Thermal Expansion of Ceramic Materials at −200° to 0°C

Abstract

HE structure of U2Na has been described by Rundle et al.' as body-centered cubic (Mn20a type) with a lattice parameter of 10 6 i 8 A. Vaughan,2 on the other hand, found a hexagonal structure (La203 type) with a = 3.69 A and c = 5.83 A He concluded that the body-centered cubic and the hexagonal forms are allotropic modifications of the same compound, UzN3.The significant difference in the two investigations that yielded these results was in the methods by which the compounds were prcpared The U2N3 examined by Rundle and co-workers was prepared as a powder (by treating U N with excess nitrogen). That investigated by Vaughan occurred as an intermediate layer between UN2 and UN formed on the surface of a massive uranium bar by reaction with nitrogen.I t is suggested that the hexagonal form of U2N3 is in fact what may be termed a "coherency structure," akin to epitaxial growth, dictated by the structure of the outermost nitride layer, UN2. .4ltliougli no orientation relations have (to the writer's knowledge) been rcported for a layered sequence of the nitrides UNZ, U Z N~, and UN there would be a very good match if (0001) and [2110] T 305 of the hexagonal U2N3 were parallel to (111) and [lTO], respectively, of the UNZ. Rundle et al. measured the lattice parameter of UN2 and found it to be 5.310 A. The corresponding spacing along [lT0] is therefore 3.755 A. The value of a (3.69 A) quoted by Vaughan thus represents a mismatch of only -1.7% in terms of the UN2 [170] spacing, along [ZiTO] in U2N3. Received March 13, 1962. The writer is senior lecturer in metallurgy,

Cryogenic Properties of Inorganic Insulation Materials for ITER Magnets: A Review

“…( in the thermal expansion coefficients of less pure alumina ceramics from the expansion coefficient of 100% A1203 [Burk, 1962]. However, as indicated in Data on single-crystal A1203 from Arp et al [1962] are not included in these graphs because data from Wachtman et al [1962] were presumed to be more accurate.…”

“…The data from a commercial specimen were from the manufacturer of Lucalox. The thermal conductivity of single crystal Burk [1962] and Touloukian et al [1977; citations therein].…”

“…Data from Borodai and Suzdal'tsev [1975] .........10 Berman [1952], Berman et al [1960], Alterovitz et al [1975], Nemoto et al [1985], and citations therein] Data from Burk [1962] and Touloukian et al [1977;citations therein] Data from Wachtman et al [1962] and Touloukian et al [1977;citations therein] Data from Gmelin [1967;1969] (sintered) and Barron et al [1959] Burk [1962] and Touloukian et al [1977;citations therein] Breaking strength of annealed soda-lime glass rods vs. temperature for three periods of load application.…”

Cryogenic properties of inorganic insulation materials for ITER magnets:

“…As [ 1977] are also given. [1977] o A A Burk [1962] White [1966] Browder [1969] Ganesan [1961] Schaake [1969] …”

“…o Burk [1962] • Schauer [1965] A Itskovich [1967] A Yates [1972]; c axis 0 -Recommended polycrystalline Touloukian et al [1977] [ 1962] are not included in these graphs because data from Wachtman et al . [1962] were presumed to be more accurate.…”