about molybdenum

8/9/2019 About Molybdenum

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I N T R O D U C T I O N

H I S T O R Y

R E S O U R C E S

E XT R AC T I O N &

P R O DU C T I O N P R O CE S S E S

P R O D U C T S

P R I C E S

A P P L I C A T I O N S

R E C E N T D E VE L O P ME N T S

H E ALT H & T H EE N V I R O N M E N T

Fr o n t c o ve r ph o t o : Eu r o pe a n Co u r t o f H u ma n Rig h t s ,

S t r a s b o u r g , c l a d w it h 5 0 0 0 m2

o f S 3 1 6 0 0s t a in l e s s s t e e l , c o n t a in in g 2 -3 % Mo .

Ba c k gr o u n d : Mo P in s f o r S in t e r Gl a s s Dio d e s

4

6

7

8

10

11

2 1

22

23I M OA

1 9 9 8 In t e r n a t io n a l Mo l yb d e n u m As s o c ia t io n

P r i n t e d b y B S C P r i n t L t d , 4 8 We i r R d , Wi mb l e d o n , Lo n d o n S W 1 9 8 U G


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Molybdenum is a metal l ic

element which is most

frequent ly used as an al loying

addi ti on in all oy and stainless

steels. Its al loying versati l i ty i s

unmatched because its

addition enhances strength,

hardenabil i ty, weldabil i ty,toughness, elevated

temperature strength and

corrosion resistance.

Although molybdenum is

primarily used in steels, its

complex and uni que

properties have proved

invaluable in a constantly

expanding range of other al loy

systems and chemicals.

One of the unique features of

molybdenum, as distinct from

other heavy metals, i s that

laboratory tests have shown i ts

compounds to be of low toxicity.

I N T R O D U C T I O N

3

MO.. .MOLY.. .MOLYB DE NUM:

P E R I O D I C T A B L E

P R O P E R T I E S

Atomic Weight: 95.95 g/gatom

Density: 10.22 g/ccHigh MeltingTemperature 2610

oC

Lowest ThermalExpansionCoefficient of theEngineering Metals: 4.3 x 10-6/ C

High ThermalConductivi ty: 142 W/m K

at 20oC

Crystal Str uctur e:Body-Centr ed Cubi c;Latt i ce Constant: a= 3.1468

P RIMARY CONS UMP TION

SECTORS BY END-USE*

Stainless Steels &Super Al loys 30%

Low Al loy Steels 30%

Chemicals &Mo Metal 20%Tool & H ighSpeed Steels 10%

Foundry 10%

* IMOA estimates

V Cr Mn

Nb 42Mo Tc

Ta W Re


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Molybdenum was not discovered untilthe latter part of the 18th century, anddoes not occur in the metallic form innature. Despite this, its predominant

mineral - molybdenite - was surelyutilised in ancient times but wouldhave been indistinguishable from othersimilar materials such as lead, galena andgraphite. Collectively, these substanceswere known by the Greek wordmolybdos, which means lead-like.

A 14th century Japanese sword hasbeen found to contain molybdenum.However, it was not until 1778 that the

Swedish scientist, Carl Wilhelm Scheele,was able positively to identi fy molybdenum.

He decomposed molybdenite by heatingit in air to yield a white oxide powder.Shortly thereafter, in 1782, Peter JacobHjelm reduced the oxide with carbon toobtain a dark metallic powder which henamed molybdenum.

Molybdenum remained mainly a

laboratory curiosity throughout most ofthe 19th century until the technology forthe extraction of commercial quantitiesbecame practical. In 1891, theFrench company Schneider & Co. firstused molybdenum as an alloyingelement in the production of armourplate. It was quickly noted that, with adensity of only slightly more than halfthat of tungsten, molybdenum was aneffective replacement for tungsten in

numerous steel alloying applications.

World War I caused tungsten demand tosoar and severely strained its supply.As a direct result, molybdenum wassubstituted for tungsten in many hardand impact resistant steels. The resultingincreased demand initiated an intensivesearch for new sources of molybdenumsupply, culminating with the development

of the massive Climax deposit in Colorado,

USA and its init ial operation in 1918.

H I S T O R Y

4

Whilst the word molybdenum was only introducedinto the English language around 1816, an analysis of

parts of the sword of the famous 14th centuryJapanese artist, Masamune, proved that it contained

molybdenum. (ref. Sutu lov A., Int. MolybdenumEncyclopedia, Intermet Publ., Chile 1978)

Wills Saint Claire - First automobile constructed with Mo steels

ATOMIC WEIGHT OF MOLYBDENUM: 95.95 g/g atom

ATOMIC WEIGHT OF TUNGSTEN: 183.85 g/g atom


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The end of the war and the consequentreductions in demand triggered researchefforts to develop new civilian applications

for molybdenum. A number of new

low-alloy molybdenum automotive steelswere soon tested and accepted. The bigbreakthrough, however, occurred in the1930s with the determination of propertemperature ranges for the forging andheat treatment of molybdenum-bearinghigh-speed steels. From this beginning,research eventually developed a fullunderstanding of how molybdenumimparts its many cost-effective benefits asan alloying element to steels and other

systems.

