JPH07260663A - Gas analyzing method in thermogravimetry - Google Patents

Abstract

PURPOSE:To improve analyzing capacity for gas even if a thermobalance and a mass spectrometer are connected directly, by devising temperature control of a sample. CONSTITUTION:A thermobalance includes a sample container 12 and a standard sample container 14 in its protecting tube 10, and an infrared ray lamp 20 is placed around the protecting tube 10. In an automatic program temperature control device 42, specified numeric formulas with which temperature-up speed becomes a simple reduction function of reduction speed, is stored. The gas generated from the thermobalance is taken out of the upper part of the protecting tube 10, and then introduced into a mass spectrometer 50. Even if a different reaction occurs with the sample at a similar temperature, since temperature control of the sample is devised, the generated gas in each reaction stage can be taken out separately. So, with the mass spectrometer, identification of the generated gas by pattern matching becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a generated gas analysis method for analyzing a gas generated in thermogravimetric measurement.

[0002]

2. Description of the Related Art There are several known methods for analyzing evolved gas in thermogravimetric measurement. For example, an evolved gas analysis method is known in which a thermobalance, a gas chromatograph, and a mass spectrometer are combined. In this method, the gas generated by a thermobalance is introduced into a gas chromatograph, the generated gas is separated into each component, and then each separated component is introduced into a mass spectrometer, and each component is specified by pattern matching. .

By the way, the upper limit temperature at which the gas chromatograph can be used is about 300 ° C., and if the temperature exceeds this temperature, the gas chromatograph cannot be used. For example, in paraffin hydrocarbons, when the molecular weight exceeds 500, the boiling point exceeds 300 ° C., and therefore it becomes impossible to use a gas chromatograph for such a substance.

There is also known a method of analyzing generated gas in which a thermobalance and a mass spectrometer are directly connected. This method is effective when there is only one type of gas generating reaction in the sample, or when the reaction temperatures of a plurality of gas generating reactions are considerably different from each other. On the other hand, when there are a plurality of gas generation reactions and the reaction temperatures are close to each other, the generated gases are mixed, and when this is directly introduced into the mass spectrometer, the generated gas components are Cannot be specified. When performing gas analysis with a mass spectrometer, the mass analysis pattern of the gas to be analyzed is measured and compared with the standard pattern of various gases to identify the type of gas. When the generated gas of is mixed, it becomes impossible to specify by such pattern matching.

In the conventional method for analyzing the generated gas in which the thermobalance and the mass spectrometer are directly connected, the sample temperature control in the thermobalance is performed as follows. The simplest method of changing the sample temperature is a method of heating (or cooling) the sample at a constant heating rate (or cooling rate). This method
There is a drawback that the resolution of the weight measurement is poor. The fact that the resolution of the weight measurement is poor means that the measurement accuracy of the starting temperature and the ending temperature of the weight change, and the amount of weight change during that period is poor. The reason why the resolution is inferior when the constant speed temperature increase (or temperature decrease) is used is as follows. Even if a large weight change occurs in the sample, the sample temperature rises or falls at a constant speed, so that the sample temperature may shift to another sample before the state change of the sample is sufficiently completed. In such a temperature control method, when different reactions that cause a change in weight of the sample occur at close temperatures, it becomes impossible to measure these separate reactions separately. Therefore, pattern matching by a mass spectrometer is also impossible. In order to avoid such a drawback, it is conceivable to make the rate of temperature rise (or rate of temperature decrease) very small so that separate reactions having close temperatures are separated as much as possible. However, in this case, the measurement time becomes very long, which is not realistic.

By the way, as a method for controlling the sample temperature in the thermobalance, a method is known in which separate reactions having close temperatures can be separated with high accuracy. For example, a method is known in which the temperature rise is stopped when the weight reduction of the sample starts. That is, when the absolute value of the weight reduction rate of the sample becomes equal to or more than a predetermined set value, the temperature increase is stopped and the sample is held isothermally. When the temperature becomes equal to or lower than the predetermined set value of, the temperature rise is started again. Such a temperature control method uses SIA (Step
wise Isothermal Analysis), which is referred to as "Thermochimica Acta. 138 (1989), p.107-1".
14 ”. According to this method, it is possible to accurately separate a plurality of decomposition phenomena whose decomposition temperatures are close to each other, and the resolution is improved as compared with the conventional constant temperature rising method.

