Fine powder and new refractory materials

Author: Li Xiaoming
Publisher:
Publish Date: 2002-03-01
Features:
Introduction to the Book
This book is a compilation of the author's recent research achievements in the fields of micropowders and novel refractory materials. It describes the properties, types, and bonding mechanisms of various micropowders used in refractory materials, and introduces 16 new refractory materials studied. The book is intended for reference by technical personnel engaged in refractory materials and students and teachers of relevant disciplines in universities and colleges.
Excerpt:
Chapter 1: Introduction
Section 1. Industrial Robots and Their Development
1. Industrial Robots and Their Manipulators
Due to the inclusion of the word "human" in the term "robot," coupled with the promotion of science fiction and film, people often imagine robots as electromechanical devices resembling humans. However, this is not the case. Robots, especially industrial robots, bear no resemblance to human appearance. In national standards, industrial robots are defined as: "A machine tool capable of automatic positioning control, programmable, multi-functional, and multi-degree-of-freedom. It can transport materials, parts, or hold tools to perform various tasks." The mechanical entity (referred to as a manipulator or actuator) on which robots rely to perform various tasks is defined as: "A mechanical device with motion functions similar to human arms, capable of grasping objects or performing other operations in space." It is clear that an industrial robot is an electromechanical system, and the manipulator (actuator) is its executive mechanism, which is closely related to electronic components. Its flexibility and dynamic performance directly affect the quality of the robot system's work. The purpose of this book is to elaborate on the methods of analyzing and designing manipulators, with the hope of benefiting professionals engaged in the design and application of industrial robots.
2. The Development and Generations of Industrial Robots
In 1954, an American (George C. Devol) proposed a technical plan for industrial robots, which was later patented. In 1960, experimental prototypes of industrial robots were introduced. In 1961, a manipulator named "Unimate" (as shown in Figure 1.1) was introduced for die-casting production. At the same time, the American AMF company also introduced a numerically controlled automatic general electromechanical device, marketed as "Versatran," and categorized it into three sizes: large, medium, and small. While 0.1–10 μm is referred to as sub-ultrafine particles.
The author tends to agree with the classification method in the book "Ultrafine Particles," which categorizes particles as follows:
- Microparticles (Micropowders): Particle size 10–103 μm
- Ultrafine particles (Ultrafine powders): Particle size 0.1–10 μm
- Sub-ultrafine particles: Particle size 1–102 nm
- Ultra-submicroparticles: Particle size <1 nm
This classification not only clearly defines the particle size limits but also aligns closely with the characteristics and applications of these micropowders, making it relatively scientific. Since the commonly used fine powder sizes in ceramics and refractory materials fall within the aforementioned powder size range, and the commonly used ultrafine powders that distinctly exhibit their characteristics are also within the aforementioned microparticle size range, this book uniformly refers to what was previously called "ultrafine powders" as "micropowders." Currently, most of the ultrafine and sub-ultrafine powders used in ceramics and refractory materials fall within the 0.1–10 μm range. Moreover, referring to commonly used fine powders as "powders" and ultrafine powders as "micropowders" is also more in line with the conventions of the refractory industry.
2. Properties of Micropowders
What we are discussing here are not the properties of all ultrafine particles but those particularly useful for ceramics and refractory materials within the particle size range of microparticles (micropowders). The theoretical basis for the properties exhibited by micropowders is the theory of surface phenomena. Taking solids as an example, when they are broken, their surface area increases rapidly. Table 1–1 shows the data on the total surface area and specific surface area (dispersion degree) of cubic particles when they are divided. Table 1–2 shows the increase in the specific surface area of SiO2 particles commonly used in the refractory and ceramic industries when they are broken down to 1 nm. From the data in both tables, it can be clearly seen that as particle size decreases, the increase in surface area is significant. The interaction forces between surface particles and internal particles under the influence of surrounding particles (atoms, ions, or molecules) are different. As shown in Figure 1–1, under unbalanced forces, surface particles will deviate from their equilibrium positions. Additionally, the tendency of corner particles to reduce the surface area further contributes to the deviation of particle positions. Moreover, the mechanical crushing effect continues to damage the surface after reaching a certain particle size. All these factors result in surface particles having higher energy (surface energy) and greater mobility compared to internal particles. This allows micropowders with high specific surface area to exhibit greater reactivity in reactions and sintering processes that must be completed through particle migration, thereby promoting the completion of these processes.