JPH01290552A - Material for detecting element of gaseous carbon dioxide and production thereof - Google Patents

Abstract

PURPOSE:To increase sensitivity to the detection of CO2 and to maintain detecting performance over a long period by using a compounded material obtd. by adding an inorg. halide and an Al compd. to hydroxyapatite. CONSTITUTION:A compounded material consisting of hydroxyapatite represented by a formula M10(ZO4)6(OH)2 (where M is Ca, Ba, Sr, Pb and Cd, preferably Ca and Z is P, As and V, preferably P), an inorg. halide, preferably CaCl2 or NH4Cl and an Al compd., preferably alumina is used as the material for detecting element of gaseous CO2. When the element is produced, a press-molded body of hydroxyapatite is sintered preferably at 850-950 deg.C for 1.5-2.5hr and the resulting porous sintered body is immersed in an aq. soln. contg. the inorg. halide and the Al compd., taken out, dried and sintered by heating to >=500 deg.C, preferably 700-1,000 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a carbon dioxide gas detection element material, and more particularly, to a carbon dioxide gas detection element material that can detect carbon dioxide gas with high accuracy. The present invention relates to a carbon dioxide gas detection element material that can detect carbon dioxide gas with high accuracy even after repeated use over a long period of time.

The carbon dioxide detection element material of the present invention can be used for agricultural purposes such as controlling carbon dioxide gas in greenhouse cultivation, for industrial purposes such as monitoring carbon dioxide gas in exhaust gas, and for environmental hygiene purposes such as detecting carbon dioxide gas in living environment control. It can be used as a detection element for carbon dioxide, which can be used in a wide range of applications, such as disaster prevention, such as early detection of fires caused by rapid increases in the amount of carbon dioxide.

[Technical background and explanation of conventional technology]

Hydroxyapatite is known to be used as a moisture-sensitive element in a moisture- and temperature-sensitive gas element (Japanese Patent Laid-Open No. 58
(Japanese Patent Application No. 166249), and a method of detecting carbon dioxide gas by utilizing the electrical loss or increase in impedance value of hydroxyapatite that occurs when hydroxyapatite comes into contact with carbon dioxide gas (Japanese Patent Application No. 59-211287). ), adding an inorganic carbonate (for example, calcium carbonate or sodium carbonate) to hydroxyapatite to form a hydroxyapatite-inorganic carbonate complex, thereby improving the detection accuracy of carbon dioxide gas (Japanese Patent Application Laid-Open No. 1989-1999) -102666), and adding an inorganic halide (e.g. calcium chloride or ammonium chloride) to hydroxyapatite to form a hydroxyapatite-inorganic halide complex, thereby improving the detection accuracy of carbon dioxide ( Patent application 1986-851
No. 26) has been proposed.

The present inventors have been conducting research on hydroxyapatite for many years, and in their research, they added calcium chloride and ammonium chloride to hydroxyapatite, and added alumina to the hydroxyapatite composite. , the rate of change in the impedance value in air and the impedance value in air containing carbon dioxide (reaction rate with carbon dioxide) improves, and the rate of increase in impedance value in air due to contact with carbon dioxide (baseline The present invention was achieved based on these findings.

[Object of the invention and summary of the invention]

An object of the present invention is to provide a carbon dioxide gas detection element material that can produce a carbon dioxide gas detection element with high detection sensitivity. An object of the present invention is to provide a material for a carbon dioxide gas detection element that can be used to produce a carbon dioxide gas detection element with a small increase 8 (increase rate of baseline) and no decrease in carbon dioxide detection sensitivity.

The present invention is based on the general formula: % formula % (1) [In formula (1), M is an element selected from the group consisting of calcium, barium, strontium, lead and cadmium, and Z is an element selected from the group consisting of calcium, barium, strontium, lead and cadmium, and Z is phosphorus, arsenic and Vanadium is an element selected from the group consisting of This is a carbon dioxide detection element material composition characterized in that the following is added.

The present invention also provides the above-mentioned hydroxyapatite and inorganic halide, which comprises immersing the hydroxyapatite represented by the above formula (+) in an aqueous solution of one or more inorganic halides and then drying the hydroxyapatite and the inorganic halide. In the method for producing a composite material of one starch or two or more types, an aluminum compound is added to the composite material.

