Difference engine Nikola Tesla's revenge

摘要

ONCE again, worrywarts are wringing their hands over possible shortages of so-called "critical materials" crucial for high-tech industries. In America the De partment of Energy is fretting about mate rials used to manufacture wind turbines, electric vehicles, solar cells and energy efficient lighting. The substances in ques tion include a bunch of rare-earth metals and a few other elements which-used a pinch here, a pinch there-enhance the way many industrial materials function. It is not as though the rare-earth ele ments-scandium, yttrium and lantha num plus the 14 so-called lanthanides-are all that rare. Some are as abundant as nick el, copper or zinc. Even the two rarest (thu lium and lutetium) are more abundant in the Earth's crust than gold or platinum. A decade ago America was the world's largest producer of rare-earth metals. But its huge open-cast mine at Mountain Pass, California, closed in 2002-a victim main ly of China's drastically lower labour costs. Today, China produces 95% of the world's supply of rare-earth metals, and has start ed limiting exports to keep the country's own high-tech industries supplied.