Further, as a method superior to the SIA method described above, there is also known a method of controlling the sample temperature so that the temperature change rate of the sample continuously changes according to the weight change rate of the sample (No. 1). Proceedings of the 29th Symposium on Thermal Measurement, published by The Japan Society for Thermal Measurement, 1993, p.330-331).

[0008]

In the evolved gas analysis method in which the thermobalance and the mass spectrometer are directly connected to each other, there is a possibility that the evolved gas may be mixed in the general sample temperature control method by constant temperature rising. In that case, it becomes impossible to specify the generated gas by pattern matching by the mass spectrometer. Further, a more excellent temperature control method is known in which the sample temperature is controlled according to the rate of weight change of the sample. unknown.

An object of the present invention is to provide an evolved gas analysis method which has an excellent analysis ability even when the thermobalance and the mass spectrometer are directly connected by devising the temperature control of the sample.

[0010]

According to the method for analyzing evolved gas of the present invention, the temperature of the sample is controlled by controlling the temperature of the sample according to the rate of change of the weight of the sample, and the gas generated from the sample is analyzed by a mass spectrometer. It is characterized in that the type of gas generated in each reaction stage of the sample is identified by introducing into In the conventional evolved gas analysis using a mass spectrometer, the sample temperature was not controlled in accordance with the weight change rate of the sample, but in the present invention, the sample temperature is adjusted in accordance with the weight change rate of the sample. Are in control. For example, when the weight reduction rate of the sample becomes equal to or higher than a predetermined value, the rate of temperature rise is made extremely small or the temperature rise is stopped.

In another invention, as a method of controlling the sample temperature in accordance with the weight change rate of the sample, the sample temperature is controlled so that the temperature change rate of the sample continuously changes in accordance with the weight change rate of the sample. is doing. That is, when the weight of the sample changes from moment to moment, the weight change rate is calculated, and the temperature change rate suitable for the weight change rate is set,
The temperature of the sample is controlled so that the temperature change speed becomes such a rate. The temperature change rate is continuously changed with respect to the weight change rate. In other words, the rate of temperature change can be expressed as a continuous function of the rate of weight change.

The temperature change rate of the sample is a continuous function of the sample weight change rate. This means that when the rate of change of weight changes, the rate of temperature change continuously changes accordingly. Examples of continuous functions that can be used include rational integer functions, irrational functions, exponential functions, and logarithmic functions.

Further, it is preferable that the absolute value of the temperature change rate of the sample be a monotonically decreasing function of the absolute value of the sample weight change rate. This means that the larger the absolute value of the rate of change in weight of the sample (the more rapid the decrease in weight or the increase in weight), the smaller the absolute value of the rate of change in temperature of the sample (the increase or decrease in temperature). Means to be slow). As an example of the monotonically decreasing function that can be used, a region in which the monotonically decreasing function is used can be used in the above examples of the continuous function.

In order to control the sample temperature according to the rate of weight change of the sample as in the present invention, it is desirable to use a sample heating furnace having a good control response. For that purpose, the infrared heating furnace is the most suitable.

[0015]

In order to carry out the present invention, the weight change rate of the sample is measured by the thermobalance, and the temperature of the sample is controlled according to the measurement result. Then, the generated gas in the thermobalance is introduced into the mass spectrometer, and the type of the generated gas is specified. Since the sample temperature is controlled according to the rate of weight change of the sample,
When the weight change rate of the sample is large, the temperature change is reduced so that the generated gas in each reaction stage can be separated and taken out even when different reactions occur in the sample at close temperatures. Therefore, the generated gases are not mixedly introduced into the mass spectrometer, and the generated gases can be identified by pattern matching in the mass spectrometer.

