DEVICE FOR TRAPPING HYDROGEN

Abstract

Liquid metal degassing device comprising a chamber containing a liquid metal bath, a device for circulating a gas through a purification chamber and in that the purification chamber comprises a getter material configured to trap dihydrogen from the circulating gas. Method for degassing a liquid metal bath to reduce the hydrogen concentration of the liquid metal comprising the following steps a) Preparing a liquid metal bath, preferably an aluminum alloy b) Circulating a gas, c) Exchanging hydrogen from the circulating gas with the liquid metal such that the hydrogen dissolved in the liquid metal bath diffuses into the circulating gas and enriches the circulating gas with dihydrogen, d) Purifying the circulating gas enriched with dihydrogen in a purification chamber comprising a getter material configured to trap dihydrogen from the circulating gas.

Claims

1. Liquid metal degassing device comprising a chamber (1) containing a liquid metal bath (2), a device (4) for circulating a gas through a purification chamber (5), said circulating gas and said liquid metal bath being in contact and forming an interface (3, 3′, 3″), characterized in that the purification chamber (5) comprises a getter material (6) configured to trap dihydrogen from the circulating gas.

2. Liquid metal degassing device according to claim 1, characterized in that said circulation device (4) has blowing and/or suction means (9, 9′) capable of placing said circulation gas and the liquid metal bath in contact.

3. Liquid metal degassing device according to claim 1, characterized in that the getter material (6) is a material suitable for trapping dihydrogen from the gas by physisorption or by chemisorption.

4. Liquid metal degassing device according to claim 1, characterized in that the getter material (6) can be regenerated, so as to replenish the trapping capacities thereof.

5. Liquid metal degassing device according to claim 1, characterized in that the circulating gas is in contact with the liquid metal bath via an exchanger (7) submerged in the liquid metal bath (2) and capable of forming an interface (3′) between the liquid metal bath (2) and the circulating gas.

6. Liquid metal degassing device according to claim 5, characterized in that the exchanger (7) is a porous ceramic (8).

7. Liquid metal degassing device according to claim 1, characterized in that the circulating gas is an inert gas, preferably argon.

8. Liquid metal degassing device according to claim 1, characterized in that the chamber is configured to prevent the circulating gas from coming into contact with the external atmosphere (11).

9. Liquid metal degassing device according to claim 1, characterized in that the liquid metal is an aluminum alloy.

10. Method for degassing a liquid metal to reduce the hydrogen concentration of the liquid metal comprising the use of the liquid metal degassing device according to claim 1.

11. Method according to claim 10, comprising the following steps: a) Preparing a liquid metal bath, preferably an aluminum alloy or an iron alloy or a titanium alloy or any other metal or alloy capable of containing dissolved hydrogen, b) Circulating a gas in the degassing device, preferably an inert gas, preferably argon such that the circulating gas is in contact with the liquid metal bath and forms a liquid metal bath/circulating gas interface, c) Exchanging hydrogen between the circulating gas and the liquid metal through the liquid metal bath/circulating gas interface such that the hydrogen dissolved in the liquid metal bath diffuses in the circulating gas and enriches the circulating gas with dihydrogen, d) Purifying the circulating gas enriched with dihydrogen in a purification chamber comprising a getter material configured to trap dihydrogen from the circulating gas.

12. Method according to claim 11, characterized in that during step b) the circulation of the gas is performed via an exchanger (7), preferably made of porous ceramic, submerged in the liquid metal bath (2).

13. Method according to claim 11, characterized in that during step b) the circulation of the gas is performed via an injector (8) submerged in the liquid metal bath (2).

14. A casting device comprising the liquid metal degassing device according to claim 1.

15. The casting device according to claim 14, wherein the liquid metal degassing device is installed in a degassing ladle and/or a distribution trough or any other part of the casting device containing circulating liquid metal.

16. The casting device according to claim 14, wherein the liquid metal degassing device is installed in a furnace or any other part of the casting device containing liquid metal waiting to be cast.

Description

FIGURES

[0034] FIG. 1 is a schematic view of the device according to the invention according to a first embodiment where the circulating gas is in contact with the liquid metal bath, the interface being a free surface of the liquid metal.

[0035] FIG. 2 is a schematic view of the device according to the invention according to a second embodiment where the circulating gas is in contact with the liquid metal bath via an exchanger.

[0036] FIG. 3 is a schematic view of the device according to the invention according to a third embodiment wherein a gas injector is used in the liquid metal.

