JP4793921B2 - Hydrogen chloride gas sensor - Google Patents

Description

  The present invention relates to a gas sensor for measuring a hydrogen chloride gas concentration in the air or in a specific atmosphere.

  Since hydrogen chloride (HCl) gas is generated in the process of manufacturing chemical plants and activated carbon and becomes an environmental impact substance, emission standards are set by the Air Pollution Control Law. In recent years, it has become important to constantly measure the concentration of HCl gas discharged for the indirect monitoring of dioxin formation in cement manufacturing processes and various incinerators. Is required.

  The most widely used method for measuring the HCl gas concentration is the ion electrode method. However, it is susceptible to temperature, and automatic analysis equipment has the disadvantage of being large and expensive. Other methods include ion chromatography, titration, and absorptiometry, but there are problems such as the need for pretreatment of the target gas and the inability to perform continuous analysis, and HCl such as combustion exhaust gas. Not suitable for continuous measurement of concentration. (For example, see Non-Patent Document 1)

On the other hand, although a chemical sensor using an all-solid-state element is proposed in Patent Document 1, since an oxygen ion conductive solid electrolyte is used, an error in the measured value is caused by the influence of oxygen concentration in principle. There's a problem.
JIS K0107: 2002 JP-A-8-021820

  The problem to be solved by the present invention is to provide a low-cost HCl gas sensor with small measurement error.

  The present invention provides an HCl gas sensor having a cation conductor as an electrolyte and a metal oxide or zeolite as an electrode layer on at least one surface of the electrolyte.

  In the present invention, a cation conductor (for example, a sodium superionic conductor) is used as an electrolyte, and a metal oxide or zeolite is used for an electrode layer. A high HCl gas sensor can be realized.

The cation conductor as the electrolyte, uses sodium super ionic conductor, sodium ion conductor, or a lithium ion conductor. As the electrolyte, Na ₅ DySi ₄ O ₁₂ which is a sodium superionic conductor is preferable, but Na ₅ XSi ₄ O ₁₂ (any of X = Y, Nd, Sm and Gd) can also be used. On the other hand, RuO ₂ or Nb ₂ O ₅ is preferable as the electrode layer, but MoO ₃ , WO ₃ , Y-type zeolite, and ZSM5 type zeolite can also be used.

  In this HCl gas sensor, an electromotive force is generated between the electrolyte and the electrode layer in accordance with the HCl gas concentration in the measurement target gas. Therefore, by measuring this electromotive force by a known method, It is possible to know the HCl gas concentration.

  The above-described HCl gas sensor of the present invention can be manufactured by a simple method in which a cation conductor plate is manufactured and a metal oxide electrode layer or a zeolite electrode layer is formed thereon, and the configuration of the completed sensor is also simple. Therefore, it can be provided at a lower cost than conventional HCl gas measurement methods.

  According to the present invention, inexpensive measurement of HCl gas can be realized, and the influence of other gas components such as oxygen can be reduced.

  Embodiments of the sensor according to the present invention will be described below based on examples. However, the present invention is not limited to this embodiment.

  FIG. 1 is a side sectional view showing a structure of a sensor according to the present invention. As shown in the figure, the sensor according to the present invention is configured by forming an electrode layer 2 made of a metal oxide or zeolite on one surface of an electrolyte 1 made of a cation conductor (a sodium superionic conductor in the embodiment). It is what is done.

  First, an example of a method for manufacturing a sensor according to the present invention as shown in FIG. 1 will be described.

As a raw material of the sodium superionic conductor used in the present invention, ethyl silicate ((C ₂ H ₅ ) ₄ SiO ₄ ), sodium silicate nonahydrate (Na ₂ SiO ₃ .9H ₂ O), ammonium dihydrogen phosphate using _{((NH 4) H 2 PO} 4) and dysprosium nitrate hexahydrate _{(Dy (NO 3) 3 ·} 6H 2 O). These were mixed and stirred for 1 hour, warmed to 75 ° C. to evaporate the water, and the resulting residue was dried at 120 ° C. overnight. The solid thus obtained was sintered at 720 ° C. for 4 hours, and then silicon dioxide (SiO ₂ ) was added and pulverized for 4 hours to obtain a powder.

This powder was pressed at 520 MPa and fired at 1050 ° C. for 6 hours to obtain a plate of sodium superionic conductor Na ₅ DySi ₄ O ₁₂ .

Next, a paste of Nb ₂ O ₅ with turpentine oil as a metal oxide electrode was applied onto a sodium superionic conductor plate produced by the above method, dried and fired at 500 ° C., A sensor having a thin film of metal oxide Nb ₂ O _{5 on} one surface of a sodium superionic conductor Na ₅ DySi ₄ O ₁₂ plate was obtained.

  As shown in FIG. 2, a gold mesh was placed on the electrode layer 2 of the sensor obtained by the above method as the test electrode 3, and platinum black and platinum mesh were placed on the electrolyte 1 as the reference electrode 4.

