CA1086025A - Process for producing alumina - Google Patents
Process for producing aluminaInfo
- Publication number
- CA1086025A CA1086025A CA244,804A CA244804A CA1086025A CA 1086025 A CA1086025 A CA 1086025A CA 244804 A CA244804 A CA 244804A CA 1086025 A CA1086025 A CA 1086025A
- Authority
- CA
- Canada
- Prior art keywords
- alumina
- process according
- aluminum
- neutral
- activated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/42—Preparation of aluminium oxide or hydroxide from metallic aluminium, e.g. by oxidation
- C01F7/428—Preparation of aluminium oxide or hydroxide from metallic aluminium, e.g. by oxidation by oxidation in an aqueous solution
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/10—Solid density
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/20—Powder free flowing behaviour
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/21—Attrition-index or crushing strength of granulates
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
TO ALL WHOM IT MAY CONCERN:
Be it known that We, CHEMOKOMPLEX VEGYIPARI
G?P ?S BERENDEZ?S EXPORT-IMPORT V?LLALAT, a body corporate organised under the laws of Hungary of Budapest, Hungary, made the invention entitled: "A PROCESS FOR PRODUCING
ALUMINA" and the following disclosure contains a full description of the invention and of the best mode known to the inventors of taking advantage of the same:
ABSTRACT OF THE DISCLOSURE
Pure alumina is produced from aluminium metal by steps of activation by stripping the oxide layer in an acidic aqueous medium; washing in a neutral medium;
reacting in a neutral, acidic or alkaline medium to give hydrated alumina; and igniting the hydrated alumina.
Be it known that We, CHEMOKOMPLEX VEGYIPARI
G?P ?S BERENDEZ?S EXPORT-IMPORT V?LLALAT, a body corporate organised under the laws of Hungary of Budapest, Hungary, made the invention entitled: "A PROCESS FOR PRODUCING
ALUMINA" and the following disclosure contains a full description of the invention and of the best mode known to the inventors of taking advantage of the same:
ABSTRACT OF THE DISCLOSURE
Pure alumina is produced from aluminium metal by steps of activation by stripping the oxide layer in an acidic aqueous medium; washing in a neutral medium;
reacting in a neutral, acidic or alkaline medium to give hydrated alumina; and igniting the hydrated alumina.
Description
~ V25 - The invention concerns a process for the production of pure alumina, principally alpha-alumina.
Because of the high present-day demands of technology, industry processing alumina for the production of oxide-based ceramic products requires the highest quality basic materials. The most important basic material of the oxide-based ceramic industry is alumina.
The quality of alumina is generally judged by its purity, its particle size and i~s crys~alline form or modification. In the processing industry a purity of 99.99% or better is expected from the alumina starting material. In addition to the purity, requirements are a particle size generally less than one micrometre and the presence of only the alpha crystalline form, since these factors significantly influence the quality of the final product as well as the economy of the processing.
A difficulty in producing alpha-alumina arises from the stable alpha form being obtainable only by means of heat treatment taking place at a high temperature, in excess of 1500 C. At such a temperature the desired stable alpha form is given but the crystals coalesce into large groups or lumps, agglomerate and shrink. In this form the alumina is barely suitable for the manufacture of oxide-based je ~Q ~
ceramic products. Consequently, it must be~ Ject for example to grinding and even to classifying. Ho~ever, in the course oE
comminution most of the alumina crystals are damaged, cracked~ broken or crumbled and thereby lose some of their strength. The quality and strength of oxide-based ceramic products made from damaged crystals I OWQ p_ are ~æ~ than the quality and strength of products produced from . :~ . , ' : ' ' .
';~ , .
.
~ ;25 undamaged crystals. To this should be added that during comminution the high purity alpha-alumina necessarily takes up contaminants which disadvantageously influence its quality.
Alumina of greater purity than technical grade alumina is produced from bauxite, but although generally these materials are produced to satisfy predetermined aims and demands, they do not satisfy demands for the highest quality materials, where the basic alumina materials are analysed for 10-15 components with an attendant purity requirement of 99.99%.
