Yu Shu-Qin

Studies on the thermal behavior of polyurethanes

The number of fires appear to be increasing all over the world with some big fires started from burning sofa polyurethane foam (PUF). The general public is quite concerned about the risk of fire due to the extensive use of polyurethane-based materials. Better understanding of the fire behavior of the materials would provide guidelines on fire safety provision. The first step is to review the thermal decomposition mechanisms of polyurethane under different environmental conditions, which will be reported in this paper. Recent studies on the thermal decomposition kinetics and thermal stability of polyurethane are described. Thermal decomposition and combustion reactions of polyether-polyurethane and polyester-polyurethane in air and nitrogen atmospheres investigated by using thermogravimetry analysis will then be outlined. The kinetic processes of polyurethane decomposition studied by the model fitting method are discussed. Polyester-polyurethane was found to be thermally more stable than polyether-polyurethane. The presence of oxygen would significantly affect the breaking down of the polymeric chains. Fire retardants for polyurethane are also briefly reviewed. Results are useful for developing fire retardants for polyurethane-based materials with better fire behavior.

Electroless Copper Deposition in the Photographic Gelatin Layer

An electroless copper deposition process consisting of two stages: (1) forming gold catalytic centers, and (2) electroless copper deposition, was studied in this paper. The changes of the chemical state of sulfur in photographic gelatin before and after electroless copper deposition were studied by X-ray photoelectron spectrometry. The depth distribution of copper and gold within the electrically conductive layer produced by electroless copper deposition was determined and the mechanism of electroless copper deposition catalyzed by gold in the photographic gelatin layer was discussed. The results indicated that under acidic conditions (pH 3.20), methionine sulfoxide in the gelatin macromolecule had relatively high reducing power. When the gelatin sample was immersed into the chloroauric acid solution, methionine sulfoxide and methionine were oxidized to methionine sulfone, reducing Au 3+ to colloid gold which acted as the catalytic center at the initial stage of the electroless copper deposition. During the electroless deposition, the reduction of Cu 2+ by HCHO could continue, and even the copper completely covered the gold because the reaction was autocatalyzed by newly formed copper.

The UV laser photolysis of stibine

Abstract The 403–700 nm emission spectrum observed in ArF laser photolysis of stibine was recorded for the first time and was assigned to the SbH 2 (A 2 A 1 → X 2 B 1 ) transition. More than fifty emission lines arising from the transitions of Sb(6s → 5p) were also observed.

Resonance-enhanced multiphoton ionization spectra of the halogen atoms

The resonance-enhanced multiphoton ionization (REMPI) spectra of atomic chlorine and bromine in the range of 230-245 nm and 250-285 nm were obtained by using REMPI and time of flight (TOF) techniques. There are twenty-six lines for Cl and twenty-three for Br in the spectra, among which five transitions of Cl and four of Br are observed for the first time. These lines are due to transitions from the Cl(3p 2P3/20, 2P1/20) and Br(4p 2P3/20, 2P1/20) states to upper states induced by two-photon excitation. It is found that the Stark shift of different excited states are almost the same, and they are independent of the S, L, and J quantum numbers of the excited state.