Abstract:
A chemical sensor for assessing a chemical of interest. In typical embodiments the chemical sensor includes a first thermocouple and second thermocouple. A reactive component is typically disposed proximal to the second thermal couple, and is selected to react with the chemical of interest and generate a temperature variation that may be detected by a comparison of a temperature sensed by the second thermocouple compared with a concurrent temperature detected by the first thermocouple. Further disclosed is a method for assessing a chemical of interest and a method for identifying a reaction temperature for a chemical of interest in a system.

Description:
GOVERNMENT RIGHTS 
       [0001]    The U.S. Government has rights to this invention pursuant to contract number DE-AC05-00OR22800 between the U.S. Department of Energy and Babcock &amp; Wilcox Technical Services Y-12, LLC. 
     
    
     FIELD 
       [0002]    This disclosure relates to the field of detectors for chemicals. More particularly, this disclosure relates to in-situ sensors for detecting, quantifying, and/or analyzing chemicals. 
       BACKGROUND 
       [0003]    In many chemical processes it is often desirable to detect the presence, quantity, and/or qualities of certain chemicals of interest. For example, in many closed chemical processes (either batch or continuous) the generation or infiltration of certain deleterious chemicals can damage or ruin the effectiveness of the process. By continually or periodically monitoring such processes the presence and/or amount of a deleterious chemical may be timely reported and damage to the system may be averted. As another example many systems include a residual or “background” concentration of an undesirable chemical that is acceptable. However, once the background level increases to a certain threshold limit, the higher concentration of the undesirable chemical becomes unacceptable and some action must be taken to avert danger to persons or damage to man-made materials and/or the environment. Accurate and sensitive monitoring techniques are tools that are used for these and similar types of applications. 
         [0004]    One difficulty in monitoring certain chemical processes is that such monitoring may in itself have a negative effect on a system being monitored. For example, the presence of a monitoring device may interrupt system flow or adversely affect system output quality. Often, negative effects associated with certain monitoring equipment are due to the size of the monitoring equipment or the requirement of actively interjecting such monitoring equipment into a system from outside the system. Additionally, many chemical monitor devices or monitoring systems are limited in that only the presence of a particular chemical may be indicated as opposed to indicating quantity and/or quality information. 
         [0005]    What are needed therefore are chemical sensors that are capable of passively monitoring a particular application in-situ so that the application is substantially unaffected by the presence of the sensor. What are also needed are chemical sensors and/or sensor systems that are capable of generating accurate and detailed quantification information based on differences in temperature gradients over time. What are further needed are in-situ chemical sensors that are capable of indicating a threshold event using an expendable and very small sensing apparatus. 
       SUMMARY 
       [0006]    In one embodiment the present disclosure provides a chemical sensor for assessing a chemical of interest in a system having an operational temperature that varies over a temperature range. The sensor includes a first thermocouple disposed in the system and configured for exhibiting a first electrical property that varies over the temperature range according to a first calibration curve. The sensor further includes a first detector assembly including a second thermocouple and a proximate first reactive component, the first detector assembly disposed adjacent the first thermocouple in the system and wherein the second thermocouple is configured for exhibiting a second electrical property that varies over the temperature range according to a second calibration curve, and wherein the first reactive component undergoes a first chemical reaction correlating to a first maximum temperature property variation if the first reactive component is exposed to a first chemical of interest, and wherein the second electrical property changes according to a temperature change caused by the first chemical reaction. In one embodiment, the first reactive component is attached adjacent a first surface along the second thermocouple and the first detector assembly further includes a second reactive component attached adjacent a second surface along the second thermocouple. In another embodiment, the second thermocouple further includes a selective barrier attached adjacent the second thermocouple such that the first reactive component is substantially prevented from being exposed to chemicals that are substantially incapable of transporting through the selective barrier. 
         [0007]    The embodiments described above preferably include a reader configured to compare the first electrical property and the second electrical property, to use the first calibration curve and the second calibration curve to calculate a first maximum temperature property variation between the first thermocouple and the second thermocouple wherein the first maximum temperature property variation varies according to a third calibration curve associated with the chemical of interest, and to use the first maximum temperature property variation between the first thermocouple and the second thermocouple along with the third calibration curve to indicate the presence of the first chemical of interest. The reader is preferably further configured for recording time stamped temperature property data for the first thermocouple and the second thermocouple. In a related embodiment, the reader is further configured for using the time stamped temperature property data to generate first chemical reaction data based on the time stamped temperature property data associated with the first chemical reaction. In yet another related embodiment, the reader is further configured for analyzing the first chemical reaction data according to an analysis program known to a person having ordinary skill in the art and generating output data based on an analysis of the first chemical reaction data 
