Halogenated gas sensor

Abstract

A halogenated gas sensor for sensing a halogenated gas comprising at least a first metal electrode and a second metal electrode connected to a sensing material comprising at least one of NaAlSiO4, KAlSiO4, RbAlSiO4, CsAlSiO4.

Description

[[Technical Field]]

[0001] A bead-type sensor for a highly sensitive and selective sensor for detecting halogenated gas is manufactured using a material containing at least one component having a chemical formula of NaAlSiO₄, KAlSiO₄, RbAlSiO₄ or CsAlSiO₄. The sensor includes a central electrode, a coil and a sensing material. The coil is heated when current flows through the coil. The sensing material is porous. The conductance between the central electrode and the heated coil changes depending on the concentration of the halogenated gas.

[0002] The present invention relates to an improvement of a bead-type sensor for highly sensitive detection of refrigerant gases such as hydrofluoroolefins (HFO) and hydrofluorocarbons (HFC), which exhibit a much lower global warming potential than halogenated gases, particularly hydrochlorofluorocarbons (HCFC). [[Background Art]]

[0003] There are several existing techniques for detecting halogenated gases. Tin oxide-based metal oxide semiconductor (MOS) sensors are used for detecting halogenated gases, but these sensors exhibit cross-sensitivity to many hydrocarbons and humidity. Non-dispersive infrared (NDIR) optical sensors are also used for detecting halogenated gases, but the sensitivity of these sensors is limited and they are expensive to manufacture.

[0004] Solid bead sensors for detecting halogenated gases are relatively inexpensive to manufacture. These sensors are disclosed by Loh in U.S. Patent No. 3,751,968, by Lee in U.S. Patent No. 5,104,513, by Stetter in U.S. Patent No. 5,226,309, and by Yannopoulos in U.S. Patent No. 5,932,176. Loh disclosed a sensing element comprising a glass ceramic containing a mixture of lanthanum oxide, lanthanum fluoride, and sodium silicate. Lee disclosed a ceramic sensing element comprising a mixture of potassium silicate and a compound selected from the group consisting of silicon dioxide and aluminum oxide. Stetter disclosed a sensing material comprising sodium lanthanum fluoride silicate having the chemical formula NaLa(SiO4)3F. Yannopoulos disclosed a sensing element comprising sodium titanate.

[0005] The operating temperature of the sensor described in U.S. Patent No. 5,226,309 is 500°C to 600°C, which is too low to detect HFOs and HFCs with adequate sensitivity. Lee disclosed a ceramic sensing element containing a mixture of potassium silicate and aluminum oxide in a ratio between approximately 0.25 to 4.0 parts by weight of potassium silicate and 1 part by weight of aluminum oxide. Due to the wide ratio range and the lack of a clearly defined phase of the sensing material, achieving reproducible sensor performance is not easy. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 3751968 [Patent Document 2] U.S. Patent No. 5104513 [Patent Document 3] U.S. Patent No. 5226309 [Patent Document 4] U.S. Patent No. 5932176 [Overview of the project] [Problems that the invention aims to solve]

[0007] An object of the present invention is to find a defined material for the selective and highly sensitive detection of HFOs and HFCs. Another object of the present invention is to find a sensing material having a high melting temperature, thereby enabling highly sensitive sensor operation at high temperatures from 800°C to 1000°C. [Means for solving the problem]

[0008] The halogenated gas sensor of the present invention is defined by independent claim 1. Accordingly, the gas sensor comprises at least a first metal electrode and a second metal electrode, which are connected to a sensing material comprising at least one of NaAlSiO4, KAlSiO4, RbAlSiO4, and CsAlSiO4.

[0009] The sensing material may be in the form of beads, in which two electrodes are at least partially embedded.

[0010] One of the two electrodes may be a coil that surrounds the other of the two electrodes acting as the central electrode.

[0011] The first electrode may be made of platinum or contain platinum, and / or the second electrode may be made of platinum or contain platinum.

