Differential calorimeter with high sensitivity

Abstract

The invention relates to a differential calorimeter for detecting a thermodynamic characteristic variable of a sample, wherein at least one heating element (2) and at least one thermal element (3) as temperature sensor are formed in each case in the form of a coating on the surface of a planar substrate (1) which is formed from a glass, glass ceramic, glass carbon or ceramic material having a thermal conductivity of less than 20 W / (m K).

Description

TECHNICAL FIELD

[0001] The present invention relates to a differential calorimeter for detecting a thermodynamic characteristic variable of a sample with high sensitivity. BACKGROUND

[0002] Thermal analysis processes are used to determine thermodynamic characteristic variables, such as the thermal conductivity, the specific heat capacity of a sample or the thermal energy absorbed or output by a sample during a phase transition. In so-called dynamic differential thermal analysis (DSC), two measurement principles are generally distinguished, namely the heat flow principle, which measures the temperature difference between a sample and a reference with known properties, and the power compensation principle, which measures the heating power required to completely compensate for the temperature difference between sample and reference.

[0003] A device suitable for DSC processes, namely a so-called differential calorimeter, generally comprises at least one crucible, for example a silver crucible, in which a sample and / or a reference are arranged. Depending on the measurement principle, sample and reference are located here in the same crucible (heat flow principle) or are completely separated and equipped with separate heating elements (power compensation principle). However, the application and deployment options of such a differential calorimeter are greatly limited by the very complex and space-occupying construction when using silver crucibles.

[0004] By contrast, differential calorimeters in which the heating elements and sensor elements are applied to a substrate in a layer process can be manufactured inexpensively and in a compact construction. However, sensors integrated in this way are generally insufficiently mechanically or thermally stable and exhibit disadvantageous dissipation effects, which greatly limit the resolution and measurement accuracy of the differential calorimeter. SUMMARY

[0005] The object of the present invention therefore includes proposing a differential calorimeter which can be manufactured inexpensively in a compact construction and which does so with high stability and high measurement accuracy.

[0006] According to the invention, this object is achieved by the features specified in claim 1. Advantageous variants result from the features specified in the dependent claims.

[0007] The differential calorimeter for detecting a thermodynamic characteristic variable of a sample according to the invention has at least one planar substrate, at least one thermal element as a temperature sensor and at least one heating element. In this regard, the at least one thermal element as a temperature sensor and the at least one heating element are each formed in the manner of a coating on at least one surface of the planar substrate. The planar substrate is formed from a glass, a glass-ceramic material, a glassy carbon or a ceramic material, each of which has a thermal conductivity of less than 20 W / (m K).

[0008] The planar substrate can be formed, for example, from quartz glass or aluminum oxide. The planar substrate can also be formed from a commercially available glass-ceramic material, for example Ceran (known trade name for a glass-ceramic material). The thermal conductivity is preferably less than 10 W / (m K), particularly preferably less than 2 W / (m K). The use of a glass with a small thermal conductivity enables particularly effective thermal insulation and the formation of a large stable temperature gradient between the sample and the reference, which is particularly advantageous when detecting the characteristic variable according to the heat flow principle. The thickness of the planar substrate is preferably less than 1 mm. The thickness of the planar substrate is particularly preferably in the range from 0.2 mm to 5 mm.

[0009] The coating for forming the temperature sensor and the heating element is arranged on at least one surface of the planar substrate. In both thin-film technology and thick-film technology, the layers of the coating can be arranged, inter alia, on a planar glass substrate which is mechanically and thermodynamically very stable. The individual layers of the coating can also be applied as thin intermediate films for bonding or passivating subsequent layers of the coating on the surface of the planar substrate or on another layer of the coating. Such layers or further layers of the coating can be formed, for example, by a plasma-assisted chemical vapor deposition or sputtering process.

[0010] The surface of the planar substrate or a layer of the coating of the planar substrate and / or the at least one thermal element or the temperature sensor formed by the at least one thermal element can have at least one first region as a measurement location in or on which the reference can be arranged and at least one second region as a measurement location in or on which at least one sample can be arranged. The measurement locations in which the sample or the reference can be arranged can be formed by recesses arranged in one or more layers of the coating or by semi-open or closed hollow spaces.

[0011] The at least one thermal element is formed by at least two thermal arms which are electrically connected to one another. A particularly high resolution and sensitivity of the temperature sensor can be achieved in that a plurality of thermal elements are electrically connected in series and are arranged at least partially in parallel and spaced apart from one another. The first and second regions formed as measurement locations can thereby be at least partially surrounded, for example in a circular manner. A temperature sensor formed in this way can also be referred to as a thermopile or thermoelectric chain.

