Hydration calcium silicate

Hydrated calcium silicate minerals such as xonotlite, truscottite, and gyrolite are rare but have been reported from several Au-Ag deposits. They do not coexist with Au-Ag minerals but instead are found with quartz, carbonates, and johannsenite. However, in the Keisen No. 3-2 vein in the Hishikari Au-Ag deposits, a close association of electrum with truscottite, smectite and calcite is observed (Imai and Uto, 2001). 

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. 

Hydrated calcium silicates-------> calcium silicates + water... 

F. Saito, G. Mi, M. Hanada, Mechanochemical Synthesis of hydrated calcium silicates by room temperature grinding, Solid State Ionics, 1997, 101-103, 37. 

We worked with a variety of synthetic silicates and their modifications by various physical or chemical treatments or by various chemical additives. We particularly evaluated many synthetic hydrated calcium silicates, with and without additional treatments. These treatments included various organic and inorganic acid compounds, organic surface-active agents, and inorganic salts. We also studied samples dried to remove free moisture and/or some water of hydration. The modifications were selected to effect favorably the properties of the carriers. 

If the reaction follows the first route, the interaction of monosilicic acid with calcium hydroxide molecules appears to be a direct reason of polymerization and precipitation of hydrated calcium silicates. The scheme of the reaction can be written as follows [20] ... 

Thus, based on above-considered data one can conclude that hydrothermal and mechanochemical synthesis brings to similar products -hydrated calcium silicates. 

Saito F., Mi G., Hanada M. Mechanochemical synthesis of hydrated calcium silicates by room temperature grinding. Book of Abstracts. Xlll Int. Symp. Reactivity of Solids. Hamburq, 8-12 Sept. 1996. 

Leach-Resistant Chemicals. Insoluble Complexes. Leach-resistant fire retardants can be formed by reacting soluble salts with metal salts to form insoluble, metallic salt complexes. Sodium silicate reacted with calcium chloride formed an insoluble, hydrated calcium silicate (95). Application of a 20% diammonium phosphate solution, followed by a 20% magnesium sulfate solution, has been proposed as a ready-to-use treatment for wood roofs (96). This combination forms an insoluble magnesium ammonium phosphate and is recommended for roofs that are 5 years old or older. Test results indicate that this treatment provides increased flame-spread protection. 

J. Hagymassy, Jr., I. Odler, M. Yudenfreund, J. Skalny and S. Brunauer, Pore structure analysis by water vapour adsorption 111. Analysis of hydrated calcium silicates and Portland cement. /. Colloid Interface Sci., 38 (1972) 20. 

A hydrated calcium silicate sulfate carbonate has a discrete Si(OH)6 ion as part of its structure.27... 

The free lime [Ca(OH)2] and carbonate (CaC03) contents of calcium silicate hydrates, ranging from 1.0-20%, were determined by a thermogravimetric method by Biffen (33). The mass-loss curves for a series of calcium silicate hydrates, calcium silicate hydrates plus varying amounts of calcium hydroxide, and calcium silicate hydrates plus varying amounts of calcium carbonate are given in Figure 4.15. 

Shaw S, Henderson CMB, Komanschek BU (2000b) Dehydration/reciystallization mechanisms, energetics, and kinetics of hydrated calcium silicate minerals an in situ TGA/DSC and synchrotron radiation SAXS/WAXS study. Chem Geol 167 141-159... 

Reaction with silica and alumina. Hydrated lime reacts with pozzolans (materials containing reactive silica and alumina) in the presence of water to produce hydrated calcium silicates and aluminates. The reactions may take months to proceed to completion at ambient temperatures, as in mortars (section 26.6) and lime treated soil (section 26.3), but proceed within hours at elevated temperatures and water vapour pressures (e.g., in steam at 180 °C and a pressure of 10 bar — see sections 26.10,26.11 and 26.12). This pozzolanic reaction is the basis of the strength generated by hydraulic quicklimes (section 26.9). 

Sandlime bricks, also called calcium silicate bricks, are produced by moulding, under high pressure, a moist mixture of silica sand (or crushed siliceous stone, or flint) and hydrated lime. The green bricks are then autoclaved using steam pressures of at least 11 atmospheres. Under these conditions, the hydrated time reacts with the silica to form hydrated calcium silicate, which bonds the aggregate particles into a strong and durable brick [26.47]. Other shapes, such as blocks and building elements are also produced. 

