Oxygen diffusion in polycrystalline ZnO particles has been measured by the solid-gas isotope exchange technique using O18 as a tracer at temperatures in the range 689-1290°C. A new method of calculating the volume diffusion from the exchange data of particles was developed, and the plausibility was discussed experimentally. The oxygen diffusion in ZnO was characterized by three regions having the activation energies of 22.1, 63.2 and 172.7 kcal/mol. On the basis of the results, it is suggested that the origin of semiconducting behavior of ZnO is due to the electrons trapped around oxygen vacancies created at elevated temperatures.
The surface area, pore size distribution and pore volume of powderly CaHPO4·2H2O heat-treated were investigated by nitrogen adsorption and desorption measurements at 77K. The surface area of the sample powder was found to increase markedly at 200 and 400°C. It is well known that the crystal water of CaHPO4·2H2O is removed in the temperature range of 115-215°C and the dehydration-condensation of CaHPO4 occurs at 360-450°C. X-ray diffraction and weight loss measurements indicated that considerable parts of CaHPO4 and Ca2P2O7, which are the heating products at the above respective temperature, were both amorphous. Moreover, a large increment of the pore volume was recognized to be accompanied by the occurrence of each dehydration. Therefore, an increase of surface area is considered to be mainly due to the formation of mesopores. On the other hand, decreases of the surface area and pore volume at above 550°C may be explained in terms of crystal growth and sintering of the sample.
The reduction of MoO3 in hydrogen or hydrogen sulfide was studied by means of high temperature X-ray diffraction. It was revealed that MoO3 was reduced to MoO2 through the formation of MoO3-x (Mo4O11, Mo8O23 and Mo17O47). It was also observed that the rate of the reduction of MoO3 was much enhanced when H2S was employed as a reducing gas. This could be explained by the fact that the dissociation constant of H2S is much higher than that of H2 at any temperature studied. The effect of the addition of Al2O3 on the reduction of MoO3 was also investigated. It was found that the rate of the reduction of MoO3 becomes faster by the presence of Al2O3, though the mechanism of the reduction of MoO3 by Al2O3 could not be explained in the present work.
The aim of this paper is to describe an apparatus for determining scattering characteristics of suspension by the dissymmetry method which enables the average particle size to be estimated quickly. This dissymmetry method is based on the fact that the intensity of scattered light is not distributed symmetrically around the axis passing throught the particles in a direction perpendicular to the light beam, because the particle is not a point light-source. Rays scattered from different parts of the particle may give interference. Therefore, it is possible to estimate the average particle size from the ratio of the intensities of scattered light at two angles, e. g. Z45 at 45°and 135°. The dependence of the average particle size Dav(μm) by the photo-extinction method of kaolin minerals and sediment on the dissymmetry parameter Z45 is given as follows: Z45=-0.841Dav+8.363 The dissymmetry method with a He-Ne gas laser as a light source is considered applicable to the estimation of the average particle size in the disposal process of factory wastes containing suspended particles, and to the control of particle size in the wastes as well as the quality control in the production process of factory.
In order to avoid troubles for samplining, it is worthwhile to work out a simple method whereby the degree of mixing is measured immediately, non-destructively. The purpose of the present work is to develop a simple method which enables to measure the degree of mixing of binary systems having particles of different electric resistances. In this report, the system composed of 13 spheres is treated with a particular emphasis on the edge effect (boundary effect). When the larger numbers of spheres with low electric resistances gather at the terminal position of the system, the apparent total electric resistance of the system will be increased. On the contrary, when the larger numbers of particles (spheres) with high electric resistances gather at the terminal position of the system, the apparent total electric resistance of the system will be decreased. The amount of increase or decrease in apparent total electric resistance is proportional to the number of spheres located at the edge. An appropriate correction for the edge effect should be made, that is, Correction factor for edge effect=(Total electric resistance of system (a) in Fig. 5)-(Total elec. res. of sys. (b) in Fig. 5)/(Number of spheres-B located at the edge of sys. (a) in Fig. 5)-(Number of spheres-B located at the edge of sys. (b) in Fig. 5)
The porosity ε and radial compression strength St of uniaxial dry-pressed powders were examined in several mixtures which are composed of alumina fine particles (AFF or AFC), coarse (ACF or ACC), talc fine (TF) and coarse (TC). It should be noted that the shape of talc particles is flaky while that of alumina is blocky. Flaky particles easily orientate at right angles to the compression direction. The relations among ε, St and compression force P were represented by Eq. 1, 2 and 3 in all the mixtures examined. The packing efficiency was improved by mixing two components in AFF-ACC system, but deteriorated in AFC-TF, ACF-TC and TF-TC. This is because small particles can enter into the inter-spaces of large particles in the case of mixture of blocky-shape powders. On the other hand, particles with blocky shape may disturb the orientated layer structure of flaky ones in the case of mixtures containing both blocky and flaky particles. It was shown that a logarithmic mixture rule for St under the same porosity is approximately valid in AFF-ACC, AFC-TC and TF-TC.
