Process for producing high strength alumina (original) (raw)
1995
A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution thereof; relatively low, predominantly transgranular porosity; and a density approaching the theoretical density of pure alumina produced by vacuum hot pressing alumina powder which contains at least 98.0% alumina, is substantially free of any sintering aids or any other additives, and has a median particle size less than about 3 microns, in a vacuum hot press operated at a temperature of at least about 1350° C. and a pressure of at least 28 MPa (3500 PSI) for a sintering period of at least 1.5 hours. The vacuum hot pressed alumina material also has compressive strength, flexural strength, impact strength, and wear resistance superior to that for most conventional sintered alumina materials.https://digitalcommons.mtu.edu/patents/1072/thumbnail.jp
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Proceeding_ECERS_1993_Huisman_lq.pdf
a-alumina ceramic pans were produced via centrifugal slip casting. This rather new fonning technology combines the advantages of colloidal powder preparation with a very efficient and pressure gradient free densification method to produce massive (up to 10 cm) and near-net-shape ceramic parts. High green densities of 68 % TD and high sintered densities (~99.5 %TD) were reached at a simering temperature as low as 1400 • c with 6 h holding time. Differential sedimentation during centrifugation was neglegible for slurries with high solids loadings. Homogeneous and fine microstructures were obtained. 4-point-bending tests revealed an average strength of 598 MPa with a Weibull modulus of 17. Therefore centrifugal slip casting seems to be a very promising alternative to dry processing, if ceramic parts with highest reliability are required. Int.rod uction According to Griffith's equation, more reliable ceramic components can be achieved by either minimizing the flaw size, or by increasing the fracture toughness, Kie. Since for unreinforced a-alumina the fracture toughness cannot be altered increased reliability can only be achieved by decreasing the flaw size. Colloidal processing is one route for fabricating ceramics with a minimum of flaw size and number of flaws (1, 2]. Centrifugal slip casting combines the advantages of wet chemical powder preparation with a very efficient and pressure-gradient-free densification method to produce massive (in this study up to 10 cm) and near-net-shape ceramic parts. Isostatic pressing is a commonly used method to produce massive ceramic parts from binder-free powders and therefore chosen as the standard technology for comparison reasons. The wet processing route provides the possibility of breaking up agglomerates by milling or ultrasonic treatment or removing them and other flaw sources from the slurry by decantation or sedimentation. However, the drawback of this technology is that particle size separation might occu r due to differential settling during the consolidation stage (2, 3, 4]. There are three approaches to overcome this problem: To consolidate a system (I) in the flocculated (3) or (2) in the coagulated state [SJ or (3) to use highly concen1ra1ecl slnrries [6]. The first two approaches have been successfully used in various binary systems but lead to an open structure which is undesirable for subsequent densification (7, 8]. The latter approach has produced very good resul ts in case of one component systems [6, 9, 10]. The aim of the present study was to compare the quality of centrifugal slip cast a-alumina with isostaticaUy pressed alumina. Of
2012
Provided here is a method of producing a monolithic body from a porous matrix, comprising: (i) providing a porous matrix having interstitial spaces and comprising at least a first reactant; (ii) contacting the porous matrix with an infiltrating medium that carries at least a second reactant; (iii) allowing the infiltrating medium to infiltrate at least a portion of the interstitial spaces of the porous matrix under conditions that promote a reaction between the at least first reactant and the at least second reactant to provide at least a first product; and (iv) allowing the at least first product to form and fill at least a portion of the interstitial spaces of the porous matrix, thereby producing a monolithic body, wherein the monolithic body does not comprise barium titanate.
Micrometer size grains of hot isostatically pressed alumina and its characterization
Alumina samples were prepared from two different particle size powders. Finer particle compacts when heated along with coarser particle compacts at same processing temperatures produce bigger grain microstructures due to higher grain growth. An unconventional method of etching by molten V2O5 was adopted to look at the microstructure for accuracy in reported data. On an average starting with finer particles give microstructure with a grain size of 5⋅5 μm and starting with coarser particles, give microstructure with 2⋅2 μm average grain size. The flexural strength is around 400 MPa for alumina samples prepared from finer powder in comparison with about 550 MPa for alumina samples prepared from coarser powder. The Vickers hardness in 5⋅5 μm grain microstructure is around 20 GPa in comparison to about 18 GPa in microstructure with smaller grains of 2⋅2 μm size.
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