A higher degree of purity can be achieved with processes wherein, as starting material, a water-soluble aluminium ~alt or a thermally decomposable aluminium compound is employed. The weak point of these processes is generally the fact that for a unit amount of alumina a very large quantity and/or large volume of starting material is required. A good example of this is aluminium sulphate, which 9 contains 18 molecules o water of crystallization, or ~ aluminium ammonium sulphate, a frequently employed starting material for alumina produced by thermal decomposition. Undoubtedly, considering the ratio of the amounts of starting material and final product, the most favourable processes are those employing aluminium as starting material. Thus from 5~0 g metal 1020 g alumina can be produced.
Clearly it is to this that one can attribute the fact that numerous processes are known for producing alumina from aluminium.
Thus it is known to powder aluminium and ignite to constant ~eight, and also to produce alumina by heating hydrated alumina produced in water by spark machining of aluminium. Further, numerous processes are known for producing hydrated alumina in pressurized ., ~ ~ . , ; ' '~
. ~ .
86~)25 reactors in the presence of mercury or a mercury salt.
' It is also known to reac~ aluminium at normal a~mospheric pressure in the presence of water vapour, water, and mercury or a mercury salt, as a re-sult of which hydrated alumina is obtained as long loose flakes or in an agglom-erated state. In ignition of these loose flakes utili~ation of oven capacity is extraordinarily poor and the heat transfer between individual flakes is un-even; consequently undesirably high temperatures are necessary and the quality of the alumina is uneven.
In another method so-called thermal grinding is used for comminuting the agglomerated hydrated alumina. In this process, there is placed in an oven of suitable heat capacity that amount of wet hydrated alumina which can be heated in a slngle batch within at most two minutes to at least 1100C. Under the efEect of the vapour generated the material is comminuted, i.e., as it were, is thermally gound.
The aim of the present invention is to provide a process, simpler than those known hitherto~ for the economic production of high purity alpha-alumina, expediently of sub-micronic particle si~e.
Accordingly the invention provides in a process for the preparation of pure alumina wherein metallic aluminum is activated, the activated aluminum is reacted in an aqueous solution to obtain an intermediate and then the inter-mediate is heat treated to obtain an alumina end product, the improvement in producing said intermediate which comprises employing aluminum having a purity of at leas~ 99.5% and a specific surface of at least eight cm 2/g, activating only the surface of the aluminum by contacting it with a member selected from (1) an aqueous acidic solution selected from NaCl, KCl, NH4Cl, NH~IHCO3, ICI, and HgC12, and (2) water containing dissolved C0~, S02, CI2 or F2 then washing ~ _ 4 _ :. :
~ -,, ;
s said aluminum, having only its surface activated wi~h an aqueous medium having a neutral pH; then reacting the washed only surface activated aluminum in aqueous solution and adjusting the pH of such solution to produce alumina.
- 4a -. ' ' ' . '.. :; , .. . :
: . , ' : ` - :.
, ~' ' . . :' ' . . .' ' :
: . :: . , .
The essence of the invention lies in that the activation (removal of oxide layer) is performed exclusively in an aqueous solution of acidic pH value, a subsequent washing is performed exclusively in an aqueous solution of neutral pH value, and the reaction (to give hydrated alumina) is performed in an aqueous solution of alkaline, neutral or acidic pH value. In dependence on the alkaline, neutral or acidic pH value of the reaction solution, the hydrated alumina reaction product consists of fine particles and plate-like cyrstals or is in gel form. It is heat~treated in a known manner to produce the final p~oduct of alumina of fine, particulate, plate-like or chip-like form.
As starting material according to the invention-aluminium metal of at least 8 cm tg specific area is desirable.
In a preferred process according to the invention, the alumina is produced from metallic aluminium (plate, foil, shavings, powder) of at least 99.5% purity and at least 8 cm ~g specific area.
In removing the protective oxide layer of the metal in a per se known manner, i.e. chemically, the aluminium metal is activated in an of acidic aqueous solutionlpH value. Subsequent washing is performed in water of neutral pH value. Then the activated and washed metal is transformed to hydrated alumina, in the presence of water, at normal atmospheric pressure and in a temperature range of 10 to 100C. Then after heat treatment alumina is obtained.
The great advantage of the invention is that by changing only one technological parameter, alumina may be produced in a most simple manner and with apparatus which may easily be automated, which alumina has excellent properties and is, if desired, of fine particle .
.
... , ., ' ' ~ '.
. .
