Hydrogen, nitrogen, and oxygen behavior in boron
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Some of the problems of hydrogen, nitrogen, and oxygen behavior in boron, which is a promising material for the development of sensitive elements in gas sensors of improved radiation resistance, were studied. Using gas and thermal gravimetric analysis methods the interaction of these gases with boron was investigated, and the influence of temperature and annealing on the sorptivity of boron, the interaction of disperse boron powder with the environment, and thermal gas release from boron and boron-containing materials were studied.
I. INTRODUCTION Development of semiconductor and ceramics based sensing elements for electronic measuring transducers and sensors is of great importance today.1"3 One problem of the sensing element materials is that of determining the qualitative characteristics of gas sensors of both resistive and MIS type; their efficiency depends on the physico-chemical and electrophysical properties of sensing elements.4 Boron, together with other semiconductor materials used for sensing element development for gas impurity sensors, is a rather promising material. Boron is a widerange high-temperature semiconductor with a prohibited energy zone of about 1.5 eV. High heat resistance and the possibility to change the isotope content from 10B to n B in almost every concentration range provide possibilities to improve the radiation resistance of the boron-based gas impurity sensors.5'6 The present study on hydrogen, nitrogen, and oxygen impurities in amorphous and crystalline boron samples provides important information on their adsorption and separation kinetics. II. EXPERIMENTAL RESULTS AND DISCUSSION To learn more about the character of the interactions of hydrogen, nitrogen, and oxygen gas with boron samples the following experiments were performed. One gram samples of boron powder (with mean particle size of 1 fxm) were dried in air at 470 K for 1 h, and their mass change in time was estimated during cooling after the amorphous and crystalline boron powder drying; identical samples were measured in silica gel-filled containers (Fig. 1). Mass increase of the amorphous and crystalline boron powder due to gas adsorption from the air was 1.1-1.2 and 0.6-0.7 mass %, respectively. Note that desorption and adsorption processes during the powder drying and cooling were reversible within the weighing accuracy limits. To decrease adsorption, weighted bottles with the boron powder were placed in the containers filled with silica gel. Under these 1822 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 7, Jul 1992 Downloaded: 18 Mar 2015
T FIG. 1. Time dependence of mass change for boron powders: amorphous (1), crystalline (2), and amorphous and crystalline in containers with silica gel (3).
conditions the weight change of the amorphous and crystalline boron powder is the same within the experimental accuracy limits, i.e., 0.18 mass %. To study the interaction of boron with the environment, disperse powders were used which were obtained by potassium tetrafluoroborate electrolysis (sample 1), diborane
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