Free Alumina Research Articles

Effects of different alumina carriers on the phase formation and mechanical properties of sulfoaluminate cement clinker

Finding alumina carriers that can replace bauxite to produce sulfoaluminate cement (SAC) is a significant issue. The effects of bauxite (Ba), industrial aluminium hydroxide (I-AH), industrial aluminium oxide (I-AO) and analytically pure aluminium oxide (A-AO) on the phase formation and mechanical properties of SAC clinkers were studied by differential scanning calorimetry/thermogravimetry, Rietveld quantitative analysis, scanning electron microscopy/energy dispersive spectrometry and isothermal calorimetry. It was found that sintering SAC clinker with Ba and I-AH as alumina carriers accelerated the rate of the solid-phase reaction, promoted the formation of the target phase and led to the formation of ye'elimite with a small grain size. The compressive strength at each age was thus higher. However, when amorphous alumina was used as the alumina carrier to sinter SAC clinker, the solid-phase reaction rate was slow, which hindered the formation of the target phase, free alumina appeared and ye'elimite with a large grain size was formed, so the compressive strength at each age is lower. Aluminium oxide with finer particle size can be decomposed from I-AH and Ba during calcination, which can accelerate the solid-phase reaction rate and promote the formation of the target phase. The associated element in Ba (titanium) can lead to the formation of more α′H-C2S, but obstructed the formation of ye'elimite.

Optimization of lapping process parameters of CP-Ti based on PSO with mutation and BPNN

This work aims to improve the surface quality of commercially pure titanium (CP-Ti) with free alumina lapping fluid and establish the relationship between the main process parameters of lapping and roughness. On this basis, the optimal process parameters were searched by performing particle swarm optimization with mutation. First, free alumina lapping fluid was used to perform an L9(33) orthogonal experiment on CP-Ti to acquire data samples to train the neural network. At the same time, a BP neural network was created to fit the nonlinear functional relation among the lapping pressure P, spindle speed n, slurry flow Q and roughness Ra. Then, the range of the neuron numbers in the hidden layer of the neural network was determined by empirical formulas and the Kolmogorov theorem. On this basis, particle swarm optimization with mutation was used to search for the optimal process parameter configurations for lapping CP-Ti. The optimal process parameter configurations were used in the neural network to calculate the prediction value. Finally, the accuracy of the prediction was verified experimentally. The optimum process parameter configurations found by particle swarm optimization were as follows: the lapping pressure was 5 kPa, spindle speed was 60 r·min−1 and slurry flow was 50 ml·min−1. Then, the configurations were applied to a neural network to simulate prediction: the roughness was 0.1127 μm. The roughness obtained by experiments was 0.1134 μm. The error was 0.62%, which indicates that the well-trained neural network can achieve a good prediction when experimental data are missing. Applying the particle swarm optimization (PSO) algorithm with mutation to a neural network will obtain the optimal process parameter configurations, which can effectively improve the surface quality of CP-Ti lapped with free abrasive.

The nickel-support interaction as determining factor of the selectivity to ethylene in the oxidative dehydrogenation of ethane over nickel oxide/alumina catalysts

Nickel oxides supported on γ-alumina (Ni-loading from 5 to 30 wt% NiO) have been synthesized and tested in the oxidative dehydrogenation (ODH) of ethane in order to determine the importance of the NiO-support interaction. The best performance was achieved by the catalyst with 15 wt% NiO; higher NiO-loadings lead to the formation of unselective bulk-like NiO and lower Ni-loadings present high proportion of free alumina surface sites. The presence of oxalic acid and/or niobium in the synthesis gel resulted in the formation of NiO particles with similar size, but higher crystallinity and reducibility than the standard 15 wt% NiO catalyst. The obtained results have revealed that, in addition to NiO crystal size, the nickel oxide-support interaction determines the catalytic performance of these catalysts.

Effect of alumina occurrence on sintering performance of iron ores and its action mechanism

Iron ores always contain several forms of alumina, which may have different effect on sintering performance. In this paper, sinter pot tests were systematically conducted with various alumina types and contents by means of alumina additives substituting for the corresponding types of alumina, and the relevant action mechanism on sintering performance was clarified by the mineralogy of product sinter. The results show that kaolinite is beneficial to the granulation process rather than other three alumina types. In addition, it contributes to relatively better sintering performance while aluminous goethite ranks the only next, followed by gibbsite and free alumina. Mechanism analysis indicates that kaolinite and aluminous goethite are preferable to achieve relatively lower sinter porosity and higher amount of silico-ferrite of calcium and alumina (SFCA) compared with gibbsite and free alumina. Besides, the former two alumina types are apt to promote the formation of higher strength SFCA such as dendritic and acicular SFCA. Furthermore, much tighter interlocking texture in product sinter is formed as alumina occurs in kaolinite or aluminous goethite. Kaolinite and aluminous goethite are the preferably desirable alumina types for sintering rather than free alumina and gibbsite.

