Title of Invention	" A PROCESS FOR THE PREPARATION OF BORON PHOSPHATE USEFUL FOR HUMIDUTY SENSING AND A HUMIDITY SENSOZ MADE THEREFROM"
Abstract	1. A process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate

Title of Invention

" A PROCESS FOR THE PREPARATION OF BORON PHOSPHATE USEFUL FOR HUMIDUTY SENSING AND A HUMIDITY SENSOZ MADE THEREFROM"

Abstract

1. A process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate

Full Text	This invention relates to a process for the preparation of boron phosphate useful for humidity sensing. The boron phosphate prepared as per the process of the present invention is especially useful for making ceramic humidity sensors. In the prior art boron phosphate is prepared by John Moffat and K.F.Tang ( Ind. Eng. Chem. Prod. Res. Develop., Vol. 9 No. 4, 1970) by refluxing boric acid and phosphoric acid at 100°C for 6 hours wherein during refluxing 5ml of distilled water for every 100 grams of phosphoric acid was added. After 6 hours water was evaporated and the product was evaporated at 10"4 mm of Hg at room temperature. In the method described by Akio Tada, Hiroyasu Suzuka, and Yuzo Imizu Chemistry Letters, pp 423-424, 1987. boron phosphate is prepared by heating a mixture of boric acid and phosphoric acid at 40°C in a rotary evaporator, it is then heated at 40°C under 17 Torr, further it is heated at 150°C for 24 hours and finally calcined at 360°C for 12 hours. Boron phosphate is known to be a catalyst having dehydration capability however, properties of this compound are very sensitive towards its method of preparation as well as subsequent treatment. In consideration of these facts we have prepared boron phosphate by the reported methods as described in the text and tested for their humidity sensitivity. It is found that boron phosphate prepared by the reported routes do not show significant sensitivity towards humidity whereby it can be used as a humidity sensing material. It is reported that the structure and characteristics of boron phosphate are sensitive towards preparation route as well as initial ratio of phosphorus to boron. BP04 possessing appropriate phosphorus to boron ratio, synthesized by the modified preparation method as described in this patent however, shows good response towards humidity as number of acid sites and the strength of the acid sites can be modulated by the present preparation route. Preparation of humidity sensing materials which can estimate change in relative humidity rapidly with accuracy as well as reliability is an important necessity for the design and manufacture of several industrial control systems. Porous ceramic humidity sensing materials are used in monitoring and controlling the amount of water vapor in the surrounding environment especially in applications with respect to agriculture, medical instrumentation, food processing, weather control, automobile, paper and textile industries and related fields. Different types of humidity sensors are available which comprise mainly of ceramic, polymeric, composites and electrolytic types where some of the physical or chemical properties of these sensors change with respect to the amount of water vapor present in the surrounding air. However, each one of these material has some limitations either regarding the temperature of operation, range of humidity sensitivity or selectivity. Due to these shortcomings, humidity sensors are selected according to their utility and different humidity sensors are used for the measurements of different relative humidity (RH) ranges wherein, relative humidity (RH) is the ratio of partial pressure of water vapor in the atmosphere to the saturation of water vapor at that temperature of air. For example, automobile industries need temperature range between -20 and 80°C at 50 to 100% RH variations while domestic electric appliances require control of humidity sensitivity between 5 and 100%RH for the operating temperature ranging between 5 and 100°C. Similarly most of the medical appliances need humidity control between 5 and 80% RH at 10 to 30°C. For use in such wide ranging applications, different types of sensors based on different principle and temperature compatibility are necessary. The main object of present invention is to provide a process for the preparation of boron phosphate (BPO4), which is highly sensitive towards change in the relative humidity. A further object is to provide humidity sensor using modified