JP3047552B2 - Adsorption amount measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the amount of adsorption based on a constant volume method.
The present invention relates to an apparatus for measuring a specific surface area, a pore distribution, and the like.

[0002]

2. Description of the Related Art Among the techniques for determining the adsorption (desorption) isotherm of a sample such as a powder, the constant volume method is regarded as the most reliable method. This is because it makes sense to "maintain the absorption (desorption) equilibrium at each measurement point". FIG. 6 schematically shows a general configuration example of an adsorption amount measuring apparatus using a constant volume method, and with reference to FIG.
A method for obtaining the isotherm will be described.

The sample cell 61 and the manifold 62 are separated by an on-off valve 63. The manifold 62 has a known internal volume, and the sample cell 61 is filled with a degassed sample. A part of the sample cell 61 is immersed in a Dewar bottle 64 containing a refrigerant such as liquid nitrogen before the introduction of the adsorption gas. Manifold 62
Is provided with an on-off valve 65 that communicates with a vacuum pump, an on-off valve 66 that communicates with a nitrogen gas source that is an adsorption gas, and an on-off valve 67 that communicates with a helium gas source that is a non-adsorption gas.
The internal pressure can be measured by a pressure detector 68, and the degree of vacuum can be measured by a vacuum gauge 69.

[0004] In the measurement, first, the on-off valves 63 and 65 are opened with the sample sealed in the sample cell 61,
After the insides of the sample cell 61 and the manifold 62 are evacuated with the on-off valves 66 and 67 closed, the on-off valves 63 and 65 are closed.
Close. Next, the helium gas is introduced into the manifold 62 by opening the on-off valve 67. After the on-off valve 67 is closed, the helium gas is diffused into the sample cell 61 by opening the on-off valve 63. From the pressure values before and after the opening and closing of the on-off valve 63 and the internal volume of the manifold 62, the volume of a portion excluding the sample volume of the sample cell 61 is obtained. Thereafter, the on-off valve 65 is opened and the inside of the sample cell 61 and the manifold 62 is evacuated again.
4 soak.

[0005] Next, (1) after all the on-off valves are closed, the on-off valves 66 are opened to introduce nitrogen gas into the manifold 62, and the pressure is detected by a pressure detector 68 to reach a predetermined pressure. At this point, the on-off valve 66 is closed. After closing the on-off valve 66, and stores the detected pressure value P ₁ by the pressure detector 68 at the time when the pressure in the manifold 62 is stable in the memory of a computer (not shown).

Next, (2) the on-off valve 63 is opened to diffuse the nitrogen gas into the sample cell 61, and the nitrogen gas is physically adsorbed on the sample. Then, (3) stores the pressure value P ₂ at the time of reaching adsorption equilibrium in memory, based on the difference between P ₁ stored in the P ₂ before, the amount of adsorption of the sample at a pressure P ₂ calculate. That is, P ₁ corresponds to the number of molecules of the nitrogen gas introduced into the system, and P ₂ corresponds to the number of molecules of the introduced nitrogen gas that have not been adsorbed on the sample. Therefore, the difference between the two becomes a value correlated with the number of molecules of nitrogen gas adsorbed on the sample, that is, the gas adsorption amount, and the adsorption amount can be obtained from the value. However, at this time, it is necessary to correct the behavior of the gas at the refrigerant temperature.

[0007] The above operations (1) to (3), by repeating while changing the value of P _1, it is possible to obtain the adsorption isotherm of the sample. Further, when the P ₂ reaches the saturated vapor pressure, by performing the same processing as replacing the above gas introduction process in vacuum processes (1) to (3), it is possible to obtain a desorption isotherm . Here, it may take several hours or more to obtain the adsorption / desorption equilibrium, and the adsorption / desorption isotherm for which such an adsorption / desorption equilibrium state needs to be formed a plurality of times is required. It often takes tens of hours to get. Recently, most commercially available devices automatically perform the measurement operation for a long time. In an apparatus having such an automatic measurement function, for each measurement point, the operator previously sets a plurality of equilibrium pressures (or relative pressure = equilibrium pressure / saturated vapor pressure), and sets the vicinity of each set pressure value. The main method is to control gas introduction and discharge and data sampling so as to obtain adsorption-desorption equilibrium.

