JP2015504174A - Zinc oxide sulfur sensor measurement system - Google Patents

Abstract

A measurement system for determining sulfur concentration in a liquid (34) such as liquid (34) fuel is disclosed. The measurement system includes a first electrode (32) that is at least partially coated with zinc oxide, more particularly with a zinc oxide microstructure (31). The zinc oxide microstructure (31) has a crystal lattice structure with a (002) plane orientation. The first electrode (32) may be connected to the electrometer (36), and may itself be connected to the second electrode (35). The second electrode (35) may be disposed on a common substrate (30) with the first electrode (32) or may be disposed substantially parallel to the first electrode (32). It may be in the form of a flat plate

Description

  The present disclosure relates generally to sensors and measurement systems that detect and measure sulfur concentration in a liquid. More particularly, the present disclosure relates to a sulfur measurement system comprising an improved zinc oxide sulfur sensor that measures sulfur concentration in a liquid and a method for manufacturing an improved sulfur measurement system that can be used on site by an operator.

The ability to accurately and reliably measure the concentration of sulfur in a liquid is important because various chemical reactions can release harmful sulfur compounds into the atmosphere or physical structure around the sulfur-containing liquid. is there. For example, when diesel fuel burns, sulfur oxide (SO ₂ , SO ₃ ) and sulfuric acid (H ₂ SO ₄ ) are generally generated, and these are components of acid rain and are subject to environmental regulations. In addition, these sulfur compounds are associated with catalyst poisoning in diesel exhaust particulate filters (DPFs), and sulfuric acid corrodes engine components such as coolers and piston ring liner components. there is a possibility. These phenomena can occur when using both high sulfur (> 350 ppm) and low sulfur (15-350 ppm) fuels.

  For these reasons and including the sensitivity of aftertreatment components to sulfur compounds, modern diesel engines are designed to use ultra-low sulfur diesel (ULSD) fuel (<15 ppmS). As a result of these design changes, low sulfur concentrations in diesel fuel are now essential for optimal performance of many modern diesel engines. Although detection of sulfur levels below 15 ppm in liquids is feasible in laboratories and other test facilities, such detection is currently accurate, portable, reliable, fast, and / or Or it cannot be done in the field with inexpensive sensors. Examples of known means for detecting very low levels of sulfur include flame photometric detection (FPD) and inductively coupled plasma (ICP) devices, both of which are instrument size and test cycle length. Therefore, it is suitable for the laboratory.

  Accordingly, there is a need for a sulfur measurement system that is small and easy to use and that allows equipment operators to quickly measure the concentration of sulfur compounds in diesel fuel on site.

  In one aspect, a liquid sulfur concentration measurement system is disclosed. The sulfur concentration measurement system may include a substrate that is at least partially coated with zinc oxide. If the substrate is an insulator, the first and second electrodes may be spaced apart between the substrate and the zinc oxide coating. Apply either a current source or a voltage source between the first and second electrodes and measure the voltage or current between the first and second electrodes including an electrometer, voltmeter or potentiometer Well this can correlate with the sulfur concentration in the liquid.

  In another aspect of the present invention, a sulfur concentration measurement system is disclosed that includes a sensor, which may include a plate-like first electrode that is at least partially coated with zinc oxide. Zinc oxide may have a microstructure with a (002) -oriented crystal lattice structure, and the sensor may also include a plate-like second electrode, which is spaced from the first electrode. And installed substantially parallel thereto. An open circuit potential between the first and second electrodes is generated by the adsorbed zinc oxide. The voltage stabilizes after a short time. The stable voltage level and / or the time taken for the voltage to stabilize can be used to measure the concentration of sulfur compounds in the liquid.

  In yet another aspect, a method for determining a sulfur concentration in a liquid is disclosed. The method includes applying a liquid to a sulfur sensor. The sensor may include a first electrode that is at least partially coated with a zinc oxide microstructure that protrudes from the first electrode. At least a part of the zinc oxide microstructure may have a (002) -oriented crystal lattice structure. The sulfur sensor may also have various forms of the second electrode. First, when one electrode (“working” electrode) is formed on an insulating substrate, the second (“reference”) electrode is also formed on the substrate away from the first electrode. Also good. Thereafter, both electrodes and the substrate are at least partially coated with a zinc oxide coating. Second, the first electrode is conductive and may be at least partially coated with a zinc oxide coating, or the first electrode may be deposited on an insulating substrate and then coated with zinc oxide. The second electrode is coupled to the first electrode / substrate, but may be spaced apart therefrom and disposed at least substantially parallel to the first electrode / substrate. When both the first and second electrodes are deposited on the insulating substrate under the zinc oxide coating, the method includes supplying a constant current between the first and second electrodes; Monitoring the voltage between the first electrode and the second electrode and correlating the stable voltage with the sulfur concentration in the liquid after the voltage has stabilized. When the substrate / first electrode / zinc oxide coating is physically separated from the second electrode, no current source or voltage source is required and a stable voltage between the first and second electrodes can be Alternatively, it may be measured with an electrometer or potentiometer.

