Patent Application
20080080591
Next, an embodiment of the present invention will be described with reference to the accompanying drawings. For ease of understanding of the description, in each drawing the same reference numeral is given to the same component, and the duplicating description is omitted.
As shown in
The furnace body 11 is made of silver and is symmetrical about the center axis, and the cross section thereof is H-shaped. Then, one concave space of the H-shape serves as a sample chamber 11a for installing a sample. The furnace body 11 transmits a heat transmitted from the heater wire 12 to the entire inside of the sample chamber. The heater wire 12 is wound around the furnace body 11 and generates heat to thereby heat the furnace body 11. The power supply to the heater wire 12 is adjusted by the furnace body temperature control circuit 20 described below to thereby control the heat generation.
The furnace body cover 13 is made of silver and has a cylindrical shape to cover the furnace body 11 and heater wire 12. The sensor base 14 is made of silver and has a long plate shape. The end face of the sensor base 14 has a circumferential face shape along the inner wall of the furnace body, and the sensor base 14 has, in the center thereof, side surfaces that are depressed inward along the outer peripheries of heat sensitive plates 35, 36 described later. The sensor base 14 is fixed with screws onto the bottom face of the sample chamber 11a in the furnace body 11. The insulating sheet 15 has the same contour as that of the upper surface of the sensor base 14, and is arranged covering the upper surface of the sensor base 14. In order to prevent the thermocouple element from being short-circuited to the silver-made sensor base 14, the insulating sheet 15 electrically isolates the both from each other. Moreover, if there is a sufficient gap between the bottom face of the base plate 31 and the thermocouple element, there is no need to provide the insulating sheet 15.
The furnace body temperature control circuit 20 has a furnace body temperature sensor 21, a temperature measurement circuit 22, a heater temperature control circuit 23, and a power supply circuit 24. As the furnace body temperature sensor 21, a thermocouple can be used, for example. The furnace body temperature sensor 21 sends a signal indicative of the temperature of the furnace body to the temperature measurement circuit 22. The temperature measurement circuit 22 outputs a signal from the furnace body temperature sensor 21 as a temperature value. The heater temperature control circuit 23 controls the power supply so that the furnace body temperature follows a set temperature pattern, with reference to the value of the obtained furnace body temperature. The power supply circuit 24 supplies power to the heater wire 12 under the control of the heater temperature control circuit 23. In this way, the furnace body temperature control circuit 20 controls the temperature of the furnace unit 10.
The sensor unit 30 has a base plate 31 (base part), a multiple thermocouple 32, a heat sensitive plate (heat sensitive part) 35 used for a measurement sample, and a heat sensitive plate (heat sensitive part) 36 used for a reference sample. The sensor unit 30 transmits heat from the furnace body 11 to the sample and also has the function to detect the temperature of the sample.
The base plate (base part) 31 is made of aluminium nitride and is long-plate shaped. The base plate 31 also has substantially the same contour as that of the sensor base 14. The base plate 31 features the shape of the groove and the like, which will be describes later. The base plate (base part) 31 is fixed with screws onto the sensor base 14 with the insulating sheet 15 interposed therebetween. Thus, the base plate 31 is in contact with the furnace unit 10, but a gap may be provided between the base plate 31 and the furnace unit 10. In either case, the base plate 31 is provided in the vicinity of the furnace unit 10. The vicinity refers to the range in which thermal interaction occurs.
Aluminium nitride used for the base plate 31 is an insulating material, and has such a high thermal conductivity as that of metal and is excellent in junction property with metal. As the material of the base plate 31, a ceramic with a high thermal conductivity is suitable, and the use of this increases the measurement sensitivity. In addition, as the ceramic with a high thermal conductivity, silicon carbide other than aluminium nitride is also suitable. In addition, the base plate 31 serves also as a heat sink, and by transmitting heat to each sample container, the both are placed under the thermally same condition.
The multiple thermocouple 32 is formed by alternately joining the elements made of two kinds of thermocouple materials, wherein four pairs of thermocouples are formed. As the two kinds of thermocouple materials, a combination of constantan-chromel that generates a high voltage with respect to a temperature difference is suitable. However, a combination of platinum-rhodium having a different component ratio of rhodium, a combination of platinum-platinum rhodium, a combination of Nisil-Nicrosil, a combination of alumel-chromel, a combination of constantan-iron, a combination of constantan-copper, and the like may be employed, and the combination is not limited.
Moreover, the multiple thermocouple 32 is formed by overlaying and joining flat plate shaped elements made of each thermocouple material at a element junction, thus producing a step due to the joint, but the multiple thermocouple 32 is substantially flat plate shaped. This improves the ease of installation into the furnace body 11. Moreover, the multiple thermocouple 32 is more immune to oxidization than the thin wire shaped one. In each element, a region (a particular part) overlapping with the base plate 31 is joined to the base plate 31. Due to this joint, the lower surface of the multiple thermocouple 32 is floated by the base plate 31, thus producing a gap between the same and the insulating sheet 15. Accordingly, the heat of the furnace body 11 is transmitted to the multiple thermocouple 32 from the joining part between the base plate 31 and the thermocouple element mainly via the base plate 31.
