GB2222885A

GB2222885A - Thermal analysis apparatus

Info

Publication number: GB2222885A
Application number: GB8921134A
Authority: GB
Inventors: Yoshihiko Teramoto; Nobutaka Nakamura
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1988-09-20
Filing date: 1989-09-19
Publication date: 1990-03-21
Anticipated expiration: 2009-09-19
Also published as: GB8921134D0; GB2222885B; KR900005162A; JPH0282145A

Abstract

Thermal analysis apparatus e.g. a differential scanning calorimeter comprises four sample holders (4 to 7), a cylindrical heat sink (3) for conducting thermal exchange with the sample holders, a temperature controller (1) for controlling the temperature of the heat sink, thermo-couples (8 to 11) provided on the sample holders, and a recorder (12) for recording an output from the four thermo-couples. The sample holders are disposed symmetrically on two crossing diagonal lines (21, 22) drawn between the centres of each pair of opposing sample holders, equi-distantly from the crossing point (23) of the two diagonal lines. As shown the temperature controller (1) regulates an electric furnace (2) to control the heat sink temperature; the thermocouples in a pair of opposed sample holders are connected in parallel with the parallel pairs in series opposition. Other thermocouple connections are, however, envisaged. <IMAGE>

Description

THERMAL ANALYSIS APPARATUS This invention relates to thermal analysis apparatus, for example, differential scanning calorimeters.

A conventional differential scanning calorimeter has two sample holders, each of which is provided with a thermo-couple. Opposing polarities of the thermocouples are connected to detect the difference in thermo-electromotive output there-between.

In such a conventional differential scanning calorimeter, when a temperature gradient exists in one particular direction, the apparent thermal change caused by such temperature gradient can be compensated.

However, compensation is less when a temperature gradient exists in directions other than this particular direction. When a temperature gradient exists in a direction along a line drawn between the two sample holders, the compensation is at its lowest. Therefore, temperature gradients existing in a sensor system of the differential scanning calorimeter are measured in addition to thermal changes of a sample under consideration. This results in an apparent change in heat transmission and this varies depending upon directions of temperature gradients. Therefore the conventional differential scanning calorimeter is not satisfactory from the point of view of stability and accuracy.

Although the present invention is primarily directed to any novel integer or step, or combination of integers or steps, herein disclosed and/or as shown in the accompanying drawings, nevertheless, according to one particular aspect of the present invention to which, however, the invention is in no way restricted, there is provided a thermal analysis apparatus comprising: four sample holders; a cylindrical heat sink for conducting thermal exchange with said sample holders; means for controlling the temperature of said heat sink; a thermo-couple provided on each sample holder; and recording means for recording an output from said four thermo-couples, said sample holders being disposed on two crossing diagonal lines drawn between centres of each pair of opposing sample holders, said each opposing pair of sample holders being disposed equidistantly from the crossing point of the two diagonal lines.

Said four sample holders may be disposed on a circle.

In one embodiment the thermo-couples provided on each pair of opposing sample holders are connected in parallel and in the same polar direction, and the two pairs of parallel-connected thermo-couples are connected together in series and in the opposite polar direction.

In another embodiment said four thermo-couples are connected successively in series and in the opposite polar direction.

One pair of opposing sample holders may hold sample material to be measured, and the other pair may hold reference material. Alternatively, one of said four sample holders may hold sample material to be measured and the remaining three sample holders may hold reference material.

When the temperature of the heat sink is controlled, i.e. raised, lowered or stabilised by the means for controlling the temperature of the heat sink, temperature gradients occur in the heat sink and this affects the sample holders. The thermo-couples mounted on the sample holders detect temperatures at positions corresponding to respective sample holders. Since the sample holders are disposed in the manner described above, temperature gradients in any direction which exist and which are measured in addition to thermal changes of a sample to be measured are compensated, and apparent change in heat transmission is eliminated. As a result, the thermal change only in the sample is measured with high precision.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 shows schematically an embodiment of a differential scanning calorimeter according to the present invention; Figure 2 is a diagram illustrating an example of wiring of thermo-couples of the differential scanning calorimeter of Figure 1; and Figure 3 is a diagram illustrating another example of the wiring connection of thermo-couples of the differential scanning calorimeter of Figure 1.

Referring first to Figure 1, a differential scanning calorimeter according to the present invention has a temperature controller 1 which connects to an electric furnace 2. A cylindrical heat sink 3 is disposed in contact with the electric furnace 2. Sample holders 4, 5, 6, 7 are disposed in a concentric circle within the heat sink 3. Thermo-couples 8, 9, 10, 11 are mounted respectively on the sample holders 4, 5, 6, 7.

The arrangment of the thermo-couples provided on the sample holders 4, 5, 6, 7 is not limited to that shown in Figure 1. In general, the four sample holders are disposed on two crossing diagonal lines 21, 22 drawn between the centres of the opposing sample holders, each opposing two sample holders being disposed equidistantly from the crossing point 23 of the two diagonal lines 21, 22.

Figure 2 shows one example of the wiring connection of the four thermo-couples 8, 9, 10, 11. In Figure 2, the same polarities of the thermo-couples 8, 9 are connected in parallel, and also the same polarities of the thermo-couples 10, 11 are connected in parallel in order to average the thermo-electric outputs thereof. This wiring connection of the thermo-couples provides an output corresponding to a difference between an output provided by the combined thermo-couples 8, 9 and an output provided by the combined thermo-couples 10, 11. An output from the four thermo-couples is provided to a thermal transition recorder 12.