1 is a cross-sectional view of a zinc oxide microstructure on a substrate or first electrode as disclosed herein. FIG. 1 is a schematic diagram of one method of open circuit potential measurement, wherein a sensor according to the present disclosure is at least partially submerged in a liquid to be measured and connected to a first electrode, which is connected to a potentiometer, The potentiometer is connected to a second electrode that is at least partially submerged in the liquid. 1 is a schematic perspective view of a sensor according to the present disclosure, including a first electrode spaced from a second electrode by a predetermined distance, both electrodes connected to a potentiometer, electrometer or voltmeter. It is a side view which shows connection with the 2nd electrode and 1st electrode by the fastener manufactured from the insulating material. FIG. 3 is a plan view of one shape of a first and / or second electrode according to the present disclosure. FIG. 6 is a plan view of another shape of the first and / or second electrode according to the present disclosure. The zinc oxide sensor according to the present disclosure graphically illustrates the ability to adsorb sulfur until the sulfur concentration reaches a specific value, indicating the concentration of sulfur and liquid. 2 graphically illustrates X-ray diffraction spectra of seven different zinc oxide coatings (AG) produced using either different precursors and / or different reaction conditions. FIG. 11 graphically illustrates the ability of a zinc oxide coating placed on a copper substrate, as shown in the photograph of FIG. 10, to adsorb sulfur in liquids at concentrations ranging from 1 ppm to 350 ppm. FIG. 13 graphically illustrates the ability of a zinc oxide coating on a stainless steel substrate according to the present disclosure, as shown in FIG. 12, to adsorb sulfur in liquids at concentrations ranging from 15 ppm to 3600 ppm. FIG. 15 shows two SEM photographs at different magnifications of a zinc oxide coating including a rod-like or ribbon-like microstructure that protrudes upward from the substrate and can adsorb a sulfur compound as shown in FIG. 14. 13 graphically illustrates the ability of the coating shown in FIG. 13 to adsorb and detect 5 ppm concentration of sulfur in about 100 seconds and adsorb and detect about 386 ppm concentration of sulfur in about 80 seconds; FIG. 14 graphically illustrates the sensitivity of a sensor made from the coating of FIG. Increased by the ability of sample 67 in FIGS. 18-19 to detect low concentrations (10.7 ppm to 48 ppm) of sulfur and liquid and high crystallinity in the (002) plane as shown in FIGS. The sensitivity of the obtained sample 67 is shown by a graph. Samples 23 in FIGS. 18-19 have the ability to detect low concentrations (10.7 ppm, 20.3 ppm, 48 ppm) of sulfur and liquid, and relatively in (002) plane as shown in FIGS. The graph shows the sensitivity of Sample 23 which is reduced compared to Sample 67 due to the low crystallinity. The sample 106 of FIGS. 18-19 has the ability to detect low concentrations (10.7 ppm, 20.3 ppm, 48 ppm) of sulfur and liquid, and is relatively low in the (002) plane as shown in FIGS. The sensitivity of the sample 106 which is lower than that of the sample 67 due to the degree of crystallinity is shown in a graph. The crystallinity of 18 zinc oxide coatings, in particular 4 of these zinc oxide coatings, in particular high crystals in the (002) plane of sample numbers 65, 67, 130, 134 produced using the same process parameters The degree of conversion is shown in a graph. The high crystal structure in the (002) plane of sample 67 compared with sample numbers 23 and 106 is shown in a graph. The increase in sensitivity of sample 67 compared to samples 23 and 106 is shown graphically. The improvement in response of sample number 23 to various sulfur concentrations is shown graphically, and improved response is obtained by rinsing the sensor with pentane between measurements, and rinsing with pentane is a stable indicator of sulfur concentration. This is indicated by the curve spike between the voltage levels. FIG. 5 is another graph of the repeatability of the measurements made by sample 23, with the sample being rinsed between measurements, the measurements being performed twice, in a different order, thereby determining the repeatability of the measurements by sample 23. Show. In a side view of a sensor according to the present disclosure consisting of an insulating substrate, two spaced electrodes formed on the substrate, and a zinc oxide coating according to the present disclosure at least partially covering the electrode and the substrate. is there. FIG. 24 is a top view of the sensor of FIG. 23, with the electrodes placed under the zinc oxide coating and shown in phantom lines.

