Iranian Journal of Materials Science and Engineering

EFFECT OF POLYVINYL ALCOHOL ON FLEXURAL STRENGTH AND SOME IMPORTANT PHYSICALPROPERTIES OFPORTLAND CEMENT PASTE

A. Allahverdi,

Abstract:
This work was designed to investigate the simultaneous effect of both water-to-cement (W/C) and polymer-to-cement
(P/C) ratios on flexural strength of type V Portland cement pastes containing polyvinyl alcohol. The obtained results
confirmed the strong effect of W/C-ratio on the effectiveness of the added polymer so that there exist optimum values
for both W/C and P/C-ratios. Pastes prepared at optimum W/C and P/C-ratios of respectively 0.30 and 0.016 exhibited
the highest flexural strength which was more than two times the strength of unmodified pastes. Further measurements
on hardened paste specimens prepared at W/C=0.30 show that increasing the P/C-ratio increases dry bulk specific
gravity of the specimens and result in significant reductions in both total permeable pore volume and water absorption
of the specimens confirming the effective packing caused by polyvinyl alcohol acetate.
Some water-soluble polymers have proved potentials for improvement in properties of Portland cements.

THE EFFECT OF COOLING RATE AND AUSTENITE GRAIN SIZE ON THE AUSTENITE TO FERRITE TRANSFORMATION TEMPERATURE AND DIFFERENT FERRITE MORPHOLOGIES IN MICROALLOYED STEELS

M. Esmailian

Abstract:
transformation temperature and different ferrite morphologies in one Nb-microalloyed (HSLA) steel has been
investigated. Three different austenite grain sizes were selected and cooled at two different cooling rates for obtaining
austenite to ferrite transformation temperature. Moreover, samples with specific austenite grain size have been
quenched, partially, for investigation on the microstructural evolution.
In order to assess the influence of austenite grain size on the ferrite transformation temperature, a temperature
differences method (TDM) is established and found to be a good way for detection of austenite to ferrite, pearlite and
sometimes other ferrite morphologies transformation temperatures.
The results obtained in this way show that increasing of austenite grain size and cooling rate has a significant influence
on decreasing of the ferrite transformation temperature.
Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain
boundary ferrite nucleates. As the temperature is lowered and the driving force for ferrite formation increases,
intragranular sites inside the austenite grains become operative as nucleation sites and suppress the grain boundary
ferrite growth. The results indicate that increasing the austenite grain size increases the rate and volume fraction of
intragranular ferrite in two different cooling rates. Moreover, by increasing of cooling rate, the austenite to ferrite
transformation temperature decreases and volume fraction of intragranular ferrite increases.
The effect of different austenite grain size and different cooling rates on the austenite to ferrite

A NEW GENERATION OF OXYNITRIDE GLASSES CONTAINING FLUORINE

A. R. Hanifi,

Oxynitride glasses are found as grain boundary phases in silicon nitride ceramics. They are effectively alumino-silicate glasses in which nitrogen substitutes for oxygen in the glass network, and this causes increases in glass transition and softening temperatures, viscosities (by two to three orders of magnitude), elastic moduli and microhardness. Calcium silicate-based glasses containing fluorine are known to have useful characteristics as potential bioactive materials. Therefore, the combination of both nitrogen and fluorine additions to these glasses may give useful glasses or glass-ceramics with enhanced mechanical stability for use in biomedical applications. This paper reports glass formation and evaluation of glass thermal properties in the Ca-Si-Al-O-N-F system. Within the previously defined Ca-Si-Al-O-N glass forming region at 20 eq.% N, homogeneous, dense glasses are formed. However, addition of fluorine affects glass formation and the reactivity of glass melts. This can lead to fluorine loss as SiF4, and also nitrogen loss, leading to bubble formation and porous glasses. The compositional limits for both dense
and porous glass formation at 20 eq.% N and 5 eq.% F have been mapped. At high fluorine contents under conditions when Ca-F bonding is favoured, CaF2 crystals precipitate in the glass. The role of the different cations on glass formation in these oxyfluoro-nitride glasses is discussed.

