# Material science 9 & 10

• A  solid solution is created when the atoms of one component are added to the lattice of the host material.
• there are two types of solid solutions:
•   substitutional solid solution: atoms replace atoms of the host lattice
•   interstitial solid solution: atoms occupy interstitial sites of the host lattice • formation of a substitutional solid solution if alloying elements show similar atomic size, electronegativity and valency as well as same crystal structure, e.g. copper-nickel
• formation of an interstitial solid solution if interstitial atoms are
substantially smaller than atoms of host lattice, e.g. iron-carbon

A cooling curve is a line graph that represents the change of phase of matter, typically from a gas to a solid or a liquid to a solid. The independent variable is time and the dependent variable is temperature. Below is an example of a cooling curve used in castings. Wikipedia

The independent variable (X-axis) is time and the dependent variable (Y-axis) is temperature. Below is an example of a cooling curve used in castings. The initial point of the graph is the starting temperature of the matter, here noted as the “pouring temperature”. When the phase change occurs there is a “thermal arrest”, that is the temperature stays constant. This is because the matter has more internal energy as a liquid or gas than in the state that it is cooling to. The amount of energy required for a phase change is known as latent heat. The “cooling rate” is the slope of the cooling curve at any point.

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Phase diagrams represent the relationship between temperature and the composition of phases present at equilibrium.

An isomorphous system is one in which the solid has the same structure for all compositions. The phase diagram shown is the diagram for Cu-Ni, which is an isomorphous alloy system. Isomorphous systems are not common, although there are number of isomorphous systems used. The copper-nickel system is an example.

In isomorphous systems the two components have unlimited solubility, which means that they are like water and alcohol when they mix – they always form a solid solution regardless of the ratio of atoms/molecules.    Complete solubility of components in solid state (solid solution)