KR20090012191A - Activation of metal hydrides - Google Patents

Abstract

A method for processing metal hydride particle or metal particle which is metal hydride precursor is provided to be floated in suitable solution, to be provided to a cavitation process, to supply new hydrogen permeability surface. A method for processing metal hydride particle or metal particle which is metal hydride precursor comprises steps of: floating particle in liquid; ruining liquid-particle compound and surface film and/or destroying at least a part of particle; and providing new particle's surface for absorbing or emitting hydrogen. The liquid/particle compound provides a mixture to a cavitation by adding ultra-audible frequency vibration.

Description

Activation of Metal Hydrides

This application claims priority based on interim application 60 / 952,293, filed on July 27, 2007, and entitled "Activation of Metal Hydride", incorporated herein by reference.

The present disclosure relates to the surface treatment of metal hydride particles for activating particles for storage or release of hydrogen. More specifically, the present disclosure relates to the activation of metal hydride particles by suspending the metal hydride particles in a suitable inert liquid and providing them for cavitation to produce a hydrogen permeable surface.

In the context of the present disclosure, metal hydrides are intermetallic compounds of elements and alloys or elements capable of reversibly absorbing hydrogen. As used herein, metal hydrides and metal hydride-alloys include metal alloys in the non-hydrogenated state, sometimes metal hydride alloys, and also in the hydrated state, including metal alloys with hydrogen. Refers to both of the metal alloys. These metal hydride alloys are embodied as solid solution alloys or as intermetallic compounds. Hydrogen is incorporated into the matrix of metal elements for storage in the solid state. The matrix may comprise a metal crystal structure lattice, with hydrogen atoms interspersed among the metal atoms.

Metal hydride alloys are used, for example, for hydrogen storage for fuel cells and for hydrogen-consuming power plants for automobiles. Hydrogen may be stored in an unhydrated metal composition (metal hydride precursor) by cooling the metal hydride precursor to a suitable, relatively cold, storage temperature and contacting the hydrogen gas under a suitable, usually relatively high pressure. . Hydrated metal hydride materials are stored (often on automobiles) until hydrogen is needed. The metal hydride is then heated and discharged to a transfer system that supplies hydrogen to a device using hydrogen.

Examples of combination of the metal and a corresponding hydride Pd and PdH _{0 .6,} LaNi ₅ and LaNi ₅ H _7, ZrV ₂ and ZrV ₂ H _{5 .5,} FeTi and FeTiH _2, and Mg ₂ Ni and Mg ₂ NiH ₄ Include.

Indeed, many metal hydride precursors may not readily absorb and store hydrogen. The particles require pretreatment before they can absorb hydrogen. The pretreatment (often referred to as "activation") involves removing the oxide film on the metal particles or crushing the particles to expose the unoxidized surface for absorption of hydrogen. This practice included cooling the particles, pressurizing with hydrogen, heating and depressurizing the particles to chemically remove the oxidation barrier to hydrogen uptake. Sometimes repeated cycles were required.

There is a need to spend less cost and time in implementation for the activation of hydrogen storage materials.

Particles of the metal hydride material or metal hydride precursor can be evaluated to see if they are sensitive to the absorption or desorption of hydrogen. If it is determined that the surface of the particles is blocked or impedes hydrogen exchange, the particles can be treated as follows.

Metal particles (or metal hydride particles) are dispersed in a suitable inert liquid (eg, non-oxidizing liquid) and the particle-liquid mixture is cavitation by a suitable cavitation actuator do. Ultrasonic gernerators are suitable for generating cavitation. Cavitation is typically the sudden formation and collapse of low pressure bubbles in the liquid by mechanical forces. The liquid composition must withstand the application of the mechanical energy of ultrasonic waves and must not cause disturbance of continuous hydrogen uptake by the treated particles. The liquid and hydride particle mixture is placed in a container for cavitation of the mixture. Cavitation of the liquid is performed to cause removal of oxides (or others that inhibit coating) on the particle surface. Cavitation can also result in the destruction of metal or metal hydride particles, exposing new, unblocked surfaces for the uptake and release of hydrogen.

