Transformation, heat cerium

Many metal chlorides when heated with an excess of nitric acid are converted into the nitrates. Thus, J. L. Smith found that the transformation occurs with potassium or sodium chloride in the presence of 7 to 8 parts of nitric acid J. S. Stas said that at 40°-50°, potassium, sodium, or lithium chloride require respectively 3, 4, and 5-5 parts of nitric acid. J. L. Smith said that ammonium chloride and nitric acid yield nitrous oxide. H. Wurtz found that auric, cadmium, cerium, lanthanum, didymium, ferric, and platinic chlorides are decomposed by nitric acid incompletely and with difficulty. S. Schlesinger said that the two copper chlorides, mercurous, zinc, and lead chlorides, are decomposed, but, added H. Wurtz, with difficulty and incompletely while mercuric ajid silver chlorides are not attacked. F. Rose found cobalt amminochlorides are readily converted into the nitrate. 

Three thermal effects are observed in the heating curve of initial Mm the first one - at 595 °C, his nature is unknown, and two thermal effects at 780 °C and 810 °C. The effect at 780 °C is associated with a polymorphous transformation in pure Ce y -5 726 5 °C, and the second one is responsible for melting pure cerium at 815 °C. Evidently the presence of the thermal effects and the difference in their temperature ranges as compared with the literature data are related to the chemical composition of starting mishmetal. Chemical analysis has shown that the base of the mishmetal is Ce 82.9 wt. % and La - 16.7 wt. %. 

Owen and Scott (1976) were able to test samples which were, before testing, virtually all /3-cerium. The /3-cerium samples were prepared by a clever method devised by Koskimaki et al. (1974), also see ch. 4, section 3.3. The strength and ductility of /3-cerium are shown as a function of temperature in fig. 8.20. The 0.2 percent offset yield strength decreases smoothly as temperature is raised from 77 K to about 400 K where it begins to decrease more rapidly. The temperature 400 K correlates well with the temperature of the /3 to y transformation on heating. Thus, the more rapid strength decrease is caused by the presence of y-cerium in the material. The reduction in area of -cerium ranges between 20 and 40 percent until about 350 K and then it rises rapidly to values characteristic of y-cerium. 

Lanthanum and cerium form a continuous series of solid solutions as shown in fig. 1. The melting points of the pure metals have been adjusted to the accepted values (table 1) from those given with the reported lanthanum-cerium phase diagrams. Lanthanum undergoes two phase transformations on heating from the double-hexagonal close-packed form (dhep) to the face-centered cubic (fee) form at 310°C and then to the body-centered cubic (bcc) form at 865°C. Cerium exhibits only the... 

Fig. 19. Phase diagram of the cerium-praseodyinium system. The 61 °C value for the y P (fcc-dhcp) transformation for pure cerium is the midpoint value of the heating (139°C) and cooling ( —16°C) transformation temperatures (see table 1).

Jayaraman et al. (1966) examined several binary alloys of a light rare earth metal with a heavy rare earth metal and found that a Ce-70 at% Gd specimen transformed from its normal Sm-type structure to dhcp structure during a 5 hr treatment at 4.0 GPa and 450°C. Since this alloy did not decompose to the elements during the heating-pressure cycle, Jayaraman et al. concluded that cerium remains in its trivalent state under the above conditions. 

An effective C—H phosphonation of pyrimidylphosphonates has been reported (Scheme 4.250) [405]. Manganese (HI) acetate served as the promoter for this chemistry, and simply heating to 50 or 80 C in acetic acid successfully phosphonated the C-5 position on the pyrimidine. Curiously, the cerium nitrate [399] was an ineffective catalyst for this transformation. An attractive aspect of this chemistry was that the primary and secondary alcohols on the sugar did not need to be protected prior to the phosphonation reaction. One drawback to this approach was that three equivalents of the manganese reagent and four equivalents of the secondary phosphite were needed for high conversions. However, these issues are overshadowed by the ability to functionalize a C—H bond under such mild conditions. Overall, this is a very attractive process for the synthesis of pyrimidylphosphonates. 

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