boron phosphate prepared by the process of the present invention. Accordingly the present invention provides a process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate In one of the embodiment of the present invention the source of boron used may be such as, sodium borate, boron oxide, or triethyl borate. In another embodiment the source of phosphorous used may be such as diammonium orthophosphate, ammonium hydrogen phosphate or triethyl phosphate, preferably from diammonium orthophosphate. In another embodiment the organic solvent used for mixing the salts is selected from acetone, carbon tetrachloride, benzene or alcohol, preferably from acetone. In yet another embodiment the ratio of boron to phosphorus ranges from 1:1 to 1:4. X-ray diffraction pattern of these material shows single phase nature with tetragonal structure as in agreement with the available reports in the literature. According the present invention provides a humidity sensor made using boron phosphate prepared by the process as described above. The humidity sensing property of these pellets was tested by measuring the electrical resistance using boron phosphate prepared as per the procedure of the present invention as sensors. Following examples are given by way of illustration and should not construed to limit the scope of the present invention. EXAMPLE-1 3.0915 gms of Boric Acid and 6.713 gms of diammonium orthophosphate, were mixed in agate pastel and mortar using dry acetone for 1 hour. Mixture was heated in vacuum at 100°C for 2 hours followed by heating in air at 450°C. The powder was mixed with 3% of polyvinyl alcohol and then pelletized in the form of 10 mm diameter and 3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 1°C/min till 500°C and kept at this temperature for 10 hours. Electric contacts were provided by air silver paste. These pellets were then tested for humidity sensitivity. The result of these measurements (Fig.1) are given in the form of a graph of relative humidity (%RH) Vs log Resistance(R). As seen in Fig.1, accompanying this invention, the resistance of the pellet varies systematically from 10^ ohms to 105 ohms with variation of relative humidity from 25 to 95%RH. EXAMPLE-2 3.056 gms of sodium borate and 7.956 gms of ammonium hydrogen phosphate, were mixed in agate pastel and mortar using dry acetone for half hour. Mixture was heated in vacuum at 100°C for 2 hours followed by heating in air at 470°C. The powder was then pelletized in the form of 10 mm diameter and 3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 2°C/min till 500°C and kept at this temperature for 10 hours. These pellets were then tested for humidity sensitivity. The resistance of the pellet varies systematically from 2x109 ohms to 3x105 ohms with variation of relative humidity from 25 to 95%RH. EXAMPLE -3 1.716 gms of triethyl borate and 2.213 gms of triethyl phosphate, were mixed in agate pastel and mortar using dry alcohol for 2 hour. Mixture was heated in vacuum at 120°C for 3 hours followed by heating in air at 500°C. The powder was mixed with 3% of polyvinyl alcohol and then pelletized in the form of 10 mm diameter and 3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 1°C/min till 550°C and kept at this temperature for 8 hours. The main advantages of the process described in the are as follows: 1. Phosphorus to boron ratio can be monitored 2. Acid sites on the boron phosphate can be controlled 3. Strength of acid site can be controlled 4. Humidity sensitive boron phosphate can be prepared 5. The boron phosphate material prepared by the process of the present invention provides fast response, considerable change in electrical resistance with change in relative humidity, lower hystersis values when used as humidity sensor. We claim 1. A process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate 2. A process as claimed in claim 1 wherein the source of boron is selected from boric acid, boron chloride or triethyl borate. 3. A process as claimed in claims 1 to 2 wherein the source of phosphorus is selected from diammonium orthophosphate, orthophosphoric acid or triethyl phosphate. 4. A process as claimed in claims 1 to 3 wherein the dry organic solvent used for mixing the salts is selected from acetone, carbon tetrachloride, benzene or alcohol. 5. A process for the preparation of boron phosphate useful for humidity sensing substantially as herein described with reference to examples.

