JP3147015U - Differential scanning calorimeter - Google Patents

Abstract

The present invention provides means for improving a decrease in detection sensitivity caused by an increase in radiant heat transfer of a differential scanning calorimeter. In addition, without limiting the heating temperature range or the working atmosphere, the detector is caused by the stress generated in the detector at a high temperature due to the difference in the coefficient of thermal expansion between the detector and the furnace or heater surrounding the detector. A means for preventing deformation and breakage and improving the durability of the detector is provided.
A contact surface between a furnace body 6N of a heating furnace and a heat conduction path provided at both ends of a detector 21 is slidable, and this structure extends the heat conduction path length at high temperatures to conduct heat. Thus, the amount of heat transmitted to the detector 21 per unit time is reduced, and the thermal stress resulting from the difference in thermal expansion coefficient between the furnace body 6N and the detector 21 is absorbed.
[Selection] Figure 1

Description

  The present invention relates to a differential scanning calorimeter that heats a reference material and a sample and measures a change in temperature of the enthalpy of the sample accompanying a temperature rise and fall from the temperature difference between the two.

  A differential scanning calorimetry (hereinafter, referred to as DSC in principle) apparatus places a sample and a reference material in a heating furnace, and raises or lowers the temperature of the heating furnace according to a predetermined program. This is a device that detects the temperature and temperature difference between the sample and the reference material every time and measures the enthalpy change of the sample (see Patent Document 1).

  As the reference substance, a thermally stable substance having no phase transition within the temperature rise / fall range is selected. When there is no thermal change such as phase transition in the sample, both the reference material and the temperature of the sample change smoothly following the furnace temperature. In addition, when the sample has a phase transition such as melting and endotherm / exotherm is generated, the temperature difference between the sample and the reference material changes rapidly during the phase transition.

  The change in the enthalpy of the sample is measured from the temperature difference between the reference substance and the sample. The reference material and the sample are placed on respective placement tables (hereinafter referred to as detectors) provided in the heating furnace. The temperature of the reference material and the sample is measured by a thermocouple welded to the lower surface of the detector. For example, chromel wire and alumel wire are used as the thermocouple material.

  FIG. 6 is an example of a cross-sectional structure of the heating furnace of the DSC main body, and FIG. 7 is a plan view of the detector 4. A reference material container 2 and a sample container 3 containing a reference material and a sample are placed on a detector 4, and the detector 4 is fixed in a furnace body 6 by a detector fixing plate 5. The detector fixing plate 5 is screwed to the furnace body 6 together with the detector 4 by four fixing screws 7. The furnace body 6 is heated and lowered by a heater 8 according to a predetermined program.

  FIG. 7 shows the structure of the detector 4 as described above. The disk-shaped detector 4 is cut out in black in the figure, and the heat flow flowing from the periphery of the detector 4 into the reference material container 2 or the sample container 3 by heat conduction is performed at three locations on the left and right sides. The heat resistance of the conduction path 12 is limited to an appropriate value. FIG. 8 is a plan view of the heating furnace as viewed from above the detector fixing plate 5 of FIG.

  Incidentally, the material of the furnace lid 1, the furnace body 6 and the detector fixing plate 5 shown in FIG. 6 is usually made of silver having a high thermal conductivity, and the detector 4 is made of a constantan plate or the like. A furnace body thermocouple 9 for measuring the temperature of the furnace body 6 is embedded in the furnace body 6. Further, a reference material thermocouple 10 for measuring the temperature Tr of the reference material container 2 and a sample thermocouple 11 for measuring the temperature Ts of the sample container 3 are fixed on the lower surface of the detector 4, and the temperature between the sample and the reference material is fixed. The difference ΔT = Ts−Tr is measured.

  FIG. 11 shows an example of the relationship between the temperature of each part and time during DSC operation. As shown in the figure, when the temperature of the furnace body 6 is raised with a constant gradient with respect to time, the temperature Tr of the reference material rises monotonously following the temperature of the furnace body 6. The temperature Ts of the sample also rises following the temperature of the furnace body 6, but when a thermal change (endothermic change or exothermic change) due to phase transition or the like occurs in the sample, the temperature gradient changes at that temperature. FIG. 11 shows the case of melting as an example of the endothermic change. By analyzing the relationship between the above Ts and ΔT including this change, the enthalpy change of the sample is measured.

JP-A-11-201924

  The structure of the conventional DSC is as described above. However, as the heating furnace temperature rises, the amount of heat transfer due to radiation increases and the temperature difference detection sensitivity decreases. In other words, the thermal resistance between the furnace body and the detector is determined by the shape and thermal conductivity of the heat conduction path, but usually the thermal conductivity does not have a very large temperature dependence, so the thermal resistance fluctuates gradually with temperature, and the temperature difference As shown in FIG. 9, the detection sensitivity does not greatly depend on the temperature.

  However, in practice, in the region where the heat transfer amount due to radiation increases as the temperature rises as described above, the apparent thermal resistance decreases, and the temperature difference detection sensitivity is as shown by the S curve in FIG. It decreases greatly with temperature.

