JP2006274297A - Dual phase alloy for hydrogen separation and refining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dual phase alloy for hydrogen separation and refining having high rolling workability and also having a high hydrogen permeation coefficient. <P>SOLUTION: The dual phase alloy for hydrogen separation and refining is composed of a composite phase of a phase having hydrogen permeability and a phase having hydrogen embrittlement resistance. The dual phase alloy has the alloy composition of, by mol%, Ni<SB>x</SB>Ti<SB>y</SB>Nb<SB>100-x-y</SB>(wherein, x=10 to <25%, and y=10 to 40%). The dual phase alloy has excellent ductility, and its thickness can be controlled to 0.05 to 3 mm by plastic working. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a hydrogen separation / purification double-phase alloy used for producing high-purity hydrogen, and in particular, a hydrogen-separation / purification double-phase alloy having a novel Ni-Ti-Nb alloy composition. About.

Since hydrogen, which is a fuel for fuel cells, does not exist in nature alone, it must be artificially produced. Ideally, hydrogen is produced by decomposing water using electricity made from renewable natural energy such as solar heat, but the current technical level is expensive and difficult to apply. For the time being, it is considered realistic to produce hydrogen by steam reforming natural gas (methane) or the like. Steam reforming is to obtain hydrogen using the following chemical reaction. If only H ₂ is removed in this reaction, the equilibrium shifts to the right side according to Le Chatelier's law, a higher conversion can be obtained, and energy loss can be suppressed by lowering the reaction temperature, resulting in hydrogen production costs. Can be reduced. A hydrogen permeable alloy membrane is used to selectively remove hydrogen. Only hydrogen passes through the hydrogen permeable alloy membrane.

  Hydrogen penetrates into the metal crystal lattice in the form of interstitial impurities, and has a feature that its diffusion rate is ten orders of magnitude higher than that of nitrogen, carbon and oxygen. The hydrogen permeable alloy film utilizes such characteristics of hydrogen. In order to separate and purify the impure hydrogen, the impure hydrogen on the supply side is set to a high pressure across the hydrogen permeable alloy membrane, while the pressure collecting side is set to a low pressure to generate a pressure difference. Hydrogen molecules on the high pressure side dissociate into atomic hydrogen on the surface of the alloy film and dissolve in the metal. Hydrogen atoms are diffused from the high pressure side to the low pressure side using the hydrogen concentration gradient in the metal film caused by the pressure difference as a driving force, recombine on the low pressure side and become hydrogen molecules and flow to the low pressure side. At this time, impurity gases other than hydrogen cannot be dissociated in an atomic form on the high pressure side, and cannot be transmitted to the low pressure side because the diffusion speed in the metal is much slower than that of hydrogen atoms. According to the method using a metal film, theoretically, hydrogen having a purity of 100% can be obtained, and hydrogen having a purity of 99.999999% can be actually obtained. Currently, the hydrogen permeable alloy film in practical use is an alloy based on Pd, but since Pd is a very rare and expensive metal, development of an inexpensive alloy to replace it is required.

As another system, for example, Nb-Ni system as described in Patent Document 1, Nb- (Ni, Co, Mo)-(V, Ti, Zr, Ta, Hf) based hydrogen permeable alloys have been studied.
JP 2001-170460 A (0026) JP 2004-42017 A (0007 to 0011, Table 1)

  Hydrogen permeable alloys are required to have a large hydrogen permeability coefficient and high hydrogen embrittlement resistance. Here, when a large amount of hydrogen is dissolved, the hydrogen permeability coefficient is improved, but at the same time, hydrogen embrittlement becomes remarkable. That is, the increase in the hydrogen permeability coefficient and the hydrogen embrittlement resistance are contradictory, and it is generally very difficult to achieve both with a single phase (solid solution) alloy, and there is still room for studying the combination of the compositions.

  Further, when the hydrogen permeable alloy is used as a thin plate (membrane), more hydrogen can be produced efficiently, and the cost can be reduced. As a method for producing a thin plate, (1) an alloy is sliced thinly. (2) Preparation of an amorphous film by liquid quenching. (3) Rolling can be considered. Of these, slicing takes time and costs, and it is not easy to produce a film with a larger area. Although liquid quenching can form a thin film in a short period of time, it is technically difficult to produce a wide film and a thin plate having a different thickness. On the other hand, rolling is simple, easy, low cost, can produce a film with a large area, is widely used industrially, and has developed technically. If a thin plate can be produced by a simple method called rolling, it is expected that an alloy film having excellent hydrogen permeation characteristics can be mass-produced at a low cost. Therefore, it can be said that the rolling workability of the hydrogen permeable alloy is an important item. If the hydrogen permeable membrane can be made thinner, the cost of raw materials can be reduced, which is industrially important.