Full Text

This invention relates to a process for the preparation of boron phosphate useful for humidity sensing. The boron phosphate prepared as per the process of the present invention is especially useful for making ceramic humidity sensors.
In the prior art boron phosphate is prepared by John Moffat and K.F.Tang ( Ind. Eng. Chem. Prod. Res. Develop., Vol. 9 No. 4, 1970) by refluxing boric acid and phosphoric acid at 100°C for 6 hours wherein during refluxing 5ml of distilled water for every 100 grams of phosphoric acid was added. After 6 hours water was evaporated and the product was evaporated at 10"4 mm of Hg at room temperature. In the method described by Akio Tada, Hiroyasu Suzuka, and Yuzo Imizu Chemistry Letters, pp 423-424, 1987. boron phosphate is prepared by heating a mixture of boric acid and phosphoric acid at 40°C in a rotary evaporator, it is then heated at 40°C under 17 Torr, further it is heated at 150°C for 24 hours and finally calcined at 360°C for 12 hours.
Boron phosphate is known to be a catalyst having dehydration capability however, properties of this compound are very sensitive towards its method of preparation as well as subsequent treatment. In consideration of these facts we have prepared boron phosphate by the reported methods as described in the text and tested for their humidity sensitivity. It is found that boron phosphate prepared by the reported routes do not show significant sensitivity towards humidity whereby it can be used as a humidity sensing material. It is reported that the structure and characteristics of boron phosphate are sensitive towards

preparation route as well as initial ratio of phosphorus to boron. BP04 possessing appropriate phosphorus to boron ratio, synthesized by the modified preparation method as described in this patent however, shows good response towards humidity as number of acid sites and the strength of the acid sites can be modulated by the present preparation route.
Preparation of humidity sensing materials which can estimate change in relative humidity rapidly with accuracy as well as reliability is an important necessity for the design and manufacture of several industrial control systems. Porous ceramic humidity sensing materials are used in monitoring and controlling the amount of water vapor in the surrounding environment especially in applications with respect to agriculture, medical instrumentation, food processing, weather control, automobile, paper and textile industries and related fields.
Different types of humidity sensors are available which comprise mainly of ceramic, polymeric, composites and electrolytic types where some of the physical or chemical properties of these sensors change with respect to the amount of water vapor present in the surrounding air. However, each one of these material has some limitations either regarding the temperature of operation, range of humidity sensitivity or selectivity. Due to these shortcomings, humidity sensors are selected according to their utility and different humidity sensors are used for the measurements of different relative humidity (RH) ranges wherein, relative humidity (RH) is the ratio of partial

pressure of water vapor in the atmosphere to the saturation of water vapor at that temperature of air. For example, automobile industries need temperature range between -20 and 80°C at 50 to 100% RH variations while domestic electric appliances require control of humidity sensitivity between 5 and 100%RH for the operating temperature ranging between 5 and 100°C. Similarly most of the medical appliances need humidity control between 5 and 80% RH at 10 to 30°C. For use in such wide ranging applications, different types of sensors based on different principle and temperature compatibility are necessary.
The main object of present invention is to provide a process for the preparation of boron phosphate (BPO4), which is highly sensitive towards change in the relative humidity. A further object is to provide humidity sensor using modified boron phosphate prepared by the process of the present invention.
Accordingly the present invention provides a process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product

under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate
In one of the embodiment of the present invention the source of boron used may be such as, sodium borate, boron oxide, or triethyl borate.
In another embodiment the source of phosphorous used may be such as diammonium orthophosphate, ammonium hydrogen phosphate or triethyl phosphate, preferably from diammonium orthophosphate.
In another embodiment the organic solvent used for mixing the salts is selected from acetone, carbon tetrachloride, benzene or alcohol, preferably from acetone.
In yet another embodiment the ratio of boron to phosphorus ranges from 1:1 to 1:4.
X-ray diffraction pattern of these material shows single phase nature with tetragonal structure as in agreement with the available reports in the literature.
According the present invention provides a humidity sensor made using boron phosphate prepared by the process as described above.

The humidity sensing property of these pellets was tested by measuring the electrical resistance using boron phosphate prepared as per the procedure of the present invention as sensors.
Following examples are given by way of illustration and should not construed to limit the scope of the present invention.
EXAMPLE-1
3.0915 gms of Boric Acid and 6.713 gms of diammonium orthophosphate, were mixed in agate pastel and mortar using dry acetone for 1 hour. Mixture was heated in vacuum at 100°C for 2 hours followed by heating in air at 450°C. The powder was mixed with 3% of polyvinyl alcohol and then pelletized in the form of 10 mm diameter and 3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 1°C/min till 500°C and kept at this temperature for 10 hours. Electric contacts were provided by air silver paste. These pellets were then tested for humidity sensitivity. The result of these measurements (Fig.1) are given in the form of a graph of relative humidity (%RH) Vs log Resistance(R). As seen in Fig.1, accompanying this invention, the resistance of the pellet varies systematically from 10^ ohms to 105 ohms with variation of relative humidity from 25 to 95%RH.
EXAMPLE-2
3.056 gms of sodium borate and 7.956 gms of ammonium hydrogen phosphate, were mixed in agate pastel and mortar using dry acetone for half hour. Mixture was heated in vacuum at 100°C for 2 hours followed by heating in air at 470°C. The powder was then pelletized in the form of 10 mm diameter and