  In addition, due to the difference in thermal expansion between the furnace body 6 and the detector 4, a large thermal stress is generated when the temperature is raised and lowered, and the detector 4 is deformed. That is, as described above, silver having a high thermal conductivity is usually used as the material of the furnace body 6 and the detector fixing plate 5, and the coefficient of thermal expansion is different from that of the detector 4 such as constantan. The linear expansion coefficient of constantan is smaller than that of silver, and in this combination, tensile stress is generated in the detector 4 in the direction along the surface when the temperature is raised, and compressive stress is generated when the temperature is lowered.

  In general, since DSC is repeatedly heated to a temperature of 700 ° C. or higher, deformation of the detector 4 occurs due to this difference in thermal expansion, and this is not always uniform, so the symmetry between the sample side and the reference material side is lost. The same thermal environment cannot be maintained, and DSC baseline drift occurs.

  Conventionally, in order to avoid the above problem, (1) a method of making the furnace body material copper, which is a material similar to the detector, or (2) a slidability with a graphite sheet sandwiched between the detector and the furnace body However, the upper limit temperature is limited or the working atmosphere of the furnace body is limited. In particular, in the case of (1), the upper limit temperature is limited to about 600 ° C. due to oxidation problems, and in the case of (2), the graphite sheet burns in the air and cannot be used in an atmosphere other than an inert gas atmosphere at a high temperature. The present invention solves this problem.

  In order to solve the above problems, the differential scanning calorimeter provided by the present invention is spanned across the inner space of the heating furnace, and both ends thereof are in slidable contact with the inner periphery of the heating furnace. And a thermal expansion coefficient of the detector is made of a material smaller than that of the heating furnace, and when the heating furnace expands and enlarges in diameter by heating, the relative distance between the detector and the heating furnace is changed.

  According to the present invention, since the heat conduction path length changes depending on the temperature, the amount of heat supplied from the heating furnace to the detector also fluctuates according to the temperature. The amount of heat supplied decreases, and the decrease in detection sensitivity is improved by operating in a direction to eliminate the increase in heat transfer due to radiation. In addition, the generation of thermal stress is absorbed by the sliding of the heat conduction path, preventing deformation and breakage of the detector due to heat cycle, and to the heating temperature range and measurement atmosphere when other methods of ensuring the durability of the detector are applied Therefore, it is possible to achieve both a wide range of usage conditions and maintenance of device performance.

  This will be described with reference to the illustrated example. In the following illustrated example, the structure and function of the parts having the same numbers as those in FIG. 6 are the same as those in FIG. FIG. 1 is a cross-sectional view of the heating furnace, and FIG. 2 is a plan view of the heating furnace with the furnace lid 1 removed.

  1 and 2, the detector fixing plate 5N is fixed inside the furnace body 6N by four fixing screws 7N. The detector 21 is fixed to the bottom inner surface of the furnace body 6N through a collar 23 by a central detector fixing screw 22. In order to minimize the amount of heat flowing from the furnace body 6N to the detector 21 via the detector fixing screw 22 and the collar 23, the detector fixing screw 22 and the collar 23 have a low thermal conductivity such as ceramic. Select material and make it elongated. The reference material container 2 and the sample container 3 are placed on two disc-shaped portions on the left and right sides of the center of the detector 21. Also, the left and right ends of the bridge form a heat conduction path that can slide in contact with the furnace body 6N.

  The inner wall of the furnace body 6N includes an upper upper side wall S and a lower lower side wall T having a diameter smaller than that of the upper side wall S, and the lower side wall T is in contact with the bottom surface B of the furnace body. FIG. 3 is a perspective view showing a main structure below the detector fixing plate 5N of FIG. The upper edge portion of the lower side wall T on which the detector fixing plate 5N is placed is provided with a groove processing on the left and right to match the plate thickness of the detector 21, and the detector 21 is slidably disposed on the upper edge portion. Established.

  FIG. 4 shows the mutual positional relationship between the furnace body 6N and the detector 21 at a high temperature compared with that at a normal temperature. As indicated by the broken lines in the vertical direction, the inner diameter of the furnace body 6N expands more outward than at normal temperature due to thermal expansion at high temperatures.

  The detector 21 also extends outward from the center due to thermal expansion. However, when the thermal expansion coefficient of the material of the detector 21 is selected to be smaller than the thermal expansion coefficient of the material of the furnace body 6N, the inner diameter of the furnace body 6N is increased. Since the extension is larger, the heat conduction path length D shown in FIG. 5 is relatively longer at a higher temperature than at room temperature, and per unit time transmitted from the furnace body 6N to the detector 21 by heat conduction at a higher temperature. The amount of heat decreases compared to normal temperature. Further, the detector 21 is not restrained by the furnace body 6N due to the sliding structure of the present invention. Therefore, if the frictional force accompanying the sliding is removed, no thermal stress is generated and the risk of detector deformation is greatly reduced. 4 and 5 are the same as those in FIG. 1, and the detailed description thereof is omitted.

