p-Type skutterudites RxMyFe3CoSb12 (R,M = Ba,Ce, Nd,and Yb): Effectiveness of double-filling for the lattice thermal conductivity reduction

Ab-initio calculations of the resonant modes and frequencies for a number of possible fillers in p-type RFe₃CoSb₁₂ and RFe₄Sb₁₂ were carried out. The results indicate that, although the exact values of fillers’ resonant frequencies in p-type skutterudites are somewhat different from those in n-type Co-based skutterudites, the Einstein-like resonant modes of the fillers are similar to those in n-type materials. Experimentally, several pairs of the fillers were selected and double-filled p-type skutterudite compounds R_xM_yFe₃CoSb₁₂ (R, M = Ba, Ce, Nd, and Yb) were successfully synthesized. The reduction in the lattice thermal conductivity was realized by extending the range of resonant frequencies. As a result, enhanced ZT values above unity were achieved in these double-filled p-type skutterudites.     

Relating carbon monoxide photoproduction to dissolved organic matter functionality

Aqueous solutions of humic substances (HSs) and pure monomeric aromatics were irradiated to investigate the chemical controls upon carbon monoxide (CO) photoproduction from dissolved organic matter (DOM). HSs were isolated from lakes, rivers, marsh, and ocean. Inclusion of humic, fulvic, hydrophobic organic, and hydrophilic organic acid fractions from these environments provided samples diverse in source and isolation protocol. In spite of these major differences, HS absorption coefficients (a) and photoreactivities (a bleaching and CO production) were strongly dependent upon HS aromaticity (r2 > 0.90; n = 11), implying aromatic moieties are the principal chromophores and photoreactants within HSs, and by extension, DOM. Carbonyl carbon and CO photoproduction were not correlated, implying that carbonyl moieties are not quantitatively important in CO photoproduction. CO photoproduction efficiency of aqueous solutions of monomeric aromatic compounds that are common constituents of organic matter varied with the nature of ring substituents. Specifically, electron donating groups increased, while electron withdrawing groups decreased CO photoproductivity, supporting our conclusion that carbonyl substituents are not quantitatively important in CO photoproduction. Significantly, aromatic CO photoproduction efficiency spanned 3 orders of magnitude, indicating that variations in the CO apparent quantum yields of natural DOM may be related to variations in aromatic DOM substituent group chemistry.     

Einfluß von Schwefelverbindungen auf die Inhibition der Thermooxidation von Polypropylen

The influence of mixtures of substituted phenols with sulphur compounds on the thermooxidative stability of polypropylene was studied. Following substituted phenols were used: 4,4′-butylidene-bis(3-methyl-6-tert.-butylphenol), 2,2′-methylidene-bis(4-methyl-6-tert.-butylphenol) and 4,4′-thio-bis(3-methyl-6-tert.-butylphenol). As sulphur compounds phenylalkylsulphides, p-nitrophenylalkylsulphides and some other p-substituted phenylsulphides were used. The effect of these mixtures was studied at 180°C in oxygen atmosphere.     

Thermal conductivity of several exfoliated graphites from 2 k to 300 k

The thermal conductivity of several exfoliated graphites (Grafoil, Foam, and UCAR-ZYX graphite) has been measured in the range 2 to 300 K. The temperature dependence of the thermal conductivity is similar to that of near-single-crystal pyrolytic graphite, but the value is two orders of magnitude lower.     

Electron transport properties of palladium-ruthenium alloys from 50 mK to 4.2 K

The thermopowerS, resistivity , thermal conductivity , and thermoelectric ratioG of alloys nominally of 0.1, 0.5, 1.0, and 5 at % Ru in Pd have been measured from 50 mK to 4 K. The thermopowerS varies essentially linearly withT, and is only a slowly varying function of concentration up to 1 at % Ru. The characteristic thermopower of Ru in Pd for the 0.1 at % alloy is (0.23±0.01) T µ V/K. At temperatures below 0.15 K there are departures from linearity, presumably caused by magnetic impurities. In the same temperature rangeG shows large departures from the expected constant value. The Lorenz ratioL obtained from two independent sets of data,S/GT and /T, are in good agreement. Departures ofL from the Sommerfeld valueL ₀ are discussed.Work supported by the National Science Foundation under Grant number DMR-75-01584.