By the end of the 1930s, molybdenumwas a widely accepted technical material.The conclusion of World War II in 1945once again brought increased researchinvestment to develop new civilian appli-cations, and the post-war reconstructionof the world provided additional marketsfor structural steels, many of which

already contained some molybdenum.

The years from 1945 to the present haveseen a dramatically expanding range ofapplications for molybdenum, its alloys

and its compounds. Rising demand hasbeen comfortably balanced by newsources of assured supply and by newprocessing technologies with superiorrecovery rates.

Although steels and cast iron comprise

the single biggest market segment,molybdenums diversity has also proveninvaluable in superalloys, nickel basealloys, lubricants, chemicals, electronicsand many other applications.

H I S T O R Y

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Architectural application of S31600 stainless steel, (2-3% Mo), Fin land

Other Countries: Mexico, Peru, Iran, CIS, Mongolia.Other may be understated as estimates for production in the CIS vary.

Mine production is supplemented by recycled material, mainly from spent catalysts*I MOA Estimate

70,000

50,000

30,000

40,000

60,000

0

10,000

20,000

1993 1994 1995 1996

94,000 107,000 130,000 119,000Totals

USA

China

Chi le

Canada

Other

Min e Pr odu c t ion *(MT of Mo con t a in e d)

1997

131,000


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Molybdenum is only known to occur in anatural state chemically combined withother elements. Although a number ofmolybdenum-bearing minerals have beenidentified, the only one of commercialsignificance is molybdenite (MoS2) - anatural molybdenum sulphide. In orebodies, molybdenite is generally presentin grades from 0.01- 0.50% and isoften associated with the sulphideminerals of other metals, notably copper.

Reserves are mainly located in thewestern mountain regions of North andSouth America. The USA is by far thelargest producing country, and also has

the largest reserve base of 5.4 milliontonnes, nearly half of the worlds total.

Ore bodies and mines can be classifiedinto three types:

Primary mines, where therecovery of molybdenite is thesole objective;

By-product mines, whichremove molybdenite duringcopper recovery;

Co-product mines, wherecommercial viabili ty is dependentupon the extraction of bothmolybdenite and copper-bearingminerals.

M I N E S

R E S E R V E S

R E S O U R C E S

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Molybdenite parti cles coat bubbles during flotation process

USA

5,400,000 MT

Chi le

2,500,000 MTOther2,190,000 MT

China1,000,000 MT

Canada910,000 MT

Wor l d Mol ybde n um Re s e r ve s (12 ,000 ,000 MT)

Source: USGS


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The relatively low grade of most Mo oresnecessitates the use of high volume low

cost mining extraction techniques, mostcommonly:

Massive open cast pits; or Underground block caving,

wherein large blocks of ore areundercut and allowed to collapseunder their own weight.

Many molybdenum mines are amongstthe most productive in the world, withthe largest capable of moving over 50,000tonnes of ore per day.

Mined ore is pulverized through a seriesof crushers and rotating ball and/or rodmills to fine particles that may be onlymicrons (1/1000th mm) in diameter. This

liberates the molybdenite from its hostrock. A water slurry of the ore is thenconditioned with reagents - including

some fuel or diesel oil - which coats themolybdenite particles, rendering themwater-repellant.

Separation by flotation takes place inaerated tanks. Molybdenite particlesattach to ri sing air bubbles and concentrate

in the surface froth which is swept into

overflow troughs. Subsequent regrindingand reflotation stages increase themolybdenite content of the new concen-trate stream, by steadily removingunwanted material. The final concentratecontains between 70-90% molybdenite.If required, an acidic leach may beemployed to dissolve impurities such ascopper and lead.

The roasting process converts molybdenite

concentrate into technical molybdenumoxide by the following chemical reactions:

These take place at 600-700oC in large

multihearth furnaces or roasters.Sulphide concentrate is rabbled from the

centre to the periphery of one hearthwhere it drops to the hearth below and israbbled back to the centre. It reactscontinuously with a steady supply offorced air during the 10 hours it takes tocomplete the circuit across a dozen ormore hearths. The resulting technicalgrade molybdenum oxide typicallycontains a min imum of 57% molybdenum,

and less than 0.1% sulphur. Desulphurisation

systems remove sulphur dioxide from theeffluent roaster gases.

Some of the by-product molybdeniteconcentrates from copper mines containsmall quantit ies (< 0.10%) of rhenium, ametallic element used in catalysts for theproduction of unleaded gasoline and inadvanced superalloys for turbine bladesof the latest jet engines. Molybdenumroasters equipped to recover rhenium

are one of the principal commercialsources for this rare metal.R O A S T I N G

M I L L I N G

M I N I N G

E XT R A C T I O NA N D P R O D U C T I O N

P R O C E S S E S

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Bingham Canyon molybdenum by-product mine

2MoS2

+ 7O2= > 2MoO

3+ 4SO

2

MoS2

+ 6MoO3= > 7MoO

2+ 2SO

2

2MoO2

+ O2= > 2MoO

3


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P r od u ct ion of Mol ybde n u mPr odu c t s

Roasted molybdenite concentrates(generally known as tech-oxide) is the

principal product for adding molybdenumto alloy and stainless steels. In order toaccommodate individual steel-makingrequirements, tech-oxide is available in avariety of forms and packaging, eg

Powder: packaged in bulk-bags,drums or cans.

Briquettes: carbon-free pil lowshaped, and packed inbulk-bags or drums.

