Preparation of high uniformity polycrystalline ceramics by presintering, hot isostatic pressing and sintering and the resulting ceramic
First Claim
1. A method of producing a ceramic body comprising:
- providing a green compact of appropriate configuration and composition;
presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage;
hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and
resintering said body to induce further grain growth and further densification by reducing the number density of pores by a factor of at least 125.
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Accused Products
Abstract
Polycrystalline ceramic bodies having uniform transparent optical characteristics are produced by providing a green compact, presintering that compact at a temperature in the range from about 1,350° C. to about 1,650° C. until the closed porosity stage is reached, hot isostatic pressing the presintered compact to collapse substantially all pores disposed at grain boundaries and resintering the hot isostatically pressed compact at a temperature in the range from 1,700° C.-1,950° C. to cause grain growth under conditions in which pores, within those grains which are consumed by the growth of other grains, collapse as the grain boundary of the growing grain passes through the location of the pore in the smaller grain being consumed.
93 Citations
39 Claims
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1. A method of producing a ceramic body comprising:
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providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and further densification by reducing the number density of pores by a factor of at least 125. - View Dependent Claims (2, 3, 4, 5, 34, 35)
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6. A method of making a high density ceramic with low residual porosity comprising:
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providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and sintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 36, 37)
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18. A polycrystalline ceramic body:
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having a volume of at least 1 mm3 ; having an optical attenuation coefficient of less than 10 cm-1, at a measurement frequency in the visible region of the electromagnetic spectrum whereby said body is transparent; and being free of pore clusters larger than 10 microns across. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A polycrystalline ceramic body:
exhibiting an optical attenuation coefficient which, at a fixed measurement frequency in the visible region of the electromagnetic spectrum, is uniform throughout said body to within 3% and less than 10 cm-1. - View Dependent Claims (29, 30, 31)
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32. A polycrystalline ceramic body:
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having a non-cubic crystal structure; having a volume of at least 1 mm3 ; having an optical attenuation coefficient of less than 15 cm-1, at a measurement frequency in the visible region of the electromagnetic spectrum; and being free of pore clusters larger than 12 microns across. - View Dependent Claims (33)
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38. A method of producing a transparent ceramic body comprising:
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providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and densification by reducing the number density of pores by a factor of at least 125 and to render said body transparent.
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39. A method of making a transparent high density ceramic with low residual porosity comprising:
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providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and resintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates to thereby render said body transparent.
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Specification