JP3027331B2 - Adsorption amount measuring method and apparatus using temperature-compensated constant volume adsorption apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a constant volume adsorption amount suitable for measuring a surface area of a sample having a small surface area of 3000 cm ² or less, particularly 100 cm ² or less.

[0002]

2. Description of the Related Art Constant volume adsorption measurement methods including the BET method are widely used mainly for measuring (specific) surface area of granular samples. Such surface area measurement is important not only for the evaluation of the characteristics of the catalyst, which is mostly performed as a surface reaction, but also for the microscopic unevenness or surface roughness (surface area and geometrical area obtained from the amount of adsorbed gas) of various solid materials. This can be easily determined as a roughness coefficient as a ratio of chemical surface area), and other useful surface properties.

[0003] Here, the constant volume adsorption amount measurement method (the BET method using the BET method as the adsorption isotherm is most typically known) refers to a container having a fixed volume at a temperature T (called a burette, The adsorbed gas (pressure p ₁ ) confined in the volume (V _A ) is expanded into a vessel (called an adsorption cell, the volume of which is V _B ) containing the adsorbent (pressure p ₁ ).
₂ ) A method of measuring the amount of adsorption from the material balance.
FIG. 1 shows a schematic diagram of an apparatus for this. Since the constant volume adsorption amount measuring method has versatility and high measurement sensitivity, it is the most common adsorption amount measuring method.

In the constant volume adsorption amount measuring method, the adsorption amount A is basically calculated by the following equation.

A = (22414 / RT) (p _{1 VA−} p ₂ ( _VA + V _B )) (1) where R is a gas constant. Also, (2241) of the equation (1)
4 / RT) indicates the amount of adsorbed gas in a standard state (0 ° C., 1 at).
m; abbreviated as STP) (1 mole is 224)
(Corresponding to 14 STP cm ³ ).

From the pressure dependence of the amount of adsorption (adsorption isotherm), the amount of adsorption (referred to as the amount of single molecule adsorbed) that further covers the surface is determined. It is known that this relationship is often represented by, for example, the following BET infinite layer formula.

[0007]

(Equation 1) Here, x = (p / p ₀ ) is the ratio between the adsorption equilibrium pressure p (= p ₂ ) and the saturated vapor pressure p ₀ of the adsorbed gas at that temperature, and is called relative pressure. A is the equilibrium adsorption amount, _AML is the adsorption amount (single-molecule adsorption amount) in which the sample surface is covered with one layer of adsorbed gas molecules, and C is the BET constant depending on the difference in the heat of adsorption between the first and second layers. .

As will be described later, a linear plot for obtaining the single molecule adsorption amount obtained from the above equation (2) is called a BET plot. The relative pressure (x = p / p ₀ ) is 0.05 to 0.
In the range of 35, the linearity of the BET plot is good. The surface area of the sample is obtained by multiplying the obtained single-molecule adsorption amount _AML by the cross-sectional area of the adsorbed gas molecule.

The nitrogen adsorption method, which is the most standard BET method, is an adsorption amount measurement using nitrogen as an adsorbate at the temperature of liquid nitrogen, and p ₀ is 760 mmHg. Therefore, the nitrogen adsorption method measures the amount of adsorption up to p ₂ = 250 mmHg. For a sample with a small amount of adsorption, the first term (p ₁ V _A ) and the second term p ₂ (V _A + V _B ) becomes smaller, making it difficult to measure the amount of adsorption. Since V _A = V _B = 50 cm ³ in a normal apparatus, for example, for a sample having a surface area of 1 m ² , 1 is obtained from the difference between approximately 130 and 129 in equation (1). That is, such a strict subtraction must be performed for a sample having a small amount of adsorption.

Since the pressure of the gas is proportional to the temperature, the temperature control of the device determines the accuracy of the mass measurement of the adsorbed gas, which in turn determines the lower limit of the surface area measurement. It is due to such a situation that the measurement limit of the surface area by the nitrogen adsorption method becomes about 1 m ² .

In order to alleviate the difficulty of controlling the temperature for measuring the amount of adsorption to a small surface area sample by the conventional constant volume adsorption amount measuring method, the present inventor impairs the accuracy of measuring the amount of adsorbed gas. An adsorption amount measuring device devised to compensate for a change in ambient temperature, that is, a temperature-compensated constant volume adsorption amount measuring device has already been developed (Rev. Sci. Instru.).
m. 53 (7), July 1982, 1061-1066.
P .; "catalyst" 24 (6) 1982, 426-429.
page). FIG. 2 is a conceptual diagram thereof. The apparatus volume to the left and right differential pressure gauge, a sample substantially equal pair of reference bullet shape (volume V _A) as a sample for buret (V _A + DV _A) and a pair of reference adsorption cell (V _B) Adsorption cell (V
_B + DV _B ) are arranged symmetrically. A structure is provided in which even if there is a slight temperature change, a pressure change in the burette and the adsorption cell arranged symmetrically to each other offsets one of the pressure changes.

At this time, the equation (1) for obtaining the amount of adsorption is transformed into the following equation (3).

A = (22414 / RT) “(V_A+ DV_A+ V_B+ DV_B) Dp-((V _A DV_B-V_BDV_A) / (V_A+ V_B)) P₁(3) Here D p is the adsorbed air on the reference side and the sample side after expansion of the adsorbed gas
The differential pressure of the body.

If the device is made as symmetrical as possible, D V_A
≒ DV_B≒ 0, and ignore the second term of equation (3)
Since equation (3) can be used, equation (3) is
Simplified.

A = (22414 / RT) (V_A+ V_B) D p (3 ′) That is, the surrounding area that impairs the measurement accuracy of the adsorption amount described above.
Temperature change is compensated, and the accuracy of adsorption amount measurement is greatly improved
It is expected.

With such a temperature-compensated adsorption amount measuring apparatus, the lower limit of surface area measurement by nitrogen adsorption at liquid nitrogen temperature has been expanded to 0.03 m ² (300 cm ² ). For a sample having a surface area of 0.03 m ² , this is equivalent to obtaining 0.03 from the difference between 129.03 and 129.00 in equation (1). This means that when the apparatus shown in FIG. 1 is used, environmental temperature control is performed at about 0.07 ° C. (= 300 × (0.0
3/129)) is a value that disappears if there is an error.

On the other hand, if a gas having a saturated vapor pressure p ₀ lower than N ₂ is used as the adsorbed gas, a smaller surface area can be measured. Because, in order to obtain the relative pressure 0.35 required for obtaining the monolayer adsorption amount _AML , when N ₂ is used as the adsorbate, an adsorption experiment at an equilibrium pressure up to 250 mmHg is required. For example, if krypton (Kr) is used as the adsorbate, an equilibrium pressure of up to 0.6 mmHg is sufficient. That is, since the saturated vapor pressure p ₀ of krypton at the temperature of liquid nitrogen is 1.8 mmHg, the relative pressure 0.35 is 0.6 m
mHg. Thus, the first term and the second term of the equation (1)
Both terms are small, and the measurement error is small.

For example, by krypton adsorption, 0.03
To obtain a surface area of m ² , 0.4
0.03 is obtained from the difference between 8 and 0.45, and the error is greatly reduced as compared with nitrogen adsorption. From such a viewpoint, in a normal constant volume adsorption amount measuring apparatus, a surface area measuring method using a noble gas having a small vapor pressure as an adsorbate has been conventionally performed, and xenon, krypton, and the like have been used.

[0019]

Therefore, even in a temperature-compensated adsorption amount measuring apparatus, a smaller adsorption amount can be measured by using a low vapor pressure adsorption gas such as Kr.
Therefore, the possibility of small surface area measurement is expected. However, in practice, the adsorption amount is measured by a temperature-compensated adsorption amount measuring device using Kr as the adsorption gas, and the BET plot of the adsorption amount obtained from the equation (3) is as shown in the experimental examples described later. , Markedly deviated from the straight line, and the single molecule adsorption amount _AML could not be determined.

In view of the above-mentioned circumstances, a main object of the present invention is to provide a method and an apparatus which can measure the amount of adsorption on a sample having a smaller surface area using the above-mentioned temperature-compensated adsorption amount measuring apparatus. The purpose is to do.

[0021]

As a result of further research conducted by the present inventor for the above-mentioned object, BE obtained when the above-mentioned temperature-compensated adsorption amount measuring apparatus is used, particularly when a low vapor pressure adsorption gas is used.
The cause of the nonlinearity of the T plot is that when measuring the amount of adsorption to a small surface area sample of about 10 cm ² or less, 30
0cm Most reference adsorption cell (e.g. the inner surface area did not cause a problem with the sample surface area measurement as that ² or 15
It has been found that the amount of adsorption of the adsorbed gas to about ( cm ² ) cannot be ignored. Then, by compensating for the adsorption amount of the adsorption gas to the reference adsorption cell,
It has been found that accurate surface area measurements are possible, even for small surface area samples such as 1 cm ² .

That is, the adsorption amount measuring method suitable for applying a sample to a small surface area sample according to the present invention comprises symmetrically arranging a pair of reference burettes and a buret for a sample having substantially equal volumes and shapes. A reference adsorption cell having substantially the same volume and shape as the two burettes, and
A temperature-compensated constant volume comprising: an adsorption gas supply source coupled to each of the sample adsorption cells; and an adsorbent gas supply source coupled to the two burettes so as to be able to be introduced into the burettes; Using the adsorption device, the adsorbed gas once introduced into both burettes is further expanded and absorbed into each adsorption cell.
After the adsorption, based on the resulting pressure difference between the two burettes, when determining the amount of adsorption of the adsorbed gas, the amount of adsorption to the reference adsorption cell is compensated to obtain the amount of adsorption to the sample adsorption cell. I do.

Also, the adsorption amount measuring apparatus of the present invention comprises the above-mentioned temperature-compensated adsorption amount measuring apparatus; the pressure of the adsorbed gas introduced into both burettes, and the adsorbed gas expanded and adsorbed in both adsorption cells thereafter. And a calculating device arranged to obtain the amount of adsorption to the sample adsorption cell while compensating the amount of adsorption to the reference adsorption cell from the pressure difference between the two burettes.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method and apparatus for measuring the amount of adsorption according to the present invention will be described below with reference to the drawings.
This will be described more specifically.

FIG. 3 is a schematic layout diagram of an adsorption amount measuring apparatus using a temperature-compensated adsorption amount measuring apparatus according to a preferred embodiment of the present invention.

(Apparatus System) The apparatus main body 10 includes a Pyrex glass pipe 1 having an inner diameter of 6 mm, and stopcocks C1 to C1.
6 (and C11 to C19), and
Through a pipe 12, directly through a pipe 12, through a pipe 13 to a vacuum system VAC 1 through a low pressure diaphragm type pressure gauge 14, and further through a pipe 15 to a high pressure mercury pressure gauge 16. I have. A reference burette 2 is formed by a portion defined by the stopcocks C1, C2, C3 and the diaphragm of the differential pressure gauge 7 in the pipe 1, and a diaphragm of the stopcocks C1, C2, C4 and the differential pressure gauge 7 in the pipe 1 as well. Buret 3 for sample by section defined by
Is formed. The reference burette 2 and the sample buret 3 are connected to the reference adsorption cell 4 and the sample adsorption cell 5 containing the adsorption medium 5a via the stop cock C1, respectively. For the measurement, the adsorption cells 4 and 5 are generally contained in a dewar 6 filled with liquid nitrogen. Further, in order to improve the temperature compensating property, it is preferable that the burettes 2 and 3 and the adsorption cells 4 and 5 are arranged as symmetrically as possible as much as possible, and that both are arranged close to each other. Bullet 2 for reference
The sample burette 3 is partitioned by a stop cock C2, and a differential pressure gauge 7 is provided between both burets via stop cocks C5 and C6.

The outputs of the pressure gauge 14 and the differential pressure gauge 7 are as follows:
The signals are input to a calculator 20 for calculating an adsorption amount and a surface area, which will be described later, via converters 18 and 19 for integration and / or A / D conversion, respectively.

Further, it is preferable that the burettes 2 and 3 and the differential pressure gauge 7 are covered with aluminum foil to prevent radiation and minimize the temperature difference between the reference system and the sample system.

(Measurement of Adsorption Amount) In order to measure the adsorption amount for accurate surface area calculation, the adsorption equilibrium pressure must be changed.
After obtaining the adsorption amount at a certain equilibrium pressure, without performing the desorption operation,
Further, it is desirable to adopt an integrated adsorption method in which an adsorption experiment is continuously performed by introducing an adsorption gas.

