It is the physical properties of metals that for the most part determine the areas of their application by people in technology and industry. Among the main characteristics, their melting point is of no small importance. Knowledge of this parameter allows you to successfully combine various ingredients and create convenient, durable and high-quality alloys that are most suitable for use in everyday life.
Melting and boiling points of metals
For each representative, this indicator is different. However, all metals have a heating limit. At a certain temperature, they begin to melt, passing from solid to liquid. If you bring the indicator to a critical value, then the metal will go into a gaseous state, that is, the process of boiling and evaporation will begin.
Therefore, there is a whole classification reflecting the ability of metals to melt. All of them are divided into the following groups.
Fusible. This group includes those that melt at temperatures below 600 ° C. Example: zinc, sodium, gallium, bismuth, tin, cesium and others.
- Medium melting. The indicator is in the range of 600-1600 ° C. For example, the melting point of gold in its pure form is 1063 ° C, which means it belongs to this group of metals.
- Refractory. Over 1600 . Examples: titanium, tungsten, chromium and others.
It should be noted that this classification is valid only for pure metals. When it comes to alloys, the numbers change dramatically, and the values can differ greatly from the original indicators.
The boiling point of metals is much higher than the considered parameter. So, if the melting point of gold is 1063 , then the boiling point is already 2947 . The difference is almost twofold!
Gold: general description
Aurum, or gold, is the chemical element number 79 in the periodic system. The atomic mass is 196.967 units. It is located in group I, a subgroup. Refers to precious metals, along with:
- platinum;
- silver
- palladium.
From the point of view of chemical activity, it is practically inert, it does not enter into a reaction without special conditions. It has special physical properties that allow it to be used in jewelry, technology, and industry.
Physical properties of gold
What is so unique about this metal that people have been chasing for many centuries in a row and which has become a symbol of financial prosperity around the world?
- Color. Pure gold is characterized by a beautiful saturated yellow color with a pronounced metallic luster. The liquid metal has a pale green color. Pairs of its yellow-green color.
- Hardness. According to this parameter, gold is inferior to many other representatives, since it is a soft metal. On a scale of hardness of substances (Mohs scale), this indicator is 2.5-3.
- The melting point of gold is 1063 about C.
- The electrical conductivity is good, accounting for 75% with respect to copper as a superconductor.
- Thermal conductivity and heat capacity are also excellent. Gold items instantly heat up and also quickly heat up.
The special properties that add high value to gold are considered separately. It:
- ductility;
- plastic;
- density.
Metal density
The density characteristic itself means the weight of a substance in a unit volume. So gold has almost the maximum rate for this parameter. So, for example, half a glass of pure gold sand will have a weight of about 1000 grams.
The density of gold purified from impurities is 19.3 g / cm 3 . If we talk about natural gold-bearing rocks, then in it the indicator is slightly lower - 18-18.2 g / cm 3 . This indicator allows you to conveniently extract the metal in question from the rocks. He makes gold so expensive for a very small amount of grams.
Durability and ductility
The melting point of gold, as well as its extreme malleability and ductility, make it convenient and obedient in the hands of experienced people. So, the notion of "gold leaf" is well known. What it is? These are golden pieces rolled into the thinnest translucent sheets, which at the same time do not lose their bright and beautiful shine. Gold leaf can cover the surfaces of products, walls, domes of churches and so on.
Only 1 g of this amazing metal can make a very thin wire, the length of which will be almost 3 thousand meters! Gold easily undergoes the following deformations without loss of properties and structural integrity:
- squeezing;
- crumple;
- curvature;
- shredding;
- rolling;
- stretching;
- giving any desired shape.
Naturally, such a set of physical properties cannot go unnoticed by people, and therefore gold finds application in a wide variety of branches of science, technology and industry.
Being in nature and human use
In its original form, gold is found in nature in the form of ingots, sand or interspersed in rocks. Gold placers are places of their extraction by man. In a mixture with sand, clay and other parts, it is extracted and then separated in its pure form.
Also, gold is contained in:
- plants;
- animals;
- the human body;
- groundwater;
- seas and oceans;
- lithosphere.
From all these places, people have learned to extract metal for use in their needs. Why is it needed?
- The most important industry is, of course, jewelry. Beautiful jewelry made from different alloys of gold is the main sign of the financial heritage of almost every woman. They are presented to loved ones, invested in them, they are admired and appreciated.
- Equipment. The melting point of gold and platinum, as well as palladium, nickel and some other metals makes them very valuable for technical use. And the property of gold to have a high degree of malleability and ductility in combination with chemical inertness allows the use of wire from this metal in the smallest details, chips. For example, phones, televisions, calculators and other electronic devices.
- Gold is a hard currency around the world that never depreciates. He is not afraid of inflation and default, so many people keep their savings in bars of this metal.
- The awards for achievements in various sports, tournaments and games are made of gold, silver and bronze, which once again emphasizes their high value.
Gold alloys
The listed characteristics of the metal in its pure form make it not only unique and in demand, but also affect the quality of the products. So, due to its high softness, jewelry made of pure gold is easy to deform, mash and spoil. Therefore, metal alloys with other representatives of the periodic system are most often used.
- Gold 585. This alloy is the best-selling and most common in our country and abroad. What does it consist of? 58.5% is pure gold, 34% is copper, 7.5% is silver. The melting point of 585 gold is approximately 840 ° C, which is significantly lower than that of a pure sample. However, in general, the properties of the alloy are much better, since impurities compensate for the disadvantages of a simple metal. Copper serves to increase the strength and hardness of the product. However, if there is too much of it, the product will quickly corrode. Silver affects color. Thanks to him, the alloy is more yellow, shiny, without an admixture of green. The fact that the melting temperature of gold 585 of the sample is so low compared to the pure version suggests that you should handle the products with extreme caution and care and not leave them near open flames.
- Gold 999. This alloy is based on an almost pure metal with a small fraction of copper. Because of this, the melting point of gold 999 increases compared to the previous indicator. It is 1063 ° C, that is, the same value as for a simple substance. Products made of such an alloy are softer and more susceptible to deformation; therefore, they require careful handling and special care.
Gold 375
The melting point of gold 585 is an average. After all, there is still an alloy in which the precious metal accounts for only 37.5% (375 samples). In this case, the melting index generally approaches 770 ° C, which is the minimum value.
If we talk about an alloy based on gold and silver, then such options are not used at all. The product is too soft. Therefore, copper is required. The melting point of silver and gold is approximately the same, the scatter is small. In white metal, it is 961.8 about C. Therefore, their joint alloy does not lower the overall index in the product too much.
What determines the color of gold jewelry?
What color the decoration will cast in the light depends on what additives are in the mixture and what is their percentage. A red shade will have a product in which 50/50 gold and copper-silver.
White - if palladium, nickel and more silver are added to the mixture. Green is silver and copper, pink is silver, palladium and copper.