         [0008]    In a related embodiment, a chemical sensor is disclosed wherein the first reactive component includes a first chemical substance that yields a product when exposed to the chemical of interest during the first chemical reaction and wherein the product reacts with a second chemical substance in the reactive component, defining a second chemical reaction that includes a second maximum temperature property variation, wherein the magnitude of the second maximum temperature property variation is greater than the magnitude of the first maximum temperature property variation. 
         [0009]    Another embodiment includes one of the chemical sensors described above wherein the sensor further includes a calibration assembly including a third thermocouple adjacent the first thermocouple and a first non-reactive component proximate the third thermocouple, the third thermocouple configured for generating a third electrical property that varies over the temperature range, wherein the first non-reactive component is selected so as to substantially imitate the heat transfer properties of the first reactive component, wherein the variation of the third electrical property may be compared by the reader to the variation of the first electrical property, and wherein the effect of any difference between the variation of the first electrical property and the variation of the third electrical property may be accounted for during the calculation of the first maximum temperature property variation. 
         [0010]    Yet another related embodiment includes one of the chemical sensors described above and further includes a second detector assembly comprising a third thermocouple and a proximate second reactive component, the second detector assembly disposed adjacent the first thermocouple in the system and wherein the third thermocouple is configured for generating a third electrical property that varies over the temperature range according to a third calibration curve, and wherein the second reactive component undergoes a second chemical reaction if the second reactive component is exposed to a second chemical of interest, and wherein the third electrical property changes according to a temperature change induced by the second chemical reaction. 
         [0011]    An embodiment of one of the chemical sensors described above may further include a second detector assembly including a third thermocouple and a proximate second reactive component, the second detector assembly disposed adjacent the first thermocouple in the system and wherein the third thermocouple is configured for generating a third electrical property that varies over the temperature range according to a third calibration curve, and wherein the second reactive component undergoes a second chemical reaction if the second reactive component is exposed to a second chemical of interest, and wherein the third electrical property changes according to a temperature change induced by the second chemical reaction, the reader configured to compare the first electrical property and the third electrical property, to use the first calibration curve and the third calibration curve to calculate a second maximum temperature property variation between the first thermocouple and the second thermocouple wherein the second maximum temperature property variation varies according to a fourth calibration curve, and to use the second maximum temperature property variation between the first thermocouple and the third thermocouple along with the fourth calibration curve to indicate the presence of the second chemical of interest. 
         [0012]    Another embodiment provides a closed system including an enclosed structure and an embodiment of one of the chemical sensors described above attached to the interior of the enclosed structure. 
         [0013]    The disclosure also provides embodiments of a method for assessing a chemical of interest in a system. One embodiment includes the steps of (a) measuring a first electrical property value based on the conditions at a reference location within the system; (b) triggering a first chemical reaction by exposing a reactive material to a chemical of interest at an experimental location inside the system; (c) measuring a second electrical property value based on the conditions at the experimental location within the system; (d) comparing the measurement of the first electrical property value with the measurement of the second electrical property value; and (e) identifying the chemical of interest based on calibration data and the comparison of the measurement of the first electrical property value with the measurement of the second electrical property value. 
         [0014]    In a related embodiment, the method described above further includes the steps of (f) recording a plurality of first electrical property values during a first time period Δt 1 ; and (g) recording a plurality of second electrical property values during a second time period Δt 2 . 
         [0015]    In another related embodiment, the method described above wherein the second time period Δt 2  is substantially identical to the first time period Δt 1 . 
         [0016]    In a related embodiment, the method described above further includes the step of (h) calculating temperature variation deviation data based on a deviation between first temperature variation data associated with the plurality of first electrical property values and second temperature variation data associated with the plurality of second electrical property values, wherein the plurality of first electrical property values are associated with the first temperature variation data based on a first calibration curve, and wherein the plurality of second electrical property values are associated with the second temperature variation data based on a second calibration curve. 
