فهرست مطالب amirabbas nourbakhsh

Alumina-C refractories have been widely used as slide gate submerged entry nozzles and mono block stoppers in steelmaking due to their unique physical and mechanical properties.In this research,the effect of different source of alumina having unlike surface areas(nano and mesoporous)and MWCNT additives on physical and mechanical properties of Al2O3-C refractories was investigated.In this regard mesoporous alumina was synthesized by sol-gel method.Then the mesoporous and nano alumina precursors were added to the functionalized MWCNT.In order to better distribution of 0.5-1.5 wt% nano additives the additives were firstly added to the matrix and then mixed with coarse particles of Al2O3-C refractories. Following in order to physical and mechanical properties investigation, all samples pressed under 150Mpa pressure by uniaxial then pressed and tempered at 200 ℃ for 6h, and afterward fired under coke atmosphere at 1450℃ for 2 h.The bulk density apparent porosity and cold crushing strength were determined according to their respective standard. Moreover their microstructure and phase analysis was investigated by XRD and SEM.The results confirmed that the sample containing1wt% nano Al2O3-MWCNT composite showed the highest CCS of about 137 Mpa,and sample with1.5 wt% mesoporous Al2O3 showed the lowest CCS (94 Mpa).The improvement of mechanical properties could be related to the higher SiC formation in the presence of nano Al2O3- MWCNT by vapor- solid mechanism. The main reason for decreasing mechanical properties in the presence of mesoporous additives could be attributed to limiting of gas-solid reaction due to trap of gases and therefore lower formation of SiC whiskers through the matrix.

Implant surface modification by creating laser surface texturing is the best known method to increase adhesion. The best pattern of laser surface texturing is still unknown. In order to investigate other features of the new pattern proposed by the authors, in this research, first, the new surface patterns of intersecting lines with angles of 0, 15, 30, 45, 60, 75, and 90 degrees on the surface of Ti6Al4V alloy using pulse Nd: YAG laser was created. Then the contact angle of water droplets was measured by two 1- recording and analyzing the image of the droplet and 2- using Extrand and Moon equations. Water droplets were selected in two volumes of 1 μlit and 25 μlit. Using metallurgical microscope, SEM, applying Wenzel and Cassie equations and drawing the corresponding diagrams, the effect of the angle between the lines, height, separation, and width of the surface texture columns on the contact angle of the droplet was investigated. The classical model of textures wettability was determined. The results showed for droplet with volume of 1 μlit the contact angle in both methods is almost constant and independent of the angle of the intersecting lines which is in good agreement with the results of previous researches. For droplet with volume of 25 μlit the contact angle in both methods is variable and dependent on the angle of the intersecting lines. The classical model of textures wettability in both droplet volumes is consistent with Wenzel's model.

One approach for the preparation of Mg-3Zn-1Mn nanobiocomposite is powder metallurgy. After preparing the alloy by the milling process, hardening is conducted during the sintering process. The condition for obtaining high strength and corrosion resistance of as-sintered specimens is the uniform distribution of zinc and manganese elements in the magnesium matrix and the maximum particle size reduction to increase the surface area. In this research, under certain conditions, the milling process has been conducted to fabricate this nanocomposite. The result of XRD analysis exhibited that the optimal sample is obtained after 25 h milling. At this time, the grain size was 27 μm, and the crystallite size was 24 nm. Evaluation of X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and field emission scanning electron microscopy (FE-SEM) results for samples shows uniform distribution of zinc and manganese particles in the matrix of magnesium and confirms the reduction of particle size with spherical shape for nanobiocomposite specimens.

