Pure cement compounds

The chemical reaction of cement compounds with water is very complex because the hydration of each compound (C3S, C2S, C3A, and C4AF) is closely related with the reactions among the rest of the compounds. The OPC is a mixture of four major compounds, as mentioned in Section 13.1. Therefore, at first, it is important to understand the hydration of pure cement compounds in order to have complete understanding of the hydration mechanism of OPC. 

The mechanisms that have already been described for pure cement compounds form abasis for a study ofthe hydration mechanism of portland cement. The conduction calorimetric curves of C3S and portland cement are similar except portland cement may yield a third peak for the formation of monosulfate hydrate (Fig. 1). The detailed influence of C3A and C4AF on the hydration of C3S and CjS in cement is yetto be worked out. The delayed nucleation models and the protective layer models, taking into account the possible interactions, have been reviewed. 1 1 Although the initial process is not clear for C3S (in cements), it appears that C3A hydration products form through solution and topochemical processes. 

The hydration of the ferrite phase (C AF) is of greatest interest in mixtures containing lime and other cement compounds because of the strong tendency to form soHd solutions. When the sulfate in solution is very low, soHd solutions are formed between the cubic C AH and analogous iron hydrate C FHg. In the presence of water and siUca, soHd solutions such as C3 ASH4-C3FSH4 may be formed (33). Table 7 Hsts some of the important phases formed in the hydration of mixtures of pure compounds. 

Sample Portland cement (%) Compound-slag powder (%) Pure-slag powder (%)... 

Hydration of fly ash cement differs from pure cement in terms of the hydration rates of the clinker phases, amount of calcium hydroxide formed, composition of the clinker hydration products, and additional hydration products from the reaction of the fly ash.I l Lower amounts of lime are formed in the presence of fly ash because ofthe pozzolanic reaction between the fly ash and lime formed in cement hydration. Fly ash generally retards the reaction of alite in the early stages and accelerates the middle stage reaction. The accelerated reaction is attributed to the existence of nucleation sites on fly ash particles. The aluminate and ferrite phases hydrate more rapidly in the presence of fly ash, and also there is a significant difference in the hydration rate of the belite phase up to 28 days. Table 1 gives the relative hydration rates of cement compounds in the presence of fly ash as derived from conduction calorimetry. [" 1 It can be seen that the earlier rates of hydration are generally retarded, and the later stage hydration rates are accelerated. 

Hafnium Carbide. The need of pure zirconium [7440-67-7] for nuclear reactors prompted the large-scale separation of hafnium [7440-58-6] from zirconium. This in turn made sufficient quantities of hafnium dioxide [12055-23-17, Hf02, or Hf metal sponge available for production of HfC for use in cemented carbides (see Hafniumand hafnium compounds). 

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... 

A number of other studies of AB cements have used X-ray diffraction. For example, Sorrell (1977) and Sorrell Armstrong (1976) employed the technique in the study of oxychloride cements formed in aqueous solution by interaction of oxides and chlorides of either zinc or magnesium. Individual phases were identified, again using Cu K radiation, this time comparing results with those previously obtained for pure compounds. Results from these two studies are described in detail in Sections 7.2 and 7.3 respectively. 

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. 

Aliphatic solvents, alkyllithium compounds and, 14 250-251 Aliphatic sulfonates, 26 145 Aliquot samples, 13 413-415 analysis of, 13 416 Aliskren, 5 158 Alitame, 12 42 24 232 Alite, phase in Portland cement clinker, 5 471, 472t, 473t Alitretinoin, 25 790 Alizarin, color of, 7 331 Alizarin derivatives, 9 337 Alizarin pure Blue B, 4 361t Alkadienes, metathesis of, 26 923 Alkali/alkaline-earth cation recognition,... 

The results reported by Carrasco et al. (1998) revealed that nearly all studied metal emissions, measured at the exit of a cement kiln stack, were significantly higher when a blend of 80 wt% coal + 20 wt% TDF was combusted instead of pure coal. Especially notable are increased emissions in Cr, Mn, Cu, Zn, and Pb (Table 9). The exception to this trend is Hg, which exhibited a 30% reduction in its emission rate when the coal + TDF mixture was burned. The data further document reductions in NO and organic compound emissions, including PAHs, where the most drastic decrease was observed for dioxins and furans. On the other hand, emissions of CO, S02, and HC1 increased considerably with the addition of TDF (Table 9). The total particulate emissions from combustion of the blend were only slightly greater than those from pure coal. Carrasco et al. (1998) used their data to model atmospheric dispersion of the emitted contaminants in the vicinity of the... 

Many complex silico-aluminates or aluminosilicates are formed in nature. Of these, clay in more or less pure form (pure clay, kaolinite kaolin, china clay. HrjSiiA Oc) or AI2O3 2SiC>2 2H2O) is of great importance. Clay is formed by the weathering of igneous rocks, and is used in the manufacture of bricks, pottery, porcelain, Portland cement. Sodium aluminosilicate is used in water purification to remove dissolved calcium compounds. 

In solubility tests of the pure compounds in distilled and cement-equilibrated water, iodate concentrations in both liquids were near the expected theoretical values for 68(103)2 and Ca(I03)2 For (103)2 the concentration in distilled water corresponded to the expected value however, the concentration in the cement-water was a factor of 1000 higher. This higher concentration was attributed to hydrolysis due to the high pH ( 12) of the cement-water. Hydrolysis would account for the release of iodine from the Hg(IO3)2-cement. The iodate concentrations found in the leachates of the cements containing 68(103)2 and Ca(I03)2 were a factor of 10 lower than expected. No metallic ion concentration was sufficiently high to cause precipitation of the iodate. 

Rankin and Wright (1915), although they were not particularly concerned with the interpretation of burning conditions, firmly established the optical properties of pure compounds and the principal phases in commercial cements. These authors systematically investigated approximately 1000 combinations of lime, alumina, and silica with fully 7000 heat treatments and microscopical examinations. 

Collepardi, M. et al. (1980,1982) Combined effect of lignosulfonate and carbonate on pure Portland clinker compounds hydration. Cement and Concrete Research 10,455-461 12, n -lll, 425-435. 

In most analytical procedures, calibration is carried out by means of a calibration curve using com-pound(s) prepared with chemicals of an appropriate purity and verified stoichiometry. Matrix effects must often be taken into account and, consequently, the calibration solutions should be matrix-matched. CRMs of pure compounds may be used for calibration. However, matrix CRMs should in principle not be used for the purpose of calibration unless no other suitable calibrants are available, with the exception of those methods (e.g., spark source mass spectrometry, wavelength-dispersive XRF, etc.) that require calibration with CRMs of a similar, fully characterized matrix (e.g., metal alloys, cements). For such methods, accuracy can only be achieved when certified RMs are used for the calibration. 

Table 3. Mix ratios for Portland cement with the Compound-slag or Pure-slag powder...

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