[0037] FIG. 4 is a schematic view of the device according to the invention according to a fourth embodiment which comprises the first and the second embodiment together.

DETAILED DESCRIPTION OF THE INVENTION

[0038] FIG. 1 discloses a first embodiment of the invention. It discloses a liquid metal degassing device comprising a chamber 1 containing a liquid metal bath 2, a device 4 for circulating a gas which passes through a purification chamber 5. The gas, preferably an inert gas, for example argon, is in contact with the liquid metal bath via an interface 3. This interface 3 is in this embodiment a free surface of the liquid metal. The gas can be injected into the circulating device 4 thanks to a gas inlet. A valve device makes it possible to open or close the gas supply as needed. A vent system can also be added to the device. Similarly, a valve system is used to discharge the circulating gas if needed (for example during maintenance of the purification chamber 5).

[0039] A blowing means 9 can be added to the circulation loop 4 to ensure a sufficient gas flow in contact with the interface 3. However, it is necessary to ensure that this flow is not excessive to prevent excessive agitation of the liquid metal. It is possible to use a suction device 9′ in addition to or instead of the blowing means 9.

[0040] According to the principle of Sieverts Law, at the interface 3, the quantity of hydrogen dissolved in the liquid metal is at thermodynamic equilibrium with the partial pressure of dihydrogen gas contained in the gas. Thus, the lower the partial pressure of dihydrogen gas, the greater the decrease in the dissolved hydrogen concentration in the liquid metal. Prior art installations use a continuously replenished inert atmosphere to obtain the lowest partial pressure of dihydrogen. The aim of the invention is that of continuously treating the circulating gas in a purification chamber by placing it in contact with a getter material configured to trap dihydrogen and thus lower the partial pressure of dihydrogen of the circulating gas. Preferably, the circulating gas is in a closed circuit.

[0041] The purification chamber 5 comprises a getter material 6 configured to trap dihydrogen from the circulating gas.

[0042] Materials exist that are capable of forming compounds with hydrogen and therefore of trapping this gas in solid form, hereinafter referred to as “getter material” or “getter”.

[0043] Dihydrogen can be trapped by physisorption or by chemisorption. The material for trapping dihydrogen from the gas by physisorption is preferably a material based on Ni or any other material enabling the physisorption phenomenon. The material for trapping dihydrogen from the gas by chemisorption is preferably an intermetallic compound based on zirconium for example FeZr.sub.2, or magnesium or yttrium or rare earths or titanium or any other material enabling the chemisorption phenomenon.

[0044] In order to accelerate trapping, it is preferable to associate a catalyst with the getter material.

[0045] The getter material can be sensitive to the presence of oxygen and can require the use of an inert circulating gas, preferably argon. Preferably, the chamber is configured to prevent the circulating gas from coming into contact with the ambient atmosphere. This containment can be obtained by cover means 10 of the chamber 1 or any other means for preventing the circulating gas from coming into contact with the external atmosphere 11.

[0046] FIG. 2 discloses a second embodiment of the invention. As in the first embodiment, it discloses a liquid metal degassing device comprising a chamber 1 containing a liquid metal bath 2, a device 4 for circulating a gas which passes through a purification chamber 5. The purification chamber 5 is of the same type as that described in the first embodiment and can use the same types of getter material. A gas inlet and a vent system can also be added as in the first embodiment. A blowing means 9 can be added to the circulation loop 4 to set the circulating gas flow.

[0047] In this second embodiment, the circulation device comprises an exchanger 7, submerged in the liquid metal bath 2. The gas is placed in contact with the liquid metal bath via the exchanger 7. The gas circulates inside the exchanger. The exchanger is configured to enable contact between the circulating gas and the liquid metal bath. Preferably, the exchanger is a porous ceramic wherein the geometry of the pores is adapted to prevent the liquid metal from entering the ceramic pores. Preferably, the pore size is between 50 μm and 1 mm.

[0048] Preferably, it is of interest to maximize the interface 3. This is possible by choosing an exchanger geometry with the greatest apparent surface area. Preferably, the exchanger is a ceramic foam made of SiC.

[0049] FIG. 3 discloses a third embodiment. As in the first and second embodiments, it discloses a liquid metal degassing device comprising a chamber 1 containing a liquid metal bath 2, a device 4 for circulating a gas which passes through a purification chamber 5. The purification chamber 5 is of the same type as that described in the first embodiment and can use the same types of getter material 6. A gas inlet and a vent system can also be added as in the first embodiment. A blowing means 9 and suction means 9′ can be added to the circulation loop 4 as in the two other embodiments.

