Hafnium oxide fluorides

The RM device consists of a high-index substrate ( 1 mm thick lead glass, = 1.72825), a thin low-index spacer (about 1000 nm of magnesium fluoride or silica) and a very thin monomode waveguiding layer (about 100 nm of titanium oxide, zirconium oxide, hafnium oxide or silicon nitride). It can be used to monitor re-... 

There are many compounds of various chemical classes that crystallize in this structural type fluorides of alkaline-earth elements, lead and cadmium high-temperature modifications of zirconium and hafnium oxides, solid solutions Mi xRxF2+x (M = Ca, Sr, Ba, Pb, Cd R = RE elements) [7,21, 31 and others] Bai ,.Bi ,.(0,F)2+6 [32], fluorite-Uke modifications of MOF (M = RE elements, Bi) and Mi xTex(0,F)2+ oxyfluoride phases [33,34], solid solutions in the BiOF-YOF system [24] etc. 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

In the fluorides, chlorides and oxides of the Group-A main-group metals and the transition metals zirconium and hafnium, aliovalent cation substitutions are generally charge-compensated by the introduction of native defects (e.g. an oxygen vacancy in Zr, ,Ca 02 x) because the intrinsic is large however, in some oxides neutral oxygen or water may... 

Recent Group IV chemistry has seen an upsurge in the number of amide derived species, and this has included fluoride derivatives. None of these compounds are of oxidation state -(-III or less, which are the subject of this review, but refer to titanium, zirconium or hafnium where the metal is the +IV state [1,9-12] and, consequently, not covered here. 

ARSENIC (7440-38-2) Finely divided material forms explosive mixture with air. Decomposes on contact with acids or acid fumes, emitting fumes of arsenic. Contact of dust or powder with strong oxidizers can cause ignition or explosion. Violent reaction with bromine azide, bromine pentafluoride, bromine trifluoride, dichlorine oxide, hypochlorous acid, nitrogen trichloride, tribromamine hexaammoniate, nitrogen oxyfluoride, potassium chlorate, potassium dioxide, powdered rubidium, silver fluoride. Incompatible with strong acids, cesium acetylene carbide, chromic acid, chromium trioxide, hafnium, halogens, lead monoxide, mercury oxide, nitryl fluoride, platinum, potassium nitrate, silver nitrate, sodium chlorate, powdered zinc. 

TELLURIUM (13494-80-9) Finely divided powder or dust may be flammable and explosive. Violent reaction with strong oxidizers, bromine pentafluoride, halogens, interhalogens, iodine pentafluoride, hexalithium disilicide, lithium silicide, nitrosyl fluoride, oxygen difluoride, sodium peroxide, sulfur, zinc. Incompatible with cadmium, cesium, hafnium, strong bases, chemically active metals, iodic acid, iodine oxide, lead chlorite, lead oxide, mercury oxides, nitric acid, peroxyformic acid, platinum, silver bromate/iodate/ fluoride, nitryl fluoride, sodium nitrate. 

Fig. 3. The ionization energy of the 4f shell in oxides (empty cirdes), fluorides (squares) and other compounds (filled circles) of lanthanides, hafnium and tantalum. The effects of spin-pairing energy are compared with values of I derived from the calculated uncorrected optical electronegativities (116) for M(IV) and given as full curves appropriate for the ionization of M III). The dashed lines connect the iso-electronic 4f and 4f systems with differing oxidation state.

Extraction of columbate-tantalates, titanocolumbates, and titanosilicates may also be initiated by treatment of the mineral with hydrofluoric acid. The procedure has the advantage that columbium, tantalum, uranium(VI), scandium, titanium, zirconium, and hafnium are dissolved, while silica is volatilized as silicon tetrafluoride and the rare earth elements, together with thorium and uranium(IV), remain as slightly soluble fluorides. The residue is then heated with concentrated sulfuric acid to remove hydrogen fluoride and to oxidize uranium (IV), the thorium is separated by precipitation of the phosphate (synthesis 12), and the rare earths are precipitated as oxalates. 

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