The arrangement of ions in a crystal is greatly influenced by the ratio of radii of the ions. The limiting ratio for a cation to fit in an octahedral arrangement of anions is greater than 0.414 (i.e. r+/r- > 0.414). Only in such a situation a cation will be able to keep the six anions from touching each other. Smaller [...]
The following points highlight the three main methods for determination of crystal structure of materials. The methods are: 1. Laue Spot Method 2. Rotating Crystal Method 3. Powder Method. 1. Laue Spot Method: In this method, a single crystal specimen is held stationary in a beam of X-rays of continuous wavelength. The crystal selects out and diffracts the discrete values [...]
X-rays can be diffracted by crystals just in the same way as the visible light is diffracted by a diffraction grating; in other words, we can say that crystals can be used as diffraction gratings for the diffraction of X-rays. This important concept was first conceived by Von Laue in 1912, and subsequently tested by Freidrich and Knipping who demonstrated [...]
In this article we will discuss about:- 1. Miller Indices of Direction 2. Miller Indices of Planes 3. Miller-Bravais Indices 4. Important Features. Miller Indices of Direction: In a crystal, there exist directions and planes which contain a large concentration of atoms. Therefore, it is necessary to locate these direction and planes for crystal analysis and to use some conventions [...]
It is well known that ionic solids consist of positive and negative ions arranged in a manner so as to acquire minimum potential energy. This can be achieved by decreasing the cation anion distance to a minimum and reducing anion-anion repulsions. The structures which these solids adopt can be described in terms of the large anions/cations occupying one or the [...]
The following points highlight the three main defects occurs due to the imperfection in solids. 1. Point Defects: Those associated with one or two atomic positions. They are: (i) Vacancies. (ii) Self-interstitials (iii) Substitutional impurity (iv) Interstitial impurity Equilibrium, no. of vacancies are given as: Nu = Nexp (-Qv/kτ), Qv = energy required for vacancy formation, T = temperature Thus, [...]
In this article we will discuss about:- 1. Meaning of Fracture in Metals 2. Types of Fractured end in Ductile Failure 3. Creep Curve 4. Improving the Fatigue Life 5. Methods of Protection against Fracture 6. Ductile-Brittle Transition. Meaning of Fracture in Metals: Separation of a solid into two or more parts under application of load or stress is called [...]
In this article we will discuss about the physical and mechanical properties of engineering materials. Physical Properties of Engineering Materials: These properties concerned with such properties as melting, temperature, electrical conductivity, thermal conductivity, density, corrosion resistance, magnetic properties, etc. The more important of these properties will be considered as follows: 1. Density: Density is defined as mass per unit volume [...]
Testing of materials are necessary for many reasons. The tests are:- 1. Tensile Test 2. Compression Test 3. Ductility Testing 4. Impact Testing 5. Creep Testing 6. Hardness Testing 7. Non-Destructive Testing. 1. Tensile Test: The main principle of the tensile test is denotes the resistance of a material to a tensile load applied axially to a specimen. It is [...]
Here is a list of commonly used engineering materials: 1. Smart Materials (Or Intelligent Materials) 2. Shape Memory Alloys (SMA) 3. Functionally Graded Materials (FGMS) 4. Biomedical Materials. 1. Smart Materials (Or Intelligent Materials): These are magical materials which are suitable to our needs. These materials can sense, process, stimulate and actuate a response. Their functioning is somewhat similar to [...]