Answer:
Explanation: All real solids are impure. A very high purity material, say 99.9999% pure. Impurities are often added to materials to improve the properties. For instance, carbon added in small amounts to iron makes steel, which is stronger than iron. Boron impurities added to silicon drastically change its electrical properties.
The properties of materials are profoundly influenced by the presence of imperfections.
TYPES OF IMPURITIES
1. Point defects
• Vacancy atoms (vacant atomic sites in a structure causing a distortion of planes). They are common, especially at high temperatures when atoms are frequently and randomly change their positions leaving behind empty lattice sites. In most cases diffusion (mass transport by atomic motion) can only occur because of vacancies.
• Self-Interstitial atoms ("extra" atoms positioned between atomic sites causing a distortion of planes) A self interstitial atom is an extra atom that has crowded its way into an interstitial void in the crystal structure. Self interstitial atoms occur only in low concentrations in metals because they distort and highly stress the tightly packed lattice structure.
2. Impurities:
- Substitutional (mpurity atom in lattice). Substitutional impurity atoms are usually close in size (within approximately 15%) to the bulk atom. An example of substitutional impurity atoms is the zinc atoms in brass. In brass, zinc atoms with a radius of 0.133 nm have replaced some of the copper atoms, which have a radius of 0.128 nm.
- Interstitial atoms (impurity atom not in regular lattice sit) . An example of interstitial impurity atoms is the carbon atoms that are added to iron to make steel. Carbon atoms, with a radius of 0.071 nm, fit nicely in the open spaces between the larger (0.124 nm) iron atoms.
3.
Line defects
• Dislocations
4. Area defects
• Grain Boundaries
Answer:
The effective overall heat transfer coefficient for the combination,
Explanation:
According to the question, the total area includes the areas of the wall, window and door.
Total area, A = 100 * 10 = 1000 ft²
Area of the window,
Area of the door,
Area of the wall,
<u>Heat transfer coefficients:</u>
For wall,
For window,
For door,
To get the overall heat - transfer coefficient for the combination:
Answer:
Answer is D
Explanation:
a and b have ignorance so we cancel them ,c has no knowledge so it's wrong and the remaining is D so D I the correct answer
Answer:Mechanical Engineers
Explanation: Mechanical engineering is an engineering branch that combines engineering physics and mathematics principles with materials science to design, analyze, manufacture, and maintain mechanical systems. It is one of the oldest and broadest of the engineering branches.
Explanation:
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