Materials calcium-containing alloys

The raw material should contain at least 50 per cent, of Ca3P208 and be as free as possible from sesquioxides. It may be ignited if high in organic matter, reduced to a fine powder, and fed continuously into tanks lined with wood or hard lead alloy, where it meets on the counter current principle hot sulphuric acid of about 5 per cent, concentration. The reaction is quickly completed and the precipitated calcium sulphate is allowed to settle and filtered off continuously through filter presses. This sulphate is phosphatic gypsum and contains 3 to 4 per cent, of phosphoric acid of which 1 per cent, is soluble in water. The solution is evaporated in wrought-iron pans up to a concentration of 50 per cent, phosphoric acid, which may be further refined for use in pharmaceutical products or foods. 

The first fractions will contain some bromine and a small quantity of silicon tetrabromide. The disilicon hexa-bromide distills at a fairly constant temperature, depending upon the pressure employed. Thus a considerable proportion comes over at 130 to 140°, if the pressure is varied from 15 to 20 mm. This material may have a pale-yeUow color, but on redistillation or sublimation a pure-white well-crystallized substance may be obtained (m.p. 95°). Yield 80 per cent based on the bromine used or 60 per cent based on the calcium-silicon alloy. 

Sodium—lead alloys that contain other metals, eg, the alkaline-earth metals, are hard even at high temperatures, and are thus suitable as beating metals. Tempered lead, for example, is a beating alloy that contains 1.3 wt % sodium, 0.12 wt % antimony, 0.08 wt % tin, and the remainder lead. The German BahnmetaH, which was used ia axle beatings on railroad engines and cars, contains 0.6 wt % sodium, 0.04 wt % lithium, 0.6 wt % calcium, and the remainder lead, and has a Brinell hardness of 34 (see Bearing MATERIALS). 

Silver white, relatively soft metal that is only applied in alloys. Oxygen and water attack pure Ca. The most prominent compound is the oxide (CaO) = burnt calcium, which hardens to calcium carbonate in mortar. Annual production of about 120 million tons. Burnt gypsum (CaS04 0.5 H20) hardens with water. A great step in evolution was the replacement of hard shells of brittle calcium carbonate by an internal skeleton of tough calcium phosphate (hydroxylapatite)-protein composite. Calcium is essential for all life forms. The daily requirement is 0.7-1.0 g. Humans (70 kg) contain 1 kg of calcium. Calcium silicate is the main component of cement. Marble is calcium carbonate in polycrystalline form and the favorite material of sculptors. 

This section presents a brief overview of a few other compounds that have not been described in previous sections. Because it can function as a nonmetal, silicon forms sihcides with several metals. These materials are often considered as alloys in which the metal and silicon atoms surround each other in a pattern that may lead to unusual stoichiometry. Examples of this type are Mo3Si and TiSi2. In some sihcides, the Si-Si distance is about 235 pm, a distance that is quite close to the value of 234 pm found in the diamond-type structure of elemental silicon. This indicates that the structure contains Si22-, and CaSi2 is a compound of this type. This compound is analogous to calcium carbide, CaC2 (actually an acetylide that contains C22- ions (see Chapter 10)). 

As a consequence of experimental runs and changes in process salt mixtures, a variety of waste salts and alloys have been produced, and much of this material is in storage. These waste products contain varying quantities of magnesium, sodium, potassium, calcium, and aluminum as well as plutonium and americiurn. 

The phase structure of the products, the high rates and the selective character of these interactions pointed to the use of sodium and calcium sulphates as oxidizers of multicorrponent iron-based alloys in the processing of raw materials containing refractory rare metals. 

Markova et al. (1967) investigated the terbium-yttrium system by means of microscopy, X-ray diffraction, thermal analysis, hardness and electrical resistance measurements. Their starting materials were distilled yttrium of 99.6 to 99.7 (wt )% purity and terbium of 98.5 to 99% purity. Impurities in their terbium included yttrium, gadolinium, dysprosium, calcium, copper, iron and tantalum. Both metals contained gaseous impurities. Alloys were melted in an arc furnace under a helium atmosphere and annealed at 850°C for 70hr. 

Pozzolanic materials such as natural poz-zolans (volcanic origin), fly ash (product of combustion of carbon in thermoelectric power stations) or silica fume (very fine powder obtained as waste in the metallurgy of silicon or iron-silicon alloys) do not contain calcium oxide and thus cannot react with water. Instead, these pozzolanic materials react with the free lime (produced by the OPC clinker) according to the pozzolanic reaction... 

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