</•/.//•".' DedicAted to the centenary of the Luginin's tHerttGcHanlcal tabor-atom oP Moscow St*ta UnfverHtg International Synpaslun an Calortnetra and Ctieniual ThornadyiMitii» June 33-38, 1991, noseow, USSR ABSTRACTS Dedicated to tke centenary ef the Luginiii's tHernoohanlcftl l«bar*tor* of ПОБВОИ Stata *nlvar»tt«i International SyMpasiuM MI C*lorinetra. «ml Cbaninal ИмгатАцмиИав June 83 - 3Bf 1991t Некоей• USSR ABSTRACTS Печатаетоя по решение оргкомитета международного симпо­ зиума по термохимии и термодинамике Оформление литературно-иэдатехьокое агенто!о Pi Злинина 1 CHEMICAL THERMODYNAMICS IN THE FUTURE DEVELOPMENT OF CHEMISTRY INCLUDING ENVIRONMENTAL PROBLEMS Leo Brewer Department of Chemistry, University of California, and Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA. High-temperature science will be facing unusual challenges in the decade ahead. New technological advances are requiring new materials with unusual properties that will either be prepared by high-temperature techniques or will need to have long-term stability at high temperatures in various environments. One of the major driving forces for new materials arises from the increasing public concern about environmental pollution. Equipment using volatile fluids that can survive up to the stratosphere and destroy the ozone will have to be replaced. Processes that emit sulfur oxides win have to be modified to reduce sulfur emission to very low values. The efficiency of solar energy devices wilt have to be improved and nuclear power plants win have to be designed to make serious accidents extremely unlikely so that energy production by combustion to carbon dioxide is greatly reduced. Many other examples can be given of the need for new materials. The possible combinations of the elements are enormous. The problems cannot be solved by trial and error procedures. Practical predictive models must be developed to narrow down the range of materials that might have the desired products. Examples of possible models win be discussed. 4 THERMODYNAMIC STUDY OF ICE AND CLATHRATE HYDRATES H. Suga Department of Chemistry and Microcalorimetry Research Center, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan Discovery of glassy crystals leads us to recognize that the glass transition is not the characteristic property of liquids but just one example of freezing-in processes of disordered systems which must occur widely in condensed systems including crystals. Ice provides a good example of disordered crystal. Water molecule in the lattice can have six orientations under constraint of the ice conditions. The heat capacity anomaly observed around 100 К in pure ice was explained in terms of freezing out of reorientational motion of water molecules in the lattice before the crystal reaches a hypothetical transition temperature. Following the suggestion of Onsager, we have tried to do heat capacity measurements on ice specimens doped with various kinds of impurity which might hopeful3.y accelerate the reorientational motion of water molecules by relaxing the ice conditions constraining the motion in the lattice. Among others, alkali hydroxides were found to be highly effective in inducing a long-awaited ordering transition. The transition took place at 72 К with latent heat effect. The associated entropy change depended on the amount of dopant. Maximum entropy change 2.3 JK-^mol-^ was obtained for the sample doped with KOH in 1.3xlO~3 mole fraction and annealed for 3 days around 65 К. A neutron diffraction experiment showed that the low temperature phase is orthorhombic with the protons polarized in a ferroelectric way along the c-axis of the original hexagonal lattice. The name ice XI was given to the proton-ordered ice under atmospheric pressure. The same technique was applied to clathrate hydrate crystals which are composed of several types of Archimedes' polyhedra made of water molecules through hydrogen bonding with guest molecules enclathrated in the polyhedral cages. Many literatures show that both the water and guest molecules are in orientationally disordered state. Dynamic disorder of the guest is known in some cases to persist down to tempe­ ratures as low as 30 K. Tetrahydrofuran (THF) forms type II clathrate hydrate of the cubic structure with formula THF.17H20. Previous heat capacity measurement did not show any anomalous behavior. Our remea- surement clarified the existence of a glass transition around 85 К in" the pure specimen. This indicates that reorientational motion of the host water molecules freezes out at 85 К in a similar way to that of ice around 100 K. A THF clathrate hydrate specimen doped with KOH in 10~4 mole fraction exhibited a first-order transition at 62 К with the associated entropy change of 40.12 JK-1mol"l. If the magnitude is re­ duced to 1 mole of water, the corresponding value is close to that of hexagonal ice. Our dielectric study showed that the real part of permittivity became small in magnitude corresponding to e„of the crystal just below 62 K. This means that the quest molecules become ordered concomitant­ ly