The effect of metal hydride activation and use of energy nonequilibrium hydrogen

Int. J. Hydrogen Energy, Vol. 18, No. 7, pp. 591-599, 1993.

0360 3199/93 $6.00 + 0.00 Pergamon Press Ltd. International Association for Hydrogen Energy.

Printed in Great Britain.

THE EFFECT OF METAL HYDRIDE ACTIVATION AND USE OF ENERGY NONEQUILIBRIUM HYDROGEN A. N. PODGORNY,V. V. SOLOVEYand A. V. BASTEEV Institute for Problems in Machinery, Ukrainian Academy of Sciences, 310046 Kharkov, Ukraine

(Received for publication 11 December 1992) Abstract--The means of production and fieldsof application of energy nonequilibrium hydrogen states in processes of energy conversion are briefly reviewed. The effect of metal hydride hydrogen activation is considered, which can be applied to reactions of heterogeneous catalysis, ignition of hydrogen-oxygen mixtures, devices using hydrogen as a working medium with energy supplied from an external source, as well as to electrophysical units. The probability of the thermodynamically nonequilibrium concentration of excited particles near the surface of hydride-forming materials is quantitatively estimated.

a~ e

Eexcess Eform - - Edi s

E,*, AEgy~ G m mi

M Nh P Ap S T V

ZJ x ~ Greek letters ~t ~i e(p, T) #

NOMENCLATURE Intermediate multiplier Electron charge Above-thermal excess energy Energy change due to the phase transition Lattice deformation energy per hydrogen molecule Energy change induced by hysteresis The Gibbs isobaric-isothermal potential Ion mass ith component mass Metal hydride mass Atomic hydrogen concentration Pressure Pressure change Entropy Temperature Volume Deviation of total thermodynamic potentials of system components from the additive characteristic potential

has a number of unique energy-ecological properties. The ability of a hydrogen molecule to be in an excited metastable state makes it possible to extend the fields of its practical application in the processes of energy conversion or production of refined compounds. For example, it is shown experimentally and theoretically that application of atomic and molecular hydrogen as an activation dopant to the main fuel results in saving the latter and reducing the content of toxic products in the exhausted gases. Moreover, the 0.5~o admixture of atomic hydrogen to the combustion zone is as effective as a 10-12~o addition of molecular hydrogen with regard to the production of toxic components. While realizing hydrogen activation of conversion of energy, utilization of excited energy nonequilibrium types of hydrogen seems to be one of the most promising ways to solve the problem of raising the effectiveness of energy production equipment. Hereafter the term "activated hydrogen" implies hydrogen is its thermodynamically nonequilibrium states.

Degree of dissociation Degree of ionization Relative hydrogen mass content of hydride Chemical potential

At present, each type of activated hydrogen is studied in some detail, except for regions of extremely scarcely available values of the determinant parameters. A high level of comprehension is achieved in the physics of elementary processes with the participation of excited and energy nonequilibrium hydrogen states. Proceeding from the published data, Fig. 1 presents the generalized digram indicating, in temperature-concentration coordinates, the up-to-date achievements of production, accumulation and utilization of one of the possible nonequilibrum states, namely atomic hydrogen.

1. I N T R O D U C T I O N Hydrogen power engineering is of great importance among the problems which are related to searching for alternative working media, due to the fact that hydrogen

2. ACTIVATED HYDROGEN AND ITS FIELDS O F APPLICATION

591

592

A. N. PODGORNY et al.

[...... L..... J..... L,(~),] ...... L~ 6J~

[

1021 100 E

1019 Z

10-2

0.1

1

10

100

103

104

T (K) Fig. 1. Generalized conventional diagram indicating achievements in accumulation and utilization of atomic hydrogen. Region (1) corresponds to conditions which are realized in direct-drive electric heat thrusters operating on hydrogen, such as hydrogen plasmatrons, pulse processes in light gas launchers I-1-3]; region (2) corresponds to hydrogen frequency standards, hydrogen masers, etc. [4, 5]; region (3) shows the atomic hydrogen concentration in branching chain chemical reactions in flames [6]; region (4) gives concentrations corresponding to a hypothetical atomic hydrogen propellant [7-]; region (5) represents the observed concentration of atomic hydrogen at radiolysis of a cryogenic medium [8]; region (6) corresponds to unverified Hess experiments (see relevant references in [9]); region (7) shows results of Webeler experiments on IZI accumulation in a condensed cryogenic system {H 2 + T2} [10]; region (8) shows calculated Rosen and Zeleznik relations, based on the Webeler experiments, for the system {H 2 + T2} in the absence of a magnetic field [11, 12]; region (9) represents experiments on accumulation of spin-polarized atomic hydrogen in the gas phase in a high magnetic field I-9]; region (10) shows the Bose-Einstein condensation boundary; region (11) shows the accumulation of atomic hydrogen in solid hydrogeneous matrices as a result of radiolysis, atomic hydrogen in solid minerals, etc. [13]; (12) is the region of hydrogen transition to the metal state [14]; region (13) represents results of experiments on metal hydrogen generation; and (14) is the region of nonperfect hydrogen plasma 1,15]. For more detailed references relevant to that problem, see Ref. 1-16]. The above problem of generation and application of nonequilibrium hydrogen states can be conventionally divided into two groups. The first group should include

