Spinels silicon nitrides

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. 

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... 

There are quite some insertion materials. Here it is classified based on their elements and includes oxides, carbonaceous materials, multiatom anion compounds, inverse spinels, sulfides, nitrides, silicon, and tin alloys [1]. Here the main topic will be related to lithium insertion. For the other kinds of insertion compounds such as sodium, potassium, sulfate, and the like, please refer to other references [2]. 

Silicon nitride crystallizes in two hexagonal forms (a- and fl-SisN and also a cubic y-modification with spinel structure that is stable at high pressure and temperature (>15GPa, >2000 K Zerr et al, 1999 Leitch et al, 2004). The a-phase occurs in nature as a rare mineral (nierite) in ordinary and enstatite chondritic meteorites (Lee et al, 1995). 

Leitch, S., Moewes, A., Ouyang, L., Ching, W.Y., and Sekine, T. (2004) Properties of non-equivalent sites and band gap of spinel-phase silicon nitride. /. Phys. Condens. Matter, 16 (26), 6469-6476. 

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]. 

Conductive heat transfer has a phononic nature, which means that the heat is transferred due to the oscillation of the atoms in the crystal lattice. Crystals with a simple lattice, such as sihcon carbide or carbon, have a lower dissipation of heat waves and a higher thermal conductivity compared to crystals with a more complex lattice. For example, the conductive thermal conductivity of aluminium nitride or silicon carbide (binary compounds with approximately equal atomic weights) is higher than alumina, magnesia, and zirconia. And the conductive thermal conductivity of said alumina, magnesia, and zirconia is higher than that of spinel, mullite, and zircon. 

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