مجله مواد مهندسی
پیاپی 1 (2009)

The application of inexpensive materials such as copper، zinc، lead، iron and steel slag’s in manufacturing of glass and glass-ceramic products in construction industry، lining materials as anti-corrosion and anti-abrasion coatings in metals and etc، has led to considerable progress in glass technology in recent years. The composition of slag glass-ceramics is mainly located in the SiO2-Al2O3-CaO-MgO system، in which one of the most important problems is nucleation and crystallization of initial glass. In the present work، the crystallization behavior of various compositions containing different nucleating agents Cr2O3، Fe2O3 and TiO2 in the single، double and triple forms was studied by differential thermal analysis (DTA). Crystalline phases were determined by the X-ray diffractometry and the micro-structural analysis was studies using the SEM micrographs after determination of proper nuclei. The three point bending strength، micro-hardness and the chemical resistance of the best glasses and glasses ceramics samples were determined. According to the results، the resulted glass-ceramic had a better specification than the stoneware floor tiles and the granite. The mechanical and surface properties of products considered as decoration stones and tiles.

In recent decade، use of terrestrial laser scanners (TLS) are rapidly grew up for reconstruction of environment، buildings، and various objects in different applications. Though، TLS is capable to rapidly acquire a huge volume of 3D point clouds، it involves with several problems such as non-selective sampling، shadows and occluded areas، variable point density due to different object surface distance and orientation، dependency of laser signal gain and so measurement noise to surface material، roughness، color، temperature and moisture. These problems cause to not anybody able to prepare a perfect observational plan before filed measurement، in order to acquire a complete and high quality raw data by this expensive equipment in the field. The observational plan means network design which is optimal determination of TLS stations and required targets. In this paper، general idea of TLS network design is presented on a 2D simulated data. The result demonstrates it is possible to implement the idea of automatic TLS network design using artificial intelligent tools.

Study on some of the mechanical، physical and electrical properties of graphite as the heating element in a high temperature vacuum furnace has been reported in this paper. Two types of graphite have been selected as the heating element of the furnace after searching the domestic market، and studies of their mechanical and physical properties have been carried out. Then، study of electrical properties of the more suitable type has been done under the high electric current and vacuum conditions. The results show that EK-40، graphite is a good option for use in high temperature vacuum furnace.

The systems of Al2O3+Si، Al+SiO2 and Al + Si were prepared to study the effect of reaction bonding process on the mullite formation in temperature range 700-1600°C. Results showed that the reaction bonded mullite (RBM) starting from Al2O3+Si raw materials، starts to form at 1450°C and the reaction is not complete by 1600°C. XRD patterns for samples in the Al+SiO2 system showed reduction of SiO2 by Al، formation of α-Al2O3 and SiO2-derived Si oxidation and finally mullite formation. XRD patterns for the Al+Si system showed that there is a thermodynamic reaction between Al and Oxygen at 900°C to form α- Al2O3. Si oxidation and mullite formation were not detected in this system.

In this paper the samples based on MoSi2 in Mo-Si-Al triple system were produced. Their densification was studied without using complementary methods and external pressure during synthesis via SHS method. Initially، raw materials (Mo-Si-A) were weighted and mixed together corresponding to Mo (Si 1-x، Alx) 2 with 0. 2≤X≤0. 5. Mixed powders were pressed by a uniaxial pressing. Then the obtained pellets were preheat and synthesized in combustion reactor. Finally، the parameters affected the samples properties such as percentage of Si substitution with Al، particle size of Si powder، pressing pressure; preheating process and ignition temperature were optimized. The results show that the final densities of synthesized samples were up to 90% TD and their microstructure were uniform.

The aim of this study is investigation of phases and microstructure of synthesized products. DSC analysis proved that with addition of Al to Mo-Si system، the synthesis temperature is decreased from 1400 °C to 750 °C. The microstructural analysis by SEM showed homogeneous distribution of Al particles in microstructure so that with increasing the percentage of Al the grains growth and curvature of grain boundaries occur. XRD analysis confirmed that in X=0. 2 (Mo (Si1-x، Alx) 2) the major phase is Mo (Si، Al) 2 and in 0. 3≤X≤0. 5 the major phase transformers to Mo2. 85Al1. 91Si4. 81 as a new phase.

Thermal behavior of 25% mol Yittrium – Bismuth Oxide was investigated by Differential Thermal Analysis (DTA) and X-ray Diffraction (XRD) techniques. Result showed that monoclinic (α-Bi2O3) to cubic (δ-Bi2O3) phase transformation was occurred at 750 C and cubic phase stabilized at room temperature. Also، sintering behavior of these samples was investigated by measuring of relative density and radial shrinkage. According to these measurements the optimum temperature and time for sintering of 25% mol Y2O3 doped Bismuth Oxide were 950 C and 36 h.

75% mol Bi2O3 – 25% mol Y2O3 has the highest conductivity in Bi2O3 - Y2O3 system. This compound will create δ-Bi2O3 cubic phase due to sintering at high temperatures. The mixtures were prepared by solid state reaction technique. After preparing granules، Experimental samples were fabricated by uniaxial pressing and followed isostatic pressing، then samples have sintered at 950°C for 36 h. X-ray diffraction (XRD) analyses detected δ-Bi2O3 as the sole stable phase in all samples. Also، the annealing process was carried out on samples at 600°C duration between 72 to 300 h. X-ray diffraction (XRD) analyses on samples detected that the δ-Bi2O3 phase transfer to rhombohedral phase.

Many studies have been done about decreasing or even eliminating of wastes such as extra inventory since lean concept appeared. Although these studies have not taken into account seriously expected reliability. So in this paper، a MODM model has developed by conflict of these subjects. They are decreasing wastes and increasing maintenance system reliability. Wastes that have been decreased are maintenance requirements (i. e. labor، spare parts، reserve system and productive maintenance activities) and maintenance system reliability that has been increased is a function of maintenance requirements. A set of SAIPA2 data has been used to running the case study and test the effectiveness and the efficiency of the proposed model.

Variations in electrical conductivity of SnO2 thick film exposed to ethanol vapor before and after aging process were investigated. Aging is performed continuously at 350-750ºC and 96 hours. The Results show that room conductivity (Iair) decreases with aging temperature. However، the maximum conductivity in presence of ethanol (IMAX g) remains approximately constant. Consequently، these variations result in the increase of electrical conductivity of tin oxide layer.