The container can be adapted to provide a protective atmosphere when the cavitation mixture is needed. Furthermore, the vessel can be applied for the release of hydrogen from the treated particles, or for the injection of hydrogen to be absorbed by the particles. In many embodiments of the invention, the initial liquid-hydride particle mixture may be present at a temperature (or temperature range) measured to be suitable for effective treatment of the particles when using a particular liquid suspended solids. This temperature may be ambient temperature (typically in the range of about 17 ° C. to 25 ° C.). Any temperature increase can be caused by the cavitation process. The vessel may be applied with a system for controlling the liquid and particle mixture to the desired temperature during the cavitation process.

Examples of suitable liquid treatment media include supercritical carbon dioxide and liquid nitrogen. These liquids will require storage vessels capable of sustaining the temperature and pressure to maintain these fluids in cavitation mode. The advantage of these cavitation liquids is that they can easily evaporate from the activated metal or hydride particles. Other suitable liquids include non-aqueous, organic liquids that are inert to the particles and enable cavitation near or at other predetermined temperatures.

The liquid may be separated from the activated particles and the particles used for the hydrogen storage function upon completion of the cavitation activation of the particles. Hydrogen can be added to or removed from the activated particles. In another embodiment of the invention, hydrogen may be added to or removed from the activated particles while the particles are still suspended in the liquid.

Some metal-metal hydride combinations can store or release significant amounts of hydrogen by varying the pressure of hydrogen to which they are exposed in a closed volume. Some metal hydride combinations release hydrogen under sufficiently high hydrogen pressures to facilitate the transport of the released hydrogen from the hydride storage material to nearby hydrogen consuming devices. The practice of the present invention is applicable to many metal hydrides, including such high pressure metal hydrides.

Other objects and advantages of the invention will be apparent from the following further description of more preferred embodiments of the invention.

The most likely chemical reaction for the storage of intrinsic H2 is an equilibrium reaction that selectively stores and releases H2 depending on the condition, temperature and pressure of the system. Some of these chemical reactions include metal hydrides. Metal hydrides sometimes undergo reversible chemical reactions under conditions of suitable temperature and pressure to absorb or release hydrogen for interior vehicles. The parent metal of the metal hydride takes one of the following forms: A, AB ₅ , AB ₂ , AB, A ₂ B, where A and B are typically mixtures of transition metals or rare earth or alkaline earth metals. It is a mixture of transition metals having. Table 1 shows examples of metal hydrides and their hydrogen storage properties.

Table 1 Examples of Metal Hydrides with Known Hydrogen Storage Properties

type metal Hydride rescue H ₂ wt% Peq, T A Pd PdH _{0 .6} Fm3m 0.56 0.02 bar 298 K AB ₅ LaNi ₅ LaNi ₅ H ₇ P6 / mmm 1.37 2bar, 298K AB ₂ ZrV ₂ ZrV ₂ H _{5 .5} Fd3m 3.01 10 ^-8 bar, 303 K AB FeTi FeTiH ₂ Pm3m 1.89 5bar, 303K A ₂ B Mg ₂ Ni Mg ₂ NiH ₄ P6222 3.59 1bar 555K

The formation of metal hydrides from the reaction of hydrogen with the parent metal (s) proceeds by setting up a well characterized process. Hydrogen molecules are first separated on the surface of the separated hydrogen before it dissolves in the host metal and are present at intercrystalline lattice positions of the crystal structure. However, the molecular hydrogen must be able to contact the surface of the pure metal hydride for separation and dissolution to occur. In other words, the surface of the metal hydride precursor material should be free of films that inhibit hydrogen uptake.

At higher hydrogen pressures, as the positions between the larger number of crystal lattice are filled, the concentration of dissolved hydrogen increases and the intermolecular distance decreases. At any given temperature and pressure, the formation of hydride proceeds until the material is fully hydrated, wherein an increase in hydrogen gas concentration does not produce additional hydrides and the pressure increases. This step can be explained by the pressure-composition-isothermal is illustrated by way of example in FIG. 1. In these examples, at 0 ° C. and 40 ° C., it is believed that higher hydrogen pressures are required to achieve equivalent hydrogen uptake in the hydrogen storage composition. However, at much higher pressures, different interstitial positions can be filled, eventually forming different states of metal hydride. For many known metal hydrides, the thermodynamics of inter-crystal lattice positions that can undergo hydrogen storage at higher hydrogen pressures are not well known or are under investigation.

Examples of metal hydrides shown in Table 1 are binary and ternary types, which are typically represented by AHx, A ₂ BHx, and ABnHx. Quaternary metal hydrides also exist and are represented in general form by ABnCmHx. As a result, the number of possible metal hydrides that can be found is almost unlimited.

An example of a typical metal hydride shown in Table 1 is LaNi ₅ H ₇ . The formation of this hydride occurs at the appropriate pressure and temperature, as shown in Table 1. This hydride has a relatively low heat of formation; Therefore, the energy required for hydrogen evolution is low. Furthermore, it releases hydrogen at relatively low temperatures so that it can release hydrogen using the heat of consumption from the fuel cell. As a result, the uptake and release of hydrogen occurs under conditions most suitable for embedded hydrogen storage vehicles, and the parasitic losses associated with the release of hydrogen from these hydrides are small.

Therefore, metal hydrides composed of many different combinations of different metals can be used, and their possibility of storing hydrogen is improved. However, sometimes these materials must be activated before their possibility of storing and releasing hydrogen is fully realized. The activation process often involves removing the oxide coating from the hydride or hydride precursor material and / or exposing a new, unoxidized portion of the material. The activation process that has been used has been complicated, time consuming and expensive. For example, one process uses a process of activating high pressure metal hydrides using temperature and pressure circulation. In the process, each cycle consists of cooling the metal hydride to −190 ° C., pressurizing with hydrogen at 175 bar, and then heating the metal hydride to 350 ° C. while evacuating the chamber. A plurality of such heating / pressurization and cooling / vacuum cycles are required for activation. Another activation process consists in heating the metal hydride to 1200 ° C. for a long time.

For example, irradiation of liquids with ultrasonic waves induces cavitation. Ultrasonic-induced cavitation creates bubbles in the liquid that can reach 5000K and pressurizes to 1000 atmospheres. These bubbles will form on the surface of the solid suspended or present in the cavitation media. Bubbles produced by cavitation have been shown to grow during cyclic expansion and compression due to the lean state and compression sites of the ultrasonic wavelengths in the liquid media. The bubble eventually reaches an unstable size and undergoes a violent collapse at the solid surface. During bubble collapse, the liquid media forms liquid jets directed at solid surfaces up to speeds of hundreds of meters per second. Such liquid jets have been described as having a "shaped charged" effect that is removed from the surface of a solid. This decay force is sufficient to remove the oxide layer from some metals and destroy fragile particles.

After all, this effect is strictly the required result for the activation of metal hydrides and these precursors. The present invention uses non-aqueous media in which cavitation is induced through an ultrasonic generator. The metal or metal hydride particles are suspended in the cavitation media. Bubbles generated through cavitation in the media shape on the particle surface and collapse by implosion of these bubbles on the particle surface remove the oxide layer and thereby expose a new, unoxidized surface of the hydrogen storage material. The surface of the particles is also destroyed by the force of the liquid jet against the surface, thereby increasing the surface area. The removal and increased surface area of the oxide layer allows the material to be activated for hydrogen uptake and release.

2 illustrates a laboratory cavitation device that uses an ultrasonic generator to induce cavitation to metal hydride precursor particles (and / or metal hydride particles). Referring to FIG. 2, the ultrasonic generator includes an ultrasonic oscillator container 10 having a liquid bath 14 for delivering ultrasonic vibration energy to the covered cavitation container 12. The metal hydride particle-liquid mixture 16 is contained in the cavitation vessel 12. The top of the cavitation vessel 12 is closed with a sealed lid that can pass through a thermometer 20, a gas sparger 22 to the gas inlet 24 (as needed), and a gas outlet 26. Any gas inlet 24 and gas outlet 26 may be used to provide a protective gas atmosphere, such as argon, via the contents of the cavitation vessel. Alternatively, the inlet and outlet can be used for the introduction or removal of hydrogen into vessel 12. Covering the cavitation vessel 12, and temperature control of the vessel 12 is carried out using fluid circulating thermostat-controlled (thermostat 8) lines 30 and 32.

