Window materials calcium fluoride

According to the specific task, different materials are used for the windows. Typical materials are sapphire, calcium fluoride, zinc selenide, diamond, and normal quartz. The selection of the materials depends on the pressure and, for spectroscpic investigations, also on the wavelength corresponding to the bonds of the species to be analysed. 

The opposed anvil cell consists of two optical anvils and a gasket, located between the parallel faces of the two opposing anvils. Samples are placed in the hole of the gasket and are pressurized when the opposed anvils are pushed towards each other. The most common material for anvils is diamond. For mid and far infrared spectra, type Ila diamonds are used, while low-fluorescent type la diamonds are used for Raman spectroscopic measurements [5]. We have also devised a glass anvil cell for Raman spectroscopic measurements [6], and a calcium fluoride anvil cell for infrared spectroscopic measurements [7] with attainable working pressures of 13 and 6 kbar, respectively. Diagrams, for the interested reader, of the window and opposed anvil cells can be found in reference 1. 

Calcium fluoride occurs naturally as the mineral fluorspar, and is commercially important as the raw material for the manufacture of HF (equation 11.6) and F2 (see Section 16.2). Smaller amounts of Cap2 are used as a flux in the steel industry, for welding electrode coatings, and in glass manufacture prisms and cell windows made from Cap2 are used in spectrophotometers. 

Latex emulsions, containing water, are best handled with either barium or calcium fluoride, or silver halide windows, or with an ATR accessory (see later). It is important to ensure that separation does not occur at the window or the IRE interface. Also, care must be exercised with materials that contain ammonia—at high concentration this will etch many of the window materials. 

A simple and convenient method for viscous, nonvolatile materials is to produce a capillary film between a pair of transmission windows or, if the material is very viscous, to form a thin smear film on a single window. It is recommended that barium or calcium fluoride, or comparable window materials, be used for aqueous-based materials. It is very difficult to fill traditional sealed cells with viscous liquids, attempts to force-fill the cell can result in permanent damage, particularly to the seals. Also, once filled, the... 

Water is a commonly used solvent for biological systems. Hence for infrared, sodium chloride and potassium bromide (as well as other water-soluble salts) cannot be used as window materials for cells. Silver chloride, calcium fluoride, and barium fluoride are more commonly used. Small pathlengths, of the order of 0.010 mm, are often used to reduce the intensity of the very strong infrared... 

Choice of Material for the Window. The material used for the window has to meet certain criteria. First, the wavelength range over which the transmission is satisfactory is important. The stability of the material in contact with the solution is also of importance (particularly for aqueous acid or alkaline electrolyte solutions). However, other parameters such as the refractive index, the hardness, the thermal expansion coefficient, the standard form in which the material is available, and even the price also influence its choice. Practically, for aqueous solutions, the selection is restricted to a few materials, including silicon, calcium fluoride, zinc sulfide, and zinc selenide. The main properties of these materials, together with those of KRS-5, KRS-6, and CdTe, are gathered in Table VI. Various examples of transmission curves are given also in Figure 21. 

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