Papers by Keyword: Alumina Ceramic

Abstract: To obtain complex shape alumina ceramic parts, a composite powder of epoxy resin binder E-06 and alumina powder are laser sintered combined with cold isostatic pressing(CIP). An orthogonal experiment is carried out to probe the influencing factors of selective laser sintering (SLS) alumina green parts. When preheating temperature, laser power, scan speed, scan spacing and layer thickness are, respectively, 60°C,14 w, 2000 mm/s, 0.10 mm/s and 0.10 mm, the density and bending strength of alumina parts are relatively high. Then, airproof canning prepared for CIP is manufactured in the vacuum environment. Finally, the optimized SLS/CIP alumina parts are degreased and sintered in 1600 °C to produce crack-free alumina parts. The sintered relative density of the parts however is limited to only 57% but the forming integrity during SLS and CIP remains after sintering.

Abstract: This article describes the alumina ceramic mixed with two kinds of additives in order to improve the performance of ceramic, such as mixed with submicron ZrO₂ and Nano-SiC. The main use of monoclinic zirconia (m-ZrO₂) and tetragonal zirconia (t-ZrO₂) of reversible phase transition of volume change and use of nano-SiC particle dispersion toughening mechanism to improve the toughness and wear resistance of composite alumina ceramic. Through doing various tests about fired products, including hardness testing, SEM test and bulk density measurement, we can understand the microstructure and mechanical properties of some of the products for analysis.

Abstract: Infiltration of a nano-sized alumina sol into the green bodies is proposed to facilitate the ceramic sintering. The green samples were prepared by a colloidal processing based on drying induced forming, and then were immersed in a nano-sized alumina sol prior to their sintering at 1350-1600 oC. The alumina sol was characterized by using transmission electron microscopy and the grain structure of sintered alumina ceramics were examined by scanning electron microscopy. Significant densification of sintered samples was evidenced, in a depth of ~ 0.5 mm, on the samples treated with the alumina sol infiltration. It is indicated that filling of nano-sol into the micro-pores between particles of green samples enhanced the sintering densification process. The infiltration treatment by nano-sol may also provide an effective way to produce structurally gradient ceramics with a gradual changing density and/or composition from the surface into bulk.

Abstract: The 316 stainless steel-alumina joining was prepared by a modified moly-manganese (Mo-Mn) process and a Ni net-embedded brazing method. The modified Mo-Mn process had a reaction layer between the Mo-Mn layer and the alumina substrate, followed by brazing with steel. The reaction products of the reaction layer with substrate and the Mo-Mn layer were investigated. The brazing method had a braze foil/compressed Ni net/braze foil set sandwiched between steel and alumina. The reactions among the Ni net, braze alloys and substrates were studied.

Abstract: In this paper, effects of temperature and erosion-wear particle on solid particle erosion-wear behavior of alumina ceramics were studied. The erosion-wear experiments were performed using self-designed sand blasting high-temperature solid particle erosion-wear equipment in air atmosphere. The results show that alumina ceramics presented the characteristics of brittle fracture at the high temperature of 1200°C. Erosion-wear rate increased with increasing temperature and rise obviously above 1000°C. For the same kind of erosion-wear particles, the erosion-wear rate of samples increased with the larger particle size. For the different ones, the greater hardness, the more serious erosion-wear.

Abstract: This work deals with the preparation and characterization of macroporous alumina ceramics and permeable laminates with a stepwise (layerwise) porosity gradient in the range of approx. 20–50 %. Layered structures are made by sequential casting and draining of ceramic suspensions containing corn starch (median size approx. 14 micrometers), using both traditional slip casting (TSC) and starch consolidation casting (SCC). In both techniques starch acts as a poreformer, which is eliminated during firing. The influence of the alumina concentration and starch content in the suspension on the porosity, pore size and pore connectivity in the individual layers is studied. It is shown that differential shrinkage of the layers in the case of SCC, caused by the different starch content, may be avoided by controlling the alumina content. The distribution of pore throat diameters (cell window sizes) is determined by mercury porosimetry, whereas the distribution of pore cavity diameters (cell sizes) is measured by microscopic image analysis.

Abstract: Nanocrystalline alumina (Al2O3) powders were sintered by Spark Plasma Sintering (SPS) method in a vacuum atmosphere to obtain highly dense and fine grained final ceramic products. In the first section of experiments, 0.4 % wt MgO doped and 0.4 wt % Y2O3 doped Al2O3 were sintered at high temperatures and under high pressure with a SPS system. Later sintering procedures were carried out with codoping Y2O3 with the cathodic ratio of 0.4 wt % in order to investigate dopant effects on spark plasma sintered alumina. The microstructures of all samples were observed using scanning electron microscope and the properties such as density, hardness and fracture toughness were examined.

Abstract: Based on the structures and composition of ceramic materials, the microstructure design and new preparations were used to induce in situ grain growth by adjusting the main factors which had impacts on grain morphology. By adding CAS (CaO-Al2O3-SiO2) and Nb2O5, the complex toughened alumina ceramics with columnar grain was fabricated under pressureless sintering systematically. The influences of additives on the alumina ceramics with columnar grain were analyzed by means of TEM, SEM, XRD etc. The dynamic conditions of anisotropic growth of columnar grain were researched, and superior growth in some grain directions was induced by doping CAS and Nb2O5. The growth mechanism of columnar grains of alumina ceramics was explored, and established growth model.

Abstract: Ni-MF/Al2O3 composite was fabricated using traditional method. The specimens covered with graphite were sintered at 1400°C, and the microstructure and mechanical properties of Ni-MF/Al2O3 composites were studied. Results showed that the flexural strength and fracture toughness of the composites were dramatically changed with the content of nickel. When the content of Ni was 15 wt% and no-coated MF was 10%, the composite obtained better mechanical properties, its flexural strength and fracture toughness were up to 734.40 MPa and 10.17 MPa•m1/2 respectively. The toughening mechanisms of the composites were attributed to the fiber extraction and debonding, metal bridging and deforming plastically.

Abstract: Two alumina based ceramics with 99.99 % and 95 % of Al2O3 were evaluated after dissolution in an aqueous solution containing 0.5 mol/l NaCl at temperatures of 150 and 200 °C. The weight loss of liquid phase sintered alumina was mainly attributed to congruent dissolution of SiO2 and CaO from grain-boundary amorphous film, which is accelerated at higher temperature, accompanied by precipitation of silicaceous phases from oversaturated solution at 200 °C. Pure polycrystalline alumina corroded by loss of alumina grains, which do not dissolve in the corrosion media.