Papers by Author: Xiu Hui Wang

Abstract: The sintering of alumina ceramics with high-purity has gained much attention due to their wide range applications. The improved sinteirng methods, such as the spark plasma sintering, super-high pressure sintering, two-step sintering, and so on, have advantages on the decreasing the sinteirng temperature or inhibiting the grain coarsening, compared with the conventional sintering.

Abstract: The solid-reaction was applied to synthesize perovskite-phase Lanthanum Aluminate powders by using AlOOH and La2(C2O4)3 as raw materials, mineralizer AlCl3 and AlF3 as the additives, graund and mixed, then calcined at 800°C and 1200°C for 3 h. The XRD pattern shows that mono-phase LaAlO3 powders can be obtained at 1200°C, and the SEM analysis indicates that the AlCl3 and AlF3 can promote the grain growth and have a good control of morphology.

Abstract: Ultrafine MgAl2O4 powders have been successfully synthesized by solid-state reaction from the mixture of AlOOH and MgO at the lower temperature. The samples were investigated by DTA/TG、XRD and SEM analyses. The results showed that AlOOH can be decomposed into γ-Al2O3 from DG/TDA curves, which can improve the activity of Al2O3 and promote the process of solid-state reaction. The XRD analysis showed the single-phase MgAl2O4 was formed at 1400°C. Meanwhile it was detected by ICP-MS that the purity of powders was 99.995%. The SEM images showed that the mineralizer containing fluoride such as AlF3, NH4F can promote the resultant to grow into regular octahedrons and disperse the particles. The XRD analysis indicated the mixture containing 5% AlF3 can transform the integrated MgAl2O4 powders at 1200°C, nearly 200°C lower than general solid-state reaction. Furthermore, The SEM images showed that fluoride can crystal the fine particles into the larger MgAl2O4 crystals, about 0.5～1.5µm.

Abstract: YAG crystal possesses chemical stability, mechanical intension, thermal conductivity and isotropy. These properties make it widely be used as functional and structural materials. YAG powder was successfully synthesized by gel solid-state reaction. AlOOH were reacted respectively with Y2(C2O4)3•10H2O (Route YІ) and Y2O3 (Route YІІ). The XRD indicated that the main phases were from YAM to YAP, finally to YAG with the increase of temperature in both routes, and YAG began to generate at 1250°C. The single-phase YAG generated after holding for 4h at 1450°Cin the YІ, but a little bit of YAP and Al2O3 was still remained in the YІІ. It was that Y2(C2O4)3•10H2O might be decomposed into high-activity, loose-structure yttrium oxide, which promoted the diffusion of Al3+ ion. According to XRD analysis, YAG generated slowly during 1250°C~1300°C and then fast during 1300°C~1450°C. The SEM images showed that the primary particles of YІ were 2-3µm, larger than that of YІІ. Particle distribution indicated that the average diameter is 18.68μm in the YІ and 9.35μm in the YІІ.

Abstract: The crystallization behaviors and microstructural developments in the CaO-MgO- Al2O3-SiO2 glass with Fe2O3, ZrO2 and F as additives were investigated by using scanning electron microscopy, X-ray diffraction and differential scanning calorimetry techniques. In the glass sample with 1.0wt% Fe2O3, only surface crystallization were observed, in which a three-layer compound surface containing the fine dendrite, finer fibrous morphology and particle-shaped crystals was formed respectively from the near free surface to the inner region. The crystalline phases precipitated were anorthite and wollastonite at 1000°C, and diopside at 1040°C. The addition of ZrO2 suppressed the nucleation and growth of the crystalline phases. The addition of another 4.0wt% fluorine into the glass with a pair of 1.0wt% Fe2O3 and 2.0wt% ZrO2 induced the bulk crystallization, the surface and bulk crystallizations were both observed at 1040°C. At the surface, a three-layer morphology, which had similar morphology to the glass with 1.0wt% Fe2O3 was formed. In the bulk region, the block-shaped crystalline phases were precipitated homogeneously in the residual glass.