aluminium powder-epoxy composite wear

KyungHee Univ.

Surface Modification of Aluminium Powder To

Improve Mechanical Properties of Aluminium

Powder-Polymer Composite.

Part B : Wear-Friction hardness

June 3th, 2011

Jorge Ivan Cifuentes

MECHANICAL ENGINEERING

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Introduction

Wear Mechanism

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Experiment

Aluminium powder 99.7 % from Strem chemicals, U.S.A. The reagents for the

aluminium powder surface modification were pure water J.T. Baker, U.S.A., distilled

water (99.5 %) Dae Jung Chemical (Korea), ethanol (99 % Aldrich, USA) , 3-

aminopropyltriethoxysilane with a purity of 99 % (Aldrich U.S.A.) was used as a silane

functionalization agent.

The epoxy used was diglycidil ether or Bisphenol A, resin (YD-115, Kukdo Chemical,

Korea) , and the curing agent was polyamidoamine (G-A0533, Kukdo chemicals

Korea).

Materials & Methods

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Experiment

Surface Modification of aluminium powder :

- 60 g. of unmodified aluminium powders were dispersed in 250 ml of

ethanol, then 4 ml of APTES dissolved in 25 ml of pure Baker water

was added to the aluminium dispersion

- The aluminium powder and APTES solution was mixed and stirred at 550

rpm for 6 hours at 60 °C.

- After refluxing the solution was filtered with distilled water and acetone

until the ph values approaches 6-7

- Silanized aluminium powders were dried in vaccum oven for 24 hours at

80°C.

Materials & Methods

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Experiment

Epoxy resin was heated at 60 °C and, then 10 % wt of aluminium powder was mixed

within the epoxy by stirring at 400 rpm for 12 hours using a mechanical stirring

-The epoxy resin mixed with hardener (2:1 v/v) were made using 80 g of hardener

added and manually mixed, then poured inside Teflon molds.

-The composite was degassed in a vacuum oven at 760 mm Hg for about 30 min at

room temperature

-- The mold with the composite was kept in an oven and cured at 100 °C for

approximately 15 hours, the it was post cured for 2 hours at 125 °C.

Materials & Methods

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Experiment

Preparation of tensile and fracture specimens:

The fabricated composites plates were machined as the dog-bone tensile samples,

according to ASTM D 638. Thickness and gage length of the tensile specimens are 5

and 80 mm, respectively.

Single edge notch specimens (SENT) 4 mm thick18 mm wide a 6 mm initial crack

was prepared for fracture strength toughness measurements.

Materials & Methods

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Characterization

Fourier transform infrared (FTIR) spectra were recorded in unmodified and

silane surface modified aluminium powder and composites on a Jasco

FTIR spectrometer with KBr pellets at a resolution of 4 cm -1 wave

number, in the midinfrared range of 4000 to 400 cm -1 .

Tensile and fracture tests were performed in an Instron Universal Testing

Machine (Model 8841, Dyna Might) a head rate of 0.2 mm min -1. Fracture

test were performed a head rate of 0.1 mm min -1 . At least 3 specimens of

each composite were tested to ensure reliability of test results.

The fracture surface of tensile and fracture mode I specimes were studied

by Fiel emission scanning elctron microscope (FE-SEM) (Leo Supra 55,

Carl Zeiss, Germany). The fracture surface were aputered coated with

platinum prior to their observation.

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Results & Discussion/FTIR

figure 1 show Characteristic Vibrational

modes (cm-1) , for unmodified and silane surface modified aluminium powder

a=modified

b=unmodified

Tra

nsm

itance

%

4000 3500 3000 2500 2000 1500 1000

Wave number (cm -1)

Al-OH

Al-O

Si-O-Al

Si-OH-Al

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Results & Discussion

http://web.khu.ac.kr/~nanocomp/

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Results & Discussion/FTIR

Vibrational mode Unmodified Al

FT-IR

Silanized Al

FT-IR

Unmodified Al-ep

oxy FT-IR

surface modified

Al-epoxy FT-IR

OHstretch(hydroxl ~3400 ---------- ~ 3400 ---------------

(CH2)sym.stretch. -------------- ------------------- ~2848 ~2848

Al-OH ~910 and 3600 ------------ ~3600 ----------------

Si-O-Al ----------- ~1070 ------------- ~1070

C==C stretch ---------------- ~1657 ~1657 - 1713 ~1657 - 1713

Al-O stretch ~900-750 -------------------- --------------------

Si-O-Si(siloxane g) --------------- ~ 1000-1200 -----------------------

-

~1000-1200

Si-OH (Silanol gr.) -------- ~3200-3600 --------------------- ~3200-3600

Table 1. FTIR Characteristic Vibrational modes wavenumber (cm -1) Peak positions and

assignments for unmodified and silane surface modified aluminium powder

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STRESS -STRAIN


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Fig. 2. The elastic modulus was decided by measuring the slope in the

beginning linear region in the stress-strain curve in the elastic area. Is 20

% greater in silane surface modified alumium powder-epoxy composite

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.

