Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF LOW APPARENT DENSITY AND BRIGHT WHITE ALUMINA TRIHYDRATE POWDER"
Abstract	The invention describes an improved process for the preparation of low apparent density and bright white alumina trihydrate. The invention consists of addition of alkali solution to aluminium metal followed by precipitation of alumina trihydrate by vigorously stirring with water. Alumina trihydrate was then filtered and dried to get low apparent density and bright white alumina trihydrate powder. The apparent density and particle size are controlled by controlling the reaction rate and the whiteness of alumina trihydrate is due to use of pure Al metal.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF LOW APPARENT DENSITY AND BRIGHT WHITE ALUMINA TRIHYDRATE POWDER"

Abstract

The invention describes an improved process for the preparation of low apparent density and bright white alumina trihydrate. The invention consists of addition of alkali solution to aluminium metal followed by precipitation of alumina trihydrate by vigorously stirring with water. Alumina trihydrate was then filtered and dried to get low apparent density and bright white alumina trihydrate powder. The apparent density and particle size are controlled by controlling the reaction rate and the whiteness of alumina trihydrate is due to use of pure Al metal.

Full Text	The present invention relates to an improved process for the preparation of low apparent density and bright white alumina trihydrate powder. Alumina trihydrate (ATH) is a non-abrasive, white, crystalline powder with Moh's hardness of 3 and a theoretical density of 2.4gm/cc. ATH is available in acid soluble and acid insoluble form. The acid insoluble form is very much suitable as fillers in paint industry, as fillers in marble and plastic industry, as fillers in printing ink industry, as fillers in paper industry and as fire retardant. In addition to acid insolubility, the ATH need to be bright white (free or very low Fe2CO3, TiO2 impurity level) and should posses low apparent density or tap density. The tap density being measured by tapping loose powder taken in a cylinder till it attains fixed volume and then dividing the weight of powder by the volume of the powder. The acid soluble variety is generally prepared by precipitating aluminium salts such as sulphates, nitrates and chlorides. The acid insoluble variety of ATH is generally prepared by the Bayer's process. The Bayer process production of alumina hydrate has been practised since 1888, and the process involves digestion of bauxite with an aqueous caustic medium at elevated temperatures and pressures. Digestion results in a slurry consisting of a liquor containing the alumina dissolved in the form of sodium aluminate and a caustic-insoluble digestion residue, the so-called "red mud". The red mud is generally separated from the liquor and the alumina content of the liquor is recovered by precipitation. Precipitation is usually induced by seeding the sodium aluminate liquor with solid alumina hydrate and the precipitated alumina hydrate is recovered. Precipitation of alumina hydrate from the sodium aluminate liquor is an involved operation due to the many process variables and the product quality requirements. The process variables involved in the precipitation step are temperature, seed charge, holding time, concentration of alumina, concentration of caustic soda, impurity content. Therefore, this operation requires close control, as well as a thorough understanding of the precipitation process. According to US Patent No.4,637,908 which deals with the invention for manufacturing a highly active, disperse form of low apparent density aluminium hydrate is such that more than 99% of the aluminium hydroxide grains are at most 3 µm in size, is introduced continuously into a reactor along with a dry hot air stream, heated to 400°C-600°C, whirled up and strongly dispersed and shock dehydrated such that after a few seconds a stationary condition is reached in the reactor, whereby the amount of partially dehydrated low apparent density aluminium oxide flowing out is the same as the amount of aluminium tri-hydroxide being added, the low apparent density aluminium hydroxide flowing out of the reactor in the air stream is precipitated by suitable mechanical means, dispersed in mildly acidic or mildly basic water and re-hydrated by heating, as a result of which aluminium hydroxide is produced in the form of pseudo boehmite and / or bayerite gel, and is dried at temperatures below the activation temperature. According to US patent 4,786,482y the brightness of alumina trihydrate generated by Bayer's process was improved by subjecting some purification process. The process comprises the steps of subjecting caustic solution containing dissolved aluminium hydroxide to a purification step to remove dissolved impurities including colour producing humate material. The purification is effected by passing the solution through a semi-permeable membrane