  FIG. 1 shows a cross section of a substrate 30, which may be a first electrode that is at least partially coated with a plurality of zinc oxide microstructures 31. The microstructure 31 protrudes upward from the substrate 30 or the electrode. The term “microstructure” is used herein to describe the nature of the size of the zinc oxide protrusions, as will be appreciated by those skilled in the art, the actual size of the zinc oxide protrusions 31. The thickness may be close to the nanoscale or within its range, or greater than the microscale.

  The substrate 30 may be conductive or non-conductive. The non-conductive substrate 30 may be either ceramic or various non-conductive substrates that will be apparent to those skilled in the art. The conductive substrate may also be of various types, extra process steps for forming the first electrode 32 (see FIG. 2), attaching or coupling the first electrode 32 to the substrate 30, or oxidation. A separate manufacturing step for depositing on the substrate below the zinc protrusion 31 can be dispensed with. FIG. 2 is an open circuit potential system and does not require voltage or current input. The “first” electrode 32 is commonly referred to as the working electrode and the “second” electrode is generally referred to as the reference electrode. As the zinc oxide microstructure 31 adsorbs the sulfur compound, an electric potential is generated, which can be measured using the system shown in FIG.

  Other measurement systems according to the present disclosure are shown in FIGS. In this system, an insulating substrate 51 is used. After two electrodes 52, 53 are deposited on the substrate 51, a zinc oxide layer 54 is deposited thereon. Either a known current or voltage may be applied between the electrodes 52, 53, and the resulting potential or current between the electrodes 52, 53 may be measured by a voltmeter or electrometer 55. The resistance change caused by the adsorption of sulfur compounds to the microstructure 31 (FIG. 1) of the zinc oxide coating 54 can be manipulated by doping, changing the distance between the electrodes 52, 53, electrode pattern, etc. Is within the range suitable for measurement.

  The sulfur sensor and measurement system according to the present disclosure is designed based on the physical adsorption of organic sulfur compounds on zinc oxide. The inventors surprisingly found that the rate of physisorption of the organosulfur compound onto zinc oxide depends on the crystallinity of the zinc oxide and the (002) plane, ie from the substrate 30 or electrode of FIG. It has been found that the crystallinity of zinc oxide in the plane protruding outward from the surface 33 of the first electrode 32 shown in FIG. As described below, it has surprisingly been found that the rate of physisorption depends also on the rod-like or ribbon-like form of the zinc oxide coating and the oxygen-deficient state of the zinc oxide coating.

  The physical adsorption of organic sulfur compounds to zinc oxide is based at least in part on the high adsorption affinity of zinc oxide to organic sulfur compounds, which is due to the zinc oxide coating or the crystalline phase of the microstructure. When the organic sulfur compound is physically adsorbed on the zinc oxide protrusion, the resistance of the outer layer of the zinc oxide microstructure changes. The amount of change in resistance of the zinc oxide microstructure directly corresponds to the amount of sulfur compound available for reaction with zinc in the zinc oxide microstructure 31 in the liquid. In FIG. 2, this change in resistance can be measured by measuring the voltage change between the first and second electrodes 32, 35. Furthermore, as will be described later, the sulfur concentration can be determined by measuring the length of time it takes for the voltage to stabilize.

  With reference to FIG. 2, in one aspect, the substrate 30 has a zinc oxide coating (not shown) on the surface 33 of the substrate 30 and is at least partially submerged in the liquid 34. The second electrode 35 is also at least partially submerged in the liquid 34. The first and second electrodes 32 and 35 are connected to a potentiometer, electrometer or voltmeter 36. When the adsorption of the sulfur compound to the zinc oxide microstructure 31 (FIG. 1) on the substrate 33 proceeds, as shown in FIG. 7, an equilibrium state is established based on the concentration of the sulfur compound in the liquid to be measured.