Briquettes: carbon-bonded pillowshaped, and packaginge.g.: in 10 kg. boxes.

Ferromolybdenum (FeMo) is producedby the thermite reduction of tech-oxide

in the presence of iron. With a typicalanalysis of 60-70% Mo (remainder iron),it is used as a molybdenum addition inthe ladle or in melting processes, such asinduction melting, which cannot reducethe oxide. Higher molybdenum contentvariations are also available. Westernworld FeMo production is approximately45 million lbs Mo annually.

F E R R O M O L Y B D E N U MT E C H N I C A L O X I D E

P R O D U C T S

8

MINEDORE

CRUSHING

GRINDING

FLOTATION

LEACHING

MOLYBDENITE CONCENTRATESMo S2

ROASTING

TECHNICAL GRADEMo 0 3

FURTHERPROCESSIN G

PURE MoS2

SMELTING

BIG-BAGS DRUMS

BI G-BAGS DRUMS

BRIQUETTES

BI G-BAGS CANS

POWDER

DRUMS

CHEMICALROUTE

LUBRICANTS

FeMo

Some molybdenum containing alloys, such as super-alloys, cannot tolerate iron andmust be melted with molybdenum metal. This is produced by a hydrogen reduction ofpure molybdic oxide or ammonium molybdate. The molybdenum powder is pelletisedfor ease of handling in the melt shop.

M O M E T A L


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Some technical oxide is furtherprocessed into a number of chemical

products, and into pure molybdenummetal.

Technical oxide is upgraded bysublimation to produce pure MoO3, andby wet chemical processes to produce awider range of pure molybdenumchemicals (mainly oxides andmolybdates). The latter involves theinitial dissolution in an alkaline medium(ammonium or sodium hydroxide)

followed by removal of impurities byprecipi tation and fil tration and/or solventextraction.

The resulting ammonium molybdatesolution is then converted to any one ofa number of molybdate products bycrystallisation or acid precipitation.

These can be further processed bycalcination to pure molybdic tr ioxide.

Molybdenum chemicals are extensively

appl ied due to their unique characteristics,such as:

Catalytic activity in petroleumdesulphurising catalysts;

colourful pigments; corrosion inhibitors; micronutr ients in fertil isers;

flame and smoke suppression; lubricity under extreme pressureand temperature conditions.

C H E M I C A L P R O D U C T S

P R O D U C T S

9

P r oduc t ion o f mo l ybde n um Che mic a l s

OREMOLYBDENITECONCENTRATE

LUBRICANTGRADE MoS2

TECHNICALMOLYBDENUM

OXIDE

SODIUMMOLYBDATE

AMMONIUMDIMOLYBDATE

AMMONIUMPOLYMOLBDATE

PUREMOLYBDENUM

TRIOXIDE

AMMONIUMHEPTAMOLYBDATE

Mo METAL

ROASTING

CHEMICAL TREATMENT

CALCINATION

UPGRADING

SUBLIMATION


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Samples of technical oxide and ferromolybdenum

P R I C E S

10

9

1992

0

1

2

3

4

5

6

7

8

20

5

10

15

1993 1994 1995 1996US$/Lb

MoO3

FeMo

US$/Kg

Source: Mo03: Metals Week Dealer Oxide price FeMo: Metals Week European FeMoprice

Ann ual Aver age Pr ice s of Te ch n ica l Gr ade Mol ybde n um Oxide

in US$/Lb Mo an d Fe r r omol ybd e n u m in US$/Kg Mo


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Mol ybde n um Con s umpt ion by End-Us e in 19 97 (excl . China & CIS)

Molybdenum demand is primarilydependent upon the production of alloy,

stainless and tool steels, and cast ironswhich extensively use molybdenum to:

minimise the cooling rate necessaryto obtain a hard martensite structure

and thereby increase strength,hardness, and toughness in largeheavy section components;

reduce temper embrittlement; resist hydrogen attack;

resist sulphide stress cracking (SSC);

increase elevated temperaturestrength; improve the resistance of stainless

steels to a wide variety of corrosiveenvironments, especially chloridepitting resistance;

improve weldabili ty, especially inhigh-strength low-alloy (HSLA) steels.

Molybdenum is an important constituent

in most superalloys and many nickel andtitanium based alloys, wherein: it is apotent solid solution strengthener atelevated temperatures; it increases chloride

pitting resistance; it increases corrosionresistance in reducing solutions.

Molybdenum and its alloys are findingever widening use because of their highstrength up to 2000

oC, low coefficient

of expansion combined with goodthermal and electrical conductivity; highresistance to corrosion by molten glass,

salts and metals; and good wearresistance in thin coatings.

Molybdenum is an exceptional steelalloying element that not only impartsmany unique and useful characteristics tosteel but is also easy to add to the mol tenmetal. Melt losses are minimal, whetherthe molybdenum is added as oxide, FeMo

or as Mo-containing steel scrap.

