Autoclaved lime

Mutoclaved lime is a special form of highly hydrated dolomitic lime, used largely for stmctural purposes, that has been hydrated under pressure in an autoclave. 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

Although hydration under hydrothermal conditions may be rapid, metastable iatermediate phases tend to form, and final equiUbria may not be reached for months at 100—200°C, or weeks at even higher temperatures. Hence, the temperatures of formation given ia Table 6 iadicate the conditions under saturated steam pressure that may be expected to yield appreciable quantities of the compound, although it may not be the most stable phase at the given temperature. The compounds are Hsted ia order of decreasiag basicity, or lime/siHca ratio. Reaction mixtures having ratios C S = 1 yield xonotHte at 150—400°C. Intermediate phases of C—S—H (I), C—S—H (II), and crystalline tobermorite ate formed ia succession. Tobermorite (1.13 nm) appears to persist indefinitely under hydrothermal conditions at 110—140°C it is a principal part of the biader ia many autoclaved cement—silica and lime—silica products. 

Other Phases in Portland and Special Cements. In cements free lime, CaO, and periclase, MgO, hydrate to the hydroxides. The in situ reactions of larger particles of these phases can be rather slow and may not occur until the cement has hardened. These reactions then can cause deleterious expansions and even dismption of the concrete and the quantities of free CaO and MgO have to be limited. The soundness of the cement can be tested by the autoclave expansion test of Portiand cement ASTM C151 (24). 

A chemical compound of lime and silica with fiber reinforcement for added strength. It is cast as a wet slurry into molds and charged into autoclaves, finally being machined to accurate size. 

The USP stipulates a test and limits for alkali extraction from container soda-lime glass (5). Specially prepared double-distilled water is used to extract the glass for one hour at 121 °C in a steam autoclave on a strict cycle program. An aliquot of the extract is then back titrated with... 

The binders are silica, lime, slag, or cement. The balls are somewhat dried, if necessary, and then cured in steam autoclaves. During the hydrothermal treatment lime and silica react to form hydrosilicate gels, which act as binders. 

The initial process to achieve success was developed by Miyata of Kyowa in the mid 1970s [101].This process is based on the hydrothermal conversion in an autoclave of the fine agglomerated particles formed by addition of ammonia or lime to a magnesium salt solution. This hydrothermal conversion results in the formation of particles of about 1 micron in size and with a fairly low aspect ratio. This original process appears to be expensive to operate because of the low value of the ammonium or calcium chloride co-product which has to be disposed of and because the reported reaction conditions give a low yield and a relatively slow reaction. 

S. Peacock heated a mixture of powder felspar and coal in a reducing atm., and treated the product with superheated steam in an autoclave in order to recover the water-soluble potash. B. F. Halvorsen heats to 050° a mixture of ground felspar, cyanamide, and alkali salts with superheated steam. Ammonia and soluble potash are formed. H. W. Charlton digested greensand with lime and water in an autoclave. 

Ornes and Roddy (1960) investigated the elastin content of animal skin before and after treatment for leather manufacture. Two methods were used for the determination of elastic tissue. In the first, squares of limed calfskin, after deliming, were treated with a commercial pancreatic preparation containing elastase to dissolve the elastin. The squares were then autoclaved for 4 hr at 15 lb steam pressure, and the residue was treated alternately with hot 0.5 N HCl and hot water to remove lime and acid. Finally the residue was extracted with acetone to remove fat and was... 

Sand-lime bricks are manufactured by mixing lime, sand and water in a ratio of ca. 1 13 0.7, forming and then hardening in autoclaves at 180°C and 7 to 9 bar. 

The two doors of double-ended autoclaves should be interlocked in such a way that it is impossible to have both open at the same lime. If there is no need to bridge areas, it is cheaper arnl simpler to purchase single-ended autoclaves. If possible, double-ended autoclaves should be unidirectionalL It should only be possible to open the doors at one end of the autoclave by operating controls at that end. This means that a loading operator should not be able to open the unloading doors by some remote means, and the same applies to the unloader. In other words, the equipment should dictate that the staff in each area be wholly responsible for their own access to the autoclave in their respective areas. 

The heating of the autoclave is continued for 16 hr at 175°C, at which time the conversion to amine is practically complete. Some of the ammonia gas is vented to the absorption system, and when, the residual pressure on the autoclave has dropped to 200 lb, the pressure-relief line is closed, as it is then safe to effect a transfer of the charge from the autoclave to the ammonia still (containing the calculated quantity of hydrated lime) by means of the ipsidual autoclave pressure (see Fig. 8-22). 

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