Key Engineering Materials Vols. 602-603

Abstract: The ceramic microsphere was prepared by the ball milling and sintering using Dolomite and Coal Gangue as raw materials. The effects of ratio of raw materials, sintering temperature on bulk density and apparent density, phase constitution, microstructure of the ceramic microspheres were studied. The results indicated that the ratio of raw materials, sintering temperature has some effects on the bulk density and apparent density, phase constitution, microstructure of the ceramic microspheres. The bulk density and apparent density of the ceramic microspheres increased with sintering temperature rising. With the increasing of the ratio of dolomite, the bulk density of ceramic microspheres improved firstly and then dropped slightly, the apparent density of ceramic microspheres increased constantly. The bulk densities of the prepared ceramic microspheres were in the range of 0.570 g/cm³ to 0.754 g/cm³, the apparent densities of the prepared ceramic microspheres were between 2.419 g/cm³ and 2.661 g/cm³.

Abstract: A fast method of microwave pyrolysis was provided to prepare α-Al₂O₃ powders. Aluminum hydroxide and Aluminum ammonium sulfate doclecahydrate were used as raw materials to obtain α-aluminum oxide powder by microwave pyrolysis, respectively. Thermo-Gravimetric/Differential Thermal Analyzer (TG/DTA) and X-ray Diffraction (XRD) analysis were employed to investigate pyrolysis process and the transformation of metastables Al₂O₃ in the process of heating different precursors. Meanwhile, Flied Emission Scanning Electron Microscopy (FESEM) was applied to observe microstructure and grain growth, and the phase composition was characterized by XRD. The results indicated that the high purity α-Al₂O₃ was obtained which met the demands of market, and the sample obtained from aluminum hydroxide performed high purity, small particle size and, while the sample from ammonium aluminum sulfate showed lower purity and larger grain size.

Abstract: In this study, the γ-Al₂O₃ nanowires were prepared by a simple surfactant assisted precipitation method using the cetyltrimethyl ammonium bromide (CTAB) as a structure-directing agent (SDAs). Homemade sodium aluminate (NaAlO₂) and H₂O₂ were used as raw materials. The influences of CTAB concentration and calcination temperature on the morphology of product were discussed. The obtained samples were investigated using transmission electron microscopy, X-ray diffraction analysis and TG-DSC. In the end, a possible formation mechanism of wire-like γ-Al₂O₃ is proposed.

Abstract: CaO(15%)-ZrO₂ nano-powders were prepared by microwave pyrolysis in a multi-model chamber at the temperature ranging from 650°C to 800°C, with the precursor processed at different reaction temperature from 0°C to 80°C by chemical co-precipitation method. XRD and SEM techniques were used to characterize the phase transition and micrograph of powders. It is found that the content of m-ZrO₂ phase decreased with the increasing of reaction temperature and pyrolysis temperature. The high dispersed and superfine nano-powders were obtained at the pyrolysis temperature of 750°C for 20 min at 80°C. And only cubic ZrO₂ phase were detected in CaO (15%)-ZrO₂ powders and the average size of the powders is about 41 nm.

Abstract: Using TiO₂B₂O₃ powders as oxidizer,AlMg powders as reducer,the TiB₂ multiphase ceramic are preparated with SHS, and analysed with SEM and XRD.The effect of HCl, H₃PO₄ to pickling of TiB₂-based multiphase ceramics is explored by SEM and XRD analysis. Research suggests that: the main ingredients of TiB₂-based multiphase ceramics is TiB₂, MgO and MgAl₂O₄ three phases, few of reaction residual objects and impurities also exists; the multiphase ceramics is forming by many of hexagonal crystal type products and small particles reunion, hexagonal crystal type product is TiB₂, small particles may be MgO, MgAl₂O₄ and other impurities product; MgO can be effectively washed by HCl and H₃PO₄ , but TiB₂ and MgAl₂O₄ invalid. At room temperature, 30% HCl pickling has the best effect, the concentration of TiB₂(ω) is up to 59.3%; the higher of the concentration, the better of acid-effect; In the pickling process, as the temperature rises, the concentration of TiB₂ grows, but the temperature should not be too high. When temperature reach 75 °C, HCl volatilizes too quickly and inefficiently. At room temperature, 20% H₃PO₄ has the best pickling effect, the concentration of TiB₂(ω) is up to 52.6%, but the best pickling effect is not well with concentration increasing; as the temperature increasing, purity of TiB₂ is also increased; At 70°C, the concentration of TiB₂(ω) after H₃PO₄ pickling is up to 61.9%, refine effect is good.