M O LY B D E N U M & ST EE L

M O B A S E A L L O Y S

N O N - F E RR O U S A L L O Y S

F E R R O U S M A T E R I A L S


11

x 115,000MTMo Content

Tool andHigh SpeedSteels10%

FoundrySteels10%

Chemical

and Mo Metal20%

Low Al loySteels30%

StainlessSt eels &Super Al loy s30%

Source: IMOA estimates


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Molybdenum (0.15-0.30%) is usedin carburising steels to increase

simultaneously the hardenability of thelow carbon core and toughen the highcarbon case. It is especially effective inlarge cross sections, such as gears.Molybdenum is not oxidised duringcarburisation, making it an effectivehardening agent which does not causeincreased surface cracking and spall ing.

The molybdenum atom is very largerelative to other alloying elements. As

such, it is a very potent strengthener andincreases creep strength up to about600

oC. Its size effectively impedes

migration of arsenic atoms to grainboundaries and thereby providesresistance to temper embrittlement.Hydrogen diffusion is also impeded andthis minimises hydrogen cracking.

One of the earliest high temperaturesteels to use these attributes was thecarbon-0.50% Mo steel. It has beensuperseded by a family of Cr-Mo steels

which contain from 0.50-2.0% Mo.2.25 Cr-1.0 Mo steel is a work-horse alloyused worldwide in oil refineries, powerplants and petrochemical plants.

Molybdenum has played an importantrole in the development of low carbon,microalloyed HSLA steels. The addit ion

of 0.1-0.3% molybdenum produces a finegrain structure of acicular ferrite andsubstantially enhances the precipitationhardening effects achieved from otheralloying elements.

High yield strengths of 450-600 MPa(65-85 ksi) are achieved in HSLA steelswithout extensive heat treatment. With aductile/brittle transition temperature aslow as -60oC, these materials have beenused in large quantities to build pipelinesfrom remote Arctic oil and gas fields.Thinner gauges of Mo-containing HSLAsteels have excellent formability and theirhigh strength/weight ratios make themideal for the production of automotivestructural parts.

H I G H S T R E N G T H L O WA L L O Y ( H S L A ) S T E E L S

H I G H T E M P E R A T U R ES T E E L S

C A R B U R I S I N G S T E E L S


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Valve casting in Hastelloy CW6M, containing up to 20% Mo towithstand severe corrosion at high temperatures


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The continuous search for new sources

of oil has necessitated the explorationand development of very deep reservoirs,often contaminated with corrosivehydrogen disulphide, carbon dioxide andhigh chloride brines. The AISI 4100 seriesof Cr-Mo steels, containing 0.15-0.25%Mo, are widely used. A modified AISI 4140

with 0.4-0.6% Mo is the most sulphidestress cracking (SCC) resistant lowalloy steel available for use in sourwells. As depths increase and service

conditions become more severe, highermolybdenum stainless steels andnickel base alloys, such as alloy C-22(13% Mo) and alloy C-276 (16% Mo) areincreasingly used.

Stainless steels are corrosion resistantbecause the chromium content

spontaneously forms a thin, protectivepassive film on the surface of the steel.Molybdenum enhances this passive filmby making it stronger and helping it tore-form quickly if it is disrupted bychlorides. Increasing the molybdenumcontent increases the pitting and crevicecorrosion resistance of stainless steels.

Type 316 (2-3% Mo) is the most widelyused Mo-containing stainless steel. It isspecified for the tanks, piping and heatexchangers used in food handling andprocessing and in the productionof pharmaceuticals. Increasing themolybdenum content heightens theresistance to wind-borne chlorides andso Type 316 is the material of choice forarchitectural applications in marine,coastal environments. Type 316 was used

to clad the exteriors of the Canary Wharfbuilding in London and the tallestbuilding in the world, the PetronasTowers in Kuala Lumpur, Malaysia.

Duplex stainless steels (3-4% Mo)

combine high strength and excellentchloride stress corrosion crackingresistance. Initially used for gatheringlines in the oil and gas industry, theseversatile stainless steels are increasinglybeing used in the chemical processand petrochemical industries and fordigesters in the pulp and paper industry.

The most corrosion resistant stainlesssteels contain 6 - 7.3% Mo. These gradesare used for power plant condensers,offshore piping, and critical componentsin nuclear power plants such as servicewater piping. In 1996, 6% Mo stainlesssteels were selected for the absorbertowers of more than twenty fluegas desulphurisation scrubbers beinginstalled in coal-burning power plants inSouth Korea.

S T A I N L E S S S T E E L S

O I L C O U N T R YT U B U L A R G O O D S


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Giusti S31600 stainless steel pharmaceuticalmanufacturing vessels, (2-3% Mo content)


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The passive chromium oxide layer ismost vulnerable near grain boundariesand non-metallic inclusions where minute

galvanic cells can form and cause rapidpitting. Oxygen depleted regions, such asthose found under gaskets or lap joints,are susceptible to similar attack, but it isusually called crevice corrosion.

Molybdenum is the most potent and costeffective alloying element for preventingpitting and crevice corrosion. Stresscorrosion cracking (SCC) can occurwhenever applied or residual tensilestresses are present within a stainlesssteel that is exposed to a corrosive media,

especially those containing chlorides andsulphides at elevated temperatures.Higher molybdenum contents are one ofthe most efficient ways to improve asteels resistance to SCC.

The illustration above shows Type 304(0% Mo) and Type 316 (2-3% Mo) testpanels exposed for 56 years at themarine atmospheric test facility of LaQueCorrosion Services on the Atlant ic Ocean,

North Carolina. While Type 316 is notcorrosion free, it is in excellent condition

after more than half a century in a verysevere environment. The stainless steelwithout Mo is extensively corroded. Thephoto il lustrates dramaticall y the beneficial

effect of molybdenum additions instainless steels.