The flow properties of various powders in a vibrating field have been measured by a rotating cylinder fluidity meter. The shear stress-rate of strain diagram obtained by the fluidity meter exhibits typical three types corresponding to the powder characteristics. These diagram have been discussed on the bases of the particle size, the interparticle force and the aggromeration phenomena of particles under fluidization. The interparticle force of the aggromerate was obtained by an apparatus for direct compressive strength measurement. In a low amplitude region, the fluidity of powders is influenced by their packing structure. But, at high amplitudes, especially the fine powders begin to aggregate, giving rise to a decrease in the number of particles in the fluidized bed. Therefore, the fluidity of the powder increases in this region and exhibits a hysteresis on the shear stress-rate of strain diagram.
Internal friction coefficients have been measured by a direct shear tester for a number of powders having different particle diameters and densities, and for their binary mixtures. The binary powders have been mixed by V-type (V), horizontal cylinder (HC), horizontal ribbon (RH) and vertical ribbon (RV) mixers to assess the effect of internal friction coefficient on the rate of mixing and the final degree of mixing. The performances of the solid mixers have been correlated much better with the internal friction coefficient than with the change in particle diameter or density. While the rate of mixing and the final degree of mixing in the rotary-vessel mixers such as V and HC decrease as the internal friction coefficient increases, those in the stationary-vessel type ones such as RH and RV are hardly influenced by the coefficient.
In order to investigate the effect of the feed ratio of binder to powder on the sizes of products in a simultaneous and continuous operation of granulation and separation by using a single horizontal conical vessel which has a pair of the outlets of the each end, the experiments have been carried out by feeding CaCO3-powder and dropping water into the centre of the vessel rotated at the critical speed ratio, 0.2, and by discharging the granulated and separated products from the both outlets of the vessel. The size and shape of the products granulated were found to be affected by the feed ratio and the average residence time. The small spherical particles were discharged from the narrow end of the vessel at a relatively low feed ratios, while the large spherical particles from the wide end at a high feed ratios.
The mechanochemical reaction of polyethylene was investigated at room temperature up to 15 kbar static pressure by using a self-made high pressure apparatus capable of generating simultaneous shear deformation. All shearing curves reached an equilibrium value after the gradual increase of shear-strength. This tendency was not observed in the cases of polymethyl methacrylate and polystyrene reported in the previous paper. From the small divergence of equilibrium shear-strength data and the changes in molecular weight and its distribution, it was concluded that the mechanochemical reaction of polyethylene took place by selective breaking of longer chain molecules and the molecular weight distribution became sharp as the reaction proceeded. However, the mechanochemical reaction rate was considerably slow in comparison with the other polymer materials reported previously.
The relation between the Stefan condition during liquid-solid phase transformation process and the general energy jump equation was discussed and a heat conduction equation, in which material constants have jump discontinuities across the melting temperature, was derived for practical use. An elastic-viscoplastic constitutive relation was also presented considering the viscous effects in the high temperature range after solidification. The theory was applied on the casting processes of pure lead and carbon steel, and the temperature and stress distributions were numerically calculated by the finite element method. Casting experiments were also carried out for these two materials, and the temperature distribution and residual stresses were measured to verify the present theory.
To investigate the time and temperature dependences of the transverses tensile strength of unidirectional CFRP, tension tests were conducted at various temperatures and strain rates. The transverse tensile strength of CFRP showed remarkable dependence upon time and temperature in the same manner as the tensile strength of the matrix. The master curve for the transverse tensile strength was able to be constructed by using their thermo-rheologically simple properties. The time and temperature shift factors for the fracture behaviors of both the matrix resin and the CFRP were quantitatively in good agreement, and also coincided well with those concerning the creep compliances of these materials. The observations by a scanning electron microscope showed that the appearance of fracture surface changed considerably with temperature.
Compressive residual stress is considered to be useful for arresting of fatigue crack propagation in welds, composite metals and case hardened metals. However, there are few reports on the quantitative relation between the distribution of residual stress and fatigue crack propagation. In this study, homogeneous thin plates which had mainly longitudinal compressive residual stress around crack were made by water quenching from relatively low temperatures below 723°C. In fatigue tests, the compressive residual stress around crack was confirmed to be an important factor controlling the fatigue crack propagation. This influence was quantitatively discussed by using a linear fracture mechanics model. The effective stress intensity factor range calculated by this model was useful for understanding of the fatigue crack propagation in cracked specimens. This analysis also was applied for the fatigue crack propagation through compressive residual stress field in the plate composed of low carbon steel and midium carbon steel. The results of this study suggest that not only the defect size but also the residual stress field have to be discussed for evaluation of defects detected by nondestructive methods.
In order to evaluate the effect of retained austenite on the fatigue strength of carburized steels, the rotating bending fatigue tests were carried out by the steel used for marine propulsion gears. It was found that the fatigue strength has a maximum value at a certain quantity of retained austenite in the specimen with an effective carburized depth. The reason for the presence of this optimum retained austenite quantity is considered on the basis of the residual stress, microstructure and the fracture surface of the carburized surface layer.
The characteristics of fracture surface of flake graphite cast iron were investigated by means of fractography in order to obtain informations needed for failure analysis. From the view point of the difference in fracture mechanism between fatigue and static bending, it was clarified that the both fracture could be distinguished by measuring the percentage of pearlite fracture surface. The results obtained are summarized as follows: (1) The fracture surface of fatigue and static bending consisted of graphite fracture, intergranular fracture and transgranular fracture of pearlite block. There was no difference in graphite fracture surface between fatigue and static bending. (2) The intergranular fracture of pearlite block comprised the lamellar parts by fatigue and dimple pattern by static bending. Most parts of the static fracture surface of pearlite block showed a dimple-like pattern. Quasi-cleavage fracture surface was observed at both of the above fracture surfaces. (3) The percentage of pearlite fracture surface by fatigue was 34-41% and that by static bending was 11-14%. (4) It was confirmed that the statical fracture took a shorter path among graphites than the fatigue fracture did. This means that the former has smaller percentage of pearlite fracture surface than the latter.
Powdered polystyrene was compacted into cylindrical specimens having various void fractions. These specimens were triaxial-compressed and triaxial-extended under various confining pressures σ3. Yield loci were obtained from Mohr's stress circles using the confining pressure σ3 and the axial stress σ1 at which the specimens broke down. These results were expressed by the equation τ2=μi2σ2+4σt(1+μi2)(σ+σt), where τ was the shear stress, σ was the normal stress, μi was the coefficient of effective internal friction and σt was the tensile strength of the powder compact. This equation was preferable to the conventional power law of the yield locus because of the conformity to the test results, and furthermore the constants contained are the most basic ones for powder-like materials. The yield locus obtained by the triaxial extension test differed from that by the triaxial compression test, but both approached each other with an increase in the initial void fraction of specimens. his fact was attributed to the difference in two kinds of tensile strengths, that is, one was the value in the perpendicular plane to the precompaction plane and the other was the value in the parallel plane. The former determines the yield locus obtained by the triaxial compression test and the latter determines the one by the triaxial extension test.
Acoustic emission of fiberglass reinforced plastics (FRP) with flaws was examined. One group of FRP used was those exposed to out-door or accelerated weathering and the other was those subjected to falling weight impact tests. In the case of weathered FRP, AE from these specimens was apparently different from that of the blank one depending on the weathering conditions. This suggests that more detailed tests should be carried out in order to apply AE technique to outdoor FRP structures. In the case of FRP with flaws due to falling weight impact, a characteristic AE pattern was observed which may be useful to predict the initiation and growth of cracks in FRP with such history of damage.