Oxime-modified aluminum (III) isopropoxide: A promising sol-gel precursor coating to improve mechanical strength of an aluminum alloy

This research is concerned with the investigation of the capability of alumina coatings, deposited by dip coating methods to improve mechanical properties of aluminum alloys and anodized aluminum alloy. Alumina coatings were deposited using oxime-modified aluminum (III) isopropoxide as a sol–gel precursor. The Scanning electron microscopy (SEM) images of the coated samples suggest deposition of uniform and crack free alumina coatings. The mechanical property of the bare, dip coated, anodized and coated anodized aluminum alloy samples were investigated by the slow strain rate test. It indicates that simply dip coated surface have higher ultimate tensile strength as compare to other samples.

Migration characteristics of heavy metals in the weathering process of exposed argillaceous sandstone in a mercury-thallium mining area

Lanmuchang mercury-thallium mine, a typical polymetallic mine is located in southwestern Guizhou, China, is the most serious and typical area resulted from multi-metal contamination (Tl, Hg, As, and Sb). After the mercury-thallium mining, a large area of surrounding rocks such as argillaceous sandstone with high contents of Tl, Hg, As, and Sb is exposed to air. Weathering caused the argillaceous sandstone to form different weathering layers, including the grey-black external layer, the brown-yellow middle layer and the gray-white inner layer, and the external layer was enriched with higher heavy metals. However, the reason of heavy metal migration and transformation in argillaceous sandstone caused by weathering is unclear. The objective of this paper was to investigate the migration, transformation and release characteristics of Tl, Hg, As, and Sb in argillaceous sandstone during the weathering. The results indicated that weathering not only promoted an acidic oxidation environment in argillaceous sandstone, but also increased its specific surface area, pore volume and hydrophilicity, which are beneficial to the permeability of oxygen and etching liquids during the process of weathering and leaching. Meanwhile, weathering led to the transformation or decomposition of hydrophilic groups, such as -OH and -C˭O in the grey-black external layer of argillaceous sandstone, resulting in the further release of heavy metals bound to these groups. The concentration of Tl, Hg, As, and Sb in the leaching solution of argillaceous sandstone represented a positive correlation with that of Fe, Ca, Mg at different levels, indicating that Tl, Hg, As, and Sb were released with the dissolution of Fe, Ca and Mg during weathering and leaching. In summary, these results indicated that weathering caused the dissolution and migration of heavy metals in the argillaceous sandstone. Tl, Hg, As, and Sb migrated from the grey-white inner layer to the grey-black external layer and partially adsorbed by free alumina (Ald), jarosite and Ca-bearing minerals, showing enrichment phenomena, partially released into the environment, causing environmental pollution.

An investigation into aluminum occurrence impact on SFCA formation and sinter matrix strength

The alumina content of iron ores for sintering is gradually increasing with the growing depletion of high-grade iron ores, which is harmful to the sintering process. Therefore, it is essential to reveal the action mechanism of alumina on sinter quality. In this paper, the aluminum occurrence of various iron ores was determined by applying X-ray diffraction (XRD), optical microscopy, scanning electron microscopy and energy dispersive spectrum analysis (SEM-EDS). Then, the effects of iron ore type, aluminum occurrence (free alumina, gibbsite, diaspore, alumogoethite and kaolinite) and alumina content on formation characteristics of SFCA bonding phases as well as sinter matrix strength were investigated based on laboratory compact sintering tests. The results show that the discrepancy of aluminum occurrence contributes to different SFCA formation characteristics and then sinter matrix strength, due to different reactivity of various aluminum-containing minerals with iron oxides and fluxes. Increasing alumina content generally results in an increase in the porosity of sinters and deterioration of sinter matrix strength for all aluminum occurrence. Aluminum in the form of kaolinite is more conducive to form dendritic or acicular SFCA with superior sinter matrix strength compared with other aluminum occurrences. In contrast, aluminum occurring in free alumina presents greatest adverse impacts on sinter matrix strength due to its poor reactivity and high porosity of resultant sinters.

