نشریه علم و مهندسی سرامیک
سال سوم شماره 2 (پیاپی 9، تابستان 1393)

In this research، Al2O3-ZrB2 composite was produced by mechanically activated self-propagating high temperature synthesis (MASHS) using mixture containing Al، ZrO2 and H3BO3. The effect of Al particle size and mechanical activation on the combustion characteristics was investigated. The XRD and DSC analyses show that Al particle size and mechanical activation affects the mechanism and temperature of combustion behavior of the system. As a result، the ignition temperature of mechanically activated samples decreased from 1114 °C to 972 °C and 650 °C for samples containing coarse and fine Al particles، respectively.

Recently، composite materials have been widely used as orthopedic materials but there are some problems which cause only clinical research perform on these. In this study، hydroxyapatite nanoparticulate (Nano-HA) (10، 20، 30، 40، and 50 wt. %) reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposite was fabricated by compounding Nano-HA and UHMWPE mixtures in paraffin oil by medical grade using internal mixer at 180 ºC. Mechanical and tribological properties of samples were investigated by nanoindentation and nanoscratching method. Nanoindentation results showed sample with 50 wt. % Nano-HA exhibited a Young’s modulus and hardness 362. 5% (4. 625 times) and 200% (3 times) higher than control sample (pure UHMWPE)، respectively. According to nanoscratching results sample with 50 wt. % Nano-HA had 63. 57% (1. 63 times) lower than control sample.

In the present study، activated carbon (AC) with high surface area prepared by using of nutshell (waste of agriculture) as starting material. Chemical activation method was chosen for this purpose. Effective parameters such as impregnation ratio (IR)، temperature of activation and time، were investigated by design experiment. The results showed that the optimized sample which has highest surface area and pore volume can be achieved by fixing the IR، temperature of carbonization and time to 3، 500 ℃ and 2 hours، respectively. Increasing temperature resulted in decrement of the surface area of AC، while increasing time and IR lead to higher surface area and pore volume of AC. Furthermore، contribution factor showed that effect of temperature is higher than two other parameters.

The freezecasting is a novel method with great possible control for preparing porous ceramic materials. The goal of this study is to investigate the effect of initial freezing temperature on the microstructure and mechanical properties of porous hydroxyapatite samples prepared by freeze-casting method. In this study، stable slurries of hydroxyapatite were first prepared and then،poured into the plate in different temperatures (+7، 0، -7، -14، -21 °C) and after solidification with rate of 1 °C/min، the ice crystals were sublimated in freeze dryer and finally sintered in 1350°C. The size and morphology of pores wereevaluated by SEM. The obtained images indicate that an increase in starting freezing temperature leads to the increase in the pore size and the interstructural bridges. The mechanical properties of the samples werealso investigated which reveals that by decreasing the starting freezing temperature both compressive strength and porosity percentage simultaneously increased.

In this study، the glass with SiO2-B2O3-Fe2O3-Na2O-ZnO systemwas set in the various atmosphere ofhydrogen reducing، nitriding ammonia gas and neutral argon gas and also graphite-bed at 590 ̊C for 1 h and the effect of the formed phases during crystallization of the magnetite and also the magnetic characteristics of the magnetite glass-ceramic were investigated. The characterization of the phases was carried out by X-ray diffraction and the magnetic properties were studied by vibrating sample magnetometer (VSM). The magnetite phase was formed in the heat treated samples in graphite-bed and argon atmosphere and saturation magnetization of the primary glass was measured 19 emu g-1 in both samples. After the heat treatment of the glass in reducing atmosphere، magnetic phases of magnetite and α-Fe were detected in X-ray diffraction pattern. The existence of α-Fe was resulted in the improvement of the magnetic properties and also the increase in the saturation magnetization to 27 emu g-1. In The heat treated glass in ammonia gas atmosphere، there was no iron nitride phase and just the magnetite phase was crystallized. The saturation magnetization of this sample was estimated to 18. 3 emu g-1.

Nowadays; utilization of simulation methods for prediction material behavior particularly in the development of powder metallurgy is increasing. The major importance of this method in powder metallurgy is reducing of costs and also، try and error of experiments. Furthermore Possibility to perform many experiments in normal conditions due to lack of facilities and also high cost of doing them، is not possible. In this paper the macromechanical and micromechanical models used for simulation of powder compaction process. Additionaly، the drucker-prager/cap model as the most complete and widely used model for ceramic powders are investigated. Contour of density distribution for zirconia sample with finite element method are obtained and the results compared with experimental results that obtain from other researchers and good agreement are observed. All results show the undeniable role of friction on the density distribution and stresses in the powder samples. Friction causes a density gradient and heterogeneity of density distribution in samples.

In this work، effect of refractory thickness on temperature drop of liquid steel، was researched. Simulation and modeling has done by FEM method. By computer simulation with Ansys software thermal profile in refractory lining was modeled and temperature to thickness formulas ware developed. Refractories types are AMC، MgO-C and monolithic with thickness varies from 50% to 150% of real dimensions. Finally validation tests were done on steel making refractory and good compatibility between measured data and simulated data was achieved. Main simulation was based on ladles real dimensions and achieved Mobareke''s real data.