A porous material prepared from the layer-type complex consisting of montmorillonite and α-naphthylamine

Aqueous mixtures of montmorillonite and -naphthylamine with various mixing ratios were kept at 353 K for 3 days with stirring to convert them into the layer-type complex (MNC) consisting of both components, and then dried at 403 K. The resulting blocks, several centimetres in size, were heated below 1473 K under nitrogen. The addition of -naphthylamine (NA) in the equivalent amount to the cation exchange capacity of montmorillonite resulted in the most attractive porous material which includes homogeneous pores of 35nm radius and exhibits a maximum pore volume of 0.8 ml g^–1 at 873 K. The samples containing greater and lesser amounts of NA gave a very brittle block and a less porous block after heating to high temperature, respectively. The materials obtained were also characterized by the waved card-house structure. The amount of NA added and the heat-treatment temperature did not vary the pore size so widely.     

Thermal degradation behaviour of montmorillonite-α-naphthylamine complex under nitrogen

A thin film of montmorillonite--naphthylamine complex (MNC) was prepared, and then subjected to -ray radiation and heating to 473 K for polymerization of the inserted naphthylamine. MNC was subsequently heated to various temperatures below 1473 K under nitrogen. Montmorillonite film (Mont) was also treated in the same way as the reference sample. Compared with Mont, the MNC-layered structure was remarkably thermally stable and remained so slightly, even after heating to 1273 K. MNC was found to have a homogeneous porous structure after heating to 1273 K. Through comparison with Mont, the thermal degradation behaviour of MNC is discussed on the basis of X-ray diffraction, FT-IR, TG-DTA, elemental analysis, mass spectrum and SEM observations.     

Oxidation resistivity of montmorillonite-α-naphthylamine complex heated under nitrogen

A thin film of montmorillonite--naphthylamine complex (MNC) was heated to various temperatures below 1473 K for 5 min under nitrogen. The resulting samples were further heated to 1073 to 1473 K for 30 min or 5 h in air to examine their oxidation resistivities. A thin montmorillonite film was also treated in the same manner for reference purposes. The layered structure of MNC was retained up to 1273 K under nitrogen, although it changed gradually to an amorphous state with increase in temperature. MNCs after heating below 1073 K under nitrogen were changed to montmorillonite by subsequent heating to 1073 K for 30 min in air, whereas, MNCs heated to 1173 and 1273 K under nitrogen retained somewhat their layered structures, even after heating to 1173 K for 30 min in air. The causes for such differences are discussed on the basis of the results obtained from X-ray diffraction, thermogravimetry, FT-IR and SEM observation.     

Iontophoresis from a micropipet into a porous medium depends on the ζ-potential of the medium

Iontophoresis uses electricity to deliver solutes into living tissue. Often, iontophoretic ejections from micropipets into brain tissue are confined to millisecond pulses for highly localized delivery, but longer pulses are common. As hippocampal tissue has a ζ-potential of approximately -22 mV, we hypothesized that, in the presence of the electric field resulting from the iontophoretic current, electroosmotic flow in the tissue would carry solutes considerably farther than diffusion alone. A steady state solution to this mass transport problem predicts a spherically symmetrical solute concentration profile with the characteristic distance of the profile depending on the ζ-potential of the medium, the current density at the tip, the tip size, and the solute electrophoretic mobility and diffusion coefficient. Of course, the ζ-potential of the tissue is defined by immobilized components of the extracellular matrix as well as cell-surface functional groups. As such, it cannot be changed at will. Therefore, the effect of the ζ-potential of the porous medium on ejections is examined using poly(acrylamide-co-acrylic acid) hydrogels with various magnitudes of ζ-potential, including that similar to hippocampal brain tissue. We demonstrated that nearly neutral fluorescent dextran (3 and 70 kD) solute penetration distance in the hydrogels and OHSCs depends on the magnitude of the applied current, solute properties, and, in the case of the hydrogels, the ζ-potential of the matrix. Steady state solute ejection profiles in gels and cultures of hippocampus can be predicted semiquantitatively.     