         [0017]    In a related embodiment, the method described above further includes the step of (i) calculating quantitative mass data of the chemical of interest based on the generated thermal excursion data and the calculated temperature variation deviation data. 
         [0018]    In yet another related embodiment, the method described above further includes the step of (j) estimating the remaining shelf life of an object located in the system based on the calculated quantitative mass data of the chemical of interest and a known relationship between the chemical of interest and the object. 
         [0019]    The disclosure also provides embodiments of a method for identifying a reaction temperature for a chemical of interest in a system. The method includes the steps of (a) measuring a plurality of first electrical property values based on the conditions at a reference location within the system; (b) exposing a reactive material to a chemical of interest at an experimental location inside the system; (c) measuring a plurality of second electrical property values based on the conditions at the experimental location within the system; (d) comparing the measured plurality of first electrical property values with the plurality of second electrical property values; (e) measuring the temperature of the system adjacent the reference location and the experimental location; and (f) controlling the temperature of the system so that the measured temperature in the system remains substantially unchanged and is therefore known when measurements are taken of the plurality of first electrical property values and the plurality of second electrical property values. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
           [0021]      FIG. 1  shows a somewhat schematic side view of an embodiment of a chemical sensor in a system; 
           [0022]      FIG. 2  shows a somewhat schematic side view of a related embodiment of a chemical sensor in a system; 
           [0023]      FIG. 3  shows a somewhat schematic side view of another related embodiment of a chemical sensor in a system; 
           [0024]      FIG. 4  shows a somewhat schematic side view of an embodiment of a thermocouple joint; 
           [0025]      FIG. 5  shows a somewhat schematic side view of another related embodiment of a chemical sensor in a system; 
           [0026]      FIG. 6  shows a somewhat schematic side view of another related embodiment of a chemical sensor in a system in which a selective barrier is shown; 
           [0027]      FIG. 7  shows a diagram of an embodiment of a method for detecting, quantifying, and/or analyzing a chemical of interest; 
           [0028]      FIG. 8  shows a diagram of a related embodiment of a method for detecting, quantifying, and/or analyzing a chemical of interest; and 
           [0029]      FIG. 9  shows a diagram of an embodiment of a method for determining a reaction temperature of a chemical of interest. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration the practice of specific embodiments of chemical detection sensors and systems. It is to be understood that other embodiments may be utilized, and that structural changes may be made and processes may vary in other embodiments. 
         [0031]      FIG. 1  illustrates one embodiment of a chemical sensor  10 . The sensor  10  includes a reference thermocouple  12  and a first experimental thermocouple  14  adjacent the reference thermocouple  12 . The basic functioning and structure of thermocouples are known to a person having ordinary skill in the art, so background information on thermocouple structure and basic function will not be covered in depth here. The first experimental thermocouple  14  forms part of a first detector assembly  16  including both the first experimental thermocouple  14  and a first reactive component  18  attached proximate to the first experimental thermocouple  14  at a first joint  20 . In the embodiment shown in  FIG. 1 , the sensor  10  is located in a closed system  22  defined at least in part by an enclosing structure  24 . The sensor  10  is preferably very small so that it does not interfere with any processes or functioning of the system  22 . For example, the width of the first experimental thermocouple leads preferably ranges from about 3×10 −3  inches to about 5×10 −3  inches, and most preferably is about 3×10 −3  inches, shown as length “W” in  FIG. 1 . The preferred small size range also allows for many thermocouples to be present in the system  22  for monitoring, analyzing, and/or detecting various chemicals of interest simultaneously. The width W may be significantly larger in other applications. Additionally, the length “L” of the first experimental thermocouple  14  leads may vary depending on the application. Although the system  22  in  FIG. 1  is defined as a closed system, the sensor  10  may also be used in open systems. The sensor  10  is preferably provided in the system  22  in-situ during manufacturing of the system  22 . 
         [0032]    During sensor  10  operation, the reference thermocouple  12  yields an electrical property, more preferably, a slight voltage variation (ΔV R ) at a first reference location  26  wherein the voltage variation ΔV R  corresponds to a temperature variation (ΔT R ) according to a first calibration curve. An example of a calibration curve for a Type J thermocouple correlating ΔV to ΔT is given by the fifth order polynomial Equation (1) below wherein “T” represents temperature variation in degrees Centigrade, “x” represents voltage variation given in volts, and coefficient values for a 0 , a 1 , a 2 , a 3 , a 4 , and as are given in Table 1 below. 
         [0000]        T=a   0   +a   1   x+a   2   x   2   +a   3   x   3   +a   4   x   4   +a   5 x 5    Eq. 1 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 a 0   
                 −0.048868252 
               
