GB2080941A - Differential thermal analysis and apparatus therefor - Google Patents

Abstract

The apparatus comprises block 1 defining chambers 2, 3 having openings 4, 5 in bottom portions 6, 7. In chamber 2, is crucible 14 for sample 15, and in chamber 3, is crucible 16 for standard 17. In block 1, between opening 4 and sample 15 is baffle 19, and between opening 5 and standard 17 is baffle 21. The baffles are made from a material similar to that of the block. Photoelectric pyrometer 24 points through opening 4 at baffle 19, and photoelectric pyrometer 25 points through opening 5 at baffle 21. Recording instruments 30, 31 are electrically connected to the outputs of the pyrometers. Instrument 30 is connected to outputs 26, 27 and instrument 31 is connected to outputs 26, 29 to form a comparison circuit. <IMAGE>

Description

SPECIFICATION Apparatus for differential thermal analysis The present invention relates to the design of equipment for investigating material properties, in particular to apparatus for differential thermal analysis. The invention can prove advantageous under laboratory conditions for investigating phase transformations in refractory materials.

Though the principle of differential thermal analysis has been known for a while and has found - wide application in investigating various materials, the requirements for increased accuracy and reliability of results are only now becoming urgent.

- In addition, the maximum operating temperature of the majority of manufactured devices intended for thermal analysis does not exceed 1 8000 C. This considerably limits the measuring capability of such devices, since the phase transformations in many refractory materials cannot be investigated.

Thus, the present invention consists in a differential thermal analysis in which photoelectric pyrometers measure the surfaces of containers containing respectively a sample and a standard.

The invention also consists in an apparatus suitable for differential thermal analysis comprising a block having two chambers each containing a container, one for a sample and one for a standard, and two photoelectric pyrometers one arranged to measure the surface of the sample-container and one arranged to measure the surface of the standard-container.

We prefer that baffles are provided between the surfaces of the containers and the pyrometers and in contact with the surfaces; in this case the pyrometers will of course measure the surfaces indirectly. The baffles are preferably convex facing the surfaces and concave facing the pyrometers.

The temperatures of the baffles correspond to the temperatures of the sample and of the standard. In this case it is possible to calibrate a temperature scale of the recording instruments in accordance with the critical temperatures of well known materials. This allows a possible difference between the temperature of the baffle and that of the sample to be automatically taken into account.

Thus, the above design features (orientation of the photoelectric pyrometers with respect to the baffles) eliminate the need for simulating an absolutely black body, and, hence, it is possible to investigate comparatively small samples of material, having a weight of 1 to 2 g. Such a procedure results in a considerable decrease in power consumption and in experimental cost.

Since the materials of the block and of the baffles are similar, inventable spraying of the block material into the baffles does not result in change of the surface composition of the baffles and does not exert any practical influence upon its degree of blackness. Accuracy of measurement is enhanced by the fact that the pyrometers are orientated to the baffles rather than to the material being investigated, as in the prior art apparatus. Also, any vaporization products of the material exert a significantly lower influence upon the light path sensed by the photoelectric pyrometers. The apparatus makes it possible to investigate materials being either in solid and in molten states.

The simplest embodiment structurally is one where the bottom portions of the crucibles themselves serve as the baffles. In this case the crucibles should be made from a material similar to that of the block.

More preferred is a modification of the apparatus where the baffles are constructed in the form of plates mounted beneath the bottom portions of the crucibles, and are in contact with them. The block may be made from a first material, e.g. a metal, while the crucibles may be made from a second material, e.g. a ceramic.

To prevent the plate buckling, it may be made convex, and the bottom portion of the corresponding crucible may be supported by the top portion of this convex surface.

From an economic point of view, it is advisable that both the block and the plates be made of tungsten.

Now the invention will be further described, by way of specific examples, with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic front view of an apparatus for differential thermal analysis; Figure 2 is a diagrammatic representation of a modification of the apparatus, provided with baffles in the form of plates; and Figure 3 is a diagrammatic representation of a modification of the apparatus, provided with convex plates.

