Microwave sintering of multiple aritcles Page: 7 of 18
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made by unaxial pressing of alumina powder obtained from
Sumitomo Chemical Company of Osaka, Japan (grade AKP-50) at
about 1000 psi followed by isostatic pressing at about
50,000 psi. The articles were right circular cylinders
05 having a diameter of about 0.595 inch, a height of about
1.25 inches, and a weight of about 12.5 grams (please note
that the dimensions in the above-incorporated paper are
reversed). It is expected that the present invention will
be useful in sintering two or more articles at one time
10 where each has a mass of up to about 50 grams. The
sintering chamber must be reasonably consonant in size with
the number of articles to be sintered; that is, for
example, 2 articles should not be sintered in a chamber
which will hold 20 articles. The density of the articles
15 before sintering was about 55% of theoretical density. The
articles were heated to a temperature of about 16000C and
held at that temperature for about 10 minutes. The rate of
heating was maintained at a value less than about 480C
per minute, as other experimentation had shown that heating
20 at a greater rate caused cracking of the articles. It is
expected that the hold temperature may be varied within a
range of from about 1400 to about 17000C and the time for
which the temperature is maintained within the hold
temperature range may be from about 5 to about 60 minutes.
25 The microwave power level was reduced to maintain the
articles at the hold temperature. Temperature was measured
by means of an optical fiber thermometer inserted through a
small horizontal channel drilled through zirconia element 4
and ring 2 (not shown on the drawings), so that the
30 temperature of the surface of one of the articles is
measured. The temperature measuring equipment does not
measure temperatures below about 5000C; however, it is
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Blake, R. D. & Katz, J. D. Microwave sintering of multiple aritcles, patent, December 31, 1992; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1389885/m1/7/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.