Question

What characteristics do influence on the properties of the solids? why ....

1)  Elemental composition

2) Phase composition

3) Defects density

4) Microstructure

Answer 1

A. ELEMENTAL COMPOSITION:

An elemental composition expresses which and how many atoms constitute a particular chemical compound. Although each elemental composition has an unique molecular weight (mass), a molecular weight does not have a unique elemental composition. This situation is complicated by the instrumental precision, and the accuracy of the mass measurements limits this viability.

Elemental composition can change the properties of solids as there are some experiments which bears testimony to the proof :

Conversion of Solid Wastes to Fuels and Chemicals Through Pyrolysis

Elemental compositions of carbon, hydrogen, nitrogen, and sulfur contents are determined from ultimate analysis at temperatures in the range of 900–1050°C. Each elemental quantification (C, H, and N) is determined from the corresponding gases of CO₂, H₂O, and NO_x after oxidation and reduction reactions of samples. The quantified elements are used to determine the quality of bio-oil and biochar and the stoichiometric ratio for a complete combustion.

2 PHASE COMPOSITION: Experimental aspect:

Plasma electrolytic oxidation treatment of magnesium alloys:

The phase composition of the PEO coating is mainly influenced by the electrolyte composition, and the energy intensity during the discharge is also considered to play a role. Coatings produced on an AZ91D alloy using an aluminate–fluoride electrolyte were found to be constituted with MgAl₂O₄ and Al₂Mg. A large number of research publications on PEO using silicate-based electrolytes have shown the formation of Mg₂SiO₄ as the major phase

PHASE COMPOSITION DIAGRAM:
		A plot of temperature versus composition of a solid solution mineral. Unlike a phase diagram, there is a region where the material will exist in a partially solid and a partially liquid phase. The line dividing this region and the solid is known as the solidus line; that separating the liquid region is the liquidus line. When a material with the composition at A is cooled at equilibrium, the solid which precipitates will have the composition given by the intersection of the horizontal temperature line AB and the solidus line, point C. As the temperature slowly decreases, the solid remains in equilibrium with the melt. This means that the composition of the solid changes to that lying on the solidus line at a given temperature (C shifts to the right). Therefore, when the solid reaches the composition of the original (directly below A) the solid and liquids share the same composition, so all subsequent crystals will have the original composition of the melt. The analogous situation holds for melting, with the composition of the solid shifting to the left until it lies above point B, at which point melt and solid share the same composition. All subsequent melting will therefore have the original composition of the solid.

3. DEFECTS DENSITY:

Defect Density is the number of confirmed defects detected in a component during a defined period of development or operation, divided by the size of the component. It is one such process that enables one to decide if a piece of component is ready to be released.

Defect density do not change the property of solids, it only changes the size of the solid.

4.MICROSTRUCTURE: This characteristic can also change the property of solids

Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymers, ceramics or composites) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour or wear resistance. These properties in turn govern the application of these materials in industrial practice.

The behavior of many materials is governed by microscopic structures invisible to the naked eye. Nature often uses a complex hierarchy of scales to obtain materials with high strength and small weight, e.g. finely structured surfaces as the skin of fishes can reduce the resistance to flow. Also man-made materials exhibit often a complex internal structure: light materials can be strengthened through a network of strong fibers providing high traction resistance with small weight; porous materials have also a very small weight, and their complex pore network gives good shock-absorption properties. Also the behavior of apparently homogeneous materials as steel is strongly modified by an internal structure of microscopically small grains.

At high temperature only the cubic crystalline structure is possible, when the temperature is lowered under the critical one, one side of the cube is stretched, and the other two contracted. This way three different parallelepipedal structures are originated.

Figure 1 Cubic and tetragonal crystal lattices

Figure 2 From a single cubic phase three different tetragonal phases can arise

The existence of many different possible microscopic mixtures of these three basic structures is what allows one to easily deform the material at low temperature (Figure 3). However, rising again the temperature there is only a single cubic structure left, hence the material comes back to a fixed, prescribed shape under heating (Figure 4).

Figure 3 Depending on the different mixing of the various phases the crystal can be elongated or compressed

Figure 4 Idealized representation of the memory-shape effect