Calcium Silicate Products

In another example, two quicklimes, produced from very different limestones, but with virtually identical slaking curves in the standard test, were found to perform differently on the full scale. When a reactivity test incorporating some cement was used, the slaking time increased from about 20 to 60 min. and the difference between the quicklimes became apparent. 

There are three principle advantages to the aircrete producer of using more reactive quicklimes. 

Calcium silicate wall-board is produced from cellulose fibre, calcium silicate-forming materials (e.g., hydrated lime, silica and cement) and fire protective fillers. 

The raw materials are blended with water in a hydro-pulper and the slurry is transferred to the board-making machine. Excess water is removed through a filter cloth by suction. The uncured boards are then transferred to autoclaves, where they are heated under steam pressure to react the lime and silica and to hydrate the cement. 

The particle size distribution of the hydrated lime should be sufficiently fine to give the slurry the required rheological properties and to produce a green board with the required mechanical properties. It should, however, be sufficiently coarse to enable the de-watering process to proceed at an acceptable rate. 

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For certain metal alloys, a calcium silicon alloy is required. This alloy also is used as a steel deoxidizer and is favored because it forms a low-melting-point calcium silicate product A representative composition of the alloy is 30-33% Ca, 60-64% Si, 3-5% Fe, 1-2% Al, 0.3-0.6% C, and less than 0.15% S and P. 

Cement is made by forming a calcium silicate product from limestone and clay minerals in a kiln which requires very hot temperatures, releasing high levels of CO2 as it bums. Most low carbon cements on the market are based on magnesium silicate, which takes less energy to heat. 

Mainly aircrete, sandlime bricks, other calcium silicate products and refractories. Mainly mortar, render, plaster, and drying/improvement/stabilisation of soils. Mainly potable water, sewage, liquid effluent and gaseous effluent treatment. 

Construction and building (building materials and trade). The use of quicklime and hydrated lime in soil treatment for the construction of road foundations and large areas, such as airfields, car parks, etc, is well established in the USA and France and is growing elsewhere. Lime products have been used for many thousands of years to produce mortars which have stood the test of time. Mortar for masonry, render and plaster remains an important outlet for lime. Other outlets include the production of various calcium silicate products, aircrete, and limewash, and the use as an additive for hot-mix asphalt. 

Fired cl bricks are generated as a waste product from construction and demolition activities, and their value is an additive in the manufacture of PC-based construction products. It was established that the aluminosilicate phase in the fired clay bricks promoted the development of the tobermorite, the principal binder in most calcium silicate products under hydrothermal conditions. The use of CB waste as a cement replacement for the manufacture of these products was also demonstrated as a viable option. 

Cements are commonly made by heating a mixture of limestone and clay to about 1700 C. The product is ground with gypsum. Chemically cements consist of a mixture of calcium silicates and aluminates with some sulphate present. World production 1976 730 megatonnes. 

Calcium Silicates. Cements aie hydiated at elevated tempeiatuies foi the commercial manufacture of concrete products. Using low pressure steam curing or hydrothermal treatment above 100°C at pressures above atmospheric, the products formed from calcium siUcates are often the same as the hydrates formed from their oxide constituents. Hence lime and siUca ate ftequendy used in various proportions with or without Portland cement in the manufacture of calcium siUcate hydrate products. Some of these compounds are Hsted in Table 6. 

Elemental phosphorus is prepared by the reduction of calcium phosphate, Ca3(P04)o, with coke in the presence of sand, SiO>. The products are phosphorus, calcium silicate, CaSiOa, and carbon monoxide. 

Alternatives to fossil fuels, such as hydrogen, are explored in Box 6.2 and Section 14.3. Coal, which is mostly carbon, can be converted into fuels with a lower proportion of carbon. Its conversion into methane, CH4, for instance, would reduce C02 emissions per unit of energy. We can also work with nature by accelerating the uptake of carbon by the natural processes of the carbon cycle. For example, one proposed solution is to pump C02 exhaust deep into the ocean, where it would dissolve to form carbonic acid and bicarbonate ions. Carbon dioxide can also be removed from power plant exhaust gases by passing the exhaust through an aqueous slurry of calcium silicate to produce harmless solid products ... 

At blast furnace temperatures, calcium silicate is a liquid, called slag. Being less dense than iron, slag pools on the surface of the molten metal. Both products are drained periodically through openings in the bottom of the furnace. 