production of exotic forms of a material whose utilization seems to be problematical in engineering at present, namely metallic hydrogen, the spin-polarized condensate of atomic hydrogen having the properties of a superfluid gas; a free radical substance accumulating energy. Up to now we have failed to verify experimentally the possible production of appreciable quantities of hydrogen of any of the above three exotic types of hydrogen state. The second group of problems is directly related to practical application of activated types of hydrogen in energy converters and their wide use in engineering, i.e. jet engines, technological reactors, atomic hydrogen welding, hydrogen lasers and masers, as well as to promote combustion. When hydrogen is used as a working medium in energy converters and is supplied with electrical energy from an external source (e.g. light gas launchers) the controlling step is ionization. Preliminary activation of hydrogen, exciting vibrational degrees of freedom of molecules or their transfer to the atomic state, makes it possible to increase appreciably hydrogen's susceptibility as ~i working medium to the energy supplied. In combustion, chain reaction branching of hydrogen oxidation is based on the generation of active centres. For most practically important cases, the active centres are hydrogen atoms. In this case, to maintain or evolve the combustion reaction the generation stage of active centres, i.e. hydrogen atoms, is controlling. Recently, it has been shown that the application of hydrogen as an active admixture to the fuel of internal combustion and gas turbine engines permits us to solve a number of problems where toxicity of exhaust gases, a decrease of fuel consumption, simplification of the engine start, etc. are regarded as important technical factors (the effectiveness criterion) [17, 18]. Thus, the above second group of applied problems gives evidence for the implicit necessity of searching for rational means of hydrogen preactivation. One of the effective (however, poorly studied) hydrogen activation methods is application of solid matrix structures, in particular metal hydrides and intermetallic compounds. 3. METAL HYDRIDE ACTIVATION O F HYDROGEN Metal hydride activation of hydrogen is of interest due to the variety of applied problems which may be solved with it. The most significant problems are as follows: reactions of heterogeneous catalysis; hydrogen activation aimed at increasing its susceptibility to the external energy; intensification of vacuum treatment in electrophysical equipment; catalytic ignition; and production of hardhydrogenated materials (see References of Ref. 1-16]). As a result of interaction with hydride-forming materials, hydrogen acquires excess energy. The difference between the chemical potentials of hydrogen in its solid and gas phases is responsible for the above-thermal excess energy and the existence of the nonequilibrium concentration of hydrogen molecules with excitation of different internal degrees of freedom near the surface.

