Can somebody point out the difference to me, a beginner, between ceramic and carbon fibre, i.e. the pros and cons if they were to be used as backing for a new iPhone?
I'm not a materials engineer by any means but as I understand it (and copying wholesale from Wikipedia):
Ceramics
Ceramics are hard non-metallic materials made by using heat. So porcelain dinner sets, commercial bathroom floor tiles and some of the things dentists use to fix your teeth are ceramics.
The good things about ceramics are that they are often very heat/acid/stain/wear resistant. Great for serving tomato based dishes, lining the walls and floors of public lavatories, and reshaping broken teeth that will be chewing on things for the next 50 years.
At the sexy end of the field, the turbine blades in the hot section of large jet engines are believed to contain ceramic/metal mixes, the node cones of ballistic missiles are often ceramic and so are some medical implants.
The down-side of ceramics is that they tend to be more brittle than metals - they suffer impact damage more easily. Drop a china plate and see what happens!
Having said that, a lot of dollars have been put into ceramics research the last 20 years by a lot of companies and governments, including ceramic-metal mixes, glass-ceramics and who knows what else. Generally the search is for better impact resistance, higher temperature tolerance or electrical conductivity. (A friend of mine was doing research a few years ago for the world's largest aluminium company, trying to find a ceramic replacement for the huge cathodes they use in aluminum refining.)
You tend to make ceramics like you would pottery. Make up a mix, shape it, fire it. Although I'm sure there are more exotic ways of doing it out there.
Carbon Fibre
Carbon fibre is a form of carbon that is little crystals of carbon atoms that align in a similar direction, forming a tiny little thread. You wind several thousand of them together to form a bigger thread that we can see, and voila, carbon fibre yarn.
Then you weave those yarns into a mat or a tape - there are dozens of different ways of weaving them, depending on where you want the strength in the mat to lie at the finish.
Then you sandwich the mat between two sheets of a type of plastic resin an then you cut and curve the mats/sheets around a mould to whatever shape you want. Finally, heat the whole shebang up to a pretty high temp - enough to melt the plastic.
The molten plastic seeps through the carbon mat and when it cools, the resin forms the shape and the carbon mat inside gives incredible strength.
Good examples are racing yacht masts or Formula 1 car bodies - or most of the new Boeing 787.
iPhone Pros and Cons
Carbon Fibre would be fine for the case of the iPhone. It's pretty transmissive to radio waves and very, very strong. However, the down sides are that it doesn't look real pretty - you can generally see the carbon weave inside. Some people like that, by all means, but it's not the clean look Apple often go for. Also, when it fractures, it gives off small particles that are not good to take into your lungs - something to consider when you're a rich company circled by hungry fee-for-win lawyers. (That's also worrying the airport fire depts around the world, for when the first B787 crashes and spews a fine cloud of asbestos-like particles all around the crash site.)
Ceramics I really can't say. There has been a lot of development in this field the last 20 years, but a lot of it is secret and patented, so who knows. It's entirely possible that a modern ceramic or ceramic/metal mix could be used, or there might be nothing suitable. The problem would almost certainly be brittleness - iPhones take a lot of impacts! But having said that, Wikipedia points out that there are high-end watches with ceramic cases now, so that problem might be overcome.
We know from past job ads that Apple has people on staff who know about them, so I'm sure ceramics are something they keep an eye on.
