Translucent polycrystalline alumina is very useful as a material for trimmer capacitors in microwave tele-communication systems because of its excellent electrical and mechanical properties. In this paper, raw materials for alumina, additives, and manufacturing conditions were investigated for the improvement in properties of capacitors. The followings are the main conclusions. (1) The preferred raw materials for alumina are aluminium sulfate, ammonium salt, and hydrated alumina from the methyl ester process. (2) The preferred additives are Y2O3 or HfO2 in addition to MgO. (3) The preferred manufacturing conditions are the molding pressure higher than 700kg/cm2, calcination at 1000 to 1100°C in air, and firing at 1800 to 1820°C for 1 hour in vacuum (1×10-4-10-5mmHg).
The very fine oxide particles in TiO2-SnO2 system were prepared by the hydrolysis of titanium isopropoxide and tin isopropoxide in propanol solution. The following hydrolysis conditions were found to be necessary for the controlled synthesis of crystalline oxide precipitates, 1) process of water addition to propanol solution of metal isopropoxides, 2) the amount of water added to the metal isopropoxide solution, 3) hydrolysis time and aging time of the precipitate at boiling temperature (reflux time). The crystalline TiO2 of anatase structure was precipitated by the hydrolysis of 0.05mol/l titanium isopropoxide with the amount of water 300 times more of the equivalent value for the oxide formation and the subsequent reflux, while the decrease of the amount of water to 70 times of the equivalent value resulted in the formation of amorphous TiO2. The crystalline phase of the precipitate changed depending on the amount of SnO2 in the system. The precipitate of the composition Ti0.9Sn0.1O2 was the mixture of anatase and rutile phases with the particle size of 50Å, and the increase of SnO2 to x=0.2 in Ti1-xSnxO2 solid solution gave the oxide precipitate composed of only rutile phase with the particle size of 23∼25Å. On heating the precipitates, the grain of the anatase phase of TiO2 precipitates grew significantly at about 630°C, at which the phase transformation from anatase to rutile phase took place. On the precipitates of rutile structure, grain growth seemed to be more constrained and the neck growth between the grains became remarkable with an increase of the amount of SnO2.
The pressureless sintered Si3N4 compacts which contained 6%Y2O3, 2%Al2O3 and 3% MgO were HIP'ed without container, using nitrogen as a HIPing medium. The effects of sintering and HIPing conditions on density, flexural strength, α to β phase transformation and microstructure were studied. The main results obtained were summarized as follows: (1) Sintered Si3N4 compacts were highly densified by a liquid sintering mechanism when they were HIP'ed at the conditions above 1500°C, 10MPa and 10min. (2) The improvement of strength by HIPing depended on the sintering or HIPing conditions, and it was found that the strength was more strongly affected by the amount of α to β phase transformation than the density. Moreover, a good correlation was found between the α to β phase transformation and the fibrous grain's formation in Si3N4 compacts. (3) The kinetics of α to β phase transformation during HIPing was the same as the pressureless sintering, and its activation energy was 108kcal/mol.
High Pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and α→β phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder. The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39MN/m3/2 and independent of temperature up to 1400°C.
Four series of glass matrix/glass particle composites where the thermal expansion coefficient of the matrix is similar to or higher than that of the dispersed particles were prepared by hot-pressing technique. Optical microscopy indicated that, in the case of larger thermal expansion mismatch between particle and matrix, microcracks were formed radially around particles during cooling of the composite body from its fabrication temperature. The Young's modulus for each composite was determined from the load-deflection curve of a rectangular bar specimen tested in three-point bending. Using a two-dimensional model, a theoretical analysis was made of the elastic modulus of two-phase, particulate composites containing microcracks. This analysis enabled the overall Young's modulus of such composites to be correlated with the size and density of the microcracks. The Young's modulus behavior of the prepared composites could be well explained on the basis of the analysis, and the size and density of the microcracks existing in the composites were reasonably estimated.
The fracture toughness (KIc) of two kinds of polycrystalline β-alumina (hot-pressed (HP) and normally sintered (NS)) were measured by the controlled surface flaw method as a function of temperature up to 1400°C. The obtained KIc values for HP and NS decreased from 2.0MN/m3/2 and 2.4MN/m3/2 at room temperature, to 1.9MN/m3/2 and 2.3MN/m3/2 at 900°C, respectively. The brittle fracture in this temperature range initiated intragranularly from the initial intragranular flaw of Vicker's indentation. On the other hand, KIc of both HP and NS apparently increased with increasing temperature above 900°C. The reason of this rapid increase in KIc may be attributed to the plastic behavior or thermal blunting effect at the crack tip, because the fracture initiated from the slow crack growth region. These results were discussed on the bases of the temperature dependence of their elastic moduli (E) and fracture energy (γ), and also compared with KIc of single crystal β-alumina measured by the micro-indentation method at room temperature.