EFFECT OF METAL HYDRIDE ACTIVATION Metal hydride hydrogen activation is induced by both heterogeneous physicochemical processes on the gas phase hydrogen-metal interface and the hydrogen interaction with the crystal lattice. The former way consists of hydrogen activation by dissociative chemisorption of a H 2 molecule on transition metal clusters or by the sequential occupation of vacant surface adsorption centres by hydrogen atoms emerging from the bulk of a metal. In those cases there is a layer of reactive hydrogen atoms on the metal hydride surface which can take part in catalytic reactions both directly from that surface [19, 20] and from the surface of intermediate carriers A1203, SiO2, HxWO3, HxMOO3, NH4C1, etc. by atomic hydrogen spillover [21, 22]. The active hydrogen transfer at the mechanical contact of LaNisH x hydride with amorphous tungsten trioxide powder was detected by a change of colour due to embedding hydrogen in interstitial oxide sites with bronze production [23, 24]. Differential thermometric analysis and thermogravimetry confirmed the production of tungsten-hydrogen bronze Ho. xWO3 in the above experiments. The production of bronze was also observed in the case when the active hydrogen source (LaNis) and acceptor (WO3) were separated by quartz glass (l ~ 10-25 mm). In all the cases, the chemochrome response (WO3) to active hydrogen was observed when gas phase hydrogen was put in contact with the surface of LaNi 5 under conditions nearly excluding hydrogen absorption by intermetallides, as well as hydrogen desorption from hydride LaNisH x [24]. The chemochromatic indicated colouring evidences that it traps activated hydrogen produced on the metal hydride surface and migrates to W O 3 (the spillover effect) with the subsequent embedding into the bulk. The colour change intensity was found to rise with an increase in the number of hydrogenation cycles, as well as with the pressure growth in a cell. The colouring intensity decreases over the layer thickness moving away from the contact zone of metal hydride LaNisH x and WO 3. Moreover, colouring with the production of tungsten hydrogen bronze was observed both at hydrogenation and at hydrogen desorption. Metal hydride activated hydrogen was observed to transfer in NH4C1 as well. The transferred hydrogen was held by the NH4C1 surface for about 100 min. Quantitative estimates of hydrogen produced were equal to 0.02 × 10 -z cm 3 H 2 g-1. Besides the well-known and commonly used compounds of the LaNis, FeTi, etc. type, a low-dimensional layered compound niobium diselenide (NbSe2) proved to be able to activate hydrogen [25, 26]. The hydrogen spillover effect was also studied by EPR spectroscopy. Fine-grained powders of SiO2 and WO 3 put in contact with metal hydride LaNisH x were alternately placed in a joint cell (a quartz ampoule welded to a glass pipe "Luch") 5 mm in diameter. In both cases, a stable signal was observed corresponding to atomic hydrogen, which exceeded the background by a factor of 2.5-3. This is consistent with the volume content of atoms N h ~ 1013 c m 3. This fact makes it possible to state that hydrogen or atomic hydrogen dissociatively

593

adsorbed on the LaNi5H x surface passed appreciable distances (l ~ 2-10 cm) to the dispersed condensed phase surface inert to hydrogen. The less-studied aspect of metal hydride hydrogen activation is the emission of excited and charged hydrogen particles from the metal hydride surface to the gas phase. Furthermore, here nonequilibrium concentrations of vibrationally and rotationally excited H* molecules, molecules with the excess kinetic energy of translational motion, nonequilibrium concentrations of ortho- and para-modifications of hydrogen, electron-excited [27-33] analysis of the redistribution mechanisms of the recombination energy of hydrogen atoms adsorbed on metal surfaces with the subsequent transfer of excited molecules to the gas phase has been performed. Recombination of hydrogen atoms on the solid surface accompanied by energy release results in the fact that a H* molecule produced leaves the surface with highly excited rotational and vibrational degrees of freedom [27]. For example, while being desorbed from the Cu surface, hydrogen molecules have an appreciable above-thermal excess vibrational energy [28], as well as an aboveequilibrium increment of the translational motion kinetic energy exceeding the metal temperature (1000K) by about a factor of 8 [28]. The H* molecule desorption from the W (001) face due to hydrogen atomic recombination on the surface was characterized by the following distribution of released energy between translational, vibrational and rotational degrees of freedom: 30, 50 and 15~o, respectively; about 5~o of the energy is transferred to the solid [30]. The calculation analysis [31] showed that for most exothermal surfaces of the potential energy, the inverse population is realized; in particular, the recombination energy is most likely realized on a level with vibrational quantum number 3. The lower estimation of the share of translational energy in the total recombination energy balance [32] was obtained on the basis of the experimental recoil effect at hydrogen atomic recombination on the surfaces of fine-grained Fe powder and was equal to ll~o for the I:I atomic recombination coefficient of 0.1. From experiments on the gas discharge characteristics of hydrogen desorbed by metal hydride, the maximum available degree of hydrogen ionization desorbed by LaNisH x was defined to be ~ti ~ 1 0 - 8 - t 0 -9 at about 1 Pa [24]. The emission of active hydrogen particles can occur not only at its removal from metal [34 37], but also at adsorption. For example, while ordering freshly deposited layers of palladium and platinum on a substrate in a hydrogen atmosphere, there occurs an ejection of I:/ atoms into the gas phase whose concentration is defined by the atomic aggregation energy of a deposited metal (the metal metal bonding energy), other conditions being equal [37]. In a number of cases, the active particle emission is observed at hydrogen adsorption on the ordered surfaces, apparently due to the spontaneous localization of hydrogen adsorption heat on vibrational levels of separate chemisorbed I:t atoms. Nonuniformity of most real solid surfaces, the preserice of defects in their