capable of separating the humate material from the solution. After separation, the purified solution is treated to precipitate aluminna hydroxide therefrom. The alumina hydroxide has an improved level of whiteness. Other impurities which can be removed include iron, silicon and sodium compounds. The main drawbacks of this process are the high apparent density of ATH powders even after ground to fine powders and difficult to obtain bright white powders because contains residual impurities (Fe2O3.TiO2). The main object of the present invention is to provide an improved process for the preparation of low apparent density and bright white alumina trihydrate (ATH) powder which obviates the drawbacks as detailed above. Another object of the present invention is to produce pure variety of alumina trihydrate. Still another object of the present invention is to prepare alumina trihydrate (ATH) powder insoluble in acids. Yet another object of the present invention is to produce moisture free ATH powder with fine particle size (d50) of 2.0 to 2.5µm. Accordingly, the present invention provides an improved process for the preparation of low apparent density and bright white alumina trihydrate powder which comprises cleaning aluminium metal of purity 90 - 98% with NaOH solution (2%) and water successively , reacting 45 to 55 wt% cleaned aluminium metal with 55 to 45 wt% alkali metal hydroxide such as herein described, of concentration in the range of 3 to 20%, under stirring for 3 hours , adding water to maintain the concentration of the reactants, allowing the reaction to be completed to obtain super - saturated aluminate solution with in-situ seeded alumina trihydrate, followed by instantaneous hydrolisation under vigorous stirring to obtain precipitate of alumina trihydrate, washing, filtering and drying at 110°C by conventional methods to get low apparent density and bright white alumina trihydrate powder. In an embodiment of the present invention, aluminium metal used may be in the form of powder, granules, sheets, pieces, blocks. In another embodiment of the present invention, the alkali metal hydroxide used may be such as sodium hydroxide, potassium hydroxide. In still another embodiment of the present invention, the water used including for hydrolisation may be de-ionised (D.I) water. In yet another embodiment of the present invention, alumina trihydrate of different particle size may be obtained by varying the ratios of aluminium metal to alkali metal hydroxide. In still another embodiment of the present invention, low apparent density of the alumina trihydrate was effected by restricting the particle agglomeration by fast rate of reaction and evolution of hydrogen gas, thereby, producing finer and low apparent density powders. In yet another embodiment of the present invention, the total precipitation of the aluminate solution was effected by self seeding of alumina trihydrate. In one more embodiment of the present invention, the bright whiteness of alumina trihydrate is due to the purity of the starting material like aluminium. In yet another embodiment of the present invention, the filtrate may be recycled for further reactions with aluminium metal. In another embodiment of the present invention, hydrogen gas produced as by product which may be collected for separate use. The process step details of the process of the present invention are: 1. Aluminium metal in the form of powders, granules, thin sheets/foils and in the form of blocks were used as the source of aluminium component of aluminium trihydrate. 2. Alkali in the form of caustic soda (typically in the concentration range of 3-20 %) were used as the other reactant. The reaction of the above two constituents was carried out to generate aluminate solution with alumina trihydrate precipitate and on hydrolysis of the above solution, alumina trihydrate was completely precipitated. The precipitate was filtered and dried at 110°C to generate free flowing powder. \| The flow chart of the process followed is presented in Figure 1. The following examples are given by way of illustrations and therefore should not be construed to limit the scope of the present invention. Example 1 Scrap aluminium pieces (4mm thick) of purity 90-98 % were cleaned by stirring for few minutes in a 2% solution of NaOH and finally washed with de-ionised (D.I.) water to get well cleaned metal surface. 