In the carbon dioxide detection element material composition of the present invention and its manufacturing method, alumina, aluminum chloride, or aluminum hydroxide can be used as the aluminum compound, but it is preferable to use alumina, and the aluminum compound has the formula (
As the hydroxyapatite represented by 1), it is preferable to use a hydroxyapatite in which Q is calcium and 2 is phosphorus, and it is further preferable to use calcium chloride and ammonium chloride as the inorganic halides.

In the Δ method for producing the carbon dioxide detection element material of the present invention, the aluminum compound is an inorganic halide IN or 2
Aluminum compounds can be added to aqueous solutions of hydroxyapatite and inorganic halides by decomposing and precipitating aluminum compounds evaporated into the gas phase in a vapor phase growth method (CVD method). By,
You can also add As the aluminum compound in the CVD method, it is preferable to use an Aiso aluminum compound that easily evaporates and decomposes by heating to easily precipitate aluminum.

In the convex production method of the carbon dioxide detection element material of the present invention, it is preferable to use a porous sintered body as the hydroxyapatite, and an aqueous solution of one or more inorganic halides of the hydroxyapatite. After the immersion in the inorganic halide is carried out under reduced pressure, the pressure is returned to atmospheric pressure, thereby removing 1 of the inorganic halide.
It is preferable to uniformly distribute the seed or an aqueous solution of two or more types to every corner of the porous hydroxyapatite, and at this time, the aluminum compound may be added in advance to the IN of the inorganic halide or the aqueous solution of the two or more types. can.

[Detailed explanation of the invention]

In this specification, the rate of change in impedance value is the percentage (%) of the impedance value of the carbon dioxide detection element in gas where carbon dioxide is present relative to the impedance value in gas where carbon dioxide is not present. It corresponds to the reaction rate of the detection element with carbon dioxide gas, and is given by the following formula.

C: Rate of change in impedance value (%) Impedance value Z, : Impedance value in gas where carbon dioxide does not exist; When it comes into contact with a gas that is present and then comes into contact with a gas that does not contain carbon dioxide, the impedance value of the carbon dioxide detection element increases significantly when it comes into contact with a gas that contains carbon dioxide, indicating the presence of carbon dioxide. However, when it comes into contact with a gas that does not contain carbon dioxide again, the impedance value does not return to the level it had when it first came into contact with a gas that does not contain carbon dioxide. However, the impedance value is now at a level slightly higher than this.

In this specification, the baseline increase rate 1 is the difference between the impedance value when the carbon dioxide detection element first comes into contact with gas in which carbon dioxide does not exist and the impedance value when it comes into contact with gas in which carbon dioxide does not exist again. This is the rate of increase in the impedance value during the period of time, and is one of the indicators indicating the deterioration of the performance of the carbon dioxide detection element due to long-term use, and is given by the following equation.

I amount: Increase rate of baseline (%) Z: Impedance value when the carbon dioxide detection element comes into contact with gas in which carbon dioxide does not exist 2: The carbon dioxide detection element first contacts gas in which carbon dioxide does not exist Impedance value t at the time of contact: Time (minutes) elapsed between the time when the carbon dioxide detection element first came into contact with gas without carbon dioxide and the time when it came into contact with gas without carbon dioxide again. The hydroxyapatite represented by the general formula (1) in the carbon dioxide detection element material of the invention can be prepared by a known method,
For example, any compound synthesized by a wet method, a dry method, or a hydrothermal method can be used, but M in formula (1) is calcium;
It is preferable to use hydroxyapatite in which 2 is phosphorus, and it is preferable to use a porous molded article of hydroxyapatite.゛Put the hydroxyapatite powder in a mold, such as a tablet molding machine, pressurize it and mold it. In C), the mixture is heated for 1 hour or more (preferably 1.5 to 2.5 hours) to sinter, thereby obtaining a porous sintered body of hydroxyapatite.

To obtain flaky hydroxyapatite sintered bodies, hydroxyapatite powder is mixed with water and an organic binder, such as methyl cellulose, to prepare a paste, which is then applied to a heat-resistant substrate to form a thin film. 800 yen as a notification letter
Sintering is carried out by heating to ~1000°C (preferably 850-950''C) for 1 hour or more (preferably 1.5-2.5 hours).

