JPH08304256A - Method and device for measuring adsorbing amount using temperature-compensated constant-volume adsorber - Google Patents

Abstract

PURPOSE: To measure the gas adsorbing amount of a sample having a smaller surface area by finding the adsorbing amount of an adsorbing cell for sample by compensating the gas adsorbing amount of an adsorbing cell for reference. CONSTITUTION: The dead volume VB of a cell 4 for reference and the differential pressure Dp between the reference side and sample side of the cell 4 are found in advance by using helium. Then, after evacuating a whole system to a vacuum, a stop cock C1 is closed and the pressures Pn(1) in both burets 2 and 3 are measured with a pressure gauge 14 when the burets 2 and 3 are filled with an adsorbing gas. Then the adsorbing gas is expanded in adsorbing cells 4 and 5 by closing stop cocks C3 , C4 , and C2 and opening the stop cock C1 and the differential pressure between the reference and sample sides is measured with a differential pressure gauge 7. The difference between the measured differential pressure and the zero point when the cock C2 is opened is used as a real differential pressure Dpn . When the differential pressure Dpn is obtained by expanding the adsorbing gas in the burets 2 and 3 at the pressure Pn(1) at a temperature T at the n-th adsorbing operation by repeating the operation, a cumulative adsorbing amount is obtained by performing calculation 20 several times based on the differential pressure Dpn . Here, compensation is made by taking the adsorbing amount of the cell 4 which has been ignored in the conventional example into consideration, thus finding the adsorbing amount of the cell 5.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a constant volume adsorption amount measuring method and apparatus suitable for measuring the 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 The constant volume adsorption amount measuring method including the BET method is widely used mainly for measuring the (specific) surface area of a granular sample. Such surface area measurement is not only important for the characterization of catalysts, which are mostly carried out as surface reactions, but it also involves the microscopic unevenness of various solid materials or the surface roughness (surface area and geometry obtained from the gas adsorption amount). It can be easily discriminated as a roughness coefficient as a ratio of biological surface area), and is a useful means for determining other surface properties.

Here, the constant volume adsorption amount measuring method (the BET method using the BET equation as an adsorption isotherm is most representatively known) means a container having a constant volume at a temperature T (called a burette, The adsorbed gas (pressure p ₁ ) enclosed in the volume V _A is expanded into a container (called an adsorption cell, whose volume is V _B ) containing the adsorbent (pressure p ₁ ).
₂ ), a method of measuring the amount of adsorption from the mass balance.
FIG. 1 shows a schematic diagram of an apparatus therefor. The constant volume adsorption amount measurement method is the most general adsorption amount measurement method because it is versatile and has high measurement sensitivity.

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. In addition, (2241) in formula (1)
4 / RT is the amount of adsorbed gas in the standard state (0 ° C, 1at)
m; abbreviated as STP) (1 mol is 224
(Corresponding to 14 STP cm ³ ).

From the pressure dependence of the adsorption amount (adsorption isotherm), the adsorption amount for further covering the surface (referred to as monomolecular adsorption amount) is determined. It is known that this relationship is often expressed by, for example, the following BET infinite layer equation.

[0007]

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

As will be described later, the linear plot for obtaining the amount of adsorbed single molecule 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 monomolecular adsorption amount A _ML 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 liquid nitrogen temperature, and p ₀ is 760 mmHg. Therefore, in the nitrogen adsorption method, the adsorption amount up to p ₂ = 250 mmHg is measured, but for the sample with a small adsorption amount, the first term (p _{1 VA} ) and the second term p ₂ (V) of the equation (1) are measured. The relative difference between ( _A + V _B ) becomes small, which makes it difficult to measure the adsorption amount. Since V _A = V _B = 50 cm ³ in a normal device, 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 the equation (1). That is, such a strict subtraction is unavoidable for a sample having a small adsorption amount.

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. This is the reason why the surface area measurement limit by the nitrogen adsorption method becomes about 1 m ² .