' ': ' . ' - ' " ;' ~ ' ' ' ' '" ~ :. ~ ' ' ~ ç60Z:~i size and plate-like crystalline structure.
The following Ex~mples illustrate the process of the ; invention, without limitation.
Example 1 To remove the oxide layer from 0.05 mm thick aluminium foil of at least 99.99% purity, and to activate its surface~ it was passed through a bath at a rate of 10 m/min, which bath consis~ed of twice-distilled water containing 0.1% HgC12 and with its pH
adjusted to 5 to 6 by means of hydrochloric acid. From the bath the foil was passed at the same rate of 10 m/min to a second bath containing twice distilled water of neutral p!l (pH 7~ wherein the salts and acids remaining on the surface of the metal after the activation were removed. The aluminium foil thus activated was further processed as follows.
The foil was passed at the rate already given to a bath containing twice-distilled water and with its pH adjusted to an alkaline value of 8-9 by means of a 25% aqueous solution of ammonium hydroxide. The temperature of the reaction solution was 80 to 90 C, the maintenance of the temperature at a constant value being ensured by equilibrium between production of heat of reaction and addition of cold make-up solution replacing reaction solution removed and passed to a filter. Vigorous exothermic reaction between the alumlnium metal and the water produced a suspension of hydrated alumina in a fine, readily sedimenting form. The hydrated alumina crystals formed did not agglomerate into larger particles and during ~he subsequent processing they retained their sub-micronic particle si~e. ~Iydrated alumina particles of similar electric polarity or :: : . ~ ` ' . ': ' ':, .. : ,. : ::
~36~Z5 ~..
charge repel each other and this property ensures good filterability and the prevention of agglomeration~
The hydrated alumina crystals were continuously removed from the aqueous solution by filtration, then, by drying, a powder was produced. This hydrated alumina powder had a crystal size of 0.005 to 0.09 micrometres. From this hydrated alumina the gamma form of alumina could be obtained wi~h a specific surface area of 25 to 30 m2/g, by heating at 800 to 1000C. By heating to 1000 to 1200C alumina a mixture of the gamma and alpha forms with a specific surface area of 15 to 25 m /g could be obtained, and by heating between 1250 to 1800C alpha-alumina with a specific surface area of 10 to 15 m /g.
Example 2 As starting mate~ial 99.99% pure aluminium foil was used, activated and washed as described in Example 1, but with twice-distilled water of neutral pH value in place of the alkaline reaction solution. As a result of the chemical reaction taking place a suspension of hydrated alumina of plate-like ~rystal form was obtained. From this material the following products could be obtained by heating: at 800 to 1000 C, gamma alumina powder o plate-like, crystal form and specific surface area 9 to 15 m /g;
at 1000 to 1200C, mixed gamma and alpha alumina powder of plate-like crystal form and specific surface area 5 to 9 m2/~; and a~
1250 to laO0 C alpha alumina powder of plate-like crystal form and specific surface area of 1 to 5 m /g.
Example 3 As starting material aluminium foil of 99.5% purity was used and the foil, activated and washed as described in Example 1, was reacted in an aqueous acidic solution of a pH between 5 and 6, , ,.
~: . , , -` . : . -.' - ' ~'~ :, :: .: . . .: . :.
~1361V25 acidified by hydrochloric acid. The product of the reaction was a gel of hydrated alumina. This material could not be filtered and thus was dried in its original condition, giving blocks or Lumps of cracked structure. ~y heating this ma~erial at 800 to 1000C lumpy ganlma alumina was obtained, specific surface area 10 to 15 m /g; by heating at 1000 to 1200 C lumpy mixed gammalalpha alumina was obtained, specific surface area 8 to 12 m /g; while by heating at 1400 to 1800 C alpha alumina with a sub-micronic lattice was obtained, with at least 3.87g/cm3 solid specific gravity, a hardness of least 92 to 94 ~a and a flexural strength of 50 to 70 ~p/mm2, the alumina being in the form of spllntery sinter bodies.
Example 4 Aluminium shavings were used as starting material.