The most severe operating environmentsencountered in power plant scrubbers,pulp and paper and chemical processequipment, require the use of alloyswith even higher molybdenum contents.A spectrum of increasingly highermolybdenum alloys includes grades withtypicall y 6 - 8% Mo and nickel base alloys

with 10% and 16% Mo.

P I T T I N G / C R E V I C EC O R R O S I O N


14

Types 304 (0% Mo) and 316 (2-3% Mo) test panels after56 years marine exposure

Sulphuri c acid plant for the desulphuri sationof flue gases


15/24

One of the earliest applications ofmolybdenum was as an efficient and costeffective replacement for tungsten in tooland high-speed steels. The atomic weightof molybdenum is roughly half that oftungsten and therefore 1% Mo is roughlyequivalent to 2% tungsten. Because thesehighly alloyed steels are used in theworking, cutting and forming of metalcomponents, they must possess highhardness and strength, combinedwith good toughness, over a broad

temperature range.

Molybdenum in tool steels increasestheir hardness and wear resistance. Byreducing the critical cooling ratemolybdenum promotes the formation ofan optimal martensitic matrix, even inmassive and intricate moulds whichcannot be cooled rapidly without

distortion or cracking. Molybdenum alsoacts in conjunction with elements likechromium to produce substantialvolumes of extremely hard and abrasionresistant carbides.

As the physical demands placed ontool steels increase, so too does themolybdenum content ...

When tool steels contain a combinationof more than 7% molybdenum, tungstenand vanadium, and more than 0.6%

carbon, they are referred to as high speedsteels. This term is descriptive of theirability to cut metals at high speeds.Until the 1950s, T-1 with 18% tungstenwas the preferred machining steel, butthe development of controlled atmosphere

heat treating furnaces made it practicaland cost effective to substitute part or allof the tungsten with molybdenum.

H I G H S P E E D S T E E L S

T O O L S T E E L S

T O O L & H I G H -S P E E D S T E E L S


15

A selection of high-speed cutting tools

% Mo

Plastic

moul ding steels up to 0.5

Cold work

steels 0.5 - 1.0

Hot work

steels up to 3.0

Typical Composit ions of SelectedHigh-Speed Steels (%)

Grade C Cr Mo W V

T-1 0.75 - - 18.0 1.1

M-2 0.95 4.2 5.0 6.0 2.0

M-7 1.00 3.8 8.7 1.6 2.0

M-42 1.10 3.8 9.5 1.5 1.2


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Additions of 5-10% Mo effectivelymaximise the hardness and toughness ofhigh-speed steels and maintain theseproperties at the high temperatures

generated when cutting metals.Molybdenum provides anotheradvantage: at high temperature, steelssoften and become embrittled if theprimary carbides of iron and chromiumgrow rapidly in size. Molybdenum,especially in combination with vanadium,minimises this by causing the carbides toreform as tiny secondary carbides whichare more stable at high temperatures.

The largest use of high-speed steels is inthe manufacture of various cutting tools:drills, milling cutters, gear cutters, sawblades, etc.

The useful cutting characteristics ofhigh-speed steel have been furtherextended by applying thin, but extremelyhard, titanium carbide coatings whichreduce friction and increase wear

resistance, thereby increasing cuttingspeed and tool life.

The exceptional high temperature wearproperties of molybdenum-containinghigh-speed steels are ideal for newapplications such as automobile valveinserts and cam-rings.

Molybdenum increases the strength andhardness of cast irons by depressing the

pearlite transformation temperature. Italso increases elevated temperaturestrength and creep resistance. Highchromium irons, containing 2-3%molybdenum, exhibit significantly greaterimpact toughness than Mo-free grade andare ideal for severe abrasive conditionslike those encountered in mining,milling, crushing etc. These cast ironshave acceptable properties as cast. Thiseliminates the need for a costly heattreatment and makes them a costeffective alternative to other grindingmaterials. Reduced levels of austeniteformers, such as nickel and manganese,also minimise the retention of lowtemperature austenite - a potential causeof premature failures.

There has been growing interest in theuse of high silicon-molybdenum ductileirons with up to 4% Si and 1% Mo. Theirgood strength up to 600

oC makes them a

viable and cost effective replacement formore highly alloyed irons and steels inelevated temperature applications suchas turbocharger housings, engineexhaust manifolds and furnacecomponents. The austempered nodularirons develop a unique microstructurecapable of strengths in excess of1000 MPa (145 ksi) with good impacttoughness. Their exceptional propertiesare ideal for critical applications such as

the large gears and crankshafts requiredfor power generation, ship propulsionand large mining equipment.

The main limitation to increasing thealloy content of highly alloyed, ingot castmaterials like high-speed steels is theirtendency to segregate during the slowcooling. Powder metallurgical (PM)techniques atomise molten steel into tiny

droplets that cool so rapidly that internalsegregation is prevented. Steels producedby compaction of these particles have a

P O W D E R M E T A L L U R GY

C A S T I R O N S


Mo/Cu and W/Cu Heat Sinks for Thermal Management in

Microelectronic Devices

16


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far more uniform microstructure, whichprovides numerous advantages overequivalent conventional grades. ManyPM high-speed steels, stainless steels

and nickel-base alloys are commerciallyavailable and, in the future, thistechnique promises to make possiblenew generations of highly alloyed steels.

