نشریه علم و مهندسی سرامیک
سال یازدهم شماره 3 (پیاپی 42، پاییز 1401)

In this study, the optical and magnetic properties of compounds in hexagonal and orthorhombic phases are investigated. The calculations have been carried out in the framework of the functional density theory with various approximations such as local density approximation, Generalized gradient approximation with the pseudopotential and stationary load method, and using the quantum-espresso computational code. In this study, the optical and magnetic properties are calculated and the results obtained Compare with other available data. The dynamic contribution of the dielectric function indicates that the gap is zero with the strip structure. In calculating the total torque, the uranium atom has the highest share in both combinations. The share of gallium and germanium atoms is negligible.

Ceramic borides, carbides and nitrides with high melting point, relatively good resistance to oxidation and corrosive environments are considered by many researchers in various high temperature industries, which is known from the family of materials as high temperature ceramic (UHTC). To be. All UHTCs have very strong bonds that give them structural stability at high temperatures, and among them diboride compounds offer the highest degree of oxidation resistance, which compared to carbides and nitrides, diborides have high thermal conductivity and their strength Increases against heat shock. Further studies on diborides, especially zirconium diboride (ZrB2), were selected as the most promising candidate for use in high temperature applications. This review article discusses their mechanical and thermal properties, especially ZrB2, and also focuses on the effect of additives such as SiC to improve mechanical or thermal properties and / or to improve oxidation resistance in harsh environments at temperatures above 2000 ° C.

WC-Co cermets are among the advanced engineering materials that are considered for their special properties such as abrasion resistance and high hardness. The aim of this study was to determine the optimal amount of carbon in raw materials and industrial production of WC-8Co cermet powder from metal oxides WO3, Co3O4 and activated carbon by solid carbothermic reduction method in situ and under a hydrogen gas atmosphere. The main challenge in this case is the incomplete formation of tungsten carbide and the fact that tungsten remains free in the mixture of materials, which is related to the lack of carbon in the composition of raw materials and the need to add more carbon compared to its stoichiometric amount. Therefore, it is necessary to change the amount of carbon experimentally. For this purpose, the raw materials were homogenized in 5 different ratios with different amounts of activated carbon as the main variable in a mixer for 3 hours. The powder samples were then subjected to carbothermic reduction at 1200oC for 3 h at a heating rate of 10 oC.min⁻¹ and subjected to a hydrogen atmosphere at a pressure of 1 atmosphere. According to the results of phase studies and X-ray dispersion spectroscopy and microstructural studies of the sample electron microscope with the combination (10.108gr WO3, 10.90gr Co3O4 and 58.62gr C) show the best conditions in terms of the obtained phases. The hydrogen atmosphere applied in the furnace acts both as a facilitator of the reduction process and as a protective layer against re-oxidation of the products.In this case, the majority phase is tungsten carbide, which is placed next to small amounts of cobalt as the adhesive phase. So that the results of scanning electron microscope image also confirm this and the average number of composite particles in this case is about 100 microns.

Mesoporous gamma-alumina granules, which are known as a common catalyst support in industrial applications were synthesized via the sol gel-oil drop method having a diameter of 1-2 mm. The effect of calcination temperature (450 and 750 °C) on the properties of gamma alumina granules were studied and the functionality of 20 wt% iridium catalyst on the alumina granules for hydrazine decomposition was evaluated. The presence of gamma-alumina as the only constituent phase up to 750 °C was revealed by XRD analysis. According to N2 adsorption-desorption analysis, the specific surface area of gamma alumina granules calcined at 450 and 750 °C was 303.05 and 227 m2/g, respectively. HR-TEM analysis was used to investigate the granules’ morphology, and the capability of the granules as a support for iridium catalyst was evaluated during the hydrazine decomposition test. Using alumina granules calcined at 750 °C as the catalyst support, the hydrogen selectivity reached 22% and the decomposition rate was 235 h-1, and the granules’ crushing level was as low as 7% during the test, indicating that the granules have an acceptable surface area, pores diameter, and interconnectivity.

Magnesium phosphate cements (MPC) are the most developed kind of chemically bonded ceramics which form through the reaction of magnesium oxide and soluble phosphate salts. Therefore, study of different magnesium phosphate cement systems is considered important according to the type of phosphate agent used. In this study, effect of mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP), and sodium dihydrogen phosphate (MSP) on the properties of magnesium phosphate cement paste including setting time, flowability, bulk density, apparent porosity, and pH were investigated. The type and amount of hydrated phases and how the cement is dehydrated are also determined by phase analysis (XRD) and Simultaneous thermal analysis (STA). The results showed that the setting time and flowability of cement containing di-ammonium phosphate is higher than the other two types. In addition, the XRD results indicated that the type of hydrated phase was the same for ammonium phosphate salts, while the use of monosodium phosphate would not lead to the formation of a crystalline hydrated phase.

In this research, Montmorillonite clay nanoparticles were produced using mechanical methods and the effect of different percentages of tetra n-butyl ammonium chloride (TNBAC) as a surfactant and butyl ammonium chloride as a modifier (TNBAC) was performed. The microstructural and morphological properties of montmorillonite clay nanoparticles in the presence and absence of surfactant as well as surface modifier were investigated using modern identifying materials methods including XRD, FTIR, FESEM, ZETA POTENTIAL. XRD results show that, the montmorillonite and quartz phases in all samples, which was consistent with the FTIR results. The results of electron microscopy show that, with increasing surfactant the agglomeration was decreased and the range of particle size was about 10 to 30 nm. The results of zeta potential test and its comparison indicated a good modification of the surface of nano-montmorillonite and with increasing the modifier, the amount of charge increased and the zeta potential become more positive.

So far, nanoparticles of porous zinc sulfide have been synthesized in solvent mediums. Cyclohexane was used as the first insoluble medium for the reaction between zinc precursors, zinc chloride (ZnCl2) and zinc nitrate (Zn (NO3), 2.6H2O), and sulfur precursors, thioacetamide (C2H5NS), thiourea (C2H5NS) and Na2S.5H2O. Dodecyl amine has been used as the structural guiding agent. Various analyzes such as X-ray diffraction, nitrogen uptake and desorption, as well as transmission electron microscopy and field emission scanning electron microscopy have been used to analyze the morphological features and characteristics of the obtained products. The results of X-ray diffraction prove the successful synthesis process in the non-solvent cyclohexane medium. The results of nitrogen adsorption-desorption isotherms show that the synthesized materials using different precursors have different pore sizes and specific surface area. The highest specific surface area of about 190 m2g-1 was obtained by the proposed synthesis procedure. The synthesis and porosity formation mechanism of the mesoporous ZnS particles has also been discussed and it was demostrated that the insoluble by-product has the main role in the porosity induction in the structure.