Continuous mulling of conductive plastics (electromagnetic shielding material) was performed to investigate the mulling process in which conductivity appears and to determine a mulling condition by which a satisfactory conductive material can be obtained. Continuous mulling was carried out with ABS-resin and carbon black under various experimental conditions. Examination of the mulling condition was made based on the results of time change in mixing torque, resistivity of the formed materials, and scanning and transmission electron microscopic observations of the mulled products. The results revealed a close correlation between the mixing torque and resistivity. This indicates that the sate of conduction in the mulling process can be estimated by investigating the time change in mixing torque. When the mixing torque reached to a steady state, the material was found to have high conductivity. Furthermore, when a filler (carbon black) is randomly distributed as it occurs in solid mixing, high conductivity can appear. A mulling condition that could produce a material of still higher conductivity was searched further. It is found that reduction of mixing torque by the addition of a lubricant (slip additive) produces a wellmulled conductive material (conductive plastics) in a relatively short time.
Highly pure barium hexaferrite with a homogeneous composition was synthesized by hydrolysis of barium acetate and tris (acetylacetonate) iron (III) under controlled hydrolyzing conditions and by the subsequent heat-treatment. In order to prepare an amorphous coprecipitate with desired composition by this method, the pH value of the solution, the refluxing temperature and the amount of hydrolyzing water have to be controlled. The amorphous coprecipitate of barium hexaferrite thus prepared crystallized by heat-treatment above 800°C for more than 1hr, without forming any intermediate compound. The particle size and the size distribution increase with increasing heat-treatment temperature. By heating the amorphous fine powder, the grain grew from 200Å at 700°C to submicrometer size above 800°C. The size distribution became wider after heat-treatment above 800°C, and thus the direct relationship between particle size and specific surface diameter could not be observed. With an optimum heat-treatment condition, it is possible to prepare fine hexaferrite particles of magnetic single domain size range with excellent magnetic properties.
Simulation for a mixing model of a binary system of spherical particles with different electric resistance, such as lead and stainless particles, was carried out in a stationary mixer with vertical impeller blades. The simulation model described above was compared with the actual experiment. In the actual experiment, the total electric resistance of the system, R was measured by a DC-tester, and the top and bottom views of the bed were observed. The mixing model in the previous paper based on the assumption that the particles were moved in square orbits, was modified to fit to the actual process. The modification was made by taking into account the contour of orbits, and by introducing the circulating velocity of particles (the following coefficient), phase and frequency in the equation of R. The contour of orbit seemed to be semicircle according to the photographs. The actual value of the following coefficient (the ratio of the domain of rotational movement of particles to that of each orbit) was obtained from the photograph. By considering the fact described above, the following modified equation was proposed. R=l·exp(-k1·t)·Σal·sin2(ωl·t-π/4)+m-n·exp(-k2·t) Where, R: Total electric resistance l, k1, al, m, n, k2: Constants ωl: Angular velocity: Following coefficients t: Time The proposed equation showed good agreement with the experimental data.
Compacting characteristic of fine particles is greatly affected by the aggregate structure of particles. Several kinds of silicon nitrides, which are different each other in particle shape, size and bulk density, were compacted in uniaxial direction under various conditions, and the behavior of the particles during compaction was analyzed and compared by using Cooper's equation. As a result it was found that the difference in the kind of samples and the condition of their pretreatment gave considerably different behavior during compaction, and that the apparent volume reduction rate under pressure was remarkably different at low and high pressures. The aggregate structure of each sample was estimated based on the above results together with the result of the measurement about the compaction structure of the molded bodies.
A study was made on the rheological properties of alumina-polypropylene mixture system. The effects of solid volume concentration on mixing and flow properties were investigated at a variety of concentrations. The torque after the mixing time of 1h at 453K increased with increasing solid concentration from 0% to 60%, but fell off when the concentration became as high as 70%. SEM photographs indicated that this decrease of torque corresponded to the transition of particle packing structure from the capillary state to the funicular one. The apparent viscosity of the mixture was measured by a capillary type viscosimeter in the temperature range of 436K to 453K. The effect of capillary dimension on viscosity was examined by using six kinds of dies with the same radius of 0.5mm but different lengths varying 0.5mm to 15mm. The end correction obtained at a constant shear rate of 103s-1 decreased from ten to nearly zero with increasing concentration from 0% to 70%. Also, the higher the measured temperature, the smaller the end correction became. The true viscosity, calculated by using the above values of end correction, tended to increase rapidly beyond the concentration of 40%. This increase in viscosity was, however, relatively small compared with the theoretically expected value.
