Sintered superhard materials.

Diamond or cubic boron nitride particles can be sintered into strong masses at high temperatures and very high pressures at which these crystalline forms are stable. Most of the desirable physical properties of the sintered masses, such as hardness and thermal conductivity, approach those of large single crystals; their resistance to wear and catastrophic splitting is superior. The sintered masses are produced on a commercial scale and are increasingly used as cutting tools on hard or abrasive materials, as wire-drawing dies, in rock drills, and in special high-pressure apparatus.

Thermochemical hydrogen generation.

The basic concepts for thermochemical hydrogen generation processes have been summarized in this article. A useful set of criteria has been described for the screening and selection of potentially viable, multistep, closedcycle thermochemical processes for hydrogen generation. Three illustrative, new closed-cycle processes have been discussed, indicating potential, overall thermal efficiencies ranging from approximately 40 to 60 percent. Combined thermochemical-electrolytic schemes also warrant further consideration. Principal technical problems in the development of such thermochemical closed-cycle and mixed-cycle processes are expected to include primarily materials compatibility, reaction kinetics, separation techniques, and heat-exchanger systems. As natural gas supplies decline and prices rise, new open-cycle thermochemical processes based on water and other fossil fuel feedstocks will be the first important new technology in supplying the growing hydrogen needs of industry for at least the next two decades. Conventional electrolysis technology does not appear to be a competitor for large-scale supplies in this century unless very low off-peak electrical power rates become available, although electrolysis will be the best technique for some small-scale uses. Further analysis will be required to determine if closed-cycle thermochemical or mixed-cycle methods will displace electrolysis or other methods as the principal technology for the production of hydrogen on a large scale for the longer term.

Anomalous water: attempts at high-pressure synthesis.

The high density, 1.4 grams per cubic centimeter, reported for anomalous water suggests that high pressures should be conducive to the formation of anomalous water. Six attempts at 60 kilobars in which water was cooled from about 600 degrees C in nickel or platinum tubes, with or without the presence of silica, did not produce any detectable amounts of anomalous water.