PM techniques enable the superalloyindustry to produce more highly alloyedcompositions for critical parts, such asgas turbine components.

Molybdenum metal is usually producedby powder metallurgy techniques inwhich Mo powder is hydrostaticallycompacted and sintered at about 2100

oC.

Hot working is done in the 870-1260oC

range. Molybdenum forms a volatileoxide when heated in air above about600

oC and therefore high temperature

applications are limited to non-oxidisingor vacuum environments.

Molybdenum alloys have excellentstrength and mechanical stability at hightemperatures (up to 1900

oC). Their high

ductility and toughness provide a greatertolerance for imperfections and brittlefracture than ceramics.

The unique properties of molybdenumalloys are uti li sed in many applications:

High temperature heating elements,

radiation shields, extrusions,forging dies, etc;

Rotating X-ray anodes used inclinical diagnostics;

Glass melting furnace electrodesand components that areresistant to molten glass;

Heat sinks with thermal expansivitymatching silicon for semiconductorchip mounts;

Sputtered layers, only ngstroms(10

-7

mm) thick, for gates andinterconnects on integratedcircuit chips;

Sprayed coatings on automotivepiston rings and machinecomponents to reduce friction andimprove wear.

For specialised applications, Mo is alloyedwith many other metals:

Mo-tungsten alloys are noted forexceptional resistance tomolten zinc;

Mo is clad with copper to providelow expansion and highconductivity electronic circuit boards;

Mo-25% rhenium alloys are used forrocket engine components andliquid metal heat exchangers whichmust be ductile at room temperature.

M O B A S E A L L O Y S


Rotor of a gas turbine, type FR 9001/E, 170 MW, wi th highMolybdenum-containing steel blades (Courtesy of Nuovo Pignone, Firenze)

Spherical Agglomerates of Mo Powder (lacy appearance),with solid spheres of the Ni-Cr alloy binder for the Mo powder

17


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Molybdenum enhances the corrosionresistance and mechanical properties ofnickel base alloys in the same way that itimproves the corrosion resistance ofstainless steels. Many high molybdenumcorrosion resistant nickel base alloys arewidely used in applications alreadymentioned.

Molybdenum is a very potent matrixstrengthener in the high temperature

superalloys which made jet enginespractical. Molybdenum (up to 5%)strengthens the nickel matrix andextends service temperatures bypartitioning between the nickel matrixand the gamma prime precipitate phase.These alloys are widely used in therotating components such as turbineblades and discs of jet engines. HigherMo alloys, such as alloy X (9% Mo) areused in many stationary combustioncomponents. Today, superalloys comprise

over a third of a jet engines weight.Stellite 21, a 5% molybdenum cobalt baseinvestment casting alloy, has excellentcorrosion resistance to body fluids and iswidely used in prosthetic devices.

Addi tions of up to 5% Mo are used in thealpha-beta type titanium alloys. Thesematerials can be effectively heat treatedto strengths in excess of 1000 MPa(145 ksi) and are used in the aircraftindustry for jet engine compressor andstructural components where lowweight, high strength and corrosionresistance are of primary importance.

Molybdenum-based chemicals have the

versatility of chemistry which can occurbetween the transitions of + 4, + 5 and+ 6 oxidation states. Materials madefrom molybdates are oxidation catalysts,have photo-activity, and can offersemiconducting properties. Many of theproperties of molybdenum can providedevelopment opportunities and newcommercial applications through theexploration of its chemistry. Compoundsof molybdenum can often be made which

mimic the chemistry of toxic elements,but which are a safer substitute.

The uses of molybdenum-based catalystsare extensive. When combined withcobalt and nickel, molybdenum is usedin the petroleum industry for i ts abil ity toremove sulphur from the organic sulphurcompounds usually found in crude oil.As the world supply of crude oil isfurther extended and low-sulphur crudesare less available, molybdenum-basedcatalysts will increase in use. Mo catalystscan convert hydrogen and carbonmonoxide produced by the pyrolysis ofwaste materials to alcohols in thepresence of sulphur, under conditionsthat would poison precious metalcatalysts. Mo has been used in the

conversion of coal to hydrocarbonliquids. Molybdenum not only allows foreconomical fuel refining but alsocontributes to a safer environmentthrough lower sulphur emissions.

Molybdenum, as a component ofa selective oxidation catalyst, willconvert propylene, ammonia and air toacrylonitrile, acetonitrile and otherchemicals which are important to the

plastics and fibre industries.

C A T A L Y S T S

C H E M I C A LA P P L I C A T I O N S

T I T A N I U M B A S EA L L O Y S

S U P E R A L L O Y S &N I C K E L B A S E

A L L O Y S


18


19/24

Molybdates are used for two properties,stable colour formation and corrosion

inhibition.

Molybdenum oranges are light and heatstable pigments, from bright red-orangeto red-yellow in colour, which are usedin paints and inks, plastic and rubberproducts, and ceramics. Molybdo-phosphoric acid is used to precipitate thedyes Methyl Voilet and Victoria Blue.White corrosion inhibiting pigments areused as paint primers.