               
                   
                 a 1   
                 19873.14503 
               
               
                   
                 a 2   
                 −218614.5353 
               
               
                   
                 a 3   
                 11569199.78 
               
               
                   
                 a 4   
                 −264917531.4 
               
               
                   
                 a 5   
                 2018441314 
               
               
                   
                   
               
             
          
         
       
     
         [0033]    Although a Type J thermocouple is given as an example, all types of thermocouples are contemplated by this disclosure including, but not limited to, Type E, Type K, Type R, Type S, and Type T thermocouples. 
         [0034]    During operation of the sensor  10 , the first experimental thermocouple  14  yields a slight voltage variation (ΔV E1 ) at a second reference location  28  wherein the voltage variation ΔV E1  corresponds to a temperature variation (ΔT E1 ) according to a second calibration curve. Preferably, the second calibration curve is substantially identical to the first calibration curve. The first reactive component  18  is selected based on a high likelihood of reaction with a chemical of interest. A “chemical of interest” may include one or more chemical species that may be in any physical form (e.g., solid, liquid, gas, plasma). If a chemical of interest becomes present in the system  22 , the first reactive component  18  will react through a first chemical reaction with the chemical of interest. The first chemical reaction is either exothermic or endothermic at some level, thereby causing ΔV E1  to differ from ΔV R . Thus, ΔT E1  differs from ΔT R . 
         [0035]    The sensor  10  preferably includes a reader  30  for comparing ΔV E1  to ΔV R . Reader  30  also preferably is capable of generating temperature variation data comparing ΔT E1  to ΔT R  based on ΔV E1  and ΔV R  according to the first calibration curve and the second calibration curve. The reader  30  may be in direct contact with the system  22  or, alternatively the reader may be in indirect contact with the system  22  (e.g., a wireless connection). In a preferred embodiment, the reader  30  generates a first maximum temperature variation T 1   max  which is equal to ΔT E1  minus ΔT R  and which varies according to a third calibration curve associated with the chemical of interest. If T 1   max  fits substantially with the third calibration curve within a pre-defined confidence interval, the reader  30  preferably indicates that the chemical of interest is present. In one embodiment, the reader  30  indicates the presence of the chemical of interest by signaling an alarm  32 . The third calibration curve is preferably generated from data resulting from directly testing the first reactive component  18  in the presence of the chemical of interest. 
         [0036]    A specific example of a sensor configuration for sensor  10  includes the use of lithium oxide (Li 2 O) as the first reactive component (or a portion of the first reactive component) as a “getter” for moisture (H 2 0). For example, one mole of lithium oxide will react with one mole of water at approximately 25° C. resulting in an exothermic reaction that yields two moles of lithium hydroxide (LiOH). Other thermodynamic data for this particular reaction at different temperatures is given in Table 2 below. Because the thermodynamic data for this particular reaction (and many other reactions for many other chemical species) are known, the temperature change caused by such a reaction is known and may be used to identify whether water (or some other reactant) is in fact reacting with the first reactive component (e.g., lithium oxide). More specifically (using the example of Li 2 O and water), if water is present in the system, T 1   max  should correlate directly with the anticipated difference between ΔT E1  and ΔT R  according to the third calibration curve, wherein the third calibration curve is generated based on thermodynamic data similar to that found in Table 2. Although the example given above may be used to determine the presence of one specific chemical species of interest, other embodiments using a first reactive component including only a single reactive species are contemplated that are selective to multiple chemical species (e.g., species in a particular range such as a&lt;T max &lt;b, wherein “a” represents the lower boundary of the range and “b” represents the upper boundary of the range). An example may include a first reactive component that reacts with more than one chemical of interest, thereby potentially exhibiting a plurality of T max  values correlating, respectively, to a plurality of chemicals of interest. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 T 
                 ΔH 
                 ΔS 
                 ΔG 
                   