594

A. N. PODGORNY et al.

bulk, as well as high sensitivity to the action of physicochemical, radiation and mechanical factors, are responsible for electron, ion and photon exoemission from the surface. Moreover, a particle or radiation takes the energy away which is released in the process of relaxation of the excited state after deexcitation [38]. For hydride forming metals, one of the probable factors leading to hydrogen activation with its subsequent emission to the gas phase is hysteresis. As is well known [39], the above effect appears due to the different dimensions of the crystal lattices of the initial metal matrix and metal hydride, which results in elastic stresses in the matrix. In this way, the metal matrix acquires the excess energy which can be transferred by hydrogen atoms diffusing towards the surface with subsequent desorption. Hydrogen absorption by a metal leads to the appearance of defects and cracks, as well as cleavage of the initial matrix, which results in the formation of surface areas extremely active with respect to the mechanical and theoretical nonuniform emission of excited and charged particles. The more intensive the dispersion, the greater is the localized excess energy of the crystal lattice, thereby exciting the nonequilibrium electron and activated hydrogen particle emission, since scattering of that energy in solids becomes ineffective. While analysing the above effects, one should bear in mind that mechanochemical reactions can occur similar to those described in

[40]. Thus, based on the above, the following reasons can be singled out which result in hydrogen activation on its interaction with hydride forming materials. (1) Energy release induced by elastic and plastic deformations of the metal matrix (hysteresis) and its transfer to desorbed hydrogen. (2) Exoemission of charged and excited particles under: (a) chemical action (failure of oxide and hydrate films on metal surfaces in the hydrogen atmosphere, segregation of transition metal clusters on the surface); (b) physical action (the presence of defects, nonuniformities of structure and micropores resulting in intensive charge exchange and particle acceleration in local electric fields); and

(c) mechanical action (cleavage of the metal matrix, the appearance of cracks and, as a result, the free energy rise and the appearance of"broken" chemical bonds). (3) Recombinationless desorption of protons or hydrogen atoms diffused towards the surface. (4) Recombination (associative) desorption of hydrogen atoms with excitation of different degrees of freedom in a produced H 2 molecule. (5) Nonequilibrium energy exchange processes between the emitted particles in collisions (secondary processes). In fact, all the above-mentioned mechanisms of production of activated hydrogen molecules are interconnected and, as a rule, accompany each other. In the process of hydrogen desorption from metal hydride, hysteresis seems to be the main factor. The difference between the chemical potentials of hydrogen in the gas phase and metal matrix, where it is "preserved" as the metastable nonequilibrium~ct + fl)- or fl-phase is responsible for the thermodynamic prerequisite for activation. Elastic adjustment of the different phases in the matrix induces the appearance of excess free energy in the process of desorption relaxing, in part, on hydrogen atoms. Recently, it was noted [41] that at hydrogen desorption from metal hydrides LaNisH x and YNi2H x at 323K and 5 x 10 -4 Pa, the most intensive rise of mass spectrum peaks corresponding to H ÷ and H~ and related to the hydrogen emission in the nonequilibrium excited state was observed at the transition from the (ct + fl) region to the ct one. To study the catalytic properties of LaNi 5 in reactions related to heterogeneous activation of hydrogen and its isotopes, a series of experiments was performed on the mass spectrometry of products of the interaction between deuterium and powdered intermetallide. Table 1 presents mass spectra of commercial deuterium and the same deuterium passed through a cell with LaNi 5. The experimental scheme is given in Fig. 2. At 393-403K, a sharp rise of peak intensities role = 2 was observed (by 12 times) and role = 3 (by 20 times), also a slight rise role = 1 and some decrease of the peak intensity m/e = 4. Moreover, the intensity of peak m/e = 5 (HD~) increased by a factor of 3.7, whereas the height of peak

Table 1. Mass spectra of gas samples Peak intensities of mass numbers (arbitrary units)

Gas sample

Reference deuterium Deuterium passed through a cell with LaNi s

1

2

8.3

12.5

49.1

193

3

17.7 345

Cell temperatures 393 403K, pressure 1.7 × 10-3 Pa.