Sodium molybdate has been used fordecades as a substitute for chromates forthe inhibition of corrosion in mild steelsover a wide range of pH. Molybdateshave a very low toxicity and are lessaggressive oxidants toward organicadditives that are often used in corrosion

inhibiting formulations. The protectionof mild steel used in the construction ofair-conditioning cooling water andheating systems is a prime application.Molybdate solutions protect againstrusting of steel parts during machining,and are used in water-based hydraulicsystems. It is also used as an additive inautomobile engine anti-freeze.

Corrosion inhibiting pigments, primarilyzinc molybdate, but also molybdatesof calcium and strontium, are usedcommercially in paints. These pigmentsare white and can be used as a primer oras a tint with any other colour.

In electronic technology, wire and cable

insulation represents a fire and smokehazard to firefighters and those in theconfines of aircraft and hospitals.

Ammonium octamolybdate has beenused with PVC to suppress the formationof smoke. These uses and otherdevelopments will be increasing as video,telephone and computing networksincrease.

S M O K ES U P P R E S S A N T S

C O R R O S I O NI N H I B I T O R S

P I G M E N T S


19

Precipi tation of molybdenum red pigment

Cross-section of a molybdenum disulphide film showing theplate-like structure


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Molybdenum disulphide, the mostcommon natural form of molybdenum, is

extracted from ore and then purified fordirect use in lubricants. This material byitself, since it has a layered structure,makes a very efficient lubricant. Theselayers can slide over each other at themolecular level, allowing the surfaces ofsteel and other metals to move fluidly,even under severe pressures, as bearingsurfaces. Since molybdenum disulphideis of geothermal origin, it has thedurability to withstand heat and

pressure. This is particularly true if smallamounts of sulphur are available to reactwith iron and provide a sulphide layerwhich is compatible with molybdenumsulphide in maintaining the lubricatingfilm. Molybdenum disulphide is inert tomany chemicals and will perform under avacuum where graphite fails.

A number of unique propertiesdistinguish molybdenum disulphide

from other solid lubricants:

A low coefficient of friction(0.03-0.06) which, unlike graphite,is inherent and not a result ofabsorbed films or gases;

A strong affinity for metals; Film forming structure; A yield strength as high as 3450 MPa(500 ksi) ;

Stability in the presence of mostsolvents;

Effective lubricating properties fromcryogenic temperatures to about350

oC in air (1200

oC in inert or

vacuum conditions).

A combination of molybdate and watersoluble sulphides can provide bothlubrication and corrosion inhibition incutti ng fluids and metal forming materials.

Oil soluble molybdenum-sulphurcompounds, such as thiophosphatesand thiocarbamates, provide engineprotection against wear, oxidationand corrosion. Several commercialmanufacturers supply these additives to

the lubrication industry.

L U B R I C A N T S


2 0

1-20 Greases - for manufactur ing, Ball & rol ler bear ings,mining and transportat ion splines, chassis. conveyors

20-60 Pastes - mineral or synthetic Assembly of machinery,base splines, gears, universal

joints, metal forming

0.5 - 5 Industrial and Motor Oi ls Al l automotive and

or Synthetic Fluids industrial gears, reducers,cams, etc

1-20 Water Suspensions Metalworking and processlubrication, threads, slides,packings, die casting

Up to 85 Bonded Coatings - air Threads, tool s, switches,or heat cured, organic, locks, valves, sl ides, processinorganic lubrication, metalworking

1-40 Metalworking compounds Extrusion, co ld forming,Soaps, Powders, etc wire drawing, deep drawing

10-100 Pure or Mixed Powders Punching, stamping, forming,relays, switches, packings

Composites1-10 Friction Products, Sintered Aircraft, automotive and rail

Cu brakes, Semi-metall ic brake pads & clutch liningsand Non-asbestos Pads

1-30 Plast ic, Rubber & Metal Gears, sl ides, bear ingsComposites thrust washers, O-rings

Mo Content Product Type Uses(%)


21/24

The second generation of duplex

stainless steels has become a complexfamily of great commercial significanceduring the last decade. The combination ofcorrosion performance and advantageous

mechanical properties auger well forrapid growth in applications during thenext few years.

Duplex stainless steels, with amicrostructure of about 50% austenite,50% ferrite and an Mo content of

up to 5%, provide an unusually goodcombination of properties:

typically twice as strong as thecommon austenitic stainless steels;

many of the advantages of theferritic stainless steel, for examplehigh resistance against chloridestress corrosion cracking;

the range of corrosion resistance isalmost as extensive as that ofaustenitic stainless steels.

Duplex stainless steels have a proventrack record as versatile materials both in

highly corrosive environments and ascost efficient engineering materials forstainless steel structures. Applicationsinclude:

pulp & paper industry chemical & petrochemical industries hydrometallurgy organic acid and caustic media pollution control equipment chemical tankers on/off shore applications brewery and piping systems architectureN 10276, a nickel base alloy containing15-17% Mo, is used in the construction ofseawater-based flue-gas desulphurisationplants, where the combination of seawaterand sulphur-laden flue gases produce ahighly corrosive atmosphere.

