Nitride spinels

Soignard et al. [565] have smdied the stability of the two spinels in the system Si3N4-Ge3N4, at pressures up to 20 GPa and temperatures > 2000°C. The x-ray patterns analysis shows that the two new spinel nitrides remain essentially stable over the range of conditions examined. 

Among the nitrides of the p-block elements, Sn3N4 and the 7-phase of Si3N4 represent the first examples of spinel nitrides (see Section 14.12). 

Chromium iron manganese brown spinel, formula and DCMA number, 7 348t Chromium iron nickel black spinel, formula and DCMA number, 7 348t Chromium isotopes, 6 476 Chromium magnesium oxide, 5 583 Chromium manganese zinc brown spinel, formula and DCMA number, 7 348t Chromium-nickel alloys, 77 100-101 Chromium-nickel-iron alloys, 17 102-103 Chromium-nickel stainless steels, 15 563 Chromium niobium titanium buff rutile, formula and DCMA number, 7 347t Chromium(III) nitrate, 6 533 Chromium nitride, 4 668... 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

In another example, the high temperature reaction of calcium and strontium sub-nitrides with molybdenum foil has also recently been claimed to produce novel molybdenum ternary nitride oxides which contain isolated [MoN4] tetrahedra in an ordered sub-lattice of and anions. High temperature-high pressure syntheses are also yielding novel metastable structures, such as the spinel analogues mentioned previously. There is therefore an ever-increasing base of nitrides and oxynitrides with diverse structures and potential catalytic interest. 

High Temperature Material, Proceedings of the 3rd Symposium on Material Science Research, Dept, of Atomic Energy, Bombay, India, 1972. Papers cover a variety of oxide and nonoxide high temperature materials like spinel, alumina, and silicon nitride. 

The cubic y-modification has been recently observed under a pressure of 15 GPa and temperatures above 2000 K by the laser heating technique in a diamond cell [23] and in shock-wave compression experiments with pressures >33 GPa at 1800 K and >50 GPa at 2400 K [29]. This modification is often designated as the c-modification in the literature in analogy to the cubic boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms are octahedrally coordinated by six nitrogen atoms, one silicon atom is coordinated tetrahedrally by four nitrogen atoms (Fig. 3c). The atomic coordinates for the cubic modification are given in Table 2. From calculations it is shown that this structure should have a high hardness similar to that of diamond and c-BN [23]. 

Fig. 7. Calculated isothermal section at 1873 K of the subsystem Si3N4-4(AlN)-2(Al203)-3(SiOz) [77], compared with experimental data ( ). LS = oxide nitride liquid O = Si2N20 X = Si12Allg039Ng Mullite = Al2Si3012 Spinel = Al303N...

Chondrite matrices are also the carriers of presolar grains. These phases cover a broad mineralogy and include diamonds and graphite, silicon carbide (SiC), titanium carbide (TiC), silicon nitride (SisN, ), corundum, spinel, silicates, and even rare metal grains. 

In addition to the initial work in the alumina and mullite matrix systems previously mentioned, SiC whiskers have also been used to reinforce other ceramic matrices such as silicon nitride,9-13 glass,14 15 magnesia-alumina spinel,16 cordierite,17 zirconia,18 alumina/zirconia,18 19 mullite/zirconia,18-21 and boron carbide.22 A summary of the effect of SiC whisker additions on the mechanical properties of various ceramics is given in Table 2.1. As shown, the addition of whiskers increases the fracture toughness of the ceramics in all cases as compared to the same monolithic materials. In many instances, improvements in the flexural strengths were also observed. Also important is the fact that these improvements over the monolithic materials are retained at elevated temperatures in many cases. 

As mentioned previously, the main body of research on whisker-reinforced composites was concerned with alumina, mullite, and silicon nitride matrix materials. None the less, selected work examined zirconia, cordierite, and spinel as matrix materials.16-18 The high temperature strength behavior reported for these composites is summarized in Table 2.5. As shown, the zirconia matrix composites exhibited decreases in room temperature strength with the addition of SiC whiskers. However, the retained strength at 1000°C, was significantly improved for the whisker composites over the monolithic. Claussen and co-workers attributed this behavior to loss of transformation toughening at elevated temperatures for the zirconia monolith, whereas the whisker-reinforcement contribution did not decrease at the higher temperature.17,18... 

The most remarkable facts about the enstatite chondrite CAIs are that (i) they exist at all, and (ii) they are not particularly remarkable as CAIs go. If enstatite chondrite CAIs originated by condensation under the highly reducing conditions considered necessary for forming the characteristic enstatite chondrite mineralogy, refractory lithophile elements like calcium and aluminum are expected to be largely locked up in sulfides, carbides, and nitrides (e.g., Lodders and Fegley, 1995). Phases such as melilite, hibonite, and spinel should not be present. The fact that... 

Tin(IV) nitride, Sn3N4, was first isolated in 1999 from the reaction of Snl4 with KNH2 in liquid NH3 at 243 K followed by annealing the solid product at 573 K. Su3N4 adopts a spinel-type structure, related to that of y-Si3N4 described above. Tin(IV) nitride is the first nitride spinel that is stable under ambient conditions. 

W. Schnick (1999) Angewandte Chemie International Edition, vol. 38, p. 3309 - The first nitride spinels - New synthetic approaches to binary group 14 nitrides . 

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