3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 2°C/min till 500°C and kept at this temperature for 10 hours. These pellets were then tested for humidity sensitivity. The resistance of the pellet varies systematically from 2x109 ohms to 3x105 ohms with variation of relative humidity from 25 to 95%RH.
EXAMPLE -3 1.716 gms of triethyl borate and 2.213 gms of triethyl phosphate, were mixed in agate pastel and mortar using dry alcohol for 2 hour. Mixture was heated in vacuum at 120°C for 3 hours followed by heating in air at 500°C. The powder was mixed with 3% of polyvinyl alcohol and then pelletized in the form of 10 mm diameter and 3 mm thick pellets by applying 5 tones of pressure. These pellets were then heated at the rate of 1°C/min till 550°C and kept at this temperature for 8 hours.
The main advantages of the process described in the are as follows:
1. Phosphorus to boron ratio can be monitored
2. Acid sites on the boron phosphate can be controlled
3. Strength of acid site can be controlled
4. Humidity sensitive boron phosphate can be prepared
5. The boron phosphate material prepared by the process of the present invention provides fast response, considerable change in electrical resistance with change in relative humidity, lower hystersis values when used as humidity sensor.

We claim
1. A process for the preparation of boron phosphate, useful for humidity sensing which comprises mixing thoroughly boric acid and its salt and orthophosphoric acid and its salt in dry organic solvent, for a period ranging between half an hour to 8 hours, increasing the temperature to 100°C at the heating rate in the range of 1°C and 10°C per minute and aging at 100°C for a period ranging from 1 hour to 10 hours under reduced pressure, further raising the mixture temperature to 200°C by increasing the temperature at the rate of 1°C per minute to 10°C per minute for a period ranging between 10 and 30 hours, pelletizing the product under pressure, sintering the pellets at the temperature ranging between 300°C and 600°C for 3 to 15 hours to obtain boron phosphate
2. A process as claimed in claim 1 wherein the source of boron is selected from boric acid, boron chloride or triethyl borate.
3. A process as claimed in claims 1 to 2 wherein the source of phosphorus is selected from diammonium orthophosphate, orthophosphoric acid or triethyl phosphate.
4. A process as claimed in claims 1 to 3 wherein the dry organic solvent used for mixing the salts is selected from acetone, carbon tetrachloride, benzene or alcohol.

5. A process for the preparation of boron phosphate useful for humidity sensing substantially as herein described with reference to examples.

Documents:

2440-del-1997-abstract.pdf

2440-del-1997-claims.pdf

2440-del-1997-correspondence-others.pdf

2440-del-1997-correspondence-po.pdf

2440-del-1997-description (complete).pdf

2440-del-1997-form-1.pdf

2440-del-1997-form-2.pdf

2440-del-1997-form-9.pdf

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Patent Number

191575

Indian Patent Application Number

2440/DEL/1997

PG Journal Number

49/2003

Publication Date

06-Dec-2003

Grant Date

30-Jun-2004

Date of Filing

28-Aug-1997

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG NEW DELHI-110001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	KUNTUKRISHNA PILLAI VIJAYAMOHANAN	NATIONAL CHEMICAL LABORATORY, PUNE-411 008, ,AJARASJTRA, INDIA.
2	IMITIAZ SIRAJUDDIN MULLA	NATIONAL CHEMICAL LABORATORY, PUNE-411 008, ,AJARASJTRA, INDIA.

PCT International Classification Number

C01B 35/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA