Key Engineering Materials Vols. 368-372

Abstract: A series of alumina-based ceramic cores were in situ prepared. Effect of kyanite on the properties of ceramic core was discussed. The results indicated that the microstructure of the core is characterized by the presence of unreacted Al2O3 particles having a polycrystalline composition consisting essentially of in-situ synthesized 3Al2O3 .2SiO2 on the surface of the Al2O3 particles. The ceramic cores of kyanite contents sintered at 1500oC for 3 h have almost no creep deformation.

Abstract: The performances of high-alumina ceramic are analyzed such as physical and mechanical property. In consideration of its brittleness-ductility change, the critical cutting depth agc of high-alumina ceramic is 3μm. When the cutting depth of single grain is less than the critical cutting depth of alumina ceramic in precision manufacturing, the material is wiped off with ductility. So the cutting depth of single grain agm should be selected within 0.1~2.5μm.Grinding wheel sharp edge is utilized for the spherical surface generation cutting. The ceramic-bonded fine grain diamond wheel is selected after considering manufacturing technology, machining parameters, its making and mending. The granularity of grinding wheel is M1~M5 and the consistence is 125%. The method of spherical surface generation cutting and the effect of high-alumina ceramic ductile machining were verified by the experiment of high-alumina ceramic precision grinding using precision grinding machine MGK1420. The result shows that the surface quality is very high and achieves the requirements.

Abstract: ZrO2 nano-powders were prepared by a microemulsion process with the water-in-oil system of water/cyclohexane/Triton X-100/hexyl alcohol. The influence of cosurfactant content and the heterogeneous distillation process on the structure and properties of the particles was studied. XRD analysis showed that the cosurfactant content has little influence on the crystal phase of ZrO2. With the increasing mass ratio of cosurfactant to surfactant from 0.3 to 0.5 and 0.7, the average size of ZrO2 powders increases from 23.3 to 25.2 and 27.5 nm. The heterogeneous distillation process can effectively inhibit the formation of hard agglomeration during evaporation and increase the specific surface areas of ZrO2 powders.

Abstract: Water debinding is an important debinding technique for ceramic injection molding. However cracks or blisters usually generate during water extraction. In this paper, two types of multi-component binder systems were studied: (1) a major fraction of polyethylene glycol (PEG), and a minor fraction of polyvinyl butyra (PVB) and other additives. (2) a major fraction of PEG, and a minor fraction of polymethyl methacrylate (PMMA) and other additives. Mechanism of defects generation was investigated, and PEGs with various molecular weights were introduced to avoid cracks or blisters during the process. Further more, the compatibilities of PEG/PVB and PEG/PMMA were studied. The results showed that PEG and PMMA exhibited better compatibility, with the feedstock more homogeneous and sintered ceramic parts higher strength.

Abstract: Mercury porosimeter and scanning electron microscope (SEM) were used to analyze the pore structures evolution and distributions for supercritical CO2 debinding of injection molding ceramics. Classical diffusion equation was used to describe the mass transfer of supercritical CO2 debinding of the injection molded ZrO2 ceramics. The behavior and kinetics of the debinding were studied and analyzed. Results show that the solubility and diffusivity of soluble binder are the key factors in supercritical CO2 debinding, while the diffusivity is a dominant factor. The calculation data from the theoretical model are consistent with the experiment under the condition of enough long debinding time. It is shown that the diffusivity can be obtained by simple theoretical model combined with experimental data. The extraction rate and the extraction kinetics of the process can be predicted using the theoretical model.

Abstract: Ultrafine ZrO2 suspension with stable high solid loading was prepared, and ZrO2 ceramic materials with uniform structures were fabricated through gelcasting. Zeta potential of the ultrafine ZrO2 suspensions with A-type dispersant, triammonium citrate, and without dispersant was measured. The influencing factors on suspension flowability as the content of dispersant, pH value, solid loading, and milling time were studied in detail. And the optimum premixed solution/initiator (APS)/catalyst (TEMED) ratio for gelcasting was investigated. The results showed that A-type dispersant was suitable for dispersing of ultrafine ZrO2 particles in aqueous premixed solutions; the optimized content of dispersant was 2%~2.5% of ZrO2 volume; ZrO2 suspension displayed a minimum viscosity at pH 10.66; the upper limit of solid loading was 54vol.%; and the appropriate milling time was 12 hours. When premixed solution/initiator (APS)/catalyst (TEMED) ratio was 100/1/0.5, ZrO2 suspension has a better gelcasting behavior.

Abstract: The wear properties of ADZ (alumina dispersed in Y-TZP) and MDZ (mullite dispersed in Y-TZP) were investigated by using a ring-on-block tribometer. The results showed that for Y-TZP ceramic, the addition of alumina phase (with 10-20% in mass fraction) leads to an improved wear resistance. With the increase of the normal load, the wear rates of ADZ ceramics increase. Under low and medium normal load (100N and 300N), the wear resistance is controlled by the hardness of ceramics, and under high normal load (500N) the fracture toughness is obviously contributed to the wear resistance of the ceramics. For MDZ ceramic, the wear resistance of 15MDZ (15wt% mullite dispersed in Y-TZP) is better than that of 20 MDZ (20wt% mullite) under the normal load from 100 N to 500 N. The mechanical properties of 15MDZ are worse than that of Y-TZP ceramic, but the wear resistance is enhanced due to the action of “needle roller bearing” of the fractured rod-like mullite particles.

Abstract: The dielectric ceramics of CaTiSiO5-CaTiO3 with ZnO and B2O3 as additives were sintered at 950°C. Of the ceramics with a small quantity of 2ZnO-B2O3 as the additive, the density is nearly the same as the one reported, εr= 83 ~ 99, tgδ < 7×10-4, αε= (-100~+100) ppm/°C. The crystal phases and microstructures are analyzed by X-ray diffraction and scanning electron microscope. It is found that the sintered ceramics is of biphase, comprising monoclinic CaTiSiO5 and orthorhombic CaTiO3, and the grains are mostly the small circular ones, having diameters of 1~29m. By adjusting the composing of the ceramic, a high frequency dielectric ceramic CaTiSiO5-CaTiO3, of which αε= (-50~+50) ppm/°C was attained.

Abstract: (MgO)0.1-x(YO1.5)x(ZrO2)0.9 (MYZ) and (MgO)0.1-x(CaO)x(ZrO2)0.9 (MCZ) ceramics were prepared and their phase composition, bulk density, flexural strength, and thermal shock resistance were characterized. There was an abrupt change of c/(c+m) from 29% to 75% as 0

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