[0012] A plurality of thermal elements (thermopile) can also be arranged in different layers of the coating which are formed overlapping one another. The temperature sensor can also be formed by a plurality of layers of the coating, wherein the layers in which the thermal elements are formed and the layers formed as passivation films can alternate. A plurality of mutually insulated thermal elements can also be arranged in different layers of the coating. The thermal arms preferably have a thickness of less than 1 pm.

[0013] The heating arms can be formed from conductor traces disposed on a planar substrate and / or on a coated layer. It is particularly advantageous if one heating arm is formed of a nickel-chromium alloy and the corresponding other heating arm is formed of a nickel-silicon alloy. However, at least one heating arm can also be formed of polycrystalline silicon, a silicon-containing alloy, or a thermoelectric material formed of silicon.

[0014] Heat arms formed of nickel-chromium alloys may contain 15% to 25% chromium by mass. Heat arms formed of nickel-silicon alloys may contain 3% to 8% silicon by mass. The formation of nickel-chromium alloys or nickel-silicon alloys improves the heat resistance and adhesion of the heat arms, especially on substrates formed of quartz glass.

[0015] The at least one heating element may have at least one electrically conductive trace of platinum, gold, or aluminum. The at least one heating element is preferably configured such that it can maintain a constant temperature of the planar substrate, at least in the area where the sample and / or reference is disposed, for example, during the detection of thermodynamic characteristic variables. The at least one heating element is particularly preferably disposed on the surface of the planar substrate or on the surface of a coating of the planar substrate and extends at least partially in a curved manner. The at least one heating element may also be configured such that it can be adjusted to decrease or increase the temperature of the substrate, the adjustment occurring at a rate that is as constant as possible.

[0016] The thickness of the at least one heating element can be less than 1 μm, preferably less than 500 nm. A titanium or chromium adhesive layer is preferably formed on the surface of the planar substrate or between a layer of coating and a layer of coating formed by the at least one heating element. The adhesive layer can have a thickness of less than 10 nm.

[0017] The layer of coating formed by the at least one heating element may be at least partially covered by an electrically insulating passivation film, preferably composed of SiO2 or Si3N4. The thickness of the passivation film is preferably less than 1 μm.

[0018] At least one layer of the coating disposed on at least a portion of the surface of the planar substrate and / or on a layer of coating may be formed of a top layer having low emissivity, which is composed of gold, for example, to minimize thermal radiation emissions. The thickness of the gold-formed coating layer is preferably 50 nm to 150 nm. The combination of a planar substrate formed of glass and a gold-formed coating layer results in higher final temperatures, faster heating rates, and more stable measurement results.

[0019] Differential calorimeters can have two additional, separately controllable heating elements in the form of coatings. The first and second regions, forming the measurement location, can be heated independently by the two additional heating elements. The two additional heating elements are thus particularly capable of rapidly and effectively compensating for the temperature difference between the sample and the reference, which is especially advantageous in power-compensated detection of thermodynamic characteristic variables.

[0020] Therefore, based on the principles of heat flow and power compensation, differential calorimeters are suitable for detecting thermodynamic characteristic variables. In this respect, the temperatures of both the sample and the reference material can be maintained above the substrate temperature for a certain period of time. Once an endothermic or exothermic reaction occurs in the sample, the heat absorbed or released during this process can be compensated by adjusting the heating element, thereby quickly and effectively bringing the sample temperature back to match the reference temperature.

[0021] Two additional heating elements are preferably formed with conductive traces extending in a curved manner in a first and second region, and the sample and / or reference can be arranged in or on the first and second regions. It is advantageous if the two additional heating elements are arranged together with the temperature sensor in the same layer of the coating. The conductive traces of the two additional heating elements are preferably formed of the material of the heating arm. Particularly preferred materials for the conductive traces of the two additional heating elements are nickel-chromium alloys, nickel-silicon alloys, polycrystalline silicon, gold, aluminum, or platinum.

[0022] The at least one heating element may be disposed on a first surface of the planar substrate, and the at least one heating element and / or additional heating elements may be disposed on a second surface of the planar substrate opposite to the first surface. In this respect, the at least one heating element may also be disposed together with additional heating elements in the same layer of a coating. Alternatively, the coating of the planar substrate may be configured such that at least one layer of the coating formed by the at least one heating element serving as a temperature sensor is disposed on the surface of the planar substrate, and a passivation film is disposed on the surface away from the planar substrate and on the surface of the at least one layer of the coating formed by the at least one heating element serving as a temperature sensor, and the at least one heating element and / or at least two additional heating elements are disposed on the surface of the passivation film away from the planar substrate.

