什麼是鉛

金屬化學元素，化學符號Pb，原子序數82。爲銀白色或淺灰色金屬，質地柔軟，延展性好，密度大，導電性差。其穩定的同位素爲鈾和其他重金屬放射衰變後的最終產物。自古以來人們就知道鉛的好處，它耐用且抗腐蝕，所以古羅馬人的鉛水管至今仍可使用。鉛可用作屋頂材料、電纜的包皮、水管襯裏和一些管道設備。其他用途有製造蓄電池、槍彈和低熔點的合金（如焊料和白鑞），以及隔離聲音、振動和幅射的保護裝置。鉛在自然界中很少呈遊離態，主要存在硫化物和方鉛礦中。由於鉛和鉛化物具有毒性（參閱lead poisoning），因此含鉛的顏料和汽油添加物現已被禁用。鉛化物的原子價有+2和+4價，其中鉛氧化物（密陀僧）是最廣爲使用的。鉛化合物可用於製造鉛水晶玻璃（參閱glass）、釉料、陶器、顏料、塗料和油漆的乾料、殺蟲劑、除草劑、防火材料、火柴、炸藥和煙火。將近一半的鉛可刮下重新回收使用。鉛筆中的「鉛」指的是石墨。

lead

Metallic chemical element, chemical symbol Pb, atomic number 82. Lead is a soft, silvery-white or grayish, malleable, ductile, dense metal that conducts electricity poorly. Its stable isotopes are all end products of radioactive decay of uranium and other heavy elements. Known since ancient times, lead is so durable and resistant to corrosion that Roman lead pipes are still usable. Lead is used in roofing, as cable coverings, and in pipes, conduits, and structures. Other uses are in storage batteries, ammunition, and low-melting-point alloys (e.g., solder, pewter) and as shielding against sound, vibrations, and radiation. Lead is rarely found free in nature; its major ore is the sulfide, galena. Because it and its compounds are poisons (see lead poisoning), lead-based paints and gasoline additives have been banned. Lead in compounds has valence 2 and 4; an oxide (litharge) is the most widely used. Lead compounds are added to lead crystal (see glass), glazes, and ceramics and used as pigments, drying agents for paints and varnishes, insecticides and herbicides, and fireproofing agents and in matches, explosives, and pyrotechnics. Almost half of all lead is recovered from recycled scrap. The “lead” in pencils is graphite.