28 grams of cleaned Al metal pieces were reacted in 112 ml of 20% NaOH solution. The reaction initiated slowly and became vigorous within 10 minutes. The reaction was highly exothermic followed by evolution of hydrogen gas. After 3 hours, the reaction slowed down and 112ml of D.I. water was added to compensate the loss of water due to evaporation. The solution was stirred well and left 2 hours for completion of the reaction. At this stage, the content is hydrolysed with D.I. water to produce thick suspension of ATH. The suspension was washed, filtered and dried in a oven at 110°C for 8hrs. to obtain free flowing powder. Yield-63grams(90%) Tapped density- 0.65gm/cc Particle size (d5o)-3.2µm Example-2 7 gms. of the cleaned aluminium metal pieces of purity 90-98 % were reacted with 42ml of 20% caustic soda solution. Initially, the reaction was vigorous and highly exothermic. The reaction slowed down after 1 hour because of consumption of NaOH to produce sodium aluminate solution. Due to highly exothermic nature of the reaction, water got evaporated, thereby, sufficiently D.I. was added to sustain the reaction. This favoured hydrolysis of the already produced aluminate solution to generate alumina trihydrate and sodium hydroxide. This sodium hydroxide further reacted with remaining aluminium metal to produce aluminate solution which subsequently hydrolised to produce ATH. These cycles of reactions continued till all aluminium metal reacted which took 5hrs. to complete the above reaction. The solution at this stage was saturated with aluminate solution and also contained alumina trihydrate (produced due to hydrolysis of aluminate solution generated initially) which helped hydrolysis of aluminate solution subsequently. At this stage, D.I. water was added and stirred well. The already formed ATH acted as seeding material and helped the aluminate solution to precipitate completely into alumina (ATH) . The precipitate was washed thoroughly by stirring well and finally filtered and dried to get free flowing powder. Yield- 13.5gm(76%) Tapped density- 0.44gm/cc Particle size (d5o)-2.1µm Example-3 17.3 gms of aluminium metal powder of purity 90-98 % was added in instalments to 106 ml of 20% NaOH solution. The reaction was very fast and thus water was evaporated very fast. The concentration was maintained by frequently adding water to avoid dryness of the contents. After completion of the reaction, the solution was hydrolysed with D.I water to get precipitates of the ATH. The precipitate was stirred well and washed thoroughly followed by filtering and drying to get dry powder of ATH. Yield-34gms(78%) Tapped density- 0.24gm/cc Particle size (d5o)-1.2µ,m Example-4 60gms. of Al metal powder of purity 90-98 % was added in instalments into 360ml. of 3% NaOH solution. The solution was stirred well till completion of the reaction . After the completion of the reaction, the liquid was hydrolysed with D.I. water to obtain alumina trihydrate precipitate which was washed, filtered and dried to fine ATH powders. Yield- 140gms.(95%) Tapped density- 0.85gm/cc Particle size (d5o)- >8..0µm Example-5 9gms. of Al metal powder of purity 90-98 % was added in instalments into 60ml. of 20% KOH solution. The solution was stirred well till completion of the reaction . After the completion of the reaction, the liquid was hydrolysed with D.I. water to obtain alumina trihydrate precipitate which was washed, filtered and dried to fine ATH powders. Yield-18gms.(80%) Tapped density- 0.44 gm/cc Particle size (d5o)- 2.2µm The powder produced by the above examples was of bright white category. The presence of various impurities in ATH was analysed and they were presented below. Impurity analysis of the product (Table Removed) It is seen that TiO2 and Fe2O3 are present in very less amount and hence the products are bright white in colour. The novelty of the present invention lies in two facts, namely (1) Low apparent density and (2) Bright whiteness of alumina trihydrate powder. The low apparent density was achieved by fast reaction rate of Al metal which resulted fine particles. The hydrogen gas produced as by product helped in keeping the fine particles in de-agglomerated condition. The bright whiteness was achieved due to purity of the starting materials. The main advantages of the improved process of the present invention are: 1. Low apparent density of the order of 0.2 to 0.8 gm/cc is obtained. 2. Whiteness of the ATH powder is of bright white category. 3. Alumina trihydrate self seeded during the process enabled the total precipitation of ATH. 4. The vigorous rate of reaction and evolution of hydrogen gas restricted the particle agglomeration, thereby, producing finer and low apparent density powders. 5. The process is very economical compared to earlier methods. 6. The process is very simple and requires approximately 50-60% less time compared to other processes referred . 7. Easy to control particle size 8. Minimum infrastructure required 9. One of the reactant (alkali) can be recycled. 10. Hydrogen gas evolved in the process as by product has high commercial value and hence can be collected for commercial use. We Claim: 1. An improved process for the preparation of low apparent density and bright white alumina trihydrate powder which comprises cleaning aluminium metal of purity 90 - 98% with NaOH solution (2%) and water successively , reacting 45 to 55 wt% cleaned aluminium metal with 55 to 45 wt% alkali metal hydroxide such as herein described, of concentration in the range of 3 to 20%, under stirring, adding water to maintain the concentration of the reactants, allowing the reaction to be completed to obtain super - saturated aluminate solution with in-situ seeded alumina trihydrate, followed by instantaneous hydrolisation under vigorous stirring to obtain precipitate of alumina trihydrate, washing, filtering and drying at 110°C by conventional methods to get low apparent density and bright white alumina trihydrate powder. 