Mixtures, isomorphous

Specific Heats of Solid Mixtures.—The specific heat of a homogeneous solid mixture of solid components is not usually additively composed of the specific heats of the latter. W. Spring (1886) found that the total heat capacity of alloys of lead and tin was always greater than the sum of those of the components, but above the melting-point the two were equal. A. Bogojawlensky and N. Winogradoff (1908) find, however, that the heat capacities of the isomorphous mixtures ... 

Isentropic change. 75 lsochore, 44, 337 Isolated system, 37 Isomorphous mixture, 417 Isopiestic change, 44, 337 Isopneuma, 442 Isosteres, 442... 

Induced precipitation is a collective name for processes accompanying the formation of solid phase, such as occlusion, adsorption, compound formation, formation of isomorphous mixtures, mixed crystals, colloidal solutions, etc. In... 

At room temperature, trans-8 is formed, whereas at -78 °C mixtures of cis-8 and trans-8 are obtained. Pure cis-8, which rearranges to trans-8 at 20°C, is the product when Si2Cl6 is the starting material. Crystalline trans-8 is isomorphous with the respective Ge- and Sn- complexes (d Si-Cl 2.27, d Si-P 2.35 A). 

According to Steiner et al. [69], who studied the complex of /TCD with 1,4-butanediol, a monomer model of PTHF, the crystal packing in this complex is the cage type and isomorphous to that of the jS-CD hydrate, and the methylene chain vibrates in the cavity. However, in the /J-CD-PTHF complex, the polymer chain lays fixed inside a column formed by linearly bonded CD molecules. In agreement with this picture, CP/MAS NMR spectra showed the PTHF chain in the complex to be much less flexible than that in its mixture with the CD. 

Ta/Nb minerals often occur as impurities in ilmenite, rutile, cassiterite, wolframite and perovskite, most of which contain REE. Because tantalite and columbite have similar chemical properties, they often replace each other, and are usually found as isomorph mixtures. Tantalum and niobium can also be found as separate minerals. Tantalite and microlite are primary sources of tantalum. 

Fergusson et al. were the first to report the existence of binary compounds with a general formula Se Sg in these melts. They carried out an extensive investigation by X-ray powder diffraction and by absorption spectroscopy in the infrared, visible, and ultraviolet regions over the whole composition range of molten mixtures of sulfur and selenium cooled down to 20 °C. They also examined phases obtained by recrystallization of the cooled melts from carbon disulfide. All phases were isomorphic with one of the allotropes of Sg and SCg indicating that the structures also consist of cyclic eight-membered molecules ... 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

None of the above authors ever considered the presence of a mixture of isomeric thienothiophenes in their reaction products, though some obtained different tetrabromo derivatives of 1 (m.p. 172° and 229°-230°) this was explained by isomorphism. 

The /3-form of the arsenatophosphate and /3-KAs03 contain trimeric anionic rings. This follows from the isomorphism with the low temperature form of K3(P309), which is formed when KH2P04 is treated with a mixture of acetic acid and acetic anhydride 121). It may also be concluded from the observation that in the hydrolysate of /3-arsenatophosphate it is possible to detect, in addition to monoarsenate and a little trimetaphosphate, only mono- and diphosphate, but no tri- or higher polyphosphate 121). The /3-forms of arsenatophosphates contain anions of the types ... 

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