Abstract: In this study, Ca²⁺ stabilized ZrO₂-SiC composite materials were prepared via carbothermal reduction, using natural zircon ore as raw material, CaO as additive, and black carbon as the reducing agent. The effects of synthesis temperature and CaO content on the phase composition of the products were investigated by XRD. The microstructure and micro-area chemical analysis of the products were characterized by SEM and EDS. The results indicate that: (1) Ca²⁺ stabilized ZrO₂-SiC composite materials could be prepared from natural zircon ore with CaO addition between 1500°C and 1600°C for 4 hours by carbothermal reduction process. (2) The synthetic temperature has an important influence on the phase composition of the carbothermal reduction products of zircon. The production of m-ZrO₂ and t-ZrO₂ got obviously enhanced with increasing temperature from 1500°C to 1600°C. (3) At the same synthetic temperature, Ca²⁺ stabilized ZrO₂ got enhanced with increasing adding amount of CaO. The optimized synthesis condition of Ca²⁺ stabilized cubic-ZrO₂/SiC composite materials is sintering at 1600°C for 4 hours with adding 40 mol% CaO as additive.

Abstract: In this paper, yttrium aluminum garnet (YAG) powders were synthesized by the normal-strike co-precipitation method (adding precipitant solution to the metal nitrate solution). Aluminum nitrate (Al (NO₃)₃ 9H₂O) and yttrium nitrate (Y(NO₃)₃ 6H₂O) were used as raw materials and ammonium hydrogen carbonate (AHC) was used as the precipitant. The precursor was calcined at the temperature of 900-1200 °C for 2 hours. The crystal structure and microstructure of YAG powders were investigated and analyzed by XRD, FESEM, TG-DTA and laser particle size analysis. The results show that the concentration of metal ion and AHC have a significant effect on crystal structure of YAG powders, and pure YAG powders were obtained at 1000 °C when the concentration of Al³⁺ was 0.1 mol/L and the concentration of AHC was 1 mol/L. The average primary crystallites particle sizes were ranged from 50 nm to100 nm in diameter. nanosize YAG powders with excellent properties and good dispersity can be produced at the temperature of 1100 °C.

Abstract: The dispersion stability of silicon carbide whisker (SiCw) which is by-product of SiC was researched using distilled water as dispersing medium, polyethylene imine (PEI), tetramethylammonium hydroxide (TMAH), poly(meth)acrylamide (PMAM) as the dispersants. The sedimentation and optical microscope technology are used to observe whisker dispersion ，FTIR and ZETA electric potential are used to explore its dispersion mechanism . The results show that the order of dispersion capacity of the dispersant was PEI> TMAH> PMAM.When 1.25vol% PEI was used as dispersant, SiCw can be dispersed homogeneously at pH=9 and 10, in the meanwhile, if TMAH was used, the added amount would be 0.75vol% in which the pH is in range of 11-12.

Abstract: Nanosized silicon carbide powders were synthesized from a mixture of silicon and carbon by microwave heating methods. The Result Indicates SiC can be formed at lower temperatures by using the Si-C reaction at 1200°C for 30min. XRD patterns shows that SiC peaks appeared as the only crystalline phase. SEM photo shows the particle size was 100～200 nanometer. At the same time, Effects of chemical reaction of silicon and carbon was researched by mechanical activated microwave synthesis.

Abstract: Ultra-fine ZrB₂ powders were synthesized by sol-gel carbothermal processing using zirconium oxychloride (ZrOCl₂.8H₂O), boric acid (H₃BO₃) and sucrose (C₁₂H₂₂O₁₁) as raw materials. Additionally, mannitol was used as cosolvent to obtain a stable high-concentration ZrB₂ sol. Since C₁₂H₂₂O₁₁ can be completely decomposed to carbon, carbon might be accounted precisely for the carbothermal reduction reaction. In the case of C/Zr(mol.)=6.0 and B/Zr(mol.)=3.0, a single phase ZrB₂ without residual ZrO₂ or ZrC was obtained. The photomicrograph revealed a spheres shape morphology with an uniform size distribution.