                   
               
               
                 (° C.) 
                 (KJ) 
                 (J/Kelvin) 
                 (KJ) 
                 K 
                 Log(K) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 −79.278 
                 2.872 
                 −80.063 
                 2.050E+15 
                 15.312 
               
               
                 25 
                 −86.090 
                 −21.940 
                 −79.549 
                 8.665E+13 
                 13.938 
               
               
                 50 
                 −86.869 
                 −24.450 
                 −78.968 
                 5.829E+12 
                 12.766 
               
               
                 75 
                 −87.610 
                 −26.658 
                 −78.329 
                 5.662E+11 
                 11.753 
               
               
                 100 
                 −88.308 
                 −28.595 
                 −77.637 
                 7.393E+10 
                 10.869 
               
               
                 125 
                 −88.967 
                 −30.306 
                 −76.901 
                 1.229E+10 
                 10.090 
               
               
                 150 
                 −89.595 
                 −31.837 
                 −76.124 
                 2.498E+09 
                 9.398 
               
               
                 175 
                 −90.204 
                 −33.234 
                 −75.310 
                 6.006E+08 
                 8.779 
               
               
                   
               
             
          
         
       
     
         [0037]    With reference to the Type J thermocouple example above, experimental data has shown that, at or about 20 degrees Centigrade, the ratio of volts to degrees Centigrade is 51×10 −6  volts per degree Centigrade or 51 microvolts per degree centigrade (μV/° C.). Thus, in order for a sensor associated with a Type J thermocouple to detect a change of 1×10 −1 ° C., the sensor must be capable of a resolution of approximately 5.1 μV. For a Type R thermocouple, for example, the ratio of volts to degrees Centigrade is 7 μV/° C. Thus, in order for a sensor associated with a Type R thermocouple to detect a change of 1×10 −1 ° C., the sensor must be capable of a resolution of approximately 7×10 −1  μV. When high resolution is necessary, the opportunity for interference or “background noise” to creep into the system is significant. 
         [0038]    A preferred embodiment of the disclosure avoids many of the issues associated with background noise. In this embodiment as shown in  FIG. 2 , the first reactive component  18  includes a first chemical substance  18 A and a second chemical substance  18 B. The first chemical substance  18 A yields a product when exposed to the chemical of interest during the first chemical reaction. The product then reacts with the second chemical substance  18 B through a second chemical reaction. The second chemical reaction causes a second maximum temperature variation T 2   max  wherein T 2   max  is greater than T 1   max . By including the second chemical substance  18 B in the first reactive component  18  and causing the variation between ΔV E1  and ΔV R  to increase, the sensor is more readily able to resolve such variation and thereby more accurately indicate the variation between ΔT E1  and ΔT R . With a more precise determination of the variation between ΔT E1  and ΔT R , the sensor is better able to precisely determine the variation between T 2   max  and T 1   max , thereby providing information regarding whether the chemical of interest is present. If the second chemical substance  18 B were not included in the first reactive component of this embodiment, the chemical of interest may be more difficult or impossible to detect because of the relatively small magnitude of the variation between ΔV E1  and ΔV R  after the first chemical reaction but before the second chemical reaction. 
         [0039]    In another embodiment, the reader  30  is configured for time stamping multiple measurements of ΔV E1  and ΔV R , thereby providing time stamped recorded values for ΔT E1  and ΔT R  based on the first calibration curve and the second calibration curve. First chemical reaction data may then be generated based on the time stamped values of ΔT E1  and ΔT R . The first chemical reaction data may include, for example, time plots that indicate reaction kinetics associated with the first chemical reaction including the duration of the first chemical reaction. Additionally, the first chemical reaction data may be analyzed to calculate the amount (e.g., concentration) of the chemical of interest detected in the system or any other calculations of interest that may be based in whole or in part on the first chemical reaction data. Second chemical reaction data may also be generated based on the time stamped values of ΔT E1  and ΔT R  and analyzed in a similar manner to the first chemical reaction data. 