Suitable cavitation liquids are selected for the cavitation process of the hydrogen storage particles. The composition of the liquid does not adversely affect the particles during cavitation, and is a fluid suitable for the cavitation process at a given process temperature. The liquid is then easily removed from the particles upon completion of the process.

The cavitation vessel is designed or applied for cavitation treatment of metal hydride precursor particles or metal hydride particles. The cavitation process will often be performed on a batch of particles or suitably formed vessel. However, cavitation reactions can also be carried out in flow-through vessels semi-continuously or continuously. The vessel is large enough to contain the cavitation liquid and particle volume. As mentioned above, the cavitation vessel requires heating or cooling depending on the selection of the cavitation liquid and the temperature at which the cavitation process is performed. The equipment is prepared to introduce the untreated liquid-particle mixture into the vessel under a suitable non-oxidizing atmosphere and to remove the activated mixture from the vessel. The installation can also be manufactured for the introduction of a protective atmosphere or for the removal of hydrogen if this process is carried out while the cavitation mixture is present in the cavitation vessel.

An ultrasonic generator (or other cavitation device) can be used with the cavitation vessel. The ultrasonic generator may operate on the wall or surface of the vessel, as shown in FIG. 2, to induce ultrasonic frequency vibrations to the cavitation mixture in the vessel. In another embodiment, the ultrasonic generator may have a horn or other transducer extending into the cavitation vessel for direct contact with the liquid particle mixture.

Although the ultrasonic generator is suitable for inducing cavitation in the activation process for metal hydride, other cavitation process means can be used in this activation process. Cavitation may also be induced by a pump, propeller or other technique that causes a partial reduction in the pressure of the cavitation media to a level below the vapor pressure of the media.

Although the implementation of the present invention has been described by way of some examples, it is not intended to limit the scope of the invention.

1 is a hydrogen pressure-hydrogen content isotherm for a typical AB5 type metal hydride. In FIG. 1, the samples were maintained at constant temperatures of 0 ° C. and 40 ° C., when the hydrogen gas pressure was increased to about 4 megapascals at very low pressure and then slowly released.

2 is a schematic explanatory diagram of a cavitation device for activating metal hydride particles or metal particles that are precursors of metal hydride.

Claims (10)

In the case where the particles have a surface film that impedes the release or absorption into the particles of hydrogen, Suspending the particles in a liquid and breaking the liquid-particle mixture with a surface film and / or breaking at least a portion of the particles to provide a fresh particle surface for hydrogen absorption or release. A method of treating metal hydride particles or metal particles that are lide precursors. The method of claim 1, wherein the liquid is not reactive with suspended particles that adversely affect continuous hydrogen uptake or desorption during cavitation. The method of claim 1 wherein the liquid-particle mixture is subjected to ultrasonic frequency vibrations to provide the mixture to cavitation. The method of claim 1, wherein the particle is a metal precursor material and the cavitation process is performed to provide a new surface to the precursor material for hydrogen absorption. The method of claim 1, wherein the particles are metal hydride particles, and the cavitation process is performed to provide precursor material to a new surface for hydrogen evolution. The method of claim 1 wherein the cavitation begins on the liquid particle mixture at ambient temperature. The method of claim 1, wherein the cavitation begins on the liquid particle mixture at ambient temperature, and the temperature at which the mixture is cavitation is subsequently controlled to a predetermined temperature range. The method of claim 1 wherein the cavitation starts in the liquid particle mixture at a temperature above ambient temperature. The method of claim 1 wherein the cavitation begins in the liquid particle mixture at a temperature below ambient temperature. The method of claim 1, wherein the cavitation starts in the liquid particle mixture at a temperature above or below ambient temperature, and the temperature of the cavitation mixture is then controlled to a predetermined temperature range.

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