Iranian Journal of Materials Science and Engineering

Properties of Cement Pastes Doped with Very High Amounts of Ground Granulated Blast-furnace Slag

A. Rashad

In the current work, the properties of cement pastes doped with high amounts of ground granulated blast-furnace slag (HVS) were investigated. Portland cement (PC) was substituted with ground granulated blast-furnace slag (donated as slag) at very high amounts of 85%, 90%, 95% and 100%, by weight. PC paste without any content of slag was used as a reference. Some fresh and hardened properties such as workability, density, compressive strength up to 56 days, pH value and drying shrinkage up to 200 days were measured. The various phases formed were identified using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The microstructure of the formed hydration products was determined by scanning electron microscopy (SEM). The results indicated that HVS has higher workability and higher drying shrinkage beyond 60 days. On the other hand, HVS has lower pH, density and compressive strength.

Effect of Calcination Kinetics and Microwave Sintering Parameters on Dielectric and Peizo-Electric Properties of(K0.5Na0.5) NBO3 Ceramics

M. Krishna

An efficient solid-state approach was established to synthesize (K_0.5Na_0.5) NbO₃ceramics using calcination kinetics and microwave assisted sintering. Milling of carbonate and oxide raw materials were carried out for 15h to obtain homogeneous nano particles. The crystallite size of 5.30 nm was obtained for the KNN system after calcination through optimized parameters and observed to be stoichiometric in nature. The obtained nano particles showed phase transition from orthorhombic to tetragonal crystal structure without any secondary phases. The high relative density and tetragonality ratio of KNN ceramics obtained through optimized sintering parameters yielded with significant piezoelectric and ferroelectric properties.

Modification of Primary Si Crystals and Fe-rich Intermetallics in LM28 Al Alloy Fabricated Through Thixoforming

H. Saghafian

In the present research, thixoforming route was carried out in order to enhance the microstructural features of LM28 piston alloy. Typical microstructure of this alloy was composed of coarse, polygonal primary silicon particles, eutectic matrix and intermetallic phases. Thermal analysis was carried out to study the solidification path of the base alloy and determine the major arrest temperatures of metallurgical reactions. Continuous and iso-thermal mechanical stirring were utilized to produce non-dendritic LM28 alloy feedstock for further processing. The rheocast samples were subjected to a rotation speed of 450 rpm. The slugs machined from the solidified rheocast specimens were heated in the mushy zone temperature and then were thixoformed via a laboratory press. The thixoformed specimens show a relatively homogenous microstructure and present no evidence of porosities. Fine, blocky primary silicon and Fe-rich intermetallic particles were uniformly distributed in the matrix of LM28 alloy. Optical microscope and scanning electron microscope linked with EDX were used to investigate the microstructure of specimens

An Investigation on the Adsorption Behavior of a Mesoporous Silica Synthesized by a Surfactant-assisted Method in an Acidic Media

M. Jalaly

Mesoporous SiO₂ nanopowder was synthesized under an acidic condition by a sol-gel method using various amounts of cetyltrimethyl ammonium bromide (CTAB) as structure directing agent. The samples were investigated with XRD, SEM, FTIR, TEM and N₂ absorption-desorption analysis. Also, the incremental effect of surfactant were examined. The results obtained from the analysis suggested that an increase in the amount of surfactant resulted in increasing specific surface area, pore size and pore volume, of the synthesized particles up to 549 m².g^-1, 17.3 nm, and 2 cm³.g^-1, respectively. Absorption behavior of the mesoporous silica was investigated for degradation of methylene blue pigments (MB) in aqueous solutions. The samples SC0, SC0.5 and SC1 showed the maximum absorption capacities of 333, 454 and 526 mg/g, respectively

Electrodeposition and Characterization of Sn-Zn Alloy Coatings from Sulfate Based Baths

S.R. Allahkaram

Tin-Zinc alloy coatings have many applications because of their unique properties such as corrosion resistance, solderability and flexibility. In this study, the effect of current density, temperature and pH on chemical composition, cathodic current efficiency, morphology and structures of the coatings was investigated. The results illustrated that, at low current densities (<0.5 mA/cm²), the coatings were relatively pure tin, but Zn content increased with enhancing the current density. At higher currents a relatively pure Zn film was obtained. Temperature and pH also affected chemical composition of the alloy films. Zn content of the coatings was decreased by increasing the temperature, while its variation with pH had ascending-descending trend. Morphological investigation of the coatings revealed that increasing Zn content of deposits led to porous, rough and fine grained films.

Cation Distribution Tuning of Solution Combusted CoFe2O4 Powders

S.M. Masoudpanah

In this work, the different fuels (citric acid, glycine and urea) were used for solution combustion synthesis of CoFe₂O₄ powders. X-ray diffraction, Raman spectroscopy, electron microscopy and vibrating sample magnetometry techniques were employed for characterization of phase evolution, cation distribution, microstructure and magnetic properties of the as-combusted CoFe₂O₄ powders. Single phase CoFe₂O₄ powders with partially inverse structure in which the Co²⁺ cations are distributed in both tetrahedral and octahedral sites were synthesized by the citric acid, glycine and urea fuels. The as-combusted CoFe₂O₄ powders by the citric acid fuel exhibited the highest inversion coefficient. The crystallite size of the as-combusted CoFe₂O₄ powders synthesized by urea fuel was 15 nm, increased to 41 and 52 nm for the glycine and citric acid fuels, respectively. Furthermore, the solution combusted CoFe₂O₄ powders showed ferromagnetic behavior with saturation magnetization of 61.9, 63.6 and 41.6 emu/g for the citric acid, glycine and urea fuels, respectively. The high crystallinity and particle size of the as-combusted CoFe₂O₄ powders using glycine fuel led to the highest magnetization and the moderate coercivity.

Effect of Wet and Dry Conditions on Wear Behavior of Amorphous Coating of Fe-Cr-Mo-Nb-C-B

H. R. Shahverdi

Recently, wear resistant properties of metallic glasses has attracted a lot of interest. Because the surface of metallic glasses are prone to phase transformation, finding the effects of test condition on structure and wear behavior of metallic glasses is important. In this research, by using an automated electrospark deposition (ESD), a layer of Fe₅₁Cr₁₈Mo₇B₁₆C₄Nb₄ was deposited on AISI 316l stainless steel. Metallographic, scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS) analyses of the coating were conducted for measuring the thickness and analyzing composition of the coating. X-ray diffraction (XRD), Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigations showed that the structure of the coating was amorphous. Ball on disc wear tests were conducted in dry and wet conditions and Ringer’s solution was chosen as the wetting agent. The wear test results showed that the coefficient of friction in dry condition was lower than the wet condition and wear modes were fatigue and corrosive wear in dry and wet conditions respectively. SEM and EDS analyses showed different features and elemental inhomogeneity on the surface of the dry wear track, which were not detectable in wet wear track. In addition, activation of diffusion process and formation of carbides and borides were observed on the wear track in dry condition.

The Hardness Behaviour of TIG Welded AL6061 Alloy Using Statistical Tool

P.K. Jayashree

CoHErrelation between weldability and improvement in properties is a key issue in materials science research. The objective of this work is to optimize the process parameters viz., aging temperature, aging time, solutionizing time, to enhance the hardness of Al6061 alloy. Hence, the present paper deals with hardness study of Tungsten Inert Gas welded 6061 aluminium alloy after age hardening under three different aging temperatures, aging time and solutionizing time using Taguchi’s L₉ Orthogonal array. Finally, a second order model has been generated for hardness using Response Surface Methodology with 20 runs for full design. The predicted and experimental results are in good agreement.