In order to alleviate the difficulty in controlling the temperature of the adsorption amount measurement on the small surface area sample by the conventional constant volume adsorption amount measurement method, the present inventor impairs the accuracy of the substance amount measurement of the adsorbed gas. An adsorption amount measuring device devised for compensating for ambient temperature change, that is, a temperature compensation type constant volume adsorption amount measuring device has already been developed (Rev. Sci. Instru
m. 53 (7), July 1982, 1061-1066.
Page; "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. Even if there is a slight change in temperature, the burettes arranged symmetrically and the pressure change in the adsorption cell cancels one pressure change.

At this time, the equation (1) for obtaining the adsorption amount 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 gas on the reference side and the sample side after expansion of the adsorbed gas
It is the differential pressure of the body.

If the device is made symmetrical as much as possible, D V_A
≒ DV_B≈0 and ignores the second term of equation (3)
Therefore, the equation (3) can be expressed as the following equation (3 ′).
It is simplified to.

A = (22414 / R · T) (V_A+ V_B) D p (3 ') That is, the surroundings that impair the measurement accuracy of the adsorption amount described above
The temperature change is compensated and the adsorption amount measurement accuracy is greatly improved.
It is expected.

With such a temperature compensation type adsorption amount measuring apparatus, the lower limit of the surface area measurement by nitrogen adsorption at the liquid nitrogen temperature was 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 is about 0.07 ° C. (= 300 × (0.0
It is a value that disappears if there is an error of 3/129)).

On the other hand, if a gas having a saturated vapor pressure p ₀ smaller than N ₂ is used as the adsorbed gas, it becomes possible to measure a smaller surface area. This is because, in order to obtain the relative pressure of 0.35 required to determine the adsorption amount A _ML of monolayer, when N ₂ is used as the adsorbate, an adsorption experiment with an equilibrium pressure of up to 250 mmHg is required. For example, when krypton (Kr) is used as the adsorbate, the equilibrium pressure up to 0.6 mmHg is sufficient. That is, since the saturated vapor pressure p ₀ of krypton at the liquid nitrogen temperature is 1.8 mmHg, the relative pressure 0.35 is 0.6 m.
It becomes mHg. As a result, the first term and the second term of the equation (1)
Both terms become smaller and the measurement error becomes smaller.

For example, by krypton adsorption, 0.03
To obtain a surface area of m ² , 0.4 in equation (1)
From the difference between 8 and 0.45, 0.03 will be obtained, and the error will be significantly smaller than in the case of nitrogen adsorption. From such a viewpoint, in a normal constant volume adsorption amount measuring device, a surface area measuring method using a noble gas having a small vapor pressure as an adsorbate has been conventionally performed, and xenon, krypton or the like has been used.

[0019]

Therefore, even in the temperature compensation type adsorption amount measuring device, 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 the temperature compensation type 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 example described later. , And it deviated significantly from the straight line, and the single molecule adsorption amount A _ML could not be obtained.

In view of the above-mentioned circumstances, a main object of the present invention is to provide a method and apparatus capable of measuring an adsorption amount on a sample having a smaller surface area by using the temperature compensation adsorption amount measuring device as described above. The purpose is to do.

[0021]

SUMMARY OF THE INVENTION
As a result of further research, the temperature compensation type adsorption amount measuring device described above
Especially when using low vapor pressure adsorption gas
The cause of T-plot non-linearity is about 10 cm²Below
When measuring the amount of adsorption to such a small surface area sample,
0 cm²Almost no problem in measuring the sample surface area
Reference adsorption cell that did not become (for example, the internal surface area is 15
m² The adsorption amount of adsorbed gas to
I found out that And such a reference sucker
By compensating for the amount of adsorbed gas in the cell
cm²Even for small surface area samples such as
It has been found that surface area measurements are possible.

That is, the adsorption amount measuring method suitable for applying the sample of the present invention to a small surface area sample is such that a pair of reference burettes and a sample burette, which have substantially the same volume and shape, are arranged symmetrically to each other. A reference adsorption cell having substantially the same volume and shape as each other on the both burettes;
A temperature-compensated constant volume comprising an adsorption gas supply source, which is connected to each of the adsorption cells for a sample, and is further connected so as to be able to be introduced into the both bullets, and a pressure gauge capable of measuring the pressure inside the both bullets. Using the adsorption device, the adsorption gas once introduced into both burettes is further expanded into each adsorption cell.
After adsorbing, when determining the adsorption amount of the adsorption gas based on the generated pressure difference between the two burettes, the adsorption amount for the reference adsorption cell is compensated to obtain the adsorption amount for the sample adsorption cell. To do.