When the temperature is controlled so that the temperature change rate of the sample becomes a continuous function of the weight change rate, the temperature control is performed as follows. The weight change rate of the sample is measured by a thermobalance, and the temperature change rate of the sample is changed according to the measurement result. The temperature change rate of the sample can be expressed as a continuous function of the weight change rate, and the temperature of the sample is controlled by, for example, the PID control method with this as a target value. The temperature change rate of the sample can be optimally changed according to the sample weight change rate. The most preferable control method is to relatively increase the absolute value of the temperature change rate of the sample when the absolute value of the weight change rate of the sample is small, and to increase the temperature change rate of the sample when the absolute value of the weight change rate of the sample becomes large. Is to be relatively small. As a result, when the weight of the sample is gradually decreased or increased, the rate of temperature increase or rate of temperature decrease can be increased, and the measurement time can be shortened.
Further, when the weight decrease or weight increase of the sample is abrupt, the temperature rising rate and the temperature falling rate can be made slow, and the resolution of thermogravimetric measurement can be improved. Further, since the temperature change speed continuously changes according to the weight change speed, it is possible to perform optimum temperature control that shortens the measurement time and improves the resolution.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front sectional view showing a schematic structure of an evolved gas analyzer for carrying out the present invention. In the thermobalance, the measurement sample container 1 is placed inside a protective tube 10 made of quartz.
2 and a standard sample container 14, which are supported by a sample holder 16. A soaking cylinder (not shown) made of Pt or Ni is arranged around the two containers 12 and 14. There are a total of four infrared lamps 20 around the protective tube 10, and the infrared lamps 20 are arranged at the focal point of the elliptical focusing mirror 22. The temperature of the sample can be measured with a differential thermocouple 18 attached to a heat sensitive plate supporting the containers 12 and 14.

The lower end of the sample holder 16 is supported by the tip of the balance beam 24. A balance weight 28 is provided at the other end of the balance beam 24, and a screen 30 is fixed at the tip thereof. The light from the light source lamp 32 passes through the screen 30 and enters the photoelectric element 34. The change in weight of the sample holder 16 appears as a change in the output of the photoelectric element 34. on the other hand,
A magnet 26 and a weight 36 are fixed to the lower end of the sample holder 16. The output of the photoelectric element 34 is input to the balance control circuit 38, and the balance control circuit 38 supplies a current to the control coil 40 according to the weight of the sample holder 16. That is, the weight of the sample holder 16 is fed back to the control coil 40. Then, according to the current of the control coil 40, the magnet 2
Power is added to 6. As a result, the position of the sample holder 16 is maintained.

The sample temperature measured by the differential thermocouple 18 is input to the program automatic temperature control device 42. Further, the differential heat temperature measured by the differential thermocouple 18 is the DC amplifier 44.
It is amplified by and recorded by the recorder 46. The output of the balance control circuit 38, that is, the weight of the sample holder 16 is also recorded by the recorder 46.

The program automatic temperature control device 42 includes the sample temperature data from the differential thermocouple 18 and the balance control circuit 3.
Weight data from 8 is input. Then, the program automatic temperature control device 42 supplies an electric current to the infrared lamp 20 so that the temperature change speed corresponds to the weight change speed of the sample. A signal from the control coefficient setting device 48 is input to the program automatic temperature control device 42 to specify the control coefficient.

The infrared heating furnace shown in FIG. 1 has a smaller thermal inertia than the resistance heating furnace and is excellent in temperature control response.

The gas generated by the thermobalance is taken out from the upper part of the protective tube 10 and introduced into the mass spectrometer 50 to specify the kind of the generated gas. With the thermobalance, the temperature when the weight change of the sample becomes remarkable can be known, while with the mass spectrometer 50, the type of gas generated at that time can be specified.

Next, a method for controlling the temperature of the sample will be described. As an example, an example in which the weight loss of the sample is measured while raising the temperature of the sample will be described. In this case, the heating rate of the sample is expressed by the following equation (1) according to the weight reduction rate of the sample.