with the ordering of the host molecules. The ordering of water molecules will produce a strong electric field at the guest site suf­ ficiently enough to align the guest molecules. Thus the electrostatic interaction between the host and guffst molecules will play an impor­ tant role In inducing the ordering transition in the clathrate hyd­ rates. In this way, we can continue the study of ordering phenomena in the hydrates enclathrating guest molecules with various magnitudes Of dipole moment in order to examine a relation between the polarity of the guest molecule and transition temperature. s THEP.HOGHEHICAL DATABASE .. PAST AND PRESENT Donald D. Wagman Measurements of the therBiochemical and thermodynamic proper­ ties of many substances and chemical reactioris were begun follo­ wing the establishment of the first two laws of thermodynamics in the middle of the nineteenth century. This soon made it desirable to bring together in one place a sum­ mary of the current state of knowleadge with respect to these da­ ta. These summaries , thermodynamic databases* have taken many different forms and cover a number of different properties . Ыв review here same of the most significant ones ( from a thermoche- mical standpoint ), starting with the compilation by Jul is Thorn- sen, which appeared in 1BB2-B6, and extending up to such recent efforts as represented by the DIPPR project of the American Insti­ tute of Chemical Engineers and by IVTAN, the program .sponsored by the Institute of High Temperatures of Academy of Sciences,U.S.S.R. 6 THERMODYNAMICS OF HIGH-TEMPERATURE SUPERCONDUCTING MATERIALS G.F.Voronin Chemistry Department,Moscow State University, 119899,Moscow,USSR Two thermodynamic aspects of superconductivity have recently attracted great interest. One of them concerns the equilibria al superconducting transition and properties of coexistent phases in magnetic fields. This way leads to many important common relations between macroscopic properties of substances, and allows to check whether in point theoretical model of the superconductivity is correct or not. Another direction does not relate to the special superconducting properties of substances at all. The thermodynamic methods are applied to them as to any other substance for determination of phase composition, for prediction of material stability in different environment to be affected by atmosphere, covers, targets etc. In such a case they have to deal with the usual problems of chemical thermodynamics, but are complicated because of existence of many components and phases in high-temperature superconducting systems. Serious difficulties in experimental investigation of the systems under consideration consist in slow relaxation especially with regard to diffusion of cations in phases and high chemical reacti­ vity of new superconductors. This lecture deals with results of both theoretical and expe­ rimental thermodynamic researches of systems with superconducting phases. The thermodynamic data were obtained more or less complete only for the Y-Ba-Cu-0 system in a solid state. At present there is a few fragmentary knowledge for the other systems with high- temperature superconductors. For the YBa2Cu30e+z(0<z<l) sold solution with superconducting transition bellow 92K there are for, example, about one thousand experimental data points from more then 30 publications. These data were obtained by virtue of different methods. In general, many of them are consistent with one another. To obtain an adequate representation of all available data on thermodynamic and structural properties of the mentioned phase, a thermodynamic model has been developed. The thermodynamic functions of almost all other phases in the Y-Ba-Cu-0 system were assessed also based on the experimental data and the theoretical models. As a result, the phase equilibria for superconductors such as YBa2Cu306+z(or '123'), Y2Ba4Cu7014+z('247') and YBa2Cu408t'124') were calculated. At this point emphasis is placed on the problem of the thermodynamic stability of. superconductors. For one below in fig. the phase diagram with stability field of '123* solid solution is shown 111. As seen in the fig.,'123' is thermodynamically stable only in the cross-hatched field limited by the bold lines. Al tempe­ rature and composition outside this field, the '123' decomposes into other phases according to the reactions mentioned in fig. caption. But when the nucleation and growth of phases with cation stolchio- metry other than '123' is kinetically suppressed, '123' phase may exist for any long time as a metastable phase. Similar diagrams were calculated for the other superconductors in this system. They are helpful for synthesis and application of superior superconducting materials. REFERENCES 1) G.F.Voronin, S.A.Degterjpv, Yu.Ya Skolis. Proc. 3rd German-Soviet Bilateral Seminar on High-Temperature Superconductivity. October 8- 12, 1990. Karlsruhe.P.862-569. 7 z in УВа2СизОб+г Fig. Stability field of the «123' phase. Thin solid lines represent temperature dependence of equilibrium composition at fixed oxygen pressure.