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.
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.
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 (Al)and sixfold- coordinated AI (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 Al (averaged for eight samples) to 1567.8 eV for Al and to 1568.3 eV for Al(averaged for 17 samples). For Al and 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 Al and 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).