The surface-treatment of cermet powder was investigated by means of X-ray photoelectron spectroscopy, X-ray diffraction method, scanning electron micrography, dispersive property measurement and pyrolysis. The influences of surface-treatment on the molding and the flow property of the blend with paraffin were also studied. The results obtained were summarized as follows: (1) The surface of cermet powder was recognized to be covered by an oxide layer which contains surface groups such as _??_TiOH, _??_COH, -COOH, _??_CO and _??_COC_??_; (2) When the cermet powder was surface-treated with alcohol, the nature of the surface changed from hydrophilic to hydrophobic; (3) From the analysis of pyrolysis products of surface-treated powder, the surface group was found to be the alkoxyl group of the alcohol used; (4) The apparent density of molded tabulet of surface-treated powder was higher than that of original powder, and the pore volume of the former was smaller than that of the latter; (5) The extrusion test of the blend with paraffin showed that the amount of paraffin needed for the surface-treated cermet powder was smaller than that for the original powder in order to obtain a similar property of flow.
The adsorption process of methanol vapour on porous materials such as molecular sieves 3A, 4A, 5A, natural mordenite, natural clinoptilolite, activated alumina, silica gel and active carbon was investigated by using a ceramic gas sensor. The measurement of methanol vapour adsorption in the range from the initial relative vapour pressure of 0.6 to the final relative vapour pressure of below 0.35 was found to be suitable for the estimation of specific surface area of hydrophobic porous materials. The results obtained were compared with the data based on the nitrogen adsorption method. The measurement by this method is considerably simple and reproducible so that the study of methanol vapour adsorption process and the estimation of specific surface area of hydrophobic porous materials become easy. Thus, the application of this method seems feasible for such line processes as solor heating and cooling, and solvent recovery from active carbon.
When plastics is used as a material for machine, it is frequently subjected to multiaxial stress. Therefore, it is very important to know what conditions the plastics yields. In the present study, fracture experiments were carried out on plastics under two different biaxial stress states created by internal pressure-tensile stress and internal pressure-compression stress conditions, and a method of predicting their fracture mode was evaluated. From the results of the experiments, it was found that the distortional energy theory was applicable to predict the type of fracture.
In this paper, the composite variability model as a stochastic model of the fatigue crack propagation rate has been examined, and compared with the intra-specimen variability model examined in the previous papers. The composite variability model assumes that the parameter C in the Paris's law da/dN=C(ΔK)m is a random variable of which randomness is composed of the variability within a specimen and that between specimens, whereas the intra-specimen variability model assumes only the former component. First, equations for the mean value, μN, and the coefficient of variation, ηN, of the crack propagation life N were derived based on the composite variability model. These equations were found to be in good agreement with our experimental results. With respect to ηN, the composite variability model was in better agreement with the experimental results than the intra-specimen variability model was. The correlation distance estimated by the composite variability model was of the same order as that estimated by the intra-specimen variability model, although the former is a little smaller than the latter. It was also shown that the scatters of CS and ms observed experimentally when the equation da/dN=Cs(ΔK)ms is applied to each specimen could be explained by the composite variability model as well as by the intra-specimen variability model. As a whole, the composite variability model was found to be in a slightly better agreement with our experiment than the intra-specimen variability model was, but more experimental examinations are necessary before reaching a definite conclusion.
Tensile properties, impact value and fracture toughness of weld metals of Ti-5Al-2.5Sn (ELI) alloy were investigated by comparing them with those of base metal at cryogenic temperatures. Two kinds of welding atmosphere were applied for gas tungsten-arc welding. One is a high purity inert atmosphere using an improved shielding. The other is vacuum. The conclusions are summarized as follows: (1) The contents of O and N in the weld metals welded in both atmospheres were less than those of the base metal. (2) The tensile elongation, impact value and fracture toughness of the weld metals welded in both atmospheres were larger than those of the base metal at 4.2K. It is reasoned that the martensitic structure of weld metal can deform plastically more than the equiaxial structure of base metal at cryogenic temperatures. (3) The 0.2% proof stress of the weld metal welded in a high purity inert atmosphere was small compared with that of the weld metal welded in vacuum. However, the tensile elongation, impact value and fracture toughness of the weld metal welded in a high purity inert atmosphere were nearly equal to those of the weld metal weled in vacuum at cryogenic temperatures.
The effects of pre-strain on the tensile, creep, and low-cycle fatigue properties of type 304 stainless steel at elevated temperatures have been investigated to evaluate the fabrication-induced cold work effect on the properties of structural materials. The tensile pre-strain was introduced in the test specimens at room temperature at plastic strain levels as high as 15% for tensile tests, 10% for creep tests, and 5% for fatigue tests. The results obtained are as follows; (1) The 0.2% offset yield strength, ultimate tensile strength, and creep rupture strength increased with increasing pre-strain. This creep strength improvement is caused by the decrease of steady-state creep rate. (2) Little difference in the low-cycle fatigue life was observed between the base metal and the pre-strained specimens. This is due to the disappearance of the pre-strain effect by cyclic hardening under fatigue conditions. (3) Tensile and creep rupture ductilities decreased with increasing pre-strain. However, the reduction in fracture elongation due to pre-strain appears to be almost equivalent to the amount of pre-strain. Therefore, pre-straining causes no additional decrease in creep ductility in long term tests.
