Characterization of Evaporating Species from B 2 O 3 , B 6 O, and Their Mixtures by Knudsen Cell Mass Spectrometry
- PDF / 819,768 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 45 Downloads / 168 Views
INTRODUCTION
BORON (B) is widely used in the forms of borides and borate glass. Because the materials degrade during exposure to high temperatures, it is necessary to understand quantitatively the oxidative evaporation of boron, or volatilization of the glass in vacuum. Additionally, semiconductors (e.g., B-doped silicon) and neodymium magnets (Nd2Fe14B) are important applications of boron. Thermodynamic information on boron compounds is essential to develop processes for the manufacture of these functional materials and for recycling valuable elements after use. Under oxidizing conditions, the species evaporating most predominantly from B2O3(l) is B2O3(g).[1] B2O2(g) is prominent under reducing conditions, as confirmed by mass spectrometry on a mixture of B and B2O3.[1–3] On the other hand, boron suboxide (B6O) has attracted attention as a hard material, and its thermodynamic property has been studied.[4–7] Figure 1 is a tentative phase diagram of the B-O binary system drawn in Reference 7. Experimental observations of B6O at high temperature, however, are limited. This study used multiple Knudsen cell mass spectrometry[8] in an attempt to provide some information about species which evaporate from B6O or a mixture of B6O and B2O3.
HIDEAKI SASAKI, Research Associate, and MASAFUMI MAEDA, Professor, are with the International Research Center for Sustainable Materials, Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. Contact e-mail: [email protected] YOSHIFUMI KOBASHI, formerly Graduate Student with the Department of Materials Engineering, The University of Tokyo, Tokyo, Japan, is now with West Japan Works, JFE Steel Corporation, Kawasakidori 1-chome, Mizushima, Kurashiki, Okayama 712-8511, Japan. Manuscript submitted May 20, 2015. Article published online October 13, 2015. 390—VOLUME 47B, FEBRUARY 2016
II.
EXPERIMENTAL
A. Sample Preparation Boron suboxide (B6O) was synthesized using an example from Reference 9. Starting materials were amorphous B (95 pct, Wako Pure Chemical Industries, Ltd.) and B2O3 powder (Kanto Chemical Co., Inc.), which was dehydrated at ca. 673 K (400 °C) before use. One gram of B was mixed with 0.42 g of B2O3, and 1 g of the mixture was heated in an Al2O3 crucible at 1573 K (1300 °C) under Ar flow for 5 hours. Calculated from the weight of the initial mixture, the mole fraction of B, xB, of the starting materials was 0.853, which was smaller than B6O (xB = 0.857). B. Apparatus and Procedure The multiple Knudsen cell mass spectrometer used in this study was explained in detail elsewhere.[10] Figure 2 shows schematic illustrations of the apparatus and samples contained in the cells. Up to 4 Knudsen cells are placed in a cell holder, and the chamber is evacuated by rotary and turbo molecular pumps. The cells are heated by a tantalum heating element, and the temperature is monitored by thermocouples placed in the cell holder. Gas species effusing from an orifice are ionized and detected as ion currents sorted by a mass-to-charge rati
Data Loading...
