Glass barium

FIGURE41.4 Microstructureofa dental composite. Miradapt [Johnson Johnson] 50% by volume filler barium glass and colloidal silica [Park and Lakes, 1992],... 

Method 2 (from potassium bromide and sulphuric acid). Potassium bromide (240 g.) is dissolved in water (400 ml.) in a litre flask, and the latter is cooled in ice or in a bath of cold water. Concentrated sulphuric acid (180 ml.) is then slowly added. Care must be taken that the temperature does not rise above 75° otherwise a little bromine may be formed. The solution is cooled to room temperature and the potassium bisulphate, which has separated, is removed by flltration through a hardened Alter paper in a Buchner funnel or through a sintered glass funnel. The flltrate is distilled from a litre distilling flask, and the fraction b.p. 124 127° is collected this contains traces of sulphate. Pure constant boiling point hydrobromic acid is obtained by redistillation from a little barium bromide. The yield is about 285 g. or 85 per cent, of the theoretical. 

If the outlet of the siphon tube at the bottom of the Soxhlet apparatus is well plugged with cotton wool so that no finely-divided bariuna hydroxide can pass into the flask, the barium hydroxide may be placed directly into the extractor until the latter is three-quarters full the remaining space is filled with glass wool. 

Prepare a solution of 41 g. of anhydrous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 25 ml. of water (as in A). Add all at once 60 ml. of 6iV-sulphuric acid to a rapidly stirred, hot (80°) solution of 63 1 g. of A.R. crystallised barium hydroxide in 600 ml. of water contained in a 2-htre beaker. Add more 6iV-sulphuric acid to render the suspension just acid to htmus (5). Introduce the palladium chloride solution and 4 ml. of 37 per cent, formaldehyde solution into the hot mechanically stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent, sodium hydroxide solution, continue the stirring for 5 minutes longer, and allow the catalyst to settle. Decant the clear supernatant hquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium - porosity sintered glass funnel, wash it with five 25 ml. portions of water and suck as dry as possible. Dry the funnel and contents at 80°, powder the catalyst (48 g.), and store it in a tightly stoppered bottle. 

Relatively smaller amounts of very high purity A1F. are used ia ultra low loss optical fiber—duotide glass compositions, the most common of which is ZBLAN containing tirconium, barium, lanthanum, aluminum, and sodium (see Fiber optics). High purity A1F. is also used ia the manufacture of aluminum siUcate fiber and ia ceramics for electrical resistors (see Ceramics AS electrical materials Refractory fibers). 

Fig. 11. Index of refraction vs dispersion and optical classification of glasses. The shaded area indicates the region of glass formation. BaF = barium flint BaK = barium crown BaLF = light barium flint BaSF = heavy barium flint BK = borosilicate crown F = flint FK = fluorcrown K = crown ...

Sulfamic acid and its salts retard the precipitation of barium sulfate and prevent precipitation of silver and mercury salts by alkah. It has been suggested that salts of the type AgNHSO K [15293-60 ] form with elemental metals or salts of mercury, gold, and silver (19). Upon heating such solutions, the metal deposits slowly ia mirror form on the wall of a glass container. Studies of chemical and electrochemical behavior of various metals ia sulfamic acid solutions are described ia Reference 20. 

In the glass (qv) and ceramic industry (see Ceramics), barite can be used both as a flux, to promote melting at a lower temperature or to increase the production rate, and as an additive to increase the refractive index of glass. The viscosity of barite-containing glass often needs to be raised. Alumina in the form of feldspar is sometimes used. To offset any color produced by iron from the barite addition, more decolorizer may be needed. When properly used, barytes help reduce seed, increase toughness and brilliancy, and reduce annealing time. Barite is also a raw material for the manufacture of other barium chemicals. 

Uses. Hiere are several different grades of barium carbonate manufactured to fit the specific needs of a wide variety of applications very fine, highly reactive grades are made for the chemical industry coarser and more readily haridleable grades are mainly supplied to the glass industry ... 

In 1989, 30% of the barium carbonate produced was used in glass manufacturing, 30% in brick and clay products, 20% in the manufacture of barium chemicals, 5% in the manufacture of barium ferrites, 5% in the production of photograpliic papers, and 10% in miscellaneous uses. 

Glass-grade barium carbonate has a high bulk density so that it does not become airborne when charged to the furnace. It also has a particle size... 

Radiopaque materials are used to determine the location of aspirated dentures and fragments (205,206). Opacifying additives include barium sulfate, barium fluoride, barium or bismuth glasses, and brominated organic monomers and polymers. The incorporation of these additives into the resin base or tooth can adversely affect physical properties. Radiopaque materials meeting the requirement for ANSI/ADA specifications for denture-base polymer have been described (207). 

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