[0024]

[Equation 1] Here, V: temperature increase rate (° C / second) Vm: maximum temperature increase rate (° C / second) U: weight loss rate (% / second) Um: limit weight loss rate (% / second) n: power index

The weight of the sample is obtained as a percentage (percentage) with respect to the initial weight, and the unit of the weight loss rate of the sample is the percentage per second. When the weight of the sample is reduced, the rate of change in weight has a negative value, but the absolute value is taken as the rate of weight reduction U. The physical meaning of formula (1) is as follows. When the weight reduction rate U of the sample becomes zero (that is, when the weight of the sample does not change), the heating rate V becomes equal to the maximum heating rate Vm. The value of Vm is determined in advance according to the properties of the sample. As the weight reduction rate U of the sample increases, the temperature increase rate V decreases, and when the weight reduction rate U becomes equal to the limit weight reduction rate Um, the temperature increase rate V becomes zero. That is, the temperature rise stops. The limit weight reduction rate Um is also determined in advance according to the properties of the sample. Generally, Um is set so that the deceleration rate U does not exceed the limit deceleration rate Um within the predetermined measurement temperature range. In the formula (1), if the deceleration speed U exceeds the limit deceleration speed Um, the value of V is formally negative, but in the actual temperature control, only the temperature rise is stopped and the temperature falls. There is no. That is, the expression (1) is valid only under the condition of U ≦ Um. Expression (1) is stored in the program automatic temperature control device of FIG.
Further, the numerical values of Vm, Um, and n in the equation (1) can be set by the control coefficient setting device 48 of FIG.

When the deceleration rate U is in the range of 0 to Um,
The rate of temperature increase V is a monotonically decreasing function of the rate of decrease U. The meaning of the monotonically decreasing function is as follows. That is, the temperature rising rate is V for each of the two arbitrary reduction rates U1 and U2.
If it is determined as 1, V2, if U2> U1, then it is always V2
≦ V1. In the case of the formula (1) of this embodiment, V2 <V1 is always satisfied if U2> U1.

To actually obtain the deceleration rate U in the equation (1), the following procedure is used. First, the weight of the sample is measured at the sampling interval Δt. If the weight at the i-th sampling time (hereinafter referred to as time i) is Wi and the weight at the immediately preceding time (i-1) is Wi-1, the weight reduction rate Ui at the time i is (Wi- 1-Wi) / Δt. Next, a four-point moving average UAi of the weight reduction speed Ui is obtained. That is, UAi = (Ui + Ui-1 + Ui-2 +
Ui-3) / 4. Weight loss speed UA of this 4-point moving average
i can be the deceleration rate at time i. This deceleration rate may be substituted for the deceleration rate U in the equation (1).

By the way, the above-mentioned four-point moving average deceleration rate is preferable in that the average deceleration rate is calculated by smoothing the variation in weight measurement. Therefore, the data shows a slight delay from the current weight reduction rate and the future weight reduction rate. Therefore, by predicting the future deceleration rate and substituting the predicted deceleration rate into the deceleration rate U in the equation (1), the target followability of the temperature control is further improved. Therefore, for example, it is possible to predict the deceleration rate UAi + 1 at a future time (i + 1) based on a plurality of four-point moving average deceleration rates UA traced back from the present sampling to a few samplings ago. The deceleration rate can be substituted into equation (1). As a method of calculating the predicted value, a known prediction calculation method can be used.

FIG. 2 is an example in which the formula (1) is displayed in a graph. FIG. 2A is a graph showing how the temperature increase rate curve changes when the limit deceleration rate Um is changed under the condition that the power index n = 1. Even if the maximum temperature increase rate Vm is the same, the smaller the limit deceleration rate Um is set, the more rapidly the temperature increase rate V becomes smaller as the deceleration rate U increases. That is, the limit weight reduction speed Um
Acts as a sensitivity coefficient for the rate of temperature increase V with respect to the rate of decrease U. The practical value of Um is 0.0001 to 0.2.
% / Sec.

