Aluminum oxide from solution

Aluminum oxide fibers have use in specialized advanced composites because of their high strength and rigidity, high melting point, and exceptional resistance to corrosion. They are usually produced by the extraction of aluminum oxide from a liquid solution, followed by drying and spinning into rodlike fibers. 

Argillic horizons often correlate with the maximum depth of effective evapotranspiration, commonly 1-2 m. Water loss initiates the precipitation of secondary clays and oxides from solutes. Such precipitation may also be related to the loss of dissolved organic species and the de-complexation of soluble aluminum. The resulting low permeabilities further retard the downward percolation of pore water, commonly creating transient perched water tables directly above the hardpans. Periodic drying in this zone focuses addition secondary mineral precipitation in the vicinity of the hardpan, which then leads to a lower permeability and more clay formation. 

Other common amphoteric hydroxides are those of aluminum, chromium(III), lead(II), tin(II), and tin(IV). The amphotaism of Al(OH)3 is commercially used to separate aluminum oxide from the aluminum ore bauxite. Bauxite contains hydrated AI2O3 plus impurities, such as silica sand (Si02) and iron oxide (Fe203). The aluminum oxide dissolves in NaOH solution as the Al(OH)4 ion. After the insoluble impurities are filtered off, the solution of Al(OH)4 can be slightly acidified to precipitate pure Al(OH)3. 

Allara D L and Nuzzo R G 1985 Spontaneously organized molecular assemblies. 1. Formation, dynamics, and physical-properties of normal-alkanoic acids adsorbed from solution on an oxidized aluminum surface Langmuir 1 45-52... 

Monobasic aluminum acetate is dispensed as a 7% aqueous solution for the topical treatment of certain dermatological conditions, where a combination of detergent, antiseptic, astringent, and heat-dispersant effects are needed (12). The solution, diluted with 20—40 parts water, is appHed topically to the skin and mucous membranes as a wet dressing (13). Burrow s solution, prepared from aluminum subacetate solution by the addition of a specific amount of acetic acid, is also used as a topical wet dressing. Standards of purity and concentration have been estabHshed for both pharmaceutical aluminum acetate solutions (13). Each 100 mL of aluminum subacetate solution yields 2.30—2.60 g of aluminum oxide and 5.43—6.13 g of acetic acid upon hydrolysis. For the Burow s solution, each 100 mL yields 1.20—1.45 g of aluminum oxide and 4.25—5.12 g of acetic acid. Both solutions may be stabilized to hydrolysis by the addition of boric acid in amounts not to exceed 0.9% and 0.6% for the subacetate and Burow s solutions, respectively (13). 

A mixture of 50 g of betamethasone, 50 cc of dimethylformamide, 50 cc of methyl orthobenzoate and 1.5 g of p-toluenesulfonicacid Is heated for 24 hours on oil bath at 105°C while a slow stream of nitrogen is passed through the mixture and the methanol produced as a byproduct of the reaction is distilled off. After addition of 2 cc of pyridine to neutralize the acid catalyst the solvent and the excess of methyl orthobenzoate are almost completely eliminated under vacuum at moderate temperature. The residue Is chromatographed on a column of 1,500 g of neutral aluminum oxide. By elution with ether-petroleum ether 30 g of a crystalline mixture are obtained consisting of the epimeric mixture of 170 ,21 -methyl orthobenzoates. This mixture is dissolved without further purification, in 600 cc of methanol and 240 cc of methanol and 240 cc of aqueous 2 N oxalic acid are added to the solution. The reaction mixture is heated at 40°-50°C on water bath, then concentrated under vacuum. The residue, crystallized from acetone-ether, gives betamethasone 17-benzoate, MP 225°-231°C. 

The ethyl acetate solution is then washed with water, dried and evaporated. To remove any selenium still present, the residue is dissolved in 200 cc of methanol and mixed with 100 g of iron powder and 2 g of active carbon. The mixture is heated for 30 minutes with stirring under reflux, then filtered with suction, washed with methanol and the solution evaporated in vacuo. The residue is then chromatographed on 900 g of aluminum oxide. The residues of the evaporated benzene and ether fractions are treated with active carbon in methanol or acetone, evaporated again, and the residue recrystallized from a mixture of acetone and ether. There are obtained 17.5 g of pure 1-dehydro-17a-methyl-testosterone which melts at 163° to 164°C. 

This compound was boiled with 12 g of dry piperidine in 120 ml of absolute benzene for 12 hours under reflux, a total of 6 g of piperidine hydrochloride being separated out. This was filtered off and the benzene solution was concentrated by evaporation. The residue was taken up in a little chloroform and the solution was applied to a dry aluminum oxide column (according to Brockmann) it was thereafter extracted with chloroform. After concentrating the solution by evaporation, an oil was obtained, which was taken up in absolute diethylether. Introduction of dry HCI gas into the cooled solution gave a precipitate which was dissolved and allowed to crystallize from isopropanol/ether. MP 193° to 199°C. 

The chloroform phase is then removed, the aqueous phase extracted twice more with 200 ml of chloroform and the united extracts shaken out 4 times, each time with 200 ml of 2N sodium hydroxide solution. The alkaline solution is then rendered acid to Congo red reagent, using hydrochloric acid and extracted 3 times with chloroform. After drying over sodium Sulfate and evaporating the solvent, the residue is chromatographed on aluminum oxide (Activity Stage V). The substance eluted with benzene and benzene/chloroform (1 1) is recrystallized from chloroform/hexane (1 1) MP 107° to 109°C. 

