The Harshaw Chemical Company

Robert H Moss

William F Spicuzza

Carl F Swinehart

Arthur C Lucas

Barbara M Kapsar

A malleable or press-forgeable ingot of barium fluoride, for use as an optical body, may be grown from an ultra-pure precipitate of barium fluoride which contains less than 10 parts per million (ppm) of strontium or calcium. A process is disclosed for crystallizing barium nitrate crystals in the presence of nitric acid, reacting barium nitrate with ammonium carbonate to form barium carbonate, recovering barium carbonate crystals, suspending the barium carbonate crystals in water and precipitating barium fluoride with hydrofluoric acid. The barium fluoride crystals are recovered, dried and then calcined in the presence of ammonium fluoride or bifluoride. Barium fluoride (BaF.sub.2) crystals obtained by the process of this invention contain less than 10 ppm of each strontium and calcium. Crystals of an alkaline earth metal fluoride which have been calcined in the presence of a fluoride of ammonium are unexpectedly densified, and are particularly suited for melt-growth of an ingot in a known manner. A maximum concentration of 10 ppm of strontium and calcium in a BaF.sub.2 ingot has been found to be the critical demarcation between a frangible prior art BaF.sub.2 ingot and an ingot of BaF.sub.2 which does not unpredictably shatter when cut, and, which may be reliably press-forged into an optical body.

Process for preparing essentially pure barium fluoride crystals

A process is disclosed for converting basic magnesium carbonate into pure hot-pressable magnesium fluoride such as is used for the hot-pressing of infra-red radiation transmitting optical bodies. The process includes contacting a slurry of basic magnesium carbonate with carbon dioxide to form enough magnesium bicarbonate or hydrates of magnesium carbonate, in situ, to alter the particles in the slurry. Carbonation of the slurry increases solubility of the solids by establishing an equilibrium relationship in solution between the unstable magnesium bicarbonate and hydrates of magnesium carbonate particles. When the carbonated slurry is contacted with a slight excess of hydrofluoric acid it precipitates solid particles of fine hydrous magnesium fluoride. Neutralization of excess hydrofluoric acid is effected with ammonium hydroxide. The solid particulate precipitate is dried and calcined to yield hot-pressable magnesium fluoride powder of exceptional purity and consistent quality. A hot-pressable magnesium fluoride powder has been prepared which has a specific and uniform refractive index, n.sub.D = 1.3850 at 20.degree. C; the powder is made up of primary particles the majority of which have an average particle diameter of greater than 5 .mu. (microns). These physical properties and a characteristic ill-defined X-ray diffraction pattern suggestive of an amorphous structure, allow the powder to be hot-pressed into an optical body without grinding the powder.

Hot-pressable magnesium fluoride powder

A method is disclosed for the use of thulium doped calcium fluoride in the form of a thermoluminescent dosimeter to measure the amount of radiation to which the dosimeter has been exposed. A new thermoluminescent material for use in a dosimeter is also disclosed. The material consists essentially of crystalline calcium fluoride doped with less than 0.5 mole percent thulium. The material has several unique properties, and displays two well separated glow maxima which permit using a lower temperature (150.degree. C) peak as a thermometer to determine a mean ambient temperature for the dosimeter. The mean ambient temperature may then be used to correct thermoluminescent data for a high temperature (250.degree. C) peak.

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Cleveland Heights, OH, United States of America

Robert H Moss