LEAD SUBSTITUTE

Mennig, m., Mennige,/. minium, red lead. Meniuge-ersatz, m. red-lead substitute, -kitt,... 

Dichlorofluoro-ethane (CCI2FCH5) The leading substitute blowing agent for CFC-11 in rigid foam insulation applications such as construction (commercial, residential, and public), appliances, and transport vehicles. 

It is common practice to refer to these compounds using numerical acronyms corresponding to the metal stoichiometries. The decoding scheme and Tc values are collected in the following table (13)(21)-(23) the lead-substituted phases are included but not generally referred to with acronyms. 

Syntheses of near-single phases of the lead-substituted thallium monolayer phases with up to 6 Cu-O layers i.e., Pb-doped 1212, 1223, 1234, 1245, and 1256, have been recently reported (21). Reactant mixtures of various proportions of Tl2Os, PbO, CaO, Ba02, and CuO were pelletized, wrapped in gold foil, and sintered at 860-900°C under flowing oxygen for 10-30 h. The Tc value reached a maximum of 121 K for the 1234 compound and declined with further increase in the number of Cu-O layers. X-ray powder diffraction data for the different phases were refined using the Rietveld method and a consistent increase in the c-axis accompanied the increase in number of Cu-O layers. 

Space precludes an extensive survey of silicon, germanium, tin and lead substituted derivatives of cyclopentadiene (the siloles and analogues). Until 1979, few plumboles were known (79RTC437), but now, with the siloles, germoles and stannoles, they represent one of the most extensively studied areas of Group IV substituted heterocyclic chemistry. The references prefacing Section 1.20.9 cover reviews for this section. 

In these spectra, a parameter sensitive to chromium and lead substitution into Fe304 is the area ratio S, defined as the area of the octahedral iron component divided by the corresponding peak for the tetrahedral component. For Fe304 ((5 = 0), S should equal approximately 2, as experimentally observed however, for the PbCr-Fe304 catalyst the value of S is about... 

Boettner, E. A., Dallos, F. C. Comperative sensitivity of the electron capture to chlorinated and lead substituted compounds. J. Gas Chromatog. 3, 190 (1965). 

A review article on silicon, germanium, tin and lead substituted carbodiimides appeared in 1982.2 ... 

This section describes methods for the cyclopropanation of alkenes with silicon-, germanium-, tin-, or lead-substituted carbenes and their equivalents. 

X-ray diffraction patterns of the lead-substituted lead ruthenates support the conclusion that they are pyrochlores of cubic symmetry. It must be noted, however, that since these materials were prepared at relatively low temperatures, the peaks in their x-ray spectra were broadened. X-ray line broadening was significant [half-height peak width at 50-60 (20) was equal to 0.5-0.8 (20)] thus any subtle evidence of distortion to lower symmetries would be difficult to... 

One additional parameter that affects the solubility of lead ruthenate pyrochlores in alkali is the extent of lead substitution on the B-site. The greater the substitution (i.e. the larger x is in formula 1), the higher the solubility of the pyrochlores is in alkali 2). If it is assumed that a solution-reprecipitation mechanism of synthesis is operative, the stoichiometry-dependent solubility could explain why it becomes significantly more difficult to crystallize lead ruthenate directly out of alkaline solution when x <0.3. 

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