CZ302753B6 - Process for preparing aluminium oxide - Google Patents

Abstract

In the present invention, there is disclosed a process for preparing aluminium oxide, said preparation process being characterized in that an aqueous reaction solution containing aluminium ions with concentration 0.001/mol and OH radical traps is irradiated by mercury discharge lamp UV radiation with radiation power in the range of 40 to 160 W or by accelerated electrons with energy in the range of 1 to 6 MeV and a dose within 40 to 140 kGy to give rise of a transparent to whitish clouded gel. The gel is then separated from the solution by ultrafiltration. Subsequently, after thorough washing with water and ethanol, the gel being compressed by filtration process is dried at a temperature up to 100 degC to yield white powder material that is subsequently heat treated at a temperature ranging from 500 to 1000 degC to obtain { gamma}-Ali2Oi3 modification, and at a temperature above 1000 degC to obtain {alpha}-Ali2Oi3 modification.

Description

Technical field

The invention relates to a process for the preparation of alumina using ionizing or UV radiation.

The state of the art

Al ₂ O ₃ is a widely used material in many industries; the γ-Α1 ₂ Ο ₃ modification, due to its high specific surface area, porosity and chemical resistance, serves primarily as a catalyst support [Tzirakis MR et al .: J. Mol. Catal. AND; Chem. 316 (2010) 65-74; Saxena A. et al., J. Hazard Mater. 175 (2010), 795-801] or as a stationary phase for chromatography, α-modification (corundum) serves as an abrasive or optically transparent material. Important applications include the use of alumina as precursors for the preparation of various composite ceramics such as YAG synthetic garnets (Y ₃ Al ₅ O ₁₂ ) [Medraj M. et al .: J. Eur. Ceram. Soc. 26 (2006), 35153524] and LuAG (Lu ₃ AJ ₅ 0 ₁₂ ) [Ogino H. et al .: J. Cryst. Growth 287 (2006), 335-338] or as a thermoluminescent or OSL dosimeter [Muthe Κ. P. et al., J. Lumin. 128 (2008), 445-450].

A large number of methods for the preparation of Al ₂ O _{3 have been} developed since precipitation [Peng Cheng-Hsiung et al .:

J. Alloys Compd. 491 (2010); An Baichao et al., Chem. Eng. J. 157 (2010), 67-72] via sol-gel techniques [Zhang Xiaoxue et al .: J. Cryst. Growth 310 (2008) 3674-3679; Ramesh S. et al., J. Am. Ceram. Soc. 83 (2000), 89-94] optionally supplemented with a spin coating for the preparation of thin films [Ozer N. et al .: Sol. Energy Mater. Sol. Cells 59 (1999), 355-366], anodic aluminum oxidation [Marsal LF et al .: Opt. Mater. 31 (2009), 860-864] to spray pyrolysis [Kim Joo Hyun et al: Microporous Mesoporous Mater. 128 (2010), 85-90]. Most of the above Al ₂ O ₃ preparation techniques, in which heat treatment is no longer included in the principle of the method, result in the formation of Al (OH) ₃ hydroxides and / or AlOOH oxohydroxides, often with low crystallinity. Depending on the temperature and the time of heating, heat treatment of the materials prepared in this way results in various transition alumina phases (γ, δ, θ, χ, κ, η) or mixtures thereof up to the stable phase aA1 ₂ O ₃ [BoumazaA. et al .: J. Solid State Chem. 182 (2009) 1171-1176]

SUMMARY OF THE INVENTION

New, previously unknown method for the preparation of alumina according to the invention consists in irradiating the reaction of an aqueous solution containing aluminum ions at a concentration of 0.001 to 1 mol.f ¹ scavenger of OH radicals or hydrogen peroxide stabilizer, or a macromolecular nanoparticles, UV mercury lamp luminosity of 40 up to 160 W or accelerated electrons ranging from 1 to 6 MeV with a dose of 40 to 140 kGy to form a transparent to white cloudy which is separated from the solution by ultrafiltration, after thorough washing with water and ethanol, the gel compressed by the filtration process is dried at 100 ° C to form a white, powdered material which is subsequently heat treated at temperatures of 500 to 1000 ° C to achieve γ-Α1 ₂ Ο ₃ modification and temperatures above 1000 ° C to achieve α-Al ₂ O ₃ modification.

OH radical scavengers are typically aliphatic alcohols or polyvinyl alcohol, or organic acid salts containing the C'OO anion.

The reaction aqueous solution preferably further comprises macromolecules a nanoparticle stabilizer, such as polyvinyl alcohol (PVA), polyethylene glycol or picric acid.

Formate ions, HCOO, were used as OH scavengers. Hydrogen peroxide served as an oxidizing agent and an important source of OH radicals in photolysis and radiolysis. The reaction mixture may advantageously contain polyvinyl alcohol as a nanoparticle stabilizer.