2. An improved process as claimed in claim 1 wherein aluminium metal used is in the form of powders, granules, sheets, pieces, blocks. 3. An improved process as claimed in claims 1 and 2 wherein the alkali metal hydroxide used is selected from sodium hydroxide, potassium hydroxide. 4. An improved process as claimed in claims 1 to 3 wherein the water used is de-ionised (D.I) water. 5. An improved process as claimed in claims 1 to 4 wherein low apparent density of the alumina trihydrate was effected by restricting the particle agglomeration by fast rate of reaction and evolution of hydrogen gas , producing finer and low apparent density powder. 6. An improved process as claimed in claims 1 to 5 wherein the total precipitation of the aluminate solution was effected by self seeding of alumina trihydrate. 7. An improved process for the preparation of low apparent density and bright white alumina trihydrate powder substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for the preparation of low apparent density and bright white alumina trihydrate powder.
Alumina trihydrate (ATH) is a non-abrasive, white, crystalline powder with Moh's hardness of 3 and a theoretical density of 2.4gm/cc. ATH is available in acid soluble and acid insoluble form. The acid insoluble form is very much suitable as fillers in paint industry, as fillers in marble and plastic industry, as fillers in printing ink industry, as fillers in paper industry and as fire retardant. In addition to acid insolubility, the ATH need to be bright white (free or very low Fe2CO3, TiO2 impurity level) and should posses low apparent density or tap density. The tap density being measured by tapping loose powder taken in a cylinder till it attains fixed volume and then dividing the weight of powder by the volume of the powder.
The acid soluble variety is generally prepared by precipitating aluminium salts such as sulphates, nitrates and chlorides.
The acid insoluble variety of ATH is generally prepared by the Bayer's process. The Bayer process production of alumina hydrate has been practised since 1888, and the process involves digestion of bauxite with an aqueous caustic medium at elevated temperatures and pressures. Digestion results in a slurry consisting of a liquor containing the alumina dissolved in the form of sodium aluminate and a caustic-insoluble digestion residue, the so-called "red mud". The red mud is generally separated from the liquor and the alumina content of the liquor is recovered by precipitation. Precipitation is usually induced by seeding the sodium aluminate liquor with solid alumina hydrate and the precipitated alumina hydrate is recovered. Precipitation of alumina hydrate from the sodium aluminate liquor is an involved operation due to the many process variables and
the product quality requirements. The process variables involved in the precipitation step are temperature, seed charge, holding time, concentration of alumina, concentration of caustic soda, impurity content. Therefore, this operation requires close control, as well as a thorough understanding of the precipitation process.
According to US Patent No.4,637,908 which deals with the invention for manufacturing a highly active, disperse form of low apparent density aluminium hydrate is such that more than 99% of the aluminium hydroxide grains are at most 3 µm in size, is introduced continuously into a reactor along with a dry hot air stream, heated to 400°C-600°C, whirled up and strongly dispersed and shock dehydrated such that after a few seconds a stationary condition is reached in the reactor, whereby the amount of partially dehydrated low apparent density aluminium oxide flowing out is the same as the amount of aluminium tri-hydroxide being added, the low apparent density aluminium hydroxide flowing out of the reactor in the air stream is precipitated by suitable mechanical means, dispersed in mildly acidic or mildly basic water and re-hydrated by heating, as a result of which aluminium hydroxide is produced in the form of pseudo boehmite and / or bayerite gel, and is dried at temperatures below the activation temperature. According to US patent 4,786,482y the brightness of alumina trihydrate generated by Bayer's process was improved by subjecting some purification process. The process comprises the steps of subjecting caustic solution containing dissolved aluminium hydroxide to a purification step to remove dissolved impurities including colour producing humate material. The purification is effected by passing the solution through a semi-permeable membrane capable of separating the humate material from the solution. After separation, the purified solution is treated to precipitate aluminna hydroxide