[0008]

[Problems to be solved by the invention] By the way, absorption (desorption)
The horizontal axis of the isotherm is the pressure (or relative pressure), and the vertical axis is the amount of adsorption and desorption. It is very important to closely observe this isotherm in measurement for research and development.For example, when evaluating or managing pore distribution data for quality control Only the relationship between the pore diameter and the pore volume (or pore specific surface area) should be understood. " The problem in such a case in the above-mentioned conventional method is that even if the equilibrium pressure or the relative pressure is set somewhat densely and uniformly on the horizontal axis of the isotherm to determine the measurement point, This means that a rough part and a dense part are formed on the distribution curve. In other words, even if the measurement points are uniformly set on the horizontal axis, the steep part of the graph, that is, the point where the amount of change in the amount of adsorption with respect to the adsorption gas pressure in the adsorption (desorption) isotherm is large, is plotted on the vertical axis. Measurement point becomes rough. It is at this point that dense data is required in the pore distribution curve, and therefore, with the above-described conventional method, the data may be coarse in the most required pore diameter range.

In order to solve such a problem, the present inventor has already set the measurement point at the time when a predetermined equilibrium pressure is reached, and also at each time when the adsorption gas is introduced or discharged into the sample cell. If the value is equal to or greater than the predetermined value, the adsorption amount data is sampled when the adsorption (desorption) equilibrium is reached, so that the measurement points at the steep part of the pore distribution curve can be automatically determined. (Japanese Patent Laid-Open No. 3-115951). Although this problem is solved by this proposal, there is a problem that the measurement time is slightly longer by an increase in the number of measurement points.

The present invention has been made in view of the above points. For example, when measuring the pore distribution or the like for the purpose of quality control or the like, the measurement time is not lengthened, and the measurement is performed in a required pore diameter range. It is an object of the present invention to provide an adsorption amount measuring device capable of reliably sampling data.

[0011]

A structure for achieving the above object will be described with reference to a basic conceptual diagram shown in FIG. 1. The present invention provides a sample cell 1 for enclosing a sample to be measured, A manifold 2 separated from the cell 1 by an on-off valve 3, gas introducing / discharging means a for introducing or discharging an adsorbed gas to or from the manifold 2;
A pressure detector 17 for measuring the internal pressure, a calculation unit b for calculating the amount of sample adsorption based on a change in pressure data before and after the opening and closing of the on-off valve 3, an on-off valve 3, gas introduction / discharge means a and A control unit c for controlling the operation of the part b, and by repeatedly opening and closing the on-off valve 3 at a predetermined timing to repeatedly introduce and discharge the adsorbed gas into the sample cell 1,
In an apparatus for measuring data of the amount of adsorption to a sample at a plurality of adsorption equilibrium points based on the output of the pressure detector 17, an analysis method selection for selecting an arbitrary one from a plurality of predetermined pore distribution analysis methods. Means d, setting means e for setting a pore diameter data string, and a relative pressure data string for converting the set pore diameter data string into a relative pressure data string based on the analysis method selected by the analysis method selection means d. Calculating means f, and storage means g for editing and storing the obtained relative pressure data, and the calculating section b calculates various physical property values from the adsorption amount based on the method selected by the analysis method selecting means d, The control means c is characterized by being configured to control the on-off valve 3 and the gas introduction / discharge means a based on the contents of the storage means g.

[0012]

When the analysis method is determined, the relative pressure and the obtained pore diameter correspond to 1: 1. Therefore, by calculating a relative pressure data sequence from the specified pore diameter data sequence, and by performing measurement control to obtain an equilibrium state at this relative pressure,
Adsorption amount data at measurement points corresponding to a desired pore diameter can be obtained, and isotherm data can be collected in a minimum necessary time. In the thus obtained isotherm, even if the data density is partially coarse, the pore distribution data analyzed based on this contains all the necessary information.

[0013]

FIG. 2 is an overall configuration diagram showing a piping system and a control circuit block diagram according to an embodiment of the present invention. A sample cell 1 for containing a sample is connected to a manifold 2 at a cell mounting section 2a. The manifold 2 is provided with seven on-off valves 4 to 10 in addition to the on-off valve 3 for partitioning between the manifold 2 and the sample cell 1. The vacuum pump 11, the on-off valves 6 and 7, a helium gas source via an on-off valve 8, a calibration volume 12 via an on-off valve 9, and a saturated vapor pressure measurement tube 13 via an on-off valve 10. ing. 14 and 15 are apertures.

