نشریه علم و مهندسی سرامیک
سال دوم شماره 4 (پیاپی 7، زمستان 1392)

Mesoporoushydroxyapatitenanoparticleshas beensynthesized usingsurfactant-block co-polymer soft templating technique. Two different surfactant removal processes were used in order to control thepore sizein the synthesized nanoparticles. Calcination at the temperature of550 ° Cled to mesostructured powder with an average pore diameter of 56-nm. Thesurface areaafter calcination was around 48m2/g. In the othergroupofsamples، the removal of surfactant was accomplished by washingusingethanol. Pore size and the surface area in the washed powder samples were about 23nmand 96m2/g respectively.

In this work، the effect of Cr2O3 dopant on optical، thermal and structural properties of glass with composition 53%SiO2-17Na2O-17CaO-13CaF2 was investigated. Heat treatment at two steps of nucleation and growth created nano-crystal into glasses without dopant and doped with Cr2O3. The presence of nano-crystal at the glasses produced new optical properties such as decreased optical band gap and Urbach energy. The kind and size of crystal calculated by XRD pattern about lower than 60 nm. Effect of Cr2O3dopant and crystal phase on optical and structural investigated by UV-Visible absorption and FT-IR spectroscopy، simultaneously.

High cost of tungsten carbide synthesis by high temperature solid-state reaction between elemental tungsten and carbon in controlled atmosphere، persuaded researchers to use of cheaper raw materials such as tungsten oxide and alternative synthesis methods which are lower costly than conventional method. In previous researches، capabilities of mechanochemical and microwave synthesis methods for tungsten carbide formation by reduction-carburization of tungsten oxide have been proved. One of the limitations of these methods is W2C formation، as an undesirable phase، in addition to WC. In the present study، a combined process including mechanochemical processing of WO3-Al-C mixtures followed by microwave heating was employed to accelerate WC-Al2O3 composite synthesis، and effect of milling time and microwave heating on the ratio of WC: W2C in the products have been investigated. The powder mixture with a molar composition of WO3-2Al-C were first treated for 2، 3 and 4 hours in a planetary ball mill، and the pellets which formed by cold pressing of the milled products were then heated in a domestic microwave oven. X-ray diffraction (XRD) analysis on the milled samples showed that، at initial stages of milling، undesirable tungsten semi-carbide (W2C) was formed، while increasing the milling time، improved tungsten carbide (WC) formation and increased the ratio of WC: W2C. Also، microwave heating of the mixture containing 50% excess graphite (WO3-2Al-1. 5C)، after milling for 4 hours، has a significant impact on the progress of tungsten carbide formation reaction so that، the ratio of WC: W2C increased from 4. 7، for the milled sample، to 17. 8، for the milled sample followed by microwave heating.

In this research، calcium hexaferrite with nominal composition (Ca1-XLaXFe12O19)، (X=0. 0، 0. 2، 0. 4 and 0. 6) and Fe3+/Ca2+ mole ratio=11 have been synthesized through the co-precipitation route. The ferrite precursors were obtained from aqueous mixtures of calcium nitrate، ferric nitrate and lanthanum nitrate by precipitating calcium، iron and lanthanum ions using 2M sodium hydroxide solution at pH=14 and room temperature. These precursors were calcined at 1200 ◦C for constant calcination time 1 h in a static air atmosphere. Several methods such as X-ray diffraction (XRD)، scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) have been used to obtain detailed information on the crystallography، formation mechanism، morphology and magnetic properties of the powders with different amounts of La. The X-ray diffraction pattern of the powders with La indicates the formation of calcium hexaferrite and also α-Fe2O3 was detected beside the M-phase. However in powders without any amount of dopant، CaFe4O7 and α-Fe2O3 phases were formed. The results of SEM showed that the CaM grains were hexagonal platelets with sizes from 1 to 2 µm. VSM measurement also indicated that maximum magnetization (MMax) and coercivity (Hc) of the calcined powders increased by using of La. Low values of coercive field (200 Oe) and of the maximum magnetization (50 emu. g-1) were obtained on powders

In this research، the synthesis of nano structure boron carbide by magnesiothermic process were investigated by different sources of carbon such as، porous carbon obtained from natural Clinoptilolite zeolite (CClinoptilolite) and carbon obtained from SBA-15 (CMK-3). To investigate the effect of chemical composition، samples with different C/B2O3 ratio were prepared and sintered in controlled atmosphere furnace at 750°C. Templates which obtained from SBA-15and Cilinptilolite as well as their porous carbon product were characterized by BET، XRD،TGA and SEM. The role of amount and type of carbon and also the reaction temperatures on the synthesis of boron carbide were studied. by comparison between X-Ray diffraction of samples with different carbon sources، it can be concluded that، factors such as using template as well as type and surface area of carbon are important factors in synthesis process of boron carbide.

A series of ordered mesoporous single phase Cu1-xZnxFe2O4 spinel ferrites، with x ranging from 0. 00 to 0. 75 with a step increment of 0. 25، are prepared by a novel nanocasting route. Wide angle XRD (WXRD) results show that all the samples have a cubic structure without any impurities. Usingvinyl-functionalized mesoporous silica as a hard template plays a crucial role for transformation of precursors to the pore channels of the silica template. The physical properties of the samples are characterized by N2 adsorption-desorption، Low angle XRD (LXRD) and TEM analysis. N2 adsorption-desorption results show that all the samples have a specific surface area higher than 100 m2g-1 and pore size distribution is in the range of 6-10 nm. TEM images for x=0 and x=0. 5 confirm the preservation of mesoporous structure after removal of the template.

In this study، nano sized Al2O3. Y2O3 (YAlO3) powder was synthesized by sol-gel combustion method. The starting materials were Al (NO3) 3. 9H2O as a source of Al3+ ions، Y2O3 and HNO3 for production of Y (NO3) 3 as a source of Y3+ ions، and glycine as a fuel. Taguchi experimental design was used to obtain the optimum condition of gaining nano sized Al2O3. Y2O3 powder. The studied parameters were concentration، pH، and the ratio of fuel to oxidant. ANOVA varianse analysis was used to obtain the least average particle size. The prepared nano powder was characterized by XRD، FESEM، and BET analysis. The optimum conditions were found to be concentration 0. 2 mol/L، fuel to oxidizer ratio 1. 25، and pH of 4. In these cnditions، the average particle size was calculated around 45 nanometers.