therefrom. The alumina hydroxide has an improved level of whiteness. Other impurities which can be removed include iron, silicon and sodium compounds. The main drawbacks of this process are the high apparent density of ATH powders even after ground to fine powders and difficult to obtain bright white powders because contains residual impurities (Fe2O3.TiO2).
The main object of the present invention is to provide an improved process for the preparation of low apparent density and bright white alumina trihydrate (ATH) powder which obviates the drawbacks as detailed above. Another object of the present invention is to produce pure variety of alumina trihydrate.
Still another object of the present invention is to prepare alumina trihydrate (ATH) powder insoluble in acids.
Yet another object of the present invention is to produce moisture free ATH powder with fine particle size (d50) of 2.0 to 2.5µm.
Accordingly, the present invention provides an improved process for the preparation of low apparent density and bright white alumina trihydrate powder which comprises cleaning aluminium metal of purity 90 - 98% with NaOH solution (2%) and water successively , reacting 45 to 55 wt% cleaned aluminium metal with 55 to 45 wt% alkali metal hydroxide such as herein described, of concentration in the range of 3 to 20%, under stirring for 3 hours , adding water to maintain the concentration of the reactants, allowing the reaction to be completed to obtain super - saturated aluminate solution with in-situ seeded alumina trihydrate, followed by instantaneous hydrolisation under vigorous stirring to obtain precipitate of alumina trihydrate, washing, filtering and drying at 110°C by conventional methods to get low apparent density and bright white alumina trihydrate powder.
In an embodiment of the present invention, aluminium metal used may be in the form of
powder, granules, sheets, pieces, blocks.
In another embodiment of the present invention, the alkali metal hydroxide used may be
such as sodium hydroxide, potassium hydroxide. In still another embodiment of the present invention, the water used including for hydrolisation may be de-ionised (D.I) water. In yet another embodiment of the present invention, alumina trihydrate of different particle size may be obtained by varying the ratios of aluminium metal to alkali metal hydroxide. In still another embodiment of the present invention, low apparent density of the alumina trihydrate was effected by restricting the particle agglomeration by fast rate of reaction and evolution of hydrogen gas, thereby, producing finer and low apparent density powders.
In yet another embodiment of the present invention, the total precipitation of the
aluminate solution was effected by self seeding of alumina trihydrate.
In one more embodiment of the present invention, the bright whiteness of alumina
trihydrate is due to the purity of the starting material like aluminium.
In yet another embodiment of the present invention, the filtrate may be recycled for
further reactions with aluminium metal.
In another embodiment of the present invention, hydrogen gas produced as by product
which may be collected for separate use.
The process step details of the process of the present invention are:
1. Aluminium metal in the form of powders, granules, thin sheets/foils and in the form
of blocks were used as the source of aluminium component of aluminium trihydrate.
2. Alkali in the form of caustic soda (typically in the concentration range of 3-20 %)
were used as the other reactant. The reaction of the above two constituents was
carried out to generate aluminate solution with alumina trihydrate precipitate and on
hydrolysis of the above solution, alumina trihydrate was completely precipitated. The
precipitate was filtered and dried at 110°C to generate free flowing powder. | The flow
chart of the process followed is presented in Figure 1.
The following examples are given by way of illustrations and therefore should not be construed to limit the scope of the present invention.
Example 1
Scrap aluminium pieces (4mm thick) of purity 90-98 % were cleaned by stirring for few minutes in a 2% solution of NaOH and finally washed with de-ionised (D.I.) water to get well cleaned metal surface. 28 grams of cleaned Al metal pieces were reacted in 112 ml of 20% NaOH solution. The reaction initiated slowly and became vigorous within 10 minutes. The reaction was highly exothermic followed by evolution of hydrogen gas. After 3 hours, the reaction slowed down and 112ml of D.I. water was added to compensate the loss of water due to evaporation. The solution was stirred well and left 2 hours for completion of the reaction. At this stage, the content is hydrolysed with D.I. water to produce thick suspension of ATH. The suspension was washed, filtered and dried in a oven at 110°C for 8hrs. to obtain free flowing powder. Yield-63grams(90%)
Tapped density- 0.65gm/cc Particle size (d5o)-3.2µm
Example-2
7 gms. of the cleaned aluminium metal pieces of purity 90-98 % were reacted with 42ml of 20% caustic soda solution. Initially, the reaction was vigorous and highly exothermic. The reaction slowed down after 1 hour because of consumption of NaOH to produce sodium aluminate solution. Due to highly exothermic nature of the reaction, water got evaporated, thereby, sufficiently D.I. was added to sustain the reaction. This favoured hydrolysis of the already produced aluminate solution to generate alumina trihydrate and sodium hydroxide. This sodium hydroxide further reacted with remaining aluminium metal to produce aluminate solution which subsequently hydrolised to produce ATH. These cycles of reactions continued till all aluminium metal reacted which took 5hrs. to complete the above reaction. The solution at this stage was saturated with aluminate solution and also contained alumina trihydrate (produced due to hydrolysis of aluminate solution generated initially) which helped hydrolysis of aluminate solution subsequently. At this stage, D.I. water was added and stirred well. The already formed ATH acted as seeding material and helped the aluminate solution to precipitate completely into alumina (ATH) . The precipitate was washed thoroughly by stirring well and finally filtered and dried to get free flowing powder. Yield- 13.5gm(76%) Tapped density- 0.44gm/cc Particle size (d5o)-2.1µm
Example-3
17.3 gms of aluminium metal powder of purity 90-98 % was added in instalments to 106 ml of 20% NaOH solution. The reaction was very fast and thus water was evaporated very fast. The concentration was maintained by frequently adding water to avoid dryness of the contents. After completion of the reaction, the solution was hydrolysed with D.I water to get precipitates of the ATH. The precipitate was stirred well and washed thoroughly followed by filtering and drying to get dry powder of ATH. Yield-34gms(78%) Tapped density- 0.24gm/cc Particle size (d5o)-1.2µ,m
Example-4
60gms. of Al metal powder of purity 90-98 % was added in instalments into 360ml. of 3% NaOH solution. The solution was stirred well till completion of the reaction . After the completion of the reaction, the liquid was hydrolysed with D.I. water to obtain alumina trihydrate precipitate which was washed, filtered and dried to fine ATH powders. Yield- 140gms.(95%) Tapped density- 0.85gm/cc Particle size (d5o)- >8..0µm
Example-5
9gms. of Al metal powder of purity 90-98 % was added in instalments into 60ml. of 20% KOH solution. The solution was stirred well till completion of the reaction . After the completion of the reaction, the liquid was hydrolysed with D.I. water to obtain alumina trihydrate precipitate which was washed, filtered and dried to fine ATH powders. Yield-18gms.(80%) Tapped density- 0.44 gm/cc Particle size (d5o)- 2.2µm
The powder produced by the above examples was of bright white category. The presence of various impurities in ATH was analysed and they were presented below.
Impurity analysis of the product

