Hydride Properties Database

This database is a collection of basic and engineering data on 47 reversible metal hydrides of historical and commercial interest. It contains more metal-hydrogen detail then the Hydride Materials Listings database.

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Descriptions of each of the datafields in the database:

Formula

Elemental composition of the base metal or alloy before incorporation of hydrogen. In the search field, use standard notation for the elements, do not subscript the atom quantities and do not include the hydrogen. An example entry would be: LaNi5 . The formulae are nominal and often represent a single intermetallic phase, but not necessarily so.

Name

Names represent commonly generic usages when available. Included in this category are registered trade names and alloy numbers used by commercial suppliers.

Composition

This field represents conversion of the nominal chemical formula into weight percent. The composition is divided into major and minor elements. Searches for major and minor elements should be made in the Formula field. Use the standard element symbol (e.g., Fe).

Pressure at 25° C
Temperature at 1 atm pressure

Unless otherwise stated, all temperatures are given in degrees C and all pressures in absolute atmospheres. Wherever possible, mid-plateau pressures from actual experimental isotherms are used; however, data are seldom available at exactly this temperature or pressure, so entries usually represent extrapolations or interpolations of the van't Hoff equation. For very stable hydrides, one may obtain unmeasurably low pressure at 25° C. The values listed should be used merely as relative indications of room temperature stability.

Hydrogen Capacity

This property is presented in both an atomic ratio, H/M, and weight percent [wt.%=(100)(H)/(H+M)]. Capacity is given as the fully hydrided value, that is, the highest hydrogen concentration measured in the hydride phase limit. It does not necessarily represent the reversible capacity for engineering purposes.

Structures

Crystal lattice structures, when known, are represented by the Strukturbericht Symbols.

PCT Properties

These thermodynamic properties are presented in direct relationship to the van't Hoff equation:

lnP = H/RT - S/R

where

lnP = natural logarithm of pressure (in absolute atmospheres)

T = temperature in K (deg C + 273)

H = enthalpy change of hydriding (in kJ/mol H2)

S = entropy change of hydriding (in kJ/K-mol H2)

R = gas constant (0.0083145 kJ/K-mol)

The user should not assume that a given batch of material will exactly reproduce the PCT properties tabulated here, since impurities, composition variations, and other metallurgical factors can influence hydride behavior. These data should be used only as a guide.

H S

Wherever possible, the values published by the investigator are given. However, in many cases the values are derived by us from our van't Hoff plots, generally using desorption data. Thus, it should be understood they do not represent the chemical parameters determined by calorimetry. The values used here effectively include such terms as strain and interface energies. It should also be recognized that test technique (especially desorption vs. absorption), prior sample history and, to some extent, test temperature can influence these results.

Plateau Slope and Hysteresis

These values are determined from published data using the following expressions:

Slope = (dlnP)/(d(H/M))

Hysteresis = ln [P(absorption)/P(desorption)]

The pressures are evaluated near mid-plateau, if possible. They are in logarithmic terms because they represent energy losses which should go to zero when slope or hysteresis are zero. It should be realized that the values cited are representative and not necessarily invariant. For example, plateau slope can increase markedly near the critical temperature or if the sample has metallurgical segregation. Hysteresis often decreases at higher temperatures where stress relief (recovery) or recrystallization can occur.

Pressure vs. Temperature Table

Wherever possible, data points are taken from experimental curves. Where few data are available, van't Hoff calculated values are given.

Plateaus

This field gives a brief summary of the plateau behavior (single or multiple) over appropriate H/M ranges and at various temperatures, if applicable.

Other Properties

Further information on the material, including references to data sources and further reading on each material.

Metallurgy and Synthesis

A brief summary of the metallurgy of the material is given along with typical alloy synthesis methods. General comments on the formation of the hydride may also be included.

Activation

Basic hydrogen activation procedures described in the literature are briefly summarized. The user should realize that activation techniques are not necessarily unique, but depend on many variables, including: particle size, grinding technique, storage time and environment, vacuum pumping system and configuration, and hydrogen purity.

Kinetics

Only qualitative or semiquantitative comments on hydriding and dehydriding kinetics are given, along with occasional references to published studies.

Cyclic Stability

Where known, data on changes in hydride performance with hydriding-dehydriding cycles will be cited.

Morphology

The form of the samples used to obtain PCT data, when known, will be given.

Gas Impurity Effects

Certain gaseous impurities are known to deteriorate hydride performance in some materials. Quantitative or qualitative data, when known, are referenced here.

Comments

Items of potential interest not covered elsewhere:

Commercial Suppliers

This section is intended for connecting potential users with suppliers. Suppliers not listed are welcome to add their names to the lists under those materials they supply.

The lists of suppliers are given for information purposes only and the IEA, the DOE and Sandia National Laboratories offer no endorsement or recommendation of the capabilities of such suppliers. Any contract made between a User of this database and any Supplier listed herein is the sole responsibility of the User and Supplier.

Applications

Examples of typical applications are listed in this section along with citations. This section is not intended to be comprehensive.

Citations and Authors

The sources of the PCT parameters, as well as other references, are included here. See the Reference Database for more citation detail.

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Last modified: March 06, 2001