Nickel —- an Important Metal for Paktong


Nickel has been thought to be firstly discovered by the Swedish mineralogist A.F. Cronstadt in 1751. Actually, China is the first country known of nickel. According to researches, as early as more than 1,800 years of the Western Han Dynasty period (first century BC) before Cronstadt, Chinese already knew how to produce paktong. In ancient China, paktong are also used for the production of cartridges, candlesticks and plates, etc. In Compendium of Materia Medica by Li Shizhen and Heavenly Creations by Song Yingxing of the Ming Dynasty, there are more detailed records on the use of arsenic ore to smelt paktong. In 1929, Wang Jin had analyzed the chemical composition of an ancient Chinese stationery of paktong, and proved it contains nickel of 6.14%, copper of 62.5% and small amounts of tin, zinc, iron, and lead, etc.

China’s ancient paktong products not only sold throughout the country, but also exported abroad. According to researches, in the Qin and Han Dynasties, Daxia State in the west of Xinjiang had currency cast in paktong, with nickel content up to 20%. Based on the analysis of its shape, composition and the prevailing historical conditions, these currencies are likely to be shipped from China. So far, in Farsi (Iran area) and Arabic, paktong is still known as “China Stone”, which shows that paktong was exported to western Asia regions in ancient China. In the 17th and 18th centuries, the East India Company purchased all kinds of products made by paktong from Guangzhou to sell to Germany, Sweden and other European countries. In the past some people regarded paktong as “German Silver”, actually the fact is completely upside down. The fact is that German in the 17th and 18th centuries learned the technology to refine paktong from China and produced a large number of counterfeit, which results in a misunderstanding that German invited paktong. Similarly, according to researches, this technology was also introduced to Sweden so that some people thought nickel was first discovered by Swedish A.F Cronstadt.

Nickel is a silvery white metal, very hard and refractory, with melting point up to 1,455°C higher than that of gold. Nickel is not easily oxidized in air; it is chemically stable and only soluble in nitric acid. Nickel is better than copper in many respects, but it is strange that nickel in Greek means “useless copper”, which probably because the nickel initially refined is impure.

In nature, the most important nickel ores are nickelite (nickel arsenide) and gersdorffite (sulfur nickel arsenide). In addition, there are also pentlandite (nickel iron sulfide) and millerite (nickel sulfide). Cuba is the most famous country for its nickel ore reserves all over the world. Dominica also has abundant nickel ore. Interestingly, meteorites, known as “extraterrestrial”, often contain some nickel (mainly iron). It is supposed that more nickel exists in the earth core.

Pure nickel is silver shiny and not easy to rust, mainly used in the electroplating industry. Fountain pen penholders and surgical instruments look like silver shiny, because their surfaces are coated with a layer of nickel (also chrome) which makes them clean and not easy to rust. Nickel powder is used as a catalyst in the chemical industry, such as the oil hydrogenation.

Nickel is extensively used for the production of various alloys. Adding nickel metal powders in steel can improve the mechanical strength. For example, when nickel content in steel increases from 2.94% to 7.04%, steel’s tensile strength increases from 52.2kg/mm2 to 73.8kg/mm2. Usually, nickel steel applies to make parts which have to withstand greater pressure, impact and reciprocating load, such as turbine blades, crankshafts and connecting rods, etc. Nickel steel containing nickel of 36% and carbon of 0.3-0.5% is known as “invar steel”. Its expansion coefficient is very small, almost no expansion with heat and contraction with cold. It uses to make all kinds of precision machinery and gauges, such as watch parts, standard scale of various measuring instruments, etc. High nickel steel containing nickel of 46%and carbon of 0.15% is known as “eka-platinum”, because its expansion coefficient is similar to platinum and glass. Such high nickel steel can be welded into the glass so that it is important for the production of lamps, as substitutes for the platinum wire in incandescent lamps. Some sophisticated lens frames are made of such eka-platinum because its expansion coefficient is similar to glass. So lens will not fall out of the frame for thermal expansion and contraction. The alloy made up of nickel of 68%, copper of 28%, iron of 2.5% and manganese of 1.5% is chemically stable for the production of chemical instruments. The alloy made up of nickel of 67.5%, iron of 16%, chromium of 15% and manganese of 1.5% has great resistance for the production of various rheostats and electric heaters. Nickel is magnetic, so it can be attracted by a magnet like iron. And alloys made up of aluminum, cobalt and nickel have stronger magnetism. When the alloy is attracted by the electromagnet, it can also hang on the object six times heavier than itself below. So it can be used to produce an electromagnetic crane. In addition, nickel and chromium are often used to make corrosion-resistant chromium-nickel steel. Most nickel salts are green. Nickel hydroxide is brown-black; nickel oxide is gray-black. Nickel oxide is commonly used to produce nickel-iron alkaline batteries.