Morphological changes of calcium hexaboride powder synthesized from condensed boric acid-polyol product

We previously reported a novel low-temperature synthesis method for calcium hexaboride (CaB₆) powder via the transient formation of boron carbide (B₄C) using a condensed boric acid (H₃BO₃)-polyol product. In this study, the effect of the type of polyol on the morphology of the CaB₆ powder was investigated. Three types of polyol, glycerin, mannitol, and poly(vinyl alcohol) (PVA), were used for the preparation of condensed H₃BO₃-polyol products since the B₄C particles prepared from these polyols exhibit different morphologies. CaB₆ powder was successfully synthesized at a low temperature of 1400?°C regardless of the polyol used. The size of the obtained CaB₆ particles varied with the polyol used, which reflected the size of the B₄C particles prepared using the corresponding polyol. These results indicate that the morphology of the obtained CaB₆ powder is derived from that of the transiently formed B₄C particles.     

Effects of dissolved oxygen in saline on corrosive wear of steel

Wear behavior in a corrosive electrolyte where the corrosion reaction is controlled by the diffusion of oxygen cannot be explained only by the removal of corrosion products. The thickness of the oxide layer which varies with test conditions greatly affects the wear rate as well as the corrosion rate. In saline containing O₂ of 1 p.p.m. surface activation was confirmed. Adhesive wear or fatigue wear was found to have a predominant influence on wear behavior. Lubrication by a small amount of oxidation product can be expected to be beneficial. In O₂-saturated saline damage caused by corrosion fatigue is important owing to the intensely corrosive environment. Under O₂-saturated conditions the wear rate is constant under a load P < 3 4 kg, whilst w increases with increasing P above 3 4 kg, which may be considered to be due to the change of contact conditions. Under conditions of O₂-1 p.p.m. wear rate decreases slightly with increase of load because of the more effective lubrication by corrosion products.     

Production of single-chain variable fragment antibody (scFv) in fed-batch and continuous culture of Pichia pastoris by two different methanol feeding methods

This study examined the effects of two methods of methanol feeding, DO-stat and methanol concentration control, in fed-batch and continuous cultures of Pichia pastoris on cell growth and single-chain variable fragment antibody (scFv) expression. By maintaining the methanol concentration at 3.9 g l(-1) in fed-batch culture, a scFv concentration of 198 mg l(-1) was obtained. In continuous culture using both methanol feeding methods, the scFv concentration in the fermentation broth increased with a decreasing dilution rate. A maximum scFv concentration of 810 mg l(-1) at a dilution rate of 0.0094 h(-1) was obtained by maintaining the methanol concentration at 3.9 g l(-1). Although the specific methanol consumption rate was the same for both methods, the specific productivity of scFv was higher in methanol concentration control from 0.0094 to 0.049 h(-1) than it was in DO-stat control. Therefore, continuous culture with methanol feeding by the concentration control method shows promise for the industrial scale production of recombinant proteins by Pichia pastoris.     

Encapsulation of hemoglobin in mesoporous silica (FSM)-enhanced thermal stability and resistance to denaturants

Hemoblogin (Hb), which is a typical oligomeric protein, was introduced into the pores of mesoporous silica (FSM: folded-sheet mesoporous material) that had a diameter of 7.5 nm. Soret CD spectra of Hb-FSM-7.5 conjugates showed a peak that was identical to that of free Hb. This suggests that Hb retained its highly ordered structure in the mesoporous silica. In addition, the UV-visible absorption spectrum showed that Hb had an increased resistance to heat denaturation in the silica. Even after heat treatment at 85 degrees C, Hb-FSM-7.5 retained its ligand-binding activity. The stability of Hb-FSM-7.5 was examined further by measuring its peroxidase-like activity. Encapsulation of Hb resulted in the retention of activity in the presence of high NaCl or Gdn-HCl levels. This suggests that encapsulation prevented dissociation and denaturing. Thus, it seems that the mesopores created a favorable environment for the oligomeric protein to perform its function, even under harsh conditions.     

Low‐Temperature Synthesis of Calcium Hexaboride Powder via Transient Boron Carbide Formation

Calcium hexaboride (CaB₆) powder was synthesized by carbothermal reduction using a low‐temperature synthesis method for boron carbide (B₄C) powder. A B₄C precursor consisting of boron oxide (B₂O₃) and carbon components was prepared from a condensed boric acid (H₃BO₃)‐poly(vinyl alcohol) (PVA) product by thermal decomposition in air, which was then mixed with calcium carbonate (CaCO₃) powder. CaB₆ was formed via the transient formation of calcium borate (Ca₃B₂O₆) and B₄C, which were in close contact owing to the finely dispersed B₂O₃/carbon structure of the B₄C precursor. CaB₆ powder with fine particles was synthesized by heat treatment at 1400°C for 10 h in an Ar flow.     

Premixed flame propagating into a narrow channel at a high speed, part 1: Flame behaviors in the channel

This paper deals with the transient behavior of a flame flowing into a narrow channel from a chamber filled with a propane---air mixture.

The flame was observed through direct or schlieren high speed photography, and at the same time the arrival at the entrance and exit of the channel were detected by ion gaps. From the experimental results it was found that in some cases the flame extinguished or hesitated in the channel before passing through. These behaviors were dependent on the equivalence ratio of the mixture, the channel width, and the flame inflow velocity.

Flame standstill in the channel is assumed to be caused by continuous quenching of hot reacting gas due to turbulent mixing with cold unburned gas at the contraction region established near the entrance of the channel. For any specific mixture, when the channel entrance is rounded or the inflow velocity is low, the minimum width of the channel for which a flame will run through without any retardation becomes smaller compared with the case of a sharp-edged entrance or a high inflow velocity. On the contrary, the minimum width of the channel for which a flame cannot pass through does not depend on the corner roundness of the channel entrance or the inflow gas velocity.     

Effect of thermal history on high‐valence chromium ion dissolution in merwinite (3CaO·MgO·2SiO2)

Solubility and local structure of transmission elements in calcium silicate compounds has not been well understood. We investigate the local structure of chromium ions dissolved in merwinite (3CaO·MgO·2SiO₂) of a monoclinic crystal structure. The acceptance of doping elements into merwinite has not been reported before. We found that chromium ions are soluble in merwinite in air and that chemical valence of the dissolved Cr ions varies with annealing temperature. The absorption edge in the x‐ray absorption near edge structure (XANES) of Cr‐doped merwinite indicated that octahedrally coordinated Cr³⁺ ions were mainly formed when annealed at 1673 K in air. A pre‐edge peak was also detected, indicating the existence of tetrahedrally coordinated high‐valence Cr ions. Conversely, through annealing of merwinite at 1123 K in air, tetrahedrally coordinated Cr⁶⁺ ions were found to be the main form of chromium. XANES spectra simulated by first‐principle calculations were used to explain the structural features in the observed spectra. We propose the coexistence of Cr³⁺ ions in octahedral Mg²⁺ sites and high‐valence Cr ions in tetrahedral Si⁴⁺ sites. In addition, a change in the chromium ion oxidation state in tetrahedral coordination sites was suggested by XANES spectroscopy of Cr‐doped merwinite synthesized at 1673 K and reannealed at 1123 K.