using argon carrier gas and sample

was heated to pre%determined temperature at the fi/ed heating rate

+fter the TP0, the samples were subjected to TPD analysis at the same

fi/ed temperature to estimate the release of hydrogen at the corresponding

temperature "rom the TP0 and TPD profile, the net hydrogen chemisorption

at the particular temperature was determined The TP0 and TPD analysis

were carried out as a function of heating rate to study the mechanism of

titanium hydrogen reaction and to calculate the actiation energy of the

reaction

N.2 characteri8ation using 90D Techni7ueG

9%ray powder diffraction ?90D@ is a rapid nondestructie

analytical techni7ue primarily used for phase identification of a crystalline

material and can proide information on unit cell dimensions and to

determine the particle si8e

90D studies were carried out for the Different Titanium

samples collected from arious sources as gien below

?i@Pure Ti Powder?+lpha +ldrich@

?ii@!ommercial Titanium hydride?+lpha +ldrich@

?iii@Titanium Powder $ubjected to full cycles of TPD04

&6| P a g e


68/92

The typical instrument related parameters were operating oltage of -' kN,

current of *' m+ for the /%ray tubeB scan speed of ''2$ %1 with counting time

of *s per step and an angular range ?2@ of 1'' to )'' The 9%ray

diffractometer was calibrated using silicon $0M &-'a as an e/ternal

standard $cintillation detector was used to detect the diffracted 9%rays

The sample was installed in 8ero reflection glass plate and

mounted on to the sample holder of the 9%ray powder diffractometer +

collimated beam of the 9%rays was allowed to fall onto the sample The

diffracted 9%rays were made to fall on the detector by moing the detector

by an angle of 2 ^ degrees relatie to the incident beam The detector output

was collected and stored in a data base The relatie intensities were plottedas a function of 2 ^ to obtain the diffractogram and were superimposed in

order to facilitate inter%comparison

N.* !haracteri8ation of Physisorption surface area

using ?:;T@

#as adsorption was the most widely used techni7ue for the

total surface area measurements #as molecules of known si8e are

condensed onto the unknown sample surface, by completely coering the

surface and opening the pores of each particle with a condensed gas The

gas surface area analy8er can be characteri8ing the surface, including

irregularities and the pore interiors down to an atomic leel The techni7ue

re7uires a clean surface, as the sample has to be taken to an eleated

temperature under acuum to Coutgas as a necessary step To measure the

Physisorption surface area of the titanium sample, Cout gassing is the firststep to remoe any impurities and moisture present in the surface of the

sample "or out gassing 1g of sample was taken in the sample holder and

subjected to out gassing at 12( _! for 2- hrs +fter out gassing the sample is

&)| P a g e


69/92

ready for analysis The instrument is used for the measurement of

Physisorption surface area

3itrogen is often the gas used as its molecular si8e was inert

and was aailable in high purity at a reasonable cost The Cout gassedsample under high acuum in the sample tube is immersed in a coolant bath

of li7uid nitrogen at %1


70/92

!%:;T constant

"inally the Physisorption surface area of the sample is calculated

using the formula,

StO5m"v"m;M5

=here

"vis +agadroUs number

"mis the cross%sectional area

M5#molar olume

5m%3umber of moles

N.-!haracteri8ation of micro structure of the Titaniumsample using ?$;M@G

The $canning ;lectron Microscopy and ;nergy Dispersie+nalysis ?$;MF;D+9@ 5ses electron instead of light to form the image .t hasa ery high resolution than any other techni7ues >ere this techni7ue is usedto determine the microstructure of the titanium sample