[0023] The differential calorimeter according to the present invention can heat samples and / or references over a very wide temperature range. During this process, a large temperature difference can occur between the sample and the reference, and this difference can be maintained for a considerable period of time without negatively impacting the mechanical, electrical, or thermodynamic stability or sensitivity of the differential calorimeter.

[0024] Thermodynamic characteristic variables can also be detected at considerably higher frequencies and / or amplitudes. Due to the integrated heating element or the filament design of the heating element, and because the thermal mass is therefore very small, the temperatures of various components of the differential calorimeter, or the temperatures of the sample and / or reference, can be modulated at particularly higher frequencies. This modulation can be superimposed on an increase in the substrate temperature to enable the determination of temperature-dependent characteristics, particularly C. P Furthermore, shorter response and latency times can be used for efficient data inspection.

[0025] It is recommended to guide the electrical conductor traces (from which at least one heating element and / or the at least one thermal element and / or the additional heating element) at least partially parallel to each other to the outer edge of the planar substrate, thereby forming an electrical contact connection in the edge region of the planar substrate.

[0026] The heating elements or heating arms can be interconnected in different ways. In this respect, at least three heating arms are electrically connected in series, wherein the first heating arm and the third heating arm are formed of a first material (e.g., NiSi or polycrystalline silicon), and the second heating arm disposed between the first heating arm and the third heating arm is formed of a second material different from the first material (e.g., NiCr or Pt).

[0027] This differential arrangement or interconnection allows conductor traces, corresponding only to the first material, to be guided to the contact connection. This avoids additional thermal voltages at the corresponding contact points that could represent interfering signals.

[0028] Electrically conductive traces, which are guided at least partially parallel to each other to the outer edge of the planar substrate and form electrical contact connections in the region of that edge of the planar substrate, are formed of the material of one of at least two electrically connected thermal arms.

[0029] The planar substrate may have an opening through which flow can be made to achieve thermal decoupling of at least one heating element and at least one heating element from an electrical contact connection. The cross-sectional area of ​​the opening through which flow can be made may be greater than 20% of the surface area of ​​the planar substrate coated with at least one heating element and / or at least one heating element. For example, air may flow through the opening.

[0030] For thermal decoupling of the at least one thermal element and the at least one heating element from the electrical contact connection, the planar substrate may also be formed of at least one plate portion that tapers or gradually tapers continuously at at least one point in the direction of the contact connection and connects the region of the planar substrate in which the at least one thermal element and the at least one heating element are formed to the region of the planar substrate in which the electrical contact connection is formed.

[0031] The specific design of the differential calorimeter described above, the use of a planar substrate, and the materials used for the thermal and heating elements that mate with it particularly enable contact with the thermal arm and conductor traces in cold regions where the temperature can be lower than that of the sample and / or reference. Attached Figure Description

[0032] The present invention will now be explained in more detail with reference to the embodiments.

[0033] It is shown that:

[0034] Figure 1 This is an illustrative membrane design of an example of a differential calorimeter according to the present invention;

[0035] Figure 2 These are schematic diagrams of the front and rear sides of an example of a differential calorimeter according to the present invention; and

[0036] Figure 3 a and b are detailed schematic diagrams of the front side of an example of a differential calorimeter according to the present invention. Detailed Implementation

[0037] Figure 1 The membrane design of the differential calorimeter according to the present invention is schematically illustrated. The planar substrate 1 is formed of quartz glass with a thickness of 0.7 mm and has an opening 9 through which flow can pass. The opening 9 at least partially isolates the hot region in which the sample and reference can be arranged from the cold region in which the contact connection 8 is arranged. The two regions are connected to each other only by a narrow plate portion 10.

[0038] A heating element 2 having platinum conductor traces extending in a curved manner is formed on a first surface of a planar substrate 1. The conductor traces of the heating element 2 have a thickness of 200 nm. A chromium adhesive layer (not shown) with a thickness of 5 nm is disposed between the planar substrate 1 and the heating element 2. Alternatively, the adhesive layer may also be formed of titanium.

[0039] Multiple heating elements 3 forming a temperature sensor, together with two additional heating elements 6 and 7, are arranged in a coating layer on the second surface of the planar substrate 1. The second surface is located on the side of the planar substrate 1 opposite to the first surface.

[0040] A SiO2 passivation film 4 with a thickness of approximately 1 μm is applied to the coating layer formed by the heating element 3 and heating elements 6 and 7. A gold film 5 with a thickness of 100 nm, forming the outer surface of the differential calorimeter, is disposed on the passivation film 4.