[0012] A voltage source may be connected to at least the first electrode and may heat the electrode to a temperature in the range of 400°C to 1200°C, 400°C to 1000°C, 600°C to 1200°C, or 600°C to 1000°C by a current or voltage applied to the electrode.

[0013] The first sensor may be in the form of a coil having a first end and a second end on the opposite side, the two ends of which are connected to a voltage source (1), and the second electrode is a central electrode in the form of a longitudinal linear element or rod that passes through the center of the coil (4) and extends along the longitudinal axis of the coil, the coil and the central electrode are surrounded by the sensing material and embedded in the sensing material.

[0014] The present invention also provides a method for detecting a halogenated gas using the above-described sensor, wherein the sensing material is heated to a temperature in the range of 400°C to 1000°C, 400°C to 1200°C, 600°C to 1000°C, or 600°C to 1200°C by applying current or voltage to the first sensor or coil.

[0015] The current passing through the coil after the sensor is exposed to the gas to be detected may be divided by the current passing through the coil before the sensor is exposed to the gas to be detected.

[0016] Furthermore, the present invention provides a method for manufacturing the halogenated gas sensor described above, wherein the sensing material comprises at least a first component (A) made from a molecular sieve (3A), the molecular sieve (3A) being heated to a first temperature of several hundred degrees Celsius and held at the first temperature for several hours, preferably 3 hours, and then heated to a second temperature higher than the first temperature and held at the second temperature for 2 hours, the 2nd hour preferably coinciding with the first hour.

[0017] The first component can then be pulverized to obtain fine particles having an average size of less than 5 μm, preferably about 3 μm.

[0018] The first component may contain NaAlSiO4 and KAlSiO4, preferably in a 1:1 ratio.

[0019] The sensing material may comprise at least a second component (B) prepared by ion exchange performed using molecular sieve (4A) and CsNO3, wherein said molecular sieve and CsNO3 are preferably mixed in deionized water.

[0020] A mixed suspension of the molecular sieve, CsNO3 and deionized water may be stirred for several hours, preferably 24 hours, after which the suspension is preferably centrifuged, then heated at a first temperature of several hundred degrees Celsius, preferably about 900°C for at least 1 hour, preferably 2 hours, and then further heated at a second temperature higher than said first temperature, preferably 1100°C for another several hours, preferably about 3 hours.

[0021] Said second component (B) may be pulverized after the heat treatment into fine particles having an average size of several micrometers, preferably about 4 μm.

[0022] Said first component (A) and / or said second component (B) can be mixed with a vehicle to form a slurry, said vehicle is preferably hydroxypropyl cellulose dissolved in water in an amount ranging from 5 wt% to 10 wt%, and the weight ratio of said component (A) and / or (B) to said vehicle in the mixture is about 2:1.

[0023] Exemplary embodiments of the present invention described below are explained with reference to the drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] [Figure 1] Fig. 1 is a schematic diagram of a sensor according to an embodiment of the present invention. [Figure 2] Fig. 2 shows steps of a typical process for manufacturing a sensor using an exemplary sensing material. [Figure 3] Fig. 3 shows scanning electron microscope images at magnifications of 30 times and 1600 times. [Figure 4] Fig. 4 shows typical sensor responses to 100 ppm of R134a and 100 ppm of R1234yf. [Figure 5] This shows typical sensor responses to various concentrations of R134a. [Figure 6] This shows typical sensor responses to various gases / vapors. [Modes for carrying out the invention]

[0025] Sensor components The schematic diagram in Figure 1 shows the sensor of the present invention, which includes a central electrode 7, preferably a platinum wire, surrounded by a metal coil 4, preferably a platinum coil. Both are embedded in a bead 5, which contains at least one of NaAlSiO4, KAlSiO4, RbAlSiO4, and CsAlSiO4. The coil is heated to a temperature of 400°C to 1000°C by an applied voltage 1. A current 6 is generated by the applied voltage 3 between the central electrode 7 and the coil 4. The nominal resistance of the sensor is the ratio of voltage 2 to current 6, which varies with the halogenated gas concentration surrounding the sensor.