4

5

6

59.7

2.0

14.5

50.5

7.5

5.5

EFFECT OF METAL HYDRIDE ACTIVATION

595 2

5 ~

400 mm

w. 7

6

1 .,,m.---

Fig. 2. Mass spectrometry studies of interaction products of deuterium and powdered intermetallide: (1) depth filter; (2) Teflon tube; (3) connecting copper pipeline; and (4) mass spectrometer ion source M 1-1201.

m/e = 6 (D~) decreased by a factor of 2.5. It should be noted that whilst analysing deuterium mass spectra, the maximum corresponding to m/e = 2 was interpreted as D+, since it was established that the contribution to the intensity of m/e = 2 from H~ ions does not exceed 1~o. Thus, the obtained results confirm that under conditions excluding the hydride phase formation ( T = 296-403K, p ~ 10 3 Pa) at temperatures above 373K, activated intermetallide LaNi s exhibits prominent catalytic activity manifesting itself in the activation of molecular deuterium. To study specific features of the gas release from hydride-forming materials treated by molecular deuterium and deuterium plasma, Ti and Ti2Ni/Ni were treated barothermally by deuterium and exposed to the deuterium plasma flux. The experimental diagram is presented in Fig. 3, notation is given in the figure caption. Then, gas release from the samples heated up to 713K with the velocity of 44K m i n - 1 was analysed by mass spectrometry. The mass spectrum analysis for mass numbers m/e = 1-6 was carried out at the leak-in pressure 3.5 × 10 -4 Pa. It follows from the results presented in Table 2 that, for both Ti and Ti2Ni/Ni, the output of

Fig. 3. Plasma treatment scheme of compounds active with respect to hydrogen: (1) hydrogen (deuterium) plasma source; (2) vacuum chamber, volume 1.5 m3; (3) support; (4) holder; (5) studied samples; (6) hydrogen (deuterium) plasma flux; (7) hydrogen (deuterium) storage and supply system; and (8) vacuum treatment system (dynamic vacuum was p < 2.93 x 10 -2 Pa for experiments).

excited D~' molecules is higher as compared with the reference deuterium. This manifests itself in a rise of peak intensities of l i D ÷ (rn/e = 3) and D ÷ (role = 2) and a decrease of D3 (m/e = 4) due to the reaction I:t + D*--* H D + 13. The effect of deuterium plasma on Ti results in an appreciable decrease of the peak H + (role = 1), apparently due to thermovacuum degassing of the initial titanium. As compared with the reference for Ti, variation of the peak intensities of D +, H D +, D~ is less prominent in the sample after the plasma treatment. At sample degassing, the decomposition of bulk phases of the T i - D system seems to play the main role in deuterium activation, since the phase compositions of titanium samples treated by molecular deuterium and deuterium plasma are different. This is due to the fact that the saturation degree by deuterium from the plasma flux is

Table 2. Mass spectra of gas samples Peak intensities of mass numbers, ~o

Gas sample

Reference deuterium Molecular deuterium treatment. Samples: Ti Ti2Ni/Ni Deuterium plasma treatment. Samples: Ti TizNi/Ni

1

2

3

4

5

6

0.46

0.23

0.32

98.99

0.02 0.78

0.77 10.00

6.64 7.29

92.19 81.07

0.03 0.63

0.35 0.23

0.01 0.01

0.69 1.65

5.98 5.32

93.19 92.48

0.01 0.04

0.12 0.50

A. N. PODGORNY et al.

596

lower since, under the conditions of arc plasma, the pressure in the reaction zone is less than the equilibrium pressure of the corresponding deuteride, so that the deuteride phase decomposition is dominant. The difference between treated samples of the composite material Ti2Ni/Ni is less pronounced than that of titanium. The peak intensity HD ÷ of the sample exposed to plasma somewhat decreased, that of peaks D + and D~ increased, whereas the peak D~" slightly changed. This seems to be assigned to a decrease of the number of recombination events of I:I and I~ which results in deuterium atoms contributing to a rise of D + and D~. A common characteristic feature of the samples studied is the fact that the quantitative relation of components desorbed from deuterium treated materials differs considerably from the reference deuterium, which is due to the deuterium molecule activation. From the generalization of the above results, one can draw the following conclusion. Under conditions excluding the hydride phase-formation, fine-grained LaNi 5 promotes production of excited deuterium molecules, intensifying isotope exchange reactions. Products of Ti and Ti2Ni/Ni degassing after both the barothermal and plasma deuterium treatment are more active as compared with the reference deuterium due to D 2 molecule excitation. For Ti exposed to the deuterium plasma, the activation effect of degassing products manifests itself to a lesser extent than after the barothermal treatment by molecular deuterium. The above examples of metal hydride activation of hydrogen are convincing illustrations of the nonequilibrium concentration of excited particles formed near the surface of hydride-forming condensed matter interacting with hydrogen or its isotopes. Let us estimate the upper limits of the dissociation and ionization degrees of hydrogen desorbed by metal hydride for a hypothetical case of complete realization of the excess energy on the broken atomic bonds in a H 2 molecule. Consider the equilibrium system of {gaseous hydrogen-hydride forming metal}, with the volume V and characterized by the equilibrium temperature T and hydrogen pressure p. Under varying external conditions, the system behaviour is described by: RT

(3)

G = Z P*ml = E -- TS + p V - - Z Xjxj, i

j

or taking into account the pressure change: AG = G(p2, T ) -- G(p 1, T ) = - - S A T + V A p -- ~, X j x j . J

(4) ~.i X j x j includes the metal lattice deformation energy on

embedding of hydrogen atoms (excess free energy), the phase transition energy and above-thermal excess energy transferred to a H z molecule due to surface processes, which lead to desorption of an excited molecule to the gas phase, viz.: x j A X j = AEgys + (Eform - - Edis) + AE .......

(5)

J where, according to Ref. [39]: E,ys = L e O - e) - ( L - A4)e2(1 -- 0,

L - AEgys(e = 0) = (V2 - Vt)2/2a~V~, ------AEgys(e~ '~max), where V2 - V1 is the variation of the metal specific volume on embedding of hydrogen. In practice, AEg*s for intermetallic hydrides can be estimated by experimental pressure-composition isotherms. For the plateau E g y s = RT In P2/Pl, where P2 is the equilibrium sorption pressure and p~ is the equilibrium desorption pressure. For most metal hydrides of practical importance, the phase transition energy (Eform - Edis) can be neglected as compared with other terms. The last term in equation (5), taking into account nonstationary processes of the surface energy income, we take equal to zero. From the view point of process power, the first two terms are fundamental (for the isothermal case):

(1)

ApV = MAe--,

RT

M(e~ E ~,) mH~

A G = M ( e 2 - el) Pn~ - AE*ys

IIH2

where Ap is the pressure change, M the metal hydride mass and Ae = e(p, T ) -- e(Po, To) is the variation of a relative mass content of hydrogen in the hydride. Disturb the system from the thermodynamic equilibrium by decreasing the pressure p above the metal hydride. Consider the equation for the system's total energy in the general case: F = T S - p V + ~ p*rni + ~ X , x j , i

entropy and ~ j X ~ x j is the term characterizing deviation of the total thermodynamic potentials of the system components from the additive characteristic potential. The Gibbs isobaric-isothermal potential is expressed by:

(2)

j

where p* is the chemical potential of the system's ith component, mi is the ith component mass, S is the

RT = M(e2 - el) ~

AEg*~ m.~ //'

(6)

where AE~*s is the lattice deformation energy per single hydrogen molecule. Going over to the excess energy per molecule near the surface, we have: E* - A G N

AGmH2 M ( e l -- •2)

_

rnrt2 RT + AEg*s. JtlH2

(7)

Table 3 gives some E* values for the hydride LaNisH x. Let us assume a hypothetical case, when the total excess

EFFECT

OF METAL

..0

HYDRIDE

ACTIVATION

¢q

X

X

A" ._~0 ~

X

o

o.

~,o

¢q

o.

o.

~,

I

I

I

.o X

o

o.

I

A-" 0

X

cO

ft..

c5

d

o

o.

o.

q

o.

I

I

I

I

X

z

I

J

O

O

..-.. O

I

597

598

A. N. PODGORNY et al.

energy is " p u m p e d o v e r " to some c o n c e n t r a t i o n of d e s o r b e d particles, so that they are completely dissociated, vibrationally excited or singly ionized. The table gives the c o r r e s p o n d i n g degrees of dissociation ~, excitation ~* a n d ionization cq. The theoretical estimation of a t o m i c c o m p o n e n t conc e n t r a t i o n s in desorbed h y d r o g e n obviously illustrates the t r a n s p o r t a t i o n m e c h a n i s m of the excess energy of a metal hydride m a t r i x if one assumes the completely " n o n - M a x w e l l i a n " energy distribution o n v i b r a t i o n a l degrees of freedom, which is impracticable u n d e r real conditions.

9. 10. 11. 12. 13. 14.

