The phrase "expensive metal" is correct and usable in written English.
You can use it when you want to talk about a type of metal that is costly. For example, "The museum had many artifacts made of expensive metal, such as gold and silver."
Its windows are original; their wooden frames have a texture that even expensive metal replacements cannot approach.
Coltan is the ore from which tantalum, the expensive metal used in mobile phones, is extracted, and almost all of it comes from the DRC.
Tiny amounts of the expensive metal are scattered in all these things; your jeans, for instance, contain unrecoverable particles of platinum.
Known from ancient times, steel had always been a very expensive metal to produce, used mostly for things like sword blades and precision instruments.
More exactly, if coins containing metal of different value have the same value as legal tender, the coins composed of the cheaper metal will be used for payment, while those made of more expensive metal will be hoarded or exported and thus tend to disappear from circulation.
Many foam footballs later, tired of making replacements with a band saw, they decided to use them in testing whether a new process, making seat cushions out of cold-molded foam for an easy chair, could be done as well with fiberglass tooling as with more expensive metal.
You don't need expensive metals, or a blacksmith, to make a linothorax.
The technology is also getting cheaper, as less expensive metals are used.
The ores of expensive metals such as chromium or tantalum and the industrial chemical soda ash are examples.
It enjoys the highest ratio of power to weight, but it needs expensive metals, such as platinum and gold, to coat its electrodes.
The storage media require salts of expensive metals such as vanadium, and the electrodes sometimes have to be coated in platinum, or similarly rare catalytic metals, if the whole caboodle is to work.
