Alloys
Water is a clear colorless liquid. So is methanol. If one were to take a quantity of methanol and pour it into some water, the result is also a clear colorless liquid. But this one is something new; a solution, an intimate physical combination of both materials. This simple illustration demonstrates some characteristic properties of solutions. To form a solution, the combined materials must be compatible and able to mix completely with each other. The component molecules that make up a solution become intimately mixed with each other in an even and consistent manner. In a proper solution there are no regions in which the concentration of any component is significantly different from any other region. To all intents and purposes, a solution looks and acts very much like a single material. Solutions are not restricted to the liquid phase. They can also be gaseous or solid. But whether solid, liquid, or gas in physical state, the basic defining properties of a solution remain the same.
Solutions made from combinations of different metals are called 'alloys'. One metal is said to alloyed with another, meaning only that the two (or more) metals have been melted and blended together in the manner of a solution. When the molten solution solidifies, the properties of the solution are 'trapped' in the solid form. As one might expect, there is an infinite range of possible combinations of the metals in any particular alloy. Brass, for example, is an alloy of copper and zinc. The possible combinations can range from pure copper (100% Cu and 0% Zn) to pure zinc (0% Cu and 100% Zn) in a continuous gradient. Any particular combination produces a brass having fairly well-defined properties of hardness, ductility, malleability, corrosion resistance, color, etc.
One property in particular is most controllable in alloys: the melting point. Each component metal of an alloy has its own melting point, but the alloy itself will have a lower melting point than any of its component metals, and melting will generally occur over a span of several degrees. Alloys can then be 'designed' to produce a material that better conforms to the conditions under which it will be used. An interesting feature of alloys is the lack of certain combinations, such as alloys of aluminum and lead. These, and others, are unknown as bulk alloys because the component metals act like 'oil and vinegar' and do not mix with each other to produce a proper alloy. In molten form, lead and aluminum separate spontaneously. Any solid alloys of these two metals may be made only in very small quantities by depositing them from the gas phase simultaneously.