[0041] The features that appear repeatedly in the following figures have the same characteristics as Figure 1 The same reference numerals are used in the accompanying drawings.

[0042] Figure 2a shows the membrane design according to the present invention. Figure 1 A schematic diagram of the front side of the differential calorimeter is shown; for simplicity, the gold film 5 is not shown. In this respect, the conductor traces of two additional heating elements 6, 7 extending in a curved manner form a first region and a second region, or measurement position, where the corresponding sample and corresponding reference can be arranged. A plurality of heating elements 3 extend largely parallel to each other between the first and second regions in the coating layer, wherein the heating elements 3 at least partially surround the first and second regions in a circular manner. A plurality of electrically conductive traces, formed of the material of the heating arms and electrically connected to the heating elements 3 and the additional heating elements 6, 7, are guided at least partially parallel to each other via a narrow plate portion 10 to the outer edge of the planar substrate 1. An electrical contact connection portion 8 is formed in this edge region of the planar substrate 1, via which the differential calorimeter can be connected to an electronic control and evaluation unit.

[0043] Figure 2 b illustrates its membrane design according to the present invention. Figure 1 A schematic diagram of the rear side of the differential calorimeter. The conductor traces of the heating element 2, extending in a curved manner and formed of platinum, are shown accordingly on the rear side, wherein the heating element 2 is configured to at least sometimes maintain the planar substrate 1 at a constant temperature. Similar to... Figure 2 a. Multiple electrical conductor traces are also implemented on the rear side of the differential calorimeter and are guided at least partially parallel to each other via the narrow plate portion 10 to the outer edge of the planar substrate 1, and an electrical contact connection portion 8 is formed in the edge region of the planar substrate 1.

[0044] Figure 3 a shows a schematic diagram of the front side of the differential calorimeter according to the invention, wherein, in particular, the electrical conductor traces (from which a temperature sensor formed by a plurality of thermal elements 3) are guided at least partially parallel to each other via a narrow plate portion 10 to the outer edge of the planar substrate 1, thereby forming electrical contact connections 8.1, 8.2 in the region of the outer edge of the planar substrate 1.

[0045] Figure 3 b shows details of the additional heating elements 6, 7 and the temperature sensor formed by multiple heating elements 3. Each of the heating elements 3 here is formed by two heating arms 3.1, 3.3 that are electrically connected in series with each other via a connecting part 3.2.

[0046] Furthermore, multiple thermal elements 3 are interconnected in different ways and electrically connected in series. The electrical conductor traces (which form the temperature sensor formed by the multiple thermal elements 3) are thus guided to the contact connections 8.1 and 8.2 by only one material corresponding to the material of the thermal arm 3.1.

[0047] The heating arm 3.1 is specifically formed of a nickel-chromium alloy and the corresponding heating arm 3.3 is formed of a nickel-silicon alloy.

Claims

1. A differential calorimeter for detecting a thermodynamic property variable of a sample, wherein, At least one heating element (2) and at least two thermal elements (3) as temperature sensor are arranged in the form of a coating on a surface of a planar substrate (1), wherein The planar substrate (1) is formed of glass, glassy carbon or a ceramic material, each having a thermal conductivity of less than 20 W / (m K), wherein, for power-compensated detection of a thermodynamic property, two individually controllable additional heating elements (6, 7) are arranged in the form of a coating, and wherein a first region and a second region formed as measurement locations are individually heatable by the two additional heating elements, respectively.

2. The differential calorimeter according to claim 1, characterized in that, The thermal elements (3) at least partially surround the first region and the second region in a circular manner.

3. The differential calorimeter according to claim 1, characterized in that, The planar substrate (1) is formed of quartz glass.

4. The differential calorimeter according to claim 1, characterized in that, The planar substrate (1) has a thickness in the range of 0.2 mm to 5 mm.

5. The differential calorimeter according to claim 1, characterized in that, The surface of the planar substrate (1), the surface of the layer of the coating of the planar substrate (1), and / or the at least two thermal elements (3) have at least one first region as measurement location in or on which a sample can be arranged and at least one second region as measurement location in or on which a reference can be arranged.

6. The differential calorimeter according to claim 1, characterized in that, The temperature sensor is formed as a thermopile or a thermoelectric chain from a plurality of thermal elements (3) which are electrically connected in series and extend at least partially parallel to each other and are spaced apart from each other.

7. The differential calorimeter according to claim 1, characterized in that, The at least two thermal elements (3) are formed from at least two thermal arms which are electrically connected to each other, wherein one thermal arm is formed from a nickel-chromium alloy and a respective other thermal arm is formed from a nickel-silicon alloy; or one thermal arm is formed from a nickel-chromium alloy or a respective other thermal arm is formed from a nickel-silicon alloy.

