Engineering topics

Smith, P. P. K.

Publications and source records attributed to Smith, P. P. K..

3 records

NASA NTRS1982

Carbyne forms of carbon - Do they exist

Carbynes, or polymorphs of elemental carbon first reported synthesized by Kasatochkin et al (1967), have generally been recognized by their characteristic hexagonal electron diffraction pattern. It is pointed out, however, that sheet silicate minerals give rise to hexagonal diffraction patterns with a similar range of interplanar spacings. A reexamination of reported occurrences of carbynes, including chaoite, by means of TEM shows that nontronite and quartz contaminants could account for most of the cases previously attributed to chaoite. It is recommended that in future searches for carbyne, energy-dispersive X-ray analyses should be conducted to verify the chemistry of individual, carbyne-candidate grains.

Smith, P. P. K.↗

NASA NTRS1982

Carbon in the Allende meteorite - Evidence for poorly graphitized carbon rather than carbyne

A carbon-rich acid residue from the Allende carbonaceous chondrite was examined by high-resolution transmission electron microscopy (HRTEM) and also by analytical electron microscopy. A TEM mount of this residue that has previously been reported to contain carbyne forms of carbon was shown to contain sheet silicate contaminants. These sheet silicate grains give electron diffraction patterns similar to those reported for carbynes, thus raising questions about the previous report of carbynes in this residue. Furthermore, two crystals from a glacier microspherule, which had previously been identified as carbyne VIII, were shown by microanalysis to be talc. In view of these observations it is suggested that identifications of carbyne by electron diffraction should be supported by microanalyses of the individual grains. HRTEM investigations of the Allende carbon indicate that it is a poorly crystalline graphite, structurally similar to 'glassy' carbon

Smith, P. P. K.↗

NASA NTRS1981

Graphitic carbon in the Allende meteorite - A microstructural study

High-resolution transmission electron microscopy shows that carbon in the Allende carbonaceous chondrite meteorite is predominantly a poorly crystalline graphite. Such material is of interest as an important carrier of the isotopically anomalous noble gases found in carbonaceous chondrites.

Smith, P. P. K.↗