Phases, silicon nitrides

The ceramic products of these pyrolyses were completely amorphous. Pyrolysis carried out at 1500 °C or lower yields only amorphous products. Amorphous materials can be converted to crystalline form by heating above the transition temperature. Pyrolysis must be carried out at 1550 °C or higher to obtain crystalline products. Thus, pyrolysis of the transamination product of Tris with ammonia at 1550 °C or higher gave high-purity, a-phase silicon nitride (33), as analyzed by powder X-ray difiraction (Figure 1 and Table I). 

Figure 1. Representative X-ray powder diffraction spectrum of [Si(NH2)2]> which is the product of pyrolysis at 1550 °C of the transamination product of Tris with ammonia, a and P refer to a- and -phase silicon nitride, respectively.

Bao, Y., Zhang, T., Gawne, D.T., and Mason, P. (2008) Quantitative model for the viscous flow and composition of two-phase silicon nitride-based particles in plasma-spray deposition. J. Eur. Ceram. Soc., 29, 1521-1528. 

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. 

Creep Resistsince. Studies on creep resistance of particulate reinforced composites seem to indicate that such composites are less creep resistant than are monolithic matrices. Silicon nitride reinforced with 40 vol % TiN has been found to have a higher creep rate and a reduced creep strength compared to that of unreinforced silicon nitride. Further reduction in properties have been observed with an increase in the volume fraction of particles and a decrease in the particle size (20). Similar results have been found for SiC particulate reinforced silicon nitride (64). Poor creep behavior has been attributed to the presence of glassy phases in the composite, and removal of these from the microstmcture may improve the high temperature mechanical properties (64). 

The starting material and shock-activated powder were mixed with 5-wt% MgO and heated for various periods. At the end of each period the phase content of the samples was determined with x-ray diffraction. In this environment it is thought that the phase is formed by a dissolution-precipitation process as shown in Fig. 7.8. As indicated in Fig. 7.9, the shock-activated silicon nitride displays substantially enhanced dissolution rates that are strongly dependent on shock pressure between 22 and 27 GPa. 

Fig. 7.8. High temperature conversion of a-silicon nitride with an MgO additive to the p-pha.se is thought to be a consequence of dissolution of the a phase in a magnesium silicate with subsequent recrystallization from the melt. Enhanced dissolution rate should then strongly influence a. p conversion [84B01].

Bauer,R., Smulders,R, Geus,E., vanderPut, J., and Schoomman, J., Laser Vapor Phase Synthesis of Submicron Silicon and Silicon Nitride Powders from Halogenated Silanes, Ceram. Eng. Sci. Proc., 9(7-8) 949-956(1988)... 

In the sintering of such materials as silicon nitride, a silica-rich liquid phase is formed which remains in the sintered body as an intra-granular glass, but this phase, while leading to consolidation, can also lead to a deterioration in the high-temperature mechanical properties. 

For imaging applications, minimisation of the damage to DNA molecules by the AFM tip is essential. One method of less-invasive imaging is based on phase (rather than height) imaging, which employs for instance 100 mm long silicon nitride cantilevers with narrow arms inserted into a fluid cell [65]. Alternatively, or better complementary, the operation in liquids [66], and... 

A review article on the CVD processes used to form SiC and Si3N4 by one of the pioneers in this area, Erich Fitzer [Fitzer, E., and D. Hegen, Chemical vapor deposition of silicon carbide and silicon nitride—Chemistry s contribution to modem silicon ceramics, Angew. Chem. Int. Ed. Engl, 18, 295 (1979)], describes the reaction kinetics of the gas-phase formation of these two technical ceramics in various reactor arrangements (hot wall, cold... 

Rogi, P. and J.C. Schuster Phase Diagrams of Ternary Boron Nitride and Silicon Nitride Systems, ASM International, Materials Park, OH. 1992. 

Silicon Fluoride or Silicon Tetrafluoride. See in Vol 6, F146-R to F147-L, and G100-L under the history of NG manufacture where the use of SiF4 to separate the liq phases and recover the NG is Silicon Nitride. Si3N4 mw 140.31 grey-white amorph powd mp 1900 (sublimes) d 3.44g/cc. Sol in HF acid, Prepn is by reaction of powd Si and nitrogen in an electric furnace (Refs 1,37 ... 

Although related SiN precursor systems have been developed, the above sets of reactions provide launch points for synthesizing the majority of SiN-containing precursors studied to date. Various groups have learned to manipulate oligomers prepared as above to develop useful precursors. We begin by discussing those that provide phase pure silicon nitride. 

Access to phase pure silicon nitride materials via processable precursors is limited to just three approaches. The first, shown in reaction 6, provides one of the first oligomers exploited as a preceramic polymer24,253. This simple polysilazane, containing only Si, N and H, is known to be relatively unstable and will crosslink on its own to give intractable gels. Furthermore, it does not offer the 3Si I4N stoichiometry required for Si3N4. Nonetheless, it is useful as a binder and for fiber-reinforced ceramic matrix composites (CMCs)31. 

Equation (6.25) not only allows us to calculate the Hamaker constant, it also allows us to easily predict whether we can expect attraction or repulsion. An attractive van der Waals force corresponds to a positive sign of the Hamaker constant, repulsion corresponds to a negative Hamaker constant. Van der Waals forces between similar materials are always attractive. This can easily be deduced from the last equation for 1 = e2 and n = n2 the Hamaker constant is positive, which corresponds to an attractive force. If two different media interact across vacuum ( 3 = n3 = 1), or practically a gas, the van der Waals force is also attractive. Van der Waals forces between different materials across a condensed phase can be repulsive. Repulsive van der Waals forces occur, when medium 3 is more strongly attracted to medium 1 than medium 2. Repulsive forces were, for instance, measured for the interaction of silicon nitride with silicon oxide in diiodomethane [121]. Repulsive van der Waals forces can also occur across thin films on solid surfaces. In the case of thin liquid films on solid surfaces there is often a repulsive van der Waals force between the solid-liquid and the liquid-gas interface [122],... 

Keywords Silicon nitride ceramics, Phase relations, Processing, Microstructure, Properties... 

Thompson DP (1993) New Grain Boundary Phases for Nitrogen Ceramics. In Chen IW, Becher PF, Mitomo M, Petzow G, Yen TS (eds) Silicon Nitride Ceramics. Mat Res Soc Symp Proc 287 79... 

Jennett TA, Harmsworth PD, Jones AG (1994) Ultra fine crystalline Silicon Nitride from a continuous Gas Phase Plasma Route. In Hoffmann MJ, Becher PF, Petzow G (eds) Silicon Nitride 93. Key Eng Mat 89-91. Trans Tech Publications Ltd, Switzerland, p 47... 

Lewis MH (1994) Crystallisation of Grain Boundary Phases in Silicon Nitride and SiAlON Ceramics. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics. NATO ASi Ser E 276, Kliiwer Academic Publishers, Dordrecht, p 217... 

Klemm H, Herrmann M, Schubert C (1996) The Influence of the Grain Boundary Phase Composition on the High Temperature Properties of Silicon Nitride Materials. In Parilak L, Danninger H, Dusza J, Weiss B (eds) Proc Int Conf Deformation and Fracture in Structural PM Materials, IMR SAS Kosice 2 75... 

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