Preface

**Section 6 The Particle Encapsulation Process 83**

Chapter 6 **The Particle Encapsulation Process 85** Jose Ignacio Huertas

Chapter 7 **Conclusions and Recommendations 111**

Jose Ignacio Huertas

Jose Ignacio Huertas

**Section 7 Conclusions 109**

**VI** Contents

**Section 8 Appendix 121**

Chapter 8 **Appendices 123**

*Nanophase materials* also referred to as nanostructured, nanocrystalline, or nanometer-sized crystalline solids, are single-phase or multiphase polycrystals, with dimensions of the order of 1–100 nm. Compared to conventional materials, nanophase materials possess unique ad‐ vantages with respect to properties and processing. As grain size decreases down to the nanometer-size range, nanophase metals generally get stronger and harder, while nano‐ phase ceramics show ductility, even superplasticity, at lower temperatures than convention‐ al brittle ceramics. For example, 1000% increase in fracture stress, 2000% increase in magnetic susceptibility, 25% decrease in density, and 165% improvement in critical tempera‐ ture for superconductivity have been observed in nanophase metals.

The high-performance properties exhibited by nanophase materials have important implica‐ tions for industry. For example, several tool companies are expected to introduce stronger, tougher, long-lasting cutting tools, drill bits, and wear parts composed of ultrafine grain co‐ balt/tungsten carbide composites. Some nanocomposites exhibit an unusual magnetic be‐ havior called "giant magnetoresistance," which is being considered for read/write information in storage devices and to make improved magnetoresistive sensors. Another application under consideration is solid-state magnetic refrigerators based on the mega calo‐ ric effect by which heat is reversibly absorbed and discharged when small ferromagnetic particles are aligned by magnetic fields. In addition, unusual magneto-optical characteristics of nanostructured iron oxide are expected to be applicable for high definition color copiers.

This book describes a novel method for the production of high purity, unagglomerated nano-particulates of tungsten (W) and tungsten titanium alloys (W-Ti) by flame synthesis. These materials possess unique properties that make them desirable for advanced applica‐ tions.

W-Ti nano-sized alloys have a combination of high strength (800–1000 MPa), high ductility (10–30%), good e1ectrical and thermal conductivity, corrosion resistance, and excellent machinability. Current applications for W and W-Ti inc1ude counterbalances in military air‐ craft, radiation shields, lighting components, ignition electrode materials, catalysts in the chemical industry, alloying elements for high speed steels, sputter targets in VLSI chip tech‐ nology, and a variety of sport related parts

> **Dr. Jose Ignacio Huertas** Tecnológico de Monterrey, Mexico

**Section 1**