In operation, first the temperature controller 1 is controlled to provide a pre-determined temperature in the electric furnace 2. Thus the temperature of the heat sink 3, which closely contacts the electric furnace 2, changes accordingly. However, the heat sink will not have a uniform temperature distribution, and will have temperature gradients. As a result, the sample holders 4, 5, 6, 7 have different temperatures, and accordingly the thermo-couples 8, 9, 10, 11 provide different thermo-electromotive outputs. When there is a temperature gradient along the line 23 drawn between the sample holder 6 and the sample holder 7, the average output of the thermo-couple 10 and the thermo-couple 11 is the same as an output of the thermo-couple 8 or the thermo-couple 9, because the average output represents an apparent thermo-electromotive output at a temperature at the crossing point 23.Therefore, outputs provided by the combined four thermo-couples are compensated with each other, and their difference becomes zero, since they are connected in a manner to produce a difference of thermo-electromotive outputs between pairs of thermocouples. As a result, there is no change in output which is provided to the thermal transition recorder 12.

When there is a temperature gradient along the direction of the sample holder 4 and the sample holder 5, and the thermo-couple 8 indicates a higher temperature than the thermo-couple 9, each of the thermocouples 10, 11 has an average temperature of the thermocouples 8, 9. Therefore outputs of the combined four thermo-couples are compensated with each other and their difference becomes zero, and consequently no change in output is provided to the temperature transition recorder 12. In the case of temperature gradients in other directions there are also similar compensating effects, and therefore apparent thermal transition which may be caused by temperature gradients does not appear on the thermal transition recorder 12.

Now, sample material to be measured is placed in one pair of opposing sample holders 6, 7 and reference material (e.g. sapphire) is placed in the other pair of opposing sample holders 4, 5. An averaged thermoelectromotive output provided by the thermo-couples 8, 9 mounted respectively on the sample holders 4, 5 which hold the reference material, represents the thermoelectromotive output at a temperature at the crossing point 23, and an averaged output of the thermo-electromotive outputs provided by the opposing thermo-couples 10, 11 mounted respectively on the sample holders 6, 7 which hold the sample material to be measured, represents the thermo-electromotive output at a temperature at the crossing point 23.Therefore, the difference between the two averaged thermo-electromotive outputs is a measure of the thermal characteristics of the sample material at the temperature of the crossing point 23.

Next, let us consider another example in which sample material is placed in the sample holder 7 and reference material is placed in the remaining three sample holder 4, 5, 6. When the reference material is placed in all of the four sample holders 4, 5, 6, 7 the output to the thermal transition recorder 12 provided by such an arrangement becomes zero. However, when one of the sample holders holds a sample material, the output is representative of the thermal characteristics of the sample material in the sample holder 7.

Further, according to the method of wiring described hereinabove in relation to Figure 2, an output Eo provided to the thermal transition recorder is defined by: E8 + E9 E10 + Ell Eo = ~ 2 2 where, E8, E9, E10, Ell are the thermo-electromotive outputs of the thermo-couples 8, 9, 10, 11 respectively.

It will be appreciated from the above equation that the output value Eo is proportional to the value obtained by the subtraction of the sum of the electromotive outputs provided by the thermo-couples 10, 11 from the sum of the thermo-electromotive outputs provided by the thermo-couples 8, 9.

As shown in Figure 3, the same result is obtained by a different wiring connection in which the thermocouples 8, 9 are connected in the same polar direction and the thermo-couples 10, 11 are also connected in the same polar direction; and the connected thermo-couples 8, 9 and the connected thermo-couples 10, 11 are connected in series but in the opposing polar direction.

In this case, the value El to be provided to the thermal transition recorder 12 is given by the following equation: El = (E8 + E9) - (E10 - Ell) = 2Eo When the thermo-couples 8, 9, 10, 11 are connedted in series as described above, the same polarities thereof should be connected. If opposing polarities of thermo-couples are connected, thermo-electro-motive outputs are generated at the connecting points. Namely, as shown in Figure 3, the thermo-couples adjoining each other are connected in series.

In the thermal analysis apparatus according to the present invention and described above, apparent thermal transitions caused by temperature gradients in the heat sink 3 are effectively eliminated and thermal characteristics of a sample itself can be observed. As a result, data on the sample can be obtained with high stability and reproducibility.

Claims

1. A thermal analysis apparatus comprising: four sample holders; a cylindrical heat sink for conducting thermal exchange with said sample holders; means for controlling the temperature of said heat sink; a thermo-couple provided on each sample holder; and recording means for recording an output from said four thermo-couples, said sample holders being disposed on two crossing diagonal lines drawn between centres of each pair of opposing sample holders, said each opposing pair of sample holders being disposed equidistantly from the crossing point of the two diagonal lines.

2. A thermal analysis apparatus as claimed in claim 1 in which said four sample holders are disposed on a circle.

3. A thermal analysis apparatus as claimed in claim 1 or 2 in which the thermo-couples provided on each pair of opposing sample holders are connected in parallel and in the same polar direction, and the two pairs of parallel-connected thermo-couples are connected together in series and in the opposite polar direction.

4. A thermal analysis apparatus as claimed in claim 1 or 2 in which said four thermo-couples are connected successively in series and in the opposite polar direction.

5. A thermal analysis apparatus as claimed in any preceding claim in which one pair of opposing sample holders holds sample material to be measured and the other pair holds reference material.

6. A thermal analysis apparatus as claimed in any of claims 1 to 4 in which one of said four sample holders holds sample material to be measured, and the remaining sample holders hold reference material.

7. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of or relates to the same, or a different, invention from that of the preceding claims.