Calcium silicate, properties

Beaudoin, J. J. Feldman, R. F. (1975). Mechanical properties of autoclaved calcium silicate systems. Cement and Concrete Research, 5 (2), 103-18. 

These can be inorganic materials such as calcium silicate, mineral wool, diatomaceous earth or perlite and mineral wool. If provided as an assembly they are fitted with steel panels or jackets. These are woven noncombustible or flame retardant materials the provide insulation properties to fire barrier for the blockage of heat transfer. 

Another field with a large potential for improvements concerns aluminosilicate minerals, which are of great importance in determining the chemistry of water in many types of rock. In backfill clays, aluminosilicates are responsible for the retention (sorption, incorporation) of trace elements and may affect both oxidation potential (incorporation of Fe(II)/Fe(III)) and pH (hydrolysis of silicate and/or exchange of H+). Related classes of compounds (i.e., calcium silicates and calcium aluminates) form the chemical backbone of cementitious materials. The thermodynamic properties of these substances are still largely unexplored. 

Calcium—Silicon. Calcium—silicon and calcium—barium—silicon are made in the submerged-arc electric furnace by carbon reduction of lime, silica rock, and barites. Commercial calcium—silicon contains 28—32% calcium, 60—65% silicon, and 3% iron (max). Barium-bearing alloys contains 16—20% calcium, 9—12% barium, and 53—59% silicon. Calcium can also be added as an alloy containing 10—13% calcium, 14—18% barium, 19—21% aluminum, and 38—40% silicon These alloys are used to deoxidize and degasify steel. They produce complex calcium silicate inclusions that are minimally harmfiil to physical properties and prevent the formation of alumina-type inclusions, a principal source of fatigue failure in highly stressed alloy steels. As a sulfide former, they promote random distribution of sulfides, thereby minimizing chain-type inclusions. In cast iron, they are used as an inoculant. 

Portland cement is classified as a hydraulic cement, ie, it sets or cures in the presence of water. The term Portland comes from its inventor, Joseph Aspdin, who in 1824 obtained a patent for the combination of materials referred to today as Portland cement. He named it after a grayish colored, natural limestone quarried on the Isle of Portland, which his cured mixture resembled. Other types of hydraulic cements based on calcium materials were known for many centuries before this, going back to Roman times. Portland cement is not an exact composition but rather a range of compositions, which obtain the desired final properties. The compounds that make up Portland cements are calcium silicates, calcium aluminates, and calcium aluminoferrites (see ). 

Develii]ied in the eurly I lHOs. tohcrinoriies have selectivity properties intermediate between those of clay minerals and zeolites. They have been considered in catalysis and nuclear and hazardous waste disposal. Tobermorilc. Ca Si H () s 4HiO. occurs naturally as a hydrous calcium silicate in calc-silicate rock. Tobermorilex have layer structures similar to those of 2 1 clay minerals, but the structure varies with the chemical composition as well as with Ihe nature of their synthesis. They have heen synthesized from a number of starting materials. 

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]. 

Titanium Silicides. The titanium—silicon system includes Ti,Si, Ti Si, TiSi, and TiS (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkaliflnorosilicate (155) reaction of TiCl4, SiCl4, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiS (156) and, for Ti Si, reaction between titanium dioxide and calcium silicide at ca 1200°C, followed by dissolution of excess lime and calcium silicate in acetic acid. 

The stability of toxicant-carrier combinations used in pesticide wettable powder formulations cannot be easily predicted by evaluating various properties of the carrier. Several types of synthetic calcium silicates and their modifications were evaluated for malathion stability and other properties. The carriers were evaluated for pH (slurry), pK (surface acidity), moisture content, absorptive capacity, and/or ion exchange capacity. These properties were correlated with actual malathion stabilities as measured at 40° C. storage for 1, 2, 3, and 7 months. The carrier properties evaluated did not offer a simple means of predicting compatibility in the variety of carriers tested. 

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. 

The second part of my talk deals with the surface of a particular solid, a calcium silicate hydrate, called tobermorite. The two main constituents of Portland cements are two calcium silicates, which make up about 75% or more of a portland cement by weight, and both of these silicates produce tobermorite in their reaction with water. This tobermorite is the most important constituent of hydrated portland cement, concrete, and mortar. That is not the reason, however, for my talking about it—the reason is that it is a fascinating substance for a colloid chemist. I will discuss only two properties of the tobermorite surface the surface area and the surface energy. 

Previous investigations of these hydration reactions at room temperature have been reviewed recently (4). Research in this laboratory has included the stoichiometry of the hydration of both silicates, employing different methods of hydration (2, 3, 5, 21), and a determination of the surface energy of tobermorite, the calcium silicate hydrate produced in the hydration of both silicates under most experimental conditions (8). The surface area and the surface energy of tobermorite are briefly discussed by Brunauer (I). These properties play vital roles in determining the strength, dimensional stability, and other important engineering properties of hardened portland cement paste, concrete, and mortar. 

Portland cement-based variations currently in use do not provide a satisfactory solution. These variations still use the same cement chemistry (i.e., calcium silicate based) in that their basic properties such as setting characteristics and thermal properties do not change much. Thus, a novel solution is needed to address the cold climate problems in the cement industry. 

In the attempt to synthesize molecular sieves with isomorphous substitutions of A1 and/or Si by the divalent calcium element in the tetrahedral positions, we obtained a new calcium silicate phase by inclusion of heteroatom calcium into silicate sols. The characterization results showed that as-synthesized calcium silicate, named CAS-1 (Calcium silicate No. 1), was a novel zeolite-like crystal material with the cation reversibly exchangeable and selectively adsorptive properties. In this paper, the effects of composition of raw materials, reaction temperature and the different alkali ion on the hydrothermal synthesis of calcosilicate crystal material CAS-1 were investigated and the uptake of different cation on the thermal stability of CAS-1 structure was also examined. The sample was characterized by XRD, TEM, SEM, DT-TGA, BET, AAS and chemical analysis. 

Examples of other property modifiers are silicone powder and liquids, fiuoropolymer powders, Pro-maxon (processed calcium silicate), mica, vermiculite, and waxes. 

The interaction of zeolite-rich materials with Ca(OH)2 is of special interest, because zeolites, like other reactive aluminosilicate systems, e.g., crushed bricks, give rise to calcium silicates and aluminates, which are able to harden upon hydration in both aerial and aqueous environments. This behaviour, already known in ancient times, is typical of a volcanic, mostly glassy material, called pozzolana, which is the genetic precursor of the mentioned Neapolitan yellow tuff, widely spread in the surroundings of Naples, Italy [61]. That is why every material able to behave as pozzolana is called "pozzolanic material" and the property to react with lime is called "pozzolanic activity". 

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