The samples were imaged using + Philips 9%*' modal ;lectron

microscope with proision for ;D+9 This techni7ue is one of the most usefulmethods for inestigating the microstructure of materials The electron beam

emitted from a heated anthanum he/a boride cathode gets focused by a

system of magnetic lens ?usually two condenser lenses and one objectie

lens@ +cceleration oltage of 2'KN is used to accelerate the electrons To

6'| P a g e


71/92

generate the re7uired acuum, ion getter pump was used which produces a

acuum leel of about 1'%)millibar The electron beam scans the specimen in

much the same way as in cathode ray tube for image formation on the

screen =hen the primary electron interacts with the specimen, electrons

and other radiation are produced that can be used to form images and to

analy8e chemically the elements present on the surface of the sample Three

modes of operations are secondary electron mode, backscattered electron

mode and 9%ray spectroscopy $econdary electrons are formed by interaction

of the primary electrons with loosely bound atomic electrons .nformation on

the chemical composition is obtained by energy dispersie spectrometry

?;D+9@ 9%rays are produced during de%e/citation of outer electrons into the

inner shell acancies of the analyte atoms These acancies are produced

due to the interaction of inner shell electrons with the high energy electron

beam + $i ?i@ detector was used for detection of 9%ray The Titanium

sample was made into small pellets and was mounted on the sample holder

and placed in the analysis chamber of $;M +fter attaining a acuum leel of

1'%6torr, the electron beam was impinged on the surface of the diffusion

electrode where catalyst was placed $ince the electrode was haing carbon

as supporting substrate, conductie coating was not re7uired The surfacemicrostructure was studied at arious magnifications and the chemical purity

of the catalyst was inestigated by ;D+9

!>+PT;0N..

N.. 0esult and discussion

The systematic study of any e/periment will not be fulfilled without

discussing its results The results and discussion are of much importance for

the analysis .t also gies an interpretation results for internal behaior of the

material structure and its properties

61| P a g e


72/92

>ence, in this chapter results of studies related to hydrogen sorption

capability carried out on titanium samples are discussed The fresh titanium

powder was characteri8ed by 90D, :;T and $;M "igure1 shows the 90D

pattern of fresh titanium powder and the alues of the sample peaks are

matching with Y!PD$ alues for Ti The titanium powder has the ma/imum

peak at -'1'and has the crystal structure of he/agonal closed pack ?>!P@

The chemisorption studies were carried out using TPD04 instrument

The structural and morphological studies of the samples were carried out by

90D, $;M and the surface area measurement by :;T

0 10 20 30 40 50 60 70 80 90

-200

0

200

400

600

800

1000

1200

1400

1600

004

112103

110102

002

100

101

Intensity

2 theta

Untreated Fresh Titani!

&igure))( 3RD pattern for fresh titanium

sample

62| P a g e


73/92


74/92

400 450 500 550 600

-2000

0

2000

4000

6000

8000

10000

12000

14000

,ea+ted-antity*.H2#!

i+r*!*'e/(&

Te!"eratre#$%&

hydr*(en +he!is*r"ti*n#T,&

&igure)/( uantity of hydrogen reacted on titanium po*der +FmoleEg-

and maintaining at the re7uired temperature The integration of TP0 graph

gae the peak area in mNs The peak area was conerted to 7uantity of

hydrogen from calibration parameters

"rom the graph it ery clear that up%to sample temperature of -'' 4!, therewas no hydrogen chemisorption on the titanium powder =hen temperature

was increased to -2(4!, the sample started to chemisorbs hydrogen The

7uantity of hydrogen chemisorbed was estimated by integration of the TP0

graph The 7uantity of hydrogen chemisorbed by sample as a function of

temperature is gien in the "ig%2- "ig%2- clearly reeals that the 7uantity of

hydrogen chemisorption increases from -2(o! and reaches peak alue of

126*- `molFg at (''o! ?which corresponds to &'A stoichiometry@

=hen the temperature was increased further to (2(4!, chemisorption of

hydrogen on titanium sample was decreasing to )1*6`molFg =hen the

sample temperature was increased further to (('4!, chemisorption of

6-| P a g e


75/92


76/92

.t is seen that the hydrogen storage capacity of Ti increases steadily with

temperature up to (''4! and further increase in temperature bring down the

hydrogen storage capacity drastically "ig2& shows the hydrogen desorption of

titanium sample at temperature -'' %&''4!.t can be found that the hydrogen

releasing from Ti sample steadily increases with temperature up to &''4

420 440 460 480 500 520 540 560 580 600 620

0

1000

2000

3000

4000

5000

6000

7000

8000

,e'eased-an

tity*.H

2#!i+r*!*'e/(&

Te!"eratre#$%&

Hydr*(en diss*r"ti*n#T&

"ig26 shows the comparison of TP0 and TPD profiles of hydrogen for

Ti .t is desirable to hae high chemisorption and less desorption of hydrogen

to hae net hydrogen storage "rom the graph it is eident that at

temperatures between -2(o! to (''o!, the net storage is high The net

hydrogen storage results obtained by TP0 and TPD studies are gien in table%

1 The temperature of (''o! was selected to be optimum to hae high net

hydrogen chemisorption +t (''o!, the study on repeatability of

chemisorption and desorption were carried out and the chemisorption was

highly reproducible and is shown in "ig2)

