PDT 256 (MATERIAL CHARACTERIZATION)
SEMESTER 3(2019/2020)
ASSIGNMENT 2
NAME:LOKMAN HAKIM BIN MAHAMUD
MATRIC NO: 181352618
LECTURER’S NAME: DR HEAH CHENG YONG/DR MOHAMMAD
FIRDAUS ABU HASHIM
QUESTION 1
1. Zirconia (ZrO2) dispersed aluminum alloy metal matrix composites
produced by stir casting techniques. Using stir casting techniques, aluminium
based composites with varying amounts of 3%, 6%, 9%, and 12% of zirconia by
weight are fabricated. The prepared samples were subjected to physical,
mechanical,tribiology and microstructure investigation. The extraordinary
performance of Aluminium MMCs was the low density that obtained after
alloying. Hardness and ductility were also increased when increase in Zirconia
particle. Ultimate tensile strength, compressive strength and impact toughness
were slightly increasing with the addition of zirconia particle. Microstructural
characteristics shows that a homogeneous distribution of particles with
reinforcement in casted composite. The investigations of the metallurgical
characterization were carried using optical, scanning electron microscope, X-
ray diffraction and Energy Dispersive Spectrometry (EDS) test to understand
the metallurgical properties.
2. The scanning electron microscope (SEM) uses a focused beam of high-
energy electrons to generate a variety of signals at the surface of solid
specimens.A series of clay and SCBA waste mixtures, were prepared, containing
SCBA waste additions . In order to enlighten the densification behaviour on
firing, the fracture surfaces of the as-fired pieces were examined via SEM. The
correlation between sintered microstructure and technological properties is well
established.Between 700 and 900 ºC , the fracture surface is rough and the
porosity is clearly visible. In this temperature range, the sintering process is
governed via solid state mechanism, especially surface diffusion. In addition, the
green pieces on heating up to 900 ºC underwent a series of phase transformations
such as dehydration of hydroxides and dehydroxylation of kaolinite to
metakaolinite formation. Necks between contacting metakaolinite platelets grow
and smoothening of the particles surfaces occurs. Thus, the clay ceramic pieces in
this temperature range tend to have a more open structure and only a small
variation of the technical properties. At 1000 ºC , the porosity starts to reduce. At
1100 ºC , however, the clay ceramic pieces presented advanced sintering stage. In
this case, the elimination of a large amount of open porosity that exists within the
structure occurred. In addition, the vitrification is in progress. In fact, the glassy
phase infiltrates the pores of the structure and cause densification via liquid phase
sintering. This justifies the improved technological properties (lower water
absorption and higher mechanical strength) of the clay ceramic pieces. The EDS
spectrum of clay ceramic fired at 1000 ºC showed mainly the presence of Si, Al,
and Fe. This is consistent with the chemical composition of the plastic clay
powder used SEM micrographs of fracture surfaces of fired clay ceramic pieces .
Thus, the SCBA waste powder as added to a clayey body causes modification on
the texture and porosity of the fired clay ceramic pieces. In particular, the
additions of very high SCBA waste amounts in clay ceramics should be avoided,
because it impairs the mechanical of the fired pieces.
QUESTION 2
Removing or avoiding charge on materials: If the material is a good conductor
like metal, touching it to ground for even a brief moment will discharge it. This
should only be done if the conductor is not close to a highly-charged object or a to
metal sheet that is at high voltage. If too close to such an object, the conductor will
pick up significant charge by charge induction the instant any part of the conductor is
connected to ground. That charge will be of the opposite polarity of the charged
object, and the conductor will carry this charge until it is discharged properly, away
from any such charged objects.
Active discharge methods: Remember that passive metal structures cannot fully
discharge an insulator, but passive methods may remove enough charge, depending
on the requirements. Other methods can fully discharge insulators, but these methods
all require some sort of energy. For example, air becomes a reasonably good
conductor if a large number of both + and – ions are present, but energy is required to
make air ions. Usually, ions are made by using either electricity or radioactivity, but
they can also be made from combustion, high heat, or evaporation. If 100,000 ions per
cm3 (both + and -) are present in air, charged insulators will discharge to half their
initial value (half life) in about a second. High ion concentrations can only be
achieved by using an ionizer; without this, a room has typically 10 to 100 ions per
cm3, which corresponds to a discharge half life of tens of minutes to a few hours.
The other way to remove charge is fully dip it in (grounded) water, or breathe on
(or humidify) it until condensation forms, making sure the water film has no gaps and
that it bridges to ground for at least an instant.
A more technical full-discharge method uses an ionizer. If a large number of both
positive and negative ions coexist in the air, the positive ions will be strongly attracted
to negatively-charged surfaces and vice-versa. Each ion transfers its charge to the
charged surface and then the ion falls apart, turning back into various air molecules.
QUESTION 3
Stirring induces shear, which plays a role in the formation of the particles, and
affects, in particular, their shape. The results show that the pore diameter of the
samples remains essentially unchanged, and the unit cell size a0 for all samples is
similar. When shaking, stirring slowly, or under static conditions, micelles can
nucleate and grow in a more stable environment. When stirring rapidly, however,
shear on the micelles is pronounced, so that micellar growth is hindered, as well as the
assembly with silica precursors to grow large, well defined particles with long-range
order of the mesopores. Poorly defined morphologies result from rapid reorganisation
or reassembly of growing particles. However, there are differences in the particle
morphology and also in the mesophase organisation, especially at very high stirring
rate. This means that fast stirring may influence the species interactions.when the
stirring rate is increased beyond 200 rpm, more and more irregularly shaped particles
are formed. Samples are aggregates composed of poorly defined particles with some
composed of the smaller platelets or large spheroidal particles . It is difficult to
attribute a particle size to these samples, because of the agglomeration of the primary
particles. Monodisperse spheres were not obtained at any stirring rate. Thus, stirring
rate has much less effect on the textural parameters, but will affect the final particle
morphology.