-1 CZ 302753 B6

Examples

Example I

The aqueous solution containing 0.025 mol.l ¹ of aluminum chloride, 0.1 M potassium formate ¹ and about 1 mol.l ¹ of hydrogen peroxide was irradiated at a linear electron accelerator dose of 80 kGy. The resulting fine gel-like suspension was separated by ultrafiltration and, after drying, the transparent scales were crushed, mixed with water and dispersed in an ultrasonic bath for half an hour in suspension. After drying, a portion of the fine white powder was heat treated at 200 ° C in air and the other part under vacuum, both for 1 hour. X-ray diffraction showed that a weakly crystalline boehmite (pseudo-boehmite) γAIOOH was present in both untreated and heat treated specimens. Subsequent heat treatment for 2 hours at 500, 800, 1000 and 1200 ° C in air or vacuum showed that the sample followed the usual calcite path of bohmite regardless of the heat treatment atmosphere - at 500 and 800 ° C it was identified by X-ray diffraction the transition phase γ-Α1 _{2 3} , which at 1000 ° C changed to a mixture (γ + Oj-AhO-j and at 1200 ° C to pure corundum ct-Al ₂ O ₃ .

Example 2

An aqueous solution containing 0.025 mol.l ¹ of aluminum chloride, 0.1 mol.l ^{1 of} potassium formate and about ¹ mol.l ^{1 of} hydrogen peroxide was irradiated with a medium-pressure mercury burner with a radiant power of about 90 W for 30 minutes, from which the reaction product was separated by ultrafiltration. After drying, the white powder was mixed with water, crushed and centrifuged. The supernatant solution was pipetted and this decanting was performed twice more. After drying, the surface area of the powder was measured by adsorption / desorption of nitrogen from the N 2 / H 2 mixture at liquid nitrogen temperature and was 111 m ^{2 /} g. The heat treatment in air at the same temperatures and times as in the previous example was in terms of X-ray diffraction identical to the phase sequence, only the phases 0 _AI2O-3 was less pronounced.

Example 3

An aqueous solution containing 0.010 mol.l ^-1 aluminum nitrate and 0.1 mol.l ¹ potassium formate was irradiated with a medium-pressure mercury vapor lamp with a radiant power of about 90 W for 60 minutes, the resulting gel separated by ultrafiltration and washed thoroughly with water. After drying, the powder was characterized by X-ray diffraction as a function of the air calcination temperature at the same temperatures as in the previous examples. Both untreated and heat treated powder up to and including 500 ° C showed no identifiable crystalline structure, at 800 ° C the phase γ-ΑΙ ₂ Ο ₃ was identified, at 1000 ° C it was a mixture (γ + Θ + aý-AI ₂ O ₃ and at 1200 ° C only by pure cc — A1 ₂ O ₃ .

Example 4

An aqueous solution containing 0.010 mol.l ¹ of aluminum nitrate and 0.1 mol.l ^{1 of} potassium formate and about 1 mol.l ^{-1 of} hydrogen peroxide was irradiated with a medium-pressure mercury burner with a radiant power of about 90 W for 15 minutes and the gel formed was separated. ultrafiltration. After drying, the white powder was heat treated at the same sludge and temperature as before, and the X-ray diffraction pattern at 800 ° C and 1000 ° C identified the transient phase γ-Α1 ₂ Ο ₃ (Θ phase not recorded) and again after baking to At 1200 ° C, pure α-Al ₂ O ₃ was present.

-2GB 302753 B6

Industrial applicability

The invention is useful for the subsequent synthesis of composite oxide materials containing 5 aluminum, for dosimetric applications, or a porous support thereof for catalytic reactions.

Claims (4)

10 PATENT CLAIMS A process for the preparation of alumina, characterized in that the reaction aqueous solution containing 0.001 to 1 mol / l aluminum ions and OH radical scavengers is irradiated with UV radiation 15 mercury vapor lamps with a radiant power of 40 to 160 W or accelerated electrons with energy ranging from 1 to 6 MeV at a dose of 40 to 140 kGy to form a transparent to white turbid gel which separates from the solution by Itrafí Itrací. The gel, compressed by the filtration process, is dried at a temperature of up to 100 ° C to form a white powder material, which is subsequently heat treated at 500 to 1000 ° C to achieve γ-ΑΤΟ modification, and at temperatures above 2o 1000 ° C to achieve α-Al ₂ O ₃ modification. Method according to claim 2, characterized in that the reaction aqueous solution further comprises hydrogen peroxide and / or a macromolecular nanoparticle stabilizer. 25 Process according to claims 1 and 2, characterized in that the OH radical scavengers are selected from the group consisting of aliphatic alcohols or polyvinyl alcohols or organic acid salts containing an anion -COO. 4. A process according to claim 1, wherein the macromolecular stabilizer of the nanoparticles is selected from the group consisting of polyvinyl alcohol, polyethylene glycol or picric acid.