Summary
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1.
The effect of various additions depends on the type of magnesium oxide. Thus, the additions investigated fail to raise the density of hot-pressed specimens from “p” magnesium oxide for luminophores, but enable the final pressing temperature to be lowered by 100–300°C. For extra-light magnesium oxide, the additions have practically no effect on the limiting temperature securing the maximum densification of specimens, but increase the density of the latter.
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2.
It was established that many of the additions lower the density of hot-pressed specimens at limiting pressing temperatures above 1600–1700°C (“p” magnesium oxide for luminophores) or above 1400°C (extra-light magnesium oxide) because of an increase of sealed porosity, which is probably due to the generation of excess vacancies on pressure removal.
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3.
When the amount of an addition is raised from 0.5 to 4 mol.%, densification shifts into the region of lower temperatures, while the density may actually increase.
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4.
The densification kinetics during the hot pressing of the two grades of magnesium oxide with additions are characterized by proportionality between ΔD/D0 and t1/3. It is shown that the increase in the width of the nonporous crust of periclase crystals at the final stages of hot pressing is also proportional to t1/3. This indicates a diffusion mechanism of the elimination of sealed (intragranular) pores during hot pressing and confirms the diffusion character of densification at the last stages of the hot pressing of magnesium oxide.
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Translated from Poroshkovaya Metallurgiya, No. 9(45), pp. 28–36, September, 1966.
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Kainarskii, I.S., Prokopenko, M.I. & Orlova, I.G. Densification during the hot pressing of magnesium oxide with additions. Powder Metall Met Ceram 5, 703–708 (1966). https://doi.org/10.1007/BF00774095
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DOI: https://doi.org/10.1007/BF00774095