Alumina polycrystalline

Burke, and also Suits and Bueche (1967), tell the history of the evolution of pore-free, and hence translucent, polycrystalline alumina, dating from the decision by Herbert Hollomon at GE (see Section 1.1.2) in 1954 to enlarge GE s research effort on ceramics. In 1955, R.L. Coble Joined the GE Research Center from MIT and... 

A.M. Meier et al., A Comparison of the Wettability of Copper-Copper Oxide and Silver-Copper Oxide on Polycrystalline Alumina, J. Materials Science, 30[19] pp. 4781 4-786 (1995). 

The 3M Company manufactures a continuous polycrystalline alumina—silica—boria fiber (Nextel) by a sol process (17). Aluminum acetate is dissolved in water and mixed with an aqueous dispersion of colloidal silica and dimethylformamide. This mixture is concentrated in a Rotavapor flask and centrifuged. The viscous mixture is then extruded through spinnerettes at 100 kPa (1 atm) the filaments are collected on a conveyor and heat-treated at 870°C to convert them to metallic oxides. Further heating at 1000°C produces the 10-pm diameter aluminum borosilicate fibers, which are suitable for... 

Several fiber types have been mentioned so far, and several other types have been neglected that have been worked on over the past few years. Some of those not discussed may become important fibers for reinforcement in the years ahead. To date though, they have not been available in sufficient quantity for thorough evaluation in composite specimens. Included in this group are boron carbide, spinel, polycrystalline alumina and silica, titanium diboride, and miscellaneous silicides and intermetallics. Ten years from now as we look back on the 70s we no doubt will have an entirely different view of some of these materials. 

ChristelPS. 1992. Biocompatibility of surgical-grade dense polycrystalline alumina. Clin Orthop Relat Res 282 10-18. 

Figure 6.1. Examples of damage sites due to single-particle impacts (a) On mild steel, a ductile metal (b) On polycrystalline alumina, a brittle ceramic (from Hutchings, 1987 reproduced with permission).

Na6Al32VAi051, respectively. This suggests that compared to //-alumina the fi" modification contains an aluminium vacancy compensated by three extra sodium ions in the conduction plane. The consequent higher conductivity of the ft" modification makes it favoured for battery electrolytes. The conductivity of polycrystalline //-alumina at 350 °C (the temperature appropriate to battery operation) is about 5Sm-1 and for polycrystalline //"-alumina about 50 8 m-1. 

Figure 3.4. Photographs taken with background illumination of sessile drops of pure A1 on polycrystalline alumina in high vacuum at 850°C (top) and 120(PC (bottom). From (Coudurier et al.

D. R. Clarke, High-Temperature Deformation of a Polycrystalline Alumina Containing an Intergranular Glass Phase, /. Mater. Sci., 20, 1321-1332 (1985). 

L. Ewart and S. Suresh, Elevated-Temperature Crack Growth in Polycrystalline Alumina under Static and Cyclic Loads, J. Mater. Sci., 27, 5181-5191 (1992). 

Fig. 8.2 Oxygen tracer diffusivities and oxygen permeabilities through liquid boron oxide, fused silica, and a polycrystalline alumina with a grain size of 5 nm. Tracer diffusivity values for B203 and Si02 were obtained from Refs. 9 and 19, respectively. Tracer diffusivity values for A1203 were obtained from data reported in Ref. 18 using a grain size of 5 /im (Ref. 13). Oxygen permeability constants were obtained using the procedure outlined in the text.2...

Fig. 10.3 Curves showing the crack extension as a function of time at temperature 1200°C.46 The material used in the study was Coors AD998 polycrystalline alumina with grain size ranging from 2 im to 10 /im. The data was obtained by testing two compact tension samples, ADCT12 and ADCT17.

W. Blumenthal and A. G. Evans, High-Temperature Failure of Polycrystalline Alumina II, Creep Crack Growth and Blunting, J. Am. Ceram. Soc., 67[11], 751-758 (1984). 

Figure 6.14 A comparison of various polycrystalline alumina and aluminosilicate fibers in the Nextel series. Note the superior creep resistance of the Nextel 720 fiber. 3M data.

The optical properties of the wall also contribute to the emitted spectra. The usual arc tube wall material, polycrystalline alumina (PCA), has rather low "in-line" transmission and scatters most of the incident radiation. That portion which is scattered back into the discharge medium and that is also in the spectral region inside or near the peaks of the self-reversed resonance lines, is likely to be absorbed. Thus we have found greater Na reversal for PCA arc tube lamps than for sapphire lamps with the same diameters, Na-Hg alloy composition and reservoir temperatures. Indeed, various authors have reported 3-8% higher efficacies for sapphire vs PCA lamps depending upon the quality of the PCA and its surface treatment 3). 

D.Ph. Hasselman, Strength behavior of polycrystalline alumina subjected to thermal shock. /. Am. Ceram. Soc., 53 (1970) 490. 

Fig. 2 The temperature dependence of tan 8 for polycrystalline alumina with the following purities 99.5% (bottom curve), 99% (middle curve), and 90-95% (topmost curve). (From...

Fig. 9 An atomic force microscope (AFM) image of a polycrystalline alumina specimen that has been polished and then thermally etched by heating for 1 hr at 1527°C in a 2.45 GHz resonant cavity microwave. (From Ref l Reprinted with permission of EDP Sciences, P.A. de Courtaboeuf, Les Ulis Cedex, France.)...

Table 8 Effect of porosity on the bend strength of polycrystalline alumina at 25°C from [2]...

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