[0050] In this third embodiment, the circulation device 4 comprises an injector 8 which enables bubbling of the circulating gas in the liquid metal, preferably an inert gas. Typically, bubbling is performed on the same principle as the applications WO9521273 or WO9934024. Each bubble defines an interface; this interface is the envelope of the bubble. The interface has a spherical or quasi-spherical shape. Each bubble is in contact with the liquid metal and thus defines an interface. In this case, the interface area is related to the sum of the surface areas of bubbles present in the liquid metal.

[0051] This interface is in contact with the circulating gas. By means of the bubbling and based on the principle of Sieverts Law, the dissolved hydrogen content of the metal tends to decrease. The bubbles rising to the surface can then be sucked in by the suction means 9′ to be subsequently treated in the purification chamber 5. Preferably, the chamber is configured to prevent the circulating gas from coming into contact with the ambient atmosphere. This containment can be obtained by cover means 10 of the chamber 1 or any other means for preventing the circulating gas from coming into contact with the external atmosphere 11

[0052] In a preferred embodiment of the invention, it is advantageous to associate the different embodiments together, pairwise or all together.

[0053] FIG. 4 discloses a fourth embodiment which associates the first and the second embodiments.

Example

[0054] In order to study the exchange kinetics between the liquid metal and the circulating gas via a ceramic exchanger (as used in the configuration in FIG. 2), the following experiment was performed.

[0055] 10 kg of an AG5 type aluminum alloy, consisting of 5% magnesium and 95% aluminum and 5 ppm of beryllium are melted in a graphite clay crucible at a temperature of about 700° C. An industrial type argon gas is circulated at a variable flow D.sub.Ar at a regulated pressure of 1.2 bar thanks to a pressure gauge-regulator via an exchanger submerged in the liquid metal.

[0056] The exchanger is a porous material made of SiC ceramic foam. Two geometries were tested; a first exchanger of dimensions 50×50×25 mm developing an apparent exchange surface area of 87.5 cm.sup.2 and a second exchanger of dimensions 100×100×25 mm of apparent exchange surface area of 275 cm.sup.2. The SiC ceramic foam is perforated to insert stainless steel tubes for circulating argon gas inside the porous material. The stainless steel tubes are sealed in the porous material with refractory cement. Flow meters are disposed at the inlet and outlet of the exchanger in order to detect any leak or any clogging.

[0057] The dihydrogen extracted by the process and contained in the gas at the exchanger outlet is quantified by an AMS 6420 type analyzer. The measurement is electrochemical type and gives the volume fraction of dihydrogen in a gaseous mixture at ambient pressure. It is then possible to deduce the volume of dihydrogen extracted for a time t according to the expression:

[00001]$\begin{array}{cc}{V}_{H2}=\frac{C_{H2}{D}_{\mathrm{Ar}}}{t}& \left[\mathrm{Math}1\right]\end{array}$

[0058] Where C.sub.H2 is the volume fraction of dihydrogen in % and D.sub.Ar is the argon flow in normal liters/hour.

[0059] The molar quantity of dihydrogen (n.sub.H2) extracted is deduced from the ideal gas law according to the formula:

[00002]$\begin{array}{cc}{n}_{H2}=\frac{P}{RT}\frac{C_{H2}{D}_{\mathrm{Ar}}}{t}& \left[\mathrm{Math}2\right]\end{array}$

[0060] Where P is the pressure and T is the temperature of the argon flow, i.e., 1 bar and 20° C. R is the universal ideal gas constant 8.31 J mol.sup.−1.Math.K.sup.−1.

[0061] Table 1 below gives the quantity of dihydrogen discharged in one hour by the porous material according to the effective exchange surface area and the argon flow scavenging inside the porous material. It is thus observed that the quantity of dihydrogen extracted increases with the effective exchange surface area of the porous materials and with the argon flow.

TABLE-US-00001 TABLE 1 Measurement of the quantity (mmol/h) of hydrogen discharged at the outlet of the submerged ceramic exchanger according to the injected argon flow (l/h) and the apparent surface area of the exchanger. Argon flow (l/h) 2 4 8 Apparent 87.5 cm.sup.2  9.2 mmol/h 15.5 mmol/h 21.2 mmol/h exchange  275 cm.sup.2 28.3 mmol/h 42.5 mmol/h 62.7 mmol/h surface area (cm.sup.2)