Measuring and testing – Gas content of a liquid or a solid – By pressure of the gas
Reexamination Certificate
2002-02-27
2003-07-22
Kwok, Helen (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
By pressure of the gas
C073S023210, C073S031050, C422S069000, C422S088000
Reexamination Certificate
active
06595036
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for measuring the amount of a gas adsorbed on a solid material.
2. Description of Related Art
For advantageous use of solid materials such as powdery materials, adsorbents and films, it is important to obtain information on the specific surface area and pore size distribution of such a solid material. To obtain such information, it is necessary to prepare an adsorption isotherm by measuring gas adsorption on the solid material while maintaining the solid material at a constant temperature.
For example, a volumetric gas adsorption measuring apparatus as shown in
FIG. 4
is employed for the measurement of the gas adsorption on the solid material. As shown, the volumetric gas adsorption measuring apparatus
50
includes: a manifold
51
maintained at a predetermined temperature (T) and having a known geometric volume (Vs); a sample cell
52
which contains a solid sample A and is connected to the manifold
51
via a valve
54
; and a constant temperature bath
53
which contains a cryogenic coolant such as liquid nitrogen. A gas inlet/outlet line is connected to the manifold
51
via a valve
55
, and a sample retaining portion
52
a
of the sample cell
52
is immersed in the cryogenic coolant contained in the constant temperature bath
53
for maintaining the solid sample A at a cryogenic temperature.
With the use of the volumetric gas adsorption measuring apparatus
50
, the amount of a gas adsorbed on the solid sample A is measured in the following manner. First, the manifold
51
and the sample cell
52
are evacuated with the valves
54
and
55
being open. Then, the gas is fed into the manifold
51
with the valve
54
being closed, and the valve
55
is closed. At this time point, a gas pressure (Pi) is measured. Subsequently, the valve
54
is opened, and the gas is introduced from the manifold
51
into the sample cell
52
thereby to be adsorbed on the solid sample A within the sample cell
52
. When an adsorption equilibrium is reached, a gas pressure (Pe) is measured.
Provided that the gas fed into the manifold
51
is an ideal gas, the following expression is satisfied:
PiVs=n
1
RT
Pe
(
Vs+Vd
)=
n
2
RT
wherein Vd is a dead volume of the sample cell
52
(i.e., the volume of the sample cell
52
excluding the volume of the solid sample A on the assumption that the gas introduced into the sample cell
52
is maintained at the same temperature as in the manifold
51
), n
1
is the number of moles of the gas fed into the manifold
51
, n
2
is the number of moles of the gas after the adsorption, and R is the gas constant. Therefore, the amount (N) of the gas adsorbed on the solid sample A is expressed by:
N=n
1
−n
2
=[(
Pi−Pe
)
Vs−PeVd]/RT
Therefore, the dead volume (Vd) of the sample cell
52
is generally determined prior to the measurement of the gas adsorption on the solid sample A. More specifically, the manifold
51
and the sample cell
52
are evacuated with the valves
54
and
55
being open. Thereafter, a non-adsorbable gas which is not adsorbed on the solid sample A is fed into the manifold
51
with the valve
54
being closed, and then the valve
55
is closed. At this time point, a gas pressure (P
1
) is measured. Subsequently, the valve
54
is opened to introduce the non-adsorbable gas from the manifold
51
into the sample cell
52
retaining the solid sample A. At this time point, a gas pressure (P
2
) is measured.
Provided that the non-adsorbable gas fed into the manifold
51
is an ideal gas, the following expression is satisfied:
P
1
Vs=nRT
P
2
(
Vs+Vd
)=
nRT
wherein n is the number of moles of the non-adsorbable gas fed into the manifold
51
, and R is the gas constant. Therefore, the dead volume (Vd) of the sample cell
52
is expressed by:
Vd
=(
P
1
−
P
2
)
Vs/P
2
Thus, the measurement of the gas adsorption on the solid sample A can be achieved by preliminarily determining the dead volume (Vd) of the sample cell
52
retaining the solid sample A. Since the aforesaid adsorption isotherm indicates a change in the gas adsorption (N) on the solid sample A observed when the ratio Pe/Ps of the gas pressure (Pe) in adsorption equilibrium to the saturation vapor pressure (Ps) of the adsorbable gas is changed from zero to one, the aforesaid process is repeatedly performed for the preparation of the adsorption isotherm. That is, the amounts (N) of the gas adsorbed on the solid sample A are determined while the gas pressure (Pe) in adsorption equilibrium is progressively changed. Therefore, the measurement of the adsorbed gas amounts (N) for the preparation of the adsorption isotherm is a time-consuming operation.
Further, the cryogenic coolant such as liquid nitrogen contained in the constant temperature bath
53
is highly evaporative, so that the surface level of the cryogenic coolant is remarkably lowered with time. Even if the sample retaining portion
52
a
is completely submerged in the cryogenic coolant, the environment (temperature) of the sample cell
52
above the surface level of the cryogenic coolant constantly changes as the surface level of the cryogenic coolant is lowered. As a result, the dead volume (Vd) of the sample cell
52
is changed.
For accurate determination of the gas adsorption on the solid sample A, the dead volume (Vd) of the sample cell
52
should be determined every time the adsorbed gas amount (N) is to be measured. Thus, the preparation of the adsorption isotherm is a troublesome operation.
Therefore, consideration is given to the conventional volumetric gas adsorption measuring apparatus
50
for constantly maintaining the surface level of the cryogenic coolant with respect to the sample cell
52
immersed in the cryogenic coolant, so that the dead volume (Vd) of the sample cell
52
initially determined can be employed for the measurement of the gas adsorption to be performed later. This eliminates the need for determining the dead volume (Vd) of the sample cell
52
every time the amount (N) of the gas adsorbed on the solid sample A is measured.
A common approach is to provide a lift mechanism for moving up and down the constant temperature bath
53
so that the surface level of the cryogenic coolant is constantly kept at a predetermined height with respect to the sample cell
52
, or to provide a coolant supplying mechanism for replenishing the constant temperature bath
53
with the cryogenic coolant so as to prevent the change in the surface level of the cryogenic coolant within the constant temperature bath
53
. In either case, the change in the surface level of the cryogenic coolant should be detected by means of a temperature sensor or the like for actuation of the lift mechanism or the coolant supplying mechanism. Therefore, an expensive temperature sensor should be employed for accurate detection of an abrupt temperature change, thereby increasing the costs. Further, the accuracy of the temperature sensor may be reduced by corrosion or frosting of a temperature sensing probe of the sensor.
Another conceivable approach is to provide a cryogenic coolant outlet at a predetermined height of the constant temperature bath
53
so that the surface level of the cryogenic coolant within the constant temperature bath
53
is kept constant by continuously supplying the cryogenic coolant to the constant temperature bath
53
and constantly letting out the cryogenic coolant from the outlet of the constant temperature bath
53
. This approach requires a cryogenic coolant circulating mechanism, thereby complicating the construction of the overall apparatus.
Rather than maintaining the surface level of the cryogenic coolant at the constant level, further another conceivable approach is to cover the sample cell
52
to a predetermined height with a cylindrical jacket of a porous material (e.g., ceramic) which can suck up the cryogenic coolant from a lower portion thereof immersed in the cryogenic coolant by capillary act
Armstrong Westerman & Hattori, LLP
Bel Japan, Inc.
Kwok Helen
Wiggins David J.
LandOfFree
Method and apparatus for measuring amount of gas adsorption does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for measuring amount of gas adsorption, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for measuring amount of gas adsorption will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3072517