JPH03115951A - Measuring device for adsorption amount - Google Patents

Abstract

PURPOSE:To efficiently perform measurement by sampling the data of adsorption amount at a point of time when adsorption is equilibrated before sampling the data of the adsorption amount for the following target value when the rate of change in the calculated value of the adsorption amount in a sample cell exceeds the preset value. CONSTITUTION:The rate of change in adsorption amount is calculated at every charging or discharging of adsorptive gas into/from a sample cell 1. When this rate of change in the adsorption amount is value not larger than the rate DELTAV of change in the value calculated by an arithmetic means c at every opening of a preset stop valve 3, the data of the adsorption amount in the vicinity of the target value are sampled. When this rate of change exceeds DELTAV, the data of the adsorption amount are sampled at a point of time when adsorption reaches equilibrium at every introduction or discharge of adsorptive gas. Therefore the data of the part in which the rate of change in the adsorption amount is made large can be densely sampled. Even when the sample W is unknown, such possibility is eliminated that the data of the important part are missed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an apparatus for measuring the adsorption amount of a sample by a capacitance method, for example, measuring the adsorption characteristics, specific surface area, pore distribution, etc. of powder or porous materials. It can be used as a device for

<Prior Art> The capacitive method is considered to be the most reliable method for determining adsorption/desorption isotherms. This is because it makes sense to wait for adsorption or desorption equilibrium at each measurement point.

A block diagram of the principle of the adsorption amount measuring device using the capacitance method is shown in FIG. 5, and with reference to this figure, how to determine adsorption/desorption crosstalk will be explained.

First, prior to measurement, the sample is degassed.

Now, when we start the adsorption measurement, we first start with the on-off valves 3 and 5.
is opened to evacuate the interior of the manifold 30 and sample cell 1, and then the on-off valves 3 and 5 are closed. Next, open the on-off valve 9 and supply He gas, which is an inert gas, to the manifold 3.
0 and close the on-off valve 9, then open the on-off valve 3 and
e gas is diffused into the sample cell 1. From the pressure values in the manifold 30 before and after opening of the on-off valve 3 and the volume of the manifold 30, the volume of the portion of the sample cell 1 excluding the sample volume is determined. However, the volume of the manifold 30 is known as a device constant. Next, the on-off valve 5 is opened to evacuate the interior of the manifold 30 and the sample cell 1, and then a portion of the sample cell 1 is immersed in LN2.

Next, ■After closing all on-off valves, open on-off valve 7 and N2
Gas is introduced into the manifold 30, its pressure is detected by the pressure sensor 13, and the on-off valve 7 is closed when a predetermined pressure is reached. After the on-off valve 7 is closed, when the pressure inside the manifold 30 becomes stable, the detected value P by the pressure sensor 13
, are stored in the memory of the computer 15. Next, (2) the on-off valve 3 is opened to diffuse N2 gas into the sample cell 1 and physically adsorb it onto the sample surface. Then, (2) the pressure value P2 at the time when adsorption equilibrium is reached is stored in the memory, and the adsorbed gas amount is calculated based on the difference between this P2 and the previously stored P. That is, P corresponds to the number of molecules of the introduced N2 gas, and P2 corresponds to the number of molecules of the introduced N2 gas that are not adsorbed. Therefore, the difference between the two is a value that correlates with the number of molecules adsorbed on the sample, that is, the amount of gas adsorbed, and the amount of adsorption can be obtained from the pressure difference. However, it is necessary to make corrections regarding the behavior of the gas under LNz.

By sequentially repeating the above-mentioned processes (1) to (2), crosstalk such as attraction can be obtained. Then, when P2 reaches near the saturated vapor pressure, crosstalk such as desorption can be obtained by replacing the above-mentioned gas introduction process with a vacuum drawing process and performing the same processes as ① to ②.

In such a method, when collecting one P2, for example, after introducing or discharging the adsorbed gas into the sample cell 1, wait for a predetermined time, and the pressure change during that time becomes "ζO". The point in time is considered to be the adsorption/desorption equilibrium state. However, if such a process is performed each time an adsorbed gas is introduced or discharged, it takes an enormous amount of time to obtain a desired adsorption/desorption isotherm.