(Table Removed)
It is seen that TiO2 and Fe2O3 are present in very less amount and hence the products are
bright white in colour.
The novelty of the present invention lies in two facts, namely (1) Low apparent density
and (2) Bright whiteness of alumina trihydrate powder.
The low apparent density was achieved by fast reaction rate of Al metal which resulted
fine particles. The hydrogen gas produced as by product helped in keeping the fine
particles in de-agglomerated condition.

The bright whiteness was achieved due to purity of the starting materials. The main advantages of the improved process of the present invention are:
1. Low apparent density of the order of 0.2 to 0.8 gm/cc is obtained.
2. Whiteness of the ATH powder is of bright white category.
3. Alumina trihydrate self seeded during the process enabled the total precipitation of
ATH.
4. The vigorous rate of reaction and evolution of hydrogen gas restricted the particle
agglomeration, thereby, producing finer and low apparent density powders.
5. The process is very economical compared to earlier methods.
6. The process is very simple and requires approximately 50-60% less time compared to
other processes referred .
7. Easy to control particle size
8. Minimum infrastructure required
9. One of the reactant (alkali) can be recycled.
10. Hydrogen gas evolved in the process as by product has high commercial value and
hence can be collected for commercial use.

We Claim:
1. An improved process for the preparation of low apparent density
and bright white alumina trihydrate powder which comprises
cleaning aluminium metal of purity 90 - 98% with NaOH solution
(2%) and water successively , reacting 45 to 55 wt% cleaned
aluminium metal with 55 to 45 wt% alkali metal hydroxide such as
herein described, of concentration in the range of 3 to 20%, under
stirring, adding water to maintain the concentration of the reactants,
allowing the reaction to be completed to obtain super - saturated
aluminate solution with in-situ seeded alumina trihydrate, followed
by instantaneous hydrolisation under vigorous stirring to obtain
precipitate of alumina trihydrate, washing, filtering and drying at
110°C by conventional methods to get low apparent density and
bright white alumina trihydrate powder.
2. An improved process as claimed in claim 1 wherein aluminium
metal used is in the form of powders, granules, sheets, pieces,
blocks.
3. An improved process as claimed in claims 1 and 2 wherein the
alkali metal hydroxide used is selected from sodium hydroxide,
potassium hydroxide.
4. An improved process as claimed in claims 1 to 3 wherein the water
used is de-ionised (D.I) water.

