Preface

Nanocrystalline materials have been attracting much attention in the field of future science and technology. Indeed, the scientific interest in these materials in the powdered and bulk form is associated mainly with expectations of various size effects on their properties. Thus, the term "*nanocrystalline materials*" relates to the sizes of structural elements. The range of application of these materials is huge, such as more efficient catalysts, films, magnetic materials, protective coatings, and biological and biomaterials. Many compounds and elements, if made in the nanoscale, behave quite differently from how they would have in their conventional state, and these new physical and chemical properties give rise to a whole new field of scientific study.

The overall purpose of this book, "*Nanocrystalline Materials*", is to present selected advanced topics on nanocrystals, allowing the book to be a good resource for scholars and students of material science, nanotechnology and physical chemistry. The chapters for this book have been contributed by the most respected researchers in this area and give an overview of selected properties and applications of nanocrystalline materials. IntechOpen and myself as the editor hope that this book will aid current research and prove to be very useful to the scientific community. If so, this will be the nicest reward for us. Ultimately, I wish to thank all the authors for their contributions and I should like to acknowledge the sustained helpfulness and dedication of the publisher's staff, in particular of *Mr. Gordan Tot* by his insistence for this interesting project.

> **Behrooz Movahedi** Associate Professor, Department of Nanotechnology Engineering, Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan, Iran

**1**

Section 1

Introduction

Section 1 Introduction

**3**

**Chapter 1**

*Behrooz Movahedi*

**1. Introduction**

component.

reasons:

crystallites.

properties.

Introductory Chapter:

Nanocrystalline Materials

Nanocrystalline materials have been a hot research topic over the past 30 years.

It is recognizable that the nanocrystals are typically specified as anything, such as small grain polycrystalline materials, nanosynthesized surfaces, nanoparticles, and polymer micelles; each of them has varied usages, from drug delivery, to super capacitors, catalysts, and sensors. These materials are of interest for the following

1.The properties of nanocrystalline materials differ from the properties of single crystals and coarse-grained polycrystals and are amorphous with the same chemical composition. This deviation is strongly related to the reduced crystallites size as well as the large amount of grain boundaries between adjacent

2.The concept of nanocrystalline materials seems to authorize the alloying of components which are immiscible in the solid or molten state. These fabricated alloys could be good candidates for advanced and technologically marvelous

It is clearly seen that at a nanometric scale, the nanocrystalline materials contain a high grain boundary volume fraction; therefore grain boundaries and their interactions with crystal play a remarkable role in the different properties. It is important to point out that those nanocrystalline materials, as a new generation of advanced materials, have superior properties to conventional coarse-grained polycrystalline materials. They exhibit outstanding mechanical and physical properties such as high strength and hardness, low elastic modulus, improved ductility/toughness, excellent fatigue and wear resistance, increased diffusivity, higher electrical resistivity, reduced density, higher thermal expansion coefficient, enhanced specific

Nanocrystalline materials can be fabricated by gas condensation, plasma deposition, spray conversion technique, mechanical alloying, and some other methods.

heat, lower thermal conductivity, and better soft magnetic properties.

These materials abound in industry, bridging the gap between molecular and macroscale objects. Nanocrystalline materials are ultrafine-grained single-phase or multiphase polycrystals with grain sizes in the range of 1–100 nm, as depicted in **Figure 1**, the transmission electron microscopy (TEM) image of Fe-based nanocrystalline coating. In fact, the extremely small sizes and a large volume fraction of the atoms are located at the grain boundaries; on the other hand, these materials consist of about 50 vol.% crystalline component and 50 vol.% interfacial