Separately, an aqueous solution of an inorganic halide is prepared and an aluminum compound such as aluminum chloride, aluminum hydroxide or aluminum oxide (alumina) is added to this.
An aqueous solution of an inorganic halide-aluminum compound is prepared, and the porous sintered body of hydroxyapatite is immersed in the aqueous solution of the inorganic halide and aluminum compound. Deposit or adhere to solid bodies. Thereafter, the porous sintered body of hydroxyapatite to which the inorganic halide and aluminum compound have adhered is pulled up, dried, and then heated to 500°C or more (preferably 700°C (-1000°C)). and firing to obtain a carbon dioxide detection element material composition of hydroxyapatite which is a composite with the inorganic halide and aluminum compound of the present invention.

The carbon dioxide detection element material G of the present invention can also be manufactured by depositing an aluminum compound onto a porous sintered body of an inorganic halide-hydroxyapatite composite by a vapor phase growth method (CVD method). can.

Vapor phase growth method (Che+++1eal Vapor D
eposition (CVD method)], an aluminum compound is attached to a porous sintered body of an inorganic halide-hydroxyapatite composite using a CVD apparatus shown in FIG. A porous sintered body 8 of an inorganic halide-hydroxyapatite composite is placed on the sample pan 2 on the high temperature furnace 6 side, and an easily evaporated aluminum compound, such as an organic aluminum compound 9, is placed on the sample pan 3 on the low temperature furnace 7 side. Then, feed the carrier gas into the quartz glass tube l from the carrier gas feed pipe 4,
While measuring the temperature with the thermocouple 5, the low temperature furnace 7 and the high temperature furnace 6 are heated to predetermined temperatures. The aluminum compound on the sample plate 3 on the low-temperature furnace 7 side evaporates and is sent to the high-temperature furnace 6 side by the carrier gas;
The inorganic halide-aluminum compound-hydroxyapatite composite of the present invention is separated by the high temperature and precipitated on the porous sintered body of the inorganic halide-hydroxyapatite composite on the sample plate 2 of the high-temperature furnace 6@. A carbon dioxide detection element material composition of an apatite composite is formed.

The vapor phase deposition method (CVD method) is suitable for adding alumina to the porous sintered body of the inorganic halide-hydroxyabatite composite. Alumina precipitates on the surface layer of the porous sintered body of the inorganic halide-hydroxyapatite composite,
Forms a complex with alumina, and this alumina-inorganic halide-hydroxyapatite complex reacts sharply with carbon dioxide that comes into contact with it, or the inorganic halide and alumina react with hydroxyapatite and carbon dioxide gas. It is thought that it exerts a catalytic effect on the reaction. In any case, the carbon dioxide gas detection element material of the present invention has a large rate of change in impedance value, and as a result, the carbon dioxide gas detection sensitivity is sensitive.

In the vapor phase growth method (CVD method), the low-temperature furnace 7 in which the aluminum compound to be evaporated 9 is placed is set at a temperature necessary and sufficient to evaporate the aluminum compound, and the porous structure of the non-porous halide-suboxyabatite composite is heated to a temperature necessary and sufficient to evaporate the aluminum compound. The high temperature furnace 6 in which the sintered body 3 is placed has a temperature necessary and sufficient to decompose the evaporated aluminum. Further, it is preferable to use an oxidizing gas such as air as the carrier gas to form alumina.

In the following, the present invention will be explained in more detail using test examples instead of examples.

Test example 1 Rate of change in impedance value of hydroxyapatite (reaction rate)
The effect of addition of calcium chloride on the increase rate of baseline was tested.

(+) Preparation of sample Dissolve butyl carbinol 209 in ethanol 45alt, add high purity hydroxyapatite [product number AN 8
30425, Central Glass Co., Ltd. product] powder 20
After adding Jl and stirring well to uniformly disperse the mixture, the resulting dispersion was formed into a sheet with a thickness of 200 μm using a doctor blade method. This sheet is cut into thin pieces of lOryu square, and these thin pieces are used as an alumina substrate [25 mm x 25 UIX.
0.5 mm (thickness)], and an electrode was applied thereon with platinum paste. After drying this at room temperature,
The material was placed in an electric furnace and fired at 800° C. for 2 hours to sinter the hydroxyapatite and bake the platinum fIIL electrode, thereby preparing an element material for measuring impedance values.

This measurement element material was immersed in a calcium chloride-ammonium chloride aqueous solution (pH: 8.0) with the concentration shown in Table 1 for 24 hours, dried at 120°C, and added with calcium chloride for measurement of impedance values. Motoko?
Made by A.

(2) Test method A quartz glass tube with an element for measuring impedance values installed inside the tube was placed in an F8 air furnace maintained at 400°C by a temperature controller, and the humidity was adjusted to 50% with a calcium nitrate saturated solution. Air is passed through a quartz glass tube at 200 i/min.
The impedance value of the measurement element is f by the AC two-terminal method.
After annealing the measuring element for 2 hours while measuring t, the air flow through the quartz glass tube was adjusted to 50% humidity with a calcium nitrate saturated solution.
% of carbon dioxide gas, and while measuring the impedance value of the measurement element using the AC 2@son method, the air flow containing 0.1% carbon dioxide gas was heated for 1 hour.
0 mff1/min was passed through the quartz glass tube. Then, air containing 0.1% carbon dioxide gas is passed through a quartz glass tube.
Similarly, the air was changed to air adjusted to 50% humidity, and the air was passed through the quartz glass tube for 1 hour while measuring the impedance value of the measurement element using the AC two-terminal method. Thereafter, the air flow passing through the quartz glass tube was switched to an air flow containing 0.1% carbon dioxide gas five times, and the impedance value of the measurement element was measured during that time.

Using the measured impedance value of the measurement element measured during this test, the impedance value in air and the rate of change in the impedance value in air containing 0.1% carbon dioxide (reaction rate ,%), and airflow and 0.1
The rate of increase (%) of the baseline of the impedance value in air when the air flow containing % carbon dioxide gas was repeatedly switched was calculated.

A) Rate of change in impedance value (reaction rate): CZ (Ai
r) Z (Co): Impedance value of the measurement element in air containing 0.1% carbon dioxide.

z (Air): Impedance value in the air.

B) Baseline increase rate: H Z: Final impedance value of the measurement element in air.

Z: Initial impedance value of the measurement element in air.

t: Time (hour) at which impedance value was measured.

(3) Test results The results of the test were as shown in Table 1.

The rate of change in impedance value (reaction rate) in Table 1 is the change in impedance value calculated at each time of switching between the air flow and the air flow containing 0.1% carbon dioxide gas four times. This is the average value of the percentage (%).

(Margin below) (4) Discussion When the amount of calcium chloride added to hydroxyapatite is increased, the rate of change (%) in impedance value increases, and the rate of increase in the baseline seems to decrease, but the increase in the baseline It can be seen that it is not clear whether the rate (%) is necessarily proportional to the increase in the amount of calcium chloride.

Test Example 2 A test was conducted on the effect of the addition of alumina on the impedance change system of hydroxyapatite to which calcium chloride was added and the rate of increase in the baseline.

(1) Preparation of sample In the same manner as in Test Example 1, sintering of hydroxyapatite and baking of electrodes were performed to obtain a hydroxyapatite measuring element material of 18.8 #/41! of calcium chloride and ammonium chloride of I7.79/l (pH: 8.79/l).
0) for 24 hours and then transferred at 120° C. to prepare a measuring element material to which calcium chloride was added.

The measuring element material B8 to which calcium chloride was added was prepared using a CVO device (Chemical Vapor D) shown in Fig. 1.
Place the aluminum isopropoxide 9 in the sample pan 2 on the high temperature furnace 6 side of the high temperature furnace 6 side (eposition equipment, vapor phase growth apparatus), and place the aluminum isopropoxide 9 on the sample pan 3 on the low temperature furnace 7 side. As a carrier gas, it is introduced into the quartz glass tube 1, and while the temperature is measured by the thermocouple 5, the low temperature furnace 7 is heated to 1408 C, and the high temperature furnace 6 is heated to 400 °C for the time shown in Table 2. By adding alumina to the measurement element material containing calcium chloride,
An element for measuring impedance values to which calcium chloride-aluminum was added was tuned.

As an element for measuring the impedance value of the control sample, the above-mentioned calcium chloride-added measurement connecting material was used as CvD.
It was used as it was without adding alumina using the device.

(2) Test method In the same manner as Test Example 1, the Srt side of the impedance value of the measurement element was conducted, and the rate of change in impedance value in air and in air containing 0.1% carbon dioxide (reaction rate) Then, the rate of increase (%) in the impedance value in the air was calculated when switching between the air flow and the air flow containing 0.1% carbon dioxide gas was repeated.

