Silicon nitride behaviors

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). 

This model goes a long way towards explaining most experimental results reported in the literature for ISFETs with oxide or nitride surfaces. Unfortunately, the properties of these materials prepared in different laboratories are very different. It is known that silicon nitride (really silicon oxynitride SisNztOx) forms an oxygen-rich layer at the surface, whose thickness depends on the deposition conditions. This passivation layer forms rapidly (in a matter of hours) and is very stable, even under continuous exposure to aqueous electrolyte. The hydration of this layer seems to fit the requirements and predicted behavior of the Sandifer model. Consequently, ISFETs that have been exposed to aqueous solution for more than one hour show no adsorption effects which would be expected from the SBT model. 

Becher PF, Lin HAT, Hwang SL, Hoffmann MJ, Chen IW (1993) The influence of microstructure on the mechanical behavior of silicon nitride ceramics. In Chen IW, Becher P, Mitomo M, Petzow G, Yen TS (eds) Silicon Nitride Ceramics-Scientific and Technological Advances. MRS Symposium Proc 287, MRS Pittsburgh, p 147... 

Dogan, C.P. and Hawk, J.A. Influence of whisker reinforcement on the abrasive wear behavior of silicon nitride- and alumina-based composites , Wear, 203-204 (1997) 267-277. 

Rouxel, T., High temperature mechanical behavior of silicon nitride ceramics, J. Ceram. Soc. Jap., 109(6) 89-98 (2001). 

In order to elucidate the effect of the whisker orientation on the erosion behavior of material SN-C, erosion tests were carried out in directions both parallel and perpendicular to the whisker orientation. It is apparent that in the highly directional whisker-reinforced silicon nitride material, solid particle erosion in the direction parallel to the whisker orientation resulted in a faster rate of material removal compared to that in the perpendicular direction (Fig. 20.4). 

Detailed discussion in respect to the erosion behavior of self-reinforced or in-situ reinforced silicon nitride materials can be found elsewhere (Zhang et al. 2005). Here we summarize the important arguments. 

The first three items relate to the chemical nature of the film. An outstanding feature of PECVD silicon nitride films is that their stoichiometry can be controlled, and that they can have as much as 30 atomic percent hydrogen in them. The last two items relate to the mechanical behavior of such films. If they are not dense enough, they will net be effective barriers to moisture... 

It is also interesting to note that the H bound into the plasma silicon nitride film can be driven off, to some extent, by annealing at low temperatures. Data for SiH4 + N2 + He and SiH4 + N2 + Ar depositions are shown in Figure 10.7 Observe that for a film deposited with He at 300°C and then annealed for 10 hours at 300 C, the hydrogen content drops from 19 to 12%. The curves marked NOT are unannealed. Depositions with Ar did not display this behavior. 

Figure 14. Corrosion behavior of reduction reactor materials samples ( 7), Inconel 625 (O), silicon (Q), silicon nitride (%), alonized Inconel 62 (M silicon carbide and ( f), Inconel 657. Furnace temperature, 482°C S03, 25 see/min steam, 58 see/min argon, 78 see/min.

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... 

C. R. Blanchard and R. A. Page, Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride, J. Am. Ceram. Soc., 73[11], 3442-3452 (1990). 

The behavior of cavities during deformation also depends on the refractoriness of the bonding matrix. In a recent study,33,34 stable cavities were observed to form at the grain boundaries of a grade of silicon nitride containing 4wt.% yttria, even though there was very tittle glass at these boundaries Fig. 4.14a. The cavities observed were reminiscent of Hull-... 

C. W. Li and J. Yamanis, Super-Tough Silicon Nitride with R-Curve Behavior, Ceram. Eng. Sci. Proc., 10[7-8], 632-645 (1989). 

Fisher M. L. and Lange F. F., Rheological behavior of slurries and consolidated bodies containing mixed silicon nitride networks. J. Am. Ceram. Soc. 83 (2000) pp.1861-1867. 

Hot gas corrosion behavior of various silicon-based non-oxide ceramic materials (e.g., silicon carbide, silicon nitride, etc.) can vary widely depending on the stoichiometry, structure and sintering aids. Silicon carbide materials exhibit excellent corrosion resistance towards sulfur-containing atmospheres even at a high temperature around 1,400X [Fdrthmann and Naoumidis, 1990]. 

The synthesis of processable precursors for Si-B-N-C ceramics became a goal of intensive investigations as soon as the outstanding thermal and mechanical properties of this system were reported [1,2]. The amorphous phase of Si-B-N-C ceramics can show excellent thermal stability up to 2000 °C without mass loss or crystallization. The role of boron is believed to be to increase the high-temperature stability and to prevent the crystallization and decomposition of silicon nitride above 1500 °C. Primarily, the atomic ratio and chemical environment of boron in Si-B-N-C precursors seem to affect the thermal behavior of resulting ceramic materials. 

Fig. 19. Creep behavior of silicon nitride ceramics. The composition of this ceramic contains 7 vol % Y3A15Oi2 as a sintering aid. The specimens were hot-pressed at 1750°C under a pressure of 20 Mpa. The holding times are marked on the curve. This curve indicates that crystallization of the grain-boundary phase improves the creep resistance. Garnet crystals were observed at the grain boundaries after annealing [3/]. , Sample A60 , Sample B60 A, Sample B150, x, failure.

Xie et al. [49] investigated the tribological behaviors of different ILs as lubricants for tribo-pairs (low-temperature silicon oxide film/SijN ball, polysilicon Si film/ SijN ball, and silicon nitride (SijN ) film/SijN ball) by varying the applied load and the sliding velocity. The ILs lubricants showed the best lubricating properties for the three tribo-pairs at the intermediate load of 150 g. 

This chapter discusses the behavior, under thermal shock conditions, of epoxy resins toughened with ceramic particulates. Alumina Al203 and silica Si02, which are usually used as filler for insulation materials, and the new ceramic materials silicon carbide SiC and silicon nitride Si3N4 are employed. For these toughened epoxy resins, the thermal shock resistance is evaluated by using fracture mechanics. The difference between experimental and calculated values of the thermal shock resistance is discussed from a fractographic point of view. 

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

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