Non-oxide materials

Compound Structural unit 8iso(PPm) fl(ppm) Skew Reference 

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For the most part, these other applications utilize boron oxides, but a small fraction of uses involves non-oxide materials such as boron hydrides and engineering ceramics. Although these non-oxide materials have received great attention in academic circles in recent decades, they are yet to gain much industrial significance in the overall scheme of the borate industry. 

Inorganic non-oxide materials, such as III-V and II-VI group semiconductors, carbides, nitrides, borides, phosphides and silicides, are traditionally prepared by solid state reactions or gas-phase reaction at high temperatures. Some non-oxides have been prepared via liquid-phase precipitation or pyrolysis of organometallic precursors. However, amorphous phases are sometimes formed by these methods. Post-treatment at a high temperature is needed for crystallization. The products obtained by these processes are commonly beyond the manometer scale. Exploration of low temperature technique for preparing non-oxide nanomaterials with controlled shapes and sizes is very important in materials science. 

The burning velocity of a gas depends on a number of variable factors, such as the ratio of oxidant to fuel gas, the amount of non-combustible material in the gas and of non-oxidizing material in the oxidant. It also depends on the conditions under which burning takes place whether vertically up or down, or horizontally and on the diameter of the containing vessel. It is known that for each gas-oxidant mixture there is a minimum... 

Fig. 44. Etch rate of polysilicon, oxide, and photoresist as a function of hydrogen addition to a CF4 discharge. Etch rate stops on non-oxide materials due to polymer build up at high % H - Oxide continues to etch due to polymer removal by the available oxygen. This yields high selectivity of etching oxide over silicon. After [220].

The present paper discusses the preparation and properties of high surface area silicon carbide and oxynitride with respect to possible application in catalysis. The synthetic work includes new routes to high surface area forms of these materials. Regarding properties, an important aspect is stability. This refers both to the stability of a pore system in a non-oxide material, on which there is very little information available, and to the stability of the surface composition in the case of the latter, oxidation to the oxide will be thermodynamically preferred in most cases. We report data on the textural stability of porous silicon carbide and on the surface stability of high surface area silicon oxynitrides. Some of the work reported in the present paper has been described at recent conferences (7,8) and in a communication (9). 

Furthermore, results obtained with respect to the thermal stability of the pore structure in porous silicon carbide and the stability towards air, hydrogen or steam of the surface of a silicon oxynitride powder indicate that the stability of high surface area non-oxidic materials can be promising with respect to potential application in catalysis. 

The CMC market is divided into two classes, oxide and non-oxide materials. Oxide composites consist of oxide fibers (e.g., alumina [AI2O3]), interfacial coatings, and matrices. If any one of these three components consists of a non-oxide material (e.g., silicon carbide [SiC]), the composite is classified as a non-oxide composite. These classes have different properties, different levels of development, and different potential applications. 

Because most development work has been done on non-oxide materials, particularly SiC fiber-reinforced SiC CMCs (SiC/SiC) with fiber interfacial coatings of either carbon or boron nitride, non-oxide CMCs are more advanced than oxide CMCs. Non-oxide CMCs have attractive high temperature properties, sueh as creep resistance and microstructural stability. They also have high thermal conductivity and low thermal expansion, leading to good thermal stress resistance. Therefore, non-oxide CMCs are attractive for thermally loaded components, such as combustor liners (see Figure 1-4), vanes, blades, and heat exchangers. 

Balanced research of oxide and non-oxide materials on their specific life-limiting characteristics appears to be necessary because neither class of materials can satisfy design and service life requirements for all of the anticipated applications. For example, SiC-based materials have the high thermal conductivities and low thermal expansion coefficients essential for some components, particularly in high performance turbines for which oxides are inadequate. Conversely, in some corrosive environments (e.g., hot gas filters in coal-fired power systems), oxides provide necessary corrosion resistance. 

The basic crystallographic data of the most important hard materials are listed in Table 1. Further access to crystallographic data can be gained through various compilations. The older literature has critically been evaluated in the Strukturberichte [1], the Structure Reports [2] and in the Landolt-Bornstein [3]. The non-oxidic materials are well covered in several editions of Pearson s Handbook [4-6]. The various structure types of these materials have been critically compiled by Parthe and coworkers [7]. Access to the more recent literature is best achieved through... 

ABSTRACT. The conventional approach to produce polymeric ceramic precursors of non-oxidic materials involves condensation reactions of reactive intermediates. In many cases these reactions lead to intractable products. An alternative approach was examined which could afford better control over the properties of the product. This involved the derivatization of preformed polymers of appropriate molecular weight and functionality. Polyethyleneimine, (CH2-CH2-NH)n was derivatized to introduce the -BH2, -BH2CN, and -BH2-CH2-NBH functionalities. These materials produced boron nitride upon pyrolysis and could be used to spin-coat a variety of substrates. 

The first CMCs to be developed consisted of three major components a ceramic matrix, fibers embedded in the matrix, and a tailored interface between the fiber and the matrix. Although these materials show damage tolerance and non-brittle behavior, the non-oxide materials that compose the CMCs are prone to oxidation, especially when matrix cracks are present. Lately, the development of an all-oxide CMC has captured the researchers attention. In these oxide/oxide composites, fracture toughness is achieved through crack deflection inside the matrix. A controlled level of matrix porosity will provide suitable conditions for crack deflection while inherently impeding oxidation during high temperature service. ... 

In this chapter, particular attention will be devoted to the study of the structure of sol-gel derived silica and modified silicates, at the molecular level, by IR absorption and reflection spectroscopies, as well as to microstructural aspects such as the elimination of residual porosity during thermal densification, which usually occurs together with a simultaneous elimination of residual OH species. Relevant results for other non-siUcate and non-oxide materials will also be reviewed. 

The IR spectra of sol-gel materials contain considerable information about their composition, structure and properties. Therefore, IR spectroscopy has been widely applied for silicate materials, but also for other oxides, as well as some non-oxide materials. 

Tlie plienomenon of half-metallicity has gained much interest in order to understand the unusual band structures in various classes of materials and their potential applications in future electronic devices. For example, zinc blend pnictides and chalcogenides e.g. CrAs) are another class of non-oxide materials (apart from Heuslers) in addition to the many oxide classes that are potentially half-metallic materials. Alkali metal doped rare earth oxomanganates, (REi- A MnOs), rutile-Cr02, spinel-Fe304 and Sr2peMo06 double perovskite oxide are examples of important half-metallic oxides. 

Figure 27.2 shows the photographs of sol-gel precursors and thin films prepared by CSD. This chapter presents a snapshot of the current status and key challenges in the field of electroceramic thin films processed by sol-gel. This chapter is mainly focused on metal oxide films, which are the most lucrative films prepared by CSD with the widest use in electroceramic devices. However, non-oxide materials have also been prepared by sol-gel and detailed overviews on them were reported by Kamiya [5,6], Fujihara [7], and Almeida and Xu [8]. 

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