In order to design a photo-selective amorphous layer to be used for a solar energy collector, it is of primary importance to study the fundamental characteristics of the amorphous candidate materials for this purpose. In this study in the first place vitrification ranges in the binary and ternary oxide systems containing high concentration of transition metal oxides have been determined by a rapid quenching technique of twin-roller method. Amorphous thin layers were obtained in the range Fe2O3=5∼25mole % in the Fe2O3-PbO system, V2O5=5∼26mole % and 35∼40mole % in the V2O5-PbO system, TiO2=5∼50mole % in the TiO2-PbO system. Secondly light transmittance has been measured for the amorphous materials prepared in the systems Fe2O3(V2O5)-PbO-SiO2, Fe2O3 (V2O5)-PbO, Fe2O3(V2O5)-NaPO3(P2O5) and TiO2-PbO in the range of visible 400mμ∼800mμ, near infrared 500mμ∼2.5μ, and infrared to far infrared 5μ∼25μ. In the infrared region the absorption peaks associated with Fe-O, V-O, Si-O and P-O vibrations shifted to shorter wave length as PbO was substituted with SiO2 or P2O5 in the Fe2O3(V2O5)-PbO-SiO2 system or in the Fe2O3(V2O5)-NaPO3 (P2O5) system, while that of Ti-O vibration shifted to longer wave length as PbO content was decreased in the TiO2-PbO system. From the absorption peaks observed in the near infrared and visible range, it is deduced that low valency ions Fe2+, V4+, V3+, Ti3+ exist together with high valency ions Fe3+, V5+, Ti4+ and Pb2+ in the multi-component amorphous systems. It is interesting to note that the absorption edges in the visible range associated with the transitions of d-electrons in Fe2+ and V4+ ions shifted to shorter wave length as PbO was substituted with SiO2 in the Fe2O3 (V2O5)-PbO-SiO2, while that of Ti3+ to shorter wave length as PbO content was lowered in the TiO2-PbO system.
SnO2:Eu powder phosphor was examined concerning to its synthesis, physcochemical properties and luminescent characteristics for the purpose of practical use in low-energy-election excitation. The oxalate coprecipitate of Sn and Eu composed of large particles with clear crystal facets was found to give bright SnO2:Eu powder phosphor. The solubility limit of Eu into SnO2 was 0.05∼0.06 at.%, and smaller mean diameter, higher resistivity (order of 106Ω·cm) and more intensive diffused reflectance were observed with increasing Eu addition. Although the same emission spectra by f-f transition (5D0-7F1 main emission) were observed in UV, high and low-energy-electron excitation, the intrinsic emission from SnO2 matrix was different in each excitation method. The Optimum addition of 0.1 at.% Eu, 5.9msec decay (1/10), and the efficiency of 2lm/W at 9-10V were obtained at low-energy-electron excitation. Efficiency increased at lower voltage and current excitation due to sublinearities of brightness-voltage and current dependences.
In order to study the crevice corrosion of austenitic stainless steels which often occurs in stainless steel piping or heat exchanger tubing used for sea water service, the effects of chemical composition of steels, contents and flow velocity of sea water, heat transfer conditions and cathodic protection have been studied. Both plates and tubes made of 20Cr-22Ni-5Mo steels with nitrogen content of 0.02 to 0.2% and of commercial stainless steels (SUS 304, SUS 316L, SUS 329J1 and 20Cr-26Ni-6.5Mo) were evaluated, and copper base alloys (aluminum brass and cupro-nickel) were also tested in an experiment. All results of electrochemical tests (anodic polarization curves, passivation behaviors and constant potential tests in 0.1N-HCl+2M-NaCl and 1N-HCl solution at 60°C), model sea water heat exchanger tests (tube side: sea water of 0.5 to 1.5m/sec., shell side: water or steam of 50°C to 140°C, 1 year ran), and concentrated sea-water flow-through tests (twofold of sea-water at ambient temperature) indicated that newly developed 20Cr-22Ni-5Mo-0.2N steel had a considerably higher resistance to crevice corrosion in sea-water environments, in comparison with commercial stainless steels and copper base alloys, but care should be taken on the using condition in actual service.
The effect of rubber sealing materials on crevice corrosion susceptibility of stainless steel was investigated. The rubbers were found to accelerate the initiation of crevice corrosion. In order to prevent crevice corrosion of rubber sealed steel surface, newly modified rubber has been developed. This rubber contains uniformly dispersed fine metallic zinc powder and carbon of high electric conductivity. It is shown that this rubber cathodically protects stainless steels by the mechanism that dissolved zinc precipitates on the surface of stainless steel in a form of hydroxide and prevents acidification of the crevice solution.
The corrosion of aluminum in saturated Ca(OH)2 solution containing NaCl has been studied from the measurements of the anodic polarization curve and weight loss. The anodic polarization curve showed a constant current density whose integration was equal to the weight loss of specimen. It is concluded that the corrosion of aluminum is controlled by the anodic polarization behavior and then closely relates to the structure of corrosion product.
Proper evaluation of corrosiveness of soil is very important for the maintenance of pipelines. The P/S potential was measured on 400 kinds of soil in laboratory and the reason for the difference in P/S potential along a pipeline to cause the corrosion of macro-cell type was discussed. It is concluded that P/S potential is closely related to the amount of moisture, relative resistance, contents of clay and silt, and is not affected by the amount of anions and pH of soil greatly.
Commercially available brake pipes for motor vehicles were tested by using a Swing Panel Corrosion Tester, and the corrosion behavior at the wet zone (AA), dry zone (CC) and wet-dry zone (AC) of the brake pipe were estimated by measuring corrosion potentials and corrosion currents. The Macro-cell was easily established between each zone of Zn plated brake pipe by“Swing” action, and corrosion was accelerated. In AA zone general corrosion occurred, but AC zone had a tendency of localized corrosion because of uneven wetness, NaCl solution was more corrosive than CaCl2 solution, but CaCl2 solution formed a macro-cell between A and C zone more easily than NaCl solution, causing easily the localized corrosion such as pitting.