نشریه علم و مهندسی سرامیک
سال چهارم شماره 4 (پیاپی 14، زمستان 1394)

The objective of this study was to determine the simultaneous effect of different variables on calcium hydroxide (Ca(OH)2) nanoparticles synthesis by precipitation method, using central composite design. The used raw materials included calcium nitrate (Ca(NO3)2.4H2O), sodium hydroxide (NaOH), and water/ethanol to dissolve the powders. In order to find optimal conditions and to achieve nanometer-sized particles, experimental design of CCD with different parameters of temperature, weight ratio of reactants, and alcohol percentage were considered at five different levels. Using experimental design of CCD and Design Expert software, a Table for 20 tests was arranged. The software was developed in order to help the user in the design and interpretation of a Multivariable Testing. In this Table, minimum and maximum of the parameters were considered as temperatures 25 and 85 ºC, weight ratio 0.5 and 1.5, and alcohol percentage 0% and 100%, respectively. Then calcium hydroxide, with the reaction of raw materials, was synthesized in an environment that contains water and alcohol. Finally, by using scanning electron microscope (SEM), X-ray diffraction, AxioVision software and Design Expert software, synthesis of nanoparticles of calcium hydroxide was approved and the influence of various parameters on the synthesis was studied.

In the present study the effect of mechanical activation on combustion synthesis of Al2O3-B4C composite materials in a microwave using metal powder Al, graphite and boric acid is studied. The results showed that mechanical activation have an important role to promote exothermic reaction and Al2O3-B4C composite synthesis via combustion method. The mechanical activation decrease reaction temperature to lower than 700°C and increase reaction intensity without any effect on combustion reaction mechanism, so that, the sample synthesis was completely carried out in microwave at 12 second and 20 hours pre-mechanical activation. The results also support the possibility of boric acid using as raw material to combustion synthesis Al2O3-B4C composites.

The preparation and characterization of Ge33As12Se55 chalcogenide glass as an infrared window was the goal of this study. In this regard, the glass composition with suitable atomic ratio was melted and quenched within quartz capsulate under different conditions. The melting process was done in the temperature range of 750 to 950° C for different periods of time and the quenching process was done in different cooling media. The structural and optical characteristics of samples were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). The results showed that the melting temperature and cooling media have significant effects on the properties of final products. The optimum processing temperature in order to achieve the best optical properties was 950°C and the optimum cooling media was a salt bath with temperature of 220°C. The addition of gettering elements (such as Mg) to glass composition had benefit effect on oxide absorption bands from FTIR curves

Dielectric ceramics have been greatly intended owing to their composition diversity and meeting the requirements of electronic industry and wireless communication. Among these ceramics, ceramic composites composed of a dielectric ceramic phase and a sintering aid glassy phase which offer dielectric features in the microwave frequency, have been utilized for application in the LTCC (low temperature co-fired ceramics) modules. The present work has been aimed to fabricate dielectric composites of mullite microparticles- ZBS (ZnO-B2O3-SiO2) glass for use as dielectric substrates in the LTCC technology. In this regard, composites with various volume ratios of mullite and ZBS glass were fabricated. Considering the sinterability evaluation at 950°C, composite of 50 mullite-50 glass (Vol. %) was chosen as the optimized sintered composite and focused for further examinations. Monitoring thermal behavior of the optimized composite during sintering by means of X-ray diffratometry and differential thermal analysis revealed that mullite reacts with glassy phase at about 880 ºC; results in the formation of gahnite (ZnO.Al2O3) phase. Microstructural observation confirmed prismatic morphology of the gahnite crystals dispersed homogeneously in the glass matrix. Dielectric characterization utilizing network analyzer showed the resonance of the optimized composite in the microwave frequency range. Dielectric permittivity (4.5) and quality factor (4704GHz) of the optimized composite is in accordance with the requirements of the targeted technology

In this work, the electrostrictive proprties of lead-free (Ba0.8Ca0.2)(Ti0.7Zr0.3)O3 piezoceramics that were synthesized via solid state sintering method were investigated. These ceramics were sintered in the sintering range of 1350-1550 °C and the effects of sintering temperature on electostrictive behavior was studied. Crystal phases and microstructure were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the polarization and strain loops were used to calculate the electrostrictive coefficients. Our results revealed that the BZT-50BCT samples at 1350 °C with the highest strain and the lowest Pr values at T=100 °C showed the best electrostrictive coefficients: Q33=0.058 m4/C2, and M33=6.1×10-16 m2/V2. These values are higher than previous reports on BZT-50BCT composition and enables this material to compete with the lead-based electrorective materilas.

The aim of this study has been the fabrication of TiC phase by Microwave- assisted Self-propagating High-temperature Synthesis (SHS) process. A TiO2:2Mg:C mixture was heat treated in a domestic microwave oven and the product was characterized by XRD and SEM devices. Results showed the formation of TiC-MgO composite powder through an SHS reaction. Un-wanted MgO compound was leached out by an HCl acid solution, yielding a pure TiC powder. In this research work, thermodynamic calculations were employed to gain an insight into the possible chemical reactions.

The corundum-mullite bodies have high refractoriness under load and resistance to creep. Different additives have been used in these bodies for improvement of sintering and microstructure. In this study, the effect of aluminium borate and magnesia additive on mechanical properties and sintering of alumina-mullite composite were investigated. Aluminum borate (9Al2O3.2B2O3) was prepared by the combustion of an aqueous solution containing stoichiometric amounts of aluminum nitrate, boric acid, and glycine. Tabular and gamma alumina, kaolin, and additives were mixed, pressed and then fired at 1400- 1500°C/3h for preparation of corundum-mullite samples. After firing the samples (without additives) at 1550°C/3h, bending strength (38 MPa), relative density (88%) with corundum and mullite as major phase and quartz as minor phase were obtained. After firing aluminium borate samples at 1550°C/3h due to high refractories of A9B2 the physical and mechanical properties werent increased .With addition of 2.5wt% aluminium borate and 2.5wt% magnesia, after firing at 1550°C/3h, bending strength and relative density were improved and reach to 115Mpa and 95.5Mpa respectively. At this sample, corundum, mullite, pyrope (3MgO.Al2O3.3SiO2) and magnesia borate (2MgO.B2O3) were established at the sample.