Silicon Seduced From Silica

Roland Piquepaille writes "Making silicon is an expensive process, which conventionally involves carbothermal reduction, in which the oxygen is removed from silica by a heterogeneous-homogeneous reaction sequence at approximately 1,700 C. Now, Japanese researchers have developed a new technique which uses electricity to remove the oxygen from silica. Their technique is based on the immersion of silica in a bath of molten calcium chloride salt at 850 C, which should reduce the costs of making silicon -- and other elements, like zirconium. Check this column for a summary or read this article from Nature for additional details."

Comments

zirconium!

[lingqi]

Zirconium plays a vital part in metallocene catalysis, which is the method of manufacturing high molecular density polyethylene, in another word, spectra. (stronger than steel (10x pound for pound), floats, i.e. stronger than KEVLAR and ~40-45% lighter, better chemical, UV resistance than kevlar, etc).

not related to silicon, but i like to point that out. in case people are looking for uses for zirconium =).

for those that thought about it - no spectra is not good enough for space elevator. only 3GPa tensile strength (steel about .25 for cheap ones and 5 for REALLY good ones). space elevator needs ~62GPa. nanotubes ~150GPa theoretical.

okay. end rant.

Delicate silicon

[asciimonster]

If you just eject oxygen from a structure, it would be likely that you are left with a very brittle structure, if not a powder. Remember the oxigen in the SiO2 (the sand) bridges the silicon atoms therfore the structure must be completely ruined.

Therefore the collected silicon mus be remelted, drawn, cleaned, sliced into tiny placks, etched, washed and polished. However this is also has to be done with silicon obtained in other ways. Nowadays there are machines who can perform most of these procedures in one run.

A short explanation of this can be found here

Cost of silicon wafers

[Randatola]

The companies that make silicon wafers for semiconductor production start with what is considered "chemically pure" silicon, and purify it some more until it is "electronics grade" silicon. A billet (I forget their technical term for it) of silicon is grown off of a seed crystal in a furnace, in a process that takes about a month. This is then sliced along a crystal axis into wafers which are polished to a rather extraordinary degree.

I don't know how much the raw silicon costs, but I suspect that most of the cost of the wafers comes from this month-long crystal growth and planarization. Good (ie, very flat) 200mm silicon wafers for semiconductor production can cost up to $1000 each, although they are probably much cheaper now due to lack of demand. Many processes also don't require the flattest wafers and so one can get by with wafers that cost a small fraction of that.

Re:3rd post!

[pyr0]

Actually, most volcanic sands don't have much quartz at all, and here is why. If it has been derived from a basaltic volcano (ie Hawaii), the composition of the sand will be extremely high in mafic (very silica poor) minerals since the source magma was low in silica. Then, if you are talking about a volcano whose melt composition is closer to the felsic (silica rich...so much so that you get quartz precipitating) side, these are typically very explosive volcanos that produce lots and lots of fine grained ash but no lava flows to weather from. What you *really* want is a sand eroding from an exposed granite. You get great big fat quartz crystals, and feldspars that turn to clay very quickly. And that's just if you want to find a loose sand that will be quartz rich. What I would do is actually get a hold of some mining rights out in the Southwest US somewhere and start a quarry operation on all the excellent quartz sandstone they've got.