Topic 1 Molecules and Atoms

Topic 1

Metal Materials

1. Several important metals

When it comes to metal materials, you should not feel unfamiliar. Look around your home for everyday objects such as pots, pots, knives, hoes, faucets, etc. Most of them are made of metal materials. Metallic materials include pure metals and their alloys. Human beings entered the Bronze Age from the Stone Age, and then entered the Iron Age, which is marked by the use of metal materials. Up to now, copper and iron have been widely used as metal materials.

The utilization of aluminum is much later than that of copper and iron, that is only more than 100 years ago. Aluminum has excellent properties such as low density and corrosion resistance. Now, the world's annual output of aluminum has surpassed that of copper, behind iron.

You have a lot of life experience, for example, you know that iron pots, aluminum pots and copper hot pots can be used for cooking, cooking and shabu-shabu, and that iron wires, aluminum wires and copper wires can conduct electricity and can be bent, etc. In fact, you have accumulated a lot of perceptual knowledge about metals. Different from non-metals such as oxygen and hydrogen, metals have some physical properties and uses .

In addition to some common physical properties, metals also have their own characteristics. For example, most metals such as iron and aluminum are silver-white, but copper is purple-red and gold is yellow; at normal temperature, most metals such as iron, aluminum and copper are solid, but mercury in a thermometer is liquid ...the electrical conductivity, thermal conductivity, density, melting point, hardness and other physical properties of metals are also quite different.

Through the above discussion, the following conclusions can be drawn:

The properties of a substance largely determine its use, but it is not the only determining factor. When considering the use of materials, it is also necessary to consider various factors such as price, resources, whether it is beautiful, whether it is convenient to use, whether the waste is easy to recycle, and its impact on the environment.

2. Alloy

Steel is the most used metal material. You might think that steel has better properties than pig iron, and therefore steel is very pure iron. In fact, steel is iron with a small amount of carbon and other metals or non-metals. Just like when chefs are cooking, they often add various seasonings to the dishes to improve the color, aroma and taste of the dishes, and to make the dishes more nutritious. If certain metals or nonmetals are fused by heating in metals, alloys with metallic characteristics can be produced. For example, pig iron and steel are two iron alloys with different carbon contents. The carbon content of pig iron is 2%~4.3%, and the carbon content of steel is 0.03%~2% . In addition to carbon, pig iron also contains silicon, abrasion, etc., and stainless steel also contains chromium, iron, etc. Due to the fusion of a certain amount of carbon, 镒 or carbon, chromium, iron, etc. in pure metallic iron, the change of this composition makes the properties of the alloy also change.For example, pure iron is soft, but pig iron is harder than pure iron; stainless steel is not only harder than pure iron, but also has much better corrosion resistance than pure iron. Therefore, in daily life, industrial and agricultural production, and scientific research, it is often not pure metals but their alloys that are used in large quantities.

Alloys have many properties that differ from the pure metals from which they are composed, making alloys more suitable for different applications. Therefore, most of the metal materials used in daily life are alloys.

90 kinds of pure metals that have been prepared so far , thousands of alloys have been prepared from these pure metals in a certain composition and mass ratio.

Titanium and titanium alloys are considered to be important metal materials in the 21st century. They have many excellent properties, such as high melting point, low density (the density of titanium is only 4.5 g/cm^3) , good plasticity, easy processing, good mechanical properties, etc. . In particular, titanium and titanium alloys have very good corrosion resistance. Even if they are placed in seawater for several years, they are still as bright as ever after being taken out, and their corrosion resistance is far superior to that of stainless steel. Titanium and titanium alloys are widely used in rockets, missiles, space shuttles, ships, chemical and communication equipment, etc.

After studying this topic, you should know

1.Metals share many physical properties. For example, they are all solid at normal temperature (except mercury), have a metallic luster, and most of them are excellent conductors of electricity and heat, with ductility, high density, and high melting point.

2.The properties of a substance largely determine its use, but it is not the only determining factor. When considering the use of materials, it is also necessary to consider various factors such as price, resources, whether it is beautiful, whether it is convenient to use, whether the waste is easy to recycle, and its impact on the environment.

3.Metal materials include iron, aluminum, copper and other pure metals and alloys. Alloys made by heating and fusing certain metals or nonmetals in metals will change their properties. The strength and hardness of alloys are generally higher than those of pure metals, and their corrosion resistance is also better. Therefore, alloys have a wider range of uses.