Formation Of Aluminum Hydroxide Research Articles

Morphological change of plain and nano-porous surfaces during boiling and its effect on nucleate pool boiling heat transfer

In order to investigate nucleate pool boiling heat transfer characteristics in saturated water, a plain aluminum alloy surface (6061, untreated) and a uniquely fabricated aluminum oxide Nano-Porous Surface (NPS) sample were prepared. Generally, the NPS exhibited a lower wall superheat at the onset of nucleate boiling and a higher nucleate boiling heat transfer coefficient than the plain surface. It was also noted that the nucleate boiling heat transfer coefficient decreased by 30% on the plain surface and by 37% on the NPS after five repeated boiling tests. It was found that such performance-degradation in both of the test samples was due primarily to the formation of aluminum hydroxide on the boiling surfaces. It is our belief that the aluminum hydroxide, formed on both boiling surfaces, significantly altered the surface morphologies as shown in the microscopic images of the post-boiling surfaces, which resulted in the decrease of the active nucleation sites. Although NPS is an excellent tool to enhance the nucleate pool boiling heat transfer coefficient, its life span and usefulness can be impeded by undesirable surface reactions with working fluids.

Polytypic transformations of aluminum hydroxide: A mechanistic investigation

The diffusion of ammonia vapors into a solution of aluminum nitrate or ferric nitrate results in the precipitation of their respective hydroxides and oxyhydroxides. Polymorphic phase formation of aluminum hydroxide is controlled by the rate of crystallization. The PXRD patterns of products obtained via vapor phase diffusion revealed that poorly ordered aluminum hydroxide is formed during the initial stages of crystallization. After 8 days, the formation of the bayerite phase of aluminum hydroxide was observed. Upon prolonged exposure to ammonia vapors, bayerite was transformed into gibbsite. The infrared spectrum of the product confirmed the presence of different polytypic phases of aluminum hydroxide. The results demonstrated that the crystal structure of metal hydroxides is controlled by the rate of crystallization, nature of the metal ion, site selectivity and specificity and preparative conditions.

Porous Alumina Ceramics Prepared by the Hydrolysis-Assisted Solidification Method

We used the hydrolysis-assisted solidification (HAS) process to form the alumina green bodies from the suspensions. A total of 2.5 wt% of AlN powder, with respect to the solids content, was added to an aqueous alumina suspension containing 53.5 vol% of solids. During the hydrolysis of the AlN powder, the aluminum hydroxide reaction product precipitated on the surface of the alumina particles. The effect of the precipitated aluminum hydroxide on the density and the bending strength, after sintering the alumina samples prepared by the HAS process at temperatures up to 1300°C, was investigated. In comparison with conventionally formed samples, a similar strength was measured at a lower sintered density for the partially sintered alumina prepared by the HAS process. These improved properties could be ascribed to the formation of aluminum hydroxide in the form of boehmite lamellas on the surface of the particles during the HAS consolidation process. Boehmite lamellas topotactically transform with temperature into various transition aluminas; however, the change in the crystal structure did not affect the morphology, which remained the same up to 1100°C. These lamellas hindered the densification of the samples up to 1100°C, but at higher temperatures, the lamellas transformed into nanosized α-alumina particles, which enhanced the neck growth, resulting in a very high measured flexural strength at sintered densities up to 70%.

Coagulation and electrocoagulation of oil-in-water emulsions

In this work the efficiencies of the chemical and the electrochemical break-up of oil-in-water (O/W) emulsions with hydrolyzing aluminium salts are compared. It has been obtained that the efficiency of the processes does not depend directly on the dosing technology, but on the total concentration of aluminium and pH. This latter parameter changes in a different way in the chemical and the electrochemical processes: the pH increases during the electrochemical experiments since the electrochemical system leads to the formation of aluminum hydroxide as a net final product, but it decreases in the conventional ones due to the acid properties of the aluminum salts added (AlCl 3 or Al 2(SO 4) 3). The break-up of the emulsions only takes place in the range of pHs between 5 and 9, and the amount of aluminium necessary to produce the destabilization of the emulsion is proportional to the oil concentration. Electrolytes containing chlorides improve COD removal as compared with those containing sulphate ions. Aluminium hydroxide precipitates were found to be the primary species present in solution in the conditions in which the breaking process is favoured. Consequently, the attachment of more than one droplet of oil at a time to a charged precipitate-particle (bridging flocculation) was proposed as the primary destabilization mechanism.

Pattern Formation and Self-Organization in a Simple Precipitation System

Various types of pattern formation and self-organization phenomena can be observed in biological, chemical, and geochemical systems due to the interaction of reaction with diffusion. The appearance of static precipitation patterns was reported first by Liesegang in 1896. Traveling waves and dynamically changing patterns can also exist in reaction-diffusion systems: the Belousov-Zhabotinsky reaction provides a classical example for these phenomena. Until now, no experimental evidence had been found for the presence of such dynamical patterns in precipitation systems. Pattern formation phenomena, as a result of precipitation front coupling with traveling waves, are investigated in a new simple reaction-diffusion system that is based on the precipitation and complex formation of aluminum hydroxide. A unique kind of self-organization, the spontaneous appearance of traveling waves, and spiral formation inside a precipitation front is reported. The newly designed system is a simple one (we need just two inorganic reactants, and the experimental setup is simple), in which dynamically changing pattern formation can be observed. This work could show a new perspective in precipitation pattern formation and geochemical self-organization.

Formation characteristics of an aluminum hydroxide fiber by a hydrolysis of aluminum nano powder

Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial pH and temperatures. The nano fibrous boehmite (AlOOH) was formed predominantly over 40°C of the hydrolytic temperature, while the bayerite (Al(OH)3) was formed predominantly below 30°C with a faceted crystalline structure. As a result, the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was found about 409 m2/g.

The microstructure of concrete made with municipal waste incinerator bottom ash as an aggregate component

The interaction of municipal solid waste incinerator bottom ash (MSWI bottom ash), when utilized as an aggregate in concrete, with the cement matrix was investigated. The most prominent reaction observed in lab and field concrete was the formation of aluminium hydroxide and the release of hydrogen gas from aluminium grains reacting in the alkaline environment. The expansive aluminium reaction was identified as a main cause of extensive spalling on the concrete surface. Due to the higher content of bottle glass as part of the ash, in all samples, reaction products of an alkali-silica reaction (ASR) could be observed as well. However, damage due to ASR were less severe than those caused by the aluminium reaction. The expansion rates were low and only a few of the lab samples showed cracking. Microstructural analysis of the samples indicated clearly that a large quantity of the alkali-silica gel which was formed was accommodated in the pores and voids without exerting any strain on the material.

Influence of ppb Levels of SO2 on the Atmospheric Corrosion of Aluminum in the Presence of NaCl

The effect of part per billion (ppb) levels of on the atmospheric corrosion on Al (99.999%) was investigated in the laboratory at 22°C. Exposure time was 20 and 672 h. The effect of concentration (46-1300 ppb), relative humidity (70-99% RH), and the amount of NaCl applied prior to exposure was studied. In addition, the effect of and on the deposition rate was addressed. The samples were investigated by gravimetry, grazing incidence X-ray powder diffraction, ion chromatography, optical microscopy, and environmental scanning electron microscopy equipped with energy-dispersive X-ray fluorescence. accelerates the atmospheric corrosion of Al, forming corrosion product “islands” containing aluminum hydroxy sulfate. Combining NaCl and has a synergistic effect on the average corrosion rate. In contrast, the chloride-induced pitting of aluminum is significantly reduced by . The corrosivity of is attributed to the acidification of the surface electrolyte that destabilizes the alumina passive film. The suppression of pitting corrosion by is attributed to the formation of aluminum hydroxy sulfates that are less soluble than the corresponding chlorides and slows down pit propagation. At relative humidities above 70% RH, there is a measurable steady-state deposition of that corresponds to the rate of formation of sulfate. The deposition rate is not limited by the oxidation of (IV)-valent sulfur on the surface. deposition is enhanced by sodium chloride because the corrosion reactions in the NaCl(aq) electrolyte result in high pH in the cathodic regions and the formation of aluminum hydroxide. Ozone in the ppb range has only transient effects on the deposition rate, whereas ppb levels of had no effect at all.

나노 및 마이크로 알루미늄의 가수분해에 의한 알루미늄 수산화물의 형성

A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than <TEX>$10\;{\mu}m$</TEX> in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.

A systematic investigation of aluminium ion speciation at high temperature. Part. 1. Solution studies

Speciation diagrams of aluminium ions in aqueous solution (0.2 M) at high temperature (90 degrees C) have been obtained from 48 h time-resolved multi-batch titration experiments monitored by 27Al NMR spectroscopy, potentiometry and dynamic light scattering. The quantitative speciation patterns and kinetic data obtained offer a dynamic picture of the distribution of soluble and insoluble Al species as a function of hydrolysis ratio h(h=[OH-]/[Al3+]) over a very broad range of conditions (-1.0 < or =h < or = 4.0). Monomeric, small oligomeric, tridecameric (the 'Al13-mer') and the recently characterised 30-meric aluminium species (the 'Al30-mer') as well as aluminium hydroxide have been identified and quantified. The Al13-mer species dominates over a relatively broad range of hydrolysis ratios (1.5 < or =h< or = 2.7) during the first 6 h of experiment, but are gradually replaced by Al30-mers at longer reaction times. Kinetic profiles indicate that the formation of the Al30-mer is limited by the disappearance of the Al13 species at mildly acidic conditions. The estimated rate constants of both hydrolytic processes show good internal correlation at h> or = 1.5. The effect of local perturbations leading to the formation of aluminium hydroxide below the electroneutrality point (h= 3.0) has been estimated quantitatively.

A study of the corrosion of aluminum alloy 2024-T3 under thin electrolyte layers

The corrosion of aluminum alloy 2024-T3 (AA2024-T3) under thin electrolyte layers was studied in 3.0 wt% sodium chloride solutions by cathodic polarization and electrochemical impedance spectroscopy (EIS) method. The cathodic polarization measurements show that, when the electrolyte layer is thicker than 200 μm, the oxygen reduction current is close to that of the bulk solution. But in the range of 200–100 μm, the oxygen reduction current is inversely proportional to the layer thickness, which shows that the oxygen diffusion through the electrolyte layer is the rate-determining step for the oxygen reduction process. In the range of 100 μm to about 58 μm, the oxygen reduction current is slightly decreased probably due to the formation of aluminum hydroxide or the change of the diffusion pattern from 2-dimensional diffusion to one-dimensional diffusion. The further decrease in electrolyte layer thickness increase the oxygen reduction current to some extent again, because the diffusion of oxygen plays more important role in thin electrolyte layers. The EIS measurements show that the corrosion is controlled by the cathodic oxygen reduction at the initial stage, showing the largest corrosion rate at the electrolyte layer thickness of 105 μm. But at the later stage of corrosion, the anodic process begin to affect the corrosion rates and the corrosion rates show a maximum at 170 μm, which may be the thickness where the corrosion changes from cathodic control to anodic control. The corrosion rate under the very thin electrolyte layer (62 μm in this study) is even smaller than that in bulk solution, this is due to that the anodic process is strongly inhibited.

Role of water during AlN-hydrolysis-assisted solidification in ceramic suspensions studied by proton nuclear magnetic resonance T2 relaxation

Using proton nuclear magnetic resonance (1H-NMR), we have studied the thermally activated hydrolysis of aluminum nitride admixed into Al2O3 aqueous suspensions. We paid special attention to the formation of aluminum hydroxide and its role in binding the host ceramic particles into a stiff solid matrix. The water–proton NMR spin-spin relaxation time (T2) was continuously measured as a function of the time of the AlN hydrolysis in the host Al2O3 ceramic suspension. T2 was found to correlate with an increasing fraction of bound water at the surface of the formed hydrogel and so provided us with information about the gel-surface growth during the hydrolysis process. These results are in good agreement with the observed time- and composition-related increases in high-frequency impedance for the analyzed suspensions.

Uptake of Au(III) Ions by Aluminum Hydroxide and Their Spontaneous Reduction to Elemental Gold (Au(0))

The behavior of AuCl4− ions during the formation of aluminum hydroxide at pH 6 was examined. With an increase in NaCl concentration, the content of gold taken up by aluminum hydroxide decreased, suggesting that chloro-hydroxy complexes of Au(III) ion were taken up due to the formation of Al−O−Au bonds. It was found unexpectedly that the Au(III) ions taken up were spontaneously reduced to elemental gold without addition of a specific reducing reagent and then colloidal gold particles were formed. The mechanisms for the uptake of Au(III) ions by aluminum hydroxide and for their spontaneous reduction are discussed.

Adsorption of H2O on Al(111) and the interaction of atomic D with the ice layer

Adsorption and desorption of water as well as the interaction of water with atomic deuterium on a clean and oxidized Al(111) surface has been studied using temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Quantitative determination of the sticking coefficient for water reveals a value of unity on the clean and the oxidized surface. In the desorption spectra three different peaks of water and hydrogen can be observed. The α-peak for water at 160K can be attributed to evaporation of water multilayers. Already at this low temperature parallel dissociation of water leads to the formation of aluminum hydroxides. The simultaneous desorption of molecular hydrogen can be explained by a reaction assisted process, due to the formation of hot H-atoms during the dissociation process of water. The β-peak at about 320K and the γ-peak at 650K, both for water and hydrogen, are due to decomposition/recombination of different aluminum hydroxides. Dosing a thick ice layer with atomic deuterium reveals only a weak interaction. The reaction coefficient for dissociation of the water molecule or the replacement of an H-atom of the water by a D-atom is about 4%.

Gellability zone for aluminium alkoxides

Ethyl acetoacetate modified aluminium sec-butoxide can be hydrolysed and gelled with alkaline, neutral or acidic media within a pH range of 3.0–8.5. Alumina precipitation occurs if pH values at any point in the sol–gel transition are outside this range. Nine different gelling agents have been evaluated for pH dependence of gel point. Based on stoichiometric considerations, only those systems with a pH of 5.7–7.7 at their gel points can be fully hydrolysed before gelling and the extent of hydrolysis is reduced with an increase in the acidity/basicity of the system. In NaOH/HNO 3 hydrolysed precursors, the extent of hydrolysis at the gel point is about 55%. An unhydrolysed precursor has a pH of 6.4 which increases rapidly as aluminium hydroxide formation begins and a pH of 5.7–7.7 for complete hydrolysis prior to gelling is only possible with weak acids, weak alkalis, surfactant solutions and standard buffers. pH data in the sol- to gel-transition is measured for NaOH, NH 4OH, soya-PC, Milli-Q water, a buffer of pH 7.0, standard solution of Tris-HCl, phenol, acetic and nitric acid. Based on observations a pH dependent “gellability zone” is proposed with the sol–gel-precipitate states existing at the inside–periphery–outside of this zone. ©

New advances in the carbonation of aluminous cement. Alkaline hydrolisis

The carbonation process of aluminous cement in presence of high alkali content is studied. In this work, the formation of a compound which formula is close to K 4 Al 6 (CO 3 ) 11-x (OH) 2x (H 2 O) y is shown for the studies samples. The aluminous cement carbonation in alkali presence take place, at least, in two stages. In a first stage the aluminium and potassium carbonate hydrate joint to CaCO 3 is formed. Later, that aluminium potassium carbonate hydrate is developed toward the aluminium hydroxide formation.

Effects of Ti, Al and V Concentrations on Cell Viability

The effects of Ti, Al and V concentrations and the extraction conditions on the cell viabilities of murine fibroblast L929 cells, murine osteoblast-like MC3T3-E1 cells and fibroblast V79 cells taken from the lungs of Chinese hamsters were investigated by the cell culture method using metallic particles. The particles were sterilized under a U.V. lamp for 14.4 ks (4 h) and suspended independently in Eagle's minimum essential medium (Eagle's medium) for the L929 cell seeding and α modified Eagle's medium (α medium) for the MC3T3-E1 cell seeding containing 10 vol% fetal bovine serum and 7.5% NaHCO 3 These mediums were kept for 172.8 ks (48 h) in an incubator under a 95%air-5%CO 2 atmosphere (defined as medium extraction). Medium without metallic particles was also kept inside the incubator under similar conditions and was used as the control for all the cell cultures. These mediums were filtered with a 0.2 μm filter. 1.0×10 4 to 5.0 × 10 4 L929 cells/mL, 5 × 10 4 MC3T3-E1 cells/mL and 10 2 V79 cells/dish were seeded in both the control and in the medium extract using the metallic particles. For the titanium particle extraction, the maximum Ti concentrations in the Eagle's medium and α medium were 0.2 and 0.3 mass ppm, respectively. Hence the L929 and MC3T3-E 1 cells proliferated in the same ratio as those of the control. Also, the colony formation ratio (number of colonies in the medium extract with metallic particles/average number of colonies in the control) of V79 cells was unity. For the Al particle extraction with ultrapure water for 172.8 ks (48 h), gel formation of aluminum hydroxide was observed. However, the relative growth ratio (the number of cells in medium extract with metallic particles/average number of cells in control) of the L929 cells was unity when the Eagle's medium was prepared after filtering with a 0.2 μm membrane filter. On the contrary, the relative growth ratios of the L929 cells for both Eagle's MEM extract without fetal bovine serum and the Eagle's medium extract were zero. For the aluminum particle extraction, the relative growth ratios of the L929 and MC3T3-E1 cells sharply decreased as the Al concentration in the medium increased to approximately 0.2 to 0.5 mass ppm. This aluminum effect on L929 cell viability tended to be stronger in the Eagle's medium containing a small quantity of V ions (≤0.03 ppm). The effects of Al concentration on the colony formation ratio of the V79 cells showed the same tendency as those of the relative growth ratios of the L929 and MC3T3-E1 cells. The relative growth ratio of the L929 cells sharply decreased when V concentration in the Eagle's medium increased to 0.2 mass ppm and became zero at approximately 0.5-mass ppm. The effects of V concentration on the colony formation ratio of the V79 cells were also similar to the relative growth ratio of the L929 cells. The relative growth ratio of the MC3T3-E 1 cells decreased from 0.002 mass ppm of V concentration and approached zero at approximately 0.2 mass ppm.