Therefore, conventionally, operators set multiple measurement points (pressure value Pz(n) at adsorption/desorption equilibrium) in advance, and repeat the processes of I try to repeat it often. In other words, the number of times of waiting for strict adsorption/desorption equilibrium is reduced, thereby shortening the measurement time.

An example of a flowchart of a program for performing such processing is shown in FIG.

First, prior to the adsorption amount measurement process, measurement point p2(n
), and the pressure tolerances ΔP1 and Δp2 in the determination step are set by the operator.

However, Δpi>ΔP2.

Now, when we start the measurement process, first, the manifold 30
Adsorbed gas is introduced into the area, and after the pressure becomes stable, the pressure value P
Store 1 in memory. Next, the on-off valve 3 is opened and adsorbed gas is introduced into the sample cell 1.

At this time, the detected value by the pressure sensor 13 is monitored, and it is determined whether the pressure value is sufficiently low for the first measurement point P, (1), and if it is low, the process proceeds to the gas introduction step. Go back and repeat this loop.

Then, when the detected value P by the pressure sensor 13 reaches a certain value with respect to pz(x), a rough equilibrium wait check is performed for the first time, and the difference between the detected pressure value P and PdD after this check is It is determined whether or not the difference is within the tolerance 621, and if it is within the tolerance, a strict equilibrium wait check is performed this time.

6 of the pressure detection value P and Pg(1) after this check is completed. It is determined whether the difference is within tolerance 622 or not.

In other words, after confirming that the pressure at adsorption equilibrium approaches the set value P2 (1), calculate the adsorption amount based on that pressure value, and correspond the calculated value (1) to P2 (1). and store it in memory. Similarly, (V (2)PZ(2
)) - (v(n), p2(n)) are stored sequentially.

<Problem to be Solved by the Invention> By the way, according to the conventional method of setting a plurality of measurement points described above, the coarser the interval between the measurement points, the shorter the measurement time can be. It becomes impossible to obtain data in minute intervals. In an adsorption amount measuring device, dense data is originally required for locations where the amount of adsorbed gas varies greatly with respect to the adsorbed gas pressure due to crosstalk such as adsorption/desorption, but in the case of unknown samples, The location is unpredictable. For this reason, when measuring an unknown sample, if the intervals between measurement points are made coarse, there is a possibility that data in a truly important range will become sparse.

<Means for Solving the Problems> The present invention has been made to solve the above problems.
The structure of the present invention will be explained with reference to the basic conceptual diagram shown in FIG. , means a for introducing adsorbed gas into the manifold 30 or discharging the adsorbed gas in the manifold 30 , a sensor b for measuring the pressure inside the manifold 30 , and pressure data before and after opening of the on-off valve 3 The on-off valve 3 is equipped with a calculation unit C that calculates the adsorption amount of the sample W based on the change in the on-off valve 3, and the on-off valve 3 is repeatedly opened and closed to sequentially introduce or discharge adsorbed gas into the sample cell 1. In an apparatus that obtains a plurality of pieces of adsorption amount data based on pressure data P before opening and pressure data p2 at the time of adsorption equilibrium after opening, the pressure data P2 is in the vicinity of a plurality of preset target values. means d for determining whether or not the target value has been reached; and a first sampling means for storing the calculated value by the calculation unit C in the storage means e in correspondence with the target value each time the determining means d determines that the target value has been reached. means g for successively comparing f and a preset value to the amount of change in the value calculated by the calculation means C each time the on-off valve 3 is opened;
When the amount of change exceeds the set value ΔV, before collecting the adsorption amount data for the next target value, the value calculated by the calculation unit C at the time when adsorption equilibrium is reached is stored in correspondence with the adsorption equilibrium pressure. It is characterized by comprising second sampling means for storing in the means e.

