Analcite - Industrial & Engineering Chemistry (ACS Publications)

Analcite - Industrial & Engineering Chemistry (ACS Publications) F...

0 downloads 62 Views 299KB Size



Means of Determining Melting and Freezing Points


Thebe alloys readily undergo undercooling unless they are constantly stirred during cooling. Several cooling curve studies were made during which tlie alloys were not stirred. In all of these cases undercooling occurred, the eutectic alloy Ireezing a t 65" to 66" C. and Wood's metal slightly above. During freezing, the temperature rose several degrees but did not reach the true freezing point. It seems quite likely, therefore, as Steinmetz suggested, that some of the lower freezing points recorded in the literature may be erroneous because undercooling was permitted.

Preparation and Solubility between 1 8 2 O and 2 8 2 O C.

Effect of Impurities 'rlie effect of the presence of impurities other than those of metals making up the eutectic is discussed by Steinnietz ( 3 ) . Unless the impurities are present in considerable amount and form a eutectic with other ingredients present, the effect on tlie melting point should be negligible.

Effect of Mercury on Melting Point The low melting points reported might also be due to another cause. These alloys take on considerable amounts of inercury and still maintain their metallic luster and nature, although malleability and luster progressively decrease as mercury is added until the solid amalgam finally becomes merely a lusterless, brittle solid. The addition of 3 per cent mercury to Lipowitz alloy lowers the freezing point about 3' C. Some 9 to 10 per cent of mercury can be added before the alloy becomes unrecognizable as a metal, the freezing point being depressed about 6" to 7" C. Since the nomenclature of tlie alloys has been loosely applied, it is possible that the melting points of mercury alloys have been reported merely under the names of Wood's metal or Lipowitz alloy. An undercooled alloy containing 6 to 8 per cent mercury should solidify a t about 60" C.

Loose Nomenclature



Siiice tlie iitliiies "Wood'F metal" and "Lipowitz alloy" 1itLve been so loosci~yapplied to Pundry fusible quaternary alloyi, these names have ceased to carry any exact meaning, yct the attempt is made to give the alloys exact melting pointb. diirce both alloy hare the same melting point, the names iiiiglrt be used intercliangeably for any alloy having a melting Imiiit coinciding with that of tlie eutectic alloy. However, 5 ~ ~ ac solution h of tlie problem could \vel1 lead to multiplicity ol naiiies to include alloy- of other compositions melting at the eutectic point. Tlie simplest solution seems to be to drop all names, call the eutectic alloy simply a quaternary eutectic, and state its melting-freezing range and composition. This solution has precedent, since the International Critical Tables give the composition of the eutectic aiid the melting-freezing range, but no name. They do not list tlie alloy composed of 50 per cent bismuth, 25 lead, 12.5 tin, 12.5 cadmium, comnioiily regarded as Wood's metal.

Literature Cited ( I ) Hiiclgw, N. l p . , 1.C / L C WI .d . , 43, 200-3T (1924). ( 2 ) Urii. St:tndnrds, Cut. 388 (1930). (3) Steinmetz, C . P., J . Am. C h n . Soc., 40, 913-100(191s) It~uckxv~cu April 2 , 1985. Preseiited before the Division of Iiidustrial aiid ISiigiueering Clieiiiistry a t the 89th Aieeting of the iliilericaii Clieiiiical Society, Kew Yorlr, N. Y., April 22 t o 26, 1935.

FREDERICK G. STRAUB Chemical Engineering Division, University of Illinois, Urbana, Ill.

Analcite crystals were prepared from aqueous solution at 282" C., and petrographic examination and chemical analyses were made of them. The solubility of analcite was determined at 182' t o 282" C. in water and a sodium hydroxide concentration u p to 3.5 millimoles per liter.

S PART of research on the preveiitioii of silica scale in steam boilers, it became advisable to obtain data relative to the type of silica compounds which would form a t boiler temperatures and to obtain further data relative to the solubility of these compounds at boiler temperatures. Analcite scale (Kaz0.Al2Od.4Si02.2H20) has been found in steam boilers ( 1 ) . Pure analcite was prepared and a study made of its solubility in water aiid dilute sodium hydroxide solutioiis a t temperatures between 182" and 282 O C. In pieparing the analcite, the necessary amounts of the desired chemicals Tiere added to uater in the larger bomb (used in solubility tests 2). The sampling tube and filter inside the bomb were left out, and a 200-mesh copper gauze was put inside of the top. The small upper bomb nas not used. After the bombs had been held at 282" C. for 46 hours, they mere removed fiom the furnace and inverted, and the sampling valve was opened, thus alloiiing the liquid to be forced out and leave the solid behind in the bomb. When the bombs were cool, the solid was removed, washed with Ivater, and dried. The solution added to the bombs mas sodium silicate in which 70 cc. contained 10.8 grams of silica Eight giams of 93.5 per cent solid sodium aluminate (equivalent to 4.6 grams of alumina) were placed in each of six bombs, 70 cc. of the silicate solution \+ere added, and then water was added (40 cc. in bombs 7 and 8,110 cc. in bombs 9 and 10, and 260 cc. in bombs 11and 12). The solids formed in bombs 11 and 12 had larger crystals than in any of the other bombs. Petrographic examination showed that these crystals were analcite in uniform rounded grains about 0.1 mm. in diameter. Table I gives the result of tlie chemical analyses of the crystals formed and shows that tlicy had almost identical composition as natural analcite. A microphotograph of sample 12 is shonn in Figure ld. The crystals mere very hard and could be easily separated from each other in a group by pressing with a spatula. The crystals could not be easily broken. Figure 1B shows a microphotograph of crystals formed in z later test (sample 2 3 ) . Tlie same conditions wrre iiwd a5 in tests 11 and 12, except that 10 grams o i sodium aluminatc.





'~.'nnr.R? 1.