         [0040]    The conductive heat transfer effects, if any, of the first reactive component  18  on the first joint  20  are preferably accounted for by including a calibration assembly  34  with the sensor  10  as shown in  FIG. 3 . The calibration assembly  34  includes a second experimental thermocouple  36  adjacent the reference thermocouple  12 . During sensor  10  operation, the second experimental thermocouple  36  yields a slight voltage variation (ΔV E2 ) which corresponds to a temperature variation (ΔT E2 ) according to a fourth calibration curve. The fourth calibration curve is preferably substantially identical to the first calibration curve. A first non-reactive component  38  is attached proximate to the second experimental thermocouple  36  at a second joint  40 . The first non-reactive component  38  is selected to substantially imitate the heat transfer properties of the first reactive component  18  so that any measurable difference between ΔT E2  and ΔT R  may be attributed to the presence of the first non-reactive component  38  proximate to the second joint  40 . Because the first non-reactive component  38  substantially imitates the heat transfer properties of the first reactive component  18 , the variation between the measured ΔV E2  and ΔV R  may be used to calibrate the reader  30  and/or the first experimental thermocouple  14  by subtracting the difference between ΔT E2  and ΔT R  from the calculated value of T 1   max  and/or the time stamped differences between ΔT E1  and ΔT R . 
         [0041]      FIG. 4  shows a close-up view of an embodiment of a modified experimental thermocouple  42  including a first modified experimental thermocouple lead  44  and a second modified experimental thermocouple lead  46  attached together along an experimental thermocouple joint  48 . The aspect ratio of the experimental thermocouple joint preferably ranges from about 1.0 to about 1.5, although the aspect ratio could be broader in other embodiments. In one embodiment, the width “W” of the leads ranges from about 3×10 −3  inches to about 5×10 −3  inches and is most preferably about 3×10 −3  inches. An embodiment of a chemical sensor may include, for example, the modified experimental thermocouple  42  oriented adjacent a similarly structured reference thermocouple to operate in a fashion similar to embodiments of the chemical sensor  10  discussed above. 
         [0042]    In yet another embodiment shown in  FIG. 5 , a chemical sensor  50  includes a reference thermocouple  12  and a first experimental thermocouple  52  adjacent the reference thermocouple  12 . The first experimental thermocouple  52  forms part of a first detector assembly  54  including the first experimental thermocouple  52 , a first reactive component  56  attached proximate a first surface  58  of a joint  60  along the first experimental thermocouple  54 , and a second reactive component  62  attached proximate a second surface  64  of the joint  60 . The variation in an electric property (e.g., voltage) across the joint  60  is attributable to one of four basic events (excluding the possibility of apparatus malfunction) including (a) a reaction between the first reactive component  56  and a first reactant of interest, (b) a reaction between the second reactive component  62  and a second reactant of interest, (c) the simultaneous reaction between the first reactive component  56  and the first reactant of interest and a reaction between the second reactive component  62  and the second reactant of interest, or (d) a reaction between the first reactive component  56  and the second reactive component  62 . Because the identities of the first reactive component  56  and the second component  62  are known, the properties (e.g., thermodynamic empirical data and reaction kinetics data) of these components are known or calculable. Therefore, the components may be (and preferably are) selected so that event (d) does not occur in any significant amount. Moreover, indicia corresponding to different absolute quantitative measurements of variation in an electric property produced along the joint  60  may be categorized as being associated with one of the three events described above (i.e., (a), (b), or (c)). 