After removal of the oxide layer and activation of the metal surface by means of chemicaL salt solutions for destroying the metal oxide (e-g- NaCl, KCl~ NH4Cl, NH4~!~03~ ICl, HgC12~ or gases dissolved in water e.g. C02, S02, C12, F2, or metallic mercury), the shavings were washed in twice-distilled water at neutral pH to remove the residues of the activation. Finally the shavings were ~
in a vibratory or ultrasonic reactor with the solutions described in Examples 1, 2 and 3. A material was obtainecl in each case which conEormed with those described in the Examples.
Example 5 Aluminium foil of at least 99.99% purity and at least 8cm /g specific surface area was passed through a twice-distilled aqueous solution of acidic p~l value of 5 to 6 and ~hrough a layer of .
.. . . . .. . . ..
~ 6~25 :
mercury at the bottom of the solution. Thereafter the procedure was as described in Examples 19 2 and 3 and with the same results as described there.
Example 6 As starting material there was used a granulate of aluminium of 99.5% purity and 8 cm Ig specific a~ea made by spraying molten metal, through a protective barrier atmosphere, into the activation solution described in Example 1. The washing and reaction took place with the solutions of Examples, 1, 2 and 3 in three serially connected, continuously operated continuous-transfer tube reactors. The reactions and heat treatments resulted in the materials already describedq In the Examples the alumina produced had a purity equal to or greater than the purity of the starting aluminium.
_ 9 _ :
.- , . .
.
::: : . .
.. . .
.
Because of the high present-day demands of technology, industry processing alumina for the production of oxide-based ceramic products requires the highest quality basic materials. The most important basic material of the oxide-based ceramic industry is alumina.
The quality of alumina is generally judged by its purity, its particle size and i~s crys~alline form or modification. In the processing industry a purity of 99.99% or better is expected from the alumina starting material. In addition to the purity, requirements are a particle size generally less than one micrometre and the presence of only the alpha crystalline form, since these factors significantly influence the quality of the final product as well as the economy of the processing.
A difficulty in producing alpha-alumina arises from the stable alpha form being obtainable only by means of heat treatment taking place at a high temperature, in excess of 1500 C. At such a temperature the desired stable alpha form is given but the crystals coalesce into large groups or lumps, agglomerate and shrink. In this form the alumina is barely suitable for the manufacture of oxide-based je ~Q ~
ceramic products. Consequently, it must be~ Ject for example to grinding and even to classifying. Ho~ever, in the course oE
comminution most of the alumina crystals are damaged, cracked~ broken or crumbled and thereby lose some of their strength. The quality and strength of oxide-based ceramic products made from damaged crystals I OWQ p_ are ~æ~ than the quality and strength of products produced from . :~ . , ' : ' ' .
';~ , .
.
~ ;25 undamaged crystals. To this should be added that during comminution the high purity alpha-alumina necessarily takes up contaminants which disadvantageously influence its quality.
Alumina of greater purity than technical grade alumina is produced from bauxite, but although generally these materials are produced to satisfy predetermined aims and demands, they do not satisfy demands for the highest quality materials, where the basic alumina materials are analysed for 10-15 components with an attendant purity requirement of 99.99%.
A higher degree of purity can be achieved with processes wherein, as starting material, a water-soluble aluminium ~alt or a thermally decomposable aluminium compound is employed. The weak point of these processes is generally the fact that for a unit amount of alumina a very large quantity and/or large volume of starting material is required. A good example of this is aluminium sulphate, which 9 contains 18 molecules o water of crystallization, or ~ aluminium ammonium sulphate, a frequently employed starting material for alumina produced by thermal decomposition. Undoubtedly, considering the ratio of the amounts of starting material and final product, the most favourable processes are those employing aluminium as starting material. Thus from 5~0 g metal 1020 g alumina can be produced.
Clearly it is to this that one can attribute the fact that numerous processes are known for producing alumina from aluminium.
Thus it is known to powder aluminium and ignite to constant ~eight, and also to produce alumina by heating hydrated alumina produced in water by spark machining of aluminium. Further, numerous processes are known for producing hydrated alumina in pressurized ., ~ ~ . , ; ' '~
. ~ .
86~)25 reactors in the presence of mercury or a mercury salt.
' It is also known to reac~ aluminium at normal a~mospheric pressure in the presence of water vapour, water, and mercury or a mercury salt, as a re-sult of which hydrated alumina is obtained as long loose flakes or in an agglom-erated state. In ignition of these loose flakes utili~ation of oven capacity is extraordinarily poor and the heat transfer between individual flakes is un-even; consequently undesirably high temperatures are necessary and the quality of the alumina is uneven.
