Slush freezing

Slush freezing Freezing with agitation, for example in a factory freezer. 

It is often necessary to obtain temperatures below that of the laboratory. Finely-crushed ice is used for maintaining the temperature at 0-5° it is usually best to use a slush of crushed ice with sufficient water to provide contact with the vessel to be cooled and to stir frequently. For temperatures below 0°, the commonest freezing mixture is an intimate mixture of common salt and crushed ice a mixture of one part of common salt and three parts of ice will theoretically produce a temperature of about — 20° but, in practice, the ice salt mixtures give temperatures of — 5° to — 18°. Greater cooling may be obtained by the use of crystalline calcium chloride temperatures of — 40° to — 50° may be reached with five parts of CaCl2,6H20 and 3 5-4 parts of crushed ice. 

Slush-casting alloys must be faidy low melting and freeze over a temperature range, that is, the Hquidus and soHdus temperatures must be significantly different to provide a slushy range. 

Salt Brines The typical curve of freezing point is shown in Fig. II-IIO. Brine of concentration x (water concentration is I-x) will not solidify at 0°C (freezing temperature for water, point A). When the temperature drops to B, the first ciystal of ice is formed. As the temperature decreases to C, ice ciystals continue to form and their mixture with the brine solution forms the slush. At the point C there will be part ice in the mixture /(/i+L), and liquid (brine) /i/(/i-t-L). At point D there is mixture of mi parts eutectic brine solution Di [concentration mi/(mi-t-mg)], and mo parts of ice [concentration mol m -t- mo)]. Coohng the mixture below D solidifies the entire solution at the eutectic temperature. Eutectic temperature is the lowest temperature that can be reached with no solidification. 

When the flask is stoppered and the contents are shaken, the solids intermingle. The reaction produces a slush-like mixture. This favourable, but endothermic, reaction absorbs enough energy to freeze a thin layer of water under the flask. 

If the temperature of the hot liquid interface is low enough to cause freezing of the surface, or even to form a viscous slush, RPTs are then rare. 

There was no damage to the facility or delivery systems. Members of the reentry party suffered minor frost-bite of their feet when their shoes became frozen to the water-wetted rear deck of the truck. The "freezing" of the shoes was caused by the extremely cold slush in which the men were standing. Operating personnel took action to control promptly all possible sources of ignition in the surrounding area, including shutdown of part of the plant. Water hoses, which... 

Because the low- melting-point liquid in the slush bath is near its freezing temperature, there is little concern over toxic fumes as when working with some chemicals at room temperature. However, in the beginning, you must work in a fume hood because of the copious amounts of fumes released from the low- melting-point liquid. Once the slush bath is made, it is safe to remove it to the lab. However, it is best to leave the slush bath in the fume hood if at all possible. If the slush bath is used in the lab, move the slush bath to the fume hood immediately after your work is completed. 

Slush baths (see Sec. 6.2.7) are effective for a greater range of vapors and can entrap many vapors by freezing. These types of cold traps require a lot of maintenance. 

Cool the Schlenk tube under argon down to -78°C (dry ice-isopropanol slush bath), and then admit the tube to a vacuum (c. 0.1 mmHg). Pump for 60 s, then admit argon gas and allow the apparatus to warm up to room temperature. Repeat this freeze-thaw process twice more. Heat the stirred mixture at 160°C under argon for 2 h. An abundant yellow precipitate of the molybdenum tricarbonyl complex develops. 

Haberbusch, M. and McNelis, N. (1996) Comparison of the Continuous Freeze Slush Hydrogen Production Technique to the Freeze/Thaw Technique. NASA Technical Memorandum 107324. 

The temperature is controlled by selecting a liquid whose freezing point is approximately the temperature at which one wishes to carry out the crystallization, and crushed Dry Ice is added with stirring to keep just a slush. There must be an intimate mixture of solid and liquid at all times. Carbon tetrachloride was used for temperatures of —20° to —25°. 

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