Xref: utzoo sci.astro:13841 sci.space:31771 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!ptimtc!nntp-server.caltech.edu!sol1.gps.caltech.edu!CARL From: carl@sol1.gps.caltech.edu (Carl J Lydick) Newsgroups: sci.astro,sci.space Subject: Re: Platinum-group metal concentrations in earth-crossing objects Message-ID: <1991Jun16.092816.3516@nntp-server.caltech.edu> Date: 16 Jun 91 09:28:16 GMT References: <sehari.676666308@du248-12.cc.iastate.edu> <5248@dirac.physics.purdue.edu> <1991Jun12.073415.12543@sequent.com>,<1991Jun16.000359.10311@world.std.com> Sender: news@nntp-server.caltech.edu Reply-To: carl@sol1.gps.caltech.edu Organization: HST Wide Field/Planetary Camera Lines: 42 In article <1991Jun16.000359.10311@world.std.com>, webber@world.std.com (Robert D Webber) writes: >Back in semiconductor fabrication class they always told us the biggest >contamination problem came from the container, and that the high vapour >pressure of arsenic led to a need for either As pressurization or some >kind of complete encapsulation for the melt. In the absence of a >container the composition of the GaAs crystal comes out wrong, so I >don't see how the "very high vacuum" will help fabrication operations >for the materials used to make devices. You're assuming that the semiconductors will be doped via a diffusion process, in which case you're right. However, if you want to use ion implantation, high vacuum is useful. >>Back to platinum: we have a total of 55 ppm platinum group, about 5 >>times better than the best Earth ore. This still wouldn't be that >>good, given the high costs of launching mining equipment, except >>that there exists a process which, taking advantage of the large >>amounts of solar-thermal power available in space, could make >>extracting the platinum economical. >> >>First, we should find grains with the above concentrations or better >>in a high-metal regolith (a task for space exploration). We >>extract the metal grains with a magnetic rake. Next, we process >>the metal regolith with the gaseous carbonyl process, as follows: > >You will need to break the hunk of rock down in size quite a bit, first. >On the ground this is generally accomplished by crushing in rather large, >heavy machines, then grinding in a mill where balls or rods are raised >from and dropped back onto the material to be ground. Obviously the >term "dropped" implies the machine's presence in a gravity field. I suppose >that some other accelerating field could be substituted. Anyway, the >grinding medium in a conventional process needs to be dense so that the >individual grinding elements have a lot of kinetic energy for a small >surface area: this allows a lot of K.E. to be transformed into the energy >of new surfaces during the grinding process in a short period of time. >What are you proposing as an alternative to this very much earthbound, >heavyweight technology? You definitely need something to get the mineral >particles down to liberation size in the process you describe. He said they'd be using the regolith. This means it's already quite friable. -------------------------------------------------------------------------------- Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL