Showing papers on "Aluminium hydroxide published in 2000"

Hydrated aluminium sulfate precipitation by enzyme-catalysed urea decomposition

Abstract: Hydrated basic aluminium hydroxide precipitates were obtained from aluminium sulphate solution at room temperature and at 92°C by using urea. Enzyme urease was used to decompose urea at room temperature. It was observed that precipitates obtained at room temperature were much finer than those obtained at 92°C but they had similar chemistry. On calcination at 1200°C, each precipitate obtained at room temperature converted to a discrete α-Al 2 O 3 crystal whereas that obtained at 92°C converted to a rather densely packed agglomerate of α-Al 2 O 3 crystals. As a result of this, α-Al 2 O 3 powder obtained from 25°C precipitates showed much better sintering behaviour.

Preparation of concrete accelerator

Abstract: An alkali-free accelerator for sprayed concrete is prepared by dissolving aluminium sulphate and amorphous aluminium hydroxide in water which optionally contains one amine, and optionally adding at least one stabiliser, selected from hydroxycarboxylic acids and phosphoric acids and non-alkaline salts thereof, and at least one defoaming agent.

Porous mullite and mullite-based composites by chemical processing of kaolinite and aluminium metal wastes

Abstract: Porous mullite and mullite-based composites have been prepared from a chemical processing route starting from a precursor obtained using an aqueous suspension of kaolinite and aluminium hydroxide. This was coprecipitated with kaolinite using ammonium hydroxide or hexamethylenediamine (HMDA), and a solution of aluminium chloride prepared from dissolved recycled wastes of aluminium metallic powders. Raw and ball-milled kaolinite during 30 minutes have been employed. The precursors and the obtained materials were characterized by X-ray diffraction (XRD) and thermal diffractometry, simultaneous differential thermal analysis (DTA) and thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), flexural strength test at room temperature and Hg intrusion porosimetry. The feasibility of using HMDA as a precipitating agent in the proposed chemical processing route for mullite preparation has been demonstrated. The advantageous use of HMDA, as compared with ammonium hydroxide, and ground kaolinite, as compared with raw kaolinite, produced single-phase mullite materials and enhanced the flexural strength of the resultant ceramic porous bodies by firing at 1550–1600 °C (porosity 50–45 vol%). These materials would have application as refractories, substrates, filters and thermal isolating materials.

Effects of Various Aluminium Compounds Given Orally to Mice on Al Tissue Distribution and Tissue Concentrations of Essential Elements

Abstract: To evaluate the risk of gastrointestinal long-term aluminium (Al) exposure, aluminium distribution and the levels of the following essential elements: Ca, Mg, Zn, Cu, and Fe in tissue were studied. Aluminium was administered in drinking water as aluminium chloride, dihydroxyaluminium sodium carbonate or aluminium hydroxide. Mice (strain Pzh:SFIS) were exposed to a total dose of 700 mg Al in long-term treatment (for each Al compound n=15). Concentrations of Al, Ca, Mg, Zn, Cu, and Fe in stomach, kidneys, bone and liver were analyzed by atomic absorption spectrometry. After AlCl 3 treatment, aluminium was found to accumulate in all tested tissues. A significant decrease in Fe concentration in liver and Zn in kidneys was observed in comparison to concentrations of these elements in the control group. In the Al(OH) 3 -treated group, accumulation of aluminium was observed in bone only and decline of Fe concentration in stomach and Cu in liver and kidney. In the NaAl(OH) 2 CO 3 -treated group the increase in Al concentration was significant in bone; there was no change in concentration of essential elements in the examined tissues. The observed aluminium accumulation was not accompanied by changes in Ca and Mg concentration except for bone. This study showed that oral administration as a route of Al exposure can result in diverging accumulation of aluminium in tissues, the concentration depending on the chemical form.

Synthesis of soluble aluminium carboxylates directly from aluminium hydroxide

Abstract: Water soluble aluminium carboxylates, of use as water based ceramic precursors and as starting materials for the synthesis of other metalloorganic materials, can be prepared in one or two steps from gibbsite [α-Al(OH)3·3H2O] and boehmite [Al(O)(OH)]n. Both starting materials can be used to synthesize aluminium formate [Al(O2CH)3] and aluminium hydroxyformate [Al(OH)(O2CH)2]. These two compounds can be used to synthesize aluminium lactate [Al{O2C(OH)CHCH3}3] and aluminium methoxyacetate [Al(OH)(O2CCH2OCH3)2·H2O]. All of the compounds synthesized were characterized using XRD, TGA, DRIFTS, NMR and wet chemical techniques.