Evaluate Mechanical Behavior of Alumina Coated Aluminum Alloy Using Slow Strain Rates Test in 3.5% of NaCl Solution

This work is concerned with the investigation of the capability of alumina coatings, deposited over aluminum alloy by dip coating methods to improve mechanical properties. Alumina coatings were deposited using oxime-modified aluminum (III) isopropoxide as a sol-gel precursor. The Scanning electron microscopy (SEM-EDX) images of the coated samples suggest deposition of uniform and crack free alumina coatings. The mechanical property of the bare, and dip coated aluminum alloy were investigated by the slow strain rate test in 3.5% of NaCl solution. The coated sample indicate higher ultimate tensile strength, it’s reflect the protective behavior of coating.

Soil Disintegration Characteristics of Collapsed Walls and Influencing Factors in Southern China

Abstract Collapsed walls cause collapsed mounds, and the disintegration characteristics of collapsed walls are thus closely linked with the occurrence of collapsed mounds. The current study examines the disintegration characteristics and the physical and chemical properties of collapsed walls. A multilevel analysis was conducted by obtaining soil samples from four layers of a collapsed wall. The results showed that 1) the physical and chemical properties of the soil samples (red soil layer, sandy soil layer, debris layer, gravel and eluvial breccia) are closely related to the weathering degree of the crust; 2) gravel and eluvial breccia disintegrated in the shortest time, whereas red soil exhibited the slowest disintegration in the vertical section of the collapsed wall. The order of the disintegrating ratio of the layers is as follows: red soil layer < sandy soil layer < debris layer < gravel and eluvial breccia. Initial water content significantly influenced the disintegration ratio of the red soil layer and sandy soil layer, whereas its effect on the debris layer and gravel eluvial breccia is minimal; and 3) most of the physical and chemical properties of the collapsed wall are significantly correlated with the disintegration ratio of the soil sample. The following physical and chemical properties, which are positively correlated with the disintegration ratio, are arranged based on highest to lowest correlation coefficient: sand content, MgO, natural water content, K2O, CaO, exchangeable sodium, pH, porosity, Na2O, and cation exchange capacity. The following physical and chemical properties, which are negatively correlated with the disintegration ratio, are organized based on highest to lowest correlation coefficient: cosmid, Fe2O3, silt particle, Al2O3, TiO2, SiO2, organic matter, free iron oxide, and free alumina. Only exchangeable calcium, saturated water content, specific gravity of soil particles, and dry density of soil particles are significantly correlated with the disintegration ratio. The correlation coefficient indicates that the disintegration ratio and soil structure, as well as the chemical content of clay minerals, are closely correlated. The study helps explain the mechanism of wall collapse and provides references for developing protective measures against erosion.

Optically transparent and durable Al2O3 coatings for harsh environments by ultra short pulsed laser deposition

Nowadays, an environmental protection is needed for a number of optical applications in conditions quickly impairing the clarity of optical surfaces. Abrasion resistant optical coatings applied onto plastics are usually based on alumina or polysiloxane technology. In many applications transparent glasses and ceramics need a combination of abrasive and chemically resistant shielding or other protective solutions like coatings. In this study, we intended to test our hypothesis that clear and pore free alumina coating can be uniformly distributed on glass prisms by ultra short pulsed laser deposition (USPLD) technique to protect the sensitive surfaces against abrasives. Abrasive wear tests were carried out by the use of SiC emery paper using specified standard procedures. After the wear tests the measured transparencies of coated prisms turned out to be close those of the prisms before coating. The coating on sensitive surfaces consistently displayed enhanced wear resistance exhibiting still high quality, even after severe wear testing. Furthermore, the coating modified the surface properties towards hydrophobic nature in contrast to untreated prisms, which became very hydrophilic especially due to wear.

Oxime-modified aluminium(III) alkoxides: Potential precursors for γ-alumina nano-powders and optically transparent alumina film

Reactions of aluminium(III) iso-propoxide with acetoxime in anhydrous benzene yielded complexes of the type [Al(OiPr)3-n{ONC(CH3)2}n], where n=1, 2 or 3. These complexes were characterized by elemental analysis, FTIR and NMR (1H, 13C, 27Al) spectral studies. Spectral studies of these complexes suggest the presence of bi-dentate mode of the oximato moieties in the solution state. Soft transformations of aluminium(III) iso-propoxide and their oxime derivatives to pure alumina were carried out by the sol-gel technique. The powder XRD patterns of all the formed alumina suggest formation of cubic phase (γ-alumina) with average crystallites size of 7–30nm. Optically transparent crack free alumina film was deposited on glass substrate using alumina sol, prepared by complex [Al(OiPr){ONC(CH3)2}], through dip coating method. The film sintered at 500°C is amorphous in nature as indicated by XRD study. The alumina film is found to be ∼95% optically transparent in the visible region. The observed particle size distribution of alumina thin film in AFM images is found to be 13±2nm.

