Kinds Of Alumina Research Articles

Control of the NiII/Surface Interaction in the First Steps of Supported Catalyst Preparation: The Interfacial Coordination Chemistry of [Ni(en)2(H2O)2]2+

Model supported nickel catalysts were prepared by deposition of the [Ni(en)2(H2O)2]2+ complex from aqueous solutions onto silica, zeolite Y, two kinds of alumina, a clay, and a pillared clay. UV−visible spectroscopy was used to monitor the d−d transitions of Ni(II) in the solution, upon contact with the support oxide, and upon drying. In comparison with the spectra of reference compounds, and with the help of data provided by other techniques (elemental analysis, thermogravimetry, IR spectroscopy), this allowed us to follow the reactions occurring in the coordination sphere of the nickel ion during the initial stages of catalyst preparation. For the alumina, zeolite, silica, and pillared clay supports, exchange of two (H2O) ligands for support surface groups was evidenced (nickel grafting). On the other hand, deposition/intercalation into clay caused the formation of square-planar [Ni(en)2]2+upon drying. Therefore, these systems allow a precise study of transition metal interfacial coordination chemistry,...

Simulation of AE Generation Behavior in 2-Dimensional Polycrystals by Using the Body Force Method

AE (Acoustic Emission) generation behavior during microfracture process of 2-dimensional alumina polycrystals is simulated along with its characteristic parameters, by assuming that a microfracture corresponds to an AE event. The microfracture process is simulated by using the body force method. Various AE generation behaviors are predicted as a function of the grain boundary toughness (Kcb), the grain size and the distribution state of residual stresses due to crystalline anisotropy. The predicted AE events have a tendency to occur at higher stress with increasing Kcb and with decreasing grain size. By the fracture-mechanical calculation of the crack opening volume, the relative variation of AE amplitude is also simulated. The actual AE measurements are tarried out in vacuum for two kinds of alumina with different grain size, and compared with the simulated results. The cumulative AE event curve for 11.5 μm grain size shows good agreement with the simulation when the Kcb is 0.35 times the grain toughness (Kcg), and that for 28.2 μm shows good agreement with the simulation at Kcb = 0.45Kcg. The results of AE location for both the simulation and the measurement show the similar characteristics of the scattered distribution over the stressed fields.

Erosion characteristics of alumina ceramics at high temperatures

The elevated temperature erosion behavior of alumina ceramics has been studied. There were five kinds of aluminas used in this study, with and without the silicate glassy phase and zirconia. The variables studied included temperature variation, material composition and microstructure, and impingement velocity and angle. The erosion mechanisms were also investigated for both the normal and oblique impacts. Erosion experiments were run in a sand-blast type of test rig using 120 grit silicon carbide particles. The variation in erosion as a function of temperature is explained in terms of the changes in material properties and microstructures. The examination of eroded surfaces revealed that the erosion characteristics of aluminas at elevated temperatures were significantly different from those at ambient temperature. There was plastic deformation occurring on the eroded surfaces at high temperatures and shallow impingement angles. The erosion of aluminas at elevated temperatures was thus not uniquely governed by the indentation fracture model and new modifications and factors needed to be considered.

High-Temperature Corrosion Testing of Alumina and Zirconia in Uranium Hexafluoride Environment

Uranium fluoride gases are proposed as primary candidate fuels for ultrahigh-temperature gas core or vapor core reactor systems for a variety of space power applications. In these systems, the peak temperature of the fissioning gas can be as high as 5000 K and the inner wall temperature of the reactor cavity is within the range of 1000 to 2000 K. Two kinds of alumina, sapphire and polycrystal alpha alumina, and CaO partially stabilized zirconia are exposed to uranium hexafluoride gas in temperatures ranging from 973 to 1473 K and from 873 to 1073 K, respectively. Exposure tests are conducted in a UF6 flowing loop with an alumina reaction tube housed in a 1500 K electric-heated furnace.The reaction rates are measured using a discontinuous gravimetric method. The morphology of the exposed surfaces was observed by optical microscopy and scanning electron microscopy, and the reaction products were identified by X-ray diffraction and energy dispersive X-ray spectroscopy. Results indicate that alumina provides a relatively higher service temperature in UF6 environment. However, due to the highly reactive and chemically aggressive nature of UF6 at high temperatures, the maximum service temperature of alumina for a UF6-based gas core reactor is limited to 1273 K. Zirconia at temperatures above 973 K is not compatible with UF6.

Forming of Ceramic Powders by Cyclic-CIP

A new quasi-quantitative constitutive equation of Cyclic-CIP, which contains maximum pressure, bias pressure and number of cycles as variables, was derived. Densification of powder was expressed as a function of maximum pressure assuming that densification rate decreases as the maximum pressure increased. Effect of number of cycles on densification was expressed assuming that densification rate decreases as the number of cycles increased. Effect of the bias pressure was derived from the experimental data as a linear function of the ratio of the bias pressure to the maximum pressure. As a result of analysis of experimental data for two kinds of alumina with this equation, their densification behavior was found to be better characterized by the equation.

Adsorptive interactions of glucose and carbon dioxide with basic sites over alumina

Two kinds of alumina (Al2O3-1, Al2O3-2) have been examined for glucose adsorption from dimethyl sulphoxide solutions. The Al2O3-1 adsorbent is found to adsorb considerable amounts of glucose while the Al2O3-2 adsorbent is found to adsorb little glucose.

各種セラミック材料における強度特性およびその欠陥寸法分布との関係 第１報 静的強度

In order to study the characteristics of static strength of ceramics, 3-point bending tests with a constant loading rate were carried out at room temperature in air, by using sintered silicon nitride, partially stabilized zirconia and two kinds of alumina. The effects of specimen geometry and temperature on the strength were also investigated by conducting ring compression tests for the silicon nitride at room temperature and 1300°C in air.In the 3-point bending tests, better fitness for the two-parameter Weibull distribution was found when the data were correlated with the true fracture stress evaluated at the fracture point of specimen, rather than the maximum nominal stress. The effect of specimen geometry on the strength was small for the case investigated in this study. The mean strength and the coefficient of variation of the strength at 1300°C were reduced to about half and one-third of those at room temperature, respectively.The fracture surface of the tested specimens was observed through a scanning electron microscope, and the predominant flaws were identified which were preexisting in the specimens. The equivalent crack length was evaluated taking account of the crack geometry and the stress state associated with the crack location. The fracture stress was correlated with the equivalent crack length. The results showed that the strength decreased with decreasing flaw size, compared with the estimate expected from the linear fracture mechanics concept. The tendency in the relation was explained by the modification that a material constant should be added to the original equivalent crack length.The fractographic observation suggested that the fracture of the silicon nitride at elevated temperatures followed the formation of semi-circular damage-region due to the slow crack growth. Another fracture mechanics approach was required in the analysis of the fracture of ceramics with inelastic behavior at elevated temperature.

Mutarotation of α-d-Glucose over Several Al2O3 Catalysts

Abstract The mutarotation of α-d-glucose to β-d-glucose has been studied at 25±0.1 °C using five kinds of alumina as catalysts. Two kinds of alumina with measurable surface basicities have exhibited high catalytic activities while the others with little surface basicities have exhibited low activities. Thus, the surface basic sites have been considered to be responsible for the catalytic activity observed. Any of crystal structures, surface areas, pore structures, and surface elemental compositions have no relation to the catalytic activity. It has also been revealed that the kinetics of the reaction is explained by a surface reaction mechanism α+1 \undersetKα\ightleftharpoons αad \oversetk1\undersetk2\ightleftharpoons βad \undersetKβ\ightleftharpoons β+1, where 1, Kα, Kβ, k1 and k2 denote the active site, the adsorption equilibrium constant for α, the adsorption equilibrium constant for β, the rate constant for the surface forward reaction, and the rate constant for the surface backward reaction, respectively, and the subscript ad denotes an adsorbed state. The result of kinetic analysis has revealed that Kβ>Kα, indicating that the adsorption of β-glucose is stronger than that of α-glucose. This also supports the view that the surface basic sites are responsible for the catalytic activity.

高濃度充てんアルミナ‐熱可塑性樹脂系の混練と流動特性に及ぼす粉末特性の影響

Kneading torque and apparent viscosity were investigated on several series of alumina-thermoplastic resin systems selected from six kinds of alumina and three kinds of resin. The curves of kneading torque vs time at 453K were classified into four patterns which were dependent on resin type and alumina grade. The change of the pattern was also brought about by the change of solid concentration in the same alumina-resin system. The torque after 1h showed a good correlation with the apparent viscosity measured at the same temperature by a capillary type viscosimeter. The apparent viscosity of alumina-polypropylene and -polystyrene systems at high solid concentrations of 50% and 60% was influenced by the tap or compaction density of powders much more than by their surface area or size. The relative compaction density was an excellent parameter to estimate the flow and kneading properties at high solid concentrations. The alumina-polyethylene system, however, behaved somewhat curiously, because the type of degradation of polyethylene caused by the mechanical and thermal mixing was different from that of polypropylene or polystyrene.

Etude thermocinetique des phenomenes de dissolution par calorimetrie Calvet a haute temperature dissolution d'alumines dans la cryolithe

Although the thermal curves given by a Calvet calorimeter can be considered representative of the thermogenesis of slow phenomena, this is not the case for the brief thermal effects of dissolution, for example, which need typically no more than twenty minutes. At high temperatures, a numerical method of deconvolution of the recorded signal was applied in order to obtain the proper thermogenesis of the phenomenon. The time constants of the calorimeter were determined from thermal effects due to the dropping into the bath of small quantities of silver and platinum. The method was applied to the dissolution of a-alumina and industrial aluminas in cryolithic baths at 1290 K. The different kinds of alumina could be classified according to their time of dissolution. The dependence of the alumina concentration of the bath on the dissolution rate was also investigated.

Formation and phase transition of cobalt molybdate in cobalt oxide-molybdenum trioxide-alumina system

In the cobalt oxide-molybdenum trioxide-alumina system with a molar ratio of 1:1:1, the amounts of the high-temperature modification ( a) of CoMoO 4 formed during heating from 500 to 800°C and the low-temperature modification ( b) formed by phase transition during the subsequent cooling to room temperature are influenced by the kinds of alumina used, such as α-, γ- and calcined γ-aluminas. Powder X-ray diffraction analysis revealed that in an α-alumina system formation of a-CoMoO 4 is most favorable at a calcination temperature of 500°C and phase transition from a- to b-CoMoO 4 during cooling is enhanced by higher calcination temperatures. In the γ-alumina system, formation of a-CoMoO 4 is slight at 500°C but increases with increase in the calcination temperature, as does slightly the degree of phase transition from a- to b-CoMoO 4 upon cooling. In a system containing calcined γ-alumina, formation of a-CoMoO 4 similar to α- and γ-alumina systems was observed to occur at 500°C and 800°C, respectively, together with phase transition to b-CoMoO 4 during cooling. The degree of dispersion in the CoOMoO 3 coexistent system is affected by the particle size of aluminas, such as coarse α-, fine amorphous γ- and calcined γ-alumina consisting of both sizes, as observed with electron microscopy. Presence of finer γ-alumina is considered to suppress or retard the solid state reaction and phase transition.

The study of conditions for the preparation and application of99Mo−99mTc generators starting from irradiated molybdenum metal

99Mo−99mTc generators were prepared starting from irradiated molybdenum metal instead of MoO3 in order to use reactor irradiation space more economically. The adsorption of molybdenum as sodium molybdate on different kinds of alumina was investigated. The effect of the pH of the column and the aqueous phase concentration of molybdenum were studied and related to the elution yield of99mTc. A study of the radiation damage effect indicated that generators having a high elution efficiency of 90% could be prepared in the 100–600 mCi range. The losses of99Mo were minimized to 10−5-10−4% and those of alumina to 2–5 μg/ml eluate.

Catalytic activities and selectivities of MoO 3NiSO 4 supported on various oxides for hydrocracking of solvent refined lignite : Novel low surface area active catalysts

The hydrocracking of solvent refined lignite (SRL) was studied over MoO 3NiSO 4 catalysts supported on TiO 2 ZrO 2, TiO 2SiO 2 and three kinds of aluminas at 450°C under an initial pressure of 2500 p.s.i. hydrogen. MoO 3NiSO 4 supported on a fibrous alumina, Al 2O 3 (FF), was found to show the highest activity, the total conversion of SRL being 92%. The activities per unit surface area of the catalysts supported on TiO 2 and ZrO 2 were much higher than those of other catalysts. A presulfided MoO 3NiSO 4Al 2O 3(FF) gave the largest amount of total liquid fractions. The best catalysts for the formation of gasoline fractions were presulfided MoO 3NiSO 4Al 2O 3(FF) and a commercially available catalyst, MoO 3NiOAl 2O 3(HT-100), which was also presulfided. It was shown that there is no correlation between acidic properties of the catalysts and their activities or selectivities.

The Heat of Immersion of Aluminum Oxide in Water

Abstract 1) The surface properties of two kinds of alumina have been studied by measuring the immersion heats and the water contents. The heat of immersion of alumina showed a maximum at about 600∼650°C, which is considerably higher than the 200∼300°C of silica, and the heat values were much greater than those of silica. 2) It has been concluded that the rehydration process of dehydrated sites plays an important role in the case of the immersion of alumina in water. The heats of hydration calculated from the immersion heats of α- and γ-alumina were 15.8 and 9.60 kcal./mol. water respectively.