Drying and Heating Up

Drying and heating up are started once the setting of the unshaped refractory is over. If fhese processes are started after long periods, then the following rules should be observed  

Deflocculated castables have a very low cement content. Also, the parhcles sizes are fine. Not only the amount of porosity but the size of the pores also matters in drying. As the pore size decreases, the drying becomes more difficult. Thus, in deflocculated castables, drying is a tedious process because of low cement content and pore size. 

Clay-bonded products lose about 75% of their water content under air drying for about 15 days. 

Krause, Refractories The Hidden Industry, The American Ceramic Society, Westerville, OH, pp. 52, 76,1987. 

Modem solution of refractory problems with unshaped refractories, in Proceedings of the UNITECR 1999, September 6-9, Berlin, 1999. 

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Preliminary dried silica is loaded into the section I by the loader 9 from vessel 10 on the gas-distribution plate 13 to be dried and heated up to 200°C. The air injected by the compressor 2 is used as a carrier gas. It is dried by the NaX zeolite up to a dew-point... 

In contrast to the conventional route, the aqueous route runs via carboxylic salt and amine salt precursors. In the first step of the synthesis, the dianhydride is refluxed in water in order to completely hydrolyze it. After cooling down to room temperature, the aqueous solution of the dicarbox-ylic acid is neutralized with the respective diamine and a salt is formed. The salt precipitates out from the aqueous solution. The precipitate is dried and heated up to 180-220°C for dehydration to form the final PI product. " ... 

The heat transfer by radiation is possible in several ways. Two well-known methods are the sun-drying and heating up of products inside ovens (kitchen stove) (Figure 12.4). 

The drying and heat-up procedures can start once the furnace has been constructed and all treatment or finishing measures completed. The following general rules should be observed if longer time periods have elapsed (weeks or months) until first heating up ... 

Consequently, drying and heat-up should start immediately respectively 48 hours after the last concrete work However, it should be taken into consideration that a refractory lining made of unshaped refractories has much more residual water than a brickwork. 

High-area aluminas (AI2O3) can be easily prepared by precipitating alumina from aqueous solution and drying and heating as for silica. This material is ciystaUine, and the major phase is called y-alumina with a surface area up to -200 mVg. Alumina forms a porous network as the water is removed. 

The purification of ammonium chloride.—Crude sal ammoniac is usually contaminated with iron or tarry matters, and in consequence, the colour varies from yellow to red it can be purified by heating it in thin layers on an iron plate hot enough to drive off the water and free acid, and to carbonize most of the tarry products. The grey mass is then sublimed. The sublimation is conducted in cast-iron pots lined internally with firebricks, and covered with a lid made of slightly concave plates. The salt to be sublimed is well dried, and heated. The pots hold about half a ton, and the sublimation occupies about five days. The sublimate forms a solid fibrous crust about 4 inches thick. The crust is easily detached from the lid it is then broken up, separated from adhering dirt, and packed for the market in barrels or sacks. W. Hempel 9 proposed converting the crystalline salt into hard stone-like masses by press, between 50° and 100°. 

A second process using complex as the catalyst was independently developed by the Standard Oil Company (Indiana) and by the Texas Company (25,26). A simplified flow diagram of this liquid-phase process is shown in Figure 17. A portion of the dried and heated feed passes through a saturator where aluminum chloride is picked up in accordance with the solubility curve shown in Figure 8. The total feed combined with re( y< le hydrogen chloride enters the bottom of the reactor and... 

The non-isothermal Knudsen eflusion technique was used to study vapor pressures of tars. The experimental details have been described previously [Oja and Suuberg 1997, 199S]. About 10 mg of dry tar was placed into a hermetic effusion cell with a small orifice, from which the saturated vapor effuses out into the vacuum outside the cell. To overcome effects caused by changes in tar con iosition during effusion, the experiment involved first a continuous cool-down followed by a continuous heat-up of the sample. From the mass loss data (by talcing into account both cool-down and heat-up as a whole cycle) the vapor pressure was calculated using the Knudsen equation. 

An instance of the formation of a neutral radical has been observed by Kortum et al. 62) for hexaphenylethane, PhjC—CPhj, which when ground up as a liquid, together with dried MgO, and heated up to 80°C... 

Hydrocarbons used in catalytic experiments were obtained by Fluka - ethylbenzene and 1-propylbenzene, and Merck - toluene and 2-propylbenzene. Catalytic experiments were performed in a 50-ml round-bottomed flask equipped with magnetic stirrer and condenser. The initial mixture containing 0.1 g catalyst, 5.0 ml solvent and 2.0 ml substrate was stirred and heated up to the reaction temperature. Then 1.0 ml 30% aqueous solution of hydrogen peroxide (Merck) was added. Small samples (0.1 ml) of the reaction mixture were taken after 1, 2 and 4 h, diluted in 4.0 ml methanol, dried and analysed by GC-MS (Hewlett-Packard). Veratrole was used as internal standard. Hydrogen peroxide conversion was followed by standard iodometric titration. 

There are four stages involved in oven sterilization. They are (a) drying, (b) heat-up, (c) exposure, and (d) cool-down. 

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