  FIG. 3 shows an improved configuration for the sensor 38, which provides faster and more reliable results than the sensor 37 of FIG. The sensor 38 includes a first electrode 32, which is separated from the second electrode 35 by a distance D, which can range from about 0.2 to about 4 mm, and in one particular embodiment About 0.4 mm. The first and second electrodes 32, 35 are connected to wires 41, 42, which are coupled to a potentiometer, electrometer or voltmeter 36 as shown in FIG.

  The sizes of the first and second electrodes 32 and 35 may be greatly different, and the distance between the first and second electrodes 32 and 35 is the same. For example, the width of the first and second electrodes 32, 35 may be at least about 10 mm, and the length of the first and second electrodes 32, 35 may be at least about 25 mm. Good dimensions include 17 mm × 34 mm and 33.8 mm × 84.6 mm. In both combinations of dimensions, the gap distance D was set to about 0.4 mm.

  Since the sulfur measurement system according to the present disclosure can be used for dielectric fluids, for example, fuels including diesel fuel, the resistance between the second electrode 35 and the first electrode 32 is too high to open as shown in FIG. It has been found that accurate voltage measurement may not be possible in the circuit potential configuration. It has also been found that capacitive noise is generated by factors relating to positioning such as the distance and direction of the second electrode 35. As a result, the inventors surprisingly increased the surface area of the second electrode 35 from a rod-shaped structure to a flat-plate structure, and shortened the distance D between the first and second electrodes 32, 35. It has been discovered that both a reduction in resistance and an increase in capacitance are possible at the same time. For example, by changing the gap distance D to 3 mm and changing the second electrode 35 from a rod-shaped structure to a flat-plate structure having the same or similar dimensions as the first electrode 32, the first and second electrodes The resistance between 32 and 35 is reduced by a factor of about 60, thereby increasing the capacitance of the sensor 38 shown in FIG. 3 to about 60 times the capacitance of the sensor 37 shown in FIG. Dimensions found to be suitable for the stainless steel first and second electrodes 32, 35 include 17 mm × 34 mm and 33.8 mm × 84.6 mm. Of course, other sizes and dimensions are possible, as will be apparent to those skilled in the art.

  FIG. 4 shows the sensor 38 shown in FIG. 3 in which the electrodes 32, 35 are connected together at a fixed distance D by a plurality of fasteners 43. Fastener 43 should be made of an insulating material, including but not limited to polytetrafluoroethylene, polyamide or polyimide. The electrodes 32 and 35 are connected to a potentiometer, voltmeter or electrometer 36 by conductive wires 41 and 42 (FIG. 2). In FIG. 4, the electrodes 32 and 35 are provided with two openings 44 for receiving the insulating fasteners 43. FIG. 6 shows an alternative working or second electrode 132, 135 having six openings 45 for receiving insulative fasteners.

  In FIG. 7, the X axis is the concentration of the sulfur compound in the liquid to be measured, and the Y axis is the equilibrium constant for the adsorption of the sulfur compound on the zinc oxide microstructure. As can be seen from FIG. 7, when a specific concentration is reached, the adsorption equilibrium constant is the same even if the concentration is increased. Therefore, as will be described later, various sensor coatings effective for measuring various sulfur concentrations according to the (002) in-plane crystallinity, the form of the zinc oxide microstructure, and the oxygen-deficient state of the zinc oxide coating. Can be provided.

  As described above, a high degree of crystallinity in the (002) plane (generally perpendicular to the substrate or electrode) may indicate good adsorption of sulfur compounds to the zinc microstructure. Referring to FIG. 8, X-ray diffraction spectra for seven types of samples A to G are shown in a graph. The (002) in-plane crystallinity is indicated by a peak at or near 34 on the X-axis (2θ scale). Therefore, Samples A and C show no or little crystallinity along the (002) plane, whereas Samples B and D-G show crystallinity along the (002) plane. Sample G exhibits the highest level of crystallinity along the (002) plane.

  Referring to FIGS. 9-12, a comparison of different electrodes and different coating densities is shown. In FIG. 9, the copper electrode was coated with zinc oxide as shown in FIG. 10, but compared to FIG. 12, the zinc oxide coating of FIG. 10 was coated on the stainless steel electrode of FIG. Less dense. The lower density coating of FIG. 10 detects low concentrations of 1 ppm and 15 ppm and a higher concentration of 350 ppm sulfur, as shown in FIG. The higher concentration of 350 ppm was detected faster with the coatings of FIGS. 9-10 than with the concentrations of 15 ppm and 1 ppm. In contrast, the high density coating of FIG. 12 cannot detect a low concentration of about 1 ppm of sulfur compounds, and can detect higher concentrations of 15 ppm, 350 ppm, 3600 ppm of sulfur compounds. The 9-10 electrodes also detected concentrations of 15 and 350 ppm much faster than the electrodes of FIGS. Therefore, from FIGS. 9-12, higher density zinc oxide coatings are more beneficial for higher concentrations of sulfur compounds in the liquid, and lower density zinc oxide coatings are lower concentrations of sulfur compounds in the liquid. It can be concluded that it is more beneficial for faster measurement of

  Referring to FIG. 13, two SEM photographs of the same coating at different magnifications are shown. The sample of FIG. 13 was prepared using a furnace temperature of 500 ° C. and a high manifold temperature of 300 ° C. A zinc acetylacetone precursor was used and the coating process was performed for 2 hours at a pressure of 10 Torr. The flow rate of argon and oxygen was 50 ml / min. This procedure produces oxygen-deficient zinc oxide as shown in FIG. 13, which is an excellent rod-like structure that protrudes upward from the substrate (not shown), and therefore has a (002) in-plane crystal structure. The degree of conversion is high. As a result of measurement, it was found that the coating of FIG. 13 contained 3.31% by weight of carbon, 17.9% by weight of oxygen, 1.04% of chromium, 4.53% of iron, and 73.22% of zinc. It was proved by doing. The fully saturated zinc oxide (ZnO) coating has a zinc to oxygen ratio of 3.75, ie, the molecular weight of zinc (30) divided by the molecular weight of oxygen (8). Therefore, a ratio of 4.09 (73.22 / 17.9) indicates an oxygen-deficient zinc oxide coating.

  FIG. 14 graphically shows the response of the sensor coated with the coating of FIG. 13 to liquids with different amounts of sulfur compounds, specifically 5 ppm and 386 ppm. Since the voltmeter used for the measurement shown in FIG. 14 could not detect more than 15 volts, the combination of the sensor and the voltmeter used in FIG. 14 had a sufficient concentration of 4940 ppm as shown in FIG. Cannot be detected. FIG. 14 is also a sensor suitable for both low concentration sulfur compound detection (5 ppm) and relatively high concentration sulfur detection (386 ppm) due to the 0.7 micrometer thick rod-like structure of the coating of FIG. Is also provided. Furthermore, the response time is substantially reduced to about 100 seconds for a 5 ppm sulfur compound concentration liquid and to about 80 seconds for a 386 ppm sulfur compound concentration liquid.

  18-19 are bar graphs of X-ray diffraction (XRD) analysis of the crystal structure of zinc oxide coatings made with different parameters. Specifically, the cycle time, vacuum pressure, bubbler temperature, manifold temperature set point, and chamber temperature were all varied. Referring to FIG. 18, the same parameters are used for sample numbers 65, 67, 130, and 134. The parameters used to produce the sensor coating for samples 65, 67, 130, 134 are shown in the first or left column of Table 1 below. The other sample parameters shown in FIGS. 18 and 19 are also shown in Table 1.

  15-20 illustrate the importance of high crystallinity in the (002) plane for the zinc microstructure 31 coated on the first electrode 32. FIG. Specifically, in FIG. 15, the sample number 67 is shown as a graph in FIGS. 18 to 19, and as shown in FIGS. 18 to 19, shows a high crystallinity in the (002) plane. Sample 67 in FIG. 15 shows the ability to measure relatively low sulfur compound concentrations of 10.7 ppm and concentrations in the range of 20-24 ppm, but the sensitivity between 20 ppm and 24 ppm is somewhat less than desirable. Sample 67 in FIG. 15 also shows the ability to detect relatively high sulfur compound concentrations of 48 ppm and 36 ppm. The 36 ppm line shows a significant amount of noise due to controllable environmental factors.

  Referring to FIG. 16, the sample 23 of FIGS. 18-19 is shown. FIGS. 18-19 show that the crystallinity of the sample 23 in the (002) range is low, resulting in a first electrode coated with a zinc microstructure, but from 10.7 ppm to 20 .Sensitivity between 3 ppm is relatively low. The same is true for sample 106 in FIG. 17, which has a low (002) plane crystallinity as shown in FIGS. 18-19, resulting in sulfur between 10.7 ppm and 20.3 ppm. Low sensitivity at compound concentration.

  From Table 1, it can be seen that a plurality of elements affect the (002) plane crystal lattice orientation. These factors include cycle time, vacuum pressure, bubbler temperature, manifold temperature, and chamber temperature. Vacuum pressure and cycle time are the main factors, and manifold temperature, bubbler temperature, and chamber temperature appear to be secondary factors. Sample No. 67 made using the same parameters as Samples 65, 130, and 134 has a high (002) to (101) orientation ratio, so the vacuum pressure is somewhat higher at 15 Torr and the cycle time is about 7 hours. While maintaining the chamber temperature at about 500 ° C. by maintaining the chamber temperature at about 225 ° C. and the bubbler temperature at about 125 ° C., and less importantly, the zinc oxide micro has a strong (002) orientation. It is clear that a structure is provided. Of course, these parameters can vary greatly, and the parameters can be selected for specific applications, such as ultra low sulfur fuel versus high sulfur fuel.

  Referring to FIG. 20, it is clear that sample 67 provides the highest sensitivity between concentrations 10.7 ppm and 48 ppm. It can also be seen that all samples saturate or equilibrate in a relatively short time. Specifically, although somewhat slower than samples 23 (FIG. 16) and 106 (FIG. 17), sample 67 is 48 ppm, equilibrating at about 30 seconds at higher concentrations and about 50 seconds at lower concentrations.

  Finally, FIGS. 21-22 illustrate the reusability and repeatability of measurements using sensors and measurement systems according to the present disclosure. Referring to FIG. 21, the voltage stabilizes at about 6 volts, which correlates to a liquid sulfur compound concentration of about 11 ppm. The voltage is also stable below 5 volts, which correlates to a sulfur compound concentration of about 48 ppm. The voltage is also stable at about 7 volts, 7.5 volts and about 11 volts, which correlate to sulfur compound concentrations of about 135, 155 and 183 ppm, respectively. Since the instrument limit is about 15 volts, concentrations above 297 ppm are not detectable in sample 23. The peak between stable pressure values indicates that the sensor was rinsed with pentane between exposures to different liquids with different sulfur compound concentrations.

  The repeatability of the measurement of the sample 23 is shown in FIG. Specifically, reversing exposure to five liquids, 11 ppm, 48 ppm, 135 ppm, 155 ppm, 183 ppm and rinsing with pentane after the sensor is exposed to one liquid and before the sensor is exposed to the next liquid Was executed. The stabilization voltage values for sulfur compound concentrations of 11 ppm, 48 ppm, 135 ppm, 155 ppm, and 183 ppm are substantially equal in both cycles.

  The measurement system disclosed herein allows an operator to measure the sulfur content of a fuel before injecting it into a machine that may be designed to operate with a fuel of a specific sulfur concentration. Especially useful for field applications. The measurement system disclosed herein may be modified to make the sensor or electrode pair disposable or reusable, or the system may have a fuel tank prior to injecting a reasonable amount of fuel. It may be used as an on-board measurement system that determines the sulfur content of the fuel at the neck.

  As shown in FIG. 14, one sensor according to the present disclosure exhibits good sensitivity at both low concentration (5 ppm) and high concentration (386 pm). The sensor of FIG. 14 reaches the saturation point in about 100 seconds with 5 ppm liquid, while the sensor of FIG. 15 reaches the saturation point in about 1 minute or less for all concentrations. Therefore, the sensor and measurement system according to the present disclosure are sufficiently fast and can be used in the field with little inconvenience.

  As an alternative, the operator may monitor the length of time required to saturate the ZnO sulfur sensor, as indicated by the stabilization of the voltage in the sensor when the current remains constant. The operator may use a look-up table to correlate the stable voltage to the sulfur content, or the correlation can be automated using well-known automation techniques such as access to a series of look-up tables by a computer. Or an absolute sulfur reading may be issued to the operator.

  Any suitable deposition and / or growth scheme known in the art may be used to form the ZnO microstructure on the substrate. For example, as described above, MOCVD may be used to form a ZnO deposit on a conductive or ceramic substrate. FIG. 18 and Table 1 show the effect of vacuum pressure and cycle time or deposition time on (002) crystallinity, while the secondary factors are manifold temperature and bubbler temperature. FIG. 13 shows a suitable ZnO microstructure that can grow in about 2 hours, whereas a denser and thicker ZnO microstructure can grow in about 3.5 hours under the same conditions. The thickness of the ZnO microstructure shown in FIG. 13 is about 0.7 micrometers, and the density is suitable for allowing the ZnO microstructure to grow in a very random direction opposite from the substrate. On the other hand, by extending the deposition time to 3.5 hours, a ZnO microstructure having a thickness of about 1.0 micrometers can be obtained. Although this thickness itself is acceptable, the density of ZnO on the surface of the conductive substrate may be too high for low sulfur compound concentrations, which would prevent the interaction between the microstructure and the liquid Because it is done. With such a high density, the ZnO microstructure may have to grow very compact and orderly in the opposite direction from the substrate. Therefore, two or more sensors may be used for fuels having different sulfur concentrations.

  Although this disclosure refers to microstructures as ZnO microstructures, those skilled in the art will recognize incidental amounts of other elements that the microstructures may be extracted from the substrate during the deposition and growth process. It should be understood that it may have. For example, if the conductive substrate is stainless steel, the microstructure is about 1.0-5.0 wt% C, about 14.0-24.0 wt% O, about 0.5-1.5 wt%. % Cr, about 2.5-7.0 wt% Fe, and the remaining percentage Zn. In one example, the analysis showed that the ZnO microstructure grown on the stainless steel substrate had the following weight percent composition: That is, C-3.31, O-17.90, Cr-1.04, Fe-4.53, Zn-73.22.

  Regarding the time required to accurately measure the sulfur compound content in the liquid, among other factors, as shown in FIGS. 9, 11, 14-17, 21, 22, this is the material and dimensions of the electrode. , Depending on the spacing between the electrodes, the total liquid exposure surface area of the ZnO microstructure, and the sulfur concentration of the liquid. As can be seen from the data, when measuring the sulfur level of a fuel using a ZnO sulfur sensor formed in accordance with the present disclosure, increasing the liquid sulfur level results in a shorter response time and higher regulated voltage.

  FIGS. 23-24 illustrate a small and easy to manufacture system in which electrodes 52, 53 are formed on an insulating substrate, such as a silicon substrate, and then a zinc oxide coating 54 is formed thereon using the techniques described above. It is formed.

Claims (10)

In the sulfur concentration measurement system for liquids,
A first electrode (32) at least partially coated with zinc oxide;
A second electrode (35) spaced from the first electrode (32);
An electrometer (36) for measuring the voltage between the first and second electrodes (32, 35);
Including system.   The system of claim 1, wherein the zinc oxide has a crystal lattice structure having at least partially (002) plane orientation.   The system according to claim 1 or 2, wherein the first and second electrodes (32, 35) are flat plates placed at least substantially parallel to each other and spaced apart by a predetermined distance.   The system of claim 3, wherein the predetermined distance is in the range of about 0.2 to about 4 mm.   The system of claim 3, wherein the predetermined distance is about 0.4 mm.   The system according to any one of the preceding claims, wherein the reference and first electrodes (32) comprise stainless steel plates mounted at least substantially parallel to each other.   The first and second electrodes (32, 35) are connected to each other by at least one fastener made from at least one insulating material, but spaced at least partially parallel to each other. The system according to any one of claims 1 to 6.   The system of claim 7, wherein the insulator is selected from the group consisting of polytetrafluoroethylene, polyamide, polyimide.   The system according to claim 1, wherein the zinc oxide is in an oxygen-deficient state. In a method for determining a sulfur concentration in a liquid (34),
Applying a liquid (34) to the sulfur sensor (37), the sulfur sensor (37) including a first electrode (32) that protrudes at least partially from the first electrode (32); The zinc oxide microstructure (31) is coated, at least a part of the zinc oxide microstructure (31) has a (002) -oriented crystal lattice structure, and the sulfur sensor (37) is also connected to the first electrode (32 A second electrode (35) coupled to but spaced therefrom and disposed at least substantially parallel to the first electrode (32);
Monitoring the voltage between the first and second electrodes (32, 35);
Correlating the voltage with the sulfur concentration in the liquid (34) after the voltage has stabilized;
Including methods.

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