Figure 3 Typical stress-strain curve, in unmodified and

silane surface modified aluminium-epoxy composite

Tensile Test Results

-10

0

10

20

30

40

50

60

0.25 0.26 0.27 0.28 0.29

Tensile

stress (M

Pa)

Tensile strain (mm/mm)

Specimen 1 to 1

Specimen #

1

Elastic

modulus

0 1 2 3 4

tensile strain (mm/mm) 10 -1

Tensile

Str

ess (

Mpa

)1

0

20

3

0

40

5

0 modified

unmodified

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Stress-Strain


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Table 2 Tensile stress-strain results of unmodified and silane surface

modified aluminium powder epoxy composite

tensile strength Mpa. Young’s,mo

dulus Gpa.

toughness Elongation- %

Unmodified

Al

38 2 140 3.7

Modified Al 50.10 2.5 210 4.2

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Results & Discussion

Figure 3 shows typical tensile stress-strain curves of the Aluminium powder/epoxy

composites with unmodified, ummodified Aluminium powder . As shown in the figure, the

stress increased almost linearly with strain at an early stage, and then nonlinear behavior

occurred before reaching the maximum stress for the both nanocomposites.

In particular, the tensile strength and Young’s modulus of the Aluminium/epoxy

composites were improved by the silane functionalization. The modified composite

support higher strength , however still is more ductile compare to unmodifed aluminium

powder epoxy composite. Elastic modulus is 20 greater in modified aluminium/epoxy

composite

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Fracture Results

Fig. 4. Load displacement curve / crack propagation in

fracture test, SENT specimen.

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Fracture result


Figure 4 shows the comparison of the fracture load and displacement , modified alumium

powder/epoxy composite support 25 % greater fracture load and have 45 % longer

displacement before the collapses .

As shown in the figure 5, the stress intensity factor Kcr is equal to the fracture

toughness of the material, was calculated by the formula.

KIC = Y Pcr/BW (√a) , where “Pcr” is the fracture strength, “B” is the thickness of the

specimen, “a” is the initial crack length, and Y is the shape function. Table 3 collect the

data of fracture test.

-Fracture toughness is 25 % greater in silane functionalized aluminium powder/epoxy

composite

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Elastic Modulus


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Table 3 . Fracture test result data in surface modified and unmodifed

aluminium/epoxy composite

Fracture load (N) Displacement –du

ctility %

Elastic area ~ resi

lience

Kcr=Fracture tou

ghness

Unmodified Al 408 3.0 29.7 1.53

Modified Al 538 5.55 55.6 2.007

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Fracture Toughness

figure 5 Fracture Toughness, Mpa √m

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FESEM


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Silane modified unmodified

Figure 6. FESEM on fracture surface of both

composites

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FESEM


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Fig. 6 shown Field emission scaning microscope images on fracture section on both silane surface modified and unmodified alumium/epoxy composite.

- Debonding occurs in unmodified alumium/epoxy composite

-Several microcracks in different direction in silanesurface modified aluminium epoxy composites is indicating stronger link and adhesion between aluminium filler and the epoxy matrix, is the reason why is necessary more energy to break this inter-link and start the fracture of the composite,

-- opposite occurs in unmodified aluminium epoxy composite, fracture unidirectional occurs due to weaker interfacial adhesion between the aluminium filler and the epoxy matrix..

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Conclusions

This study demonstrated the improved mechanical properties of silane

surface modified aluminium powder epoxy composite

Silane surface modification of aluminium powder produce better

dispersion in the epoxy matrix and increase the intercalation effect.

Silane alters the hydrophilicity of the of the surface of inorganic

aluminium powder as filler material and improves the adhesion to the

epoxy matrix. The hydrolyzed silane reacts with the hydroxyl from the

aluminium surface by hydrogen bond formation. Then Si-O crosslink are

formed between aluminium surface and the adjacent functional groups in a

condensation rection-elimination of water.

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Conclusions

This enhacement is attributed to the good dispersibility and strong

interfacial bonding energy between the functionalized aluminium powder

and the epoxy matrix. It was concluded that the functionalization of

aluminium powder with 3-aminopropyltriethoxysilane is effective in

improving dispersion and adhesion in an epoxy matrix.

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THANK YOU FOR YOUR

ATTENTION

aluminium powder-epoxy composite wear

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