4. C O N C L U S I O N The m o d e r n level of d e v e l o p m e n t of metal hydride technique a n d technology m a k e s it possible even n o w to state a n d solve various engineering p r o b l e m s c o n c e r n i n g power p r o d u c t i o n a n d h y d r o g e n processing. The effect of metal hydride activation of h y d r o g e n in question, consisting of h y d r o g e n desorption in the energy n o n e q u i librium state is of considerable scientific a n d practical interest for further d e v e l o p m e n t of m e t h o d s to m a k e p o w e r - p h y s i c a l a n d chemical engineering plants more effective. Final conclusions a b o u t a specific form of h y d r o g e n molecule or a t o m i c excitation near the surfaces of intermetallic hydrides or o t h e r active c o m p o u n d s with respect to h y d r o g e n c a n n o t yet be d r a w n o n the basis of the a b o v e brief review a n d some experiments, t h o u g h in the first a p p r o x i m a t i o n one can assume t h a t the ways to solve the p r o b l e m are outlined. In spite of the lack of quantitative d a t a o n metal hydride activation of hydrogen, the fields of practical application of the effect have been defined.

Acknowledgements The authors are grateful to Prof. A. P. Kudryash for support and interest in their work, as well as to V. Popov and A. Prognimak for their assistance in performing the experiments.

15. 16. 17. 18. 19. 20. 21. 22. 23.

24.

25.

1. 2. 3. 4. 5. 6. 7. 8.

REFERENCES V. P. Burdakov and Yu. I. Danilov, Physical Problems of Space Propulsion Power. Atomizdat, Moscow (1969). L. L. Klochkova, Working Media of Power Plants of Aircraft. Mashinostroenie, Moscow (1984). N. A. Zlatin and G. I. Mishin (Eds), Ballistic Systems and their Application to Experimental Studies. Nauka, Moscow (1974). G. M. Strakhovsky and A. V. Uspensky, Principles of Quantum Electronics. Vysshaya shkola, Moscow (1979). I. McDaniel and W. Nigan (Eds), Gas Lasers. Mir, Moscow (1986). V. T. Gontkovskaya, I. S. Gordopolova and N. I. Ozerkovskaya, Hydrogen oxidation under nonisothermal conditions. Phys. Combust. Explos. 24, 53-61 (1988). G. Rosen, Manufacture and deflagration of an atomic hydrogen propellant. AIAA J. 12, 1325 1330 (1974). I. M. Carpenter, Thermally activated release of stored

26.

27. 28. 29. 30. 31.