Thermal degradation behaviour of the layer-type complexes of montmorillonite/α-naphthylamine,saponite/α-naphthylamine and their mixtures

Samples of montmorillonite/-naphthylamine complex (MNC), saponite/-naphthylamine complex (SNC) and their mixtures were heated at temperatures below 1473 K under a nitrogen atmosphere to examine macroscopic structural change and crystalline phases deposited after pyrolysis. SNC resulted in a dense structure after pyrolysis. Heating of samples of MNC/SNC mixtures gave a porous structure which became dense as the proportion of SNC increased. No porosity measured by the mercury porosimeter was detectable in samples pyrolysed from MNC containing more than 25% SNC. After pyrolysis, the MNC/SNC mixtures gave crystalline phases which were never formed in the pyrolysed pure MNC and SNC. The formation of these crystalline phases was explained by reference to the chemical compositions of the mixtures and the phase diagram.     

Properties of hydrothermally modified silica gels — Effect of the parameters of porous structure on the course of the modification process

The effect of the parameters of globular structure (diameter of globules and number of their contact points) on the course of a texture modification process has been examined. Modification of silica gels was carried out in an autoclave at elevated pressure in the temperature range 110–300°C and in a water vapour atmosphere. Silica gels having specific surface area of 64–830 m²/g and predominant pore radii of 40–1000 Å were modified. The mechanism of hydrothermal treatment is relatively complex. It depends, among other things on different parameters of globular texture, the temperature of a process and on the presence of different admixtures in the adsorbent being modified. Above 200°C the course of hydrothermal modification depends only slightly on the nature of the silica gel (narrow or wide porous).     

Preparation and thermal degradation behaviour of a layer-type complex consisting of TaS2 and α-naphthylamine

A layer-type complex TaS₂ (α-naphthylamine)_0.46 having a basal spacing of 2.2 nm was prepared by soaking a mixture of the components in an ampoule at 433 K for 25 to 35 days. This complex was resealed in an ampoule after purification, followed by γ-radiation and heating to 473 K. The resulting sample was again heated at various temperatures below 1273 K. On heating to 643 K, the insertedα-naphthylamine polymerized, although with some removal from the complex, with a decrease in basal spacing to 1.35 nm. Another complex appeared faintly simultaneously. This second complex with a basal spacing of 0.96 to 0.92nm formed more abundantly on heating to 773 K and then decreased in amount at higher temperature. The complex decomposed at1273 K to result in TaS₂. Such thermal degradation behaviour is discussed from the standpoint of preparation of the layer-type complex consisting of TaS₂ and carbon.     

Effects of ageing on the temperature coefficient of resistivity of a β titanium alloy

The temperature coefficient of electrical resistivity (TCR) of the commercial Ti-15-3 alloy is negative, if the alloy is in the 100% condition. The TCR increases from negative to positive values as a result of precipitation of the and phases during ageing. An incubation or transient period, during which the value of TCR remains essentially unchanged, precedes the formation of the phase; this transient period decreases with increasing ageing temperature over the range 250–400 °C. Changes in the value of TCR signal the initiation of beta decomposition before the phase can be detected by conventional TEM and diffraction techniques. Reversion of the phase by up-quenching after ageing restores the original negative value of TCR. If both and phases are present in the aged condition, only partial recovery of the quenched TCR value is possible, indicating that the alpha phase is not reverted by up-quenching. The results point to the potential value of TCR determinations for monitoring the initiation of decomposition in titanium alloys exposed to temperatures above room temperature.     

Effects of pore sizes on the electrical properties for porous 0.36BS–0.64PT ceramics

Porous BiScO₃–0.64PbTiO₃ (0.36BS–0.64PT) ceramics were fabricated by using burnable plastic sphere technique. Self-synthesized polystyrene microsphere (PS, φ0.36 μm) and poly methyl methacrylate (PMMA, φ2, 10 and 18 μm) micro-balls were selected as PFA. The porosity, microstructure and electrical properties were investigated for porous 0.36BS–0.64PT ceramics fabricated with different particle sizes of pore forming agents (PFA). With increasing particle sizes of PFA, the pore size and porosity increased. Meanwhile relative permittivity (ε _r), piezoelectric coefficient (d ₃₃, ?d ₃₁) and electromechanical coupling coefficients (k _p, k _t) decreased. The mechanical quality factor (Q _m), elastic coefficient (s ¹¹), hydrostatic voltage coefficient (g _h) and hydrostatic figure of merit increased accordingly. Finally, the effects of particle sizes of PFA on the microstructure and electrical properties were discussed.     

