Key Engineering Materials Vols. 602-603

Abstract: In this paper, the process of the transformation from kaolin to metakaolin was investigated. The kaolin was calcined at different temperatures and analyzed by Xray diffraction (XRD), Fourier transform infrared spectra (FTIR) and solid state nuclear magnetic resonance (NMR). The formation of metakaolin structure was based on the stacking polyhedrons changes, which originated from dehydroxylation of kaolinite. With increasing temperature, kaolin kept structure of kaolinite unchanged in the course of dehydroxylation and then structure of kaolinite transformed to metakaolin when the dehydroxylation was over. It was demonstrated that the essence of pozzolanic activity of metakaolin. The result revealed that the pozzolanic activity of metakaolin increased with increasing temperature at the range of 600~900 °C.

Abstract: Tris (hydroxymethyl) ethane (PG) as a phase change material, micro-porous xonotlite (CS) as matrix, PG/CS composite PCMs were prepared by melt-soaking method, and the effect of micro-porous structure of xonotlite on heat absorption capacity, bending strength and insulation performance of composites, and the exudation of PG was studied. Otherwise, for the work environment and characteristics of propulsive device of vehicle, this paper explored the feasibility that phase change materials (PCMs) worked as the insulation material in short-time insulation system of the vehicle. Experimental results show that, when the most probable pore diameters of xonotlite was not less than 63nm, the composites presented better and almost same absorption capacities of matrix (CS) to PCM (PG) in different composites; when up to 85nm, the composite exhibited the lowest leakage rate (less than 5%), the optimal mechanical property and thermal insulation performance. This Study proposed a new idea for the design of the insulation material in the thermal protection system of propulsive device of vehicle.

Abstract: Two types of mullite-Al₂O₃ composites were designed and sintered in situ from different composition containing Al composites e.g. kaolin, alumina hydroxide and calcined bauxite etc, and auxiliary additives. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Bulk density, apparent porosity, thermal expansion coefficient and bending strength were also measured. The two samples exhibited XRD reflections characteristic of alumina and mullite phases. The amount of these phases depended on starting batch compositions, and reaction of starting and auxiliary materials together to form mullite. Because of in-situ formation of mullite fiber, the bulk density and bending strength were improved and apparent porosity was decreased for the composites with uniform microstructure. The presence of high mullite phase was found to decrease the thermal expansion coefficient. The potential effect of these morphologies and phase on properties was discussed. These mullite-Al₂O₃ composite was expected to have major applications in the areas of refractory material.

Abstract: Al₂O₃-C refractory has many advantages, high strength, good corrosion resistance and good thermal shock resistance, so Al₂O₃-C refractory is widely used in the steel-making process. In this paper, the effect of different soaking time on the properties of Al₂O₃-C refractory at 1450°Cin nitrogen atmosphere was studied. The phase composition of the sintered sample has little change when the soaking time was from 2h to 5h. Cylindrical sialon appeared as the soaking time being 3h, and its grain size increased and became uniform, about 2.5um when the soaking time being 4~5h. In the general performance, with the soaking time changing from 2h to 5h, the samples increment percentage in weight decreased gradually, and the compressive strength of the sintered was first increased, and then decreased, reaching the maximum when the soaking time is 4h. Both the apparent porosity and bulk density of the samples had little different changing.

Abstract: Waste foundry sand is a kind of solid wastes produced during casting process, the casting output of China ranks first in the world for many years and the amount of waste foundry sand is huge. But the utilization rate of the waste foundry sand is low in China. It is not only a threat to the environment but also a waste.In this paper, waste foundry sand was taken as main starting material, adding proper amount of additives. The shaped samples were heated in the electric oven at the temperature of 1300°C, 1400°C and 1500°C respectively, the soaking time is 3h for all samples.The microstructure and phase composition of the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The effect of the temperature on the synthesis of mullite-silica-rich glass was investigated. The results showed that the main phases were mullite and glass when the samples were heated at 1500°C, mullite grain grew well and formed network structure. This network was benefical to improve the thermal shock resistence.It opens up a new method to utilize the waste foundry sand.

