Calorimetric sensor setup based on the Tian-Calvet principle

Abstract

Calorimetric sensor setup according to the Tian-Calvet principle, which is formed with adjacent insulating segments (9) and sensitive segments (10) which are plate-shaped or have a circular segment-shaped cross-section, wherein the insulating segments (9) and the sensitive segments (10) are designed to form a sample chamber (3a) and enclose a sample arranged therein and temperature sensors, in particular thermocouples, are present on and / or in sensitive segments (10) which are electrically connected in series and / or connected to electrical contact terminals (5), wherein insulating segments (9, 11) and sensitive segments (10) are formed from different materials, and the materials from which insulating segments (9, 11) and sensitive segments (10) are formed have different thermal conductivities, wherein the material from which insulating segments (9, 11) are formed has a lower thermal conductivity than the material with which sensitive segments (10) are formed.

Description

[0001] The invention relates to a sensor setup for a calorimeter based on the Tian-Calvet principle. Calorimeters are often used to determine the energy absorbed or released by a sample during chemical or physical processes. Examples include the determination of free enthalpies of chemical reactions and the measurement of heat capacities. Typically, a sample and an inert reference sample are placed on identical temperature sensors in a furnace. During the measurement, a defined temperature program is run in the furnace, which induces the exothermic or endothermic calorific processes to be measured in the sample. The temperature profile in the inert reference sample then solely reflects the characteristic thermal properties of the temperature sensor. These depend on the design and material selection of the respective sensor.The measured temperature profile of the sample results from the identical thermal properties of the identically constructed sensor and the calorific processes to be measured. If the difference between the signals from the sample and the reference is then calculated, the characteristic thermal properties of the temperature sensors can be eliminated, leaving only the pure measurement signal of the sample. If a sample with known properties is measured, a device-specific calibration constant can be determined. This represents the relationship between the measured differential temperature signal and the absorbed or released energy. The device can thus be used to measure unknown calorific processes.

[0002] Currently, most calorimeters are of the Boersma or Tian-Calvet type. Boersma-type devices are typically constructed such that a sample and reference sample are placed in a crucible and positioned at two different positions on a disk-shaped sensor. Using thermocouples mounted on the disk beneath both crucibles, the temperature difference at the two positions is then determined. This system is widely used because it is very sensitive for small sample quantities and has a short time constant. A disadvantage is the high heat loss due to convection from the sample to the furnace, as the sample is exposed on a plate in the furnace without thermal insulation. This heat loss lowers the sample temperature, which reduces the measurement signal level and worsens the detection limit.

[0003] Tian-Calvet instruments are designed with thermocouples arranged radially symmetrically around a cylindrical sample cuvette, which determine the respective temperature difference between the sample and the reference sample relative to the surrounding furnace. This allows the system to be better insulated than with Boersma instruments, increasing measurement sensitivity. The major advantage of this design is that the sample volume can be larger, thus providing space for a large number of temperature sensors, usually thermocouples. This allows for very high volume-specific measurement sensitivity.

[0004] EP 1717566 A1 discloses a thermoanalytical sensor using multilayer technology. Several thermocouples are incorporated into a disk consisting of several ceramic layers. This disk serves as a calorimetric sensor. The sample is positioned on the disk, as is common with Boersma devices. A large number of thermocouples are intended to provide the actual measurement signal. EP 1717566 A1 refers to a sensor that can be manufactured in a single sintering step and consists of only a single component. To increase the number of usable thermocouples, it is mentioned that the sensor can also consist of multiple layers of thermocouples. However, this limits the size of the sensor, as monolithic ceramic components of increased size are difficult to manufacture. This is due, among other things, to the fact that with increasing volume of ceramics, the probability of component failure also increases.As a consequence, there is currently no monolithic ceramic sensor on the market that operates according to the Tian-Calvet principle.

