Alite

The primary phases all contain impurities. In fact these impurities stabilize the stmctures formed at high temperatures so that decomposition or transformations do not occur during cooling, as occurs with the pure compounds. For example, pure C S exists in at least six polymorphic forms each having a sharply defined temperature range of stability, whereas alite exists in three stabilized forms at room temperature depending on the impurities. Some properties of the more common phases in Portland clinkers are given in Table 2. 

Portiand cement clinker structures (18,19) vary considerably with composition, particle size of raw materials, and burning conditions, resulting in variations of clinker porosity, crystallite sizes and forms, and aggregations of crystallites. Alite sizes range up to about 80 p.m or even larger, most being 15—40 )J.m. 

Fig. 3.7 Qu alitative picture of the energies of different spin states of Fe(TpivPP) (1,2-Melm) (02), as a function of the Fe-0-0 angle. Small energy differences are enlarged to aid visualization (the exact values are given in the text).

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,... 

Conversely, coarsely ground clinkers with lower alite content are preferred for situations where cement emplacement is slow or temperatures can be high, as in the lining of oil wells. In such circumstances, organic... 

Rapid cooling of the clinker is preferred for many reasons, notably to prevent the reversion of alite to belite and lime in the 1100 1250 °C regime and also the crystallization of periclase (MgO) at temperatures just below 1450 °C. The magnesium content of the cement should not exceed about 5% MgO equivalent because most of the Mg will be in the form of periclase, which has the NaCl structure, and this hydrates slowly to Mg(OH)2 (brucite), which has the Cdl2 layer structure (Section 4.6). Incorporation of further water between the OH- layers in the Mg(OH)2 causes an expansion that can break up the cement. Accordingly, only limestone of low Mg content can be used in cement making dolomite, for example, cannot be used. Excessive amounts of alkali metal ions, sulfates (whether from components of the cement or from percolating solutions), and indeed of free lime itself should also be avoided for similar reasons. 

An alternative to silicate-based Portland cement is the calcium aluminate cement, ciment fondu, which originated with the Lafarge company in France in 1908. Ciment fondu is typically made by heating limestone with bauxite, which is mainly AIO(OH) but contains much iron oxide (see Section 17.2). As noted above, calcium aluminate hydrates and hardens much more rapidly than alite, and so ciment fondu, either as such or mixed with Portland cement, can be used whenever a rapidly setting cement is required, for example, for construction at low temperatures. Concretes made from aluminate cements remain serviceable at higher temperatures than Portland cements and so are used to make cast refractories for pyrometal-lurgical applications. 

Calculate the overall Ca and Si contents (expressed as CaO and Si02) of a Portland cement clinker that has 55% alite, 30% belite, 5% alumi-nate phase, and 10% ferrite (assume ideal compositions for the latter two). Would you expect this to behave as a fast or a slow setting cement ... 

IF N0=1 THEN H=AIEXP(ALIT) iRETURN 360 IF ES=1 THEN H=A EXP(fiHT)+BtEXP(BEIT iRETURN 362 IF EB=2 THEN H=(A+B T)IEIP hUT) iRETURN 364 H=(SIC0Si3E T)tBISIN(EEIT))IEXP(AL T) iRETURN... 

Diphenyldi butyl urea. See Centr alite, Butyl, under CENTRALITES in Vol 2, p B140-L... 

Typical levels of fluoride found in fluoridated public drinking water is about 1.0 ppm. If you were to drink a quarter of aliter (250 mL) of this water, how many micrograms of fluoride would you have ingested ... 

Saccharin (954) 300 (200-700) Slow onset, persistent, bitter metallic eye, asp, aces, sucral, alit, stev, sue High Na-salt667 g/L, 22°C Stable pH 3-10 Good 0-5 (1993)... 

QU ALITATIVE COMMENTS (with 25 mg) At three hours after having taken the material, I felt that there might have been a little exhilaration. And maybe a hint of tremor and of teeth clench. Perhaps this is a threshold dose. ... 

The lime is then added to silica, usually obtained as an aluminosilicate pozzolan (clay or shale), and the mixture is heated in a kiln to produce tricalcium silicate (called alite) ... 

A. Haas, Fluorine modified compounds synthesis and biological activities, L actu-alite Chimique 5 (1987) 183-188. 

Figure 5.8 The crystal structure of olivine, (a) The structure projected onto (100) showing serrated chains of octahedra running parallel to the c axis (b) oxygen coordination polyhedra projected about the Ml and M2 positions. Metal—oxygen distances in each coordination site are indicated. Cell parameters and interatomic distances are for fay-alite (from Smyth Bish, 1988).

The subjects of investigations were diamond catalysts produced by various methods of modification of the initial diamond nanopowders synthesized by the ALIT Company using the detonation of oxygen-deficient explosives. 

Figure 1. Average CKa-spectra of a- nanodiamond Alit, b - Alit-H, c - granulated Alit, d - granulated Alit-H, e - pure diamond.

The spectral features d d transform into broad peculiarity tf after diamond nanopowder Alit treatment in hydrogen. As a result, after diamond nanopowder Alit treatment, its CXa-emission band becomes similar to reference refined diamond powder (Fig. le). So far as nanodiamond powders CKa-bands investigation was carry out at minimum anode current densities (1 mA), the unrefined diamond powder surface remained chemisorbed atoms and molecules. However, owing to electron bombardment in sample emission focus, some of chemisorbed atoms disappeared. Therefore it was important to obtain CA -spectra... 

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