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  • Author: G. X. Pan x
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Abstract

This study elucidates the relationship between the dissolution of pulp components and the development of fiber bonding properties in alkaline peroxide bleaching of aspen mechanical pulp. In general, bleaching reactions cause the removal of pulp substances from the fibers, which in turn improves pulp strength properties. Nonetheless, alkaline hydrolysis is particularly important to the development of strength because this reaction mechanism plays a key role in imparting additional carboxylic acid groups onto the fibers. The strong correlation between fiber carboxylic acid group concentration and the amount of anionic dissolved substances makes it possible for us to predict the strength properties of bleached pulps by estimating the anionicity of bleaching filtrates using analytical methods such as cationic demand. The paper also provides insights into the importance of the alkalinity in peroxide bleaching to the dissolution of pulp materials and the strength development.

Summary

The present paper reports our investigation into the use of two peroxygen reagents, peroxymonosulfate (PMS) and dimethyldioxirane (DMD), in bleaching sequences with peroxide to bleach wheat straw mechanical pulp, their reactivity with ferulic acid model compounds, and the likely relation between the two aspects. It was observed that combinations of PMS or DMD with peroxide offered a synergy leading to substantially improved brightness development in bleaching of wheat straw pulp. At the same time, these oxidizing reagents, especially DMD, were shown to be highly reactive with ferulic acid derivatives and increased the removal of ferulic acid from wheat straw pulp in bleaching. The results would suggest that the presence of non-lignin, peroxide-resistant chromophoric components, such as ferulic acid derivatives, might be an important factor limiting the brightness development of wheat straw mechanical pulp by conventional peroxide bleaching.

Nontransferred direct current (dc) laminar plasma jets of pure argon were generated at atmospheric pressure, with a generator having an interelectrode insert. Associated with the experimental investigation, similarity theory was adopted to examine the arc voltage characteristics, thermal efficiency, and jet length change of the laminar plasma. Jet flow temperature and velocity were evaluated by various methods. The jet shows good stability, reproducibility, and regular flow field change as functions of generating parameters. Applications of laminar plasma jets for ZrO2 ceramics spray coating and remelt strengthening of metal surface were attempted. The results indicated favorite process efficiency and controllability of the laminar plasma heating.

Abstract

C11H14Cl4CuN2O, orthorhombic, P212121 (no. 19), a = 7.737(2) Å, b = 10.131(2) Å, c = 20.229(3) Å, V = 1585.6 Å3, Z = 4, R gt (F) = 0.040, wR ref (F 2 ) = 0.079, T = 298 K.

Abstract

Al K-edge X-ray absorption near-edge structure (XANES) spectra of a range of aluminosilicate and aluminum oxide minerals were collected using synchrotron radiation. The Al K-edge spectra of aluminosilicates containing fourfold-coordinated Al ([4]Al)and sixfold- coordinated AI ([6]Al)are qualitatively interpreted on the basis of a comparison with the Si K-edge spectra of α quartz and stishovite and MO calculations for tetrahedral and octahedral clusters. Some near-edge features are attributed to the multiple scattering (MS) effect from the more distant shell atoms. The Al K-edge (peak C) shifts toward higher energy with an increase in the coordination number (CN) of Al, from 1566.7 eV for [4]Al (averaged for eight samples) to 1567.8 eV for [5]Al and to 1568.3 eV for [6]Al(averaged for 17 samples). For [4]Al and [6]Al aluminosilicates, respectively, the Al K-edge shifts to higher energy with increase in the Al-O bond distance (dAl-O), distortion of the Al polyhedron (ΔAl-O),and decrease in the Al-O bond valence (SAl-O). Also for [4]Al and [6]Al aluminosilicates, the relative intensity of the Al K-edge is correlated with the content (in weight percent) of Al in tetrahedral and octahedral sites, respectively. This correlation therefore establishes Al K-edge spectroscopy as a potential technique for semiquantitatively determining the distribution of Al between fourfold- and sixfold-coordinated sites.

The two-dimensional arrays of various metal nanowires with diameters ranging from 15 to 70 nm have been fabricated by electrodepositing metals of Cu, Ag, Au, Ni, and Co into the nanoholes of the anodic aluminum oxide (AAO) films, followed by partial removal of the film. The strong surface-enhanced Raman scattering (SERS) effects were observed from the metal nanowire arrays including Ni, Co metals that were normally considered to be non-SERS active substrates. It has been shown that metal nanowire arrays can serve as very good SERS active substrates, especially for transition metals. The SERS intensity of the probe molecule adsorbed at the nanowires depends critically on the length of the nanowires explored at the surface. And the band frequency is very sensitive to the diameter, which reflects the change in the electronic property of metal nanowires. Applying this probe molecule strategy, SERS could develop into a diagnostic tool of metal nanowires (nanorods).