Order Of Al2O3 Research Articles

Investigation on Application Prospect of Refractories for Hydrogen Metallurgy: The Enlightenment from the Reaction between Commercial Brown Corundum and Hydrogen.

Hydrogenous environments put forward new requirements to refractories for the hydrogen metallurgy field. The temperature and impurities in refractories played an important role in stability. A commercial brown corundum with many impurities was adopted as a raw material, thermodynamic calculations and reduction experiments of the brown corundum by high-purity hydrogen (99.99%) were accepted to investigate the stability of the oxides. The weight loss and mass fraction were tested to estimate the stability of the oxides in the brown corundum. XRD and SEM were used to analyze the mineral compositions and microstructures. The results showed that: the thermodynamic stability of the oxides in the brown corundum under high-purity hydrogen was in the order of Al2O3 > CaO > MgO > SiO2 > TiO2 > Fe2O3 at temperatures lower than 1400 °C. Obvious weight loss appeared after heating at 1400 °C for 8 h. The content of CaO did not decline after reduction even at 1800 °C, owing to the formation of hibonite (CaAl12O19), high-purity Al2O3 and CaAl12O19 -based refractories had the prospect for lining materials in the hydrogen metallurgy field, owing to their excellent chemical stability under hydrogenous environments.

Evolution of Nonmetallic Inclusions with Varied Argon Stirring Condition during Vacuum Degassing Refining of a Bearing Steel

In the current study, industrial trials are performed to investigate the effect of argon stirring conditions on nonmetallic inclusions of a bearing steel during vacuum degassing (VD). Three argon stirring modes, including strong stirring, moderate stirring, and weak stirring during the last 10 min of the high‐vacuum period, are compared. The removal fraction of >1 μm inclusions and >5 μm inclusions is the highest with the moderate stirring mode, reaching 15.7% and 42.2%, respectively. Inclusions of MgO·Al2O3 are easier to remove than CaO–Al2O3 and entrained CaO–Al2O3–SiO2 ones as MgO·Al2O3 inclusions have a higher coagulation coefficient, a higher contact angle, and a lower adhesion work between the inclusion and the molten steel. Meanwhile, the removal efficiency of inclusions in the bearing steel is in the order of Al2O3 > MgO·Al2O3 > solid CaO–Al2O3 > liquid CaO–Al2O3 and entrained CaO–Al2O3–SiO2. Liquid CaO–Al2O3 inclusions with >5 μm size originate from slag entrainment and can be efficiently removed from the molten steel by the moderate stirring mode.

Effect of Mg Treatment on the Nucleation and Ostwald Growth of Inclusions in Fe-O-Al-Mg Melt.

This study aimed to investigate the effect of Mg treatment on the nucleation and ostwald growth of inclusions. Deoxidized experiments with Al (0.05%Al) and Al-Mg (0.05%Al + 0.03%Mg) were carried out at 1873 K, and the composition, number, and size of inclusions were studied as a function of holding time. Homogeneous nucleation theory and ostwald ripening were utilized to calculate the nucleation rate, the critical size of nuclei, and coarsening rate of inclusions. The results show that small inclusions were more easily found in the steels with Al-Mg complex deoxidation, and the number of inclusions with Al-Mg complex deoxidation is larger at an early stage of deoxidation. The critical size of nuclei increases in the order of MgAl2O4 (0.3–0.4 nm) < Al2O3 (0.4–0.6 nm), and the nucleation rate increases in the order of Al2O3 (1100 cm−3 s−1) < MgAl2O4 (1200 cm−3s−1), which is consistent with the experimental results. Moreover, the coarsening rate of MgAl2O4 inclusions was smaller than Al2O3 inclusions in both the value of kd(cal.) from ostwald growth and the value of kd(obs.) from inclusion size. The effect of Mg addition on coarsening of inclusion was analyzed and their mechanism was discussed based on ostwald ripening theory and Factsage calculation.

Comparing the effects of different types of inorganic nanoparticles on 17β-estradiol adsorption by graphene oxide

This study compared the effects of five types of inorganic nanoparticles (INPs) on the 17β-estradiol (E2) adsorption to graphene oxide (GO). The results showed that INPs increased the equilibrium time for the adsorption of E2 to GO. Higher Brunauer-Emmett-Teller (BET) surface area of INPs resulted in lower diffusion rate of E2, and thus the adsorption rate constant (k2) calculated from pseudo-second-order kinetic model negatively correlated with the BET surface area of INPs (p = 0.037). In addition, INPs decreased the adsorption amount of E2 to GO, and the inhibition effects declined in the order of Al2O3 > ZnO > TiO2 > SiO2 > Fe2O3. This is determined by the interactions between GO and INPs. The positively charged ZnO and Al2O3 strongly heteroaggregate with GO via electrostatic attraction, and then significantly inhibited E2 adsorption to GO. In contrast, the homoaggregation of GO was superior to its heteroaggregation with negatively charged SiO2 and TiO2, and then lower inhibition of E2 adsorption to GO was induced. Fe2O3 with less negative charge (−8.48 mV) led to the lowest inhibition effect on E2 adsorption to GO because of its preferable homoaggregation. The results were further confirmed by Derjaguin-Landau-Verwey-Overbeek calculation, transmission electron microscopy, and sedimentation experiments. This study revealed how the properties of INPs influence their effects on the adsorption of E2 by GO, and the findings are critical to understand the behavior and fate of GO and pollutants in natural aquatic environment.

Suspension calcination and alkali leaching of low-grade high-sulfur bauxite: Desulfurization, mineralogical evolution and desilication

To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in NaOH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry-differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with NaOH solution, and their activity decreased in the order of Al2O3·2SiO2, SiO2, and Al2O3.

Subcritical water gasification of lignocellulosic wastes for hydrogen production with Co modified Ni/Al2O3 catalysts

Nickel-based catalysts with different supports and cobalt loadings were synthesized for hydrothermal gasification of cellulose at 350 °C. The activity of Ni catalysts was found in the order of Al2O3 > spent bleaching clay ash > SiO2 with H2 yield of 80.6%, 69.0% and 57.0%. When 6 wt. % Co was added, 10Ni-6Co/Al2O3 showed the highest H2 yield of 88.4% i.e., 1.44 times that without Co addition. Catalysts were characterized by NH3-TPD, TPR, XRD, BET and XPS, showing that Ni-Co alloy formation promoted H2 production. Single-factor experiments were conducted to study variables in the presence of 10Ni-6Co/Al2O3 with the selected conditions of 0.5 g biomass and 20 min at 350 °C (achieving 94.9% H2 yield from cellulose) for gasification of rice straw, peanut shell and cotton straw with the increase in H2 yield by 51.4, 76.0 and 67.8 times. Ni-Co/Al2O3 catalysts enhanced hydrothermal gasification of actual agricultural residues.

Explosion suppression of porous materials in a pipe-connected spherical vessel

To study the suppression of different porous materials on the explosion of combustible gas, some experiments were implemented. The porous materials were categorized into three kinds, including six subcategories, and the explosion suppression characteristics of the thin iron hoop, one-layer porous materials, two-layer composite porous materials, and three-layer composite porous materials were studied and analyzed. The results show that a rarefaction wave appears in the spherical vessel during the rapid development stage of combustion explosion. Further, the thin iron hoop could enhance the gas explosion intensity. And the explosion intensity suppression effect of the porous materials is obvious, the best effects of one-layer, two-layer and three-layer porous materials are from Fe–Ni 10 mm/40 PPI, Fe–Ni 10 mm/90 PPI + Al2O3 10 mm/30 PPI, and Al2O3 10 mm/50 PPI + Fe–Ni 10 mm/40 PPI + SiC 20 mm/20 PPI, respectively. According to the surface morphology of the porous materials, the anti-sintering ability of the three categories of porous materials follows the order of Al2O3 > SiC > Fe–Ni. Besides, the thickness and pore size of the combined porous material was changed, which has a great influence on the explosion pressure and the explosion intensity.

Role of adsorption in combined membrane fouling by biopolymers coexisting with inorganic particles

This study was conducted in order to obtain a better understanding of the combined fouling by biopolymers coexisting with inorganic particles from the aspects of fouling index, fouling layer structure and biopolymer−particle interactions. Calcium alginate was used as the model biopolymer and Fe2O3, Al2O3, kaolin, and SiO2 were used as model inorganic particles. Results showed that the combined fouling differed greatly among the four types of inorganic particles. The differences were attributed particularly to the different adsorption capacities for calcium alginate by the particles with this capacity decreasing in the order of Fe2O3, Al2O3, kaolin and SiO2. Particle size measurement and electron microscopic observation indicated the formation of agglomerates between calcium alginate and those inorganic particles exhibiting strong adsorption capacity. A structure was proposed for the combined fouling layer comprised of a backbone cake layer of alginate−inorganic particle agglomerates with the pores partially filled with discontinuous calcium alginate gels. The filterability of the fouling layer was primarily determined by the abundance of the gels. The strength of physical interaction between calcium alginate and each type of inorganic particle was calculated from the respective surface energies and zeta potentials. Calculation results showed that the extent of physical interaction increased in the order of Al2O3, Fe2O3, kaolin and SiO2, with this order differing from that of adsorption capacity. Chemical interactions may also play an important role in the adsorption of alginate and the consequent combined fouling. High-resolution XPS scans revealed a slight shift of electron binding energies when alginate was adsorbed.

Theoretical analysis of thermal performance in a plate type liquid heat exchanger using various nanofluids based on LiBr solution

Thermal properties of nanofluids containing nano-sized particles in the working fluid are superior to base fluid. In this study, the performance of a plate heat exchanger (PHX), with chevron angles 30°/30° and 60°/60°, is analyzed with various nanofluids based on LiBr solution as working fluid. The performance of the chevron PHX was analyzed with hot-side fluid mass flow rate, the overall heat transfer coefficient, effectiveness, and rate of the heat transfer were calculated. As a result, the performance was improved in the order of Fe2O3, CuO, Al2O3, TiO2, ZnO, SiO2, CNT, sequentially, at same volume concentration. The performance improvement of PHX was similar for both Fe2O3 and CuO nanofluid because their thermal properties are similar. Besides, the effect of performance improvement by nanofluids remarkably appeared in a 30°/30° chevron angle PHX. Considering the limitation concentration of dispersion stability for various nanofluids, the PHX performance improvement was in the order of Al2O3, TiO2, Fe2O3, CuO, CNT, SiO2. To improve chevron PHX performance, Al2O3 or TiO2 nanofluids have added advantages over other nanofluids.

Systematic screening and modification of Ni based catalysts for hydrogen generation from supercritical water gasification of lignin

In this study, systematic screening of 29 catalysts synthesised using five supports: Al2O3, activated carbon (AC), TiO2, ZrO2, MgO, and three promoters: Co, Cu, Ce (with two different Ce precursors) was performed. Then, the optimization of the Ni–Ce/Al2O3 catalyst was carried out by varying Ni loading (four levels) and Ce/Ni molar ratio (two levels). All these catalysts were screened for supercritical water gasification (SCWG) of lignin under the operating conditions of 650°C, 26MPa and water to biomass mass ratio of 5 in a tubular batch reactor. Various characterization techniques were used to investigate the properties of these catalysts further. As the result, using different supports, the activity of Ni-based catalysts for SCWG of lignin was found in the order of Al2O3>TiO2>AC>ZrO2>MgO. As the best promoter, Ce enhanced the hydrogen selectivity by promoting the Ni dispersion and weakening the Ni–Al2O3 interaction. Use of different precursors for the Ce promoter (CeCl3·6H2O or Ce(NO3)3·6H2O) showed no effect on the hydrogen yield. For a fixed Ni loading, hydrogen yield increased with an increase in Ce/Ni molar ratio. The 20Ni–0.36Ce/Al2O3 catalyst showed highest hydrogen yield of 2.15mmol/g, which is 35% higher than that for non-catalytic run. The better performance of Ni–Ce/Al2O3 catalyst can be attributed to enhanced coke resistance as well as increased reducibility for Ni by addition of Ce promoter.

Dependence of Photothermal Conversion Characteristics on Different Nanoparticle Dispersions.

The efficiency of nanoparticle-based direct absorption solar collector (DASC) is strongly dependent on the materials, where a systematic study is still lacking. This work conducts an experimental study of the photothermal conversion characteristics of a number of nanoparticle dispersions including Au, Si, Fe3O4, Al2O3 and diamond under the same experimental setup. The results show that comparing with the base fluid, the introduction of nanoparticles can increase the photothermal conversion efficiency significantly, and the efficiency increases in the order of Al2O3, diamond, (Fe3O4 and Si) and Au. For a given total mass concentration, the Fe3O4-Au hybrid nanofluid is found to possess a higher efficiency than that of pure Au alone. Three possible mechanisms are proposed for the influence of nanoparticle materials, which can qualitatively explain the experimental results.

High temperature carbon dioxide capture on nano-structured MgO-Al2O3 and CaO-Al2O3 adsorbents: an experimental and theoretical study.

Nano-structured alkaline-earth metal oxide adsorbents (denoted as MgO-Al2O3 and CaO-Al2O3) were prepared by an epoxide-driven one-pot sol-gel method, and they were applied to the dynamic and static CO2 adsorption. For comparison, a nano-structured aluminum oxide adsorbent (denoted as Al2O3) was also prepared by a similar method. MgO-Al2O3 adsorbent exhibited a well-developed mesopore structure through the formation of MgAl2O4 spinel phase, whereas CaO-Al2O3 adsorbent was composed of nano-sized CaO and CaAl2O4, resulting in a pore plugging. It was revealed that total basicity increased in the order of Al2O3 (0.11 mmol-CO2/g) < MgO-Al2O3 (0.37 mmol-CO2/g) < CaO-Al2O3, (1.21 mmol-CO2/g), which is in concurrent with adsorption energy obtained from DFT calculations. However, it was found that both basicity and base strength of the adsorbents played an important role in determining the CO2 adsorptive performance at different operating temperature. Among the adsorbents tested, MgO-Al2O3, which mostly retained medium basic sites, exhibited a best CO2 adsorptive performance at 200 degrees C. Furthermore, the experimental results are well supported by theoretical estimation, suggesting a useful design method of adsorbents for facile and regenerative adsorption in the applications of CO2 capture.

Modification of Inclusions in Liquid Iron by Mg Treatment

Effect of Mg addition on the compositions of inclusions were studied. The results show that Mg can minimize the inclusions of steel obviously. Under the present condition, Mg deoxidation products of low-S content experimental steel would be changed in the order of Al2O3→MgAl2O4→Mg→Al–O–S→Mg–O–S. Mg deoxidation products of high-S content experimental steel generate Mg–S(–O)+MnS type inclusions, except for usual oxysulfide. And it is consistent with the results of thermodynamics calculation. Mg is preferred to react with oxide, compared with sulfide. The reaction reaches the equilibrium after 1 min or 5 min. It shows that the number and diameter of inclusions in all experimental steel samples are well under control, helping to improve the properties of steel.

Effect of TiO2, Al2O3, and Fe3O4 nanoparticles on phosphorus removal from aqueous solution

Phosphorus (P) removal from aqueous solutions was investigated using TiO2, Al2O3, and Fe3O4 nanoparticles (NPs). Adsorption study was performed to determine the optimum operation conditions such as adsorption time, temperature, pH, and adsorbent dosage. Sorption isotherms were well described by linear, Freundlich and Langmuir models. The maximum adsorption capacity of P was 28.3, 24.4, and 21.5 mg g−1 for TiO2, Fe3O4 and Al2O3, respectively. Desorption analysis showed that the desorption capacities were in an order of Al2O3 &gt; Fe3O4 &gt; TiO2. Kinetic data were best fitted with pseudo‐second‐order and intra‐particle diffusion kinetic models. Scanning electron microscopy (SEM), energy dispersive X‐ray (XRD), and NPs solution saturation indices (SI) before and after P sorption showed that the main mechanism of P sorption by TiO2 was adsorption, whereas P sorption by Al2O3 and Fe3O4 were due to adsorption and precipitation. Results showed that double layer model (DLM) could be modeled P adsorption onto adsorbents over a wide range of pH. Thermodynamic parameters confirmed the endothermic and not spontaneity nature of the P adsorption. These NPs have potential for use as efficient sorbents for the removal of P from aqueous solutions and TiO2 NPs were identified as the most promising sorbent due to their high metal uptake. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1209–1219, 2014

Characterization of TiO2-Doped Yttria-Stabilized Zirconia (YSZ) for Supercritical Water-Cooled Reactor Insulator Application

In this study, TiO2-doped YSZ samples were tested in supercritical water (SCW) to evaluate their corrosion behavior. The doped samples were produced by mechanically alloying standard 7 wt.% Y2O3-ZrO2 with 5, 10, and 15 wt.% of TiO2 first. The bulk sample pieces were then obtained using plasma spraying of the alloyed powder materials followed by sintering. The results showed that the weight changes for 5TiYSZ and 10TiYSZ after 1000 h of exposure in SCW were negligible and the sample surfaces did not exhibit any indication of corrosion. In comparison to the reference materials (Al2O3 and 7YSZ) processed using the same method, the rate of weight change followed the order of Al2O3 > 7YSZ, 15TiYSZ > 10TiYSZ > 5TiYSZ. As several TiO2-doped 7SYZ compositions also display increased fracture toughness and reduced thermal conductivity, they may be considered as potential candidates for thermal insulation in a SCW-cooled nuclear reactor.

Effects of Dissolved Oxygen and Size Distribution on Particle Coarsening of Deoxidation Product

The growth mechanism for deoxidation products of MgO, ZrO2, Al2O3, CaO–Al2O3 and MnO–SiO2 in an Fe–10mass%Ni alloy has been studied under the condition of no fluid flow by considering the effects of dissolved oxygen and size distribution on Ostwald ripening. The coarsening rate of particles is largely dependent on the dissolved oxygen content. The spread of particle size distribution decreases in the order of Al2O3>ZrO2>MgO>CaO–Al2O3>MnO/SiO2 particles and that of solid Al2O3, ZrO2 and MgO particles becomes narrower with holding time. The coarsening rate is also affected by the spread of size distribution curve and this is the reason that the coarsening rate of Al2O3 particles is larger than that predicted from dissolved oxygen content.

ファインセラミックスのホーニング加工 被削性と切りくず生成機構

The mechanism of chip formation and the machinability of fine ceramics are investigated by both honing operation and scratching test using a conical diamond tool. The workpieces are alumina Al2O3, silicon nitride Si3N4 and silicon carbide SiC which are sintered under atmospheric pressure, and borosilicate glass (SiO2). Based on the experimental results which were done by the authors, the specification of the diamond sticks is decided to obtain superior honing performance. The results are as follows. The machinability of work materials is best in SiO2 and deteriorates in the order of Al2O3, Si3N4, and SiC. Comparing the shape and size of chips made by honing with the grain structure of Al2O3 and Si3N4, it can be estimated that the chips are mainly formed by the fracture occurred along the grain boundary, although chips of Si3N4 are also formed by the fracture occurred through the grain. Two types of material removal are observed depending on the load acting on the cutting grits. When the load is small, the cutting grits are in the condition of wear and the surface roughness of the work material is improved. When the load is set above the critical value, a lot of chips are created and there remains many large craters on the surface honed.

金属酸化物および水酸化物添加りん酸三ナトリウム浴中でのアルミニウムの陽極酸化

Anodizing of aluminum was investigated in sodium phosphate (0.2M) baths saturated or dispersed with metal oxides (Al2O3, CuO, FeO, SnO2, ZnO) or metal hydroxides (Al OH3, Cr(OH)3).Anodizing was carried out at a constant current density of 2A·dm-2 for the baths containing cupric oxide, ferrous oxide or stannic oxide, and at 1A·dm-2 for the bath containing zinc oxide.In the case of the baths containing aluminum oxide, anodizing was carried out at a constant voltage of 40V.Film thickness converted for electrolysis at 1A·dm-2 for 30min. was found to be greater in the bath dispersing aluminum oxide (about 4.6μm) than in the non metal oxide bath (adout 2.2μm). The effect of the additon of metal oxides on film thickness decreased in the order of Al2O3>ZnO>CuO>SnO2≤FeO.In the case of the baths containing metal hydroxides, anodizing was carried out at a constant voltage of 60V. A thick film (about 4.2μm) was formed in a bath dispersing aluminum hydroxide.Thicker films were formed in dispersed baths than in saturated baths of metal oxides or hydroxides.The fact that a thicker film was formed in baths containing metal oxides or hydroxides may be explained by the action of the additives as a oxygen supplier and an enhancing medium of electric current.