[0005] One way to circumvent the problem of limited thermocouple density when applying the Tian-Calvet principle is through ceramic multilayer technology. Commercially available ceramic green sheets are printed with metal-filled screen printing pastes. This step enables very precise layer application and optimal utilization of the available space. Subsequently, several green sheets are bonded together in a lamination step to form a multi-layer structure. The shape of the structure can be reworked with a laser or a punch. After sintering, a solid ceramic component is created that can be contacted externally.

[0006] For example, US 3,059,471 A and US 3,798,003 A each disclose structures based on the Tian-Calvet principle, in which thermocouples are arranged one above the other in the form of a column.

[0007] The object of the invention is therefore to provide a calorimetric sensor structure based on the Tian-Calvet principle that has the greatest possible measurement sensitivity and the smallest possible time constant. According to the invention, this object is achieved with a sensor structure having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the subordinate claims.

[0008] The key is optimizing the sensor design. This can be achieved through two steps: First, creating a sensor with the greatest possible thermal insulation while simultaneously maintaining a low heat capacity. This can increase the temperature fluctuations during a thermal event while simultaneously reducing the heat absorption into the sensor design, which leads to an increase in the measurement signal while simultaneously reducing the time constant. Second, the number of usable thermocouples can be optimized so that they can measure the respective temperature difference as precisely as possible. Another general goal is to make the sensor design as simple as possible to manufacture.

[0009] The solution was found in the novel stacked structure of a Tian-Calvet sensor according to claim 1. This essentially consists of a combination of two segments with different functions. The actual measurement signal can be determined using temperature sensors, in particular thermocouples, which are located on and / or in at least one segment type used in a sensor structure according to the invention. Thermal insulation is achieved using segments that function as spacers. These are made of thermally and electrically insulating material.

[0010] The calorimetric sensor structure according to the Tian-Calvet principle according to the invention is formed with adjacently arranged insulating segments and sensitive segments. The insulating segments and the sensitive segments are designed to form a sample chamber and enclose a sample arranged therein. Temperature sensors, in particular thermocouples, are provided on and / or in the sensitive segments. These sensors are electrically connected in series and / or connected to electrical contact terminals. The adjacently arranged segments are plate-shaped or have a circular segment-shaped cross-section.

[0011] To form a sample chamber, insulating segments and sensitive segments can be circular, frame-shaped, plate-shaped, or with a circular-ring-segment-shaped cross-section. Circular ring-shaped segments are preferred when arranged one above the other. Ring-segment-shaped cross-sections are advantageous when arranged side by side and can thus be arranged in a circular ring. Samples can then be arranged inside the circular ring. Frame-shaped or plate-shaped insulating and sensitive segments are preferably used for samples with a corresponding external geometric shape, for example, cuboid-shaped or cube-shaped samples.

[0012] Adaptation to the geometric shape of samples and / or a specific favorable arrangement of temperature sensors, hereinafter referred to exclusively as thermocouples, can also be achieved by forming a sensor structure with at least one region of insulating and sensitive segments arranged one above the other and at least one further region of insulating and sensitive segments arranged next to each other. These regions can, in turn, be arranged one above the other.

[0013] Insulating segments and sensitive segments should be made of different materials. The materials used to form insulating segments and sensitive segments should have different thermal conductivities, with the material used to form insulating segments having a lower thermal conductivity than the material used to form sensitive segments, in particular a thermal conductivity of less than 5 W / mK.

[0014] Insulating segments can advantageously be formed with a porous material whose porosity is preferably greater than 60%.

[0015] Isolating segments should also have a larger volume than sensitive segments, with this volume preferably being at least three times larger.

[0016] A suitable porous material for insulating segments can be a ceramic material or mineral wool.

[0017] Recesses and / or openings can be formed in insulating segments and / or sensitive segments. These can be used for various functions. For example, electrically conductive connections can be formed through aligned openings. Fixing elements, such as rod-shaped elements, can also be passed through such openings, so that at least segments arranged directly above or next to one another can be positively and / or non-positively connected to one another, which can increase the stability of the sensor structure.