FORMATION AND GROWTH OF TITANIUM ALUMINIDE LAYER AT THE SURFACE OF TITANIUM SHEETS IMMERSED IN MOLTEN ALUMINUM

M. Soltanieh

Abstract:
titanium sheets in pure molten aluminum at 750
and X-Ray Diffraction Analysis results, TiAl
intermetallic layer thickness increases slowly at primary stages. After that an enhanced growth rate occurs due to layer
cracking and disruption. Presumably, reaction starts with solving titanium into the molten aluminum causing in
titanium super saturation and TiAl
intermetallic layer which consequently leads to TiAl
energy of intermetallic layer formation and growth was developed by measuring titanium thickness decreases.
In this work, kinetics of intermetallic compounds formation in Al-Ti system was studied by immersingoC, 850 oC and 950 oC. According to Scanning Electron Microscopy3 is the only phase can form at the interface. Observations revealed that3 formation. At this stage, growth may be controlled by aluminum diffusion through3 formation at the interface of Ti-TiAl3. Furthermore, activation

EVALUATION OFDISLOCATION STRUCTURE AND CRYSTALLITE SIZE IN WORN AL-SI ALLOY BY X-RAY DIFFRACTION

M. Zandrahimi

Abstract:
powerful method for the characterization of microstructures of crystalline materials in terms of crystallite size and
dislocation structures. In this paper the effect of the sliding on the microstructure of A356 in the as-cast and heat
treated conditions are studied, The X-ray phase analysis shows that with increasing applied load, the dislocation
density is increased, whereas the crystallite size is decreased. It was found that heat treatment raised dislocation
density during wear. The screw or edge character of dislocations in worn specimens were determined by analyzing the
dislocation contrast factors, it was demonstrated that the character of the prevailing dislocations in high loads is
nearly pure screw.
Diffraction peak profile analysis has recently been developed to such an extent that it can be applied as a

FORMATION OF GLOBULAR STRUCTURES IN ALUMINUM A356 ALLOY BY NARROWMELT STREAM (NMS) TECHNIQUE

F. Akhlaghi

Abstract:
structures in alloys. This method is based on pouring the melt through a small sized nozzle into a mould located at a
certain height under the crucible. This simple method generates globular structures without using equipments such as
impellers, electromagnetic stirrers, ultrasonic probes and cooling slopes. Therefore it is cost effective. In the present
study, the effect of casting size and mould casting modulus on the globular structure evolution in A356 aluminium alloy
specimens prepared by NMS process was investigated. The results showed that regardless of the different casting
modulus and their sizes, all the specimens exhibited globular structures. However, the size and shape factor of the
globules decreased with increased casting modulus and casting size indicating the influential effect of the surface area
of the mould in generating globular structures in this process.
Narrow Melt Stream (NMS) is a relatively new semisolid metal processing technique for producing globular

THE GREEN SYNTHESIS OF GOLD NANOPARTICLES USING THE ETHANOL EXTRACT OF BLACK TEA AND ITS TANNIN FREE FRACTION

A. R. Shahverdi

Abstracts:
nanoparticles. All the extracts were used separately for the synthesis of gold nanoparticles through the reduction of
aqueous AuCl
gold ions to gold nanoparticles. The ethanol extract of black tea and its tannin free ethanol extract produced gold
nanoparticles in the size ranges of 2.5-27.5 nm and 1.25-17.5 nm with an average size of 10 nm and 3 nm, respectively.
The prepared colloid gold nanoparticles, using the ethanol extract of black tea, did not show the appropriate stability
during storage time (24 hours) at 4
showed no particle aggregation during short and long storage times at the same conditions. To the best of our
knowledge, this is the first report on the rapid synthesis of gold nanoparticles using ethanol extract of black tea and
its tannin free fraction.
In this research the ethanol extract of black tea and its tannin free fraction used for green synthesis of gold4¯. Transmission electron microscopy and visible absorption spectroscopy confirmed the reduction ofoC. In contrast, gold colloids, which were synthesized by a tannin free fraction