Extended data:
1. Silver is a simple metal with the symbol of Ag, which has ductility and good thermal and electrical conductivity.
Silver, namely silver, is called silver because of its white color, as opposed to gold. Think of it as money and decorations. In ancient times, money was called silver. Pure silver is white in color, metallic in luster with impurities, soft in quality, hardened with impurities, and grayish red in color. Pure silver has a specific gravity of 10.5, a melting point of 960.5℃, good conductivity, and is soluble in nitric acid and sulfuric acid. Silver is one of the metals found in ancient times. Although silver also exists in the form of simple substance in nature, most of it exists in the form of combined state. Silver has high ductility, so it can be rolled into a transparent foil with a thickness of only 0.3 microns, and silver particles with a weight of 1 g can be drawn into filaments about two kilometers long. The thermal conductivity and electrical conductivity of silver are among the best among metals.
First of all, the importance of silver
Pure silver is white, metallic and soft. The melting point is 96 1.93℃, the boiling point is 22 12℃, and the density is10.5g/cm3 (20℃). Silver is soft, flexible and malleable, second only to gold. It can be pressed into sheets and drawn into filaments. Soluble in nitric acid and sulfuric acid. The reflectivity of silver to light reaches 9 1%. At room temperature, halogen can slowly combine with silver to form silver halide. Silver does not react with dilute hydrochloric acid, dilute sulfuric acid and alkali, but can react with strong oxidizing acid concentrated nitric acid and concentrated hydrochloric acid.
The main uses of silver are mainly based on three pillars: industry, photography and jewelry and silverware. The total demand of these three types of silver accounts for about 85% of the demand for silver.
Since ancient times, silver and gold have been regarded as a symbol of wealth together. The chemical symbol of silver is Ag, which comes from the Latin Argertum, meaning "light and brightness". Because silver is white, it is called "silver".
Silver not only has good electrothermal conductivity, but also has high photosensitivity and luminous characteristics, and is used in industry, photography, jewelry, currency manufacturing and so on.
Compared with gold, silver was used for coinage more and earlier and entered the circulation field because of its large supply and low value. Many countries have established the silver standard, with silver coins as the mainstream currency.
Second, the history of silver
In ancient times, people knew about silver. Like gold, silver is a precious metal with a long history of application, which has a history of more than 4,000 years. Because of the unique and excellent characteristics of silver, people give it dual value of money and decoration. The pound and silver dollar used before the liberation of China were silver and copper alloys. 1 silver in Qing dynasty is equivalent to 400-500 yuan RMB today.
Silver is more active than gold. Although its abundance in the crust is about 15 times that of gold, it rarely exists as a single substance, so it was discovered later than gold. In ancient times, people already knew how to mine silver ore, because the amount of silver obtained at that time was very small, which made its value more expensive than gold. From BC 1780 to BC 1580, the Egyptian code stipulated that the value of silver was twice that of gold. Even in the17th century, the value of Japanese gold and silver was equal. Silver was first used as decorations and tableware, and later used as currency.
Silver, namely silver, is called silver because of its white color, as opposed to gold. Think of it as money and decorations. In ancient times, money was called silver. Silver always shines like the moon. The original meaning of silver paper is "bright". In China, silver characters are also commonly used to describe white and shiny things, such as the Milky Way, Ginkgo biloba, whitebait, tremella, screens and so on.
In ancient China, silver was often juxtaposed with gold and copper, which was called "only gold". Gong Yu records that "gold is the only product", which shows that silver was discovered in China as early as the 23rd century BC, that is, more than 4,000 years ago. In nature, silver often exists in the form of pure silver. People once found a piece of pure silver weighing 13.5 tons! In addition, it also exists in the form of chloride and sulfide, and often coexists with minerals such as lead, copper, antimony and arsenic.
Third, the nature of silver.
physical features
It is malleable and a metal with good thermal and electrical conductivity. The first ionization energy is 7.576eV. The chemical properties are stable and have no effect on water and oxygen in the atmosphere. Soluble in dilute nitric acid, hot concentrated sulfuric acid, hydrochloric acid and molten sodium hydroxide.
Crystal structure: the unit cell is a face-centered cubic unit cell, and each unit cell contains 4 metal atoms.
chemical property
The characteristic oxidation number of silver is+1, and its chemical properties are worse than that of copper. At room temperature, even if heated, it will not react with water and oxygen in the air, but it will turn black and lose its silver luster after a long time in the air. This is because silver and H_S in the air synthesize black Ag _ S, and the chemical reaction equation is:
Silver can't react with dilute hydrochloric acid or dilute sulfuric acid to release hydrogen, but it can be dissolved in nitric acid or hot concentrated sulfuric acid.
Silver reacts slowly with halogen at room temperature and can generate halide when heated.
Silver has a strong affinity for sulfur, and can be directly combined with sulfur to synthesize Ag _ S； when heated.
Fourth, industrial application.
Electrical products
Electronic appliances are the industry with the largest amount of silver, and their uses are divided into electrical contact materials, composite materials and welding materials. Silver and silver-based electrical contact materials can be divided into pure silver, silver alloy, silver oxide and sintered alloy. The annual output of silver and silver-based electrical contact materials in the world is about 2900~3000t, and composite materials are prepared by composite technology, which can be divided into silver alloy composite materials and silver-based composite materials. From the point of view of silver saving technology, silver composite material is a new material with great development prospect. Silver welding materials such as pure silver solder and silver copper solder.
Sensitive materials
Silver halide photosensitive material is one of the fields with the largest amount of silver. At present, several photosensitive materials with the largest production and sales volume are photographic film, photographic paper, X-ray film, fluorescent information recording film, electron microscope photographic film and printing film. In 1990s, the world photographic industry used about 6000 ~ 6500 tons of silver. Due to the development of electronic imaging and digital imaging technology, the amount of silver halide photosensitive materials has decreased, but the application of silver halide photosensitive materials is still irreplaceable in some aspects, and there is still a great market space.
chemical
Silver has two main uses in this respect. One kind is silver catalyst, which is widely used in redox and polymerization reactions, and is used to treat industrial waste gas containing sulfide. Second, industrial preparations for electronic plating, such as silver paste and silver potassium cyanide.
Craft ornaments
Silver has attractive white luster, high chemical stability, collection and ornamental value, and is favored by people (especially women). Therefore, it has the reputation of women's metal, and is widely used as jewelry, decorations, silverware, tableware, congratulatory gifts, medals, commemorative coins and so on. Silver ornaments have a broad market in developing countries, and silver tableware is welcomed by families. Silver commemorative coins, with exquisite design, small circulation and value-added function, are favored by coin collectors and investors. In the 1990s, the amount of silver used for coinage alone remained around 1 1,000 ~11,500t every year, accounting for about 5% of the silver consumption.