In this study, the effect of superheat temperature of cooling slope process on the microstructure and electrochemical behavior of Al-Zn-In sacrificial anode has been investigated. Cooling slope Semisolid Casting was performed at three different temperatures of 660, 680, and 700 °C and the microstructure investigated by optical microscopy, electron microscopy and image analysis software. The electrochemical behavior of the alloy was determined by electrochemical impedance and polarization tests. According to the results, the sample produced by cooling slope at a temperature of 680 °C with a sphericity number of 0.68 and grain size of 45 microns had the maximum sphericity and minimum grain size. Also, the mentioned sample had the corrosion rate of 0.086 mm/year, which was the highest corrosion rate compared to other samples, and the results of the electrochemical impedance test confirmed the better behavior of its. Increasing the superheat temperature to 700 °C has led to a decrease in the electrochemical and microstructural properties of the sample.

In this research in order to disperse nano additives through the matrix of mag- chrome refractories, a novel approach by using the silanol surface group was reported. In this regard, the modified of nano MgCr2O4 particles have been done by functionalizing of MgCr2O4 by 3-(thriethoxsilyl)propyl amine (APTES) silanol group. Then 1% MgCr2O4 nano additives (with and without surface group) were added to mag- chrome matrix and pressed under a uniaxial press at 120 MPa pressure and then fired at 1600 ℃. XRD and TEM analysis were used to evaluate the synthesis of nano particles. FTIR and XRD analysis were carried out to investigate the presence of surface group of nano particles. Phase analysis and microstructure investigation have been done by XRD and SEM analysis.  The physical and mechanical properties, were determined according to the respective DIN standards. Also XRD and FTIR analysis confirmed the presence of functionalized groups on the surface of nano particles. DLS analysis of functionalize and not functionalized nanoparticles shows the the decrease of particle size in presence of silanol groups,  the UV analysis confirmed better dispersion of nano particles due to higher adsorption of functionalized nano particles.  XRD results of mag-chrome samples showed increasing of secondary spinel in presence of functionalized nano additives which could related to better dispersion of nano additives which caused to promote nucleation of spinel phases and result in solid state sintering and could effect on the physical and mechanical properties.

An investigation of the corrosion problems of the mag-chrome refractories used in the cylindrical component (snorkel) of Ruhrstahl-Heraeus (RH) vacuum degassing units is reported. The snorkel consists of a steel shell surrounded by a monolithic refractory and enclosing mag-chrome refractory bricks. Operational factors (degassing duration, time between heating cycles, number of heating cycles in a degassing sequence and the snorkel temperature) can overheat the steel shell and decrease the life of the snorkel. In the present study, the average temperature between the top and bottom of the steel shell was estimated by FDM (Finite Difference Method), indicating that thermal degradation due to creep will occur in the steel shell. In addition, the increasing number of hydrogen removal process during the degassing operation from the steel, the consumption of Fe-Si increased, producing more FeO and resulting in greater chemical corrosion of the refractory bricks. An investigation of these two mechanisms (thermal degradation and chemical corrosion) suggests that snorkel degradation could be mitigated by adjusting the number of daily heat sequences and cooling the steel shell, whereas the addition of MgCr2O4 nano additives to encourage spinel formation can be used to increase the hot modulus of rupture and increase the corrosion resistance.

Carbon bonded alumina foam filters have been successfully using for steel melt filtration. Enhancement of the filtration capacity of Al2O3-C foam filters is a key factor in order to make them applicable to be used for large steel casting parts or continuous casting of steel. In the present study, filtration performance of hercynite coated carbon bonded alumina foam filters containing 1 Wt.% of nano-TiO2 were evaluated by the exposure to an Al-killed 304 low carbon stainless steel melt. Successful impingement of steel melt into the filters revealed the filter structure strength and effectiveness under casting temperature and molten metal exposure conditions. Microstructural investigations using a field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) analysis of the active hercynite coated filter surfaces after steel melt filtration revealed the entrapment of the oxide inclusions from the steel melt on the surface of the filter. In addition, filtration mechanisms for whiskers and dendritic Al2O3, and hercynite inclusions at different Al/oxygen activity conditions of the steel melt were proposed. To this end, the feasible potential for the application of hercynite coated Al2O3-C filters for low and ultra-low carbon steel casting processes could be promising.

