نشریه علم و مهندسی سرامیک
سال چهارم شماره 2 (پیاپی 13، تابستان 1394)

In this study, synthesis and characterize investigation of barium hexaferrite doped with ions of cobalt, chromium and tin with the formula of BaCoxCrxSnxFe12-3xO19 was performed via mechanochemical method. For this purpose two samples were prepared with x values of 0.3 and 0.5. Phase and structural investigation by X-ray diffraction (XRD) and infrared spectroscopy (FT-IR) respectively,confirm the formation of barium hexaferriteswith minor amounts of hematite as secondary phaseafter heat treatment for 5 h attemperature of 1000 °C.Also, according to scanning electron microscope images (SEM) morphology of particles was perfectly hexagonal with an average particle size 600-650 nm.Based on magnetic parameters measured by vibrating sample Magnetometer (VSM) based on the value of coercivity, both samples were magnetically semi-hardand the highest saturation magnetization was obtained for the sample with composition of BaCo0.3Cr0.3Sn0.3Fe11.1O19.The values of saturation magnetization (Ms) and the coercivity (Hc) were measured for this compound, 42.21 emu/g and 656 Oe respectively.Doped barium hexaferrite electromagnetic parameters was evaluated using a vector network analyzer (VNA) in the frequency range of 8-12.5 GHz.According to the results the maximum absorption was related to BaCo0.5Cr0.5Sn0.5Fe10.5O19/resin epoxy composite with thickness of 5 mm at the frequency of 12.2GHzwas-15 dB.

ZrB2 base composites containing SiC, MoSi2 and AlN have good sinterability and mechanical properties. In this study, 20 vol% nanometric SiC and 4wt% micrometric MoSi2 with different amount of AlN whiskers (0-10%vol) added to ZrB2. After mixing, composite samples were formed by cold isostatic press (CIP) with 200MPa pressure, and then samples were fired at 2100°C/1hr in Ar atmosphere with heating rate of 10°C/min. After firing bulk density, open porosity, microhardness, toughness, microstructural and phase analysis were determined. The results showed that optimum properties obtained at 7.5%vol AlN whiskers with relative density (96.3%), open porosity (1%vol), Vickers hardness (18.5 GPa) and fracture toughness (4.37 MPa.1/2). The SEM+EDS and XRD analysis showed that SiC and AlN solid solution and formation of Zr2Al3C4 phases due to probably high vapour pressure of AlN at 2100°C were promoted sintering and improvement of properties of composites.

W-ZrC composite is on of the most important metal matrix composites، because the carbide phase in the composite causing hardness and creep resistance at high temperatures and tungsten flexibility causing resistance to failure of composite. Such as weight of the composite is less than Integrated Tungsten. Various techniques for making composite W-ZrC in the world provided that the choice of method depends on the equipments and the needed properties of the composite. At the present work the properties of W-ZrC composites made from reaction sintering method with different molar WC and ZrO2، were studied، because in this method raw materials are cheap، requires less equipments، and economically affordable sets. In this method، WC and ZrO2 powders with a molar ratio of 3 to 1 and 2 to 1 were mixed in planetary mill. powders formed by uniaxial pressing and final stage after pyrolysis at 600°C، samples in 2200 ◦C have been sintered in a vacuum environment. the XRD pattern and SEM image indicates that the W-ZrC composite has been formed at temperature 2200°C، but some unreacted compounds still exist and some unwanted components have been created. In this method relative density of 91. 09%، and 80. 06 % obtained for the molar ratio of 3:1 and 2:1، respectively. Also it was observed that with increasing temperature، Young's modules increased as for the molar ratio of 3:1 and 2:1، Young's module 254 Gpa and 178Gpa was obtained respectively.

The backed bricks applied in Chogha Zanbil historical building are simple, glazed and beard with inscription types, and all are from Elamite era (13th century BC). This Elamit complex has been located in the Khuzestan province of Iran. The body colors of the bricks include yellow, brown, red and green-blue and they have the dimensions 10 cm× 35 cm× 35 cm and 8 cm× 37.5 cm× 37.5 cm. Despite, the bricks suffered environmental deteriorations over thousands of years, some of them have relative high hardness and they are still strength. The firing temperature and the baking condition of the bricks is one of the questions posed in Archaeometry. On the other hand, making the new bricks for the restoration purposes of the building requires the technical information about historical ones. Hence, after sampling the various historical bricks, chemical and mineralogical studies carried out by using XRD, FT-IR and chemical analysis (wet chemistry).The studies have shown that adequate amounts of Calcite and Dolomite with fine amorphous silica caused pyroxene phases such as Diopside at a low temperature around 700 oC in some bricks, which has made them more strength. The various color and quality of the bricks is due to lack of temperature control and atmospheric conditions in the preliminary kiln with wood fuel. The use of straw fibers in raw materials prevented cracking over drying and backing. The plant fibers also helped to back the core parts of bricks however incomplete combustion of carbon compounds and imprisonment of soot in the body, causing the defect "Black core" in them.

Gel-casting is a novel method to fabricate ceramic and metal bodies based on colloidal process. The main goal of this study is to prepare and investigate about porous silicon bodies via gel-casting. To this end, gel-casting parameters and rheological behaviour of silicon suspensions in different amount of solid content were studied. The results show that increasing in the amount of solid content from 30vol% to 35vol% have a strong effect on the viscosity of the Si suspensions. On the other side, increasing the solid content by 5% causes 50% decreasing in the time of gelation. As a result of gel-casting, the green sample having 30vol% solid content has 43vol% porosity and 19MPa flexural strength. The sample with 35vol% solid content has 38vol% porosity and 23MPa flexural strength. Considering to the DTA/TG the polymeric materials burn out between 350-600 C°. Based on SEM analysis, the final silicon-bodies have uniform microstructures with high levels of interconnectivity porosity.

In this study, in order to increase biocompatibility, Ca-deficient hydroxyapatite with a compound that was similar to bone hydroxyapatites was coated on biodegradable Mg-2 wt. % Zn scaffold. To this end, preparation was performed through the electro deposition process and the thickness and chemical composition of the prepared coating was measured through scanning electron microscopy, infrared spectroscopy and elemental analysis. The results indicated that the obtained coating included low calcium hydroxyapatite with a needle-like and a flake-like morphology. In addition, the FTIR and EDS analyses showed that, in addition to calcium, oxygen, and phosphorus, other ions like magnesium and carbonate were also available in the coating. Furthermore, the atomic ratios of calcium to phosphorous (Ca/P atomic ratio) on hydroxyapatite were 1. 51 and 1. 47, using needle-like and flake-like morphology, respectively. Available hydroxyapatites in bone minerals involved needle-like ones which were not completely pure but included Mg2+، Na+، HPO42-, and CO32-. Therefore, because of morphological and compound-based similarities with hydroxyapatites of human natural bone, the prepared hydroxyapatite can provide a good condition for the growth and adhesion of bone-forming cells and hasten the healing process of damaged bone.