Abstract: The specification discloses a process for the preparation of ultrapure thorium fluoride (ThF.sub.4) having minimized water content and consequent maximized optical transmission of 10.6 micrometer radiation. First, thorium oxide is reacted with aqueous hydrofluoric acid to form a solid reaction product, which is then dried under controlled heating to form a hydrated thorium fluoride with a predetermined amount of hydration, namely ThF.sub.4.xH.sub.2 O where x is equal to 0.39. The hydrated thorium fluoride is exposed to a reactive atmosphere of hydrofluoric acid vapor and a selected fluoride compound in the gas phase at elevated temperature for a predetermined period of time. The reactive atmosphere removes substantially all of the water and water-derived impurities from the hydrated thorium fluoride to produce ultrapure thorium fluoride which is highly transmissive to 10.6 micrometer radiation.

Abstract: The specification discloses new and improved processes for forming water-free metal or non-metal oxide materials, which may then be melted and formed into optical components in vitreous or crystal form, which are free of the hydrogen-impurity absorption in the near infrared wavelength range. In one process, a water-free oxide is prepared by reacting a chosen nonpolar compound containing the desired metal or non-metal with an aprotic oxygen-containing compound to form the oxide as a precipitate in a chosen aprotic nonaqueous liquid solvent which provides a water-free environment during the formation of the oxide, to prevent the inclusion of water and water-derived impurities in the oxide as formed.

Abstract: The specification discloses a process for forming a water-free rare earth oxychloride powder by exposing a water-containing rare earth oxide powder to a reactive atmosphere of chlorine and oxygen at 1000.degree. C. for 24 hours to remove water impurities from the oxide powder and to simultaneously convert the oxide powder to the oxychloride powder.

Abstract: The specification discloses new and improved processes for forming water-free metal or non-metal oxide materials, which may then be melted and formed into optical components in vitreous or crystal form, which are free of the hydrogen-impurity absorption in the near infrared wavelength range. In one process a water-free oxide is prepared by reacting a chosen organic compound containing oxygen bonded to an atom of the metal or non-metal, with a chosen organic acid anhydride to form an intermediate product which is then decomposed to form the desired oxide and to simultaneously regenerate the organic acid anhydride. The regenerated organic acid anhydride reacts with and removes traces of water and water-derived impurities during the formation of the desired oxide and prevents the inclusion of these impurities in the oxide as formed.

Abstract: The specification discloses a process for converting the surface layer of a body of vitreous silica to the more stable crystalline form of silica known as cristobalite. The surface of the body of vitreous silica is exposed to a gas phase reactive atmosphere comprising atomic iodine at a predetermined elevated temperature for a predetermined period of time to convert the surface layer of the vitreous silica to polycrystalline cristobalite and thus passivate and enhance the stability of the treated surface. The disclosed process is particularly useful for forming improved crucibles, such as those used in crystal growth from a melt.

Abstract: The specification discloses a process for forming a coherent, uniform oxide layer on the surface of a selected semiconductor material by heating a wafer of the selected semiconductor material at a temperature of about 750.degree. C. or lower in the presence of a chosen oxygen-containing precursor and a chosen gas phase halogen-containing molecular reactant which reacts with the oxygen-containing precursor to form atomic oxygen. The substrate is heated in the presence of these reactants for a period of time sufficient to enable the atomic oxygen to react with the surface atoms of the wafer and thus form the coherent uniform oxide layer. The temperature of about 750.degree. C. is sufficiently low to avoid adverse effects, such as dopant migration, on the wafer. In a preferred embodiment of the present invention, a coherent, uniform layer of silicon dioxide is formed on the surface of a silicon wafer.

Abstract: The specification discloses a process for forming a coherent, uniform oxide layer on the surface of a selected semiconductor material by heating a wafer of the selected semiconductor material at a predetermined elevated temperature in an atmosphere conducive to the formation of atomic oxygen for a period of time sufficient to enable the atomic oxygen to react with the surface atoms of the wafer and thus form the coherent, uniform oxide layer. The predetermined elevated temperature is sufficiently low to avoid adverse effects, such as dopant migration, on the wafer. In a preferred embodiment of the present invention, a coherent, uniform layer of silicon dioxide is formed on the surface of a silicon wafer by heating the wafer in a vapor mixture of iodine and water at a temperature of 750.degree. C. and one atmosphere of pressure.