Gelation mechanism and mechanical properties of Tetra-PEG gel

Tetra-PEG gel has drawn much attention as a polymer gel with extremely suppressed heterogeneity, which is known as the intrinsic characteristics of polymer networks, and is difficult to control. Tetra-PEG gel is formed by a novel fabrication method, i.e., AB-type crosslink coupling, which is polycondensation between mutually reactive multi-armed polymers forming a polymer network. AB-type crosslink coupling has advantages on suppressing the heterogeneity over conventional polycondensation. In this review, we focused on the gelation reaction and the relationship between the mechanical properties and structure. The reaction proceeded as a simple second order reaction of A and B end-groups from the initiation to the end (approx. 90%), suggesting the homogeneous mixing of two prepolymers. The model predicting the elastic modulus of Tetra-PEG gel shifts from the phantom to affine network models with an increase in polymer concentration. The fracture energy is well predicted by the Lake–Thomas model. These experimental studies also suggest that Tetra-PEG gel has extremely homogeneous network structure and is a candidate material for evaluating the basic physical properties of polymer gels.     

Spheroidization of Titanium Carbide Powders by Induction Thermal Plasma Processing

Highly spherical particles of titanium carbide (TiC) have been produced by in-flight heat processing of irregularly shaped TiC powders in an aerosol reactor under argon-hydrogen and argon-helium induction thermal plasma. The spherical powders obtained by the plasma treatment consist of unagglomerated and uniform particles with mean diameters between 25 and 28.5 μm, which is smaller than the original TiC particle mean diameters (29.5 μm) because of partial evaporation of the particles during the plasma treatment. The spheroidization ratio of the treated TiC powders increases with the increase of hydrogen flow rate in plasma gases and the reduction of powder feeding carrier gas flow rate. Under certain processing conditions, the TiC powders have been completely spheroidized. The morphology and structure of individual spherical particles were examined and their formation mechanism was discussed based on calculation of heat transfer kinetics of the particles in the thermal plasma.     

Experimental study about the agglomeration behavior in slurry prepared by adding excess polyelectrolyte dispersant

In our previous paper we found that the particles in the slurry can agglomerate by adding larger amount of polyelectrolyte dispersant compared to that needed to attain well dispersion. Thus, the dependency of initial particle concentration on the agglomeration and its mechanism in slurry prepared by adding excess polyelectrolytes was experimentally discussed. It was shown that agglomeration behavior strongly depends on the additive amount of polyelectrolytes, not on the polyelectrolyte concentration in the solution. It was also found that the dominant factor of agglomeration in slurry prepared by adding extra polyelectrolytes should be the compression of the electrical double layer by the increased counter ion concentration, not by the so called depletion effect or by pH change. Interestingly, the final sediment had a relatively high packing fraction and good flowability in the case of the agglomerated slurry with extra polyelectrolytes compared to that of the agglomerated slurry with an additional NaCl solution.     

Surface modification of titanium oxide in pulse-modulated induction thermal plasma

Recently, it was reported that RF induction plasma of a pulse-modulated operating mode had been successfully generated, for the first time, at a sufficiently high electric power level for materials processing. The unique conditions in the plasma, such as a non-equilibrium situation at the instance of pulse-on and -off and the increase of chemically reactive radical species, as well as the time-dependent change of plasma temperature, is expected to offer the unique physico–chemical conditions necessary for materials processing. As the first step of the work directed to materials processing, the thermal and chemical interactions between plasma and solid materials were examined for both cases of pulse-modulated and continuous modes. Green compacts of titanium dioxide (TiO₂), whose characteristics strongly depend on the formation of lattice defects and the incorporation of hydrogen, were treated in Ar---H₂ plasma of continuous and pulse-modulated generation modes. The oxide disks were placed at the downstream of plasma flow. The sample position and the plasma generation pressure were changed as processing parameters. The plasma-treated specimens were characterized by X-ray diffractometry and the hydrogen content was measured. The plasma treatment gave a thermal effect, rather than a chemical one, on the surface of oxide specimens. The oxides were thermally reduced by the plasma treatment and showed a change of color at the surface, while XRD did not show a change of crystal structure. Comparing specimens treated in the pulse-modulated plasma with those treated in the continuous plasma, the disk specimens had less of a thermal effect on the plasma.     