Figure 1 shows an apparatus for differential thermal analysis comprising a block 1, defining two chambers 2 and 3 having openings 4 and 5 respectively. The opening 4 is provided in a bottom portion 6 of the chamber 2, while the opening 5 is provided in a bottom portion 7 of the chamber 3. The chambers 2 and 3 of the block 1 are closed from above with a cover 8. The block 1 is positioned on tubular stands 9 and 10, supported by an upper surface of a base 1 An upper end of the tubular stand 9 is mounted into a lower portion of the block 1 coaxially with the opening 4 of the chamber 2, while an upper end of the tubular stand 10 is mounted into a lower portion of the block 1 coaxially with the opening 5 of the chamber 3. Beneath the lower ends of the tubular stands 9 and 10 in the base 11 there are provided through openings 12 and 13.The opening 12 is made coaxial with the tubular stand 9 while the opening 13 is made coaxial with the tubular stand 10.

In chamber 2 of block 1 there is mounted a crucible 14 for a sample 1 5, while in chamber 3 there is mounted a crucible 1 6 for a standard material 1 7. A bottom portion 1 8 of the crucible 14 serves as a baffle 1 9 positioned between the sample 15 and the opening 4 of the chamber 2.

Similarly, a bottom portion 20 of the crucible 16 serves as a baffle 21 positioned between the standard material 17 and the opening 5 of the chamber 3. The baffles 19 and 21 are made from a material similar to that of the block 1.

A branch pipe 22 having an opening 23 positioned at its lower end is fixed to the lower surface of the base 11 beneath the openings 12 and 13.

The apparatus has two photoelectric pyrometers 24 and 25 shown positioned beneath the opening 23. The photoelectric pyrometers may be constructed in any suitable way, but we prefer to use a photoelectric pyrometer having a photodiode serving as the sensing element.

The photoelectric pyrometer 24 is directed, according to the invention, at the baffle 19 positioned between the sample 1 5 and the opening 4. The pyrometer, therefore, views through the opening 12 of the base 11, through the tubular stand 9 and through the opening 4 of the chamber 2.

Similarly, the photoelectric pyrometer 25 is directed at the baffle 21 positioned between the standard material 17 and the opening 5, via the corresponding elements.

The photoelectric pyrometer 24 has two outputs 26 and 27, and the photoelectric pyrometer 25 has outputs 28 and 29. Recording instruments 30 and 31 may be electronically connected to the outputs of the pyrometers.

Millivoltmeters or potentiometer-type recorders may be used as the recording instruments 30 and 31. The recording instrument 30 is connected to the outputs 26 and 27 of the photoelectric pyrometer 24 to measure the temperature of the sample 15.

Similarly the recording instrument 31 is connected to the output 26 of the photoelectric pyrometer 24 and to the output 29 of the photoelectric pyrometer 25 in the comparison circuit. In this way the difference between the temperature of the sample 1 5 and that of the standard material 1 7 can be measured.

The photoelectric pyrometers 24 and 25 are connected via their outputs 27 and 28 in seriesopposed connection.

A lens 32 is positioned between the photoelectric pyrometers 24 and 25, and opening 23.

Figure 2 shows a modification of the block 1 of the invention wherein the baffles 19 and 21 are made in the form of plates 33 and 34, respectively. The flat plate 33 is mounted beneath the bottom portion 1 8 of the crucible 14 and is in contact with it, and the flat plate 34 is mounted beneath and in contact with the bottom portion 20 of the crucible 1 6. The plates 33 and 34 are made from a material similar to that of the block 1.

The block 1, and the plates 33 and 34 are preferably made of tungsten.

Figure 3 shows a modification of the block 1, provided with convex plates 33 and 34.

The convex plate 33 is positioned beneath the bottom portion 18 of the crucible 14 to support it.

Similarly, convex plate 34 is positioned beneath the bottom portion 20 of the crucible 16, which it supports.

The apparatus described above may be operated as follows. With the cover 8 open, a sample 1 5 of the material to be investigated is placed in the crucible 12, and a standard material 1 7 is placed in the crucible 1 6. Then the cover 8 is closed, and the block 1 is heated. A material which undergoes no phase transformations over the temperature range investigated should be used as the standard when heating-the block 1, the crucibles 14 and 16, containing the sample 15 and the standard 17 respectively, are also heated. The baffles 19 and 21 (the bottom portions 18 and 20 of the crucibles 14 and 1 6 respectively in Figure 1) are also heated, their temperature substantially oorresponding to the temperatures of the sample and the standard respectively. Theflux of light radiation emitted by the baffle plate 1 9 is sensed by the photoelectric pyrometer 24 and the radiation emitted by the baffle 21 is sensed by the photoelectric pyrometer 25.

The recording instrument 30 when properly calibrated, indicates the temperature of the sample 15 and the recording instrument 31 indicates the difference between the temperature of the sample 1 5 and that of the standard material 1 7. When using recorders (not shown) as the recording instruments 30 and 31, a graphic display of the temperature variation of the sample 15 and of the temperature difference between the sample 15 and the standard material 17 is obtained. During a phase transformation in the material being investigated (the sample.15), the temperature difference between the sample and the standard changes to a considerable degree.

Critical temperatures of the material being investigated are determined by recording the initial and end temperatures of the phase transformations, both in the solid state and in the process of melting the material.

The modifications of the apparatus shown in Figures 2 and 3 can be operated substantially as described above. However, the plates 33 and 34 serve as radiation- sources of the measured light flux.

The temperatures of the plates 33 and 34 vary according to the temperatures of the sample 1 5 and of the standard 17, due to the intensive heat exchange between the crucibles 14 and 1 6, and the plates.

Claims (12)

1. A differential thermal analysis in which photoelectric pyrometers measure the surfaces of containers containing respectively a sample apd a standard.

2. An analysis according to Claim 1, in which the pyrometers measure the surfaces of the containers indirectly via baffles in contact with the surfaces.

3. An apparatus suitable for differential thermal analysis, comprising a block having two chambers each containing a container, one for a sample and one for a standard, and two photoelectric pyrometers one arranged to measure the surface of the sample-container and one-arranged to measure the surface of the standard-container.

4. An apparatus according to claim 3, in which baffles are provided between each pyrometer and the corresponding surface, so that the pyrometers measure the surfaces indirectly.

5. An apparatus according to claim 4, in which the baffles are convex facing the surfaces and concave facing the pyrometers.

6. An apparatus according to any one of claims 3,4 and 5, which additionally comprises a recorder connected to the outputs of the pyrometer of the sample, and a recorder connected to the outputs of the two pyrometers together as a comparison circuit.

7. An apparatus for differential thermal analysis comprising a block defining two chambers having openings in bottom portions thereof; a crucible for a sample, and a crucible for a standard material, which crucibles are mounted in the corresponding block chambers; baffles of which one is positioned within the block between the corresponding opening and a sample while another baffle is positioned between the corresponding opening and a standard material, said baffles being made from a material similar to thatr of the block; photoelectric pyrometers of which one is pointed through the corresponding opening at the baffle positioned between the sample and said-opening; recording instruments electrically connected to the outputs of the photoelectric pyrometers.

8. An apparatus as claimed in claim 7, wherein the crucible bottom portions serve as the baffles, said crucibles being made from a material similar to that of the block.

9. An apparatus as claimed in claim 7, wherein the baffles are made in the form of plates mounted beneath the crucible bottom portions and are in contact therewith.

10. An apparatus as claimed in claim 9, wherein each plate is convex, and the bottom portion of the corresponding crucible is supported by the top of the convex surface thereof.

11. An apparatus as claimed in claim 10, wherein said plates and the block are made from tungsten.

12. An apparatus according to claim 3, as herein described with reference to any one of the accompanying drawings.

1 3. An analysis according to claim 1, as herein described with reference to any one of the accompanying drawings.