Because hydrated calcium silicate is white, the autoclaved products are an attractive near-white colour. This enables pigments to be used to produce a wide range of coloured products. 

High density calcium silicate concrete products are made, particularly in Eastern Europe [26.46], by co-grinding silica sand and lime, adding controlled amounts of water and unground sand, and casting the mix into moulds. The products are then autoclaved at elevated temperature and steam pressure to produce hydrated calcium silicate concrete. A range of products, including slabs, beams and lintels, are produced, with and without metal reinforcement. 

For instance, magnesium sulfate has a more marked effect than other sulfates because it also leads to decomposition of the hydrated calcium silicates. Ammonium sulfate is especially aggressive, because the ammonia produced escapes as a gas. 

Set Biodentine material consists substantially of hydrated calcium silicate [79], some of which forms more rapidly in Biodentine than in MTA because of the presence of calcium chloride and calcium carbonate. This latter component, which accounts for 15% of the powder by mass, acts as nucleation sites for the deposition of calcium silicate hydrate. Consequently, the precipitation of calcium silicate hydrate occurs more rapidly within this material, which leads to a shorter setting time [79]. 

Fig. 7a-c show images of the products of hydration in the cement paste. Ettringite, hydrated calcium silicates and Ca(OH)2 were detected due to their typical morphologies. 

The CsAH phase or ettringite is in the form of rods and fibers that interlock. The second reaction, which causes the cement to harden, is slower. It starts after about 10 hours, and takes more than 100 days to complete. The product is tobermorite gel, a hydrated calcium silicate (Ca3Si207-3H20), which bonds everything together. 

According to Taylor [160] the mechanism of hydrated calcium silicate phases formation is strongly related to the properties of silicate anion substmcture. The SiO tetrahedra condensate simultaneously with the calcium-oxygen polyhedral, influencing on one another. Alternatively, the calcium-hydroxide layers can be formed firstly, and the condensation of SiO tetrahedra occurs on this matrix. 

Pulverised fuel ash, sawdust, spent lime and many other waste products can and have been used in some apphcations usually where a rou separation is required. Other eciahy prepared solid powder materials such as hydrated magneaum silicate, hydrated calcium silicate, bentonite, fuller s earth, or activated carbon are used in some applications piinc ally because of their adsorptive properties but they may also act as a filter aid in the separation of the particulate solids fi om the liquid. 

Bagosi, S., and Csetenyi, L.J. (1998) Caesirrm irrrmobilisation in hydrated calcium-silicate-alurainate systems. Cement and Concrete Research 28,1753-1759. 

Taking into account their stoichiometry, both reactions are similar and produce the same products in different proportions [30, 65, 66]. Hydrated calcium silicate (3Ca0.2Si0, AY[ O) is the principal hydration product and is the component that provides resistance to cement matrix and is formed on the surface of cement particles. The calcium hydroxide (Ca(OH)2) is responsible for the pH 12 of the cement matrix and is critical in protecting the steel reinforcement against corrosion however it deg-radates the hemicellulose and lignin of natural fibers decreasing the properties of the composite material. 

Pozzolanic additions are siliceous minerals added during mixing of cement matrix to react with hydration products, especially with CaCOH). This reaction is exothermic and occurs between pozzolan and Ca(OH)2 to form hydrated calcium silicate [30,65,66]. 

Water can be used to measure the area of materials containing micropores into which the larger nitrogen molecules cannot penetrate. The MP. or corrected modelless method of analysis was used in this case for data obtained on hydrated calcium silicate by Bodor, Skalny, and Brunauer (179). 

Various inexpensive adsorbents have been examined briefly for their ability to resolve sugars on thin-layer plates. Some of these show promise for hydrophilic compounds but as yet there are few reports describing their use. Tobe [28] obtained a resolution of simple sugars on layers of SOene E. F. (Firm 40) (a hydrated calcium silicate) and Silene E. F.-Cehte 535 mixtures. Magnesium silicate layers have been used [29] as well as gypsum [30]. 

Afwillite. A hydrated calcium silicate, 3CaO. 2Si02.3H2O it is formed when Portland cement is hydrated under special conditions and when calcium silicate is autoclaved (as in sand-lime brick manufacture). 

TLV. Threshold Limit Value. Tobermorite. A hydrated calcium silicate approximating in composition to 5CaO.6SiO2.5H2O. Tobermorite gel is... 

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