Barium general properties

In general, the chemistry of inorganic lead compounds is similar to that of the alkaline-earth elements. Thus the carbonate, nitrate, and sulfate of lead are isomorphous with the corresponding compounds of calcium, barium, and strontium. In addition, many inorganic lead compounds possess two or more crystalline forms having different properties. For example, the oxides and the sulfide of bivalent lead are frequendy colored as a result of their state of crystallisation. Pure, tetragonal a-PbO is red pure, orthorhombic P PbO is yeUow and crystals of lead sulfide, PbS, have a black, metallic luster. 

Compounds containing such metals as copper, barium, lead, molybdenum, and nickel generally are not used in processing solutions. However, trace quantities of certain metal dopants occasionally are used to impart desired soHd-state and photographic properties to emulsion grains. Because of its... 

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

Hydrothermal Method. Iron [Fe(III)], barium, and the dopants are precipitated as their hydroxides and reacted with an excess of sodium hydroxide solution (up to 6 mol/L) at 250-350 °C in an autoclave. This is generally followed by an annealing treatment at 750-800°C to obtain products with the desired magnetic properties. Many variations of the process have been described [5.36]-[5.40], the earliest report being from 1969 [5.41], In later processes, hydrothermal synthesis is followed by coating with cubic ferrites, a process resembling the cobalt modification of iron oxides (see Section 5.1.2). The object is to increase the saturation magnetization of the material [5.42]-[5.44],... 

Group II consists of the five metals beryllium, magnesium, calcium, strontium and barium, and the radioactive element radium. Magnesium and calcium are generally available for use in school. These metals have the following properties. 

An extensive series of phases of general formula Ba Ti5,0 +2y are formed from the reaction of Ti02 with barium oxide. The simplest, BaTiOs, is known as barium titanate. These materials are of interest because of their ferroelectric properties, which result from the differences in the relative sizes of the Ba andTi ions. The Ti ions are located between six Ba ions, which occupy octahedral positions. However, the Ti ions are small compared to the Ba and so are free to move within their octahedral Ba holes . 

Anderson AH, Newton JM. Influence of moisture content and particle size of barium sulfate on the extrusion properties of mixtures with microcrystalline cellulose. In Carter, R, ed. Rheology of Food. Pharmaceutical and Biological Materials with General Rheology. London Elsevier Applied Science, 1990 25S--67. 

Barium titanate, which has many novel properties, is a mixed oxide ceramic. It has the same structure as the mineral perovskite, CaTiOs (Fig. 22.13), except, of course, that Ba replaces Ca. Perovskites typically have two metal atoms for every three O atoms, giving them the general formula ABO3, where A stands for a metal atom at the center of the unit cube and B stands for an atom of a different metal at the cube corners. 

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