8. The differential calorimeter according to claim 1, characterized in that, The at least two thermal elements (3) are formed from at least two thermal arms which are electrically connected to each other, wherein at least one thermal arm is formed from polysilicon, a silicon-containing alloy, or a thermoelectric material formed from silicon.

9. The differential calorimeter according to claim 7, characterized in that, one thermal arm formed from a nickel-chromium alloy contains chromium in a mass fraction of 15% to 25% and one thermal arm formed from a nickel-silicon alloy contains silicon in a mass fraction of 3% to 8%.

10. The differential calorimeter according to any one of claims 7 or 8, characterized in that, The at least one heating element (2) is formed from an electrical conductor track of platinum, gold or aluminum.

11. The differential calorimeter according to claim 1, characterized in that, The coating of the planar substrate (1) formed by the at least two thermal elements (3) is at least partially covered by an electrically insulating passivation film (4).

12. The differential calorimeter according to claim 1, characterized in that, At least one layer (5) of the coating arranged at least on a portion of the surface of the planar substrate (1) and / or on the layer of the coating is formed from gold to minimize thermal radiation emissions.

13. The differential calorimeter according to claim 1, characterized in that, The two additional heating elements (6, 7) are formed from conductor tracks which extend in a curved manner in a first region in or on which a sample can be arranged and in a second region in or on which a reference can be arranged.

14. The differential calorimeter according to claim 1, characterized in that, The two additional heating elements (6, 7) are arranged together with the temperature sensor in the same layer of the coating.

15. The differential calorimeter according to claim 12, claim 13 or claim 14, characterized in that, The conductor tracks of the two additional heating elements (6, 7) are formed from a nickel-chromium alloy, a nickel-silicon alloy, polysilicon, gold, aluminum or platinum.

16. The differential calorimeter according to claim 1, characterized in that, The at least one heating element (2) is arranged on a first surface of the planar substrate (1) and the at least two thermal elements (3) and, if present, the additional heating elements (6, 7) are arranged on a second surface of the planar substrate (1) which is arranged opposite the first surface.

17. The differential calorimeter of claim 10, wherein, The electric conductor tracks are at least partially guided parallel to one another up to an outer edge of the planar substrate (1) in order to form an electrical contact connection (8, 8.1, 8.2) in the region of this edge of the planar substrate (1), the at least one heating element (2) and / or the at least two thermal elements (3) and / or the additional heating elements (6, 7) being formed from the electric conductor tracks.

18. The differential calorimeter of claim 17, wherein, The electric conductor tracks which are at least partially guided parallel to one another up to an outer edge of the planar substrate (1) in order to form an electrical contact connection (8, 8.1, 8.2) in the region of this edge of the planar substrate (1) are formed from the material of one of the at least two thermal arms which are electrically connected to one another.

19. The differential calorimeter of claim 1, wherein, The planar substrate (1) is formed with an opening (9) which can be flowed through for thermal decoupling of the at least two thermal elements (3) and the at least one heating element (2) from the electrical contact connection (8, 8.1, 8.2).

20. The differential calorimeter of claim 19, wherein, An opening cross-sectional area of the opening (9) which can be flowed through is greater than 20% of a surface of the planar substrate (1) which is coated with the at least one heating element (2) and / or the at least two thermal elements (3).

21. The differential calorimeter according to any one of claims 17 to 19, characterized in that, For thermal decoupling of the at least two thermal elements (3) and the at least one heating element (2) from the electrical contact connection (8, 8.1, 8.2), the planar substrate (1) is formed from at least one plate portion which tapers or continuously tapers at at least one point in the direction of the electrical contact connection (8, 8.1, 8.2) and connects the region of the planar substrate (1) formed by the at least two thermal elements (3) and by the at least one heating element (2) to one another with the region of the planar substrate (1) formed by the electrical contact connection (8, 8.1, 8.2).

22. The differential calorimeter of claim 1, wherein, The planar substrate (1) is formed from a glass-ceramic material.

23. A differential calorimeter for detecting a thermodynamic property of a sample, wherein, At least one heating element (2) and at least two thermal elements (3) as temperature sensors are configured in the form of a coating on a surface of a planar substrate (1), wherein The planar substrate (1) is formed from aluminum oxide, each having a thermal conductivity of less than 20 W / (m K), wherein, for power-compensated detection of the thermodynamic characteristic variable, two separately controllable additional heating elements (6, 7) are configured in the form of a coating, and wherein a first region and a second region formed as measurement locations can be separately heated by the two additional heating elements, respectively.

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