Further, FIG. 2B shows the maximum heating rate Vm.
2 is a graph showing the influence of a power index n under the condition that the limit deceleration rate Um and the limit deceleration rate Um are the same. Vertical axis shows temperature increase rate V
Is normalized by the maximum temperature increase rate Vm, and the horizontal axis indicates the weight reduction rate U by the limit weight reduction rate Um.
When n = 1, the heating rate V becomes a linear curve (that is, a straight line) of the deceleration rate U. When n = 2, the heating rate V becomes a quadratic curve of the deceleration rate U. Since U / Um is smaller than 1, this 2
The next curve is convex downward. On the contrary, when n = 0.5, the curve is convex upward. The value of n determines how the rate of change of the heating rate with respect to the rate of change of the weight reduction rate (that is, the slope of the curve) changes in accordance with the value of the weight reduction rate. That is, when n is larger than 1, the slope of the curve becomes large in the region where the value of the deceleration rate is small, and conversely,
When n is smaller than 1, the slope of the curve becomes large in the region where the value of the deceleration speed is large. After all, the exponent n is
It acts as a local sensitivity coefficient for the temperature increase rate V with respect to the weight reduction rate U. The value of n is also determined according to the properties of the sample. The practical value of n is in the range of 0.1 to 3.

FIG. 3 is a graph in which the weight loss rate (percentage with respect to the initial weight) of the sample is measured by three kinds of temperature control methods for the same sample. The horizontal axis represents the temperature of the sample, and the vertical axis represents the weight loss rate of the sample. However, these graphs are shown schematically. (A) is a conventional method, that is, a sample in which the temperature of the sample is controlled by using a resistance heating furnace by a constant-rate heating method,
(B) shows the temperature control of the sample using the resistance heating furnace based on the formula (1), and (C) shows the temperature control of the sample using the infrared heating furnace based on the formula (1). It is a thing. In the constant velocity heating method of (A), a remarkable weight loss is observed in two temperature regions. Each weight loss is about 20%. However, the change curve of the weight loss rate at that time is gentle. On the other hand, in the example of (B) according to the present invention, remarkable weight loss is observed in four temperature regions, and the weight loss is 10%, 10%,
15% and 5%. That is, it was clarified that what was observed as one weight loss phenomenon in the constant velocity heating method of (A) was actually two weight loss phenomena in which the decomposition temperatures were close to each other. Furthermore, an infrared heating furnace was used (C)
In the example, the phenomenon similar to that of (B) is shown, but it can be seen that the change curve of the weight loss rate becomes sharper and the resolution of thermogravimetric measurement is further improved.

FIG. 4 is a graph in which the vertical axis represents the weight loss rate and temperature of the sample, and the horizontal axis represents time. FIG. 4 (A)
(B) and (C) correspond to (A), (B) and (C) of FIG. In (A) of FIG. 4, the manner of constant temperature rise can be clearly understood. Further, it can be seen that there is a useless region where only the time elapses without the sample weight loss rate changing so much. On the other hand, in FIGS. 4B and 4C, it can be seen that there is almost no useless time region. Further, it can be seen that the rate of temperature rise is very low when the weight of the sample is being reduced, whereas the rate of temperature rise is very high between the weight loss phenomenon and the weight loss phenomenon.

FIG. 5 is a graph showing actual experimental data. (A) shows the temperature on the horizontal axis and the weight loss rate on the vertical axis, and (B) shows the time on the horizontal axis and the weight loss rate and temperature on the vertical axis. The sample is copper sulfate pentahydrate, the standard sample is alumina powder, and the initial weight of the sample is 53 mg.
Further, in the above formula (1), the maximum heating rate Vm = 5
C / min, limit weight reduction rate Um = 0.002% / sec, and power index n = 2. The sampling interval Δt is 0.9 seconds. In the graph of (A), it can be clearly seen that the dehydration reaction occurs in 5 stages. In particular, the third stage (80.
The dehydration reaction at 7 ° C) and the fourth stage (86.1 ° C) can be clearly distinguished.

