Application of a Two-Dimensional Computer Simulation to Cake Growth in Slip Casting with Complicated-Shape Gypsum Molds

A two-dimensional computer simulation method, developed by the authors using the method of finite differences, was applied to estimate the cake growth in slip casting of alumina with a triangular gypsum mold and a box-type gypsum mold with a convex bottom. The cake growth patterns, water penetration patterns, water flow rate distributions, and pressure distributions were simulated in the molds and/or cakes. The simulated cake growth patterns were in good agreement with those observed experimentally in both molds. Moreover, the cake growths could be well understood from the results of the water flow rate distributions in each case. The present method is applicable to cake growth simulation in slip casting with complicated-shape gypsum molds.     

Miscibility and pressure‐sensitive adhesive performances of acrylic copolymer and hydrogenated rosin systems

Relationship between the miscibility of pressure‐sensitive adhesives (PSAs) acrylic copolymer/hydrogenated rosin systems and their performance (180° peel strength, probe tack, and holding power), which was measured over a wide range of time and temperature, were investigated. The miscible range of the blend system tended to become smaller as the molecular weight of the tackifier increased. In the case of miscible blend systems, the viscoelastic properties (such as the storage modulus and the loss modulus) shifted toward higher temperature or toward lower frequency and, at the same time, the pressure‐sensitive adhesive performance shifted toward the lower rate side as the T_g of the blend increased. In the case of acrylic copolymer/hydrogenated rosin acid systems, a somewhat unusual trend was observed in the relationship among the phase diagram, T_g, and the pressure‐sensitive adhesive performance. T_g of the blend was higher than that expected from T_gs of the pure components. This trend can be due to the presence of free carboxyl group in the tackifier resin. However, the phase diagram depended on the molecular weight of the tackifier. The pressure‐sensitive adhesive performance depended on the viscoelastic properties of the bulk phase. A few systems where a single T_g could be measured, despite the fact that two phases were observed microscopically, were found. The curve of the probe tack of this system shifted toward a lower rate side as the T_g increases. However, both the curve of the peel strength and the holding power of such system did not shift along the rate axis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 651–663, 1999     

Effect of Mo on corrosion behavior of Ni20Cr–xMo alloys in air with NaCl–KCl–CaCl2 vapor at 570°C

The effect of Mo on the corrosion behavior of Ni20Cr–xMo alloys in an oxidizing chlorine-containing atmosphere using air mixed with the salt-vapor mixture of NaCl–KCl–CaCl₂ at 570°C was investigated. The results revealed that the corrosion performance of the Ni20Cr alloys in the oxidizing chlorine atmosphere was improved by Mo addition of up to 3 wt%. The Mo-free alloy formed a potassium chromate during corrosion as a result of the reaction between the Cr₂O₃ scale and KCl vapor. The chromate formation increased the chlorine potential at the scale surface and induced the breakdown of the protective Cr₂O₃ scale, resulting in internal chromium chloride precipitates and a Cr-depleted zone. In contrast, the presence of Mo resulted in the formation of a NiO scale, which did not react with the salt vapors and, therefore, prevented the formation of chromates. The beneficial effect of Mo on the high-temperature chlorination of Ni–Cr alloys in salt-vapor-containing atmospheres was ascribed to the suppression of chlorine generation due to NiO scale formation.     

Fast and Almost Complete Nitridation of Mesoporous Silica MCM-41 with Ammonia in a Plug-Flow Reactor

The title reaction proceeded well to yield silicon (oxy)nitride at 973–1323 K using a plug-flow reactor. The degree of nitridation was studied as a function of temperature and time of nitridation, the sample weight, and the flow rate of ammonia. It was dependent on the reaction temperature and the amount of ammonia supplied per sample weight. The nitridation at 1273 K for 10–25 h yielded the oxynitride with 36–39 wt% nitrogen, which was very close to 40 wt% of Si₃N₄. Characterization with X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy measurements, and nitrogen adsorption revealed the conversion of MCM-41 to the corresponding oxynitride without essential loss of the mesoporous structure, the decrements of the lattice constant and the pore diameter by 20–35%, and the increments of the wall thickness by ca. 45%. Solid-state ²⁹Si nuclear magnetic resonance spectra during the nitridation clearly showed fast decrease in SiO₄ species and slow in SiO₃(OH). Various intermediate species, SiO _x N _y (NH₂ or NH) _z , were observed to be formed and finally, ca. 70% SiN₄ species, ca. 20% SiN₃(NH₂ or NH), and ca. 10% SiON₂(NH₂ or NH) were produced, being consistent with the results of the above mentioned elemental analysis.     

