Slush

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. 

C bol the solution of re-butyl-hthium to — 35° in a Dry Ice - acetone bath and add, whilst stirring vigorously, a solution of 48 g. of ni-chlorobromo-benzene (Section IV,62) in 75 ml. of anhydrous ether. Stir for 8-10 minutes and pour the mixture with stirring on to a large excess of sohd carbon dioxide in the form of a Dry Ice - ether slush contained in a -htre beaker. Isolate the acid as detailed above for p-Toluic acid and recrystal-lise it from hot water. The yield of ni-chlorobenzoic acid, m.p. 150-151°, is 27 g. 

The table below gives the lowest temperature that can be obtained from a mixture of the inorganic salt with finely shaved dry ice. With the organic substances, dry ice (—78°C) in small lumps can be added to the solvent until a slight excess of dry ice remains or liquid nitrogen (—196°C) can be poured into the solvent until a slush is formed that consists of the solid-liquid mixture at its melting point. 

H. M. Roder, The Thermodynamic Properties of Slush Hydrogen and Oyygen, PB Rep. No. PB-274186, National Technical Information Service,... 

Seafood. Sorbates are used to extend the shelf life of many seafood products, both fresh and processed (103,104). For smoked or dried fish, an instantaneous dip in 5 wt % potassium sorbate or a 10-minute dip in 1.0 wt % potassium sorbate prior to drying or smoking inhibits the development of yeast and mold (105,106). For fresh fish, sorbates can be incorporated at approximately 0.5 wt % into the ice, refrigerated seawater, or ice-water slush in... 

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. 

Zinc slush-casting alloy compositions are based on the Zn—A1 system. The two commonly used alloys have nominal aluminum contents of 4.75%... 

The cast zinc—aluminum—copper slush alloy, after aging for ten years indoors, shows a tensile strength of 238 MPa (34,500 psi) with Charpy impact strengths of 1.4—4.1 J (1—3 ft4bf) (87). 

R. O. Voth, J. D. Siegworth, J. F. Welch and M. J. Hi2a, Process Design Criteria, Data and Metrology Related to Slush Hydrogen Technology, NASA Tech. Memo 1006, NASA Langley Res. Cntr.,Mar., 1987. 

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. 

Alternatively, the following liquids can be used, partially frozen, as cryostats, by adding solid CO2 from time to time to the material in a Dewar-type container and stirring to make a slush ... 

Ketene [463-51-4] M 42.0, b 127-130 , d 1.093, n 1.441. Prepared by pyrolysis of acetic anhydride. Purified by passage through a trap at -75° and collected in a liquid-nitrogen-cooled trap. Ethylene was removed by evacuating the ethylene in an isopentane-liquid-nitrogen slush pack at -160°. Stored at room temperature in a suitable container in the dark. See diketene on p. 209. 

In recent years rotational casting methods have made the slush moulding process virtually obsolete. In these processes an amount of material equal to the weight of the finished product is poured into a mould. The mould is then closed and rotated slowly about two axes so that the paste flows easily over the cavity walls in an oven at about 200-250°C. When the compound has gelled, the moulds are cooled and the moulding removed. Compared with the slush moulding process there is no wastage of material, little flash, and more even wall thickness. Completely enclosed hollow articles such as playballs are most conveniently made. 

In the laboratory, a range of slush baths may be used for speciality work. These are prepared by cooling organic liquids to their melting points by the addition of liquid nitrogen. Common examples are given in Table 8.2. Unless strict handling precautions are instituted, it is advisable to replace the more toxic and flammable solvents by safer alternatives. 

Table 8.2 Working temperatures of cryogenic slush baths ...

Polyvinyl Chloride (PVC) 1940 M-H VG G G G Extrusion, injection, rotational, slush, transfer, compression, blow mold Pipe conduit and fittings, cable insulation, downspouts, bottles, film... 

PVC Plastisols 1940 M-H VG G G G Slush and rotationally molded, foamed, extruded Used in coating machines to cover paper, cloth and metal... 

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