5. An improved process as claimed in claims 1 to 4 wherein low
apparent density of the alumina trihydrate was effected by
restricting the particle agglomeration by fast rate of reaction and
evolution of hydrogen gas , producing finer and low apparent
density powder.
6. An improved process as claimed in claims 1 to 5 wherein the total
precipitation of the aluminate solution was effected by self seeding
of alumina trihydrate.
7. An improved process for the preparation of low apparent density
and bright white alumina trihydrate powder substantially as herein
described with reference to the examples.

Documents:

1123-del-2000-abstract.pdf

1123-del-2000-claims.pdf

1123-del-2000-correspondence-others.pdf

1123-del-2000-correspondence-po.pdf

1123-del-2000-description (complete).pdf

1123-del-2000-drawings.pdf

1123-del-2000-form-1.pdf

1123-del-2000-form-19.pdf

1123-del-2000-form-2.pdf

1123-del-2000-form-3.pdf

« Previous Patent

Next Patent »

Patent Number

217586

Indian Patent Application Number

1123/DEL/2000

PG Journal Number

15/2008

Publication Date

11-Apr-2008

Grant Date

27-Mar-2008

Date of Filing

08-Dec-2000

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI- 110 001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	PRASANTA KUMAR PANDA	MATERIALS SCIENCE DIVISION, NATIONAL AEROSPACE LABORATORIES, BANGALORE-17, INDIA
2	VELLORE ABDUL JALEEL	MATERIALS SCIENCE DIVISION, NATIONAL AEROSPACE LABORATORIES, BANGALORE-17, INDIA
3	THANDALI SRINIVASAN KANNAN	MATERIALS SCIENCE DIVISION, NATIONAL AEROSPACE LABORATORIES, BANGALORE-17, INDIA

PCT International Classification Number

C01F 7/34

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA