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9Hydrogen storage
INFLUENCE OF THE COMPOSITION COMPONENTS AND STRUCTURAL CRITERIA ON HYDROGEN PERMEABILITY OF GLASS
E. F. Medvedev
Russian Federal Nuclear Centre — All-Russian Research Institute (RFNC-VNIIEF), 37 Mira pr., Sarov, Nizhniy Novgorod Region, 607188, Russia Phone: (83130) 4-56-46, e-mail: medvedev@otd13.vniief.ru
Containers from various materials are used for hydrogen storage. Glass is one of these materials. The compositions for these glasses are most often chosen in the system of R2O-RO-B2O3-SiO2 (where R2O — Li2O, Na2O, K2O; RO — MgO, CaO) according to the required strength properties [1]. The influence of composition and the structural criteria Kr of glasses on the hydrogen permeability has not been studied in sufficient detail and there is no procedure for the calculation of compositions with the account of this property. One should note that 83 chemical elements of 109 are used in the glass production process, therefore, it is practically impossible to take into account all probable combinations in the design of compositions.
This research is a continuation of previously started investigation of the hydrogen permeability from the point of view of chemical glass processing. In this work, an attempt has been made to study the influence of the composition components and structural criteria on the hydrogen permeability.
The analysis of information sources has shown that the authors, as a rule, consider the hydrogen permeability of glass without accounting for the composition and structure, which is not logical from the point of view of a material science specialist. In glass processing, for the understanding of the permeability behaviour tendency, one can use the equation proposed by the authors of Ref. [1] but with the account of drawbacks noted in [2]:
KH=8.110-14exp[-(1/T)(17330-127.8C)], where KH is the hydrogen permeability coefficient, molem/ (m2 s Pa); C is the content of SiO2+B2O3+P2O5, mole %.
As structural criteria of the sodium-silicate system glasses, in which the basic glass-forming component is SiO2, and the modifier is Na2O, the silicate module nSi and the structure connectivity factor Y are considered; the excess coefficient K of the modifier content in the compositions stud-
exc 1
ied has been calculated (altogether N=89 [1, 2]). As a result of correlation and regression analysis, a close connection has been established between the K and K coefficients;
H exc '
the coefficient KH and the factor Y; the factor Y and the coefficient Kexc; as well as a priority influence of the modulus on the coefficients K„, K and the factor Y. With the account of
H exc
the above, the nomogram lgKrm-lgKexc-N (see the Figure below) has been plotted. In subarrays (the glass groups to the left and to the right from the dotted line) at the constant content of intermediate components, the permeability reduction can be caused by a 1.5 times difference between the contents of modifiers and glass-forming elements; however a double difference will already enhance the glass permeability. At the same time, with retaining the ratios of the contents of modifiers and glass-forming elements in subarrays, the dif-
ference in the content of intermediate oxides will considerably increase the permeability, due to their capability to take part in formation of the structural lattice of glass at a sufficient oxygen concentration in the system.
So the designing of glass compositions for the manufacture of hydrogen storage cylinders should be preceded by the analysis of relations between the components and the structural criteria assumed. This will allow one to design a permeability change model, reveal significant factors, optimise compositions, decrease the uncertainty factor and reduce unjustifiable labour hours and material consumption to the minimum taking into account unlimited possibilities for
Fig. 1. Nomogram of lgKr^-lgK^—N: m — lgKit lgns{ IgY; GF are glass-forming elements, MOD are the modifiers, INT are the intermediate components; «left» subarray Cmod:Cgf:Cinj=1.45:1.84:0.07~20:30:1; ««right»subarray CMODf CGF, Cint=1.14:1.90:0.48~2:4:1; subscripts: l— to the left, r — to the right from the vertical line;
C,
C,
MOD,r 1.14 :L45
= 1
C
GF л 1.90
MOD,I
C
GF,n
1.
= 1,
C
C
int r 0.48 : 0.07
= 7,
INT ,I
K
H ,r 3 10-
K
H ,l
2 10-
- = 150
the combination of substances being available with a chemical technologist.
References
1. Tsugawa P. T., Moem J., Roberts P. E., Souers P. G. Permeation of helium and hydrogen from glass-microsphere laser targets//J.Applied Physics. - 1976. - V. 47, N 5. -P. 1987-1993.
2. Медведев E. Ф. Выбор структурных параметров при проектировании химических составов стеклянных микросфер//Стекло и керамика. - 2001. - № 7. - С. 8-11.
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ISJAEE Special issue (2003)