The measurement consists of the following three steps, but it will be clear that the second step can be omitted later.

[0031] [1] (Measurement of _{V B} and DV _B in the formula (3)) Measurement of dead volume (1) for reference adsorption cell 4, reference buret 2, the pipe 1
After true <br/> air exhausted through 3 and a pressure gauge 14 stopcock C19, close the stopcock C1, C2, C 5 Contact and <br/> C16. Ginseng Teruyo burette 2, put helium (He) of a predetermined amount to a pipe 13 and a pressure gauge 14, stopper
After closing the Pukokku C11, read the pressure at the pressure gauge 14, and _{p 1.} Introducing helium, open the cock C1 is expanded to the reference adsorption cell 4, to the pressure and p _2. Since adsorption of helium substantially negligible, the volume _{V B} of the reference adsorption cell 4 is _{V B = V o ((p} 1 /
p ₂₎ -1) to be evaluated. Here _{V o} is, C1, C
2, C5, C11, C16 and the volume defined by the diaphragm of the pressure gauge 14.

(2) The reference suction cell 4, sample suction cell 5, reference buret 2 and sample buret 3 are evacuated, and the stop cock C1 is closed. Fill both burets with helium and read the pressure p. The stopcocks C3 and C4 and the stopcock C2 separating the reference side and the sample side are closed, and the stopcock C1 is opened to allow helium to expand in both adsorption cells. At this time, the indication of the differential pressure between the reference side and the sample side is read by the differential pressure gauge 7. Differential pressure gauge 7 used in this example (“P90DL” manufactured by Celesco Sokken)
Is displayed depending on the pressure of the atmosphere even if the differential pressure on the left and right is zero, open C2 and read the display of the pressure (zero point), and the difference from the previous reading of the differential pressure is true. Differential pressure D
give p. Because helium does not adsorb, from mass balance helium, the following expression is obtained for the unknowns DV _B.

[0033] _{(V A + DV A + V} B + DV B) (V A + V B) Dp = (V A DV B -V B DV A) p (4) when the absolute value of the differential pressure Dp is large, the reference suction A solid glass rod or the like is placed in the upper part of the cell or the sample adsorption cell, and adjustment is made so that the absolute value of the differential pressure Dp (and thus DV _B ) becomes as small as possible.

[2] Preliminary Adsorption Experiment Using a normal adsorption amount measurement method, using an adsorption gas (for example, Kr) used for an adsorption experiment, a rough adsorption isotherm A _R (for a reference adsorption cell and a sample adsorption cell) is used. Determine p) and A _s (p). When the BET infinite adsorption method (the above expression (2)) is adopted, the single molecule adsorption amounts _AML and B
The ET constant C may be determined for each of the reference system (A _MLR and C _R ) and the sample system (A _MLS and C _S ).

[3] Adsorption Experiment After the entire system was evacuated, the stop cock C1 was closed, both burettes were filled with the adsorption gas, and the pressure p _n (1) was read. After closing the stopcocks C3, C4 and C2,
The stop cock C1 is opened, and the adsorbed gas is expanded into both adsorption cells. After once reading the differential pressure, open the stopcock C2 and read the zero point. The difference between the previous differential pressure give a true differential pressure Dp _n. Thereafter, the stop cock C1 is closed, and such an operation is repeated to perform an integrated adsorption operation.

In the n-th adsorption operation in such a situation, the adsorption gas in the burette at the temperature T and the pressure p _n (1) is expanded into the adsorption cell to obtain a differential pressure Dpn when _n is obtained.
The first adsorption amount _A'n is given by the following equation.

[0037] _{A 'n = (22414 / RT} ) [(V A + DV A) p n (1) + (V B + D V B) p n-1 - (V A + DV A + V B + DV B) (p n _{(2) -Dp n)] (} 5) where p _n (2) in is the pressure in the reference adsorption cell after adsorption gas expansion, p _n-1 is both adsorbed gas remaining in the previous adsorption cells Pressure.

The above p _n (2) can be easily calculated because the adsorption on the reference adsorption cell was conventionally ignored. However, in the present method, it is obtained from the following equation in consideration of the amount of adsorption to the reference adsorption cell.