Effect of heating process on the formation of nanoparticles of elastin model polypeptide, (GVGVP)251, by gamma-ray crosslinking

Nanoparticles were prepared by the thermosensitive aggregation of the elastin model polypeptide, (GVGVP)₂₅₁, and gamma-ray crosslinking. Three different heating processes, “slow heating,” “fast heating,” and “heat shock,” were used for the aggregation of the peptide, followed by gamma-ray crosslinking. Only the “heat shock” process successfully yielded stable nanoparticles with diameters of less than ca. 150 nm and a narrow size distribution. Circular dichroism (CD) spectrometry showed that this polypeptide formed a type-II β-turn structure when the temperature was increased to above the cloudy point in the case of the “heat shock” process; suggesting that this structure might contribute to stable nanoparticle formation by gamma-rays. CD spectrometry also suggested that this structure would be affected during the formation of stable crosslinked particles.     

Continuous synthesis of Zn2SiO4:Mn fine particles in supercritical water at temperatures of 400-500 °C and pressures of 30-35 MPa

Sub-micron sized Zn₂SiO₄:Mn²⁺ phosphors particles were continuously synthesized in supercritical water with a flow reactor. Colloidal silica or sodium silicate was used as the Si source. Zn and Mn sources were chosen from their nitrates, sulfates, and acetates. The syntheses were carried out at temperatures from 400 to 500 °C, at pressures from 30 to 35 MPa, at NaOH concentrations from 0.014 to 0.025 M, and for residence times from 0.025 to 0.18 s. Sodium silicate formed α- and β-Zn₂SiO₄:Mn²⁺ phases regardless of the Zn and Mn sources, while colloidal silica formed phases dependent on the type of Zn and Mn sources used in addition to the use of alkali. As the reaction temperature increased, the crystallinity of α-Zn₂SiO₄:Mn²⁺ phase increased and the Mn substitution into the Zn sites of the α-Zn₂SiO₄ phase decreased. Of the conditions studied, the most highly crystalline α-Zn₂SiO₄:Mn²⁺ was produced at a temperature of 400 °C, a pressure of 30 MPa, a NaOH concentration of 0.14 M, and a residence time of 0.13 s with Zn and Mn sulfates and colloidal silica as starting materials. The α-Zn₂SiO₄:Mn²⁺ fine particles synthesized were round in shape, had an average diameter of 268 nm, and exhibited a green-emission with a peak wavelength of 524 nm.     

Spatial distribution of silica fillers in phase-separated rubber blends investigated by three-dimensional elemental mapping

The distribution of nano-sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography combined with energy dispersive X-ray spectrometry (EDX). 3D distribution of silica is visualized by STEM-EDX tomography with the tilt-series of silicon elemental maps, while the phase-separated morphologies of polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) are visualized by STEM-tomography in high-angle-annular-dark field (HAADF) mode. The combination of STEM-EDX and STEM-HAADF tomography enables us to determine the distribution of silica between the two rubber phases quantitatively even with high contents of silica up to 70 phr (weight parts per hundred rubber). It is found that silica is preferentially distributed in the SBR phase, but it is also distributed in the IR phase when the IR fraction in the total rubber components is higher than 40 wt%. The preferential distribution of silica in the SBR phase improves the dispersion of the IR domains. This is the first use of this technique for a multicomponent polymer system, showing the advantage to characterize the complicated multicomponent polymer composite morphologies.     

Directed Evolution of a Cp*RhIII-Linked Biohybrid Catalyst Based on a Screening Platform with Affinity Purification

Directed evolution of Cp*Rh^III-linked nitrobindin (NB), a biohybrid catalyst, was performed based on an in vitro screening approach. A key aspect of this effort was the establishment of a high-throughput screening (HTS) platform that involves an affinity purification step employing a starch-agarose resin for a maltose binding protein (MBP) tag. The HTS platform enables efficient preparation of the purified MBP-tagged biohybrid catalysts in a 96-well format and eliminates background influence of the host E. coli cells. Three rounds of directed evolution and screening of more than 4000 clones yielded a Cp*Rh^III-linked NB(T98H/L100K/K127E) variant with a 4.9-fold enhanced activity for the cycloaddition of acetophenone oximes with alkynes. It is confirmed that this HTS platform for directed evolution provides an efficient strategy for generating highly active biohybrid catalysts incorporating a synthetic metal cofactor.     

Synthesis of thermoresponsive copolymer/silica-coated magnetite nanoparticle composite and its application for heavy metal ion recovery

To enhance chemical stability and suppress of aggregation of magnetite nanoparticles (MNPs), which are used as a support for thermoresponsive copolymer immobilization, silica coating of the MNPs is applied via the electrooxidation method. Although the resulting silica coated-MNPs also formed aggregates, the size distribution of the aggregate shifted to smaller size range. Because of that, the surface area available for copolymer immobilization increased approximately 6.7 times at maximum as compared with that of the uncoated MNPs. It contributed to the increase of the amount of the immobilized copolymer on the silica-coated MNPs, which is approximately four times larger than that on the uncoated MNPs. Fe₃O₄ dissolution test confirmed enhancement of chemical stability of MNPs. The thermoresponsive copolymer immobilized on the silica-coated MNPs shows the ability to recycle Cu(II) ion from Cu(II) containing solution by changing temperature with significantly shorter time than those in other thermoresponsive adsorbents in gel form.