1. 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
3. Nano Composite Lab.
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
4. Nano Composite Lab.
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
5. Nano Composite Lab.
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
6. Nano Composite Lab.
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
7. Nano Composite Lab.
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.
10. Nano Composite Lab.
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
12. Nano Composite Lab.
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
13. Nano Composite Lab.
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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
14. Nano Composite Lab.
Fracture Results
Fig. 4. Load displacement curve / crack propagation in
fracture test, SENT specimen.
15. Nano Composite Lab.
Fracture result
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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
16. Nano Composite Lab.
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
19. Nano Composite Lab.
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 silane
surface 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..
20. Nano Composite Lab.
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.
21. Nano Composite Lab.
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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.
