1). Used as international reserve. This is determined by the monetary commodity property of gold. Because of its excellent characteristics, gold has played a role as a currency in history, such as a measure of value, a means of circulation, a means of storage, a means of payment and a world currency. Since the decoupling of gold and the dollar in 1970s, the gold function of money has also weakened, but it still maintains a certain monetary function. Gold still occupies a very important position in the international reserves of many countries, including major western countries.
2). Used as jewelry decoration. Gorgeous gold ornaments have always been a symbol of one's social status and wealth.
3). Application in industry and science and technology. Because of its unique and perfect characteristics, gold has extremely high corrosion resistance stability. Good electrical and thermal conductivity; The gold nucleus has a large effective cross section to capture neutrons; The reflection ability of infrared ray is close to100%; It has various catalytic properties in gold alloys; Gold also has good manufacturability and can be easily processed into ultra-thin gold foil, micron gold thread and gold powder; Gold is easy to be plated on the surface of other metals, pottery and glass, and it is easy to be welded and forged under certain pressure. Gold can be made into superconductors and organic gold. It is precisely because of its many beneficial properties that it has reason to be widely used in the most important modern high-tech industries, such as electronic technology, communication technology, aerospace technology, chemical technology, medical technology and so on. In many countries, gold is the standard of currency trading and will also be used to make coins and jewelry. Because pure gold is too soft, gold is usually alloyed with copper and other base metals to increase hardness. The gold content in the alloy will be measured in carat (K), while the pure gold is 24k. The gold coins circulating from 1526 to 1930 are usually 22k alloy, which is called crown gold because of its high hardness. But today, gold no longer plays the role of daily currency circulation.
Historically, gold naturally played the role of currency. The gold standard was formed in the middle of19th century. Although most countries in the world use paper money as legal tender (some countries prohibit gold from circulating as currency), gold is still regarded as "quasi-currency", and gold reserves occupy an important position in the financial reserves of various countries. raw material
Because 24k pure gold is soft, when making jewelry, gold is often alloyed to change its hardness, ductility, melting point, color and other characteristics. In the alloys of 22k, 18k, 14k or 10k, there will be high-content copper, silver, palladium or other base metals. Copper is the most commonly used base metal, which will make the alloy red. Hundreds of years ago, there was 18k gold in Russian jewelry-rose gold with copper content of 25% cast in copper mold. 14k gold-copper alloy is similar in color to some bronze alloys and can be used as badges. Blue gold is an alloy made of gold and iron, but it is difficult to be used in jewelry making because of its fragility. Zijin is an alloy of gold and aluminum, which is usually only used for specialized jewelry. 14k or 18k gold and silver are green and yellow after alloying, so it is called green gold. The alloy of gold with palladium or nickel can form platinum alloy. The white 18k gold alloy is silver and contains 17.3% nickel, 5.5% zinc and 2.2% copper. However, because nickel is toxic and restricted by European laws, platinum alloys are sometimes made of palladium, silver and other white metals in another way. But its manufacturing cost is higher than the former. The corrosion resistance of high-purity platinum alloy is much higher than that of silver or pure silver. Jin Mu, a Japanese handicraft, makes full use of the color contrast between different gold alloys to create a decorative effect similar to a wood grain ring.
solder
Solder or solder made of gold is usually used for high-temperature brazing or connecting gold jewelry. Goldsmiths use independent solder joints to assemble complex objects. Gold solder usually has three different hardness, the high hardness solder will be used first, followed by the low hardness solder. The purity of the gold solder must be the same as that of the connected articles. Alloys will be produced under strict supervision to match their colors with gold or platinum.
220kg of gold bricks are on display at the Jinguashi Gold Museum in Taiwan Province Province. Alternative medical treatment
In the Middle Ages, because gold was rare and beautiful, it was mistaken for being healthy. Even in today's society, the tantric religion still believes that gold has the power to treat diseases and is used as an alternative medicine. In fact, some gold salts do have anti-inflammatory properties and are used to treat arthritis. However, because gold in metallic state is inert to all chemical reactions in the body, only gold salts and their radioisotopes have medical value.
Dentistry
Gold alloys are mostly used in dental restoration, especially in dental restoration, such as crowns and permanent bridges. The good ductility of gold alloy can make the surface match other teeth, so the restoration effect is better than that of ceramic molars. From a cultural point of view, some cultures like to make gold teeth on their front teeth.
Colloidal gold
Colloidal gold is a colloidal solution of gold nanoparticles, which is crimson in water. It is made by the reduction reaction of chloroauric acid in citrate or ascorbate reduction solution, and then it is made under nanotechnology. Colloidal gold is mainly used in medicine, biology and materials science. Immunocolloidal gold labeling technology gives full play to the ability of gold particles to adsorb protein molecules to its surface. Some colloidal gold particles coated with antibodies can better detect antigens on the cell surface. Under the observation of electron microscope, immunogold gold will concentrate on antigen. In addition to medical use, colloidal gold is also used as a golden pigment, which is coated on ceramics before firing.
The isotope gold-198 (half-life: 2.7 days) of radiotherapy gold can be used to treat some cancers and other diseases. Gdansk gold foil wine.
Gold foil is a thin piece of gold or powder spread on food, which is often used as decoration on candy and drinks. In medieval Europe, gold foil was added to food and drink by nobles in the form of flakes or powder to highlight the rarity and preciousness of aristocratic wealth, food or health. The e code of gold used as a food additive is 175. Gdansk Gold Foil Wine (commonly known as Golden Water) is a traditional herbal sweet wine produced in Gdansk and Schwabach, which contains gold leaves. Some expensive cocktails are also decorated with gold foil. The conductivity is very high, and it is often used on the circuit board of 3C products.
High energy conduction application
The electron density of gold metal is 5.90× 10 cm. Gold has a very high conductivity, so it is used as a conductor of high current (although silver has a higher conductivity than gold at the same capacity, gold has the advantage of corrosion resistance), such as the atomic experiment in Manhattan Project. However, in the experiment, the magnet of the electromagnetic isotope separator uses a large current silver wire.
electronic connector
Although gold will be corroded by chlorine gas, it is widely used in the electronic industry because of its high conductivity, high oxidation resistance and environmental erosion resistance (including the ability to resist other non-hydrochloric acid), so as to make wire joints have good connections. Such as voice, image and universal serial bus connection. But the use of gold wire is controversial. It is often criticized by audio-visual experts as unnecessary and regarded as a marketing trick. The connectors of some electronic measuring instruments are also plated with gold to avoid oxidation. However, gold is still very common in other application fields, such as high humidity, high corrosive atmospheric electronic contact and high failure rate contact, such as some computers, communication equipment, spacecraft and jet engines, and it is unlikely to be replaced by other metals in the future.
switch contact
In addition to power contacts, gold is also used to switch power contacts because of its corrosion resistance, high conductivity, high ductility and non-toxicity. Because switch contacts are usually more corrosive than electronic contacts. After the initial production, gold is usually extracted by Walwell method or Miller method. Other methods for testing and purifying small amounts of gold include adding silver to separate gold, separating gold from silver and cupping, or refining based on dissolving gold in aqua regia.