Porous aluminum oxide can be used as a template for the production of nanowires and nanotubes. For example, metals can be deposited on the pore walls by the following procedures deposition from the gas phase, precipitation from solution by electrochemical reduction or with chemical reducing agents, or by pyrolysis of substances that have previously been introduced into the pores. Wires are obtained when the pore diameters are 25 nm, and tubes from larger pores the walls of the tubes can be as thin as 3 nm. For example, nanowires and nanotubes of nickel, cobalt, copper or silver can be made by electrochemical deposition. Finally, the aluminum oxide template can be removed by dissolution with a base. 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

Transfer of aluminum ions from the oxide into the solution was considered as a statistically independent process, whose kinetics are governed by a rate equation similar to Eq. (24), i.e. (neglecting the return of the ions into the oxide),... 

It is obvious that such an ion transfer must be preceded by some association of the aluminum ion from the oxide lattice with OH- ion (directly from the solution or adsorbed at the interface) [Eq. (22) or (23)] or by protonation with H+ ions from the solution (Eq. (25)]. Valand and Heusler maintain the first case to be operative. This conclusion must, however, be taken as tentative, and further arguments of an experimental nature are warranted. 

Dang et al. (1994) observed that the experimentally determined solubility lines for Zn2+ in 14 soil solutions from southern Queensland with soil pH from 7.45-8.98 and 0.08-2.07% CaC03 were not undersaturated with respect to the solubility of any known mineral form of Zn. Therefore, they suggested that Zn2+ activity was mainly controlled by adsorption-desorption reactions in these soils. Similar observation on solubility of Cr(VI) in arid soils was reported by Rai et al. (1989). In the absence of a solubility controlling solid phase, Cr(VI) aqueous concentrations under slightly alkaline conditions may be primarily controlled by adsorption/desorption reactions (Rai et al., 1989). Chromuim(VI) is adsorbed by iron and aluminum oxides, and kaolinite and its adsorption decreases with increasing pH. 

In order to understand the general behavior of the tested materials, scoping tests were conducted in 25 mg/L gold(III)-chloride solutions at 25°C and 80°C with different initial pH values, namely 1.5, 4 and 8. After the start of the experiment the pH was not further adjusted, i.e., it could change freely. It remained similar to the initial pH in all cases. From these tests it was found that, in the case of the iron-oxide based adsorbents, dissolution of the solid took place at pHaluminum oxides and titanium oxide was observed at this pH. At pH>2 all adsorbents were found to be stable and did not dissolve during the experiment. 

Figure 4.9. Log(/D)-VGS (VDS = 20V) and (inset) /D Vds characteristics for an RF-sputtered ZnO TFT on a spin-coated A1PO dielectric annealed at 300 °C. VGS is stepped from 0 to 40V in 5-V increments for the ID-VDS curves device W/L = 5 L = 100 pm. [Reproduced with permission. Meyers, S. T. Anderson, J. T. Hong, D. Hung, C. M. Wager, J. F. Keszler, D. A. 2007. Solution processed aluminum oxide phosphate thin-film dielectrics. Chem. Mater. 19 4023-4029. Copyright 2007 American Chemical Society.]...

As pH rises, the metal content of drainage water tends to decrease. Some metals precipitate directly from solution to form oxide, hydroxide, and oxy-hydroxide phases. Iron and aluminum are notable is this regard. They initially form colloidal and suspended phases known as hydrous ferric oxide (hfo, FeOOH n O) and hydrous aluminum oxide (HAO, AlOOH nH.2O), both of which are highly soluble under acidic conditions but nearly insoluble at near-neutral pH. 

The ligand is hydroxyquinoline-sulfonate (HQS) which forms fluorescent AI-HQS complexes in solution. HQS forms surface complexes with the Al-centers of aluminum oxide surface these surface complexes are also fluorescent. Fluorescence as a function of time during HQS-promoted dissolution of aluminum oxide. Surface-associated fluorescence was calculated from the difference between measured total and dissolved fluorescence. 

Theoretical calculations [43] based on first principles molecular dynamics discussed in Sect. 3.2.6 have suggested that Mg Al LDHs are most stable for n = 3 (i.e. x = 0.25) and indeed many minerals, including hydrotalcite itself, have this stoichiometry [4]. It has been reported that the synthesis of LDHs (with benzoate or terephthalate anions in the interlayers) from solutions containing Mg/Al = 2, leads to LDHs having the same composition when the synthesis is carried out at moderate temperatures but LDHs with Mg/Al = 3 (plus AlOOH) when the reaction is carried out under hydrothermal conditions [44]. It was proposed that the latter ratio represents the thermodynamically most favorable product. A similar observation has been reported [45] for solutions with Ni VPe = 2, where hydrothermal preparation led to segregation of an LDH with Ni VPe = 3 and Ni Fe 204. An attempt to synthesize a Co sAl LDH resulted in partial oxidation of the Co and formation of a Co o.yCo o.s LDH with complete migration of Al " from the layers to generate interlayer aluminum oxy-species [46]. 

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

Aluminum reacts with acids and strong alkali solutions. Once aluminum is cut, the fresh surface begins to oxidize and form a thin outer coating of aluminum oxide that protects the metal from further corrosion. This is one reason aluminum cans should not be discarded in the environment. Aluminum cans last for many centuries (though not forever) because atmospheric gases and soil acids and alkalis react slowly with it. This is also the reason aluminum is not found as a metal in its natural state. 

---