Further, the adsorption amount measuring device of the present invention comprises the above-mentioned temperature compensation type adsorption amount measuring device; the adsorption gas pressure introduced into both burettes, and the adsorption which is then expanded and adsorbed in both adsorption cells, respectively. And a calculation device arranged to obtain the adsorption amount to the sample adsorption cell while compensating the adsorption amount to the reference adsorption cell based on the pressure difference between both burettes of the gas.

[0024]

The preferred embodiments of the adsorption amount measuring method and apparatus of 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 device using a temperature compensation type adsorption amount measuring device according to a preferred embodiment of the present invention.

(Apparatus system) The apparatus main body 10 comprises a Pyrex glass pipe 1 having an inner diameter of 6 mm and stopcocks C1 to C
6 (and C11 to C19), and piping 11
Through the pipe 12, directly through the pipe 12, through the pipe 13 through the low pressure diaphragm type pressure gauge 14 to the vacuum system VAC 1, and through the pipe 15 through the high pressure mercury pressure gauge 16. There is. A reference buret 2 is formed by the portions of the pipe 1 which are partitioned by the stopcocks C1, C2, C3 and the diaphragm of the differential pressure gauge 7, and the diaphragms of the stopcocks C1, C2, C4 and the differential pressure gauge 7 also in the pipe 1 are formed. Burette for sample 3 depending on the part partitioned by
Is formed. The reference buret 2 and the sample buret 3 are connected to the reference adsorption cell 4 and the sample adsorption cell 5 containing the adsorbent 5a via the stop cock C1, respectively. During the measurement, the adsorption cells 4 and 5 are generally housed in a Dewar bottle 6 filled with liquid nitrogen. Further, in order to improve the temperature compensability, it is preferable that the burettes 2 and 3 and the adsorption cells 4 and 5 are arranged symmetrically as much as possible and the both are arranged close to each other. Bullet for reference 2
The sample bullet 3 and the sample bullet 3 are partitioned by a stop cock C2, and a differential pressure gauge 7 is provided between both bullets via stop cocks C5 and C6.

The outputs of the pressure gauge 14 and the differential pressure gauge 7 are
It is 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 to minimize the temperature difference between the reference system and the sample system.

(Measurement of Adsorption Amount) To measure the adsorption amount for accurate surface area calculation, the adsorption equilibrium pressure is changed.
After obtaining the adsorption amount at a certain equilibrium pressure, without performing the desorption operation,
Furthermore, it is desirable to adopt an integrated adsorption method in which an adsorption gas is introduced and continuous adsorption experiments are performed.

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

[1] Measurement of dead volume (measurement of V _B and DV _B in the above formula (3)) (1) Reference bullet 2, pipe 13 and pressure gauge 14
After evacuating, the stopcocks C1, C2, C5,
Close C11 and C16. A certain amount of helium (He) was put into the reference adsorption cell 4, the reference buret 2 and the pressure gauge 14, the pressure was read by the pressure gauge 14, and p ₁
And The cock C1 is opened to expand it into the reference adsorption cell, and its pressure is set to p ₂ . Since the amount of helium adsorbed can be substantially ignored, the volume V _B of the reference adsorption cell is evaluated as V _B = V _O ((p ₁ / p ₂ ) −1). Here V _O is the volume that is defined by C1, C2, C5, C11, C16 and a pressure gauge 14 septa.

(2) The reference adsorption cell 4, the sample adsorption cell 5, the reference bullet 2 and the sample bullet 3 are evacuated, and the stopcock C1 is closed. Fill both bullets 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, the stopcock C1 is opened, and helium is expanded into both adsorption cells. At this time, the display 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)
Since the display changes according to the pressure of the atmosphere even if the left and right differential pressure is zero, open C2 and read the pressure display (zero point), and the difference from the previous differential pressure reading is true. Differential pressure D
give p. Since helium is not adsorbed, the following equation with DV _B as an unknown is obtained from the mass balance of helium.

