Very interesting article here reporting on researchers who had previously announced a rapid means of producing synthetic gem sized diamonds, now believe their methods will work to produce diamonds of arbitrary size:
Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic. "A team in the US has brought the world one step closer to cheap, mass- produced, perfect diamonds. The improvement also means there is no theoretical limit on the size of diamonds that can be grown in the lab. "A team led by Russell Hemley, of the Carnegie Institute of Washington, makes diamonds by chemical vapour deposition (CVD), where carbon atoms in a gas are deposited on a surface to produce diamond crystals. "The CVD process produces rapid diamond growth, but impurities from the gas are absorbed and the diamonds take on a brownish tint. "These defects can be purged by a costly high-pressure, high- temperature treatment called annealing. However, only relatively small diamonds can be produced this way: the largest so far being a 34-carat yellow diamond about 1 centimetre wide. Microwaved gems "Now Hemley and his team have got around the size limit by using microwaves to "cook" their diamonds in a hydrogen plasma at 2200 =B0C but at low pressure. Diamond size is now limited only by the size of the microwave chamber used. "The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality," says Hemley's Carnegie Institute colleague Ho-kwang Mao."Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing. Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley Published online before print November 12, 2008, doi: 10.1073/pnas.
0808230105 PNAS November 18, 2008 vol. 105 no. 46 17620-17625The team's earlier research had showed they could make synthetic diamonds of perhaps 50% greater hardness than natural diamond. This should correspond to 50% greater compressive strength as well. Most discussion on the space elevator has centered on ultra strong materials for a cable in tension. However, according to this recent report, synthetic diamond production can now be scaled up to arbitrarily large sizes. So a compressive structure to space made of diamond might be feasible earlier, as diamond is much stronger in compression than in tension. I've seen various estimates for the compressive strength of natural diamond. If we take it as 400 GPa, then a space tower of diamond would have characteristic length of 400x10^9 Pa/(9.8m/s^2 x 3600 kg/m^3) =3D
1.13x10^7 meters, or 11,300 km. If this new synthetic diamond method really does create diamond of 50% higher compressive strength than natural diamond, then this length would be 17,000 km. And these are lengths without taper. Considering also that this maximal height for an untapered tower assumes constant gravity where in actuality the gravity is 1/16th as strong at 17,000 km altitude, it is possible that a tower made of diamond could reach all the way to geosynchronous altitude without taper. There aren't many references on the net available that do the calculations for a space tower in compression as opposed to a space elevator cable in tension. Here's one that gives the equations and some sample calculations:Optimal Solid Space Tower.
Bob Clark