No abstract

Rats, guinea pigs, and monkeys were exposed by inhalation (5.5 to 6 h/day, 5 days/week) for up to 18 months at 15 mg/m3 concentrations of three types of synthetic amorphous silicas: fume, gel, and precipitated. Autopsies on rats were performed after 3, 6, and 12 months of exposure, and on guinea pigs and monkeys after 10 to 18 months of exposure. The most significant finding was the deposition of large quantities of amorphous silica in macrophages in the lungs and tracheal lymph nodes of exposed monkeys. Relatively few or no macrophages containing particles of amorphous silica were found in the lungs and lymph nodes of the guinea pigs and rats. It is also significant that fume silica induced early nodular fibrosis in the lungs of the monkeys. Correlating these histological findings, lung-function studies indicated statistically significant differences in lung volume and ventilatory mechanics measurements between those monkeys exposed to fume silica and the control group. In addition, monkeys exposed to precipitated silica demonstrated significantly lower lung volumes compared with controls, while monkeys exposed to silica gel had significant changes in ventilatory performance and mechanical properties.

The neurotoxicity of methyl n-amyl ketone was investigated in a chronic inhalation study lasting 9 months. Rats and monkeys were exposed 6 hrs/day, 5 days/week, to mean MAK levels of 0, 131, and 1025 ppm. Electrodiagnostic measures of nervous system function revealed no neurotoxic impairment at either MAK exposure. Body weights were similarly unaffected. Gross and histopathology also indicated no adverse effects of MAK. It was concluded that MAK does not possess neurotoxic properties similar to those possessed by methyl n-butyl ketone.

Bi-Sr-Ca-Cu-O phases provide continuous manufacturing of tapes in long lengths using conventional techniques. Thick films of the BPSCCO 2223 phase [(Bi, Pb)2Sr2Ca2Cu3O10+x] were successfully prepared on Ag tapes by combining the processes of screen-printing with organic binders, cold deformation, and sintering.1 Technical and economical studies revealed that these processes have optimal properties for conductor fabrication. The effect of atmosphere and powder composition on the formation of the 2223 superconductor phase was studied on two different composites: BPSCCO/Ag (open system) and Ag/BPSCCO/Ag (closed system). For the open system, both the evaporation of lead had to be avoided and the presence of additional “catalytic” Ag grains within the layer is necessary to promote the reaction of 2223 phase. Critical current densities jc of 6–12 ± 103 A/cm2 (77 K, O T) were achieved in samples of the closed system.