Metals - a substance having a crystal structure.When heated, they are capable of melt, i.e. into a fluid state.Some of them have a low melting point: they can be melted by placing an ordinary spoon and holding a candle flame.This lead and tin.Other possible to melt only in special furnaces.Have a high melting point of copper and iron.To lower it into the metal additive is introduced.The obtained alloys (steel, bronze, cast iron, brass) having a melting point lower than the parent metal.
On what does the melting point of the metal?All of them have certain characteristics - heat and thermal conductivity of metals.Heat capacity is the ability to absorb heat when heated.Its numerical indicator - the specific heat.Beneath it is a quantity of energy which is able to absorb a unit mass of the metal, heated by 1 ° C.From this figure depends on the fuel consumption in heating a metal workpiece to a desired temperature.The specific heat of most metals is in the range of 300-400 J / (kg * K), metal alloys - 100-2000 J / (kg * K).
thermal conductivity of metals - is the transfer of heat from the hotter to the colder particles of Fourier's law in their macroscopic immobility.It depends on the structure of the material, its chemical composition and type of the interatomic bond.In metals, the heat transfer is carried by electrons, other solid materials - phonons.The thermal conductivity of metal is higher, the more perfect crystalline structure they have.The more metal impurities is, the more distorted crystal lattice, and the lower the thermal conductivity.Doping introduces such distortions in the structure of metals and lower thermal conductivity with respect to the base metal.
have good thermal conductivity of all metals, but in some higher than others.Example of such metals - gold, copper and silver.Lower thermal conductivity - from tin, aluminum and iron.The increased thermal conductivity of metals is an advantage or a disadvantage, depending on the scope of their use.For example, it requires a metal bowl for quick heating of food.At the same time, the use of metals with high thermal conductivity for the manufacture of cookware handle complicates its use - handles heated too quickly, and it is impossible to touch them.So here are used insulating materials.
Another characteristic of metal that affects its properties - thermal expansion.It appears as an increase in volume of the metal when it is heated and reduced - by cooling.This phenomenon is required to be taken into account in the manufacture of metal products.For example, cover pots do patch have also dummies gap is provided between the cover and the housing, so that when heated cover not jammed.
For each metal calculated the coefficient of thermal expansion.It is determined by heating at 1 ° C test sample having a length of 1 m. The biggest factor are lead, zinc, tin.Less he's copper and silver.Even lower - iron and gold.
chemical properties metals are divided into several groups.There active metals (e.g., potassium or sodium) capable of instantaneously reacting with air or water.Six of the most active metal, is the first group of the periodic table are called alkaline.They have little melting point and so soft that they can be cut with a knife.Combining with water, they form alkaline solutions, hence their name.
second group consists of alkaline earth metals - calcium, magnesium and so forth. They are part of many minerals, more solid and refractory.Examples of these metals, third and fourth groups could serve as lead and aluminum.It is fairly soft metals and are often used in the alloys.Transition metals (iron, chromium, nickel, copper, gold, silver) are less active, a forging, and often used in industrial applications as alloys.
position of each metal in the range of activity characterized by its ability to react.The more active the metal, the easier it picks up oxygen.They are very difficult to separate from compounds, while less active metal species can be found in its pure form.The most active of them - potassium and sodium - Keep kerosene out of it they immediately oxidized.Among metals used in the industry, copper is the least active.From tanks and make it hot water pipes and electric wires.
