Studies in the system BaO–Al₂O₃–SiO₂ III. The binary system sanbornite–eelsian

Abstract

SUMMARY. The system sanbornite-celsian has been investigated by the quenching method, and the results compared with earlier studies. The system is essentially a simple binary eutectic system with little or no solid solution. The eutectic is located at a composition of 69 % sanbornite and 3I % celsian (by weight) and at a temperature of IZ27~ 3 ~ No evidence for substantial solid solution of celsian in sanbornite, as reported in previous work, was found. Paracelsian, a naturally occurring polymorph of celsian, was not encountered in the study.THE compound BaSi205 occurs in nature as the rare mineral, sanbornite. The compound BaAlzSi~Os is the principal component of the barium-feldspar, celsian. Both compounds are important constituents of synthetic products, including fluorescent phosphors, barium crown glasses, electrical porcelains, refractories, and so-called glass-ceramics. Their phase relations with each other, as well as with other compounds in the BaO-A12Oa-SiO2 system, are thus of considerable mineralogical and technological interest. This study is the third of a series included in a comprehensive reinvestigation of the BaO-A1203-SiO ~ system. Previous reports in the series dealt with the polymorphism of celsian (Lin and Foster, 1968) and the binary system celsiansilica (Foster and Lin, i969).Previous work. Bowen (I918) determined the melting point of pure BaSi205 as I426 ~ Rogers (1932) believed that the polysynthetic twinning of natural sanbornite indicated polymorphism. Klasens, Hoekstra, and Cox (1957) and Roth and Levin (1959) detected an inversion in synthetic sanbornite at about 135o ~ Lin and Foster (1968) reviewed the latest findings on the melting and polymorphism of pure synthetic celsian. They selected 176o ~ as the melting temperature of hexacelsian, and 159 ~ ~ as the inversion temperature of celsian to hexacelsian.The system sanbornite-celsian has not previously been systematically studied. It was included however, in several general investigations of the BaO-A120~-SiO ~ system (Thomas, 195o; Toropov, Galakhov, and Bondar, 1954, I955). That by Thomas presented a theoretically possible diagram for the system, based on limited experimental data. Toropov and his co-workers (1955) gave no direct plot for the sanbornite-celsian join. However, their traverses in the ternary system at SiO2-1evels of 36, 39, and 42 % permit the deduction of a sanbornite-celsian diagram that closely resembles that of Thomas. The approximate relations deduced from these previous Present address:

Phase Equilibria in the BaO-SiO₂-Al₂O₃ Ternary System at 1500 °C

“…Due to the initial materials, there occur two high-temperature modifications of celsian whose differences are attributed to different Si/Al distribution.The problem of synthesis of BaO•Al 2 O 3 •2SiO 2 was also discussed. The polymorphism of celsian was also confirmed by Lin et al [11] based on the prolonged anhydrous and hydrothermal heating experiments made with natural and synthetic materials. It follows the polymorphic relations: monoclinic celsian is stable from room temperature up to 1590 °C and inverts to hexacelsian with the melting point of 1760 °C.…”

“…A simple eutectic point is shown to exist at 1311±4°C between the two end-members. Using the same method as in the previous work [12], Lin et al [13] investigated the BaSi 2 O 5 (sanbornite) -BaAl 2 Si 2 O 8 (celsian) system and compared the results with early studies. This sub-system is a binary eutectic system with the invariant point at 1227±3°C and 31 wt% celsian.In the work by Semler et al [14], the quenched samples in the two joins, BaAl 2 Si 2 O 8 -Al 2 O 3 and BaAl 2 Si 2 O 8 -Al 6 Si 2 O 13 (mullite), were analyzed by X-ray diffraction and petrographic microscopy.…”

Synthesis and characterization of Celsian by solid‐state reaction process from mullite

“…F I G U R E 6 X-ray diffraction (XRD) patterns of specimens at different heat treatment temperatures for 3 h. (10), and (11), which are accelerated both thermodynamically and kinetically with the increase of temperature, leading to further reactions of BS and B 2 S with SiO 2 and Al 6 Si 2 O 13 , resulting in the formation of a large number of BAS(H) and Ba 2 Si 3 O 8 , and the strength of the sample increased in this temperature range. Sintering occurred, which coincide with the previously speculated results.…”

“…8 Among them, the Celsian phase is a stable phase below 1590 • C, shows a low thermal expansion coefficient of ∼2.3 × 10 −6 / • C, 4 good thermal shock resistance and thermal stability, and has a strong versatility, 9 and is a very good matrix for ceramic composites of high-temperature materials, 4 as well as protective coatings. 10 The Hexacelsian phase, existing stably in the temperature range of 1590-1760 • C, 11 shows a high expansion coefficient of ∼8.0 × 10 −6 / • C 4 and it will reversibly transform to the orthorhombic polymorph around 300 • C, causing a ∼3% volume change, resulting in the formation of microcracks inevitably. 8,12 Therefore, when use as structural materials or composite matrix, it is generally desired to make ceramic materials with Celsian as the main crystalline phase.…”

The oxidative transformation of solid, barium-metal-bearing precursors into monolithic celsian with a retention of shape, dimensions, and relative density

“…The opposite is true for non-AE elements, such as Al and Si. Since the range of cation nonstoichiometry reported for pure monoclinic celsian is quite narrow, [8][9][10][11][12][13][14][15] significant deviations from the desired stoichiometry would have produced appreciable amounts of secondary phases. This net volume change can be further reduced by replacing some of the elemental species with oxides.…”