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Some notes on Carbon HPHT

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228                                      EXPERIMENTS ON THE
to the amount of iron of any of our experiments, the largest crystals being 0-7 mm. in length.
This experiment was repeated several times with the same result. The time of cooling of the crucible, from switching off the current to the temperature of setting, was 15 seconds, and probably sufficiently rapid to allow a skin to be formed around the ingot before the centre was solidi­fied, for the configuration of the crucible and cover was such as to ensure nearly equal and simultaneous cooling on all sides of the ingot. At the time, vacuum was erroneously thought to be the chief contributory cause and not the presence of carbon monoxide in large proportion.
High vacuum experiments
The molecular pump not having yet been evolved, a powerful pumping system was arranged, consisting of three steam-jet exhausters in series,
the last ejector of the series discharging into a jet condenser with separate air and water pumps, the former assisted by a steam jet. The two steam-jet exhausters nearest to the exhausted chamber were fed with highly superheated steam at 200 lb. pressure, and the suction pipe to the chamber was 4 inches in diameter; the chamber, 2 feet 6 inches diameter of spherical shape (Fig. 11). A vacuum of 1/6 mm. absolute could be reached. The crucible was placed on a large block of carbon, resting on the base of the chamber, and forming the bottom pole. The cover was insulated from the chamber, and through an oil-sealed gland passed a 2-inch brass
Some notes on Carbon HPHT Page of 35 Some notes on Carbon HPHT
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