Influence of starting materials on the reaction sintering of mullite–ZrO2 composites

Abstract: Mullite–zirconia composite materials were prepared by reaction sintering of α-alumina, aluminium hydroxide and aluminium nitrate as alumina sources, and zircon powder. The compaction of different calcined powders, and the reaction development, densification behaviour and microstructural investigations of different samples were examined at temperatures ranging from 1350 to 1600°C for 2 h holding time. X-ray diffraction peaks suggested fully developed mullite and zirconia phases by reaction sintering of zircon and aluminium nitrate, and showed more retained tetragonal ZrO 2 at 1600°C. Relatively dense sintered samples were obtained by the mixture of zircon and α-alumina powders. The morphology of intergranular ZrO 2 particles was found dependent on the growing conditions because of the using of different starting materials.

Aluminium hydroxide and tyre tread rubber composition and pneumatic tyre employing the aluminium hydroxide

Abstract: Aluminium hydroxide having specific characteristics, and a tyre tread rubber composition and a pneumatic tyre employing the aluminium hydroxide, which allow grip performance and abrasion resistance to increase and rolling resistance to decrease and are superior in processibility, are provided. The aluminium hydroxide has a loosed bulk density of not more than 0.60g/cm3, a DOP oil absorption of at least 70cm3/100g and less than 250cm3/100g, and a BET specific surface area of at least 30m2/g and not more than 350m2/g. 5-150 parts by weight of the aluminium hydroxide is blended with 100 parts by weight of a rubber component to obtain the tyre tread rubber composition. The rubber component preferably includes at least 60 parts by weight of styrene-butadiene rubber having a styrene content of 20-60% by weight.

Probing the formation process of aluminium hydroxide nanoparticles prepared by laser ablation with 27Al NMR spectroscopy

Abstract: The 27Al MAS NMR spectra of amorphous alumina exhibit three resonances resulting from aluminium in four-, five-, and six-coordination, whereas samples containing crystalline particles of bayerite, gibbsite, and boehmite show only a single resonance associated with six-coordinate aluminium.

Effect of mechanochemical treatment on the synthesis of calcium dialuminate

Abstract: Calcium dialuminate (CaAl4O7) powders were synthesised from mechanochemically treated mixtures of aluminium hydroxide + calcium hydroxide and aluminium hydroxide + calcium carbonate. On grinding, both mixtures produce X-ray amorphous precursor phases which show 27Al MAS NMR resonances characteristic of Al in octahedral and tetrahedral sites, and a site identified by a resonance at 37–39 ppm (possibly pentahedral Al). Although grinding does not completely destroy the carbonate XRD reflections in the carbonate mixture, both precursors show a high degree of homogeneity and behave similarly on heating, forming monophase CaAl4O7 at <1050 °C. By contrast, the same unground compositions form mixtures of α-alumina and various calcium aluminates (but not CaAl4O7) on heating as high as 1250 °C. Calcium dialuminate synthesised from the carbonate-containing mechanochemical precursor had a smaller particle size which may be advantageous for subsequent fabrication and sintering.

Process for the production of aluminium hydroxide

Abstract: Gibbsite type aluminium hydroxides are obtained by seeding a Bayer liquor with bayerite crystals. The gibbsite type aluminium hydroxides show excellent properties as fire retardant fillers in synthetic resins.

Aluminum recovery from water treatment sludges

Abstract: Aluminum sulfate and polyaluminum chloride are widely used as coagulants in water treatment plants. A chemical sludge containing aluminium hydroxide, adsorbed organic matter and other water insoluble impurities is obtained after the flocculation-clarification process. In Portugal, an estimated amount of 66 000 ton/yr. (wet wt.) water treatment sludge is being disposed of on land or at municipal solid waste (MSW) landfills. Government restrictions to this practice as well as increasing deposition costs and the potential harmful impacts proceeding from the high aluminium content of the sludge have been leading to significant research efforts in order to evaluate different treatment alternatives, namely involving aluminium recovery and subsequent reuse. Despite membrane-based separation and liquid ion exchange processes have been studied for that purpose, the traditional acidic and alkaline extraction methods may be still explored to obtain a product susceptible of use as coagulant for industrial wastewater treatment purposes. Centrifuged chemical sludge from a water treatment plant using polyaluminium chloride as coagulant was characterised in terms of humidity, volatile matter, Al, Fe, Mn, Cd, Cu, Cr, Pb, Ni and Zn. The dry sludge organic content is about 29% and the major elements determined are aluminium (≈ 12.6%), iron (≈ 2%) and manganese (≈ 0.14%). The aluminium recovery was investigated both by acidic and alkaline leaching processes. Concentrated H2SO4 was selected as the acidic leaching medium and the process efficiency was evaluated at different operating conditions. The ratio dry sludge/sulphuric acid solution was varied between 0.5 and 2%, the pH ranged from 1.0 to 4.5, different stirring and settling times were established and the aluminium, iron and manganese dissolution was assessed. A similar study was performed at pH values between 10.0 and 13.6 using 2N/10N NaOH as the extracting solution and operating conditions as those of the acid extraction procedure. Whereas maximum aluminium recovery using H2SO4 was about 61% at pH=1.0, the alkaline extraction led to aluminium recoveries of about 71% at pH = 13.6 (2% dry sludge in suspension, 90 min stirring time and 45 min settling time). Decreasing the sludge dosage to 0.5%, aluminium extraction increased to 87.4% at pH=13. As expected, acid extraction led to a higher Fe (18.2%) and Mn (42.1%) dissolution as compared with alkaline extraction at pH=13.6 (Fe=2.1% and Mn=3.2%).

The enhanced adsorption of cadmium on hydrous aluminium(III) hydroxide by ethylenediaminetetraacetate

Abstract: The adsorption of ca. millimolar concentrations of cadmium(II) on freshly precipitated aluminium(III) hydroxide is enhanced, at pH values of below 8, in the presence of ethylenediaminetetraacetate, EDTA, via stabilisation of the adsorbed cation. At levels where the hydroxide phase is in large excess to the cadmium(II), the addition of stoichiometrically equivalent concentrations of EDTA will enhance its adsorption to approximately 95%. In the presence of EDTA, cadmium adsorption increases with pH despite the fact that 99.9% of the dissolved cadmium is present as an anionic cadmium(II) EDTA complex. The adsorption observed has been modelled using the measured values of the solubility of aluminium hydroxide and its adsorption of EDTA, the normal and the EDTA-enhanced cationic binding of cadmium(II) and the accepted equilibrium constants for EDTA complexation of cadmium(II) and aluminium(III). The structures of the dissolved and adsorbed complexes have been inferred from XAFS and Al27 NMR spectroscopy.

Preparation of superfine aluminium hydroxide

Abstract: The preparation includes two steps of carbon component decomposition and hydrothermal treatment in rotating bed in ultragravity condition. The carbon component decomposition of the present invention is carried out in the protruded packing layer inside the rotating bed and is one powerful mass transfer and micro mixing process, and the aluminum hydroxide sol obtained through the subsequent hydrothermal treatment process is further converted into crystal grains. The present invention can produce fibrous aluminum hydroxide grains with average size as small as 1-5 mm, length-to-diameter ratio of 5-100 and homogeneously distributed size and has high production efficiency and product grade. The method of the present invention is easy to be used in industry.

Effect of silicone oil on the mechanical properties of highly filled HDPE composites

Abstract: The effects of aluminium and magnesium hydroxide filler, surface modifications of the fillers, and silicone oil on the mechanical properties of high density polyethylene (HDPE) composites were studied. The surface modifications of magnesium hydroxide (Mg(OH) 2 ) and aluminium hydroxide (Al(OH) 3 ) with coupling agents such as silanes and organotitanate increase the tensile strength to some extent, and have little effect on elongation at break and notched Izod impact strength of HDPE composites containing 140phr fillers. Silicone oil was found to be an effective additive for toughening highly filled HDPE composites, and this, together with an appropriate surface modification of the fillers, is an important factor in realizing the change in the highly filled HDPE composites from brittle to tough fracture under tensile and impact stress. The plastic deformation of the fracture surfaces of HDPE composites observed by scanning electron microscopy is associated with the presence of silicone oil.

Prepreg and laminated board

Abstract: PROBLEM TO BE SOLVED: To provide a prepreg, which has a superior flame resistance and heat resistance and is made non-halogenated. SOLUTION: An epoxy resin, a curing agent, an aluminium hydroxide and an inorganic filler coated with a metallic molybdate are blended in an organic solvent. An epoxy resin varnish prepared by this is impregnated into a substrate and dried. As no halogen is contained in it, no toxic material is produced and the aluminium hydroxide secures a superior flame resistance, and also the inorganic filler coated with the metallic molybdate secures the superior flame resistance and heat resistance.

Surface and Catalytic Properties of MoO3-treated Co3O4/Al2O3 Solids

Abstract: The surface and catalytic properties of Co3O4/Al2O3 solids treated with different proportions of MoO3 were investigated, the extent of MoO3 added varying between 0.50 mol% and 5.00 mol% (0.63-5.9 wt%). The pure sample was prepared by thermal decomposition at 600°C of aluminium hydroxide impregnated with a calculated amount of Co(NO3)2 dissolved in the least amount of distilled water. The MoO-treated samples were prepared by thermal decomposition at 600°C of aluminium hydroxide treated with different proportions of ammonium molybdate followed by treatment with Co(NO3)2 solution. The crystalline phases produced by thermal treatment of the pure and treated samples precalcined at 600°C were characterized using an XRD technique. The surface and catalytic properties of the various catalysts were studied using nitrogen adsorption at -196°C and CO oxidation by O2 at 100-150°C. The results obtained revealed that molybdena treatment of the Co3O4/Al2O3 solids followed by precalcination at 600°C resulted in a decreas...

New metal hydroxides with improved performance for flame retardancy in plastics

Abstract: Magnesium and aluminium hydroxide have become very important additions for plastics. The paper gives an overview of the latest developments in metal hydroxide technology taking into account the actual market requirements for flame retardancy in plastics, as well as smoke suppression.

Process for the production of aluminum hydroxide of improved whiteness

Abstract: Aluminium hydroxide of high whiteness is produced by (i) heating aluminium hydroxide obtained from the Bayer process to a temperature of 300 to 700° C. (ii) dissolving the soluble fraction of the thus obtained activated product at 85 to 275° C. in aqueous sodium hydroxide to form a sodium aluminate liquor containing an undissolved residue of very fine boehmite, (iii) filtering said sodium aluminate liquor to obtain a clear solution of sodium aluminate supersaturated with respect to dissolved alumina, (iv) cooling said clear solution to 50 to 80° C. and seeding with crystallized aluminium hydroxide to induce further crystallization, and (v) separating, washing and drying the produced aluminium hydroxide crystals.

Preparation of Inorganic Consolidated Body Using Aluminium Hydroxide Mechanically Activated by Dry Milling

Abstract: Aluminium hydroxide (Al(OH)3) was mechanically activated by dry milling. In order to develop an inorganic consolidated material, the structure and reactivity of milled Al(OH)3 were investigated and consolidated bodies were prepared using the reaction between activated Al(OH)3 and a potassium silicate solution. Milling up to 1 h apparently reduced the grain size and promoted amorphization, although milling longer than 2 h did not give a significant physical change. Milled Al(OH)3 directly transformed to χ-Al2O3 around 270°C. The transformation temperature decreased with increasing milling time. The remarkable enhancement of the reactivity was attained. The reactivity of Al(OH)3 milled for 2 h improved 1000 times more than that of as-received Al(OH)3. The preforming paste, prepared with as-received Al(OH)3, could not consolidate at room temperature without drying. On the other hand, for Al(OH)3 milled for 2 h, the preforming paste consolidated in 10 min and the consolidated material showed much better resistance against water than that prepared with as-received Al(OH)3. The possibility of a new inorganic consolidated material was suggested using the reaction between mechanically activated Al(OH)3 and the potassium silicate solution.

Comparative study of mechanochemical preparation of aluminosilicate precursors from various aluminium hydroxides and amorphous silica

Abstract: The mechanochemical formation and homogeneity of aluminosilicate precursors was investigated with respect to the influence of particle size and chemical form of the aluminium hydroxide starting material. Aluminium hydroxide in the form of bayerite with a large particle size was found to be more reactive than gibbsite of small particle size. 29Si and 27Al MAS–NMR, DTA–TG, and XRD measurements showed that ground mixtures of aluminium hydroxide and silica gel are more homogeneous than mixtures containing silicic acid.

