Citation: GHANIZADEH, S. ...et al., 2017. Improved transparency and hardness in α-alumina ceramics fabricated by high-pressure SPS of nanopowders.Ceramics International, 43 (1), Part A, pp. 275-281.Additional Information:• This paper was accepted for publication in the journal Ceram- This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
AbstractNanocrystalline alumina powder with an average crystallite size of ≤50 nm has been consolidated by spark plasma sintering (SPS) and hot pressing (HP) with a view to achieving dense, fine grained alumina bodies that display transparency. When as-synthesised powder was densified directly, excessive grain growth resulted from both the SPS and HP techniques and hence a large final grain size was observed. Attempts to improve the uniformity of the green microstructure prior to densification were unsuccessful when spray freeze dried granules were used, whether pre-pressed into a compact or not. The use of 53% dense slip cast green compacts, however, enabled final density of ~99.96% and a mean grain size of ~0.32 μm to be achieved when SPS conditions of 1200˚C and 500 MPa were 2 applied for 20 minutes. These samples offered in-line transmittance values of up to ~80%and microhardness values of 22 GPa.
SynopsisChain'transfer constants to monomer have been measured by an emulsion copolymerization technique at 44OC. The monomer transfer constant (ratio of transfer to propagation rate constants) is 1.9 X lob6 for styrene polymerization and 0.4 X 10-6 for the methyl methacrylate reaction. Cross-transfer reactions are important in this system; the sum of the cross-transfer constants is 5.8 X Reactivity ratios measured in emulsion were rl (styrene) = 0.44, r2 = 0.46. Those in bulk polymerizations were rl = 0.45, r2 = 0.48. These sets of values are not significantly different. Monomer feed composition in the polymerizing particles is the same as in the monomer droplets in emulsion copolymerization, despite the higher water solubility of methyl methacrylate. The equilibrium monomer concentration in the particles in interval-2 emulsion polymerization was constant and independent of monomer feed composition for feeds containing 0.25-1.0 mole fraction styrene. Radical concentration is estimated to go through a minimum with increasing methyl methacrylate content in the feed. Rates of copolymerization can be calculated a priori when the concentrations of monomers in the polymer particles are known.
. Can. J. Cheni. 56. 1562 (1978). A 2% crosslinked divinylbenzene-styrene copolynier, incorporating benzyl alcohol groups, was used to monoprotect the syninietrical diacid chlorides, CIOC(CH2),,COCI (where ti = 2, 3, 4, and 8), terephthaloyl chloride and isophthaloyl chloride. Subsequent reaction of the resulting polymer-bound monoester monoacid chloride with aniline, benzylamine, diniethylaniine, tertbutylamine, or aninionia yielded polymer-bound nionoester nionoaniides, which on base cleavage and esterification gave nionoester nionoaniides in high yield. Borohydride reduction of polymer-bound sebacoyl chloride, terephthaloyl chloride, and isophthaloyl chloride gave their respective polymer-bound monoester nionoalcohols, which on base cleavage from the polynier and esterification yielded the monoester monoalcohols in good yield along with some recovered dimethyl esters of the respective starting diacid chlorides.
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