P wave velocities of both dry and saturated rocks were measured during a slow temperature change (0.5K/min.) between 110K and 370K. Their thermal expansions were measured simultaneously. The change of P wave velocity was larger by about one or two orders than that expected from the net change of sample length due to thermal expansion. In the dry condition, hysteresis in the temperature-P wave velocity relation was observed in only granite among various kinds of rocks, which is explained by frictional sliding at the surface of microcracks and crushing of microcrack asperities. In the saturated condition, however, hysteresis was observed in all rocks due to the temperature difference between freezing and thawing of water within pores and microcracks. A large increase in P wave velocity was observed in all rocks between 273K and 230K during cooling. A sharp decrease in P wave velocity coincided with thermal cracking detected by the changes of both the activity of acoustic emission (AE) and thermal expansion. These observations suggest that the temperature effect on P wave velocity of rock is strongly affected by (1) thermal cracking, and (2) the phase change of water within pores and microcracks.
The dynamic moduli of three kinds of dry and saturated rocks were determined during thermal cycling between 110K and 370K at a slow heating rate (0.5K/min.). In the dry condition, the moduli of both Murata basalt and Ogino tuff increased linearly with decreasing temperature. The temperature coefficients of bulk and shear moduli were expected to be the same as those free from the effect of microcracks. On the other hand, the temperature coefficients of the bulk and shear moduli of Westerly granite were affected by both thermal cracking and the opening and closure of the pre-existing microcracks. They showed a sharp decrease when the granite was heated above 330K in the first cycle. A permanent decrease in the moduli was observed after both heating and cooling. During the second thermal cycling where few cracking presumably occurred, the coefficients of the moduli were almost positive. In the saturated condition, the moduli of the basalt, tuff, and granite increased rapidly when the rocks were cooled below room temperature. These changes coincided with those observed in thermal expansion down to 230K. Below 230K, the moduli, however, gradually increased with no change in thermal expansion. These observations suggest that the increase in the moduli is due to freezing of water within pores and microcracks between 270K and 230K, and that stiffening of absorbed water in the surface of pores and microcracks has an effect on the increase in the moduli below 230K.
The corrosion products of aluminum alloys yielded in mortar and concrete have been studied with XRD method. The corrosion products yielded in mortar contained bayerite, hydrargillite, nordstrandite and hydrated calcium aluminate. The corrosion rate was controlled by crystalline bayerite formed at the metal interface and hydrated calcium aluminate. The corrosion products yielded in concrete contained only hydrargillite which appeared to form at pH lower than 8. With an addition of 3% NaCl in mortar and concrete, the high concentration of hydroxide ions in the gel-like inner layer caused severe corrosion. Such high pH was suggested from the formation of bayerite.
The effects of sodium, calcium and chloride ions in mortar and concrete on corrosion of aluminum alloys were studied. Chloride and especially sodium ions were concentrated in the inner layer of corrosion product. The corrosion rate increased with increasing sodium content in the inner layer and was almost independent of the chloride content. Calcium ions existed only in the outer layer. It is concluded that the corrosion rate of aluminum increases with increasing hydrated sodium aluminate content. Such a compound is likely to accelate the crystallzation to trihydrated aluminum oxide and then to keep the strong alkaline environment at the metal surface.
Corrosion of aluminum alloys in mortar containing sodium, calcium and chloride ions have been studied by weight loss and electrochemical measurements. The ions were added into mortar in the amount of 3%CaCl2 and 3%NaCl. The corrosion product of aluminum alloys in mortar containing 3%CaCl2 was identified as 3CaO·Al2O3·8H2O by X-ray diffraction. The corrosion was inhibited by precipitation of the corrosion product and the rate of corrosion was almost proportional to the passivation current. When both 3%CaCl2 and 3%NaCl were added in mortar, the corrosion product was found to be trihydrated aluminum oxide. The corrosion weight loss was approximately 3 times that in mortar containing 3%CaCl2 and one-fourth that in mortar containing no CaCl2 nor NaCl. It is concluded that calcium ions inhibit and sodium ions accelerate the corrosion of aluminum alloys in mortar.
In order to investigate the influence of surface roughness on load dependence of microhardness of annealed structural rolled steel and carbon steel, hardness tests were made by changing the grade of surface roughness as a parameter. The results obtained were analyzed by means of the analysis of variance. The main results obtained were as follows; (1) Load dependence existed between the indentation load and the microhardness number above the specified value of hardness. The range of the indentation load showing load dependence was influenced by the surface roughness. (2) A logarithmic linear relationship existed between the indentation load and the microhardness number. Load dependence curves varied depending upon the surface roughness.