SEM study of the fractured surfaces of films and blocks prepared from montmorillonite and its complex with α-naphtylamine

Four samples were heated under nitrogen to determine the relations between heat-treatment conditions and the topographies of the fractured surfaces of the resulting samples. The samples used were thin films (several 10m thick) of lithium-montmorillonite (Mont) and its complex (MNC) with-naphtylamine, and the blocks of raw montmorillonite and its complex with-naphtylamine (MNC). Two characteristic topographies were obtained from MNC film. They were of a very dense structure with the memory of a layered structure after heating to about 1173 K at 1 or 5 K min^–1, and a homogeneous fine porous structure after heating to 1173 to 1273 K at 40 K min^–1. An unique porous structure was also obtained from MNC block, several millimetres thick by heating to 873 K for 1H. However, Mont, in both film and block, was not suitable for preparation of the homogeneous structure, regardless of porous or dense structures.     

Influence of Turbulence on the Deposition of Particles from a Gas‐Dispersed Flow on the Wall

Simulation of the scattering and deposition of dispersedphase particles in the region of interaction of a turbulent flow with an obstacle is considered. The regimes and distinctive features of deposition of particles in the vicinity of a critical point are investigated under different conditions. The sedimentation coefficient of the impurity is calculated as a function of the parameters of unperturbed flow and the particle size. The results of the calculations are compared to the data obtained without allowance for the influence of the fluctuations of the carrierflow velocity on the motion of the impurity.     

Environmental Effects on the Room Temperature Ductility of a TiAl Based Alloy

The effects of different environments and strain rates on the room temperature ductility of a TiAl based alloy with the composition Ti-46Al-2Cr-0.2Si-0.1Nd have been investigated in this paper. The results show that the TiAl based alloy is susceptible to environmental embrittlement at room temperature. The tensile ductility of the TiAl based alloy in difFerent test environments decreases in the sequence of oxygen> air>hydrogen>argon saturated with water vapor. The ductility is also sensitive to strain rate. It increases with increasing strain rate when tested in hydrogen gas. Both H2O and H2 cause environmental embrittlement, with the former being a more potent embrittler     

Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni3Al alloys

Abstract

The aim of this study was to elucidate the beneficial role played by platinum addition in promoting the formation of a protective Al₂O₃ scale on γ′-Ni₃Al+γ-Ni alloys during oxidation at high temperatures. To do this, the early-stage oxidation behavior of γ′-Ni₃Al-based alloys of composition (in at.%) Ni–22Al and Ni–22Al with 10, 20, and 30 Pt was investigated in terms of oxidation kinetics, scale evolution and resulting composition profiles during heating to 1150°C in air. Platinum addition did not appear to affect the nature of the native oxide layer present on the γ′-based alloys at room-temperature; however, it was found that the presence of increasing Pt content aided in promoting the establishment of a continuous Al₂O₃ scale during heating above about 600°C. This beneficial effect can be primarily ascribed to the fact that Pt is non-reactive and its addition decreases the chemical activity of aluminum in γ′. Related to the latter, Pt partitions almost solely to the Ni sites in the ordered L1₂ crystal structure of γ′, which has the effect of amplifying the increase in the Al:Ni atom fraction on a given crystallographic plane containing both Al and Ni. Such an effective Al enrichment at the γ′ surface kinetically favors the formation of Al₂O₃ relative to NiO. A further contributing factor is that the Pt-containing γ′-based alloys showed subsurface Pt enrichment during the very early stages of oxidation. This enrichment reduces Ni availability and can increase the Al supply to the evolving scale, thus kinetically favoring Al₂O₃ formation.     