In another method so-called thermal grinding is used for comminuting the agglomerated hydrated alumina. In this process, there is placed in an oven of suitable heat capacity that amount of wet hydrated alumina which can be heated in a slngle batch within at most two minutes to at least 1100C. Under the efEect of the vapour generated the material is comminuted, i.e., as it were, is thermally gound.
The aim of the present invention is to provide a process, simpler than those known hitherto~ for the economic production of high purity alpha-alumina, expediently of sub-micronic particle si~e.
Accordingly the invention provides in a process for the preparation of pure alumina wherein metallic aluminum is activated, the activated aluminum is reacted in an aqueous solution to obtain an intermediate and then the inter-mediate is heat treated to obtain an alumina end product, the improvement in producing said intermediate which comprises employing aluminum having a purity of at leas~ 99.5% and a specific surface of at least eight cm 2/g, activating only the surface of the aluminum by contacting it with a member selected from (1) an aqueous acidic solution selected from NaCl, KCl, NH4Cl, NH~IHCO3, ICI, and HgC12, and (2) water containing dissolved C0~, S02, CI2 or F2 then washing ~ _ 4 _ :. :
~ -,, ;
s said aluminum, having only its surface activated wi~h an aqueous medium having a neutral pH; then reacting the washed only surface activated aluminum in aqueous solution and adjusting the pH of such solution to produce alumina.
- 4a -. ' ' ' . '.. :; , .. . :
: . , ' : ` - :.
, ~' ' . . :' ' . . .' ' :
: . :: . , .
The essence of the invention lies in that the activation (removal of oxide layer) is performed exclusively in an aqueous solution of acidic pH value, a subsequent washing is performed exclusively in an aqueous solution of neutral pH value, and the reaction (to give hydrated alumina) is performed in an aqueous solution of alkaline, neutral or acidic pH value. In dependence on the alkaline, neutral or acidic pH value of the reaction solution, the hydrated alumina reaction product consists of fine particles and plate-like cyrstals or is in gel form. It is heat~treated in a known manner to produce the final p~oduct of alumina of fine, particulate, plate-like or chip-like form.
As starting material according to the invention-aluminium metal of at least 8 cm tg specific area is desirable.
In a preferred process according to the invention, the alumina is produced from metallic aluminium (plate, foil, shavings, powder) of at least 99.5% purity and at least 8 cm ~g specific area.
In removing the protective oxide layer of the metal in a per se known manner, i.e. chemically, the aluminium metal is activated in an of acidic aqueous solutionlpH value. Subsequent washing is performed in water of neutral pH value. Then the activated and washed metal is transformed to hydrated alumina, in the presence of water, at normal atmospheric pressure and in a temperature range of 10 to 100C. Then after heat treatment alumina is obtained.
The great advantage of the invention is that by changing only one technological parameter, alumina may be produced in a most simple manner and with apparatus which may easily be automated, which alumina has excellent properties and is, if desired, of fine particle .
.
... , ., ' ' ~ '.
. .
' ': ' . ' - ' " ;' ~ ' ' ' ' '" ~ :. ~ ' ' ~ ç60Z:~i size and plate-like crystalline structure.
The following Ex~mples illustrate the process of the ; invention, without limitation.
Example 1 To remove the oxide layer from 0.05 mm thick aluminium foil of at least 99.99% purity, and to activate its surface~ it was passed through a bath at a rate of 10 m/min, which bath consis~ed of twice-distilled water containing 0.1% HgC12 and with its pH
adjusted to 5 to 6 by means of hydrochloric acid. From the bath the foil was passed at the same rate of 10 m/min to a second bath containing twice distilled water of neutral p!l (pH 7~ wherein the salts and acids remaining on the surface of the metal after the activation were removed. The aluminium foil thus activated was further processed as follows.