         [0043]    Another embodiment shown in  FIG. 6  includes a chemical sensor  64  that further includes a reference thermocouple  12  and a first experimental thermocouple  66  adjacent the reference thermocouple  12 . The first experimental thermocouple  66  forms part of a first detector assembly  68  including the first experimental thermocouple  66 , a first reactive component  70  attached proximate a joint  72  located along the first experimental thermocouple  66 , and a selective barrier  74  (e.g., a semi-permeable membrane) attached adjacent the first reactive component  70 , thereby only allowing selected materials to contact and react with the first reactive component  70 . The selective barrier  74  may include any semi-permeable membrane or other chemical or physical barrier known to a person having ordinary skill in the art. In a related embodiment, the selective barrier  74  may substantially cover the entire exposed area of the first experimental thermocouple  66  including any reactive component thereon. The latter embodiment may be useful in applications where undesirable reactants are present that could corrode or otherwise interfere with the performance of the first experimental thermocouple  66 . 
         [0044]    The disclosure also includes embodiments of a method for assessing a chemical of interest in a system. The term “assessing” (and other forms of this term) are to be understood as including the act of detecting, quantifying, and/or analyzing. In a first embodiment shown in  FIG. 7 , the method includes a step of measuring a first electrical property value based on the conditions at a reference location within the system (Step  110 ). An example includes sensor  10  measuring ΔV R  at the reference thermocouple  12 . Another step includes triggering a first chemical reaction by exposing a reactive material to a chemical of interest at an experimental location inside the system (Step  112 ). An example of this step includes using sensor  10  to detect a chemical of interest such that a first chemical reaction is triggered when the first reactive component  18  begins to react with the chemical of interest. An additional step includes measuring a second electrical property value based on the conditions at the experimental location within the system (Step  114 ). An example of this step includes measuring ΔV E1  at the first experimental thermocouple  14 . Yet another step includes comparing the measurement of the first electrical property value (e.g., ΔV R ) with the measurement of the second electrical property value (e.g., ΔV E1 ) (Step  116 ). Step  116  may be carried out, for example, by the reader  30 . Another step in this embodiment includes identifying the chemical of interest based on calibration data (e.g., the first calibration curve, the second calibration curve, and the third calibration curve) and the comparison of the measurement of the first electrical property value (e.g., ΔV R ) with the measurement of the second electrical property value (e.g., ΔV E1 ) (Step  118 ). 
         [0045]    In a related embodiment shown further in  FIG. 7 , the method described above further includes a step of recording a plurality of first electrical property values during a first time period Δt 1  (Step  120 ). These and other recordings could be made, for example, by the reader  30 , and the reader  30  could correlate measured voltage values to time using a chronometric device either built into the reader  30  or operatively attached to the reader  30 . The embodiment may include a further step of recording a plurality of second electrical property values during a second time period Δt 2  (Step  122 ). In a preferred embodiment, Δt 1  is substantially identical to Δt 2 . 
         [0046]    In yet another embodiment further shown in  FIG. 7 , the embodiments described above, whether including Step  120  and  122  or not, may further include a step of calculating temperature variation deviation data based on a deviation between first temperature variation data associated with the plurality of first electrical property values and second temperature variation data associated with the plurality of second electrical property values, wherein the plurality of first electrical property values are associated with the first temperature variation data based on a first calibration curve, and wherein the plurality of second electrical property values are associated with the second temperature variation data based on a second calibration curve (Step  124 ). For example, a plurality of values similar to T 1   max  could be calculated by the reader  30  based on a corresponding plurality of time stamped values of ΔV R  and ΔV E1  as described above. This data could then be plotted or otherwise used to calculate thermal excursion data during Δt 1  and Δt 2 . 
         [0047]    Another embodiment includes the additional step of calculating quantitative mass data of the chemical of interest (Step  126 ) based on the results from Step  124 . 
         [0048]    In a related embodiment, a method including at least steps  110 ,  112 ,  114 ,  116 ,  118 , and  124  further includes a step of estimating remaining shelf life of an object located in the system based on the calculated results of Step  124  and a known relationship between the chemical of interest and the object (Step  128 ). For example, if components of a system are known to fail (based on, e.g., empirical data) after a specific amount (e.g., mass) of exposure to a chemical of interest, shelf life may be estimated by certain embodiments of the sensor  10  based on, for example, (1) rate of reaction data between the chemical of interest and the first reactive component  18  determined by the sensor  10  and (2) quantitative mass data of the chemical of interest determined by the sensor  10 . 
         [0049]    The disclosure further includes an embodiment of a method of assessing a chemical of interest in a system using chemical sensor  10 , the method including the steps shown in  FIG. 8  as follows: measuring a first electrical property based on the conditions at a first thermocouple (Step  210 ); exposing a first reactive component to a chemical of interest at a second thermocouple (Step  212 ); measuring a second electrical property based on the conditions at the second thermocouple during a thermal excursion at the second thermocouple caused by a first chemical reaction (Step  214 ); comparing the measurement of the first electrical property with the measurement of the second electrical property value (Step  216 ); and identifying the chemical of interest based on calibration data and the comparison of the measurement of the first electrical property with the measurement of the second electrical property (Step  218 ). 
         [0050]    The disclosure also includes an embodiment of a method for identifying a reaction temperature for a chemical of interest in a system. The method, shown in  FIG. 9 , includes a step of measuring a plurality of first electrical property values based on the conditions at a reference location within the system (Step  310 ). Additional steps include exposing a reactive material to a chemical of interest at an experimental location inside the system (Step  312 ); measuring a plurality of second electrical property values based on the conditions at the experimental location within the system (Step  314 ); comparing the measured plurality of first electrical property values with the plurality of second electrical property values (Step  316 ); measuring the temperature of the system adjacent the reference location and the experimental location (Step  318 ); and controlling the temperature of the system so that the measured temperature in the system remains substantially unchanged and is therefore known when measurements are taken of the plurality of first electrical property values and the plurality of second electrical property values (Step  320 ). The term “exposing” as used with regard to Step  312  and elsewhere herein is hereby defined to include either passive or active exposure, or both. “Passive” exposure may be broadly understood as merely placing a reactive material in a particular place. “Active” exposure, on the other hand, is to be understood as doing more than merely placing a reactive material in a particular place such as, for example, introducing a catalyst directly to or near the reactive component so that the reactive component is more or less likely to react and/or, for example, altering the temperature of the reactive component and/or its surroundings. 
         [0051]    The method for identifying a reaction temperature for a chemical of interest in a system may be accomplished using the sensor  10 . The comparing step described in Step  316  may be accomplished, for example, using the reader  30  described above or any other similar device known to a person having ordinary skill in the art. With regard to Step  318 , the temperature of the system may be controlled by a thermostat or other temperature control device known to a person having ordinary skill in the art. The temperature control device or other associated device (e.g., reader  30 ) may also be configured to record the temperature of the system at regular intervals or based on one or more specific recording signals. The temperature control device (e.g., thermostat or reader  30 ) may be configured for generating, sending, or receiving a recording signal so that the temperature of the system (e.g., system  22 ) is at least recorded substantially when a chemical reaction begins between the reactive material (e.g., the first reactive component  18 ) and the chemical of interest. Alternatively, if system temperature is recorded on a regular basis within the system, the time substantially when a chemical reaction begins between the reactive material and the chemical of interest may be calculated by interpolation or other technique based on the recorded time data, temperature data, and/or any other applicable data (e.g., voltage data). 
         [0052]    In summary, embodiments are disclosed herein for various chemical detection sensors and/or systems. The foregoing descriptions of embodiments have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of principles and practical applications, and to thereby enable one of ordinary skill in the art to utilize the various embodiments as described and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.