6&| P a g e

&igure)8( uantity of hydrogen released on titanium

po*der +FmoleEg-


77/92

.n this techni7ue, the chemisorption was measured by the amount of

hydrogen gas chemisorbed on the gien sample, .e -6))gFmol of Ti reacts

stochiometrically with 2gFmol of >2

&igure);( +et trappin8 e!!iciency uantity of hydrogen on titanium

po*der +FmoleEg-

to form -


78/92

&igure.)< 0ydrogen chemisorption on titanium po*der at 7>>5C

temperature

$a#le( trapping efficiency of hydrogen chemisorption on titanium po*der*ith )>5CEM6 on different temperature />>?8>>5c

6)| P a g e

S.+

*

3-IG1

6m87

PR

-M

P.

6 *C7

ty o!

1(

reacte

6Tmol;8

7

rapp

e ty

U

PD

-M

.

6 *C

7

ty o!

1(

release

6Tmol;87

rapp

e ty

+et

trappin8

e!!iciency

6Tmol;87

1 ''2)1 -''4

!

3. ''A -''4

!

3. ''A 3.

2 ''*'6 -2(4

!

)-&' -'A -2(4

!

66(


79/92

?#Ray i!!raction stuies on lattice moi!ication o!

titanium on chemisorption o! hyro8en

"ig 2< shows the 90D pattern of untreated Ti powder, commercial Ti>2

and Ti metal with chemisorberd >2The phase purity of the commercially

aailable titanium powder was inestigated by 90D diffraction

measurement "igure2< displays the 90D pattern of the sample and all the

major reflection can be inde/ed to the titanium phase, which were in

e/cellent agreement with the Y!PD$ The crystalline planes andcorresponding ?hkl@ alues of titanium are ?11'@,?''2@,?1'1@,?1'2@,?11'@,

?1'*@ and ?2'1@are obsered

The figure ?2@ as well as itanium ?Ti@ phase The ma/imumintensity peaks, 111 planes correspond to titanium hydride ?Ti>2@ and ''2

planes corresponds to the titanium ?Ti@ $ince we obsere titanium peaks, we

conclude that hydrogen chemisorption on titanium is taking place at the

optimi8e leel only

6


80/92

The 90D peaks gae clear indication of nano si8ed titanium

powder The particle si8eXdU of titanium was estimated by Debye%$cherrerUs

e7uation

d'


81/92


82/92


83/92

&igure>( :$ result for titanium

0.6

p/p00.0 0.1 0.2 0.3 0.4 0.5 0.6

0.5

p/(Vads

(p0-p))/cm-3

g

0.1

0.2

0.3

0.4

0.5

&igure'( :$ result for titanium hydride

Table ?-@ shows the measurements of Physisorption surface area of

the titanium and titanium hydrides powder There is much difference found

between surface area of titanium ?'))@ and titanium hydride ?))2@ The

graphs 1 and 2 were obtained from the two samples ?Ti, Ti>2@ The graphs

were obtained by plotting PF ?Nads?P4%P@ Ns ?PFPo@ and a straight line ise/pected "rom the graphs we obsere that the e/tent of adsorption

increases with increase in pressure

$a#le/( Measurement of Physisorption surface area using :$

)*| P a g e

$ample $ample wt?g@ Physisorption surface

area ?m2Fg@Titanium 1(-(( '))

Titanium hydride 16-2* )2)