Development of a novel slurry condensation method by applying dispersant instead of flocculant

A novel filtration technique has been developed by adding the dispersant instead of the flocculant used in conventional solid–liquid separation technique. Slurries were prepared by controlling the pH values in order to control the dispersion and flocculation degree of particles. The prepared slurries were condensed by gravitational settling condensation or by pressure filtration condensation. On the gravitational settling condensation for the flocculated slurry, the cake was formed on the filter media and then the filtration could not be continued unless the formed cake was excreted by a mechanical hand-scraping device. In addition, the volumetric concentration of the condensate obtained from the flocculated slurry was at most 15 vol.%. On the other hand, the condensate obtained from the dispersed slurry still possessed fluidity when the concentration reached almost 40 vol.%, therefore we could collect the condensate without any hand-scraping devices. Furthermore, cake formation did not occur for the dispersed slurry, suggesting that the continuous filtration condensation is possible.     

Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO₂) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO₂ coating can be made by performing the PEO in an ammonium acetate (CH₃COONH₄) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO₂ led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity.     

Synthesis of functional nanocrystallites through reactive thermal plasma processing

A method of synthesizing functional nanostructured powders through reactive thermal plasma processing has been developed. The synthesis of nanosized titanium oxide powders was performed by the oxidation of solid and liquid precursors. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, were used to vary the quench rate, and therefore the particle size, of the resultant powders. The experimental results are well supported by numerical analysis on the effects of the quench gas on the flow pattern and temperature field of the thermal plasma as well as on the trajectory and temperature history of the particles. The plasma-synthesized TiO₂ nanoparticles showed phase preferences different from those synthesized by conventional wet-chemical processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via reactive thermal plasma processing.     

Thermal behavior of small lithium‐ion secondary battery during rapid charge and discharge cycles

The secondary batteries for an electric vehicle (EV) generate much heat during rapid charge and discharge cycles above the rated condition, when the EV starts quickly consuming the battery power and stops suddenly recovering the inertia energy. During rapid charge and discharge cycles, the cell temperature rises significantly and may exceed the allowable temperature. We calculated the temperature rise of a small lithium‐ion secondary battery during rapid charge and discharge cycles using our battery thermal behavior model, and confirmed its validity during discharge cycle at current smaller than the discharge rate of 1C. The heat source factors were measured by the methods described in our previous study, because the present batteries have been improved in their performance and have low overpotential resistance. The battery heat capacity was measured by a twin‐type heat conduction calorimeter, and determined to be a linear function of temperature. Further, the heat transfer coefficient was measured again precisely by the method described in our previous study, and was arranged as a function of cell and ambient temperatures. The calculated temperature by our battery thermal behavior model using these measured data agrees well with the cell temperature measured by thermocouple. Therefore, we can confirm the validity of this model again during rapid charge and discharge cycles. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 17–25, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20249 Copyright © 2006 Wiley Periodicals, Inc.     

An Experimental Study on Aerodynamic Sound Generated from Wake Interference of Circular Cylinder and Airfoil Vane in Tandem

The purpose of this study is to investigate the characteristics of aerodynamic sound generated from wake inter-ference of circular cylinder and airfoil vane located in tandem and to clarify the generation mechanism of thesound source with discrete frequency.The effects of the interval between the cylinder and the airfoil on the char-acteristics of aerodynamic sound are investigated by acoustic measurement,flow visualization and explorationtest of sound source.The relation between the flow field and the sound field with discrete frequency noise(DFN)is shown,and then it is found that the downstream airfoil works as the sound source of DFN,which has the fre-quency of vortex shedding from the upstream cylinder,when the interval of two bodies is longer than a criticaldistance.     

Preparation and characterization of a nanofiber mat consisting of Tetra‐PEG prepolymers

Tetra‐PEG gel, which has been known as a mechanically tough and biocompatible gel, was processed into a nanofiber mat by electro‐spinning (ES) and 2‐step treatment process using w/o type emulsion consisted of the Tetra‐PEG prepolymer 1‐octanol/water solution. The 2‐step treatment was carried out in order to increase the cross‐linking points to the as‐spun nanofibers. From this study, we succeeded in insolubilizing poly(ethylene glycol) (PEG) nanofiber, and it was found that the Tetra‐PEG gel nanofiber mat showed high tensile property even at swollen state. The elastic modulus at equilibrium swollen state was 4.5 kPa. In addition, we compared the differences of the structure and tensile property between the Tetra‐PEG nanofiber mat and porous Tetra‐PEG gel prepared by freeze‐dry method. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41353.