The foil was passed at the rate already given to a bath containing twice-distilled water and with its pH adjusted to an alkaline value of 8-9 by means of a 25% aqueous solution of ammonium hydroxide. The temperature of the reaction solution was 80 to 90 C, the maintenance of the temperature at a constant value being ensured by equilibrium between production of heat of reaction and addition of cold make-up solution replacing reaction solution removed and passed to a filter. Vigorous exothermic reaction between the alumlnium metal and the water produced a suspension of hydrated alumina in a fine, readily sedimenting form. The hydrated alumina crystals formed did not agglomerate into larger particles and during ~he subsequent processing they retained their sub-micronic particle si~e. ~Iydrated alumina particles of similar electric polarity or :: : . ~ ` ' . ': ' ':, .. : ,. : ::
~36~Z5 ~..
charge repel each other and this property ensures good filterability and the prevention of agglomeration~
The hydrated alumina crystals were continuously removed from the aqueous solution by filtration, then, by drying, a powder was produced. This hydrated alumina powder had a crystal size of 0.005 to 0.09 micrometres. From this hydrated alumina the gamma form of alumina could be obtained wi~h a specific surface area of 25 to 30 m2/g, by heating at 800 to 1000C. By heating to 1000 to 1200C alumina a mixture of the gamma and alpha forms with a specific surface area of 15 to 25 m /g could be obtained, and by heating between 1250 to 1800C alpha-alumina with a specific surface area of 10 to 15 m /g.
Example 2 As starting mate~ial 99.99% pure aluminium foil was used, activated and washed as described in Example 1, but with twice-distilled water of neutral pH value in place of the alkaline reaction solution. As a result of the chemical reaction taking place a suspension of hydrated alumina of plate-like ~rystal form was obtained. From this material the following products could be obtained by heating: at 800 to 1000 C, gamma alumina powder o plate-like, crystal form and specific surface area 9 to 15 m /g;
at 1000 to 1200C, mixed gamma and alpha alumina powder of plate-like crystal form and specific surface area 5 to 9 m2/~; and a~
1250 to laO0 C alpha alumina powder of plate-like crystal form and specific surface area of 1 to 5 m /g.
Example 3 As starting material aluminium foil of 99.5% purity was used and the foil, activated and washed as described in Example 1, was reacted in an aqueous acidic solution of a pH between 5 and 6, , ,.
~: . , , -` . : . -.' - ' ~'~ :, :: .: . . .: . :.
~1361V25 acidified by hydrochloric acid. The product of the reaction was a gel of hydrated alumina. This material could not be filtered and thus was dried in its original condition, giving blocks or Lumps of cracked structure. ~y heating this ma~erial at 800 to 1000C lumpy ganlma alumina was obtained, specific surface area 10 to 15 m /g; by heating at 1000 to 1200 C lumpy mixed gammalalpha alumina was obtained, specific surface area 8 to 12 m /g; while by heating at 1400 to 1800 C alpha alumina with a sub-micronic lattice was obtained, with at least 3.87g/cm3 solid specific gravity, a hardness of least 92 to 94 ~a and a flexural strength of 50 to 70 ~p/mm2, the alumina being in the form of spllntery sinter bodies.
Example 4 Aluminium shavings were used as starting material.
After removal of the oxide layer and activation of the metal surface by means of chemicaL salt solutions for destroying the metal oxide (e-g- NaCl, KCl~ NH4Cl, NH4~!~03~ ICl, HgC12~ or gases dissolved in water e.g. C02, S02, C12, F2, or metallic mercury), the shavings were washed in twice-distilled water at neutral pH to remove the residues of the activation. Finally the shavings were ~
in a vibratory or ultrasonic reactor with the solutions described in Examples 1, 2 and 3. A material was obtainecl in each case which conEormed with those described in the Examples.
Example 5 Aluminium foil of at least 99.99% purity and at least 8cm /g specific surface area was passed through a twice-distilled aqueous solution of acidic p~l value of 5 to 6 and ~hrough a layer of .
.. . . . .. . . ..
~ 6~25 :
mercury at the bottom of the solution. Thereafter the procedure was as described in Examples 19 2 and 3 and with the same results as described there.
Example 6 As starting material there was used a granulate of aluminium of 99.5% purity and 8 cm Ig specific a~ea made by spraying molten metal, through a protective barrier atmosphere, into the activation solution described in Example 1. The washing and reaction took place with the solutions of Examples, 1, 2 and 3 in three serially connected, continuously operated continuous-transfer tube reactors. The reactions and heat treatments resulted in the materials already describedq In the Examples the alumina produced had a purity equal to or greater than the purity of the starting aluminium.