The photocatalytic activity of mesoporous TiO2 modified by the carbon nanotubes (CNTs) and Ag is reported. The mesoporous TiO2 was synthesized by sol-gel method and mechanically mixed with functionalized multi-wall carbon nanotubes which was decorated by different amount of Ag. Mesoporous TiO2 and the nanocomposite were characterized by XRD¡ SEM¡ TEM¡ BET surface area analysis¡ FTIR¡ AAS¡ UV-Visible¡ DRS-UV and UV-Vis absorption spectroscopy. The photoactivity of nanocomposite containing mesoporous TiO2¡ MWCNT and Ag were evaluated by the degradation of methyl orange (MO) in aqueous solution under UV irradiation. Results showed that the CNT which was decorated with the 15.5% of Ag could facilitate the phocatalytic activity of mesoporous TiO2.

In this research, the effect of sodium additive on silicon nitride synthesis has been investigated via carbothermal reduction and nitridation procedures, by using MCM-48 silicate precursor, and saccharose as a carbon agent. In this study, at first mesoporouse silicate has been synthesised, and then binary mixture was prepared by solving MCM-48 and saccharose in deyonized water. In order to investigate the effect of sodium additives, triple systems were prepared by sodium additive (in 1, 2 or 3 weight percent range) in the same time with binary mixtures. Then in temperature of 1400°C nitridation were performed under nitrogen gas atmosphere. Characterization of physical and microstructural properties of mesoporouse silicate and silicon nitride samples performed by various techniques likely X- Ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy. Results shows adding sodium cause to decreasing of liquid phases creating temperature and covering MCM-48 surfaces with this phases and will be prevent the formation of silicon nitride. Also filling the pores with liquid phases cause to prevent the formation of porouse structure.

Application of based andalusite refractories in industries is related to special properties of andalusite such as thermal stability of andalusite crystals and no changes on density after firing. In this research effect of different amount of Aluminum powder with optimized percent of Graphite and SiC were added to andalusite and physical and mechanical properties were investigated by density, porosity and CCS curves and microstructure, phase analysis and formation temperature of Al4C3 were investigated by (SEM), (XRD) and (DSC) respectively.The results showed that in coke atmosphere Al4C3 formed from 635°С and in presence of andalusite, Al4C3 reacted with andalusite, and SiC were formed from 1450°С and higher temperature. Also with mullitization of andalusite from 1400°С and formation of amorphous phase SiO2, in presence of carbon and Al, SiC and Al2O3 were formed. increase in the amount of Al and formation of Al4C3 and SiC at 1450°С, led to improvement of physical and mechanical properties of the samples.

Cerium based abrasives were studied for polishing glass surface. Raw materials used were Microsilica, Nanosilica, Silicon carbide, Cerium Oxide and Sodium Metasilicate. The procedure of powder processing was employed. Firing temperature 750ºC and 950 ºC were applied. Samples were prepared and firing temperature and strength was compared. Microscopy investigation and Image Analyzer revealed microstructure and grian distribution. XRD studies showed phases such as Ce2Si2O7, SiC and Na6Si8O19 From some reaction of CeO2 and SiO2.Then, values of density, percent by weight, volume of water absorption and the weight difference in grinding testwere measured. Finally the best composition was selected as sodium Metasilicate, Nanosilica, Silicon carbide and Cerium oxide and firing temperature of 950ºC, so that a suitable polishe for glass could be obtained.