The pressure in the manifold 2 is measured by a vacuum gauge 16
And the pressure is measured by a pressure detector 17. The measurement result is digitized by an A / D converter 18 and then taken into a computer 19. Below the manifold 2, there is provided a Dewar bottle 20 containing a coolant such as liquid nitrogen for cooling the sample cell 1, and this Dewar bottle 20 is moved up and down by an elevator mechanism 21.

The computer 19 has a CPU, ROM, R
It has an AM, a keyboard, a display, a floppy disk drive, an input / output interface, etc., and controls the elevator mechanism 21, the vacuum pump 11, and the valve driver 22 for driving each of the on-off valves 3 to 10 via the input / output interface. It is configured to give a command.

The above hardware configuration is almost the same as that of the conventional adsorption amount measuring apparatus. However, the range of the pore diameter to be measured is a mesopore region (about 2 to 50 nm in diameter) or a micropore region (about 2 nm or less in diameter). ), A different calculation method is selected. BJH in the mesopore area
Method, CI method, and the like, and in the micropore region, the MP method and the like are often used.

FIGS. 3 to 5 are flow charts showing the contents of the program written in the computer 19. FIG. Each of the routines shown in these figures is selectively branched from a comprehensive menu, and the method of use and operation of the embodiment of the present invention will be described below with reference to these figures. FIG. 3 shows a program for editing a pore diameter table. First, a required pore diameter row is set using this program. In this example, a plurality of pore diameter tables are already stored in the floppy, and the table is loaded and displayed by designating a desired table number in accordance with a command from the keyboard. When a pore diameter data string required for the current measurement is set based on a command from a keyboard or the like based on the loaded table, the data string is edited and stored in the floppy disk.

FIG. 4 shows a relative pressure table setting program. This program is for determining the relative pressure sequence that defines the measurement point. In this example, several relative pressure tables are already stored in the floppy, and when the relative pressure table number is input from the keyboard, it corresponds to it The content of the relative pressure table is loaded, and based on the loaded relative pressure, the relative pressure can be appropriately changed or used as it is to determine the measurement point (ST41, ST50, ST5).
1) A new relative pressure table can be prepared and edited using the pore diameter table edited in FIG. In this case, when the pore diameter table number to be used is input from the keyboard, the corresponding table is loaded (ST42, ST42).
(ST43) Next, when an analysis method is selected by operating the keyboard (ST44), each pore diameter in the pore diameter table is converted into a relative pressure (ST45).

[0019] Here, the relative pressure is between 0-1 a equilibrium pressure P / saturated vapor pressure P ₀ as described above, also,
The equation used for this conversion can be uniquely determined by an analysis method. For example, in the mesopore region, B
Taking the case where the JH method is adopted as an example, the pore radius is r
(Å), if the relative pressure is x

[0020]

(Equation 1) Indicated by Table 1 shows an example of the relationship between the pore radius r and the relative pressure x calculated based on this equation.

[0021]

[Table 1] Data conversion from pore diameter to relative pressure (ST45)
Is actually solving a nonlinear equation in which r is substituted in the above equation. After this conversion is completed, the computer 19 automatically executes ST46 to ST49. That is, in the relative pressure data obtained in ST45,
It is determined whether or not data of three or more points exists between the relative pressures of 0.05 to 0.30 (ST46). If there is no such data, the relative pressure data is 0.05, 0.10, 0.15 or not. 0.20,
0.25 and 0.30 are added (ST47), and if there is, the process directly proceeds to ST48.

In ST48, it is determined whether or not the relative pressure data includes data of 0.90 or more. If not, a relative pressure of 0.95 is added (ST49). Go ahead and edit the relative pressure table here. The editing result is stored in the floppy (ST51). Here, the reason why the measurement point is added at a relative pressure of 0.3 or less is that the BJH method requires BET specific surface area data among the mesopore distribution calculation methods, and therefore, even if the pore diameter in the micropore region is not specified, the BET Multiple (at least 3) in the applicable area (generally the relative pressure is 0.05 to 0.30)
-5 measurement points). In addition, specific surface area data is necessary not only for the BJH method but also for obtaining other information (for example, average pore diameter).
It may be better to acquire data in the range of the relative pressure of 0.05 to 0.30.

