Frozen-drop technique

The frozen-drop technique was naturally adopted in measuring molten metal droplet size before any other methods became available. Similarly to the methods for normal liquids, the freeze-up and collection of molten metal droplets may be carried out in many different ways. For example, metal droplets can solidify during flight in gaseous or liquid medium in a spray chamber. 13H51 The solidified particles are subsequently sieved to obtain the size distribution. 

Physicochemical. FREEZING OF DROPLETS. Taylor and Harmon (2Q) have sprayed drops of water into a bath of hexane cooled by dry ice. The drops are frozen and subsequently settle onto shutters, which are later opened. Differential settling theory is used to give drop sizes. Choudhury and Stevens (IQ) capture and instantaneously freeze an entire spray in a bath of liquid nitrogen, and later determine size distributions by screening techniques. 

Taylor and Harmon (72) designed an instrument for measuring drop-size distribution of water sprays that combined the drop-freezing technique and Stokes law of separation. The drops were frozen quickly in hexane, cooled to —20° C. with dry ice, and collected on a shutter. They were then allowed to fall, approximately according to Stokes law, onto a scale pan. The weight on the pan vs. time relationship was then used to compute the drop-size distribution. 

Special techniques must be used to avoid glass formation [131] and zone melting usually results in a sizable drop in yield. If reliable methods can be developed to produce a small, completely melted zone within the frozen IL, zone melting represents one of the most promising techniques being developed for the purification of ILs. 

However, in a later study, Stevenson and Schnitzer (1982), using a technique similar to that described by Flaig et al. (1975), determined that changes in pH had no effect on the structures of humic substances observed by TEM. The authors deposited drops of dilute aqueous solutions of humic and fulvic acids at various pH values on freshly cleaned mica sheets. The drops were frozen rapidly and freeze-dried, and the dried humic substance particles... 

The accuracy of the method depends on the technique used for measuring the radius of the drop. A camera interfaced with a computer allows the image to be frozen for an accurate measurement [388,389]. 

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