Green approach in the sol–gel synthesis of defect free unsupported mesoporous alumina films

Sol–gel synthesis of defect free alumina films by the hydrolysis of metal alkoxide precursors require proper drying and calcination procedures. In the present paper an attempt has been made to gain control over the difficult process of sol–gel synthesis of plain, porous, defect free alumina films through proper design and selection of parameters like contact angle (120°), viscosity (1–2 Pa s), drying and calcination temperature. SANS, AFM, TEM probes were used to investigate porous alumina film (α alumina) made up of parallel channels with cylindrical shape. Nitrogen adsorption studies (BET method) were carried out to determine porosity and surface area of the film. The SEM and X-ray diffraction studies were done to characterize the alumina film. The kind of technique used during synthesis of alumina film is not only cost affective but has an added advantage of controlling the shape and geometry of alumina film. The novel technique of disc furnace introduced here has overcome the difficulties of cracking and deformation in the sol–gel synthesis of alumina film during calcination. It has been shown that various sizes of porous, plain unsupported alumina films with a diameter of 30–50 mm and thickness of 0.5–5 mm were prepared by using sol–gel method.

Effects of Soil Properties and Flooding on the Mobility and Transformation of Mercury in a Temperate Riparian Wetland

Three fractions of mercury (mobile, semi-mobile, and non-mobile mercury) were detected in the soil of an estuarine wetland in Nansi Lake, which is on the east route of China's South-to-North Water Transfer Project. The correlations between these mercury fractions and soil properties were examined under different levels of toxicity. Furthermore, the effects of two flooding conditions (permanent flooding and seasonal flooding) on mercury mobility were analyzed. Results showed that soil pH was negatively correlated with mobile mercury, whereas semi-mobile mercury was positively correlated with total aluminum, iron, and manganese. Moreover, free alumina was positively correlated with all three fractions of mercury. Our study suggests that high contents of soil acid and free alumina might promote wetlands as “sinks” for mercury sequestration, along with low concentrations of organic matter and manganese. In addition, seasonally flooded wetland might limit the production of toxic mobile mercury more than permanently flooded wetland. Large areas of seasonally flooded wetlands in the watershed are permanently flooded by the water transfer project, which elevates the water level during the dry season. As a result, the potential toxicity of mercury may increase in the watershed during water transfer, which should gain more attention.

Direct Bonding Mechanism of ALD-Al2O3 Thin Films

Direct bonding mechanism of amorphous ALD alumina has been investigated from room temperature up to 1200°C. By considering the evolution with temperature of free alumina surfaces and bonded configuration we highlight strong interaction between oxidant species and defect generation through interfacial oxidation. In the first case, the combination of internal stress and adhesion loss by dry O2 oxidation results in blister formations, whereas in the case of bonding structures, wet oxidation with H2 production at Silicon-Alumina interfaces explains void formation. Based on these established mechanisms we provide insights on alumina layer integration within a large temperature range.

Al2O3 films grown by glow discharge plasma aluminising

Aluminising of 9Cr steel substrates followed by heat treatment has been attempted to generate Al2O3 films along with Fe–Al diffusion zone at the coating/substrate interface. Effect of glow discharge plasma processing on the phase and microstructure of resultant alumina films in comparison with thermally processed samples has been reported. The thermal and plasma treated samples were characterised using X-ray diffraction, scanning electron microscopy–energy dispersive X-ray spectroscopy, electron probe microanalysis, X-ray photoelectron spectroscopy (XPS) and nanoindentation techniques. X-ray diffraction and XPS studies revealed γ-Al2O3 phase in both thermal and plasma processed samples. The XPS data indicated higher binding energies in plasma processed Al2O3 films as compared to thermally processed Al2O3 films. Scanning electron microscopy observations revealed cracks in thermally grown Al2O3 films while the same was not observed in plasma processed films. The EDX analysis revealed Fe(Al) diffusion layer of ∼3 μm in plasma processed films while the same was not observed in thermally treated samples. Nanoindentation tests on plasma grown alumina films indicated 16·96 GPa hardness while hardness for thermally grown alumina films was found to be 9·95 GPa. The role of plasma in generating a crack free alumina film has been discussed.

The effect of a constraint on the sintering and stress development in alumina thick films

The microstructural and stress evolution of thick (25μm) alumina films on dense alumina substrates sintered at temperatures from 1300°C to 1600°C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300°C–1600°C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded.

