Metal Fluoride Materials

Low refractive indices and low phonon energies of metal fluoride compounds are suitable for their use in optical devices. High-purity products of metal fluorides have been produced using dry processing to avoid oxygen or other contamination. Because a sol-gel method is a typical wet process, attention should be paid to influences of solution chemistry on the purity of final products. 

Adoption of a sol-gel method to optical fluoride materials started with inorganic fluoride glasses. At first, the sol-gel processing appeared rather challenging because fluoride gels were not known and little was known about the chemical reaction between fluorinating 

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As a cousequeuce, these uew metal fluoride materials are excitiug catalysts for Lewis acid-catalyzed reactious aud were proveu to outperform iu some reactious eveu the best homog-euous catalysts [52] as will be showu for several examples below. 

Liquid polyalurninum chloride is acidic and corrosive to common metals. Suitable materials for constmction of storage and handling facilities include synthetic mbber-lined steel, corrosion resistant fiber glass reinforced plastics (FRP), ceramics, tetrafluoroethylene polymer (PTFE), poly(vinyhdene fluoride) (PVDF), polyethylene, polypropylene, and poly(vinyl chloride) (PVG). Suitable shipping containers include mbber-lined tank tmcks and rail cars for bulk shipment and plastic-lined or aH-plastic dmms and tote bins for smaller quantities. Except for aluminum chlorohydrates, PAG products are shipped as hazardous substances because of their acidity. 

However, using alkaline earth metal fluorides gives a less pronounced improvement. The use of CsF and LiF as CIM layer has the same effect. However, unlike LiF, CsF reacts directly with A1 and releases Cs metal, whereas the dissociation of LiF in the presence of A1 is thermodynamically disallowed and proceeds only in the presence of suitable reducible organic materials such as Alq3. Thus CsF is more generally applicable to many organic materials. 

Unsubstituted Group 2 bis-/3-diketonate compounds have been used extensively as precursors for the deposition of Group 2 metal-containing films. This section is organized according the nature of the material deposited. Metal fluoride films are described first, followed by metal oxide films. 

Alkaline-earth metal fluorides have been proposed for use as refractories when melting and casting Ti, Zr and Hf alloys which react with and wet most current materials (Naidich and Krasovsky 1998). 

The only other systematic route into metal fluorides is the use of metal fluoride starting materials and their subsequent substitution, such as in the reaction between [ScF3] and [NaCp] or [MgCp2] to give a mixture including [ ScF(Cp)2 3] [5], The clear restriction in this approach is the availability and isolation of appropriate starting materials. 

The most common methods of preparing anhydrous binary metal fluorides in the laboratory are based on reactions of gaseous HF or F2 with suitable solid substrates. With HF, the oxidation state of the starting material is preserved, whereas with F2, the fluoride with the highest stable oxidation state is obtained. The reactions are mostly carried out in tubes of Monel (a Cu/Ni alloy) at temperatures up to about 400-600 °C. As starting materials, hydrated fluorides (obtained from aqueous HF solutions), chlorides, carbonates, or easy decomposable ternary compounds like NH4Mnp3 may be used, as shown by the following examples (2-4) ... 

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