The pair of heat sensitive plates (heat sensitive parts) 35, 36 is a disk made of aluminium nitride, and in one principal surface thereof there is a mounting surface to mount each sample container. Then, to the other principal surface, the element junctions of the multiple thermocouple are electrically independently joined, respectively. Being electrically independent means not affecting potentials without interfering to each other. At least, each element junction is constituted so as not to conduct on the heat sensitive plates 35, 36. The heat sensitive plates 35, 36 are supported spaced apart from the base plate 31 by the multiple thermocouple 32. Accordingly, if there is an appropriate thermal resistance between the heat sensitive plates 35, 36 and the base plate 31 and there is a change in the measurement sample, a steep temperature gradient will occur between the measurement sample S and the reference sample R, thus increasing the thermal electromotive force. As a result, the sensitivity and S/N ratio of the sensor will improve. Moreover, a temperature change in the sample can be detected with high sensitivity by preventing the heat transmitting to the heat sensitive plates 35, 36.
On the other hand, the base plate 31 and the heat sensitive plates 35, 36 are connected by the multiple thermocouple 32. Accordingly, the multiple thermocouple 32 can transmit heat from the base plate 31 to the heat sensitive plates 35, 36 each, so that the time constant of sample temperature can be kept small. For example, a situation can be prevented, in which despite that a change in the measurement sample S has already finished a peak is subsequently detected because the response to the sample temperature is too slow. Since the base plate 31 and the heat sensitive plates 35, 36 are connected to each other by the multiple thermocouple, the sensor sensitivity will not be reduced. As a result, a change in the heat absorption, heat generation, or the like of the measurement sample S can be detected satisfactorily.
The heat of the base plate 31 is transmitted to each sample container via the multiple thermocouple 32 and heat sensitive plates 35, 36. On the other hand, the heat sensitive plates 35, 36 transmit a temperature change of the sample to the thermocouple with high sensitivity. As the material of the heat sensitive plates 35, 36, a ceramic with a high thermal conductivity is suitable. For example, silicon carbide other than aluminium nitride is also suitable.
The output circuit 40 has a thermocouple 41 used for a reference sample, lead lines 42, 43, a baseline correction circuit 45, a heat quantity calculation circuit 46, and an output unit 47. The output circuit 40 corrects a signal from the multiple thermocouple 32 and converts a temperature difference into a heat quantity, and outputs this on a screen, a paper, or the like.
The thermocouple 41 used for a reference sample is a thermocouple provided in the vicinity of the reference sample R, for the purpose of baseline correction. The thermocouple 41 used for a reference sample sends a signal of the temperature of the reference sample R to the baseline correction circuit 45. The lead lines 42, 43, with one end thereof being connected to the multiple thermocouple 32 and the other end being connected to the baseline correction circuit 45, send a temperature difference between both samples to the baseline correction circuit 45. The furnace body 11 has a hole opened, through which an alumina pipe is inserted, and the lead lines 42, 43 are connected to the baseline correction circuit 45 through this hole. The baseline correction circuit 45 corrects the baseline by subtracting from a temperature difference between the measurement sample S and the reference sample R a value obtained by multiplying the temperature value of the reference sample R by a suitable factor. The heat quantity calculation circuit 46 converts into a heat quantity (heat flow difference) the value of a temperature difference after the baseline is corrected. The output unit 47 is a display device or a printing device, for example, which displays the heat flow difference on a screen or prints the same on a paper. The thermal analysis equipment 1 is constituted in this manner, and especially the sensor unit 30 has a feature for increasing the sensitivity of temperature difference detection.
The base plate 31 and heat sensitive plates 35, 36 are arranged on the same side of the multiple thermocouple 32. However, the base plate 31 is not in contact with the heat sensitive plates 35, 36 and is arranged so that heat may not be directly transmitted from the base plate 31 to the heat sensitive plates 35, 36. The heat sensitive plates 35, 36 are formed thinner than the base plate 31, thus forming a suitable shape for temperature detection. Moreover, the multiple thermocouple 32 is fitted into grooves 31b, 31c of the base plate 31, producing a slight gap between the multiple thermocouple 32 and the furnace unit 10. As a result, the multiple thermocouple 32 separates the pair of heat sensitive plates 35, 36 from the furnace unit 10 and base plate 31, and supports the same.
Moreover, the sensor can be made compact because the thermocouple elements are installed into the base plate 31. Then, since the thermocouple elements are fixed to predetermined positions, it is possible to take a structural balance and form a uniform structure. In addition, if the heat transfer from the furnace unit 10 should be set high, the above-described gap may be eliminated to adhere the multiple thermocouple 32 and the furnace unit 10 to each other.
