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The advantages of using vacua in the hot pressing of refractory materials are demonstrated. A simple apparatus is described which enables powders to be pressed at temperatures up to 2500°C at gas pressures of 95% theoretical density can be prepared with an impurity oxygen content of the order of 0.01 wt.-%.

A study was made of the densification during hot pressing at 1300–1600°C of magnesium oxide activated by decomposing the hydroxide and the basic magnesium hydrocarbonate. During decomposition of these compounds at 500–700°C with a soak of 15 min, magnesium oxide forms that is actively compacted almost to the theoretical density (98.5–99.5%) at relatively low temperatures (1500–1600°C) and pressures of 150 kg/cm2.

Some refinements have been introduced into the hot press canning of internally and externally cooled fuel elements. This report outlines the specifications for the process including these refinements. Specifications cover components, dies, and punches, furnace condition, nickel plating, component cleaning, component assembly, sizing, hot pressing and inspection.

The hot press process has been altered so as to eliminate the slight wrinkling near the ID base. This was done by incorporating a three minute time delay in the pressing cycle. The pressing time was decreased to five minutes to restrict formation of the brittle intermetallic compound, Ni{sub 2}Al{sub 3}.

Hot press canning of internally and externally cooled fuel elements has been developed to a point where the process is feasible. Complete specifications have been written for the process covering component, dies and punches, furnace construction, nickel plating, component cleaning, component assembly, sizing, hot pressing and inspection. Drawings covering each major item are included.

In order to evaluate the performance of uranium slugs canned by the hot press method, several tubes of this metal were charged at C Pile and scheduled for irradiation until a specified number of ruptures had occurred. At the present time, all scheduled ruptures of hot-pressed slugs have been obtained. This report summarizes the irradiation experience under this test and the results obtained to the present time, and presents conclusions which are drawn from this experience.

Hot pressing has played a prominent part in research programs studying beryllium oxide, and has been considered on several occasions as a possible production tool. The desirable characteristics of the hot press are described by reference to advanced designs in three forms: (a) the basic research tool; (b) the vacuum hot press; and (c) the continuous hot press for production use. Techniques of operation have been learned for the reliable preparation of sound, uniform, high-purity BeO bodies of simultaneously very high density (99.7 to 100.0% of T.D.) and fine grain size (to a limit of 10μ average). The routine consists of a dwell at temperature without the application of pressure, an optimized time-temperature-pressure cycle, and rapid heating and cooling ramps. The parametric relations are described. Techniques for the controlled preparation of BeO of ultrafine grain size at somewhat less than full density have also been worked out. The resultant material parameters and corresponding mechanical characteristics are discussed, with particular reference to modulus of rupture at high temperatures. Average strengths of 48 000 psi at 1500° C have been recorded. The microstructural, size and shape limitations of hot-pressed BeO are reviewed with respect to reactor core requirements. Illustrations are taken from past experience to describe the preparation of hot pressed shapes as reactor component parts and the desired manner of conducting production runs. Cost elements of an hypothetical production activity are displayed, assuming continuous hot press operation and based on American economic conditions. A typical coldform-and-sinter operation is described for comparison.

It is said that the hot pressing gives better properties to WC-Co alloys than the cold presssinter method. At present time, graphite is mainly used as the die material for the hot pressing of WC-Co alloys. In this paper, the carbon impregnation to the sintered body which is caused by the contact of the powder (sintered body) and the graphite die was studied. The results obtained are as follows.(1) The layer depth of carbon impregnation increased parabolically with the increase of keeping time. However, it was assumed that the carbon impregnation which results in the excess carbon precipitation does not to occur during heating and also at the initial stage of keeping time, but assumed to begin to occur after the.sintering is completed. (2) The layer depth of carbon impregnation increased with an increase of hot press temperature. (3) The layer depth of carbon impregnation depended upon the property of the graphite used for the die. (4) The hot press pressure did not have a definite relation to the layer depth of carbon impregnation, but was affected by the behavior of metal which was squeezed from the die and other factors. (5) The metal which was squeezed from the die during hot pressing was mainly composed of cobalt and the WC content involved in it was by far lesser than that corresponding to Co-WC eutectic.