Modem production of elemental phosphoras uses a technique similar to the metallurgical processes described in Chapter 20. Apatite is mixed with silica and coke and then heated strongly in the absence of oxygen. Under these conditions, coke reduces phosphate to elemental phosphoms, the silica forms liquid calcium silicate, and the fluoride ions in apatite dissolve In the liquid calcium silicate. The reactions are not fully understood, but the stoichiometry for the calcium phosphate part of apatite is as follows ... 

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. 

An intimate mixture of ferro-silicon and powdered caustic soda or lime is packed in strong cylinders communicating with a high pressure storage. By means of a fuse the temperature is locally raised so that chemical reaction takes place, with the production of hydrogen and sodium and calcium silicates. 

In the cement industry, the term hydration is used to describe a range of reactions between cement and water to produce a hardened product. A cement clinker particle is a multiphase solid having massive calcium silicate grains (50-100 pm) in a matrix of interstitial aluminate and ferrite. This is described as analogous to a distorted clay sequence, which traps regions of porosity-pore size distribution from nanometer to micrometer. 

During this phase the initial self-retarding calcium silicate hydrate layer appears to break down, allowing further hydration products from the C3S and C2S phases to be formed. These appear to be produced in three... 

CASH CBM CBO CBPC CC CCB CCM CCP CDB CEC CFBC CFC CFR CMM COP CSH CT Calcium aluminosilicate hydrate Coal bed methane Carbon burn-out Chemically-bonded phosphate ceramics Carbonate carbon Coal combustion byproducts Constant capacitance model Coal combustion product Citrate-dithionate-bicarbonate Cation exchange capacity Circulating fluidized bed combustion Chlorofluorocarbon Cumulative fraction Coal mine methane Coefficient of performance Calcium silicate hydrate Collision theory... 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

Native copper ore is crushed, concentrated by washing with water, smelted, and cast into bars. Oxide and carbonate ores are treated with carhon in a smeller. Sulfide ore treatment is complex, hut. in brief, consists of smelling to a matte of cuprous sulfide, ferrous sulfide, and silica, which molten matte is treated in a converter by the addition of lime and air is forced under pressure through the mass. The products are blister copper, ferrous calcium silicate slag, and SO . Refining is conducted by electrolysis, and the anode mud is treated to obtain the gold and silver. See Fig. I. 

The purpose of the limestone is to remove the gangue from the iron ore. At the high temperatures of the furnace, the limestone decomposes yielding lime (CaO), a basic oxide that reacts with Si02 and other acidic oxides present in the gangue. The product, called slag, is a molten material consisting mainly of calcium silicate ... 

Portland cement is the product obtained by pulverizing clinker consisting essentially of calcium silicate, usually containing one or more forms of calcium sulfate, and there are five types of portland cement ... 

Mixed oxides have a widespread application as magnets, catalysts, and ceramics. Often, nonstoichiometric mixtures with unusual properties can be prepared for example, Fe203 and ZnO have been milled for the production of zinc ferrite [40], while mixed oxides of Ca(OH)2 and Si02 were described by Kosova et al. [77]. Piezoceramic material such as BaTi03 from BaO and anatase Ti02 has been prepared [78], while ZnO and Cr203 have been treated by Marinkovic et al. [79] and calcium silicate hydrates from calcium hydroxide and silica gel by Saito et al. [80]. The thermal dehy-droxylation of Ni(OH)2 to NiO or NiO-Ni(OH)2 nanocomposites has also been investigated [81]. 

No attempt is made here to explain the intricate temperature dependence of the hydrations of the three calcium silicates. Work on the kinetics of these hydration processes is not complete, so the authors could give at present only highly tentative and speculative explanations. The conclusion from Figures 2 to 7 for the purposes of this paper is that the surface area development in pastes of all three silicates is determined primarily by the degree of hydration of the silicate. For a simple reaction, in which the reactants have negligible surface areas compared with the reaction products, such a conclusion would be trivial. However, for as complex... 

However, the trial court held some of the product claims valid and others invalid thus, claims 24 and 26, which called for either metallic silicates or just silicates broadly, were declared invalid on the ground that individual silicates were old for the purpose. Claims 18, 20, 22, and 23 were upheld. These called for alkaline earth silicates or calcium silicate. 

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