Nanoporous morphology of alumina films prepared by sol–gel dip coating method on alumina substrate

Nanoporous crack free alumina thin films were fabricated in two phases gamma (γ) and alpha (α) by sol–gel dip coating method. The thickness of the mesoporous films was increased with binder by varying its concentration, and with increasing the number of coating. The porosity, pore size, surface area and phase were controlled by sintering temperature. Interconnected pore structure of 8–15 nm diameter were successfully prepared by repeating the deposition several times. FESEM, BET, AFM and XRD techniques were employed for the microstructural characterization.

Zirconia Reinforcement of Cement Free Alumina Refractory Castables by Two Routes

The cement free castables (CFC) and the ultra low cement castables (ULCC) differ from the conventional castables not only in the fact that alumina cement content and that the water required for elaboration is considerable lower, but also that they exhibit outstanding physical-chemical properties and mechanical properties. In this work we compared two routes of introducing zirconia to cement free alumina castables with a zirconia free castables, one by adding electrofused zirconia grains and the second by incorporating reused grains from electrofused AZS block formerly used as floor of glass melting furnaces. Comparable microstructures and textural properties were achieved, this fact permitted to evaluate the zirconia influence in the mechanical and fracture properties of the studied materials. There was a direct correlation with the zirconia content of both the mechanical properties at room temperature and at high temperatures (1350¡C). Finally, while at room temperature the incorporation of AZS grains proved to be more efficient to reinforce electrofused zirconia proved to be the most effective additive for reinforcement of castables studied if they were to be used at elevated temperatures.

The origin of tonsteins, an overview, and links with seatearths, fireclays and fragmental clay rocks

Abstract Tonsteins are volcanic ash falls in coal-bearing sequences that have altered to kaolinite. Only in the last twenty years or so has the volcanic origin become firmly established. The evidence for the volcanic origin encompasses bed form, including lateral extent, structures, textures, volcanogenic mineralogy and geochemistry. The lines of evidence are reviewed from a historical perspective. Tonsteins came to prominence over a hundred years ago because of their stratigraphic value. Tonsteins continue to be of value in coalfield exploration, but their stratigraphic value has been enhanced in recent years with the ability to determine radiometric ages with a high level of accuracy. The geochemistry not only provides good evidence for the volcanic origin, but also enables tectomagmatic deductions to be made for areas external to the coal basin. In addition, some tonsteins are the indicators for the discovering of rare metal ore deposits (Nb, REEs, and Ga). There is also the potential to use the geochemistry to identify specific tonsteins; essentially a chemostratigraphic approach. Tonsteins are seen as one class of bentonites; others include K-bentonites, metatonsteins, and possibly illitic-bentonites. Tonsteins have been linked to seatearths, fireclays and fragmental clay rocks. Although all such rocks contain kaolinite, the origins differ. The seatearths contain rootlets and were subjected to pedogenic activity. Alteration of the silicate minerals is limited. Under conditions of a high water table, and in the presence of organic matter, reducing conditions prevailed leading to gleization. On the other hand, the fireclays show extensive alteration to kaolinite. There is a link with the major marine bands and this has implications in terms of sequence stratigraphy. The fragmental clayrocks have also been linked to soil-forming processes, but in this case possibly the reworked soil was the product of an open system containing free alumina minerals that reacted with silica in solution during diagenesis.

Lanthanoids as an indicator of the structure of the zone of free alumina in the lateritic weathering crust of the KMA

666 Large bauxite deposits playing an important role in the economic development of the Russian Federation were discovered and studied in detail during the long history of the development of domestic geology. In addition to aluminum, rare hydrolyzer elements and REEs are accumulated during lateritic weathering; they are of special importance as well, since the quan� titative data on their concentration may be applied for bauxite processing (in perspective). Indicative possibilities of lanthanoids were consid� ered in the studies of V.I. Sirotin, V.A. Shatrov, and E.E. Belyavtseva from the example of the lateritic (alumina) weathering crust of the KMA [1–3]. In this paper we analyze the relationship between the litho� logical types of bauxites and the distribution of lanth� anoids in them (on the example of the sections of the largest Vislovskoe deposit). The zone of free alumina includes three subzones: the lower allitic, conditional bauxites, and debauxiti� zation. Rather than the lateritic stage of the profile his� tory, such a structure reflects the lateritic–diagenetic stage, when the separation of a single zone of laterite into subzones occurred [4, 5], which was accompanied by migration of iron and silicon in the profile. Alumi� num was poorly mobile: its migration was limited to zone IV and the upper part of zone III. As a result, sometimes zone IV was completely replaced by kaolinite (gley process) and shamosite (iron introduc� tion), but most often zone IV was separated into the three subzones mentioned.