[0039] _{(22414 / RT) [V A} p n (1) + V B p n-1 - (V A + V B) p n (2)] = A R (p n (2)) - A R (p _n-1 ) (6) where A _R (p _n (2)) is the isothermal adsorption amount on the reference adsorption cell, and the BET infinite layer equation (the above equation (2)) can be adopted for krypton adsorption. .

That is, A _MLR and C _R are known,
At n = 1, all terms corresponding to n-1 are zero. Since p ₁ (1) is obtained by measurement, equation (6)
Substituting equation (2) into the right-hand side of the equation gives an equation for the unknown p ₁ (2). Therefore, by the Newton method, p
₁ (2) can be obtained. Also, p
Since ₁ is obtained, as well as it provides the equation for _{p 2 (2), p 2} (2) is obtained. Therefore, p
₃ (2), p ₄ (2), that is, _pn (2) is obtained.

In measuring the zero point, the pressure in the reference adsorption cell is equal to the pressure in the sample adsorption cell. That is, the pressure of the reference adsorption cell is changed from p _R (= _pn (2)) to Dp
_R increases to _pn , and the pressure of the sample adsorption cell is p
The p _n from _{S (= p n (2)} -Dp n) increases Dp _S. At that time, new adsorption occurs in the reference adsorption cell and the sample adsorption cell. When these adsorption respectively to DA _R and DA _S, they are given by the following equation.

[0042] (22414 / RT) [(V A + DV A + V B + DV B) p S + (V A + V B) p R] = (22414 / RT) [(2V A + 2V B + DV A + DV B) p n )] + DA _R + DA _S (7) p _S + Dp _S = p _R + Dp _R = _pn (8) These correction amounts of the adsorption amount can be almost ignored in the adsorption experiment at a high pressure as in the case of nitrogen adsorption. However, it becomes relatively large in experiments at low pressure.

[0043] Also the new adsorption DA _S and DA _R when the zero point measurement using the adsorption isotherm for the sample side and the reference side obtained from the following equation.

DA _R = A _R (p _R + Dp _R ) −A _R (p _R ) (9) DA _S = A _S (p _S + Dp _S ) −A _S (p _S ) (10) If p _n (2) is obtained, p _R and p _S are determined relating to the n-th adsorption operation. Therefore, Equations (7) and (8) are simultaneous equations for Dp _S and Dp _R for the n-th adsorption operation including known parameters, and can be easily solved by Newton's method. ) p _n, DA _R and DA _S are determined from.

The cumulative adsorption amount A _n is given by the sum of the correction amount ShigumaDA _S of cumulative adsorption amount .SIGMA.A _'n the adsorption amount of up to the last by the following equation.

[0046] _{A n = Σ (A 'n} + DA S) (11) The equilibrium pressure of this case is p _n.

That is, the above calculation process is performed by the computer 20.
Measurements were introduced into (using the NEC 9801DA in this example) p _n (1), wherein the Dp _n (2) and (5)
Using ~ formula (10), obtains the p _n (2) (hence A _'n) and DA _R and DA _S, aggregation in the calculation to determine the cumulative adsorption amount A _n from these, the p _n and equation (11) Is done.

(Calculation of single molecule adsorption amount and surface area)
Here, each relative pressure x (= p_n/ P₀)
Quantity A (= A_n) Is obtained, for example, no BET
The following equation (12) obtained by transforming the above-described equation (2), which is a limited layer equation, x / A (1-x) = 1 / (A_MLC) + x · (C-1) / (A_MLC) According to (12), for each relative pressure, x / A (1-x) = p / A
(P₀-P) plot (BET plot, for example,
4 and 6 for the example shown in FIG.
_MLC and gradient (C-1) / A_ML・ Single molecule absorption from C
Amount A_ML(Unit STPcm^Three ) And BET constant C
Can be

Obtained single molecule adsorption amount A_MLFrom the following formula
More sample surface area S (cm^Two ) Is required.

S = a × 10 ⁻¹⁶ × (A _ML /22414)×6.02×10 ²³ (13) Here, a is a cross-sectional area of one molecule of the adsorbed gas, and is 23 (Å) in the case of Kr. ² ) is used.

(Embodiment of Measurement of Adsorption Amount) In this embodiment, a steel ball 5 for a ball bearing having a diameter of 1 mm using the apparatus shown in FIG.
Adsorption of krypton at liquid nitrogen temperature (saturated vapor pressure p ₀ = 1.8 mmHg at liquid nitrogen temperature) was performed on a, and it was confirmed that surface area measurement of about 1 cm ² was possible.

As the adsorption isotherm for the reference adsorption cell and the sample adsorption cell, the BET infinite layer system (Equation (2)) was employed. That is, as A _R and A _S in the above equations (6) to (10), the single molecule adsorption amounts A _MLR and A _MLS obtained in the preliminary experiment and the BET constants C _R and C _S are introduced to obtain the equation (12). The value obtained from the BET linear equation of ()) was used. Amount of single-molecule adsorption of krypton A to a previously obtained empty reference-side adsorption cell and empty sample-side adsorption cell by a conventional method.
_MLR and A _MLS are both 2.50 × 10 ⁻⁴ STPc
m ³ and the BET constants C _R and C _S were 12. FIG. 4 shows a BET plot of krypton adsorption at liquid nitrogen temperature for an empty sample adsorption cell obtained by using these. Monolayer adsorption A _ML of krypton to the sample for adsorption cell obtained from the intercept and slope of the BET plot was 2.54 × 10 ^-4 STPcm ^3.

At this time, if the amount of krypton adsorbed on the reference adsorption cell is not taken into account (that is, if it is calculated as A _MLR = 0), the BET plot deviates significantly from the straight line (FIG. 5), and it is necessary to determine the amount of single molecule adsorbed. Could not be done. Perhaps the BET plot due to xenon adsorption, which has a lower saturated vapor pressure, will have a more significant deviation.

FIG. 6 shows a BET plot of krypton adsorption on a sample adsorption cell containing 50 steel balls.
From the intercept and slope of Figure 6, the monomolecular adsorption A _ML of krypton to steel balls 50 pieces samples for adsorption cell is obtained.

AML of single molecule adsorbed on sample adsorption cell _AML
In the calculation of A, A _R (p) and A
_S (p) was used. But _AML used A
There was little dependence on _S (p), that is, A _MLS (FIG. 7). That is, it is understood that the approximate value of A _MLS is sufficient for the calculation of A _ML .

A _ML -A _MLR hardly _depended on A _MLR (FIG. 8). However too linearity of the BET plot is deteriorated as mentioned above by using the smaller A _MLR value, reliability with respect to A _ML lack. A _ML -A _MLR is
This means that the amount of adsorption to the sample adsorption cell is measured based on the amount of adsorption to the reference adsorption cell. The amount of adsorption to a sample is the difference between the amount of adsorption to a sample-containing adsorption cell containing a sample and the amount of adsorption to an empty sample-absorption cell, and both are obtained based on A _MLR .

50, 100, 150 steel balls having a diameter of 1 mm
The relationship between the number of monomolecular adsorption A _ML and steel balls of krypton for pieces containing the sample for adsorption cell shown in FIG. The section corresponds to the amount of single molecule adsorbed on an empty sample adsorption cell, and the gradient corresponds to the amount of single molecule adsorbed per steel ball unit. This gradient coincided with the value obtained from the amount of krypton adsorbed by a conventional adsorption amount measuring device for 10,000 steel balls. That is, the single molecule adsorption amount of krypton on 50, 100, and 150 steel balls coincided with the calculated value obtained from 10,000 steel balls. Steel balls 50 monomolecular adsorption (A _ML -A _MLR) is 0.27S
TPcm ³ , and the surface area is 1.
It was calculated to be 7 cm ² . This almost coincided with the geometrically calculated surface area of the steel ball (1.57 cm ² ), and it became clear that the surface area of about 1 cm ² could be measured by this method.

(Modification) In the above, referring to the drawings in FIG. 3 and subsequent figures, an adsorption amount measuring method and apparatus suitable for application to a small surface area sample of the present invention using a temperature compensation type adsorption amount measuring apparatus will be described. One preferred embodiment has been described. However, it will be understood that the embodiments described above within the scope of the present invention can be implemented with various modifications. In particular, in the above-described embodiment, the calculation process following equation (5) enables a strict calculation to ensure theoretical accuracy, but takes into account the device characteristics of the temperature-compensated adsorption amount measuring device. If so, many simplifications are possible within a range that maintains practical measurement accuracy. The following are some examples of such variations.

(1) Not only surface area measurement, but also adsorption isotherm for reference adsorption cell and sample adsorption cell, A
_By simply changing _R (p _R ) and A _S (p _S ), it can be applied to any adsorption amount measurement. In particular, the present invention will be effective for measuring the amount of water adsorption in which a large amount of adsorption occurs in the reference adsorption cell.

(2) The adsorption temperature is not limited to liquid nitrogen temperature.

(3) Of course, it is possible to make the whole device made of metal instead of glass.

(4) As a pressure gauge, a diaphragm type pressure gauge 14
And a combination of the differential pressure gauge 7, but the type of these pressure gauges is arbitrary. Instead of the mercury pressure gauge, a diaphragm type pressure gauge capable of measuring up to the atmospheric pressure can be used. Also, separate pressure gauges can be provided for the reference system and the sample system, respectively. As a result, instead of the operation of previously obtaining the adsorption isotherms of the reference adsorption cell and the sample adsorption cell ([2] preliminary adsorption experiment), the expansion of the adsorbed gas in each of the reference system and the sample system during the main adsorption experiment. Measure the pressure before and after,
It is also possible to measure A _R (p) and A _S (p) simultaneously.

(5) By using a differential pressure gauge 7 that does not need to correct the zero point, there is no need to open the stop cock C2 after the suction operation to correct the zero point of the differential pressure gauge 7, and accordingly, , The calculations of the above equations (7) to (10) become unnecessary (DA _R ≒ DA _S ≒ 0).

[0064] (6) As shown in FIGS. 7 and 8, A _ML
Are essentially A _R (p) and A _S (p),
That is, it did not depend on the values of A _MLR and A _MLS . Therefore, an experimental operation for obtaining them (see [2] above)
Omitted preliminary adsorption experiments), for A _MLR, using about 1.5 times the value of the geometric surface area, 10 for C _R
By using the degree value, the calculation can be simplified without causing a substantial decrease in measurement accuracy. As for A _MLS and C _S , approximate values can be used or they can be obtained by repeated calculations. The adsorption experiments of high adsorbate vapor pressure than krypton, DA _R and DA _S is at most A 'of about 0.1% _n, ignore them (equation (7) - omit calculation of equation (10) It is also possible. However, xenon may not be negligible.

(7) In order to accurately measure a small differential pressure in the differential pressure gauge 7, it is preferable to use a configuration in which the average value is integrated by the converter 19, but depending on the required measurement accuracy, this configuration may be used. Such an integrator is not necessary, or can be covered by internal calculation in the computer 20.

(8) In the above embodiment, the operation of the stopcock was performed manually, but it is also possible to automate the operation. By providing the movable bellows tube or the like on top of the adsorption cell, it is also possible to automatically minimized the Dp or DV _B. Although the input of the measured pressure was performed through the AD converter, manual input is also possible.

(9) As the adsorbed gas, 10 cm^TwoLess than
Is measured at liquid nitrogen temperature by Kr (p₀=
1.8mmHg), Xe (P₀= 0.001 mmHg)
Xe (p₀= 0.05mm
Hg) and the like are preferred. Also 10cm^Two ~ 1000cm
^TwoTo measure the surface area of the sample, in addition to the above adsorbate,
CH_Four(P₀= 10 mmHg) and liquid oxygen temperature
CH in_Four(P₀= 80 mmHg). 1
000cm^TwoFor the above surface area measurement, other liquids of the above adsorbate
N at body nitrogen temperature _Two(P₀= 760 mmHg) and
And Ar (p₀= 200mmHg), at dry ice temperature
CO_Two(P₀= 760 mmHg) and freezing point
N-C_FourH_Ten(P₀= 760mmHg)
You.

(10) In the above example, the Newton's method was used as a solution of the equations (5) and (6) and the simultaneous equations (7) and (8). However, the method is suitable for application to an ordinary personal computer. Of course, other numerical calculation methods can be applied.

(11) In particular, at the time of adsorption at a low pressure of 10 ^-1 mmHg or less, the dead volume or the adsorption amount of the adsorption cell can be corrected in consideration of the effect of heat penetration (Isao). Suzuki et al.
Catal. , 155 , 163-165 (1995).
Year)).

[0070]

As described above, according to the surface area measuring method and apparatus using the temperature-compensated adsorption amount measuring apparatus of the present invention, particularly, in combination with an adsorbing gas having a saturated vapor pressure substantially smaller than that of nitrogen. The surface area of a sample having a small surface area of 10 cm ² or less can be measured accurately, and the surface properties of the sample can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a schematic view of a constant volume adsorption device.

FIG. 2 is a schematic diagram of a temperature-compensated constant volume adsorption device.

FIG. 3 is a schematic configuration diagram of an embodiment of the adsorption device of the present invention.

FIG. 4 is a BET plot of krypton adsorption on an empty sample adsorption cell (single molecule adsorption amount A _MLR on a reference adsorption cell = 2.5 × 10 ⁻⁴ STP cm ³ ).

FIG. 5 is a BET plot of krypton adsorption on an empty sample adsorption cell (single molecule adsorption amount A _MLR = 0 on a reference adsorption cell).

FIG. 6 is a BET plot of krypton adsorption on a sample adsorption cell containing 50 steel balls (single molecule adsorption amount A _MLR = 2.5 × 10 ^-4 STP cm ^{3 on a} reference adsorption cell).

Figure 7 is a graph showing the A _MLS relationship using a monomolecular adsorption A _ML of krypton to steel balls 50 pieces samples for adsorption cell.

FIG. 8 is a graph showing the relationship between (A _ML −A _MLR ) of an adsorption cell containing 50 steel balls and A _MLR used.

9 is a graph showing the relationship between the number of monomolecular adsorption A _ML and steel balls of krypton to steel ball-containing sample for adsorption cell.

[Explanation of symbols]

1: Glass pipe 2: Reference buret 3: Sample buret 4: Reference adsorption cell 5: Sample adsorption cell 5a: Adsorption medium 6: Dewar bottle 7: Differential pressure gauge 10: Adsorption device main body 11 , 12 , 13 , 15 : Glass pipe 14: Pressure gauge 18, 19: Transducer 20: Computer C1 to C6, C11 to C19: Stopcock

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N ^7/ 00-7/22 G01N 15/08

Claims (4)

(57) [Claims] 1. A pair of reference burettes having substantially the same volume and shape as each other and a sample buret are symmetrically arranged, and both reference burettes and a reference adsorption cell having substantially the same volume and shape as each other are provided. Temperature-compensated constant-volume adsorption comprising an adsorption gas supply source connected to each of the adsorption cells, and an adsorbent gas supply source connected to both of the burettes so as to be able to be introduced, and a pressure gauge capable of measuring the pressure inside both of the burettes. Using the device, the adsorbed gas once introduced into both burets is
Furthermore, after expanding and adsorbing to each of the adsorption cells, the amount of adsorption of the adsorbed gas is calculated based on the resulting pressure difference between the two burettes. A method for measuring the amount of adsorption of a sample, comprising determining the amount of adsorption to the sample. 2. A pair of reference burettes having substantially the same volume and shape as each other and a burette for a sample are symmetrically arranged. Each of the adsorption cells is coupled to each other, and further, an adsorption gas supply source coupled so as to be able to be introduced into both of the burettes, and a temperature-compensated constant-volume adsorption device having a pressure gauge for measuring a pressure inside both of the burettes. ;
From the pressure of the adsorbed gas introduced into both burettes and the differential pressure between the burettes of the adsorbed gas that has been expanded and adsorbed in both adsorption cells afterwards, the amount of adsorption to the reference adsorption cell is compensated, A calculator arranged to determine the amount of adsorbed gas adsorbed on the adsorption cell; and a device for measuring the amount of sample adsorbed. 3. The adsorption gas supply source having a saturated vapor pressure substantially smaller than N ₂ (saturated vapor pressure: 760 mmHg) at liquid nitrogen temperature.
An apparatus according to claim 1. 4. A pressure gauge for measuring the pressure inside both burettes, comprising: a pressure gauge for measuring the pressure inside a reference buret; and a differential pressure gauge connected between the reference buret and the sample burette. Claim 2 or 3 consisting of a combination
An apparatus according to claim 1.