Sialon ceramics are widely used in industrial applications because of high corrosion and oxidation resistance and high temperature properties. On the other hand, due to high costs of processing and raw materials, these materials used for special applications. The oxidation resistance of sialons is higher than that of Si3N4. Comparison between sialons showed that the highest amount of oxygen is available in x phase, therefore the oxidation resistance of x phase is higher than the others. X-sialon exhibits excellent chemical stability in contact with iron-based alloys at 1200°C. In this research, andalusite, kaolin, elemental Si powder and α-alumina were used as raw materials and the effects of aluminosilicate sources on the SRN process for x-sialon formation, with and without Y2O3, were studied. In order to study x-sialon formation, the samples were analyzed by XRD in different temperature and the reaction sequence of samples of andalusite precursor determined by DSC results. Results showed that in spite of more nitridation of Si in kaolin precursor samples, Y2O3 restricted nitridation process in all samples. In overall view, andalusite is more suitable precursor for x silaon formation via SRN process in comparison with kaolin, and Y2O3 leads to facilitate formation of x sialon from reaction between mullite and Si3N4. α-alumina is not appropriate source to supply lack of Al in component and it remains especially in kaolin precursor samples.

In this research the properties of nanocomposite (poly 4-vinyle pyridine/Al-SBA-15) precursor in order to β-SiAlON formation by using Carbotermal Reduction and Nitridation (CRN) was investigated. Firstly the nanocomposite P4VP/Al-SBA-15 was synthesized and then fired under N2 atmosphere at 1450 oC with 10oC/min heating rate and soaking time (0, 6)hrs in order to β-SiAlON formation. To characterize, phase analysis (XRD), microstructure studies (SEM/TEM), 29Si, 27Al Magic Angls Spinning (MAS-NMR) specific surface areas (BET) and thermal analysis (DSC) were carried out on Al-SBA-15 and P4VP/Al-SBA-15 samples. Result of phase analysis investigation (XRD) showed that the mesoporous structure was formed and also confirmed by SEM/TEM studies by using. 27Al- NMR spectral the presence of Al in mesoporous structure (Al-SBA-15) was confirmed. Also changes in chemical shift (ppm) in 29Si-NMR spectral showed that the polymerization was done in good conditions on the surface of Al-SBA-15. Finally samples fired under N2 atmosphere and results showed that not only carbon amount, type of carbon and surface area of precursor were important factors but also considering the higher amount of carbon than stochumetric was unavoidable.

In this study the effect of in situ Si3N4 formation on the microstructure changes of a cordierite body with nitride bonded was examined. Nano silicon powder was prepared by mechanical process in a high energy planetary ball mill in an Ar atmosphere.Different mixtures of the cordierite with nano silicon particles were prepared and sintered in a tube furnace at different temperatures in a nitrogen atmosphere in order to formation of nitride bonded cordierite composite. Result showed that by using nano siliconpowder formation of silicon nitride increased. It could be related to formation of Si3N4 before formation liquid phase of cordierite during sintering. On the other hand using nano silicon powder it should be possible to produce a high porous cordierite-Si3N4composite with a good thermal shock resistance.

Strontium Hexaferrite Bodies attracted more attention in various industries such as: microwave, Dc motors, agriculture (irrigation) and etc. In this research, the effect of chromium ion addition on phase analysis, microstructure and magnetic propertiesof strontium hexaferrite bodies prepared by solid state synthesis have been investigated. Results show that not only molar ratio of iron oxide and strontium oxide(n = 6) but also first firing temperature(1210oC) to form magnetic phase of strontium hexaferrite andsecond firing temperature (1220oC) to obtain suitable magnetic properties of strontium hexaferrite bodies at presences of chromium must be considered. XRD and SEM investigations showed that optimum amount of chromium is 0/3 (SrCr0/3Fe11/7O19).Magnetic coercivity, remanent magnetization and rectangularity ratio (Hk/HCj) of sample were 3995 Oe, 3719 Gs and 83/5%, respectively.

Use of wollastonite (CaSiO3) in different industries has caused attension to produce this mineral artificially. Stone industry in Iran makes several million tones of stone waste per year which can be used as a source of CaCo3. In this study combinations of stone waste, microsilica, silica, calcium carbonate with different sizes of 400, 800, 1500, 2500 mesh are used. By different compositions, different Ca/SiO2 ratios are fired at 1100 to 1400