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Metal Hydrides Formation and Decomposition

#3190


Ascertainment of Mechanisms and Evaluation of Rate Constants of Metal Hydrides Decomposition and Formation

Tech Area / Field

  • CHE-THE/Physical and Theoretical Chemistry/Chemistry
  • PHY-SSP/Solid State Physics/Physics

Status
3 Approved without Funding

Registration date
15.01.2005

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • St Petersburg State University / Institute of Physics, Russia, St Petersburg

Collaborators

  • University of Rochester / Laboratory for Laser Energetics, USA, NY, Rochester\nSandia National Laboratories, USA, CA, Livermore\nInstitute for Energy Technology (IFE), Norway, Kjeller

Project summary

The problem to solve is connected with the necessity of using hydrogen as energy carrier and ecologically safe fuel. Hydrogen nowadays is considered as the most probable base for future power engineering. Besides, more and more hydrogen is used in chemical, oil-chemical and bio-chemical industry. One of the most prospective and safe methods of storing hydrogen is binding it in metal hydrides.

The Project objective is:

to investigate in detail kinetics of hydrogen desorption from metal hydrides, including discovering mechanisms and evaluating rate constants of hydride phase decomposition, hydrogen diffusion toward metal-gas border and its desorption, as well as kinetics of reverse process – formation of metal hydrides.

The following scientific problems are to be resolved at implementation of the proposed Project:


1. the development of experimental methods for studying the details of processes of metal hydrides formation and decomposition;
2. the study of kinetics of hydrogen sorption and desorption in metal hydrides;
3. the development of adequate models of formation and decomposition of metal hydrides;
4. the evaluation of rate constants of adsorption-recombination processes, hydride formation-decomposition reactions, and hydrogen diffusion.
5. the development of algorithms for solving inverse problems of mathematical physics which will be used to evaluate on experimental data kinetic parameters of limitative stages of hydrogen transfer; the development of the appropriate software;
6. the experimental study of heat transfer in powders of metal hydrides;
7. the creation of pilot model of hydrogen source; heat transfer and hydrogen kinetic parameters will be taken into consideration.

Main expected results:


· Experimental methods for studying hydrogen absorption in and desorption from metal hydrides.
· New experimental data about formation, decomposition, and heat transfer of metal hydrides.
· Mathematical models of hydride formation and decomposition; the models must take non-linear dynamical physical-chemical processes on the surface and boundary conditions on the moving phase bound into consideration.
· Software for numerical experiments in wide range of boundary-value problems of mathematical physics in the area of the project.
· Algorithms and appropriate software for solving inverse problems of mathematical physics. These will be used to evaluate on experimental data the parameters of different stages of hydrogen transport.
· Applying the main elements of the developed technique to hydrides with complex phae structure and hydride powders with known distribution of particle size and form.
· A set of rate constants: diffusivity, adsorption/recombination processes, hydride formation/decomposition, heat conductivity of hydride materials.
· Recommendations for using hydride-forming materials in hydrogen sources and absorbers.

Grounds of the project

Kinetics of metal hydrides decomposition and formation nowadays is poorly studied, so the project is actual. In most research works in this area the authors model influence of different limitative stages on total process of hydrogen desorption from hydrides. In experimental area the most developed direction is using catalytically active coverings that accelerate processes at the surface of hydride particles and thus increase the total rate of hydrogen desorption. This research works, however, don’t provide yet numerical evaluations of the rate constants suitable for design engineering. When studying hydrogen absorption in metal hydrides the main efforts are bent to recover mechanisms of forming hydride phase itself. Hydrogen absorption in hydrides looks even more complex than desorption, therefore there are no models suitable for parameter evaluations.

Authors of the project have more than 30 year experience in research of properties of hydride-forming materials and processes of their interaction with hydrogen isotopes. They are between leading specialists in the area of measuring equilibrium pressures of hydrogen isotopes in hydrides, as well as of metallographic research of metal hydrides. They have unique experience in studying in detail multi-stage processes and obtaining rate constants of certain stages, such as hydrogen penetrability, which takes place when rates of adsorption-recombination processes are low and which is complicated by trapping and thus is multi-channeled; hydrogen sorption and desorption by nanocarbons; kinetics of charge and discharge of duble-layer supercapacitors and so on. In the project the approach of studying the systems noticed above will be used for studying hydrogen desorption and absorption by metal hydrides. This will allow recovering their physical mechanisms, formulating models and checking them for adequacy, obtaining numerical evaluations for rate constants of elementary processes, which influence on desorption and absorption of hydrogen.

Fundamental importance of the Project consists in the following


· Analysis of metal hydrides decomposition and formation will be based on detailed study of physical mechanisms of hydrogen absorption and desorption by metal hydrides, but not on the “effective” rate values;
· Theoretical models of hydride forming and decomposition will be formulated and their adequacy will be checked;
· Approach which uses solving inverse problems of mathematical physics is going to be applied to discriminate the models and obtain numerical evaluations of the parameters on results of experiments of hydrogen absorption and desorption;
· A set of pre-exponential factors and activation energies of hydrogen transport in hydride-forming materials processes, such as diffusion, hydride forming and decomposition, and so on, is expected to be obtained;
· A boundary-value problem which takes non-linear dynamical chemical-physical boundary conditions on the surface and on the moving bound into consideration and which is a modification of the Stefan problem will be constructed;
· Hydride formation and decomposition are considered together with analysis of heat transfer.
Practical applications:
· Complex methods for studying mechanisms of metal hydrides formation and decomposition and for kinetic parameters evaluation. These methods will include experimental technique and numerical algorithms for estimating rate constants of those processes that influence on rate of hydrogen desorption from hydrides. These methods will allow evaluating not only “effective” parameter values, but also their values for certain batches of materials with different details of their production.
· Computer models for studied hydride classes. These models will allow numerical modelling of hydrogen absorption and desorption in wide ranges of temperature, gas pressure and powder particle size.
· Practical recomendations for constructing hydrogen sources when using hydrogen as compact energy carrier and ecologically safe fuel.
· Practical recomendations for constructing high-rate (emergency) hydrogen and its isotopes adsorbers for environment protection.

Technical Approach and Methodology

Technical approach and methodology for completing the project are based on the unique combination of experimental devices and qualification of the project participants both in studying hydrides and experience in studying kinetics of hydrogen interaction with solids.

RFNC-VNIIEF has at its disposal facilities and experience required to carry out the research of hydride formation/decomposition. Here a few methods are widely used, such as thermogravimetry in hydrogen medium, differential scanning calorimetry of heterogeneous processes, differential thermal analysis and thermal desorption.

Fock Institute of SPbSU has developed some methods for studying mechanisms of metal hydrides formation/decomposition, for evaluating rate constants of the processes on the experimental data. The team possesses all necessary equipment needed to fulfill the Project.

A complex method for studying hydride decomposition is suggested to be created using thermal desorption spectrometry. Experimental information about formation of hydrides will be obtained using barometric method and thermogravimetry. Good fitting of experimental curves by model ones will be a criterion of adequacy of the models. The rate constants of elementary processes that are part of macro-processes of hydride formation/decomposition will be evaluated by solving inverse problems of mathematical physics.

Role of Foreign Collaborators

Consultations and information interchange with scientists from Institute for Energy Technology (Norway), University of Rochester (USA), Sandia National Laboratories (USA) and others will take place while completing the project. Visits of the project collaborators to RFNC-VNIIEF are planned for team experimental work and discussing the models of metal hydrides formation/decomposition.

A seminar on topic of the project is planned with all foreign collaborators invited.


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