<Function> When the amount of change in adsorption amount calculated each time adsorbed gas is introduced into or discharged from sample cell 1 is less than the preset Δ■, adsorption amount data near the target value is sampled, but the amount of change is When Δ■ is exceeded, adsorption amount data at the time when adsorption equilibrium is reached each time gas is introduced or discharged is sampled. This makes it possible to collect data in areas where the rate of change in the amount of adsorption is large, and eliminates the risk of missing data in important areas even if the sample is unknown.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is an overall configuration diagram showing a block diagram of a piping system and a control circuit according to an embodiment of the present invention.

A sample cell 1 containing a sample is connected to a manifold 30 at a cell mounting section 2.

The manifold 30 has on-off valves 3 to 10 at appropriate locations.
A nitrogen gas source as an adsorption gas and a helium gas source as an inert gas are connected, and a vacuum pump 11 for evacuating the inside thereof is also connected.

The pressure inside this manifold 30 is determined by the vacuum gauge 12 and the pressure gauge 1.
3, is digitized by an A-D converter 14, and then input to a computer 15. In addition, 16
．． 17 is a throttle, 18 is a tube for measuring saturated vapor pressure, 19
is the calibration volume.

A dewar bottle 20 containing a refrigerant such as LN2 for cooling the sample cell 1 is provided below the manifold 30. It is moved up and down by 21. In addition, each on-off valve 3 mentioned above
10 are driven to open and close by control signals from the valve driver 22 based on commands from the computer 15.

The above hardware configuration is the same as that of a conventional adsorption amount measuring device.

FIG. 3 is a flowchart showing the contents of the adsorption amount measurement processing program written in the computer 15.
The operation of the embodiment of the present invention will be described with reference to this figure.

Prior to this adsorption amount measurement process, the operator previously sets the measurement point p2(n) and the pressure tolerances ΔP1 and Δp2 in the determination step. In addition, a permissible value △■ for the amount of change in adsorption amount is set.

First, before executing the adsorption amount measurement process program, the computer 15 opens the on-off valves 3 and 5 to evacuate the inside of the manifold 30 and the sample cell 1, and then opens the on-off valves 3 and Close 5. Next, open the on-off valve 9 and supply He gas, which is an inert gas, to the manifold 3.
0 and close the on-off valve 9, then open the on-off valve 3 and
e gas is diffused into the sample cell 1. From the pressure values in the manifold 30 before and after opening of the on-off valve 3 and the volume of the manifold 30, the volume of the portion of the sample cell 1 excluding the sample volume is determined. Next, the on-off valve 5 is opened to evacuate the interior of the manifold 30 and the sample cell 1, and then a portion of the sample cell 1 is immersed in LN2.

Now, when we start the measurement process, first, the manifold 30
Adsorbed gas is introduced into the area, and after the pressure becomes stable, the pressure value P
Store 1 in memory. Next, the on-off valve 3 is opened and adsorbed gas is introduced into the sample cell 1.

At this time, the detected value by the pressure sensor 13 is monitored, and an approximate value of the adsorption amount is calculated based on the detected pressure value P and the previous pressure value P. It is determined whether this adsorption amount ΣV is 67 or more, and in the following cases, it is determined whether the pressure monitor value at this point is sufficiently small with respect to the first measurement point p, (+). After determining, “Return to gas introduction J step.

That is, the estimated value of the amount of adsorption is monitored each time adsorbed gas is introduced into the sample cell 1, and when the amount of change in the estimated value is always less than the set value Δ■, the detected value P by the pressure sensor 13 becomes pz(1 ) until a certain value is reached. Thereafter, as in the past, after going through steps such as "Rough Equilibration Wait Check J" and "Equilibration Wait Check", etc., when it is confirmed that the pressure at adsorption equilibrium approaches the set value pJ, the pressure value The adsorption amount is calculated based on , and the calculated value (1) is stored in the memory in correspondence with p2(i).

On the other hand, when the approximate value Σ■ of the amount of adsorption when gas is introduced into the sample cell 1 exceeds the set value Δ■, the pressure sensor 1
3. Monitor the rate of change of the detected value in step 3, calculate the adsorption amount V based on the pressure value P at the time when the rate of change becomes constant, that is, the time when adsorption equilibrium is reached, and calculate the adsorption amount V based on the pressure value P in pg.
(The adsorption amount ■ is stored as D and the adsorption amount ■ is stored as ■ (1). This process continues until the estimated adsorption amount ΣV becomes less than the set value Δ■ each time the adsorbed gas is introduced into the sample cell 1. This is repeated, and the data V (k) each time is sequentially stored corresponding to pz(k).