_ 9 _ :
.- , . .
.
::: : . .
.. . .
.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the preparation of pure alumina wherein metallic aluminum is activated, the activated aluminum is reacted in an aqueous sol-ution to obtain an intermediate and then the intermediate is heat treated to obtain an alumina end product, the improvement in producing said intermediate which comprises employing aluminum having a purity of at least 99.5% and a specific surface of at least eight cm 2/g, activating only the surface of the aluminum by contacting it with a member selected from (1) an aqueous acidic solution selected from NaCl, KCl, NH4Cl, NH4HCO3, ICI and HgCl2, and (2) water containing dissolved CO2, SO2, CI2, or F2, then washing said aluminum having only its surface activated with an aqueous medium having a neutral pH; then reacting the washed only surface activated aluminum in an aqueous solution and adjusting the pH of such solution to produce alumina.
2. A process according to claim 1 in which the activation is carried out at pH 5 to 6.
3. A process according to claim 1 in which the reaction to give hydrated alumina is carried out at atmospheric pressure at 10° to 100°C.
4. A process according to claim 1, 2 or 3 further including igniting the alumina at a temperature from 1250°C to 1800°C and for sufficient time to give pure alpha alumina.
5. A process according to claim 3 wherein the reaction occurs in an aqueous medium of neutral pH.
6. A process according to claim 1 wherein in said pH adjusting step the pH is adjusted to a basic pH whereby said end-product has a fine grained crystalline structure.
7. A process according to claim 1 wherein in said pH adjusting step the pH is adjusted to a neutral pH whereby said end-product has a plate-like crystalline structure.
8. A process according to claim 1 wherein in said pH adjusting step the pH is adjusted to an acidic pH whereby said end-product has a chip-like structure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| HUPU-193 | 1975-02-03 | ||
| HU75PU00000193A HU171506B (en) | 1975-02-03 | 1975-02-03 | Process for preparing aluminium oxide |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1086025A true CA1086025A (en) | 1980-09-23 |
Family
ID=11000650
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA244,804A Expired CA1086025A (en) | 1975-02-03 | 1976-02-02 | Process for producing alumina |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5929526B2 (en) |
| AU (1) | AU501514B2 (en) |
| CA (1) | CA1086025A (en) |
| CH (1) | CH597097A5 (en) |
| DE (1) | DE2604083C3 (en) |
| FR (1) | FR2299272A1 (en) |
| GB (1) | GB1503073A (en) |
| HU (1) | HU171506B (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3003952A (en) * | 1957-11-04 | 1961-10-10 | Engelhard Ind Inc | Manufacture of platinum-alumina reforming catalyst |
| SE412031B (en) * | 1971-05-25 | 1980-02-18 | Abildgaard Lab | PERMITTED BOOK AND SET TO MAKE FAST |
-
1975
- 1975-02-03 HU HU75PU00000193A patent/HU171506B/en unknown
-
1976
- 1976-01-28 JP JP51007583A patent/JPS5929526B2/en not_active Expired
- 1976-01-30 CH CH134076A patent/CH597097A5/xx not_active IP Right Cessation
- 1976-01-30 AU AU10680/76A patent/AU501514B2/en not_active Expired
- 1976-02-02 FR FR7602799*[A patent/FR2299272A1/en active Granted
- 1976-02-02 CA CA244,804A patent/CA1086025A/en not_active Expired
- 1976-02-02 GB GB3970/76A patent/GB1503073A/en not_active Expired
- 1976-02-03 DE DE2604083A patent/DE2604083C3/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5929526B2 (en) | 1984-07-21 |
| DE2604083C3 (en) | 1981-09-03 |
| AU1068076A (en) | 1977-08-04 |
| DE2604083B2 (en) | 1980-07-10 |
| DE2604083A1 (en) | 1976-08-05 |
| FR2299272B1 (en) | 1981-09-18 |
| HU171506B (en) | 1978-01-28 |
| JPS51100995A (en) | 1976-09-06 |
| GB1503073A (en) | 1978-03-08 |
| CH597097A5 (en) | 1978-03-31 |
| FR2299272A1 (en) | 1976-08-27 |
| AU501514B2 (en) | 1979-06-21 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |