JP2009244224A - Moisture measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a moisture content measuring method and a moisture measuring device capable of correctly measuring moisture content even a specimen is in a stationary state or being imparted with vibration externally. <P>SOLUTION: The moisture measuring method is characterized in that on the insulative substrate, the electrodes of a sensor provided with micro-electrode cells arranged at least the interval across a pair of the cathode and the anode is 0.1 to 10 μm is immersed into the specimen, after that the electrodes are imparted with a voltage of ≥2.5 V, then the electrolytic current between the electrodes is measured. Thereby the water content in the specimen is obtained from the previously prepared calibration curve. The moisture measurement device is characterized by comprising: a sensor 1 having a micro-electrode cell; an electric source part 2; an electrolytic current measurement part 3; a current value output part 4; a reading part 5; a collation part 6; output part 7; and a display part 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a moisture measuring method and a moisture measuring device, and more specifically, a moisture measuring method and a moisture measuring method capable of easily and accurately quantifying moisture even when a specimen is in a flowing state, a stationary state, or a vibration state. Relates to the device.

  In recent years, there is a risk that the output of fossil fuels will decrease in the future, and because there is a demand for reduction of carbon dioxide emissions to prevent global warming, Mixing alcohol as fuel, such as ethanol, has been studied.

  The alcohol (ethanol) concentration in gasoline is currently about 3%, but it is said that it will be raised to about 10% in the future. As one of quality control of this alcohol, a moisture measuring means for managing the moisture in the alcohol is required.

  Conventionally, the Karl Fischer method has been used exclusively for the measurement of trace moisture. This method is a coulometric titration method using a Karl Fischer reagent, and since a trace amount of water can be absolutely determined within a few minutes, it is widely used as a batch-type desktop analyzer. However, the Karl Fischer method uses expensive reagents, which increases the cost of analysis, and complicates the equipment, leading to higher equipment costs and increased equipment maintenance costs. not being used.

  As an on-line type moisture measurement method, an infrared absorption method, a dielectric method, a conductivity method, an ultrasonic method, a thermal conductivity method, and the like are known.

  However, since the infrared absorption method measures the amount of reflection of near infrared rays, errors are likely to occur unless the sample surface is flat, and it is difficult to apply it to the measurement of dark samples. Since the dielectric constant or dielectric loss is measured, there is a problem that sufficient quantitative properties can be obtained only when the water content is in the range of about 0 to 50%. In addition, since the conductivity method is affected by the change in conductivity caused by organic acid or carbon dioxide, the measurement accuracy is lowered depending on the measurement environment (Patent Document 1). In particular, the conductivity method measures AC impedance, etc., so that there is no change in pH of the sample, and the ultrasonic method measures the amount of ultrasonic energy attenuation, so it is a homogeneous sample without bubbles, etc., thermal conductivity Since the method measures temperature changes due to heat pulses, it is required to be homogeneous data without bubbles, etc., so it is necessary to adjust the sample, and it is used only in a limited area as a general industrial instrument. This is the current situation, and it is never easy to automate.

Therefore, the present applicant measures an electrolytic current by a constant voltage electrolysis method using an electrode for a specimen containing moisture, and obtains a moisture amount based on a calibration curve prepared in advance from the current value, and A moisture measurement method was proposed previously. In this method in which the movement of electrons due to electrolysis of water depends on the stability of the diffusion layer, the distance between the cathode and the anode is set to 0.1 to 0.75 mm in order to improve measurement accuracy (Patent Document 2). . In this method, the moisture content of a wide range of specimens of about 0 to 90% can be easily measured.
JP, 2004-294448, A Capacitance type moisture sensor Japanese Patent Publication No. 7-69300

  However, the present inventors have found that there are still problems to be solved.

  If the distance between the cathode and the anode is 0.1 to 0.75 mm, the movement of electrons increases the degree of freedom to some extent, so that the accuracy is improved, but this is input particularly when measuring the moisture content of a stationary sample. Noise appeared in the output current (measurement current) for a specific voltage, and it was difficult to accurately measure the current value.

  It was also found that noise is likely to appear even when external vibration is applied.

  The inventors of the present invention have intensively studied a method capable of accurately measuring moisture even when the specimen is in a stationary state or in a state where vibration is applied from the outside, and have completed the present invention.

  Therefore, an object of the present invention is to provide a moisture measuring method and a moisture measuring apparatus capable of accurately measuring moisture even when a specimen is in a stationary state or in a state where vibration is applied from the outside.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
An electrode of a sensor having microelectrode cells arranged so that the distance between at least one pair of cathode and anode is 0.1 to 10 μm is immersed in a specimen on an insulating substrate, and then 2.5 V or more is applied to the electrode. A moisture measurement method characterized in that an electrolysis current between electrodes is measured by applying a voltage of 2 and a moisture content in the measured specimen is obtained based on a calibration curve prepared in advance.

(Claim 2)
2. The moisture measuring method according to claim 1, wherein the voltage applied to the electrode is a sine wave, rectangular wave or triangular wave of 2.5 V or more.

(Claim 3)
The moisture measuring method according to claim 1 or 2, wherein moisture measurement is performed on a specimen in a stationary state or an irregular vibration state.

(Claim 4)
A sensor having a microelectrode cell disposed on an insulating substrate so that a distance between at least one pair of cathode and anode is 0.1 to 10 μm, a power supply unit, an electrolytic current measuring unit, and a current value output unit; A moisture measuring device comprising a reading unit, a control unit, an output unit, and a display unit.

  According to the present invention, moisture can be accurately measured even when a specimen is in a stationary state or in a state where vibration is applied from the outside.

  The moisture measuring instrument according to the present invention is simple and economical and has excellent measurement accuracy, so it can be used in quality control by installing it in an alcohol tank, and is particularly useful in fields such as the chemical industry, food industry, and metal industry. It is.

  Embodiments of the present invention will be described below.

  FIG. 1 is a block diagram showing a moisture measuring apparatus of the present invention.

  This apparatus includes a sensor 1, a power supply unit 2, an electrolytic current measurement unit 3, a current value output unit 4, a reading unit 5, a control unit 6, an output unit 7, and a display unit 8.

  The sensor 1 is a microelectrode cell in which at least a pair of a cathode and an anode are arranged on an insulating substrate so that the interval is 0.1 to 10 μm. The electrode is formed on the insulating substrate by a lithography technique. , And the like manufactured by covering with an insulating film leaving the electrode.

  Further, it is preferable to form a reference electrode having a reference substance on the same substrate and a counter electrode facing the reference electrode.

  Reference numerals 11 and 12 denote lead wires connected to the anode and the cathode, respectively.

  When measuring moisture, the sensor 1 is immersed in the specimen. It is possible to deal with a specimen that contains moisture and can be immersed in the sensor 1.

  Furthermore, since the plurality of working electrodes are arranged at intervals of μm level (0.1 to 10 μm), the sensor 1 does not need to maintain a constant flow rate in the specimen in order to form the diffusion layer.

  This point will be described.

  First, diffusion is a physical phenomenon in which molecular species move from a thicker side to a thinner side.

  The formation of a diffusion layer can be defined as a state in which a steady concentration gradient is formed.

  The diffusion rate of the oxidant or reductant generated by electrolysis can be obtained as the diffusion distance (λ) by the following formula 1 obtained by modifying Fick's law.

Here, t is time (seconds) and D is a diffusion constant. If t = 1, D = 1 × 10 ⁻⁵ cm · sec ⁻¹ , and √40≈6, then λ = 6 × 10 ⁻² mm, and a diffusion rate (ion migration rate) of at least about 60 μm per second. ).

  When the distance between the cathode and the anode is 0.1 to 10 μm, the cathode and the anode are present at a distance much smaller than 60 μm, which is a range in which ions can diffuse and move in one second. An electrolytic current is generated, and an accurate current value can be measured.

  In other words, since a diffusion phase that is in a steady state is formed without causing a liquid flow, even when the specimen is in a stationary state, an electrolytic current due to steady diffusion occurs, and the current value can be measured based on the moisture content. Is possible.

  Further, in this state, it is hardly affected by mechanical fluctuation such as vibration smaller than about 10 Hz. This is because ions move between the positive and negative electrodes faster than the influence of vibration. Note that “less than about 10 Hz” means that the frequency is 10 cycles or less per second.

  For this reason, the moisture measuring apparatus of the present invention can measure the moisture content without being affected by vibration even when the apparatus of the present invention is installed in an alcohol tank loaded on a car or the like that normally generates irregular vibrations of 10 Hz or less. High versatility.

  On the other hand, if the distance between the electrodes is 0.1 mm (= 100 μm) as in the prior art, the movement of ions takes 1 second or more, so noise is likely to occur in a stationary sample.

  The power supply unit 2 applies a voltage higher than the electrolysis voltage of water to the sensor 1, preferably a voltage higher than 2.5V.

  Applying a voltage of 2.5 V or more means that the difference between the anode potential and the cathode potential is 2.5 V or more. (Figure 2)

  The voltage applied by the power supply unit 2 is preferably an alternating voltage that reverses the polarity (+, −) at regular intervals from the viewpoint of preventing the formation of an oxide film on the electrode surface and the electrodeposition of various substances on the electrode. The water content can be measured with high accuracy with little decrease in electrolytic current value.

  The application method may be simply alternating current (sine wave), rectangular wave or triangular wave, and in the case of rectangular wave or triangular wave, they may be applied continuously or at intervals.

  As a frequency of the voltage to apply, the range of 0.01-1 Hz is preferable, More preferably, it is 0.1-0.5 Hz.

  When voltage is applied, water is electrolyzed and current flows. This current (constant potential electrolysis, output current) is measured by the electrolysis current measuring unit 3. Since the capacitor current of the present microelectrode pair becomes very small, there is almost no problem of a decrease in quantification due to the capacitance current immediately after voltage application.

  The current value measured by the electrolytic current measuring unit 3 is output from the current value output unit 4, and the reading unit 5 reads the current value. The read current value is compared with a calibration curve prepared in advance in the control unit 6 to determine the water content.

  The amount of water determined by the control unit 6 can be output from the output unit 7 to the display unit 8 such as a monitor. In addition, the amount of water can be recorded constantly or intermittently in a storage unit (not shown).

  In the moisture measuring method of the present invention, since the moisture content is obtained from the electrolytic current value, it is not subject to interference by organic acids or carbon dioxide, which is a problem in the conductivity method, but correction is required in a strong acid environment.

  Examples of the present invention will be described below, but the present invention is not limited to such examples.

Example 1
The sensor was immersed in the specimen, the potential was swept in the range of −0.9 V to +0.9 V, and the electrolysis current was measured while changing the moisture content.

Sample: ethanol Water content: 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.06%, 0.1%, 0.14%

  The measurement results are shown in FIG. Even a very small amount of moisture could be detected.

Example 2
When using ethanol with a water content of 0.1% as a sample and measuring the container in which this sample is placed in a stationary and stationary state (stationary system sample), the container is shaken irregularly by hand and vibrated. When measured in the given state (vibration system sample), when stirred with a stirrer and measured in a state where a constant liquid flow is generated (stirring system sample), the sensor is immersed, and from -0.9 V to +0. The potential was swept in the range of 9 V, and the electrolysis current was measured.

  The measurement results are shown in FIG. Almost the same measurement results were obtained for the stationary sample, vibration sample, and stirring sample.

Example 3
Using a sensor having a distance of 5 μm between electrodes and applying a voltage with a sine wave, the electrolysis current was measured for a stationary specimen. For comparison, the electrolysis current was measured in the same manner using a conventional sensor (electrode spacing 0.1 mm).

  Sample: Isopropanol containing a trace amount of water (about 2 ppm)

  FIG. 5 (A) shows the input voltage, FIG. 5 (B) shows the electrolysis current measured by a sensor having a distance between electrodes of 5 μm, and FIG. 5 (C) shows the electrolysis current measured by a conventional sensor.

  (B) moves substantially the same as (A), while (C) is distorted and difficult to read.

Example 4
Using the same specimen as in Example 3, a sensor with a 5 μm gap between electrodes was used, and a voltage was applied with a rectangular wave, and the electrolysis current was measured for a stationary specimen. For comparison, the electrolysis current was measured in the same manner using a conventional sensor (electrode spacing 0.1 mm).

  FIG. 6 (A) shows the input voltage, FIG. 6 (B) shows the electrolysis current measured by a sensor having a distance between electrodes of 5 μm, and FIG. 6 (C) shows the electrolysis current measured by a conventional sensor.

  In (C), since the capacitor current flows immediately after application, the latter half (broken line circle) becomes the current reading region.

Example 5
Using the same sample as in Example 3, a sensor having a 5 μm gap between electrodes was used, a voltage was applied with a triangular wave, and the electrolytic current was measured for a stationary sample. For comparison, the electrolysis current was measured in the same manner using a conventional sensor (electrode spacing 0.1 mm).

  FIG. 7 (A) shows the input voltage, FIG. 7 (B) shows the electrolysis current measured by a sensor having a distance between electrodes of 5 μm, and FIG. 7 (C) shows the electrolysis current measured by a conventional sensor.

  (B) behaves almost the same as (A), while (C) is distorted and difficult to read.

The block diagram which shows the moisture measuring apparatus of this invention Measurement principle diagram Graph showing the measured current at each moisture content A graph showing the electrolysis current in a stationary sample, vibration sample, and stirring sample The figure which shows the relationship between the input voltage and measurement current in Example 3. The figure which shows the relationship between the input voltage and measurement current in Example 4. The figure which shows the relationship between the input voltage and measurement current in Example 5.

Explanation of symbols

1: Sensor 11, 12: Lead wire 2: Power supply unit 3: Electrolytic current measuring unit 4: Current value output unit 5: Reading unit 6: Control unit 7: Output unit 8: Display unit

Claims (4)

  An electrode of a sensor having a microelectrode cell arranged so that the distance between at least one pair of cathode and anode is 0.1 to 10 μm on an insulating substrate is immersed in a specimen, and then 2.5 V or more is applied to the electrode. A moisture measurement method characterized in that an electrolysis current between electrodes is measured by applying a voltage of 2 and a moisture content in the measured specimen is obtained based on a calibration curve prepared in advance.   2. The moisture measuring method according to claim 1, wherein the voltage applied to the electrode is a sine wave, rectangular wave or triangular wave of 2.5 V or more.   The moisture measuring method according to claim 1 or 2, wherein moisture measurement is performed on a specimen in a stationary state or an irregular vibration state.   A sensor having a microelectrode cell disposed on an insulating substrate so that a distance between at least one pair of cathode and anode is 0.1 to 10 μm, a power supply unit, an electrolytic current measuring unit, and a current value output unit; A moisture measuring device comprising a reading unit, a control unit, an output unit, and a display unit.

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