84/92

$;M Measurement

+fter the chemisorption of hydrogen on Ti powder by TP0, the sample was

characteri8ed by $;M for studying surface morphology $ince powder samples

cannot be handled in the $;M instrument, the sample was pellatised The $;Mimage of Ti with chemisorbed hydrogen ?Ti>2@ is shown in the "ig *2 "rom the "ig it

is obsered that particles si8e is around 2'%*' nm Particle si8e was also estimated

by 9%0ay diffraction using $cherrer e7uation The particle si8e for Ti> 2 formed by

TP0 was 2) nm which was in agreement with $;M results >oweer, due to the

pelleti8ation some regions in the samples were obsered to hae flattened surface

een for highest resolution

&igure )( SM image of hydrogen chemisor#ed $itanium

+$i0)-

)-| P a g e


85/92

C+a9ter III

Summary an conclusion

The earlier studies done in this field proided remarkable opportunities

for the research on the subject as it is an actie field of research in which

new inestigation are currently being carried out The literature surey done

by the author reiews the work done in the field of hydrogen chemisorptionF

desorption .t has created a thirst to research scholars to know more about

chemisorption behaior of metals and its applications

The present study is mainly focused on the hydrogen

chemisorptionFdesorption on Ti powder samples by TP0 and TPD methods

The optimum temperature for hydrogen storage on the samples was

established and the parameters will be of great importance in storing

hydrogen produced from industrial processes +t the gien parameters, the

ma/imum storing capacity of hydrogen in titanium powder samples were

demonstrated and was found to be 11( g of hydrogen per litre of titanium

sample which is in ery good agreement with literature alues and the

storage capacity is obsered to be similar to that of li7uid hydrogen

The titanium before and after chemisorption were characteri8ed by

90D, :;T and $;M techni7ues for its structure, morphology and surface

area

The structural studies with 90D shows a ery sharp peak for fresh

Titanium and broad peak for Titanium chemisorbed hydrogen ?Ti>2@ 3o

peaks of impurities are detected The 90D pattern is good agreement with

the Y!PD$ and the particle si8e calculated from the 90D pattern is found to

be of *' nm

)(| P a g e


86/92

The surface area measurement for the "resh Titanium and hydrogen

chemisorbed Titanium ?Ti>2@ sample using :;T is studied and the

measurement of surface area is found to be for Titanium ?')) m2Fg@ and

Titanium hydride ?))2m2Fg@ due to the high surface area in the Titanium

hydride

)&| P a g e


87/92

0eference

1 ight metal hydrides for reersible hydrogen storage application

Yianfeng Mao uniersity of =ollongong

2 =orld business council for sustainable deelopment,?2''-@ #enea,

$wit8erland +ailable an ine atG www =bcsd 4rg

* The impact of fuel economics regulation in .ndia, uniersity of

Maryland, college park department of economics?2'1'@ on Eline at G

wwwnscw ;duFcerrepFworkshopsF documentsFchugh%comporesources

Pdf

- ;nergy and transportation science diision ?;T$D@ on% line at

wwwornlgo?2'1*@

( >ydrogen based ehicalee research initiatie is making on line at

www 0enewable energy world !om?2'')@

& 5s department of energy hydrogen program 2''& annual merit reiew

proceedings, technology,www >ydrogen energy #o and www "uel

economy #o

6 3 3 #reenwood, + ;arnshaw, C!hemistry of the ;lements, 4/fordB

:oston, :utterworth%>einemann ?1


88/92


89/92

1allar,, " >ofmeister,

; 3ewbacher, +, Vieger, M+#3+%$T;N0 "ahr8engtechnik +# !o K#

+%)'-1 #ra8, +wstric

2' >igh capacity hydrogen storage materialsG attributes for

automotie application and techni7ues for materials discoeryG% Yum

yang +ndrea $udik, !hristopher wolerton and Denaid j siegel

published as an +dance article on the wet 1- th$eptember 2''


90/92

2) #erd utiering, Yames ! =illiams, engineering materials and

processingG titanium, second edition, $pringer publications, ?2''6@

2


91/92

*


92/92

(' $canning ;lectron Microscopy ?$;M@ $usan $wapp, uniersity of

=yoming

(1 Porous material PrimersG% $urface +rea Determination, Suanta

chrome instruments

(2 >anot et al, ;niron $ci tecnal, **, -2('%-2((, ?1

hydrogen thesis

Documents