Special Optical Glasses

Lanthanum(III) oxide (Li iOs) is used for making special optical glasses. It improves the optical properties and alkali resistance of the glass (Vinogradova et al. 2004 Royal Society of Chemistry 2015). 

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Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La203 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. 

Tantalum pentoxide (Ta O ) is used to make special optical glass, for lasers, and in electronic circuits. 

Hafnium dioxide is a high temperature refractory material. It is used for control rods in nuclear reactors. It has high stability and high thermal neutron absorption values. It also is used in special optical glasses and glazes. 

Fluorescence cells are made of quartz, silica, or special optical glass. Glass cells are cheaper and are suitable for use with excitation wavelengths above 330 nm. For shorter wavelengths, quartz or silica cells have to be used. If analysis is to be performed at low temperatures, cryorefrigerators or Dewar flasks (Fig. 6) are used. 

The earlier types of optical glasses which were melted from the traditionally employed oxides, exhibited approximately direct proportionality between refractive index and dispersion. Deviation from this rule has arisen by the introduction of new components (B2O3, BaO, ZnO, LajOj, etc.)and of quite new types of glasses. The main types and their optical properties are shown in Fig. 145. The current optical crowns and flints occupy a comparatively small region compared with that corresponding to the attainable properties of special optical glasses. 

Lanthanum Oxide. La203, m.p. approx. 2200 C sp. gr. 6.51 thermal expansion (25-1000°C) 12 X 1(H. A rare earth sometimes used in special optical glasses. Lanthanum Titanates. Two compounds have been reported LaTi203 and La2Ti209 the former has a perovskite (q.v.) structure and can be synthesized by heating a mixture of La203 and Ti203 at 1200°C in a vacuum. 

Huorophosphates are used as specialized optical glasses. For example, fluorophos-phate glasses, such as those designated FK-5 or FK-50 by Schott have very low optical dispersion. 

In order to follow progress of elimination, reactions were also performed on thin films in a special sealed glass cell which permitted in situ monitoring of the electronic or infrared spectra at room temperature (23°C). Typically, the infrared or electronic spectrum of the pristine precursor polymer film was obtained and then bromide vapor was introduced into the reaction vessel. In situ FTIR spectra in the 250-4000 cm-- - region were recorded every 90 sec with a Digilab Model FTS-14 spectrometer and optical absorption spectra in the 185-3200 nm (0.39-6.70 eV) range were recorded every 15 min with a Perkin-Elmer Model Lambda 9 UV-vis-NIR spectrophotometer. The reactions were continued until no visible changes were detected in the spectra. 

This soft, silver white metal reacts with air and water. The oxide is applied in optical glasses with high refractive indices (special lenses for powerful cameras and telescopes). Used for special effects in optoelectronics and electronics. Lanthanum exhibits catalytic properties. It is a component of flint and battery electrodes. Lanthanum boride (LaB6) is the superior electron-emitter for electron microscopes. Lanthanum is the first of the series of 14 lanthanides, also called the "rare-earth" metals, whose inner N shells are filled with electrons. They do not belong on the "red list" of endangered species they are neither rare nor threatened with depletion. China is particularly rich in lanthanide ores. 

An industrial standard method has been developed to test the lightfastness of polymers in accelerated test equipment [103]. The apparatus consists of a quartz-xenon tube with a special optical filter between the light source and the specimen to produce light that resembles window glass-filtered daylight [104], Samples are mounted at a specific distance from the arc and are supported on a frame which revolves around the arc 1 to 5 times per minute for uniform exposure. A blower unit in the base provides a flow of air which makes it possible to maintain a black panel temperature of 45°C, measured by a black panel thermometer which is positioned at level with the samples. A black panel unit consists of a bimetallic thermometer mounted on a steel frame. Both faces of the frame plate and also the stem of the thermometer are coated with a heat-resistant glossy black enamel. The relative humidity level in the exposure cabinet is closely controlled. 

A full response in the UV and vacuum UV is accessible only with detectors fitted with special fluoride windows. The cut-off wavelengths of optical glass (g) and of silica (q) are shown in Figure 7.25. For some special applications windowless detectors are used and the sensitivity is then greatly extended in the vacuum UV region and beyond. 

Optical glass Optical glass is a special type of glass. It is made... 

In optical applications, in addition to optical liber claddings, special optical adhesives matching refractive indexes of optical glass components based on fluorinated epoxyacrylates and epoxymethacrylates are used.29 Fluoroalkyl methacrylates are frequently incorporated as comonomers with siloxanyl methacrylates into contact lenses for the improvement of oxygen permeability.31... 

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