(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 adsorption A solid glass rod or the like is put on the upper part of the cell or the sample adsorption cell and adjusted so that the absolute value of the differential pressure Dp (and therefore DV _B ) becomes as small as possible.

[2] Preadsorption Experiment Using the adsorption amount used in the adsorption experiment (for example, Kr) by the usual adsorption amount measuring method, the rough adsorption isotherm A _R (for the adsorption cell for reference and the adsorption cell for sample A _R ( p) and A _S (p) are determined. When the BET infinite adsorption formula (formula (2)) is adopted, the amount of adsorbed single molecule A _ML and B
The ET constant C may be determined for the reference system (A _MLR and C _R ) and the sample system (A _MLS and C _S ) respectively.

[3] Adsorption Experiment After evacuation of the entire system, the stop cock C1 is closed, both burets are filled with adsorption gas, and the pressure p _n (1) is 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 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. After that, the stop cock C1 is closed, and such an operation is repeated to perform the integrated adsorption operation.

[0036] In the n-th adsorption operation in this situation, the temperature T, and a suction gas in the burette is expanded to adsorption cell pressure p _n (1), when obtaining the differential pressure Dp _n n
Adsorption amount A _'n times th 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 Is the pressure of.

The above-mentioned p _n (2) can be easily calculated because the adsorption to the reference adsorption cell is neglected conventionally. However, in this method, the adsorption amount for the reference adsorption cell is taken into consideration and is obtained from the following equation.

(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 for the reference adsorption cell, and for the krypton adsorption, the BET infinite layer equation (the above equation (2)) can be adopted. .

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, an equation for the unknown p ₁ (2) is obtained. 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, p _n (2) is obtained.

When measuring the zero point, the pressure in the reference adsorption cell becomes equal to the pressure in the sample adsorption cell. That is, the pressure of the reference adsorption cell is calculated from p _R (= p _n (2)) to Dp
_R increases to _pn , and the pressure in 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. Letting their adsorption be DA _R and DA _S , respectively, they are given by:

[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) The correction amount of these adsorption amounts can be almost ignored in adsorption experiments at high pressure, as in the case of nitrogen adsorption. However, it is relatively large in low pressure experiments.

Further, new adsorptions DA _S and DA _{R at} the time of measuring the zero point are obtained from the following equations using the adsorption isotherms for the sample side and the reference side.

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) By the method described above, When p _n (2) is obtained, p _R and p _S for the n-th adsorption operation are determined. Therefore, since the equations (7) and (8) are simultaneous equations regarding Dp _S and Dp _R regarding the n-th adsorption operation including the known parameters, they can be easily solved by the Newton's method, and further equations (8) to (10) ), P _n , DA _R and DA _S are determined.

The accumulated adsorption amount A _n is given by the sum of the accumulated adsorption amount ΣA ′ _n up to the previous time and the adsorption amount correction amount ΣDA _S as in the following equation.

A _n = Σ (A ′ _n + DA _S ) (11) Further, the equilibrium pressure in that case is p _n .

That is, the calculation process is performed by the computer 20.
(In this example, NEC 9801DA is used.) Measured values p _n (1) and Dp _n are used to calculate equation (2) and equation (5).
~ Equation (10) is used to find _pn (2) (hence _A'n ) and DA _R and DA _S , and from these, the calculation is carried out to find the cumulative adsorption amount A _n by _pn and Equation (11). To be done.

(Calculation of Single Molecule Adsorption and Surface Area)
At each relative pressure x (= p_n/ P₀) Integrated adsorption
Quantity A (= A_n) Data is obtained, for example, without BET
The following equation (12) obtained by transforming the equation (2), which is a layered equation, x / A (1-x) = 1 / (A_MLC) + x ・ (C-1) / (A_MLC) According to (12), x / A (1-x) = p / A for each relative pressure
(P₀-P) plot (BET plot, for example
4 and 6) for the example of FIG.
_MLC and slope (C-1) / A_ML・ From C, single molecule absorption
Wear A_ML(Unit STP cm³ ) And BET constant C
Can be

Amount of adsorbed single molecule A_MLFrom the following formula
More sample surface area S (cm² ) Is required.

