Barium BaCOs

While a binary oxide can be used as a starting material, some of these are reactive compounds that are difficult to handle. For example, BaO reacts rapidly with C02 in the air to produce barium carbonate. Other oxides, including BaO, are hygroscopic. Thus, compounds which are unreactive towards C02 and HzO at room temperature, but decompose to oxides plus volatile gases at elevated temperatures, are often used as oxide precursors. In the case of barium, BaCOs is a stable compound under ambient conditions but decomposes upon heating to 950°C according to the reaction... 

For barium, BaCOs was used. However, on addition to the propionic add, onty a very small part of the salt dissolved corresponding to a superficial layer of the grain. The barium propionate formed, covers the surface of the undissolved BaC03 salt, stopping the dissolution. By adding a small quantity of water (10 cm ), this superficial layer was dissolved, and the formation of barium propionate can continue. 

The first report concerning barium compounds occurred in the early part of the seventeenth century when it was noted that the ignition of heavy spar gave a peculiar green light. A century later, Scheele reported that a precipitate formed when sulfuric acid was added to a solution of barium salts. The presence of natural barium carbonate, witherite [14941-39-0] BaCO, was noted in Scodand by Withering. 

Most barium compounds are prepared from reactions of barium carbonate [513-77-9] BaCO, which is commercially manufactured by the "black ash" process from barite and coke ki a process identical to that for strontium carbonate production. Depending on the co-product, soda ash and/or carbon dioxide are also consumed. 

Barium is reported in the kiln spill in three different forms water-soluble, eg, BaS, BaO acid-soluble, eg, BaCO, aluminate, siUcate, ferrate and insoluble, eg, unreduced barite. 

A pliotornicrograpli of barium carbonate fomied by precipitation using pure soda asli (eq. 9), is shown in Figure 3. Tire av erage particle size is 1.2 ]lm. Tire exclusive use of soda ash results in a barium carbonate having included sodium that cannot be reduced below a certain level by repeated washings. Tire sodium can be detrimental if the BaCO is to be used for barium titanate production. 

Barium nitrate is prepared by reaction of BaCO and nitric acid, filtration and evaporative crystallization, or by dissolving sodium nitrate in a saturated solution of barium chloride, with subsequent precipitation of barium nitrate. The precipitate is centrifuged, washed, and dried. Barium nitrate is used in pyrotechnic green flares, tracer buUets, primers, and in detonators. These make use of its property of easy decomposition as well as its characteristic green flame. A small amount is used as a source of barium oxide in enamels. 

Barium is the 17th most abundant element in the Earth s crust, making up about 0.05% of the crust. It is found in the minerals witherite, which is barium carbonate (BaCO ), and barite, known as barium siflfate (BaSO ). Pure barium metal does not exist on Earth—only as compounds or in minerals and ores. Barium ores are found in Missouri, Arkansas, Georgia, Kentucky, Nevada, California, Canada, and Mexico. 

Chemists did not discover the mineral witherite (BaCO ) until the eighteenth century. Carl Wilhelm Scheele (1742—1786) discovered barium oxide in 1774, but he did not isolate or identify the element barium. It was not until 1808 that Sir Humphry Davy used molten barium compounds (baryta) as an electrolyte to separate, by electrolysis, the barium cations, which were deposited at the negative cathode as metallic barium. Therefore, Davy received the credit for bariums discovery. 

Barium Minerals Barite (BaS04) and witherite (BaCOs) are commonly used to supply barium in ceramic formulations. Purified barium carbonate, made by dissolution and repredpitation, is used most frequently in ceramic processes and as fluxing compounds in the grazes, ass, and enamels of electronic ceramics and in heavy day products to prevent scumming. The use of these minerals have the drawback that upon heating they give off gas, which can cause cracks. 

Barium hexaferrite. Barium hexaferrite, BaFei20 <<, is used as a ceramic permanent magnet. It is conventionally prepared by firing an appropriate mixture of a-Fe203 with BaCOs at high temperatures (1150-1250°C). To reduce the particle size, thus obtained ferrite should be ground. 

Violent reaction with benzoyl chloride combined with KOH, Bt2, barium carbonate, CS2, Cr(OCl)2, Cu, Pb, HNO3, BaCOs, H2SO4, hot water, (CH3)2S04, dibromomalononitrile, sulfuric acid. Incompatible with acids, ammonium chloride + trichloroacetonitrile, phosgene, cyanuric chloride, 2,5-dinitro-3-methylbenzoic acid + oleum, trifiuroroacryloyl chloride. Reacts with heavy metals (e.g., brass, copper, lead) to form dangerously explosive heavy metal azides, a particular problem in laboratory equipment and drain traps. When heated to decomposition it emits very toxic fumes of NOx and Na20. See also AZIDES. 

Some substitution of strontium (up to 14 mol.%), of lead (2 mol.% reported) but no barium has been reported in aragonite, although investigations at elevated temperatures and pressures show almost complete miscibility of these elements in the structure (Gaines et al., 1997, p. 442), and SrCOs (strontionite), BaCOs (witherite), and PbCOs (cerussite) are common minerals. A calculated plot (Figure 3(b)) for cations in ninefold coordination shows that this coordination theoretically allows trivalent rare earth elements and quadravalent and many other elements to be substituents in the structure. Ytterbium, europium, samarium, and radium carbonates with aragonite structure have been synthesized (Spear, 1983). 

Barium oxide is introduced into glass as BaCOs, less frequently as BaSO, or in the case of optical glasses as Ba(N03)2- The most frequently used lead taw materia] is Pb304 (minium, red lead) or PbO, and possibly also the less volatile lead silicate. Small amounts of AI2O3 enter glass as subsidiary components of sand and limestone. If a higher alumina content is required, use is made of aluminium oxide or hydroxide, feldspar, kaolin, phonolite, etc. 

The oxide ceramics discussed so far in this chapter all consisted of single chemical compounds, except for minor additives. A natural idea for new ceramics is to make materials that contain two (or more) oxides in equal or nearly equal molar amounts. Thus, if BaCOs and TiOi are mixed and heated to high temperature, they react to give the ceramic barium titanate ... 

BaCO.]—Barium has an oxidation number of +2 and carbonate has an oxidation number of -2, so they combine in a 1 1 ratio. No parentheses are used because we only need one carbonate. 

To the laboratory student, e.g., barium carbonate is BaCOs, sulphuric acid is H2S04, hydrochloric acid is HC1, and their equivalents are respectively 197, 98, and 2 x 36 5 = 73. In... 

We will assume that we have a source of cheap barium carbonate guaranteed to contain 95 per cent, of BaCOs delivered to us finely ground at 2, 10s. per ton. We will further assume that we can buy sufficient quantities of muriatic acid at 1, 10s. per ton delivered at the works, and that we are up to the present buying barium chloride at the rate of 6, 10s. per ton delivered at our works, of which we use 10 tons per week in another branch of our works. What will it cost to produce that quantity, and will it be cheaper to continue buying barium chloride or to make the article ourselves ... 

BaCOs. We therefore have the following data. For every ton of barium carbonate used we have available for conversion into barium chloride -95 —"0122 ton = -9378 ton BaCOs, which will require 1-392 tons of our hydrochloric acid, and should... 

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