Then, when all the data corresponding to each measurement point Pg(1) to pz(n) is collected, that P
2 Q)-p 2 (n) corresponding to the data group V (1
)-V(n) and P'2(])...p'Jc) are arranged in the order of equilibrium pressure, and the program ends.

According to the above embodiments of the present invention, when measuring a sample having isotherm data as shown in FIG. 4, for example, data that may not be obtained by the conventional method of simply setting measurement points, In other words, it is possible to obtain data at the locations marked with a circle in the figure. Note that the horizontal axis of the graph is the saturated vapor pressure P of the adsorbed gas. The ratio of the adsorption equilibrium pressure P to the adsorption equilibrium pressure P is shown.

In the above flowchart, the method for determining P is not mentioned, and various methods corresponding to each measurement process may be adopted as a method for determining P. Routines for Pl setting processing according to various P1 determination methods can be added to locations A and A'.Furthermore, although the above flowchart has been shown only for adsorption amount measurement processing, gas The introduction process may be replaced with a vacuum drawing process.

Furthermore, in the embodiments of the present invention, the most common N2 gas is used as the adsorption gas, but for example, Ar or K gas is used.
Of course, other gases such as r may also be used.

<Effects of the Invention> As explained above, according to the present invention, adsorption data is basically collected near a plurality of predetermined target values, but adsorption data is not introduced into or discharged from the sample cell. When the amount of change in the adsorption amount calculation value for each step exceeds a preset value, the adsorption amount data at the time when adsorption equilibrium is reached is collected before collecting adsorption amount data for the next target value. Therefore, even if the l'' target value is set at coarse intervals, the number of data in the portion where the rate of change in adsorption amount is large can be made dense. This eliminates the risk of missing important data even if the sample is unknown. Furthermore, since the number of data samples can be set densely for important parts and sparsely for less important parts, it is possible to perform measurements efficiently. Furthermore, the advantage is that the above effects can be achieved with the same hardware as in the past.

[Brief explanation of drawings]

FIG. 1 is a basic conceptual diagram showing the configuration of the present invention, FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 3 shows the contents of the adsorption amount measurement processing program written in the computer 15. The flowchart, FIG. 4, is an explanatory diagram of its operation. FIG. 5 is a diagram for explaining the principle of an adsorption amount measuring device using a capacitance method. FIG. 6 is an example of a flowchart showing the contents of a conventional adsorption amount measurement processing program. 1 ・ 3 ・ 12 ・ 13 ・ 15 ・ 30 ・ W ・ Sample cell, on-off valve, vacuum needle, pressure gauge, computer, manifold, sample

Claims (1)

[Claims] A sample cell for enclosing a sample, a manifold separated from the sample cell by an on-off valve, a means for introducing adsorbed gas into the manifold or discharging the adsorbed gas in the manifold, and It is equipped with a sensor that measures pressure and a calculation unit that calculates the amount of sample adsorbed based on changes in pressure data before and after opening the on-off valve. By sequentially introducing or discharging adsorbed gas into or out of the valve, the pressure data p_1 before the opening/closing valve is
In a device that obtains a plurality of pieces of adsorption amount data based on the pressure data p_2 at the time of adsorption equilibrium after opening, it is determined whether the pressure data p_2 has reached the vicinity of a plurality of preset target values. a first sampling means for storing the calculated value by the arithmetic unit in the storage means in correspondence with the target value each time the determination means determines that the target value has been reached; and each time the on-off valve is opened, means for successively comparing the amount of change in the value calculated by the calculation means with a preset value, and when the amount of change exceeds the set value, before collecting adsorption amount data for the next target value; An adsorption amount measuring device comprising second sampling means for storing a value calculated by the arithmetic unit at the time when adsorption equilibrium is reached in the storage means in correspondence with the adsorption equilibrium pressure.