Glass Fiber   Introduction   Glass fiber was invented by Russell Games Slayter in thermal building insulation. There are many different compositions available but usually glass fibers are silica based (~50-60%) and a host of oxide(iron,aluminium,etc.) is also present in the fiber. It is cheap compared to other fibers and can be achieved in a variety of forms.   Production   Glass fiber is made by requiring raw materials melting in a hopper and transferring into molten glass. Raw materials are added into the hopper through batch mixing. After that some addition of other oxides are done and then the mixture is melted in the furnace.   After achieving molten glass, it is passed through the electrically heated platinum bushings or crucibles to achieve fibers of required diameters. Usually there are 200 holes in the crucibles. Outcome after molten glass is passed through crucibles is wounded on a drum. The schematic of this production is shown in Fig.(1).     F

  CRYSTAL DEFECTS (IMPERFECTIONS) INTRODUCTION : Most Materials When solidified consist of many crystals and grains. Single crystals can be manufactured by withdrawing a crystal fragment under carefully controlled conditions just above freezing point. In case if single crystal approach a nearly perfect lattice structure it is possible to calculate theoretical strength of a metal by the force required to separate bonds between adjoining atoms. But due to defects in crystals ,   This theoretical value of strength   obtained from single crystal   would be 1000 times smaller than original crystal structure. Hence it is important to study the defects in crystals to know how they affect properties of materials   TYPES OF DEFECTS Defect in a crystal can be defined as a deviation from its ideal structure. Defects in crystals can be broadly classified into 3 types based on their dimensionality ·       Zero dimensional defects or Point defects ·       One dimensional defects

  Leaching and its kinetics What is Leaching?  ➢ Also known as liquid-solid extraction.  ➢ Two phases are in intimate contact and the solute or solutes can diffuse from the solid to the liquid phase.  ➢ The process of extracting a substance from a solid material that has come into contact with liquid.  ➢ The liquid that enters will separate the components originally in the solid.  Examples of Leaching: 1) Extracting tea from tea leaves. 2) Production of vegetable oil using hexane. 3) Copper salt leaching from copper ores. 4) Production of nickel from ore.  Kinetics of Leaching:   The above figure shows the concentration profile when a mineral surface dissolves in a leaching medium. Subscripts  S and B refer to interface and bulk respectively. The situation is simple for complete dissolution.   However when a mineral decomposes, and dissolves only partially, then a new solid residue appears. Leaching would continue if this new phase is porous. This situation is shown in figure 4.13. Sub

  BORON FIBER   Introduction Normally boron is a brittle material. Weintraub was the one who obtained the first Boron fiber in 1911 by the reduction of boron halide with hydrogen   on a hot wire (substrate). Boron fibers were developed after 1960s to increase the strength and stiffness of composite by reinforcement. Fabrication Ø Boron fibers are produced by CVD on a substrate by following two methods.                       1.     Thermal reduction of boron halide o   Low temperature. o   Carbon coated glass fiber used as a substrate. o   Weak and less dense boron fiber   is produced by this method because of gas entrapment. 2.     Reduction of Boron halide by hydrogen o   High temperature. o   Tungsten wire (12micron) used as a substrate which has a high density and melting point. o   Uniform quality of Boron fiber is the result of this method. Reaction : 2BX 3 + 2H 2 ------> 2B + 6HX Where X =   Cl, Br, I, mostly Cl. In the above reaction