Moreover, by means of the grooves 31b, 31c, the brazing filler metal for joining in the groove can be prevented from flowing out. Moreover, a stress occurring between the furnace unit 10 and the base plate 31 due to thermal expansion can be reduced by reducing the contact area with the furnace unit 10 of a flat region 31d.
The contact faces between the multiple thermocouple 32 and the grooves 31b, 31c are joined with gold brazing filler metal. Among the respective thermocouple elements constituting the multiple thermocouple 32, for the thermocouple element at both ends, the end portion thereof is joined to the base part 31, and for the other thermocouple elements, the center portion thereof is joined to the base part 31. Moreover, four alternate element junctions of the multiple thermocouple are collected, respectively, and are joined to the heat sensitive plate 35 on the measurement sample side and to the heat sensitive plate 36 on the reference sample side.
Corresponding to the depth of the groove, a thermocouple element made of a respective material is fitted therein. In the bottom face on the sensor base 14 side, the flat region 31d, in which the groove is not formed, is in contact with the insulating sheet 15, through which the heat of the furnace body 11 is transmitted. The base plate 31 has a constricted shape, with the center portion of the side face being depressed. The inwardly depressed side face 31e is formed with a radius of curvature slightly larger than that of the circumference along the circumference of the heat sensitive plates 35, 36, so that the base plate 31 and the heat sensitive plates 35, 36 will not contact to each other. This miniaturizes the sensor unit 30 to improve the ease of installation into the furnace body 11, and also separates the heat sensitive plates 35, 36 from the base plate 31. An end face 31f of the base plate 31 is circumferential-face shaped so as to be easily installed along the inner wall of the sample chamber 11a of the furnace body.
The elements are spot welded together, or joined together using a brazing filler metal, such as gold. In
The heat sensitive plates 35, 36 are made of aluminium nitride and have a thin disc shape. In the opposite surface of the sample mounting surface of the heat sensitive plates 35, 36, a collection of four alternate element junctions of the multiple thermocouple 32 are joined with gold brazing filler metal, respectively. The sensor unit 30 is constructed in this manner.
Next, the manufacturing process of the sensor unit 30 and the assembly process of the thermal analysis equipment 1 will be described.
First, two flat plates 60, 70 formed of each thermocouple material of chromel and constantan are formed in predetermined patterns by etching. The formation method is not limited to etching. The patterns remain in the shape of a punched-out flat plate, leaving outer frames 61, 71 of each flat plate and connection portions 63, 73 between the outer frame and the thermocouple elements 32b, 32a. Moreover, holes 62, 72 for alignment are opened at four corners of the outer frames 61, 71. This facilitates joining and assembling.
Subsequently, a joining metal layer is formed in the surface of a predetermined portion of two patterned flat plates 60, 70, base plate 31, and pair of heat sensitive plates 35, 36. The predetermined portion refers to: each contact surface 65, 75 of a portion where the thermocouple element 32b and the thermocouple element 32a form a element junction; contact surfaces 66, 76, and 80 between the thermocouple elements 32b, 32a and the base plate 31; and contact surfaces 77, 81 between the thermocouple element 32a and the heat sensitive plates 35, 36. In the thermocouple elements at both ends, the end portions thereof are adhered and joined to the base plate 31. For the thermocouple elements other than the ones at both ends, the central parts thereof are adhered and joined to the base plate 31. The respective four element junctions of the multiple thermocouple 32 are joined to the heat sensitive plates 35, 36. As the material of the metal layer, gold or silver is suitable, but not limited to this. Moreover, the metal layer may be formed by plating, vapor deposition, or the like, and the formation method is not limited in particular.
Next, two patterned flat plates 60, 70 are overlaid and adhered to the base plate 31 and pair of heat sensitive plates 35, 36. In overlaying, the holes 62, 72 at the corners of the outer frames 61, 71 are overlapped to carry out alignment. Then, a pressure is applied to the adhered portion, and the temperature is increased to a predetermined value for joining. In this way, by carrying out the metal layer formation processing and joining, each joining part becomes uniform. As a result, a thermal symmetry can be obtained between the measurement sample S and the reference sample R, and a structural influence can be eliminated to thereby capture a temperature change in the measurement sample. Finally, the outer frames 61, 71 of the flat plates 60, 70 made of thermocouple materials and the connection portions 63 and 73 are removed. In this manner, the sensor unit 30 can be prepared.
Moreover, the thermal analysis equipment 1 can be prepared by assembling the furnace unit 10 and the sensor unit 30 by fixing with screws.
Moreover, in the above-described embodiment, as the brazing filler metal for joining, gold is used, but other brazing filler metal such as silver or the like may be used. As the other brazing filler metals, the ones suitable for the metal layer formation processing or suitable for the surface material of the joint metal are preferable.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-272175 | Oct 2006 | JP | national |
