Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel [白铜] used to make marine hardware and coins, and constantan used in strain gauges and thermocouples [热电偶; 温差电偶] for temperature measurement. 白铜是以镍为主要添加元素的铜基合金，呈银白色，有金属光泽，故名白铜。
Copper is one of the few metals that can occur in nature in a directly usable metallic form (native metals). This led to very early human use in several regions, from c. 8000 BC. Thousands of years later, it was the first metal to be smelted from sulfide ores, c. 5000 BC; the first metal to be cast into a shape in a mold, c. 4000 BC; and the first metal to be purposely alloyed with another metal, tin, to create bronze, c. [about] 3500 BC.
- smelt: 1. a past tense and past participle of smell (smelled也是); 2. melt a rock that contains metal in order to remove the metal
Copper smelting was independently invented in different places. It was probably discovered in China before 2800 BC, in Central America around 600 AD, and in West Africa about the 9th or 10th century AD.
In the Roman era, copper was mined principally on Cyprus [塞浦路斯], the origin of the name of the metal, from aes сyprium (metal of Cyprus), later corrupted to сuprum (Latin). Coper (Old English) and copper were derived from this, the later spelling first used around 1530.
Commonly encountered compounds are copper(II) salts, which often impart blue or green colors to such minerals as azurite, malachite, and turquoise [蓝铜矿、孔雀石和绿松石], and have been used widely and historically as pigments.
Copper is essential to all living organisms as a trace dietary mineral. In humans, copper is found mainly in the liver, muscle, and bone. The adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight.
The major applications of copper are electrical wire (60%), roofing and plumbing (20%), and industrial machinery (15%). Copper is used mostly as a pure metal, but when greater hardness is required, it is put into such alloys as brass and bronze (5% of total use). For more than two centuries, copper paint has been used on boat hulls to control the growth of plants and shellfish. A small part of the copper supply is used for nutritional supplements and fungicides [杀真菌剂 fungi+cide] in agriculture. Machining of copper is possible, although alloys are preferred for good machinability in creating intricate parts.
六级/考研单词: copper, thermal, conduct, exposition, constituent, alloy, silver, jewel, marine, hardware, strain, gauge, indigenous, ore, mold, tin, bronze, tense, melt, probable, era, corrupt, derive, encounter, compound, seldom, indispensable, organism, trace, liver, plumbing, brass, nutrition, supplement, intricate
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