Advanced Materials Research Vols. 341-342

Abstract: The influence of TiO₂ nano powder on the electrical properties and microstructure of TiO₂ ceramics was studied. The results showed that nano additive reduces the size of TiO₂ grain. The results also showed that the breakdown voltage and nonlinear constant of the samples were improved and the dielectric constant was reduced by doping nano-titania. An optimal composition dopant with 6 mol% nano-titania exhibited a low breakdown voltage of 11.3 V/mm, a nonlinear coefficient of 5.5, an ultrahigh relative dielectric constant of 7.11×10⁴ and relatively low loss of 0.28.

Abstract: A procedure for the preparation of active carbon-ceramic sphere was developed. Active carbon-ceramic sphere were prepared by coating a porous ceramic sphere with a phenolic resol resin (carbon precursor). The following procedure was adopted: (a) impregnation of the ceramic substrate with phenolic resol resin; (b) curing; (c) carbonization; (d) activation with KOH etching; (d) washing and drying. Under the optimal impregnation conditions, the material obtained (PRR 70 %) at 30°C, which exhibited a high carbon percentage (~ 5.3 wt.%) with a total pore volume of 0.276 cm3g-1 and a specific surface area of 471 m2g-1 (carbon in the carbon-ceramic sphere) by N2 adsorption, respectively. By means of chemical activation (KC-120), the total pore volume increased to 0.69 cm3g-1 and the specific surface area to 1110 m2g-1 (carbon percentage: 4.73 wt. %), respectively. The activated material shows a uniform carbon distribution, good adsorption properties and a high mechanical strength (24MPa).

Abstract: Nanoparticles of silicon carbide were produced through direct pyrolysis of stoichiometerically balanced rice husk. Rice husk used in this study was treated with different type and amount of silica source in order to enhance the silica/carbon ratio and thereby increase the yield. The synthesis was carried out in argon atmosphere. To increase the yield, different process parameters were identified and experiments were conducted at various levels using Taguchi design. The process parameters optimized using this design include silica source, pyrolysis temperature, silica content and heating rate. Silicon carbide produced from rice husk was analyzed using X - ray diffraction to identify the phase. From taguchi factor effect diagram it has been found that pyrolysis temperature and silica source plays major role in improving the yield.

Abstract: Kaolin is widely used in ceramic, paper, and pharmaceutical industries. The suitability use of kaolin in industries will depend on its physical and chemical properties. The physical and chemical composition of Kaolin is dependent on its geological origin, geographic source and processing. Processed kaolin available in the market is normally graded by the manufacturer based on its physical and chemical composition. This paper is focused on the size distribution analysis of nine types/batches of processed kaolin and one raw kaolin soil by using laser diffraction technique (based on Fraunhofer diffraction theory) in accordance to BS ISO 13320:2009. The laser diffraction technique is widely used in the powder industries in determining the particle size distribution because of its simplicity and its repeatability. All the specimens were pre-sieved with a sieve of 2mm aperture size. The effective size, uniformity coefficient and coefficient of curvature of the material were also calculated to facilitate the size distribution analysis. The findings of this paper are expected to benefit industries in which size the distribution of the kaolin will directly or indirectly contribute to its suitability use.

Abstract: In order to study the explosion characteristics of nanometer aluminum, comparative experimental studies on explosion characteristics of nanometer aluminum powder and common aluminum powder with different grain diameters have been carried out by using the horizontal pipeline explosive test device. After analyzing both the explosion process and the data of explosion characteristics of two aluminum powder during the experiment, some explosion characteristics of nanometer aluminum powder different from common aluminum powder can be concluded. Research result expressed: The maximal duration of explosion pressure of nanometer aluminum powder in its explosion process is much longer, which is about 3 to 4 times longer than non-nanometer aluminum; In the nanometer range, the scope of explosion pressure is much wider (between the 40~750kPa) than others, and as a whole, explosion pressure of the nanometer aluminum powder is much higher than the micron aluminum powder; In the process of explosion propagation of aluminum powder, flame combustion wave and explosion pressure wave show the positive feedback mechanism, which is interacting with each other and accelerating each other.

Abstract: Utilization of finite element method (FEM) and warm compaction process, study on mechanical theory and FEM simulation of molybdenum powder processing. The typical warm compaction process of molybdenum powder was simulated and analyzed with MSC.Marc FEM software. Via calculating, stress field, relative density distribution of molybdenum powder and temperature field were obtained. The result show that when velocity is 5mm/s and pressure is 1000MPa densification is the best. In the molybdenum powder compaction process volume percent of densification zone is 75%.

Abstract: The tooth-surfaces of corrected planar double-enveloping worm wheel were established by programming in MATLAB with the theory of spatial engagement. The contact lines were analyzed, and the contact styles were classified with given parameters. A new method of judging the types of contact lines was brought out. Based on the theory of spatial engagement, the re-machined planar double-enveloping worm gear is established by programming with MATLAB software. The contact lines on the worm wheel tooth-surface are analyzed and given the method of the contact line kind judgment.

Abstract: The main purpose of this paper is to research on the different ion nitriding temperatures of 35CrMo effect on the surface hardness, wear resistance of the workpiece. With series of experiment and test of micro-hardness, ring-block wear, metallographic observation, to select the optimization temperature for the ion nitriding process of 35CrMo steel.

Abstract: Single sapphire crystal is an important optical element and semiconductor substrate material, widely used in industry, national defense and scientific research, etc. But, high hardness and good chemical stability of the sapphire make it hard to be polished by applying mechanical chemical polishing and other contact methods. Therefore, laser polishing will be one of polishing methods which are supposed to replace contact method polishing sapphire. This essay, based on the summary of the study on laser polishing mechanism and technique of processing sapphire by laser, from the perspective of the interaction mechanism of the laser and the substance, analyzes in theory the interaction of laser and sapphire during the sapphire is polished by the short-wavelength laser. Experiments proved that under the cases of 20mJ and 40mJ laser energy when green laser polishes sapphire, the main material removal mechanism is fracture, at the same time, light melt mechanism exists.

Abstract: We have practiced the Ga-assisted deoxidation method on GaAs(110) surface. When the deposit amount of Ga is suitable, flat GaAs(110) surface without any thermal deoxidation induced pits and excrescent GaAs islands obtained with the Ga-assisted deoxidation method. The obtained results suggested that, 9ML Ga was optimized dose for GaAs(110) surface, which is a little more than GaAs(001) surface indicating a thicker oxide layer of GaAs(110) surface.