[0018] However, this can also be achieved by forming elevations on surfaces of insulating segments facing surfaces of sensitive segments, which elevations can be inserted into recesses or openings that are complementarily formed and arranged correspondingly to the elevations.

[0019] Ceramic multilayer technology, particularly LTCC technology, is ideal for manufacturing the individual segments. The ceramic materials used exhibit low thermal conductivity, can be designed flexibly, and allow for the simultaneous integration of a large number of thermocouples on or in such a sensitive segment sensor. At the same time, the thicknesses of the individual thermocouple legs can be very small, which can reduce heat loss through conduction.

[0020] The segments can be manufactured in various ways. Coated (e.g., sputtered) segments made of ceramic, plastic, crystal, or glass can also be used. One or more legs can be applied by bonding, although this would limit the maximum operating temperature of the sensor assembly or would be more difficult to achieve technologically.

[0021] Thermocouples as temperature sensors and electrically conductive connections can be designed and arranged as described in EP 1717566 A1.

[0022] Individual sensitive segments can be arranged at different heights / levels along the sample. This allows temperature measurements to be recorded along the entire length or height of a sample. Insulating segments can be arranged between sensitive segments. An alternating arrangement of sensitive and insulating segments is preferred. Thermally insulating elements should have a very low thermal conductivity, which should be at least lower than the thermal conductivity of sensitive segments. They should also have a larger volume or thickness than the sensitive segments. The low thermal conductivity can increase the achievable temperature deflection during a calorific event in the sample. A low physical density and heat capacity lead to a small time constant of the sensor structure, as this allows it to better follow the temperature curve of the sample.For these reasons, porous materials are particularly suitable for insulating segments. For applications at elevated temperatures, porous insulation blocks are ideal for insulating segments. These can provide mechanical stability to the correspondingly designed sensor assembly and suppress convection.

[0023] A porous material also has the advantage of being slightly malleable, allowing it to adapt to the sensitive segments. Foams, such as polymer foams, can also be used at low temperatures.

[0024] Since the suppression of convection can essentially be achieved by the insulating segments, sensitive and / or insulating segments can have recesses and / or perforations that can further reduce heat conduction. However, recesses and / or perforations can also be used to achieve an improved positive and / or non-positive connection between multiple segments.

[0025] Recesses and / or openings in sensitive segments are advantageous because a ceramic material, such as LTCC, has a higher thermal conductivity than the material used for insulating segments. Recesses and / or openings can be filled with air or another material with lower thermal conductivity.

[0026] The electrical contacting of the individual thermocouples present on / in sensitive segments can be done with wires that can be welded, clamped or sintered with an electrically conductive paste, in particular a gold paste.

[0027] The individual thermocouples, which serve as temperature sensors located on / in sensitive segments, can be connected in series or in parallel. A series connection allows for a maximum measurement signal. Thermocouples can also be tapped individually to record the propagation of a reaction based on the temperature profile, which can be measured with the thermocouples arranged at different positions.

[0028] With the invention, an increased measuring sensitivity of the sensor structure can be achieved, since the convection in the segments arranged next to and / or one above the other is suppressed and the number of thermocouples that can be used can be adapted to the optimum by the structure in microsystem technology.

[0029] This is made possible by the use of the material from which the insulating segments are made. This material, with its lower thermal conductivity, is suitable because the individual sensitive segments can have a flat surface that can lie directly against the surfaces of the insulating segments, thus avoiding gaps between segments arranged next to and / or on top of one another. This was not possible with previously known devices that used the Tian-Calvet principle because the gaps, particularly those through which the wires pass, were not possible. According to the state of the art, such ceramic Tian-Calvet sensors could not be manufactured in this way because it could only be done using pure multi-layer technology. This is, to say the least, complex and expensive and, due to the fact that the probability of failure of a ceramic component scales with its size, is associated with increased scrap during production.The invention enables the use of multilayer technology to construct a Tian-Calvet sensor assembly, as the sensor assembly is now composed of multiple components. The creation of large, monolithic ceramic components is no longer necessary.

