Phase Diagram of the Binary System of Barium and Sodium n-Butanoates T. A. Mirnaya, A. P. Polishchuk, and Y. V. Bereznitski V. Vernadski Institute of General and Inorganic Chemistry of the Ukrainian Academy of Sciences, 32-34 Prospekt Palladina, Kiev 252680, Ukraine P. Ferloni* Dipartimento di Chimica Fisica and CSTE-CNR, Universita ` di Pavia, Viale Taramelli 16, I-27100 Pavia, Italy The phase diagram of the binary system of barium and sodium n-butanoates has been studied by differential thermal analysis, hot stage polarization microscopy, and small angle X-ray diffraction. Pure barium n-butanoate exhibits a complicated thermal behavior: it melts at 519 K, then immediately solidifies, and remelts at a higher temperature (589 K). The addition of a second component like sodium n-butanoate stabilizes the liquid which appears with the first melting of barium n-butanoate. This melt exists up to the temperature of the second melting, which may be called the clearing point because this liquid has been found to be slightly anisotropic and to have local bilayer smectic order. The temperature and concentration ranges of formation of the liquid crystalline smectic A solutions has been established. These liquid crystalline solutions are formed as a result of the eutectic reaction at 425 K. In this binary system, glass formation has been discovered in the composition range 0 to 70 mol % of Na n-butanoate. Introduction Phase diagrams of binary systems of metal alkanoates are known to be fairly complicated due to the strong interaction between the components which often leads to the formation of different stable and metastable solid and/ or liquid crystalline phases (Franzosini, 1988). From the group of metal alkanoate binaries with a common short- chain anion, only the systems formed with alkali metals are described in the literature (Mirnaya et al., 1990, 1993, 1995a,b). There are no data on phase diagrams of binaries from alkanoates with asymmetrically charged metal cat- ions, such as, for example, alkanoates of alkali and alkali- earth metals. But these systems may be very interesting and useful, due to the possibility of the formation of smectic ordered glasses with valuable physical and optical proper- ties (Mirnaya et al., 1989). In the present work the phase diagram of the binary system of the mesogenic barium and sodium n-butanoates has been studied in order to determine the temperature and concentration ranges of the liquid crystal region and of glass formation. It is known (Ferloni et al., 1976) that pure barium n-butanoate easily forms a glass upon cooling the liquid phase. Moreover it was found that it exhibits a very specific and strange thermal behavior, because on heating it undergoes a solid-to-solid transformation at 434 K, it melts at 520 K, and then immediately recrystallizes into a new solid phase which in turn remelts at 586 K (Ferloni et al., 1976). Similar sequences of melting, solidifying, and remelting at a higher temperature were reported previously (Findlay, 1951). In connection with such behavior it is very interesting to study the effect of the addition of a second component on the phase transitions in the mixtures. Experimental Section Barium and sodium n-butanoates were prepared accord- ing to the method described in a previous work (Mirnaya et al., 1993). Both salts were free from any water and acid, as evidenced by their IR spectra. The binary mixtures were prepared by melting known masses of the components under argon and then recrystallizing them at 353 K during several hours or days, if it was needed. The extent of crystallinity was determined by means of X-ray diffraction. Samples were stored in argon before the measurements. The phase diagram was investigated by means of both polythermal polarization microscopy and differential ther- mal analysis (DTA). A Paulik-Paulik-Erdey derivato- graph (Q-1500 D) with R-Al 2 O 3 powder as the reference substance was used to obtain thermograms on heating, the heating rates being 2.5 K min -1 . The temperature was measured with a precision of (1 K. A polarization microscope “Amplival” with a “Boe ¨mius” hot stage was used to identify mesophases and isotropic liquid phases, thus determining the temperatures of the isotropic melt-mesophase and isotropic-crystal transi- tions. Small angle X-ray diffraction measurements were used in some cases to estimate bilayer spacings and to prove the formation of mesophases such as smectic liquid crystals or locally ordered melts. A special device AMUR (Ni- filtered Cu KR radiation) was used for these purposes. The temperatures of the phase transitions for the pure salts synthesized in our laboratory were in good agreement (about (1 K) with the literature data (Ferloni et al., 1976; Franzosini, 1988). Sodium n-butanoate displays three main solid-solid transitions at 450, 499, and 508 K, melts at 527 K with formation of a smectic A mesophase, and then clears at 597 K. Barium n-butanoate undergoes a solid-to-solid phase transition at 434 K and exhibits melt- ing at 519 K, forming a liquid or a mesophase. This first melting is followed by immediate recrystallization, and this solid phase melts at 589 K with formation of an optically isotropic viscous liquid. The latter value is 3 K higher than that found in the mentioned work (Ferloni et al., 1976). * Author for correspondence. E-mail: ferloni@chifis.unipv.it. 1337 J. Chem. Eng. Data 1996, 41, 1337-1339 S0021-9568(96)00109-4 CCC: $12.00 © 1996 American Chemical Society