(3) Test results It was as shown in Table 2.

Table 2 Addition of alumina to measurement element material, rate of change in impedance value (reaction rate) and rate of increase in baseline (4) Consideration When alumina is added to hydroxyapatite to which calcium chloride has been added, alumina It can be seen that as the amount of addition increases, the rate of change in impedance value (reaction rate) between air and air containing 0.1% carbon dioxide improves, so that the detection sensitivity of carbon dioxide improves.

Furthermore, when alumina is added to hydroxyapatite containing calcium chloride, the baseline increase rate (%) decreases, which extends the performance life of the carbon dioxide detection element, but increasing the amount of alumina added , the baseline increase rate (%) decreases, which indicates that the effect of extending the life of the carbon dioxide detection element increases.

Test Example 3 When alumina is added to hydroxyapatite to which calcium chloride has been added, the carrier gas increases the rate of change (reaction rate) of the impedance value of the measurement element and the increase in the baseline. The effect on the rate was tested.

(1) In Test Example 2 made of m-sample, except that the carrier gas fed into the quartz glass tube of the CvD device was adjusted to the gas shown in Table 3, and the heating time was set to the time shown in Table 3. In the same manner as in Test Example 2, an element for measuring impedance values to which calcium chloride-alumina was added was prepared.

(2) Test method In the same manner as Test Example 1, the impedance value of the measurement element was measured, and the rate of change (reaction rate) of the impedance value in air and in air containing 0.1% carbon dioxide and Increase in impedance value in air when repeatedly switching between air flow and air flow containing 0.1% carbon dioxide =
i (%) was calculated.

(3) Test results It was as shown in Table 3.

The rate of change in impedance value (reaction rate) in Table 3 is the change in impedance value calculated at each time of switching between the air flow and the air flow containing 0.1% carbon dioxide gas four times. This is the average value of the percentage (%).

(Leaving space below) Table 3 Change rate of carrier gas and impedance value (reaction rate) and baseline increase rate when alumina is added by CVD method (4) Discussion Alumina was added to hydroxyapatite to which calcium chloride was added by CVD method. as a carrier gas to add
It can be seen that oxygen gas is superior to nitrogen gas.

This is considered to be because the aluminum isopropoxide evaporated into the gas phase is decomposed by the rise in temperature.

〔Effect of the invention〕

By adding alumina to hydroxyapatite to which calcium chloride has been added, the rate of change between the impedance value in air and the impedance value in air containing carbon dioxide gas (reaction rate with carbon dioxide gas) increases, thereby, The detection sensitivity of carbon dioxide gas of hydroxyapatite is improved.

In addition, when hydroxyapatite comes into contact with carbon dioxide gas repeatedly, the rate of increase in the baseline impedance value in air decreases, thereby maintaining the performance of hydroxyapatite as a carbon dioxide detection element for a long period of time. can do.

As a carrier gas when adding alumina to hydroxyapatite added with calcium chloride by CVD method,
By using oxidizing gas, the rate of change between the impedance value in air and the impedance value in air containing carbon dioxide gas (reaction rate with carbon dioxide gas) increases, thereby increasing the carbon dioxide detection sensitivity of hydroxyapatite. The performance of the hydroxyapatite carbon dioxide detection element can be maintained for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the inside of an apparatus for carrying out a vapor phase growth method (CVO method). Applicant Sekisui Plastics Co., Ltd.

Claims (2)

[Claims] (1) General formula: M_1_0(ZO_4)_6(OH)_
2(1) [In formula (1), M is an element selected from the group consisting of calcium, barium, strontium, lead and cadmium, and Z is selected from the group consisting of phosphorus, arsenic and vanadium. A carbon dioxide detection element material made of a composite material of one or more of hydroxyapatite and inorganic halides represented by the following, characterized in that an aluminum compound is added to the composite material. A carbon dioxide detection element material composition. (2) General formula: M_1_0(ZO_4)_6(OH)_
2(1) [In formula (1), M is an element selected from the group consisting of calcium, barium, strontium, lead, and cadmium, and Z is an element selected from the group consisting of phosphorus, arsenic, and vanadium. ] The above hydroxyapatite and one or more inorganic halides are immersed in an aqueous solution of one or more inorganic halides and then dried. In the manufacturing method of composite materials,
A method for producing a carbon dioxide detection element material composition, which comprises adding an aluminum compound to the composite material.