  FIG. 9 schematically shows the temperature dependence of the amount of heat supplied per unit time to the conventional technology and the detector of the present invention. That is, conventionally, even if the temperature changes, a constant amount of heat is supplied to the detector by heat conduction as shown by curve C. However, in the present invention, due to the relative extension of the heat conduction path, the detector 21 is heated by heat conduction. The amount of heat supplied per unit time decreases as the temperature increases, as shown by curve C ′.

  On the other hand, the amount of heat supplied to the detector 21 per unit time due to radiation increases as the temperature rises as shown by the curve R. In the present invention, the amount of heat supplied by heat conduction increases with increasing temperature as shown by the curve C ′. Therefore, the increase in heat transfer can be mitigated, and as a result, the detection sensitivity of DSC can be improved. In addition to the above, heat transfer to the detector includes convection transfer, which is not shown in FIG. 9 because there is no difference between the conventional method and the present invention.

  FIG. 10 schematically shows the relationship between temperature and DSC detection sensitivity. In the conventional structure, the detection sensitivity greatly decreases as indicated by the curve S as the temperature increases, but in the structure of the present invention, the decrease can be improved as indicated by the curve S ′.

  The present invention is not limited to the above-described embodiments, and various modifications can be given. For example, in the embodiment of FIG. 1, the hollow collar 23 is screwed to the furnace body 6N together with the detector 21 with the detector fixing screw 22, but the cylindrical body is previously screwed or welded to the furnace body 6N. The detector fixing screw 22 may be screwed together with the detector 21 with a female screw provided on the upper portion of the collar. The shape of the furnace body 6N is not limited to the shape shown in FIG. 1 as long as the surface can be in surface contact with the heat conduction path of the detector 21 and the plane of the peripheral portion is a contact surface.

  The shape of the end portion of the heat conduction path is not limited to the shape shown in FIG. 2, and may be a trapezoid or a triangle whose width decreases toward the tip, for example. In addition, in the structure of FIG. 1, in order to make the sliding more smoothly, an appropriate lubricant can be applied in advance to the contact surface between the furnace body 6N and the detector 21, or a lubricating layer can be formed by thermal spraying or the like. In FIG. 3, grooving is performed on the upper edge of the lower side wall T of the furnace body 6N according to the plate thickness of the detector 21, but the grooving may be performed on the lower surface of the detector fixing plate 5N. Further, a thin ring with a groove for mounting the detector 21 may be provided on the upper portion of the lower side wall T, and the detector fixing plate 5N may be fixed thereon. Further, in FIG. 3, the detector fixing plate 5N is cut out in the shape of figure 8, but this may be, for example, a circular cutting, and the present invention provides a cutting shape of the detector fixing plate 5N and a processing shape of the lower side wall T. It is not limited to. The present invention encompasses all of these.

  The present invention can be applied to a differential scanning calorimeter that heats a reference material and a sample, and measures a change accompanying a temperature increase and decrease in the enthalpy of the sample from the temperature difference between the two.

It is sectional drawing which shows the Example of this invention. It is a top view which shows the Example of this invention. It is a perspective view which shows the detector part of this invention. It is a figure which shows the thermal expansion at the time of the high temperature of the detector part of this invention. It is a figure which shows the heat transfer channel | path length of this invention. It is sectional drawing which shows the structure of the conventional differential scanning calorimetry apparatus. It is a top view which shows the detector of the conventional differential scanning calorimetry apparatus. It is a top view which shows the structure of the conventional differential scanning calorimetry apparatus. It is a figure which shows the relationship between the amount of heat transfer per unit time to a detector, and temperature. It is a figure which shows the relationship between DSC detection sensitivity and temperature. It is the figure which showed an example of the relationship of the furnace body in case a sample raise | generates melting | fusing, a reference material, and a sample.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace 2 Reference material container 3 Sample container 4 Detector 5 Detector fixing plate 5N Detector fixing plate 6 Furnace 6N Furnace 7 Fixing screw 7N Fixing screw 8 Heater 9 Furnace thermocouple 10 Reference material thermocouple 11 Sample thermocouple Pair 12 Heat conduction path 21 Detector 22 Detector fixing screw 23 Color B Furnace bottom D Heat conduction path length S Upper side wall T Lower side wall

Claims (1)

  Place a sample and a reference material in a cylindrical heating furnace, and raise or lower the temperature of the heating furnace according to a predetermined program to detect the temperature of the sample and reference material that are going up and down and the temperature difference between them. In a differential scanning calorimetry apparatus for measuring a change in enthalpy of a sample, a detector that is spanned across the inner space of the heating furnace and whose both ends are in sliding contact with the inner periphery of the heating furnace is provided. The thermal expansion coefficient of the detector is made of a material smaller than that of the heating furnace, and the relative distance between the detector and the heating furnace is changed when the heating furnace expands in diameter by heating. Differential scanning calorimeter.

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