[0030] The invention will be explained in more detail below using examples. Features used in the individual examples can be combined with one another in any way, regardless of the specific example.

[0031] Showing: Fig. 1 a single sensitive segment, which can also be called a sensor disc; Fig. 2a an example of an insulating segment in circular ring shape; Fig. 2b shows an example of an insulating segment in circular shape forming the bottom of a sensor structure; Fig. 3a shows an example of a sensor structure according to the invention in which several insulating and sensitive segments are arranged one above the other; Fig. 3b the example according to Fig. 3a in a sectional view; Fig. 4 shows an example of a sensor structure according to the invention in a perspective view; Fig. 5 an example of a sensor structure according to the invention, in which insulating and sensitive segments form a circular ring arrangement next to each other and Fig. 6 an example in which insulating and sensitive segments are arranged one above the other and thermocouples are connected in series via vias in an electrically conductive manner.

[0032] In Fig. Figure 1 shows an example of a sensitive segment 10. The substrate 1 for the sensitive segment 10 is circular and made of LTCC (Low Temperature Cofired Ceramic) ceramic. It has an outer diameter of 37 mm, an inner diameter of 17 mm, and a thickness of 0.5 mm. The circular recess in the center is dimensioned to accommodate a sample. For this purpose, several sensitive segments 10 and insulating segments 9, as will be described later, are arranged one above the other to form a cylindrical cavity for receiving a sample.

[0033] To reduce heat conduction from the sample chamber 3a to the edge of the sensitive segment 10, the substrate 1 has recesses 4 that can be filled with air. Since air has a lower thermal conductivity than an LTCC material, this improves thermal insulation. On the substrate 1, an electrical conductor 2 is formed between pairs of thermocouples that encircle the substrate 1 and extend to contact terminals 5. The pairs of thermocouples used for temperature measurement are made of different thermoelectric materials that are arranged alternately inside and outside and can thus measure the temperature difference between the sample chamber 3a and the environment 3c. An electrical voltage that is proportional to the radial heat flow through the sensitive segment 10 can then be tapped via the contact terminals 5.This temperature difference can be measured via two contact taps 7 as well as the absolute temperature of the sample arranged in the sample chamber 3a via further contact taps 8.

[0034] The electrical contacting of the individual sensitive segments 10 can be achieved using wires that are routed through wire feedthroughs 6 and sintered to contact terminals 5 using electrically conductive paste. Production can be performed in a single co-firing process. For this purpose, the thermocouple pattern is printed onto an LTCC ceramic foil using two different screen printing pastes. The LTCC ceramic foil is then cut to the desired shape using a laser beam or a punch. Additional openings can also be formed in this way, which can be used for electrical through-hole connections or for inserting fixing elements. The stability of the sensor structure can be increased by inserting fixing elements, such as rods. The entire structure is then sintered in a furnace.

[0035] Fig. Figure 2a shows a circular insulating segment 9, the interior of which also forms the sample chamber 3a when sensitive segments 10 and insulating segments 9 are arranged one above the other. The insulating segment 9 is made of aluminosilicate with a porosity of at least 60%.

[0036] Fig. Figure 2b shows an example of a circular insulating segment 11 forming the base of a sensor assembly. A sample can be placed on this insulating segment 11 within the sample chamber 3a in a furnace. The insulating segments 9 and 11 can be manufactured using conventional machining tools from a block of the material used, which has very low thermal conductivity and good thermal insulation.

[0037] Fig. Figure 3a shows an example of a sensor structure according to the invention. On an insulating segment 11, which forms the base, there are alternating sensitive segments 10 and insulating segments 9 according to the examples according to the Fig. 1 and Fig. 2a are arranged one above the other and form a stack within which the sample chamber 3a is formed. In addition to the alternating arrangement shown, several insulating segments 9 can also be arranged one above the other, on which a sensitive segment 10 is then arranged.

