Hello everyone. In the previous two modules, we discussed about Nano-structuring and Defect Engineering as a Key Technologies to develop Novel Inorganic materials with enhanced chemical and physical properties. In this module, we are going to talk about the Ceramic Synthesis Technology as a fundamental for developing the advance function of ceramics. In this lecture, we will talk about comminution technology. Comminution is a process to produce a small particles by mechanical forces and is a part of the typical first stage in extracting minerals from ores. And the process to prepare powders used in traditional ceramics production from natural raw materials. Normally, the comminution process involves crushing and milling. The first stage of comminution is crushing. Crushing is a crude process used in reduction of larger particles. And particles obtained after crushing process are normally in the range of millimeters. The examples of crushing machines include jaw crusher, rotary crusher and roll crusher as shown here. And in jaw crusher, we can obtain the reduced size of particles by placing the ores into compression. Milling is a process to further reduce the particles after crushing. And the process of grinding grain of other materials in a mill. So it includes breaking down, separating, sizing, or classifying aggregate material. So, particles obtained after milling are normally in the range of micrometers. The examples of milling machines includes hammer mill, ball mill, vibration mill, attrition mill and jet mill. For hammer mill, the major components includes a delivery device, a rotor, swinging hammers and a perforated screen. So particles produced have the spherical shape with a polished surface. The one main disadvantage of hammer mill is non-uniformity in particle size to distribution. For a conventional ball mill, the major component includes grinding balls, a cylindrical container, and the rolling machine, as shown here. The rotation of cylinder with grinding balls causes the balls to fall back onto the ceramic particles. The speed of the rotation determines efficiency of the milling process. And high-speed milling suggested that container acts as a centrifuge. So it is very important to determine the optimum speed required to take the grinding balls to the apex of a revolution. The milling. The grinding of solid matters occurs under exposure of mechanical forces, trench the structure by overcoming the interior bonding forces. After the grinding, the state of the solid is changed including the grain size distribution and the grain shape. So grinding in ball mill can reduce the size of a particles. This can provide us a wide variety of physical, mechanical, chemical characteristics of materials. And beside the particle size reduction, the ball milling can be used for mixing, blending and dispersing, amorphization of a materials, and mechanical alloying. Ball milling device usually consists of a cylindrical vessel mounted on an appropriate basis which allows rotation of the vessel around the center axis. The ball milling steps includes the charged with the starting material and the grinding media, it is ball. And the conditions such as dry/wet, atmosphere, the temperature during the milling process, can be controlled. And then, milling is the rotation as a result of transfer of kinetic energy. And we can use grinding media-it is ball-which is composed of the metals, ceramics, sometimes polymers and we can also use the cylpebs, it is cylindrical bodies. And widely use the ceramic balls is stabilized the zirconia. As shown in here, you can find the slight deformed structure in the pure zirconia. The pure zirconia has monoclinic structure at room temperature. So as you know, the small size of cationic radius, the ionic radius of the zirconia makes this like instant stability of a lattice structure. So, if we dropped the cesium, while magnesium and zirconium side, we can increase the cationic radius and can obtain the composite-like material with Cubic Matrix and Tetragonal precipitates. If the crack propagation energy is introduced to into this material. The tetragonal phase can use this like energy as a transformation energy from tetragonal to monoclinic. So this is a well-known mechanism of the hardening in the zirconia. Another type of stabilized zirconia is Tetragonal and Cubic zirconia. As shown here, the pure zirconia has this like monoclinic structure at room temperature. And by dropping of yttria while magnesia, we can increase the cationic radius of zirconia and then obtain the more symmetric lattice such as Tetragonal and the Cubic. Let's think about the factors that controlling the particle size during the milling process. The characteristic of the material charged in the mill include mass, volume, hardness, density and size distribution of the charge. And another important factor is characteristics of grinding media balls. So, the mass, density of balls and ball size distribution are very important. And another important factor is speed of rotation of the mill. And slurry density, in case of wet grinding operation, is important. The basic fragmentation mechanism during the ball milling process include of abrasion, cleavage, and fracture. The first, abrasion, can be occurred when local low intensity stresses are applied. So, fine particles taken from the surface of the mother particle. The second stage is cleavage. Which can be occurred when slow and relatively intense stresses are applied. So, fragments of side 50%-80% of the size of the initial particle. And the final stage of milling is fracture. Which is the result of rapid applications of intense stresses. Impact. So, fragments of small size with the relatively wide particle size distribution can be obtained after milling. In this lecture, we are talking about the several comminution techniques including some basic building technology. So, in the next, we are going to talk about Advanced Milling technology. Thank you.