FIG. 6 schematically shows the graph of the weight loss rate of the sample and the graph of the total integrated intensity in the mass spectrometer in association with each other. (A) is a conventional example of constant temperature heating,
(B) is a graph of this example. These are measured on the same sample. The upper graph shows the temperature on the horizontal axis and the weight loss rate of the sample on the vertical axis, which is measured by a thermobalance. The lower graph shows the temperature on the horizontal axis and the integrated intensity at all masses on the mass spectrometer on the vertical axis. In the temperature range shown in the graph,
Although there are two weight loss reactions with different reaction temperatures, the weight loss rate graph of the conventional example (A) does not distinguish between the two weight loss reactions, and one peak is also observed in the mass spectrometer. It has only been observed. That is, two kinds of generated gases are mixed and introduced into the mass spectrometer,
In this state, it is impossible to specify the generated gas by pattern matching. In (B) according to this example, the two weight loss reactions are clearly distinguished in the weight loss rate graph. In this case, when the total integrated intensity is measured with a mass spectrometer, two peaks are observed, and it can be seen that the two kinds of evolved gases are clearly distinguished and introduced. For each of the two peaks in the total integrated intensity, measuring the mass spectrometry pattern and comparing it with the standard pattern,
The type of each generated gas can be specified.

In the above-described embodiment, the temperature control is performed so that the temperature change rate of the sample becomes a continuous function of the weight change rate. However, the temperature rise is stopped when the weight reduction rate of the sample exceeds a predetermined value. Even if such a temperature control is used, the ability of separating generated gas is improved as compared with the conventional constant rate temperature rise, and the same result as in FIG. 6B is obtained.

The above formula (1) is an example of measuring the weight loss at the time of temperature rise, but similar formulas can be used for other phenomena. That is, in general, instead of the weight reduction rate U and the limit weight reduction rate Um, if expressed by the absolute value of the weight change rate of the sample, it can be applied to both the weight increase and the weight decrease of the sample, and the temperature increase rate V Generally, the absolute value of the temperature change rate of the sample may be used instead of the maximum temperature increase rate Vm to apply to both temperature increase and temperature decrease of the sample.

As a thermobalance for carrying out the evolved gas analysis method of the present invention, not only a differential thermal balance as shown in FIG. 1 but also a differential scanning calorimeter can be used, which is effective for any type of thermobalance. Is. As for the sample holder, not only a common sample holder as shown in FIG. 1 but also a so-called differential type sample holder in which a sample holder is separately provided for each of a measurement sample container and a standard sample container is used. May be.

[0038]

According to the evolved gas analysis method of the present invention, the sample temperature is controlled according to the weight change rate of the sample to measure the sample weight change, and the gas generated from the sample is introduced into the mass spectrometer. Therefore, even when different reactions occur in the sample at close temperatures, the generated gas in each reaction step can be separated and taken out, and the generated gas can be identified by pattern matching in the mass spectrometer.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an evolved gas analyzer for carrying out the present invention.

FIG. 2 is a graph showing changes in a temperature rising rate curve when conditions are changed.

FIG. 3 is a graph showing the weight loss rate of a sample as a function of temperature.

FIG. 4 is a graph showing the weight loss rate and temperature of a sample as a function of time.

FIG. 5 is a graph of actual experimental data.

FIG. 6 is a graph schematically showing the graph of the weight loss rate of the sample and the graph of the total integrated intensity in the mass spectrometer in association with each other.

[Explanation of symbols]

 10 Protective tube 12 Measurement sample container 14 Standard sample container 16 Sample holder 18 Differential thermocouple 20 Infrared lamp 22 Elliptical focusing mirror 24 Balance beam 42 Program automatic temperature control device 48 Control coefficient setting device 50 Mass spectrometer

Claims (4)

[Claims] 1. The sample temperature is controlled according to the rate of weight change of the sample to measure the weight change of the sample, and the gas generated from the sample is introduced into a mass spectrometer to generate the sample in each reaction step. A method for analyzing evolved gas in thermogravimetric measurement, characterized in that the type of gas is specified. 2. The weight change of the sample is measured by controlling the sample temperature so that the temperature change rate of the sample continuously changes according to the weight change rate of the sample, and the gas generated from the sample is measured by a mass spectrometer. A method for analyzing evolved gas in thermogravimetric measurement, characterized in that the type of evolved gas in each reaction stage of the sample is specified. 3. The evolved gas analysis method according to claim 2, wherein the sample temperature is controlled so that the absolute value of the temperature change rate of the sample becomes a monotonically decreasing function of the absolute value of the weight change rate of the sample. 4. The evolved gas analysis method according to claim 1, wherein an infrared heating furnace is used to heat the sample.