[0038] As already mentioned, recesses 4, other recesses, and / or openings may be formed in sensitive elements 10 in a form not shown. Fixing elements or elevations formed on the surfaces of insulating segments 9 can be inserted into these when segments 9 and 10 are arranged one above the other, thereby increasing the stability of the sensor structure.

[0039] The Fig. Figure 3b shows the corresponding sectional view. Wires 12 for an electrically conductive connection between thermocouples of the sensitive segments 10 are routed through recesses or openings.

[0040] In Fig. Figure 4 shows a perspective view of a sensor assembly. The stack, formed by the superimposed sensitive segments 10 and the insulating segments 9, forms the sample chamber 3a. The thermocouples in / on the sensitive segments 10 can be tapped individually or, as in the example, connected in series using wires 12.

[0041] Two such sensor assemblies can be arranged in a heatable metal block, one containing the sample and the other a reference sample. This allows differential temperatures to be measured.

[0042] Fig. Figure 5 shows another example of a sensor structure according to the invention. In this example, insulating segments 9 and sensitive elements 10 are arranged side by side to form a circular ring, inside which a sample chamber 3a is formed. In particular, the insulating segments 9 have a circular segment-shaped cross-section, which can also apply to the sensitive segments 10. This allows for an arrangement of the insulating segments 9 and sensitive segments 10 that is at least virtually free of joints or gaps.

[0043] Fig.Figure 6 shows a sensor structure with a plurality of insulating segments 9 and sensitive segments 10 arranged one above the other. A thermocouple acting as a temperature sensor is arranged on the opposite surfaces of the sensitive segments 10, which face toward a surface of an insulating segment 9. The thermocouples are connected to each other in series. This can be achieved with the vias 13. A contact terminal 5 is provided on each of these surfaces.

Claims

[1] Calorimetric sensor structure according to the Tian-Calvet principle, which is formed with adjacently arranged insulating segments (9) and sensitive segments (10) which are plate-shaped or have a circular ring-segment-shaped cross-section, wherein the insulating segments (9) and the sensitive segments (10) are designed such that they form a sample space (3a) and enclose a sample arranged therein and on and / or in sensitive segments (10) there are temperature sensors, in particular thermocouples, which are electrically connected in series and / or connected to electrical contact terminals (5), wherein insulating segments (9, 11) and sensitive segments (10) are formed from different materials, and the materials from which insulating segments (9, 11) and sensitive segments (10) are formed have different thermal conductivities, wherein the material from which insulating segments (9, 11) are formed has a lower thermal conductivity than the material with which sensitive segments (10) are formed. [2] Sensor structure according to claim 1, characterized by that insulating segments (9) and sensitive segments (10) are circular or frame-shaped. [3] Sensor assembly according to one of the preceding claims, characterized by that the material from which insulating segments (9, 11) are formed has a thermal conductivity which is 5 W / mK lower than the thermal conductivity of the material with which sensitive segments (10) are formed. [4] Sensor assembly according to one of the preceding claims, characterized by that recesses (4) and / or openings are formed in insulating segments (9) and / or sensitive segments (10). [5] Sensor assembly according to one of the preceding claims, characterized by , the insulating segments (9, 11) are formed with a porous material whose porosity is preferably greater than 60% and / or insulating segments (9) have a larger volume than sensitive segments (10), this volume preferably being at least three times larger. [6] Sensor assembly according to one of the preceding claims, characterized by , a porous material for insulating segments (9, 11) is a ceramic material or mineral wool. [7] Sensor assembly according to one of the preceding claims, characterized bythat elevations are formed on surfaces of insulating segments (9, 11) facing surfaces of sensitive segments (10), which elevations can be inserted into recesses or openings which are formed complementarily and arranged correspondingly to the elevations. [8] Sensor assembly according to one of the preceding claims, characterized by that insulating segments (9) and sensitive segments (10) arranged above or next to one another are arranged on a further insulating segment (11) which forms the base of the sensor structure.

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