Effects of constant magnetic field on the electrodeposition reactions and cobalt–tungsten alloy structure

The paper presents a study of the effect of constant magnetic field (CMF) on the basic processes of cobalt–tungsten alloys electrodeposition. To the author's knowledge, such an investigation has been performed for the first time for cobalt–tungsten alloys. The applied research methods included scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). SEM images of cobalt–tungsten alloys revealed numerous fractures on the samples surface, formed as a result of residual stress during alloy deposition without CMF. In CMF such fractures disappeared. The cobalt content increased, with a simultaneous decrease of the tungsten content, under CMF condition. The XRD study of cobalt–tungsten alloys allowed to identify phase Co₃W in a hexagonal system, phase Co₇W₆ in a trigonal (orthorhombic) system, phase α-Co in a regular system and phase W in a regular system. Under CMF conditions some crystal planes were deflected at angles ranging from 10 to 20°. The exposure to CMF caused also an increase of the volume fraction (by about 9% by volume) of the dominant phase (Co₃W and Co₇W₆) in the alloy. The reason for these changes was the fact that the Lorentz force, generated in CMF, caused the magnetohydrodynamic (MHD) effect. This induced movement of the electrolyte. The Nernst diffusion layer was depleted, whereas a new Navier–Stokes hydrodynamic layer appeared, which determined the velocity of electroactive molecules flow to the working electrode under CMF conditions.     

Effects of Zr and B on the structure and tensile properties of Al–20%Mg alloy

In current research, the effects of different Zr and B contents on the structure and tensile properties of Al–20%Mg alloy have been investigated by using Al–15Zr and Al–8B master alloys. Optical and scanning electron microscopy (SEM) were utilized to study the microstructures and fracture surfaces. Microstructural analysis of the cast alloy showed dendrites of primary α-phase within the eutectic matrix which consists of β-Al₃Mg₂ intermetallic and α-solid solution. After tensile testing, the optimum amounts for both Zr and B were found to be 0.5 wt.%. Ultimate tensile strength (UTS) value of the unrefined alloy increased from 168 MPa to 243 MPa and 236 MPa by adding 0.5% Zr and 0.5%B, respectively. The main mechanism for UTS enhancement was found to be due to the refinement of grains and also altering large dendrites of Al(α)-phase to finer structure. The study of fracture faces revealed that B/Zr addition changes the mode of fracture from brittle to rather ductile.     

Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots     

Effects of chitosan molecular weight on the physical and dissolution characteristics of amorphous curcumin–chitosan nanoparticle complex

Objective: To investigate the effects of varying molecular weight (MW) of chitosan (CHI) used in the complexation with curcumin (CUR) on the physical and dissolution characteristics of the amorphous CUR–CHI nanoparticle complex produced.

Significance: Amorphous CUR–CHI nanoparticle complex (or CUR nanoplex in short) recently emerged as a promising bioavailability enhancement strategy of CUR attributed to its fast dissolution, supersaturation generation capability, and simple preparation. Existing CUR nanoplex prepared using low MW CHI, however, exhibited poor colloidal stability during storage. Herein we hypothesized that the colloidal stability could be improved by using CHI of higher MW. The effects of this approach on the nanoplex’s other characteristics were simultaneously investigated.

Methods: The CUR nanoplex was prepared by electrostatically driven self-assembled complexation between CUR and oppositely charged CHI of three different MWs (i.e. low, medium, and high). Besides colloidal stability, the effects of MW variation were investigated for the nanoplex’s (1) other physical characteristics (i.e. size, zeta potential, CUR payload, amorphous state stability), (2) preparation efficiency (i.e. CUR utilization rate, yield), and (3) dissolutions under sink condition and supersaturation generation.

Results: CUR nanoplex prepared using CHI of high MW exhibited improved colloidal stability, larger size, superior morphology, and prolonged supersaturation generation. On the other hand, the effects of MW variation on the payload, amorphous state stability, preparation efficiency, and dissolution under sink condition were found to be insignificant.

Conclusions: Varying MW of CHI used was an effective means to improve certain aspects of the CUR nanoplex characteristics with minimal adverse effects on the others.