Nitrogen (N ₂ ) gas containing a trace amount of HCl or other gas (NO, NO ₂ , CO ₂ , O ₂ ) as a gas to be detected is supplied to the test electrode 3 of the measuring device, and air is supplied to the reference electrode 4. The electrode potential (potential difference ΔE (mV) between the test electrode and the reference electrode at 500 ° C.) was measured while changing the type and concentration of the gas to be detected.

The results are shown in Table 1.

  Here, “ΔE / dec” in the table indicates how the potential difference of the sensor element changes when the gas concentration becomes 10 times as the sensitivity of the sensor. The average sensitivity was calculated. That is, dec is a decade and indicates the slope when the digit is changed by one digit in the log of the logarithmic plot.

  Table 1 shows that the electrode potential depends on the HCl concentration, but the influence of other gas components such as oxygen is small.

  In addition, when the change in the electromotive force of the sensor was measured by changing the HCl concentration in the gas to be measured from 0 ppm to 500 ppm, the 90% response time was good at 5 minutes and it was suitable for continuous measurement of the HCl concentration. I understand.

On a plate of sodium superionic conductor Na ₅ DySi ₄ O ₁₂ produced by the method of Example 1, a paste of RuO ₂ in turpentine oil was applied, dried and fired at 500 ° C. A sensor having a thin film of metal oxide RuO _{2 on} one surface of an ionic conductor Na ₅ DySi ₄ O ₁₂ plate was obtained.

A test electrode 3 is installed in the sensor obtained by the above method in the same manner as in Example 1, and a small amount of HCl or other gas (NO, NO ₂ , CO ₂ , O _{2) is} detected as a gas to be detected on the test electrode 3. ) Containing nitrogen (N ₂ ) gas, air is supplied to the reference electrode 4, and the type and concentration of the gas to be detected are changed to change the electrode potential (potential difference ΔE (mV) between the test electrode and the reference electrode at 400 ° C.). ) Was measured.

The results are shown in Table 2.

  Table 2 shows that the electrode potential depends on the HCl concentration, but the influence of other gas components such as oxygen is small.

  In addition, when the change in the electromotive force of the sensor was measured by changing the HCl concentration in the gas to be measured from 0 ppm to 500 ppm, the 90% response time was good at 10 minutes and it was suitable for continuous measurement of the HCl concentration. I understand.

A paste of zeolite (ZSM-5 type) made of turpentine oil was applied on a plate of sodium superionic conductor Na ₅ DySi ₄ O ₁₂ prepared by the method of Example 1, dried and fired at 500 ° C. Thus, a sensor having a zeolite thin film on one surface of the sodium superionic conductor Na ₅ DySi ₄ O ₁₂ plate was obtained.

The sensor obtained by the above method is provided with the test electrode 3 in the same manner as in Example 1, and the test electrode 3 contains a trace amount of HCl or other gas (NO, CO ₂ , O ₂ ) as the gas to be detected. Nitrogen (N ₂ ) gas and air are supplied to the reference electrode 4, and the electrode potential (potential difference ΔE (mV) between the test electrode and the reference electrode at 400 ° C.) is measured by changing the type and concentration of the gas to be detected. did.

表３から、電極電位はＨＣｌ濃度に依存するが、二酸化炭素濃度や酸素濃度の影響は小さいことがわかる。 The results are shown in Table 3.

Table 3 shows that the electrode potential depends on the HCl concentration, but the influence of the carbon dioxide concentration and the oxygen concentration is small.

  In addition, when the change in the electromotive force of the sensor was measured by changing the HCl concentration in the gas to be measured from 0 ppm to 250 ppm, the 90% response time was 25 minutes, which is suitable for continuous measurement of the HCl concentration. I understand.

  By using the sensor of the present invention, an HCl gas concentration measuring device that is hardly affected by other gas components can be manufactured at low cost, and can be used for continuous measurement of HCl concentration in exhaust gas.

It is side surface sectional drawing which shows the structure of the sensor which concerns on this invention. It is a schematic diagram of the measuring device using the sensor concerning the present invention.

Explanation of symbols

1 Electrolyte 2 Electrode Layer 3 Test Electrode 4 Reference Electrode

Claims (3)

Cation conductor as an electrolyte, and possess at least one surface of the electrolyte of the metal oxide as an electrode layer, a test electrode on the electrode layer is provided, a hydrogen chloride gas sensor having a reference electrode in an electrolyte, the cation conductor but sodium super ionic conductor, a sodium ion conductor or a lithium ion conductor, metal _{oxide, RuO 2, Nb 2 O 5} , MoO 3 or WO ₃ is hydrogen chloride gas sensor. Cation conductor as an electrolyte, and to have a zeolite to at least one surface of the electrolyte as an electrode layer, a test electrode on the electrode layer is provided, a hydrogen chloride gas sensor having a reference electrode in an electrolyte, the cation conductor, A hydrogen chloride gas sensor which is a sodium superionic conductor, a sodium ion conductor or a lithium ion conductor . Sodium super ionic _conductor, hydrogen chloride gas sensor according to claim 1 or 2 is Na 5 DySi ₄ O _12.

Images