Polarizers calcite

Calcium carbonate (calcite) scale formation in hard water can be prevented by the addition of a small amount of soluble polyphosphate in a process known as threshold treatment. The polyphosphate sorbs to the face of the calcite nuclei and further growth is blocked. Polyphosphates can also inhibit the corrosion of metals by the sorption of the phosphate onto a thin calcite film that deposits onto the metal surface. When the polyphosphate is present, a protective anodic polarization results. 

The electrostatic valence rule usually is met rather well by polar compounds, even when considerable covalent bonding is present. For instance, in calcite (CaC03) the Ca2+ ion has coordination number 6 and thus an electrostatic bond strength of s(Ca2+) =. For the C atom, taken as C4+ ion, it is s(C4+) =. We obtain the correct value of z for the oxygen atoms, considering them as O2- ions, if every one of them is surrounded by one C and two Ca particles, z = -[2s(Ca2+) + s(C4+)] = -[2 j + ] = -2. This corresponds to the actual structure. NaN03 and YBOs have the same structure in these cases the rule also is fulfilled when the ions are taken to be Na+, N5+, Y3+, B3+ and 02. For the numerous silicates no or only marginal deviations result when the calculation is performed with metal ions, Si4+ and 02 ions. 

Calcite and quartz are commonly used for optical polarization components, such as waveplates, polarizers, and beam splitters. Such inorganic crystals have... 

When plane-polarized light traverses a crystal exhibiting double refraction, such as calcite, at right angles to its axis, it is transformed into elliptically polarized, or even circularly polarized, light. 

The crystal absorption spectra were obtained with a Zeiss instrument modified for double beam operation. It was equipped with a calcite polarizer and quartz optics which allowed accurate spectral measurements up to 45,000 cm.-1. The optical system was designed to record spectra of very small crystals (about 2 mm.). The details of the design and operation of the crystal spectrophotometer will be reported elsewhere. ... 

It is instructive to pursue the interpretation of the calcite rhomb experiment beyond the simple Huyghenian construction to learn something about the polarization of the transmitted light. The electromagnetic theory of light requires that the electric vector shall be contained in the plane of the wave front. The ordinary disturbances vibrate perpendicular to a principal section. Also the extraordinary disturbance must vibrate in the principal section plane. 

Since the polarizers discussed above involve light reflection combined with the real part of the refractive index tensor, they can be used effectively over a broad spectral range about a central wavelength. Calcite Glan-Thompson polarizers, for example, operate successfully over the entire visible spectrum. When fabricated of crystalline quartz, these polarizers can be used to polarize ultraviolet light as well as visible light. 

When light is passed through a polarizer such as a calcite Nicol prism, the electric vector is parallel to the plane of polarization. The electric vector transforms in different ways when the polarized light is transmitted through a single crystal of a mineral, depending on its crystal symmetry. 

For an example of the use of polarized Raman spectra of calcite single crystal, see Section 1.19. 

This example illustrates the usefulness of the polarized Raman technique. For a further discussion on the analysis of calcite, see Nakamoto (37), Nakagawa and Walter (62) and Mitra (47) for data on gypsum. 

Figure 1-43 Polarized Raman spectra of calcite. (Reproduced with permission from Ref. 61.)...

A similar rate phenomenon is used by mineralogists to distinguish calcite from dolomite. The smaller and more polarizing Mg+2 ions lower the polarizability of the (C03) 2 ions to such an extent that dolomite does not effervesce when brought in contact with dilute HC1. Calcite (CaCOs) reacts readily with the dilute acid. 

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