Nonflammable insulative coating composition and preparation method thereof

Abstract: PURPOSE: Nonflammable insulative coating compositions and their preparation method are provided, which compositions are light-weighted and do not generate dust. CONSTITUTION: A composition comprises 12-25 wt.% of perite whose size is in the range of 0.08 to 3.0 mm; 25-45 wt.% of cement; 1.1-2.7 wt.% of an accelerating agent for cement; 5-10 wt.% of a heat absorbing material; 25-45 wt.% of a water-soluble synthetic resin-type binder; 0.5-1.2 wt.% of a pore forming agent and coconut diethanol amide being a pore stabilizer; and 2.0-3.0 wt.% of sodium carboxymethyl cellulose. Preferably the accelerating agent for cement is aluminate and silicate, the heat absorbing material is selected from calcium hydroxide, aluminium hydroxide and sodium hydrogen carbonate, the water-soluble synthetic resin-type binder is selected from latex, chlorinated paraffin, vinyl acetate copolymer and vinyl chloride copolymer, and the pore forming agent is polyoxyethylene oxide or alcohol ethoxy sulfate.

Preparation method of aluminium hydroxide

Abstract: The preparation method of aluminium hydroxide by using aluminium sulfate-sodium metaaluminate process is characterized by that it adopts parallel-flow neutralization and jellification process, has noneed of multiple circularly pulping, and does not adding any reagent and can directly wash with clear water on washing equipment. Said invented method not only raises production efficiency, reduces labour intensity, saves the investment of equipment, but also can save water consumption and prevent serious material leakage problem due to multiple circularly pulping. It is simple and easy to implement, and its effect is obvious.

The formation of monosulphate from tetracalcium aluminoferrite and magnesium sulphate

Abstract: The formation of monosulphate, by hydration of a tetracalcium aluminoferrite powder, was investigated by isothermal calorimetry and X-ray diffraction (XRD) analyses. Hydration reactions were carried out isothermally at temperatures ranging from 25 to 80°C in 0·25 M, 0·5 M, 1·0 M, 2·0 M, and 3·0 M magnesium sulphate solutions. Gypsum was the initial hydration product in all magnesium sulphate concentrations and was the only crystalline hydration product in 2·0 M and 3·0 M magnesium sulphate solutions. Monosulphate was the dominant crystalline phase produced over the entire temperature range when hydration was carried out in magnesium sulphate concentrations between 0·25 M and 1·0 M. XRD and calorimetry also demonstrated that small amounts of calcium aluminium hydroxide, calcium aluminate carbonate hydrate and magnesium aluminate hydrate phases formed at the lower temperatures and in low (0·25 M and 0·5 M) magnesium sulphate concentrations. No crystalline phases incorporating iron were observed regardless o...

Paint for preparation of aluminium oxid ceramic coating layer and its coating method

Abstract: The present invention relates to mechanical engineering surface treatment technology The invented method is as follows: prepare phosphoric acid and aluminium hydroxide aqueous solution, prepare phosphoric acid and sodium silicate, aqueous solution, take treated diaspore, ceramic and solid micro granules of other material to mix with fore said two solutions proportioning to form paint, which is coated or sprayed on aluminium alloy surface, heat treatment under 200 degC temp Repeat the fore said coating and heat treatment to form coating layer on substrate body surface The advantages include low treatment temp, relation simple in technological condition, low cost, no pollution, abrasive resistance, corrusion resistant, heat resist etc

Phosphorus doped activated alumina

Abstract: A process for producing granules of a phosphorus doped activated alumina from aluminium hydroxide and a phosphorus source is described. The granules can be used as growth regulator, especially as low phosphorus buffer in potted plants.

Method of production of hydroxochloride of aluminium

Abstract: production of hydroxochloride of aluminium. SUBSTANCE: non-desilified or desilicified aluminate solutions formed in processing bauxites by sintering are mixed with slag or flushing water till solution at concentration of 15 to 30 g/l of Al2O3 is obtained and reducing temperature to 20-25 C followed by carbonization of mixed solutions by flue gases at content of CO2 of 5 to 7%, filtration of hydrate pulp and dissolving of amorphous aluminum hydroxide in hydrochloric acid. Aluminate solutions are mixed with slag or flushing water at ratio of 1:4 - 6. Carbonization of mixed solutions is performed at flue gas pressure not exceeding 0.68 kg/sq.cm for 1 to 1.5 hours. Filtration is performed in vacuum of 0.6 to 0.75 kg/sq, cm at supply of water at temperature of 15 to 25 C. Dissolving of amorphous aluminium hydroxide is effected in 25- to 35% hydrochloric acid at temperature of 90 to 95 C maintaining pH of medium of 2 to 4.5 during 2 to 4 hours. EFFECT: improved quality of product; low cost. 5 cl, 1 tbl