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

(Example of Measurement of Adsorption Amount) In this example, a steel ball 5 for ball bearing having a diameter of 1 mm was prepared by using the apparatus shown in FIG.
It was confirmed that krypton (saturated vapor pressure p ₀ = 1.8 mmHg at liquid nitrogen temperature) at a liquid nitrogen temperature was adsorbed to a and surface area of about 1 cm ² could be measured.

As the adsorption isotherm for the reference adsorption cell and the sample adsorption cell, the BET infinite layer system (equation (2)) was adopted. That is, as A _R and A _S in the above formulas (6) to (10), the monomolecular adsorption amounts A _MLR , A _MLS and BET constants C _R and C _S obtained in the preliminary experiment are introduced to obtain the formula (12). The value obtained from the BET linear equation of (1) was used. Single-molecule adsorption amount A of krypton by the conventional method for the empty reference side adsorption cell and empty sample side adsorption cell obtained in advance
_{Both MLR} and A _MLS are 2.50 × 10 ^-4 STPc
m ³ and the BET constants C _R and C _S were 12. The BET plot of the krypton adsorption at the liquid nitrogen temperature for the empty sample adsorption cell obtained using these is shown in FIG. The monomolecular adsorption amount A _ML of krypton on the adsorption cell for sample obtained from the intercept and the gradient of this BET plot was 2.54 × 10 ⁻⁴ STPcm ³ .

At this time, if the adsorption amount of krypton to the reference adsorption cell is not taken into consideration (that is, calculated with A _MLR = 0), the BET plot deviates significantly from the straight line (FIG. 5), and the adsorption amount of the single molecule is practically obtained. I couldn't. Perhaps the BET plot due to the adsorption of xenon, which has a lower saturated vapor pressure, will have a more marked shift.

A BET plot of krypton adsorption for a sample adsorption cell containing 50 steel balls is shown in FIG.
From the intercept and the gradient of FIG. 6, the adsorption amount A _ML of krypton for a sample adsorption cell containing 50 steel balls can be obtained.

Amount of single molecule adsorbed on the sample adsorption cell A _ML
In the calculation of A _R (p) and A obtained in advance
_S (p) was used. But A _ML used A
It was almost independent of _S (p), that is, A _MLS (Fig. 7). That is, it can be seen that the approximate value of A _MLS is sufficient for the calculation of A _ML .

Further, A _ML -A _MLR was hardly dependent on A _MLR (FIG. 8). However, if an A _MLR value that is too small is used, the linearity of the BET plot becomes poor as described above, and the reliability for A _ML is lacking. A _ML- A _MLR is
It means that the adsorption amount to the sample adsorption cell is measured on the basis of the adsorption amount to the reference adsorption cell. The adsorption amount for the sample is the difference between the adsorption amount for the sample-containing sample adsorption cell and the adsorption amount for the empty sample adsorption cell, and both are obtained based on A _MLR .

Steel balls having a diameter of 1 mm are 50, 100, 150
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 slice corresponds to the amount of adsorbed monomolecule to the empty adsorption cell for sample, and the gradient corresponds to the amount of adsorbed monomolecule per unit number of steel balls. This gradient coincided with the value obtained from the amount of krypton adsorbed by the usual adsorption amount measuring device for 10,000 steel balls. That is, the amount of monomolecular adsorption of krypton on 50, 100, 150 steel balls was in agreement with the calculated value obtained from 10,000 steel balls. Adsorption amount (A _ML -A _MLR ) of 50 steel balls is 0.27S
TPcm ³ , and the surface area was 1.
It was calculated to be 7 cm ² . This is almost in agreement with the geometrically calculated surface area of the steel ball (1.57 cm ² ), and it was revealed that the surface area of about 1 cm ² can be measured by this method.

(Modification) In the above description, referring to the drawings starting from FIG. 3, an adsorption amount measuring method and device suitable for application to a small surface area sample of the present invention using a temperature compensation type adsorption amount measuring device will be described. A preferred embodiment has been described. However, it will be understood that the embodiments described above can be implemented in various modifications within the scope of the present invention. In particular, although the calculation process of the equation (5) and the subsequent steps in the above-described embodiment enables rigorous calculation for the sake of theoretical accuracy, the device characteristics of the temperature compensation type adsorption amount measuring device are taken into consideration. If so, many simplifications are possible within a range in which the practical measurement accuracy is maintained. The following are some examples of such variations.

(1) Not only the surface area measurement but also the adsorption isotherm for the reference adsorption cell and the sample adsorption cell, A
_It can be applied to any adsorption amount measurement only by changing _R (p _R ) and A _S (p _S ). The present invention is particularly effective for measuring the adsorption amount of water in which a large amount of adsorption occurs in the reference adsorption cell.

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

(3) Of course, it is possible to make the entire device from metal rather than glass.

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

(5) By using the differential pressure gauge 7 that does not require the zero correction, the operation of opening the stopcock C2 after the suction operation to correct the zero of the differential pressure gauge 7 becomes unnecessary. The calculation of the equations (7) to (10) is unnecessary (DA _R ≈DA _S ≈0).

(6) As shown in FIGS. 7 and 8, A _ML
The calculated value of is essentially A _R (p) and A _S (p),
That is, it did not depend on the values of A _MLR and A _MLS . Therefore, the experimental procedure for obtaining them (see [2] above)
The preliminary adsorption experiment) was omitted, a value of about 1.5 times the geometric surface area was used for A _MLR , and 10 for C _R.
By using the value of the degree, the calculation can be simplified without incurring a substantial decrease in measurement accuracy. Further, for A _MLS and C _S , it is possible to use approximate values or obtain them by repeated calculation. In an adsorption experiment of an adsorbate having a vapor pressure higher than that of krypton, DA _R and DA _S are about 0.1% of A ′ _n at most, and they are ignored (calculation of formula (7) -formula (10) is omitted. It is also possible. However, it may not be possible to ignore xenon.

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

(8) In the above embodiment, the stop cock was manually operated, but it can be automated. It is also possible to automatically minimize Dp or DV _B by providing a movable bellows tube or the like on the upper part of the adsorption cell. Although the measurement pressure was input through the AD converter, manual input is also possible.

(9) Adsorption gas is 10 cm²Less than
For surface area measurement, Kr (p₀=
1.8 mmHg), Xe (P₀= 0.001 mmHg)
And Xe (p at liquid oxygen temperature₀= 0.05mm
Hg) and the like are preferable. 10 cm² ~ 1000 cm
²In addition to the above adsorbates, the surface area of
CH_Four(P₀= 10 mmHg) and liquid oxygen temperature
In CH_Four(P₀= 80 mmHg) is preferable. 1
000 cm²For measuring the surface area above
N at body nitrogen temperature ₂(P₀= 760 mmHg) and
And Ar (p₀= 200mmHg), at dry ice temperature
CO in₂(P₀= 760 mmHg) and freezing point
NC_FourH_Ten(P₀= 760mmHg) can be used
It

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

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

[0070]

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

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a temperature compensation type constant volume adsorption device.

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

FIG. 4 is a BET plot of krypton adsorption on an empty sample adsorption cell (monomolecular adsorption amount A _MLR = 2.5 × 10 ⁻⁴ STPcm ^{3 on a} reference adsorption cell).

FIG. 5 is a BET plot of krypton adsorption with respect to an empty sample adsorption cell (monomolecular adsorption amount A _MLR = 0 with respect to a reference adsorption cell).

FIG. 6 is a BET plot of krypton adsorption with respect to a sample adsorption cell containing 50 steel balls (monomolecular adsorption amount A _MLR = 2.5 × 10 ⁻⁴ STPcm ^{3 with} respect to a reference adsorption cell).

FIG. 7 is a graph showing the relationship between the adsorbed amount of single molecule of krypton A _ML and the used amount of A _{MLS in} the adsorption cell for a sample containing 50 steel balls.

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

FIG. 9 is a graph showing the relationship between the adsorption amount of krypton monomolecules A _ML and the number of steel balls in the adsorption cell for a sample containing steel balls.

[Explanation of symbols]

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

Claims (4)

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