Abstract: Mica glass-ceramics can be applied in all kinds of electrical equipment, locomotive internal circuits in high-speed rail, ordinary electric locomotive and subway locomotive. In this study, mica glass-ceramics were prepared by sintering process using flake mica and waste glass as the main raw material with low cost. Different mica glass-ceramic samples were fabricated by changing the formula of raw materials, molding process and sintering temperature. X-ray diffraction, scanning electron microscopy, three-point bending test, and balanced-bridge technique were applied to investigate the phase, microstructure, mechanical and electrical resistivities of the samples, respectively. The results show that the optimum sintering temperature is 900 to 1000 °C holding for two hours, the desirable ratio is 70 wt% of mica powder while 30 wt% of glass powder. In that condition the sample could be less porosity, high flexural strength (63.3 MPa) and eligible electrical resistivity (0.4×1013 Ω·cm).

Abstract: Novel heat insulation materials were synthesized by molten salt method by using natural forsterite and NaSO₄ molten salt. The insulation materials which have light weight and small size pore were obtained by using different particle size (44 μm, 74 μm and 250 μm) natural forsterite and NaSO₄ molten salt at 1000 °C-1150 °C for 10 h after treating by distilled water. The effects of particle size of forsterite on phase composition, sintering porperties, physical property and microstructure were studied. The results showed that the main pahse in all samples was Mg₂SiO₄Fe₂O₃ and MgFe₂O₄ which indicate that the NaSO₄ molten salt just play the role of Promoting particles sintering. The particle size of 74 μm have better bulk density and comprssive strength in all sample, at 1100 °C, the sample of bulk density is 1.54 g/cm³ and the apparent porosity is 0.498. In addition, the strength of the sample made of 44 μm forsterite materials was always higher than that used 74 μm forsterit, and was the lowest strength of sample used 250 μm forsterite.

Abstract: Alumina lightweight insulation bricks were prepared from alumina powders using foaming method. In this paper the influences of foam addition amount (600, 800, 1000, 1200ml/kg) on properties of Alumina lightweight insulation brick were discussed. The phase composition is analyzed by XRD and the microstructure is characterized by SEM. The results show that the bulk density of alumina lightweight insulation brick is 0.63g/cm³,cold compressive strength is 10.53MPa, linear change rate after firing is -4.5% and reheat linear change rate is -0.27%,which synthesized under 1000ml/kg foam amount after firing at 1550°C for 3h. The results indicate that the density of alumina lightweight insulation brick is reduced with the increase of foam addition amount, when the addition amount is more than 1000ml/kg, cold compressive strength decreased significantly and linear shrinkage increased obviously.

Abstract: In continuous casting process, the mould is the core of the continuous caster, and the vast majority of the surface defects of steel is originated in the crystallizer. Choosing a reasonable water gap in the delivery system is particularly important, especially in twin roll strip continuous casting, the flow delivery system thin belt has a close relationship with the quality of the products. Experiments to skateboard and water gap, STEEL AISI 4340 materials chosen as the simulation material at the same time, distribution water gap taking the form of a set themselves by using the finite element software COMSOL simulation calculation of different gaps opening mode of velocity field, and fluid line back to the high wall, made a comprehensive analysis in different speak way open comprehensive effect is best, the most conducive to the production of high quality material. The experiment determines the best form of water gap, improving the efficiency of the actual production. Make it to the actual production has a certain guiding significance.

Abstract: Irradiation crosslinking is one of the most important methods to modify UHMWPE, it can effectively improve the hardness, creep resistance and abrasion resistance of this material. In order to eliminate free radical, increase material strength, abrasion resistance and fatigue resistance of creep, this study uses Co60-γ to modify UHMWPE under vacuum atmosphere, with the irradiation dose of 30, 60, 90, 120 Kgy respectively. Its mechanical properties, microstructure, degree of crosslinking and crystallinity are analyzed, the results show that the modified UHMWPEs impact strength decreased, elongation basically remain unchanged, tensile fracture strength and tensile yield strength increased.