Use of this alloy, which performs well inthe aggressive environment of theabsorber towers (or scrubbers) of the

FGD plant, contributes towardsmaintenance of removal efficiencylevels of 99%, which are significantlyhigher than those for conventionaldesulphurisation methods.

D U P L E X S T A I N L E S SS T E E L S

R E C E N TD E V E L O P M E N T S

21London Tube tunnel linings use highly alloyed super duplex stainless steel


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Molybdenum plays a vital part ineveryday life, particularly in relation tomany aspects of the protection of humanhealth and the environment.

The toxicity of molybdenum is low,reducing concerns about the presence oftrace amounts in water and soils which

may enter the human food chain.Further, this low toxicity enablesmolybdenum to play a significant part inlubricants used for food processingmachinery, minimising the consequencesof accidental contamination.

There has been much concern about thegeneration of fumes when materials suchas those used for carpets and furniture,made from artificial fibres, ignite.Molybdenum compounds in certainpolymers have been found to beparticularly good smoke suppressants.

Molybdenum-containing catalysts areused in the production of petroleumproducts to remove sulphur, therebyminimising emissions. This applies not

only to the internal combustion enginebut also to gas turbines, large combustion

plants for power generation and firedheaters in the chemical, petrochemicaland process industries.

Molybdenum plays a most importantpart in processes developed to treatpollutants, such as the desulphurisationof flue gases generated by combustion ofsulphur containing fossil fuels and the

cleaning of gases from the incineration ofmunicipal and other wastes. Here, fulladvantage is taken of the classical role ofmolybdenum in enhancing the corrosionresistance of stainless steels andnickel-base alloys to withstand extremeconditions of corrosion attack.

Cost effective applications of molybdenum

containing materials are demonstrable,

taking advantage in design of inherentcharacteristics of strength, corrosionresistance and integrity.

Sponsored by IMOA and conducted inaccordance with internationally acceptedprotocols and Good Laboratory Practice,toxicity tests have shown molybdenumoxide, ammonium dimolybdate and sodium

molybdate to be non-toxic (based on EUcriteria of a harmful substance) following

acute oral, inhalation and dermalexposures. These materials were alsofound to be non-irri tating to the skin andeyes and non-sensitising.

Similar ecotoxicity tests showed puremolybdenum oxide, ammoniumdimolybdate and sodium molybdate tobe non-toxic to fish and daphnidsfollowing acute exposure. Algal growthwas inhibited only by ammoniumdimolybdate, probably due to theammonia component rather than themolybdate ion.

H E A L T H & T H E

E N V I R O N M E N T

2 2

Seawater-based flue-gas desulphurisation plant


23/24

The International Molybdenum

Association (IMOA) was founded in1989 and has become the focal point ofpromotional, statistical and technical

activities for the worldwide molybdenumindustry. Membership is broad based andincludes producers, consumers, converters,

traders and assayers. IMOAs secretariat isbased in London.

IMOAs main activities currently include:

promoting molybdenum as amaterial with superior propertiesand performance in a wide variety

of metallurgical, chemical and otherproduct applications:

monitoring molybdenum in relationto health, safety and environmentalissues; with the increasing amountof legislation in many countriesrelating to the use and disposal ofmetals and metal bearing materials,IMOA provides a centrali sed serviceincluding research studies on those

issues that may affect themolybdenum industry;

collecting the industrys mostcomprehensive historical statisticson world supply and demand ofmolybdenum products which aredistributed to all IMOA members ona regular basis;

organising meetings andpromotional conferences beneficialto the molybdenum industry;

preparing worldwide industryguidelines to improve theconsistency and quality in samplingand assaying procedures formolybdenum products.

I M O A

2 3

ACKNOWLEDGMENTSAcknowledgement and thanks are given to the

following for providing photographs

and i llustrations:

Avesta Sheff ield Ltd

Bruchsaler Farbenfabrik GmbH & Co. KG

Collins Illustrated Guide to Japan (by

Alan Booth, The Guide Book Co.)

Codelco-Chile

CSM Industr ies Inc.

Cyprus Climax Metals Co.

T. Giusti Ltd

Kennecott Utah Copper Corp.

Maca Supply Company, USA

Nickel Development Institute

Nuovo Pignone

Plansee Ak ti engesell schaft

Presto Engineers Cutting Tools

Sadaci NV

H.C. Starck GmbH & Co. KG

Technical Marketing Resources Inc.

Thompson Creek Metals Co. LLC

OTHER IMOAPUBLICATIONS INCLUDE:

Applications of Molybdenum inEnvironmental & Human Health

Protection

Procedure for Weighing and Sampling

Molybdenite ConcentratesProcedure for Weighing and Sampling

Technical GradeMolybdenum Oxide

Procedure for Weighing and SamplingFerromolybdenum

Applications of Mo Metaland its Alloys

The Evolution of High

Performance Stainless SteelsOn the In ternet: Database of

Molybdenum in the Environment[http://www.imoa.org.uk]Background to back cover photo: Precipitation of

Ammonium Polymolybdate


24/24

IN TERNATIONAL MOLYBDENUM ASSOCIATION

I M O AUni t 7 Hackford Walk , 119-123 Hack for d Road, London SW9 0QT, England

Tel: + 44 171 582 2777; Fax: + 44 171 582 0556E mail : ITIA IMOA@compuserve com ht tp://www im oa org uk

about molybdenum

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