Formation of Aluminum Hydroxides as Influenced by Aluminum Salts and Bases

AbstractThe influence of different ions in the formation of Al(OH)3 polymorphs has been studied experimentally by promoting stoichiometric reactions between the aluminum salts (AlCl3, Al(NO3)3, Al2(SO4)3) and bases (NaOH, KOH, NH4OH). In all cases the polymorphs obtained were a mixture of gibbsite, bayerite and nordstrandite or pseudoboehmite with the exception of the reaction between KOH, or NH4OH and Al2(SO4)3 which produced amorphous gels. Ageing of these gels at ambient temperature and pressure for 180 days or at 60°C for 20 days resulted in crystalline structure. Specifically, pseudoboehmite was crystallized from the reaction between Al2(SO4)3 and NH4OH. Significantly, of all ions present in solution in the present experiment, only the sulphate ones were observed to have a marked influence in the precipitation of Al oxyhydroxides.

Effect of grain boundary dopants and mean grain size on tribomechanical behavior of highly purified α-alumina in the mild wear regime

The mechanical properties and tribological behavior in the mild wear regime (9.8 and 29.4 N load on 6 mm diameter spheres) have been explored for highly purified a-alumina (> 99.5%) as a function of grain boundary dopant concentration from 0 to 1500 ppm Y 2O 3 and mean grain size from 0.49 to 1.44 μm. A pin-on-disc tribometer was used for the evaluation of friction and wear. In pure alumina, Vickers indentations produce subsurface cracks detected by Nomarski interference contrast microscopy. No such cracks are formed in the yttria-doped materials. The hardness is higher when the mean grain size is small. The higher amounts of yttria dopant generate precipitates of yttrio-garnet (3Y 2O 3·5Al 2O 3) in the grain boundaries and increase the fracture toughness; they also cause an increase in the friction coefficient. The wear rates decrease with increasing sliding distance at both loads, in agreement with previously reported results. At 29.4 N load, wear volumes in various aluminas are nearly the same; grain fall-out is observed and the wear surfaces are covered with an adherent, relatively soft, layer of wear debris. At 9.8 N, the wear rates scale with the friction coefficient; the wear surfaces are smooth and covered with a very thin layer of wear debris. Fourier transform IR spectroscopy revealed the formation of aluminum hydroxide which is enriched in yttria.

Determination of trace amounts of heavy metals in alumina by electrothermal atomic absorption spectrometry after diethyldithiocarbamate extraction and matrix precipitation

Milligram amounts of alumina powder were decomposed with 4 mol l–1 sulfuric acid and the pH of the solution was adjusted to 3 with 4.5 mol l–1 ammonia solution. After adding sodium diethyldithiocarbamate (DDTC) and chloroform, the pH of the solution was further increased to 7 with 1 mol l–1 ammonia solution, while the solution was mixed vigorously. Impurities present in the alumina sample, such as iron, copper, lead and cadmium, were quantitatively extracted into the chloroform, leaving the aluminium matrix in the aqueous phase as a bulky hydroxide precipitate. The DDTC and chloroform should be added before the formation of aluminium hydroxide, otherwise significant amounts of the desired heavy metals are lost because of coprecipitation. The heavy metals in the chloroform layer were directly determined by electrothermal atomic absorption spectrometry.