Solid-State Chemistry with Nonmetal Nitrides

Among the nonmetal nitrides, the polymeric binary compounds BN and Si3N4are of particular interest for the development of materials for high-performance applications. The outstanding features of both substances are their thermal, mechanical, and chemical stability, coupled with their low density. Because of their extremely low reactivity, boron and silicon nitride are hardly ever used as starting materials for the preparation of ternary nitrides, but are used primarily in the manufacture of crucibles or other vessels or as insulation materials. The chemistry of ternary and higher nonmetal nitrides that contain electropositive elements and are thus analogous with the oxo compounds such as borates, silicates, phosphates, or sulfates was neglected for many years. Starting from the recent successful preparation of pure P3N5, a further binary nonmetal nitride which shows similarities with Si3N4 with regard to both its structure and properties, this review deals systematically with the solid-state chemistry of ternary and higher phosphorus(V) nitrides and the relationship between the various types of structure found in this class of substance and the resulting properties and possible applications. From the point of view of preparative solid-state chemistry the syntheses, structures, and properties of the binary nonmetal nitrides BN, Si3N4, and P3N5 will be compared and contrasted. The chemistry of the phosphorus(V) nitrides leads us to expect that other nonmetals such as boron, silicon, sulfur, and carbon will also participate in a rich nitride chemistry, as initial reports indeed indicate

Nanocomposites for Machining Tools

Machining tools are used in many areas of production. To a considerable extent, the performance characteristics of the tools determine the quality and cost of obtained products. The main materials used for producing machining tools are steel, cemented carbides, ceramics and superhard materials. A promising way to improve the performance characteristics of these materials is to design new nanocomposites based on them. The application of micromechanical modeling during the elaboration of composite materials for machining tools can reduce the financial and time costs for development of new tools, with enhanced performance. This article reviews the main groups of nanocomposites for machining tools and their performance

Investigation of resin systems for improved ablative materials Final report, 19 Jun. 1964 - 31 Jul. 1965

Resin systems investigated for improving ablative materials for use with fluorine-containing liquid propellant system

Exploring 2D Materials by High Pressure Synthesis: hBN, Mg-hBN, b-P, b-AsP, and GeAs

In materials science, selecting the right synthesis technique for specific compounds is one of the most important steps. High-pressure conditions have a significant effect on the crystal growth processes, leading to the creation of unique structures and properties that usually are not possible under normal conditions. The prime objective of this article is to illustrate the benefits of using high-pressure, high-temperature (HPHT) technique when developing two-dimensional (2D) materials. We could successfully grow bulk single crystals of hexagonal boron nitride (hBN) and magnesium doped hexagonal boron nitride (Mg-hBN) from Mg-B-N solvent. Further exploration of the Mg-B-N system could lead to the crystallization of isotopically 10B and 11B enriched hBN crystals, and other doped variants of it. Black phosphorus (b-P) and black phosphorus doped with arsenic (b-AsP) were obtained by directly converting its elements into melt and subsequently crystallizing them under HPHT. Germanium arsenide (GeAs) bulk single crystals were also obtained from the melt at a pressure of 1 GPa. Upon crystallization, all these compounds exhibit the anticipated layered structures, which makes them easy to exfoliate into 2D flakes, thus providing opportunities to modify their electrical behavior and create new useful devices

Boron Nitride Nanotube Reinforced Titanium Composite with Controlled Interfacial Reactions by Spark Plasma Sintering

In this study, Boron Nitride Nanotube (BNNT) reinforced Titanium matrix composites are synthesized by Spark Plasma Sintering. Two main challenges directly affecting the mechanical performance of BNNT-metal matrix composites are addressed:(i) Homogenous dispersion of high surface energy BNNTs, and (ii) Controlling interfacial reactions at the metal/nanotube interface. High-energy ultrasonication induced dispersion resulted in the functionalization of BNNTs by -OH radicals proving its suitability over surfactant assisted dispersion routes. The sintering of Ti (99% relative density) was achieved at 50% less processing temperature than those used in conventional sintering to minimize interfacial reactions when reinforced with BNNTs. The reduction of temperatures in addition to the reduction (by 91%) in processing times was shown to control reaction phases. Bulk compressive yield strengths of Ti-BNNT sintered at low (750oC) and high (950oC) temperatures were improved by 21% and 50% respectively, as compared to Ti alloy without reinforcement. Twin boundaries, pinning of dislocations by BNNTs, and crack bridging were strengthening mechanisms identified in the composites

Self-propagating metathesis preparations of inorganic materials.

The potential of self-propagating reactions, with reagents such as lithium nitride, calcium nitride, sodium arsenide and magnesium silicide, in the production of inorganic materials has been investigated. Reactions were performed with anhydrous d-block and rare earth metal chlorides and can be described by the following generic equation where M is a Group 3-12 metal, Alk is a Group 1 or 2 element and E is Si, N, P, As, Sb, Bi or O. MClm + xAlknE → yMαE + xAlkClβ + zEγ Crude products were obtained normally as fused masses of material consisting of the products coated in the alkali chloride co-products. Grinding followed by washing with an appropriate solvent yielded the pure products with low levels of contamination from the other elements present in the reaction flux. The phases produced include rare earth and transition metal nitrides, metals and alloys, d-block phosphides, arsenides and antimonides, metal silicides and d-block oxides. The products were variously characterised by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray analysis, magnetic susceptability, X-ray photoelectron spectroscopy, microanalysisand solid state (magic angle spinning) nuclear magnetic resonance spectroscopy. Thermocouple experiments, differential scanning calorimetry, photography and constant pressure calculations were used to examine the thermal aspects and timescales of reactions. Dilution with inert solids was used to reduce voracity of reactions and to control crystallinity of products. Liquid chlorides (TiCl4 and VCl4) were successfully employed to make high quality ternary phases such as Ti0.5V0.5E (E= N, P, As). Such reactions can progress via ionic or elemental mechanisms and evidence for either of these was gathered. Examples were found for both mechanisms which supported that the process was occurring. These conclusions were based on end- product analysis since the reaction conditions and timescales precluded the use of other techniques

Single Crystal Growth Tricks and Treats

Single crystal growth is a widely explored method of synthesizing materials in the solid state. The last few decades have seen significant improvements in the techniques used to synthesize single crystals, but there has been comparatively little discussion on ways to disseminate this knowledge. We aim to change that. Here we describe the principles of known single crystal growth techniques as well as lesser-known variations that have assisted in the optimization of defect control in known materials. We offer a perspective on how to think about these synthesis methods in a grand scheme. We consider the temperature interdependence with the reaction time as well as ways to carry out synthesis to scale up and address some outstanding synthesis challenges. We hope our descriptions will aid in technological advancements as well as further developments to gain even better control over synthesis

Additives for Abrasive Materials

The overarching objective of the chapter is to acquaint the readers with the topic associated with the production of abrasive tools and presentation of the most significant research results regarding the determination of the most important functional properties of selected additives (described in the literature and established on the basis of authors’ own scientific experiences). The studies regarding various additives, which were characterized in detail in the literature, were mainly based on thorough physicochemical and microstructural analysis as well as the determination of basic strength and thermos-mechanic parameters. The attempt to implement alternative cross-linking agents, which would result in the limited release of volatile organic compounds, is also of great importance in terms of production of environmentally friendly final products. A subsequent aim is to attract the attention of a wide range of readers and popularize the topic associated with conventional abrasive materials and next-generation abrasive compositions