The reason for adding the measurement point to the relative pressure of 0.9 or more is that the total pore volume data is required when calculating the mesopore distribution, and the measurement point near the saturated vapor pressure (for example, 0.95) is always required. This is because The relative pressure table determined by the program shown in FIG. 4 is used in the measurement program shown in FIG. That is, in the measurement program, by inputting the relative pressure table number, the table is loaded, and the relative pressure based on the pressure data taken from the pressure detector 17 during the measurement is expressed as
Each time the relative pressure described in the loaded relative pressure table is reached, each open / close valve is driven to sample the adsorption (desorption) amount data and the equilibrium pressure in the same manner as in the conventional method. Stored on floppy.

It should be noted that, for example, a pore radius of 5
In the case where quality control is performed based on pore volume (distribution) data between 0 ° and 100 °, as is clear from Table 1, data must be collected densely between 0.8 and 0.9 relative pressure. In the embodiment of the present invention, in the embodiment of the present invention, the pore diameter table editing program creates a pore diameter table in which the pore radius is dense between 50 and 100 °, and the relative pressure setting program converts the table into a relative pressure table. By converting and loading this with the measurement program, dense data collection is reliably performed in the above-described pore radius range.

[0025]

As described above, according to the present invention, a pore diameter sequence to be observed is automatically converted into a relative pressure sequence by simply setting a pore size to be observed and selecting an analysis method. It is memorized, and at the time of measurement, data is automatically sampled using this relative pressure train as a measurement point,
For example, if you do not need to closely observe the isotherm and want to see only the pore distribution in a certain section, just enter the analysis method and the increment of the pore diameter, and the relative pressure table will be automatically created afterwards. Since the data is used for measurement, the data to be observed can be reliably obtained, and the measurement time can be significantly reduced as compared with the conventional method.

[Brief description of the drawings]

FIG. 1 is a basic conceptual diagram showing a configuration of the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing the contents of a pore diameter table editing program among the programs written in the computer 19 of the embodiment of the present invention.

FIG. 4 is a flowchart showing the contents of a relative pressure setting program similarly written in the computer 19 of the embodiment of the present invention.

FIG. 5 is a flowchart showing the contents of a measurement program similarly written in the computer 19 of the embodiment of the present invention.

FIG. 6 is a diagram illustrating the principle of an adsorption amount measuring device based on a constant volume method.

[Explanation of symbols]

 1 ··· Sample cell 2 ··· Manifold 3-10 ··· Open / close valve 11 ··· Vacuum pump 16 ··· Vacuum gauge 17 ··· Pressure detector 18 ··· A -D converter 19 ... Computer 20 ... Dewar bottle 21 ... Elevator mechanism 22 ... Valve driver

Claims (1)

(57) [Claims] 1. A sample cell for enclosing a sample to be measured, a manifold separated from the sample cell by an on-off valve,
A gas introducing / discharging means for introducing or discharging an adsorbed gas to or from the manifold, a pressure detector for measuring the pressure in the manifold, and a sample adsorption amount based on a change in pressure data before and after opening the on-off valve. A calculating unit for calculating, a control means for controlling the operation of the on-off valve, the gas introducing / discharging means and the calculating unit, and the on-off operation of the on-off valve at a predetermined timing to allow the adsorbed gas to enter into the sample cell. While repeating the introduction and discharge, in an apparatus for measuring the adsorption amount data to the sample at a plurality of adsorption equilibrium points based on the output of the pressure detector, any of a plurality of pore distribution analysis methods set in advance, an analysis method selecting means for selecting an object, and setting means for setting the pore size data string, the pore size data string set, is selected by the analyzing method selecting means A relative pressure data sequence calculating means for converting the relative pressure data sequence into a relative pressure data sequence based on the analysis method, and a storage means for editing and storing the obtained relative pressure data. In addition to calculating various physical property values from the adsorption amount based on the method, the control means is configured to control the open / close valve and the gas introduction / discharge means based on the contents of the storage means. Adsorption amount measuring device.