Apparatus for titration and circulation of gases and...

Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample

Reexamination Certificate

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C073S865500, C422S092000, C422S105000

Reexamination Certificate

active

06582663

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved apparatus for the titration of gases, which can be used inter alia for the determination of the storage properties of metal hydrides.
The invention also relates to an apparatus hereinafter called “cycling apparatus”, which permits to evaluate the behaviour of a substance when this substance is subjected to a large number of gas absorption/desorption cycles. This cycling apparatus can be used inter alia for evaluating the degradation of storage properties of a metal hydride subjected to cycles of hydrogen absorption/desorption.
BRIEF DESCRIPTION OF THE PRIOR ART
There are presently apparatuses especially devised for the titration of gases. These apparatuses are used in particular for determining the hydrogen absorption capacity and, therefore, the storage properties of metal hydrides. In the last case, they are particularly used for:
evaluating the storage capacity of metal hydrides as a function of the operating pressure (pressure=f(H/M) where H is the number of hydrogen atoms and M is the number of metal atoms); and
evaluating the absorption and desorption kinetics (reaction dynamics) of the metal hydrides [H/M=f(time)].
FIG. 1
schematically illustrates the structure of an example of an existing apparatus used for the titration of hydrogen. This apparatus is disclosed in an article of Pascal TESSIER entitled “Hydrogen storage in metastable Fe—Ti” of 1995.
As can be noticed, this existing apparatus comprises a main duct
1
′ which is connected by a valve V
3
′ to a source of hydrogen under pressure
5
′, and on which is mounted a pressure sensor (manometer)
7
′ for measuring the total pressure of hydrogen within the circuit.
The apparatus also comprises a first derivation duct
9
′ which connects the main duct via a valve V
6
′ to a measuring chamber (
13
′) having the shape of a tube in which can be introduced a sample of the substance for which he absorption or desorption properties are to be measured. The tube
13
′ is located in a furnace
11
′ having a temperature that can be adjusted at will as a function of the measurement to be carried out.
The apparatus further comprises a second derivation duct
15
′ having a first end
17
′ connected to the main duct
1
′ upstream of the connection between the same and the first derivation duct
9
′, and a second end
19
′ connected to the main duct downstream of the junction of the same with the first derivation duct. This second derivation duct
15
′ includes a small tank
21
′ of 50 cc and a differential pressure sensor
23
′. A valve V
11
′ is located in the main duct
1
′ between the junction
17
′ and the first derivation duct
9
′. Two other valves V
5
′ and V
12
′ are respectively located on the second derivation duct
15
′ between, on the one hand, the tank
21
′ and the junction
17
′ and, on the other hand, the differential sensor
23
′ and the junction
19
′.
Last of all, the apparatus comprises a third derivation duct
27
′ connecting a pump
29
′ via a valve VI′ to the main duct
1
′ upstream of the junction
17
′.
The valves mentioned hereinabove are operated by an informatized control system
33
′. The two sensor pressures
7
′ and
23
′ are also connected to the control system. Most of the components of the apparatus are insulated in an isothermal enclosure
35
′ shown in dotted lines. A manual valve V
10
′ is located in the derivation duct
9
′. This manual valve V
10
′ is kept permanently open except when the sample is inserted.
In use, after suitable calibration, one starts by creating a vacuum within the whole system by closing the valve V
3
′ and by opening all the other valves to connect all the ducts, the sample carrying tube
13
′ and the tank
21
′ to the pump
29
′. Then, all the valves are closed and the measurement up is bean by adjusting the hydrogen source to a given pressure. The valve V
3
′ is opened and then closed. Subsequently, the valve V
5
′, V
11
′ and V
12
′ are opened in series. After a pause, the valve V
5
′ is closed and, after another pause, the valve V
6
′ is opened and the measurement is carried out by measuring all the data given by both pressure sensors
7
′ and
23
′.
This can be repeated several times with an increase in the hydrogen pressure, in order to obtain pressure/composition isotherm curves.
If the existing apparatuses for the titration of gases like the one disclosed hereinabove are efficient, they are subject to very stringent limitations in their use, because of their response time and the saturation of their differential pressure sensors, which reduces the limits of operation of the apparatus, its sensibility and the limits of detection of the same.
This problem is particularly important in that some metal hydrides like the nanocrystalline alloys disclosed in the following recently laid-open patent application Nos. CA-A-2,117,158 and WO-A-96/23906 naming the Applicant as one of the coowners, have very fast absorption and desorption kinetics.
From a practical standpoint, it is possible to increase the operating range of the apparatus by modifying the sequences of opening of the admission valves. However, the equilibrium time of the system is slower, which leads to a substantial lost of data at the beginning of each measurement.
Accordingly, there is presently a real need for an apparatus for the titration of gases where the response time would be improved and the differential pressure sensor would be less subject to saturation, with the major drawback that such limits generate, namely a diminution of the range of use of the apparatus, expressed in amount of metal hydride needed for a given sensitivity threshold and maximum working pressure, both in PCT mode [pressure=f(H/M)] and in dynamic mode [(H/M=f(time)].
On the other hand, there are presently no apparatus available on the market, at least to the knowledge of the Applicant, which would permit to carry out rapidly and in an efficient manner, titration measurements at two different pressures and two different temperatures, in order to characterize a substance like an hydride, and more precisely, the efficiency of this hydride when it is subjected to a large number of hydrogen absorption /desorption cycles.
It has already been proposed to use conventional titration apparatuses for this purpose. However, because of the delays that are relatively long for achieving furnace temperature equilibrium as well as the pressure equilibrium (a reequilibrium is required at reach cycle), these apparatuses are poorly adapted for cycling, where it is necessary to change the temperature of the furnace as well as the pressure quickly between each cycle during the course of measurements.
Therefore, there is also the need for a cycling apparatus which would permit to carry out absorption/desorption cycles at two temperatures and two operating pressures in a fast, efficient and performing manner.
SUMMARY OF THE INVENTION
The present invention satisfies the two needs mentioned hereinabove by providing:
on the one hand, a new apparatus for the titration of gases having an improved response time, a more important dynamics range relative to the amount of powder that is used and to the maximum operating pressure and an improved sensitivity; and
on the other hand, a cycling apparatus allowing a substantial reduction of the time required for the analysis and determination of the properties of absorbing or desorbing materials during a large number of absorption/desorption cycles.
The apparatus according to the invention for the titration of a gas comprises:
a main duct (
1
) connected by a valve (V
3
) to a source of gas under pressure (
5
), said main duct being also connected to a first pressure sensor (
7
a
);
a

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