Calcium hydroxide, specific surface area

The quality and yield of carbon black depends on the quaUty of the feedstock, reactor design, and input variables. The stmcture is controlled by the addition of alkaU metals to the reaction or mixing 2ones. Usual practice is to use aqueous solutions of alkaU metal salts such as potassium chloride or potassium hydroxide sprayed into the combustion chamber or added to the make oil in the oil injector. Alkaline-earth compounds such as calcium acetate that increase the specific surface area are introduced in a similar manner. 

The alkali content in clinker is usually on the level of 1 % Na O with dominating soluble alkali sulphates. In the solution rich in CH, they increase the solubility of gypsum, while the solubility of calcium hydroxide decreases. In this condition the SO4 ions can be bonded with C-S-H. That is why the gypsum addition should be higher. When the specific surface area of cement is high and the reaction of tricalcium aluminate is therefore accelerated, the gypsiun addition should be higher too. 

Clinkers with increased C2S and reduced C3S contents are employed in the production of cements with reduced hydration heat evolution (see section 19), such as moderate heat of hardening cement (corresponding to ASTM Type II cement) and low-heat cement (corresponding to ASTM Type IV cement). To slow down the rate of heat evolution, cements employed for this purpose are usually ground to a relatively low specific surface area. Cements of this type are used in applications in which a reduced release of hydration heat is required, as in the constraction of dams and other bulk concrete structures (Kelham and Moir, 1992 Sone et al, 1992). High-C2S cUnkers, especially those with a reduced C3A content, are also constituents of some oil well cements (see section 27). L0W-C3S clinkers are less suitable for the production of blended cements, owing to the reduced amount of free calcium hydroxide produced in the hydration of such clinkers. 

A material closely related to silica firme is colloidal silica, which differs from the former by having a significantly higher specific surface area (up to 80 m /g). If added to Portland cement mixes this material reacts with the liberated calcium hydroxide at a faster rate than microsilica, and leads to the development of higher early strengths (Chandra and... 

Because of the presence of a highly reactive form of Si02 and its high specific surface area, rice husk ash reacts readily with calcium hydroxide in the presence of water, yielding an amorphous C-S-H phase (Zhang et al., 1996 Lin, 1997). In suspensions of rice husk ash in saturated calcium hydroxide solutions at 40 °C the formation of a semicrystalline calcium silicate hydrate phase of the composition Caj j.SiOj 5.XH2O has also been reported (Yu eta/., 1999). 

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