chemical energy in cryogenic media. Nature, Lond. 330, 358-360 (1987). I. S. Silvera and J. T. M. Walrawen, Spin-polarized atomic hydrogen, in Progress in Low Temperature Physics, Vol. 10, pp. 139 370. Elsevier, Amsterdam (1986). R. W. H. Webeler, Behaviour of atomic I:I in solid H 2 from 0.2 to 0.8K. J. Chem. Phys. 64, 2253-2254 (1976). F.J. Zeleznic, Generation of atomic H in a hydrogen matrix by tritium decay. J. Chem. Phys. 11, 4492-4496 (1976). G. Rosen, Stability of the equilibrium for atomic I:I in solid H 2. J. Chem. Phys. 66, 5423-5426 (1977). Yu. P. Konyushaya, Soviet Scientist Discoveries. Moscow Worker, Moscow (1979). V. L. Ginzburg, On Physics and Astrophysics. Nauka, Moscow (1985). P. P. Kulik, V. A. Ryabyi and N. V. Ermokhin, Nonideal Plasma. Energoatomizdat, Moscow (1984). A. V. Basteev, M. A. Obolensky and V. V. Solovey, Activation of Hydrogen and Hydrogen-containing Energy Carriers. Naukova Dumka, Kiev (1993). A. I. Mischenko, Hydrogen Application to Motor-Car Engines. Naukova Dumka, Kiev (1984). P. M. Kanilo, Toxicity of G TE and Prospects of Hydrogen Application. Naukova Dumka, Kiev (1982). D.A.W. Carstens and G. R. Farr, The formation of niobium dihydride from niobium catalyzed by LaNi s. J. inorg, nucl. Chem. 36, 461-465 (1974). G. V. Lisichkin and K. V. Semenenko, Transition metal hydrides in catalysis. Inorg. Mater. 14, 1585-1591 (1978). V. V. Lunin, Kh. N. Askhabova and B. V. Romanovsky, New method of catalytic reactions. Doklady Akad. Nauk SSSR 250, 896-898 (1980). W. Conner, G. M. Pajonk and S. J. Feicher, Spillover of sorbed species. Adv. Catal. 34, 1-79 (1986). V. V. Solovey, V. V. Popov, A. V. Basteev and L. A. Nechiporenko, Some peculiarities of near surface processes of hydrogen interaction with hydride forming materials, in High Purity Hydrogen-Production and Utilization, pp. 33-34. Inf. Mater. Sverdlovsk, Izd. Ur. O Akad. Sci. USSR (1989). V. V. Popov and A. M. Prognimak, Diagnostic methods of excited nonequilibrium hydrogen states formed at metal hydride decomposition. Preprint-319, Ukrainian Acad. Sci. for Problems in Machinery, Kharkov (1990). A. N. Podgorny, A. V. Basteev, M. A. Obolensky and Kh. B. Chashka, Hydrogen accumulation by niobium diselenide. Doklady Akad. Nauk Ukraine, Set. A, pp. 72-74 (1983). L. M. Kulikov, L. G. Akserrud, A. G. Semenov-Kobzar' and M. M. Antonova, Structure transition of the 2H TaS 2 2H-MoS 2 type at hydrogen intercalation 2H-NbSe z. lnorg. Mater. 27, 1186 1189 (1991). A. Schutte, D. Bassi, F. Tommasini, A. Turelli and L. S. F. Hermans, Recombination of atomic hydrogen on low temperature surface. J. Chem. Phys. 64, 4135 4142 (1976). G. D. Kubiak, G. O. Sitz and R. N. Zure, Recombinative desorption on nonequilibrium vibrational distributions. J. Chem. Phys. 81, 6397 6398 (1984). G. Comsa and R. David, The purely "fast" distribution of H E and D 2 molecules desorbing from Cu(100) and Cu(111) surfaces. Surf. Sci. 117, 77-84 (1982). J. H. McCreery and G. Wolken, Atomic recombination dynamics on a solid surface I-t2 + W(001). J. Chem. Phys. 64, 2845-2853 (1976). J. H. McCreery and G. Wolken, Atomic recombination desorption on solid surfaces: effect of various potentials. J. Chem. Phys. 67, 2551-2559 (1977).

EFFECT OF METAL HYDRIDE ACTIVATION 32. A. A. Vasilyev, V. N. Lisitsky and G. G. Savelyev, The recoil effect at atomic recombination on a solid surface. Surf. Phys., Chem., Mech., No. 4, 29-32 (1988). 33. P. S. Rudman, Enthalpy of metal-hydrogen systems. A pairbond model. Electron structure and properties of hydrogen metals. NATO Int. Symp., pp. 49 54, Richmond, VA (1983). 34. I. M. Svoren', To the question of hydrogen saturation of solids. Phys. Chem. Mech. Mater. 16, 7-12 (1980). 35. V. A. Shoshenkova, V. K. Solnyshkova, S. A. Ryabinina and A. M. Sokolskaya, On hydrogen adsorption on rhodium catalysts, in Catalytic Hydrogenation and Oxidation (Heterogeneous and Homogeneous Catalysis), pp. 66-70. Nauka Kaz.SSR, Alma-Ata (1975). 36. C. H. Bachman and P. A. Silberg, Thermoionic ions from hydrogen palladium. J. appl. Phys. 29, 2641-2643 (1958). 37. I.N. Savvin, I. A. Myasnikov and M. E. Lobashina, Nonsta-

38. 39. 40. 41.

599

tionary emission of hydrogen atoms from the surface of metal layers deposited on glass in the presence of molecular hydrogen. Zhurn. Fis. Khim. 49, 2641-2643 (1985). Krylov, I. V. New aspects of electron and ion exoemission in studies of surface chemistry, physics and mechanics. Surf. Phys., Chem., Mech. No. 1, 5 26 (1988). G. Alefeld and I. Felkl (Eds), Hydrogen in Metals, Vol. 2 Mir, Moscow (1981). B. V. Deryagin, V. A. Kluyev, A. G. Lipson and Yu. P. Toporov, On possible nuclear reactions at failure of solids. Colloid. Zhurnal 48, 12-14 (1986). A. N. Podgorny, V. V. Solovey, M. V. Lototsky and S. Valuiskaja, Hydrogen activation in hydrogen-intermetallic hydride systems. V A N T Ser. Atomic hydrogen power and engineering, No. 1, pp. 68 72 (1987).