نشریه علم و مهندسی سرامیک
سال سوم شماره 4 (پیاپی 11، زمستان 1393)

In order to studypossibility of substitution of hard chromium coatings with new coatings،chromium nitride thin films prepared in a sputtering system. Results showed that microstructure of coatings strongly depends on partial pressure of reactive gas. With increasing partial pressure of reactive gas in system at first nitride phase forms when coatings lose their crystalline order and become amorphous with increasing partial pressure of reactive gas. Change of N2/Ar ratio leads to a decrease of grain size but does not affect the lattice parameter so much. Plastic hardness of samples increased with increasing partial pressure of reactive gas which can be attributed to the grain size of the samples and Hall-Pech relation. This relation did not work for the sample with the highest nitrogen which was attributed to its very fine grain and increased grain boundary defects. Study of oxidation resistance of CrN film with the highest hardness value showed that this coatings completely oxides at 600 oC and completely separates from the substrate at 800oC. It seems that it is possible to get CrN films with better mechanical properties than that of hard chromium with precise control of deposition conditions and this coating can replace hard chromium from the view point of mechanical properties. However، this coating cannot replace hard chromium from the view point of oxidation resistance.

Having secured access to clean and healthy water sources has been a continual demand of all societies from the first date of history of mankind although it might not always be easily accessible. One of the main factors that makes this access hard to achieve is the existence of heavy cations such as Ca2+. So far، different methods have been proposed to remove these heavy cations from water. Among them، here we focus on using one of the well-known zeolites، i. e. LTA synthesis zeolite to remove heavy Ca2+ cations due to its excellent selective ionic exchange property. For this purpose، LTA zeolite is synthesized in autoclave with Ludox and aluminum isopropoxide as a source of Si and aluminum respectively alongside NaOH. SEM and XRD of samples have been studied in different temporal and thermal conditions and based on the obtained results، for the formulization of 3. 5Na2O: Al2O3:2SiO2:200H2O gel، synthesis of LTA zeolite for 28 hours in 65ºC is chosen as an optimal condition. After synthesize، we measured the absorption power of Ca2+cations and through the exchanging of Na+ ions with Li+، we improved the process of separation and absorption of Ca2+. To be more specific، after activation، in the best case the absorption power of Ca ions was increased approximately by a factor of 2. Finally، we repeated the process for different thermal conditions and compared the results.

Rice husk is one of the tonnage agricultural wastes produced annually. It is also one of the important sources for producing Si and Si-containing materials. In this research، rice husk ash is used for synthesis of silicon carbide. The mixture of graphite powder and rice husk ash with specific proportion was activated in a planetary ball mill، and the resulted powder، in form of a compact tablet، was subjected to microwave radiation. The amount of graphite (1. 5-2. 5 times of the stoichiometric amount)، milling time (1-20 h) and compaction pressure (102-374 MPa) w selected as variables. The results show that microwave heating plays a remarkable role in the synthesis reaction. X-ray Diffraction (XRD) analysis of samples indicates that activated and microwave-treated samples with 1 and 4 h activation time contain no noticeable silicon carbide product، while those with 10 and 20 h activation time -SiC، an evidence for synthesis reaction. In addition، the peaksshow peaks of intensity increases with increasing activation time. It is also determined that the amount of graphite has an important role on formation of silicon carbide.

In this study، synthesis of mesoporous SnO2 sphere was done by using polystyrene nanospheres (PS) and cetyltrimethylammonium bromide (CTAB) surfactant as hard and soft. The effect of temperature، atmosphere and calcination schedule on morphology of the particles were investigated. The templates were removed via calcination in air and mesoporous SnO2 particles were achieved. Mesoporous SnO2 spheres were characterized by Field emission electron microscopy (FESEM)، Nitrogen adsorption/desorption and Fourier transform infrared analysis. The results determined surface area about 113. 278 m2/g and particle size about 20-30 nm. These particles had nearly spherical morphology.

In this work، the HA/UHMWPE nanocomposites were manufactured using internal mixer with different weight percent of nano-HA (0، 10، 20، 30، 40، and 50 wt. %) and pharmaceutical paraffin oil to overcome the high viscosity of melted UHMWPE. Then، samples were fabricated using compression molding. The biocompatibility behavior of the samples was explored by alizarin red staining (ARS)، alkaline phosphatase (ALP) activity، and cell adhesion assay using MG-63 osteoblast cells. Scanning electron microscope (SEM) micrographs revealed that HA particles were homogeneously dispersed in UHMWPE by the internal mixer and MG-63 cells with normal phenotypic shape adhered on the surface of nanocomposites. Good biocompatibility of osteoblast cells next to the specimens was verified by ARS and ALP production. Our data exhibited that all samples are biocompatible and they have no toxicity. Especially، the sample with 50 wt. % of nano-HA had high bioactivity and it could be considered as an effective nanocomposite for bone tissue engineering applications.

In this research، sinterability، mechanical properties and microstructure of two different glass- ceramics belonging to CPNT (CaO-P2O5-Na2O-TiO2) and CPMSF (CaO-P2O5-MgO-SiO2-F) as well as their composite were monitored. To this purpose، CPNT: CPMSF composite with 40:60 weight ratio obtained by sintering the mixture of glass powders of base systems. Sinterability and crystallization behavior of the initial system glasses and composite were analyzed by means of differential thermal analysis (DTA) and X-ray diffraction (XRD). Evaluating the mechanical properties of dense and sintered specimens revealed that the Vickers Microhardness and Bending Strength of the composite specimen has been improved relative to the primary glass-ceramics. Furthermore، the composite specimen showed moderate machinability behavior without any fracture. Microstructure of specimens were analyzed by Scanning Electron Microscopy (SEM).

Fused silica is an amorphous phase of silicon dioxide، traditionally formed by heating crystalline SiO2 above its melting point، 1730 ± 5oC، and then cooling it rapidly enough to avoid recrystallization. Its density and softening point is about 2. 2 g/cm3 and 1725oC respectively. In this research fused silica bodies was fabricated with cold isostatic press. The amount of CMC، PVA and humidity was 2%، 3% and 2% subsequently. Cold isostatic press was applied at the pressure of 2000 bar. In order to receive the maximum density and minimum crystallization، bodies were sintered at temperatures of 1250، 1300، 1350oC and at 1، 2، 3 and 4 hours. Crystallization rate and phases of the samples were analyzed by X-ray diffraction and Microstructures of them were investigated by scanning electron microscopy. The sample sintered at optimal conditions was obtained with bulk density of 1. 83 g/cm3، the open porosity of 17%، closed porosity 0. 18%، relative density 83. 18 and Thermal expansion coefficient of it in the range from room temperature to 1000oC was measured 0. 4312 × 10-6 C-1.