[0026] Material A for bead 5 is Alfa Aesar's linear form K n Na 12-n [(AlO2) 12 (SiO2) 12 It is synthesized using molecular sieve 3A as a starting material, which has ]·xH2O (n is approximately 6). The process for manufacturing the sensor is shown in Figure 2. For example, 50 g of molecular sieve 3A was placed in a furnace and heated to 900 °C at a heating rate of 5 °C / min, held at 900 °C for 3 hours, then heated to 1100 °C at a heating rate of 5 °C / min, and held at the same temperature for 3 hours. After waiting for the material to cool to room temperature, it was pulverized using a planetary ball mill (Retsch PM100) to obtain fine particles with an average size of approximately 3 μm. The XRD diffraction spectrum of the pulverized material was collected using a PANalytical X'Pert PRO XRD system. It was confirmed to contain only NaAlSiO4 and KAlSiO4. Elemental analysis by energy-dispersive X-ray spectroscopy (EDS) confirmed that the ratio of NaAlSiO4 to KAlSiO4 was 1:1. Material B is molecular sieve 4A (Na of AlfaAesar) 12[(AlO2) 12 (SiO2) 12 The material was prepared by ion exchange using 4A molecular sieve (NaAlSiO4·nH2O) and CsNO3. Typically, 5 g of molecular sieve 4A and 16.5 g of CsNO3 were mixed in 85 mL of deionized water. The pH was adjusted to 8 with NaOH solution. The suspension was stirred for 24 hours. The suspension was then centrifuged. The remaining material was ion-exchanged two more times with a solution of 16.5 g of CsNO3 and 85 mL of water, and the final remaining material was washed three times with deionized water and dried overnight in air at 80°C. The material underwent additional heat treatment in air, including heating at 900°C for 2 hours and then at 1100°C for a further 3 hours. After heat treatment, the material was ground using a mortar and pestle. Fine particles with an average size of approximately 4 μm were obtained. Elemental analysis by energy-dispersive X-ray spectroscopy (EDS) showed that the ratio of NaAlSiO4 to CsAlSiO4 was 1:1. NaAlSiO4 and KAlSiO4 have melting points of 1526°C and 1750°C, respectively. Therefore, they are expected to exhibit a long lifespan at operating temperatures up to 1000°C.

[0027] Sensor manufacturing Material A or / or Material B was mixed with a vehicle to obtain a slurry. The vehicle was 5% to 10% (by weight) of hydroxypropyl cellulose dissolved in water. The weight ratio of material to vehicle was approximately 2:1. First, the slurry was coated onto the central electrode, and the coating was allowed to dry. Next, the coated central electrode was inserted into the heating coil. Additional slurry was added around the coil to form a complete bead covering the heating coil. The finished sensor was then heated to 850°C for 0.5 to 2 hours at a heating rate of 1°C / min to 5°C / min. After the sensor had cooled to room temperature, it was ready for testing. Sensors prepared with materials A / B are denoted as sensors A / B. Figure 3 shows SEM images of a typical sensor A at 30x and 1600x magnification. The high-magnification images show a highly porous morphology.

[0028] Sensor performance Sensor A is heated to approximately 800°C by passing an electric current through the coil during operation. The current (6) in Figure 1 varies with the refrigerant gas concentration. The current before gas exposure is denoted as I0, and the current after gas exposure is denoted as Ig. The ratio of Ig / I0 is defined as the sensitivity. Figure 4 shows that sensor A responds very quickly to 100 ppm R134a (CH2FCF3) and 100 ppm R1234yf (CF3CF=CH2). Figure 5 shows the sensitivity of sensor A to various concentrations of R134a. A leak detector with a typical sensor A can intermittently detect a leak rate of 0.6 g / year of R134a for at least 3 months. Figure 6 shows the sensitivity of sensor A to various gases / vapors at 100 ppm. The sensor does not respond to 100 ppm isobutene (R600a), hydrogen, isopropanol, and methane (CH4), but it shows a good response to 100 ppm R134a and 100 ppm R1234yf. The sensor made of material B exhibits similar sensor performance to sensor A, and it is possible to obtain higher sensitivity by operating sensor B at higher temperatures from 800°C to 1200°C.

[0029] While the present invention has been described in the above specification with reference to specific embodiments thereof, those skilled in the art will recognize that the invention is not limited thereto. Different features and aspects of the above disclosure can be used individually or in combination.

Claims

1. A halogenated gas sensor for detecting halogenated gases, comprising at least a first metal electrode and a second metal electrode, wherein the first metal electrode and the second metal electrode are made of NaAlSiO ４ , KAlSiO ４ RbAlSiO ４ , CsAlSiO ４ Connected to a sensing material containing at least one of the following, A halogenated gas sensor wherein the first metal electrode is in the form of a coil having a first end and a second end on the opposite side, the two ends of which are connected to a voltage source (1), and the second metal electrode is a central electrode in the form of a longitudinal linear element or rod extending through the center of the coil (4) along the longitudinal axis of the coil, and the coil and the central electrode are surrounded by and embedded in the sensing material.

2. The sensor according to claim 1, wherein the sensing material is in the form of beads, and two electrodes are at least partially embedded therein.

3. The sensor according to claim 1 or 2, wherein the first metal electrode is made of platinum or contains platinum, and / or the second metal electrode is made of platinum or contains platinum.

4. The sensor according to any one of claims 1 to 3, comprising at least a voltage source connected to the first metal electrode and configured to heat the first metal electrode to a temperature in the range of 400°C to 1200°C, 400°C to 1000°C, 600°C to 1200°C, or 600°C to 1000°C by a current or voltage applied to the first metal electrode.

5. A method for detecting halogenated gases using a sensor according to any one of claims 1 to 4, wherein the sensing material is heated to a temperature in the range of 400°C to 1000°C, 400°C to 1200°C, 600°C to 1000°C, or 600°C to 1200°C by applying current or voltage to the first metal electrode or coil.

6. The method for detecting a halogenated gas according to claim 5, wherein the current passing through the coil after the sensor has been exposed to the gas to be detected is divided by the current passing through the coil before the sensor has been exposed to the gas to be detected.

7. A method for manufacturing a halogenated gas sensor according to any one of claims 1 to 4, wherein the sensing material comprises at least a first component (A) made from a molecular sieve (3A), the molecular sieve (3A) being heated to a first temperature of 900°C, held at the first temperature for a first time of 3 hours, then heated to a second temperature of 1100°C, and held at the second temperature for a second time of 3 hours. The first component is NaAlSiO ４ and KAlSiO ４ A method characterized by including

8. The method according to claim 7, wherein the first component is then pulverized to obtain fine particles having an average size of less than 5 μm.

9. The first component is NaAlSiO ４ and KAlSiO ４ The method according to claim 7 or 8, comprising in a 1:1 ratio.

10. The sensing material comprises molecular sieve (4A) and CsNO ３ The method according to any one of claims 7 to 9, wherein the sensing material comprises at least a second component (B) prepared by ion exchange performed using

11. The molecular sieve (4A) and CsNO ３ The method according to claim 10, wherein the mixture is mixed in deionized water.

12. Molecular sieves (4A), CsNO ３ The method according to claim 10, wherein the mixed suspension of water and deionized water is stirred for 24 hours, and then the mixed suspension is centrifuged.

13. The method according to claim 12, wherein, after centrifugation, the mixed suspension is heated at a first temperature of 400°C to 1000°C for at least 1 hour, and then heated at a second temperature of 1100°C for a further 3 hours.

14. The method according to claim 12, wherein the second component (B) is pulverized after heat treatment to obtain fine particles having an average size of 4 μm.

15. The method according to any one of claims 10 to 14, wherein the first component (A) and / or the second component (B) are mixed with a vehicle to form a slurry.

16. The method according to claim 15, wherein the vehicle is hydroxypropyl cellulose dissolved in water in an amount of 5% to 10% by weight, and the weight ratio of the mixture of the first component (A) and / or the second component (B) to the vehicle is 2:1.

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