The development of recorded auditory tests for measuring hearing loss for speech.
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ABSTRACT: Silicon nitride (Si3N4) offers the advantages of high strength, high thermal shock resistance and a low coefficient of thermal expansion, which are attractive for high thermal efficiency heat engine parts such as in the automotive industry. A consolidation process is required in which the equiaxed Î± phase of the starting powders are retained along with a submicrongrain size; after forming, the strong Î² phase is then formed by heat treatment. Conventional sintering and the mechanisms of consolidation therein are discussed. The plasma-activated (or assisted) sintering (PAS) process, a form of electrical resistance sintering, uses a cycled current to create an electric discharge that would break down the oxide layers at points of contact between the particles, while the plasma would attack the oxide layers on the noncontacting areas of the particles. PAS consolidation experiments were conducted with pure and doped Si3N4. The ability to consolidate Si3N4 with additives to 99% TD while retaining >88% Î± phase was demonstrated with the PAS equipment. The additive should be a mixture of oxides rather than a single oxide, and the amount should be minimum. Once the parts have been densified and deformed, it may be possible to lock in the shape by completing the Î± to Î² transformation in a furnace.
- International Journal of Audiology 07/2009; 7(1). · 1.63 Impact Factor
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