  Therefore, an object of the present invention is to provide a method for producing a multiphase alloy for hydrogen separation / purification, which has a higher rolling processability than a hydrogen permeable membrane using a conventional non-Pd alloy and has a large hydrogen permeability coefficient. To do.

The present inventor uses a Ni—Ti—Nb-based double phase alloy for hydrogen separation / purification, and in mol%, Ni _x Ti _y Nb _100-xy (where x = 10% or more and less than 25%, y = 10% It was found that a hydrogen separation / purification double-phase alloy having a high hydrogen permeability coefficient and excellent cold workability can be obtained by setting the range to 40 or less.

  In the present invention, since a Ni—Ti—Nb alloy is used, rolling can be adopted as a plastic working means for thinning. The rolling rate can be 10% or more, and further 70% or more. Thereby, the thickness of the Ni—Ti—Nb-based hydrogen separation / purification dual phase alloy can be 0.02 to 3 mm, and high hydrogen permeation performance can be obtained.

  The Ni—Ti—Nb-based alloy is, for example, an arc melting method in an inert gas atmosphere, a high-frequency induction heating melting method in an inert gas atmosphere or in a vacuum, an electron beam melting method in a vacuum, or a laser heating melting method. It can be prepared by dissolving by, for example. It is also possible to form a Pd film or a Pd alloy film on both sides of the surface of the multiphase alloy for hydrogen separation / purification on the side where the raw material to be treated is flowed and on the side where the purified hydrogen is taken out to obtain a final form.

The composition of the Ni-Ti-Nb-based alloy used in the present invention is atomic%, and consists of Ni _x Ti _y Nb _100-xy (where x = 10% or more and less than 25%, y = 10% or more and 40% or less). It is characterized by that. When the amount of Ni is less than 10%, plastic working such as rolling is difficult, and when it is 25% or more, the hydrogen permeability coefficient is low. If Ti is more than 40% or less than 10%, hydrogen embrittlement becomes large, and it cannot be used for a long time in practical use. It is also possible to replace a part of the Ni element with an element such as Ag, Al, Fe, Mn, Cr, Cu, Ga, Zn, etc. with an upper limit of 30% with respect to the Ni element. It is also possible to replace a part of Ti with another 4A group element with an upper limit of 10% with respect to the amount of Ti. It is also possible to replace part of Nb with another 5A group element with an upper limit of 10% with respect to the amount of Nb. In addition, the inevitable impurities are preferably 5% or less.

  This alloy mainly consists of two phases: bcc- (Nb, Ti) solid solution and B2-NiTi compound. The Nb-Ti phase is responsible for hydrogen permeation properties by dissolving and diffusing hydrogen. On the other hand, the NiTi phase is difficult to be hydrogen embrittled and bears mechanical properties in hydrogen. In other words, a new alloy that has both excellent hydrogen permeation characteristics and resistance to hydrogen embrittlement has been realized. Furthermore, it is attractive that Ni—Ti—Nb double phase alloys are much cheaper than Pd based alloys.

  Since the Ni—Ti—Nb double phase hydrogen permeable alloy is used, it has excellent plastic working performance, and a high characteristic thin plate can be produced as a double phase alloy for hydrogen separation and purification by a process combined with heat treatment. A thin plate having a thickness of 20 μm or less can be produced by this method.

The hydrogen permeation test method is described. First, for the purpose of facilitating oxidation prevention and dissociation and recombination of hydrogen, an ANELVA RF, DC high frequency magnetron sputtering device (SPF-430H) was used on a disk made from an alloy sample of the alloy composition of the present invention. Pd was coated. The furnace is evacuated to 4.0 × 10 ⁻³ Pa using a rotary pump and cryopump, and then reverse sputtering is performed for 10 minutes at an RF power of 50 W, then the substrate is heated to 523 K, and this sputtering is performed at a DC power of 0.05 W. It was performed for 5 minutes, and Pd was coated about 190 nm. Next, the Pd-coated disc was sandwiched between copper gaskets and set in a transmission device. After replacing the inside of the pipe with Ar, vacuuming was performed with an oil diffusion pump until the pressure became 2.7 × 10 ⁻³ Pa or less, and the furnace was heated to 673 K and held for 40 minutes. Thereafter, hydrogen was introduced, the supply-side hydrogen pressure was adjusted to 0.20 MPa, the permeation-side pressure was adjusted to 0.10 MPa, and the hydrogen permeation measurement was started after holding for 60 minutes. For the measurement, high-purity hydrogen having a purity of 7N was used and the hydrogen pressure on the supply side was in the range of 0.20 MPa to 0.8 MPa. This operation was similarly performed at 623K, 573K, and 523K. The flow rate method was used for measurement. The flowmeter used was MODEL3300 manufactured by KOFLOK. The transmission area is 2.46 × 10 ⁻⁵ m ² (true circle with a diameter of 5.6 mm).

  The composition analysis in the present invention was performed by X-ray spectrum collection using an energy dispersive X-ray spectrometer (EDS) manufactured by Oxford Instruments.

In hydrogen permeation using a metal film, the hydrogen flow rate J can be obtained from J = Φ (ΔP ^0.5 ) / L. However, since this equation is derived from Fick's first law and the Siebels law, the sample must satisfy the Siebels law. Therefore, J × L vs ΔP ^0.5 was plotted on a graph, and it was verified from the linearity whether the Siebelz rule was satisfied. Further, the hydrogen permeation coefficient (Φ) was determined from the slope of this straight line.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Examples 1-6, Comparative Examples 1-7)
The purity (mass%) of the metal used in this experiment is Nb = 99.9%, Ti = 99.5%, and Ni = 99.9%. Each metal was weighed so as to obtain the desired composition, and then melted in an Ar atmosphere using an arc melting furnace (ACM-DS-01S) manufactured by Daiya Vacuum to produce an ingot. The alloy production procedure is as follows. After substituting the inside of the furnace with vacuum using an oil diffusion pump to 2.7 × 10 ⁻³ Pa or less, Ar gas (purity 99.99%) was introduced to about 5 × 10 ⁴ Pa, and a tungsten electrode rod was used. Arc discharge. In order to remove the impurity gas in the Ar gas, getter Ti was dissolved for about 2 minutes before the sample was dissolved. The alloy sample was then melted at an arc current of 400 A or more for about 2 minutes. Thereafter, in order to make the composition uniform, the operation of melting the alloy ingot upside down for about 2 minutes was performed about 10 times. The alloy compositions shown in this experiment are all mol%.
A 2.65 × 2.65 × 7 mm rectangular parallelepiped rolling test piece was cut out from an alloy produced by arc melting using a BROTHER HS-300 wire electric discharge machine. The prepared sample is polished with water-resistant abrasive paper made by Buramet, and the roll interval is gradually narrowed at room temperature using a cold two-high rolling mill (100Φ x 100W) made by Nihon Cross Rolling. Until cold rolling.

  Anti-hydrogen embrittlement was judged by whether hydrogen embrittlement occurred when hydrogen permeated at 400 ° C. for 100 hours, acting as a hydrogen permeable membrane.

FIG. 1 and Table 1 show the hydrogen permeation coefficient (Φ) at 673 K of a sample prepared by rolling an alloy with Nb = 56 mol% to 50%. As is apparent from the results in Table 1, the test pieces of Examples 1 to 6 show a hydrogen permeability superior to that of the conventionally reported Ni—Ti—Nb alloy of Comparative Example 1 and are excellent in hydrogen brittleness resistance. You can see that In the examples shown in Comparative Examples 2 to 7, the hydrogen permeability may be higher than that of the Ni-Ti-Nb alloy of Comparative Example 1, which is reported, but it is inferior in water hydrogen brittleness or mechanical after dissolution. It can be seen that the hydrogen permeability is not measurable because it is brittle. These composition diagrams are shown in FIG. 1. From now on, the composition range with high hydrogen permeability and excellent resistance to hydrogen embrittlement is mol%, Ni _x Ti _y Nb _100-xy (where x = 10% or more and less than 25%) Y = 10% to 40%).

It is a figure which shows the relationship between a composition and hydrogen permeability coefficient (PHI).

Claims (5)

This is a double phase alloy for hydrogen separation / purification composed of a composite phase of a phase responsible for hydrogen permeability and a phase responsible for hydrogen embrittlement resistance, and the alloy composition of the double phase alloy is mol%, Ni _x Ti _y Nb _100-xy (however, x = 10% or more and less than 25%, y = 10% or more and 40% or less) The composite phase is a eutectic (NbTi + NiTi) of a NbTi phase in which Ni is responsible for hydrogen permeability and a NiTi phase in which Nb is responsible for hydrogen embrittlement resistance, or the eutectic and the initial phase NbTi. The multiphase alloy for hydrogen separation / purification according to claim 1, comprising a phase. The multiphase alloy for hydrogen separation and purification according to claim 1 or 2, wherein the primary phase NbTi is surrounded by a eutectic. 4. The multiphase alloy for hydrogen separation and purification according to claim 1, wherein the Ni-Ti-Nb alloy has ductility at room temperature in the atmosphere. 5. The method for producing a dual phase alloy for hydrogen separation / purification according to claim 1, wherein the thickness is 0.05 to 3 mm by the plastic working.