National Institute of Advanced Industrial Science and Technology1, Temson Inc.2, Tem-Tech Lab. 3 ○Takashi Hiraga1, Jubee Aizawa2, Kouhei Kawamura2, Noritaka Yamamoto1, Toshiko Mizokuro1, Mineyuki Hattori1, Nobutaka Tanigaki1, Yoshinori Kawamura3, Mituyoshi G.Aizawa3
hiraga-t@aist.go.jp1
1. Introduction
Pressure measurement between 105 Pa (~100 Torr) and 10-2 Pa (~10-4 Torr) is important for industrial use. However, it is difficult to measure these wide ranges of pressure by single manometer. A capacitance manometer made of metal diaphragm is commonly used between 105 Pa and 10-2 Pa. At higher temperature over 100 degrees, however, a metal diaphragm exhibits large hysteresis by changing temperature, which makes large discrepancy between real pressure and measured value. A newly developed capacitance manometer made of sapphire diaphragm composed of single-crystalline sapphire achieves ultra-high accuracy and repeatability against temperature changing.1, 2)
Here, we have applied this excellent sapphire manometer for measurement of vapor pressure of organic materials with wide ranges between room temperature and about 200 degrees.3)
2. Experimental setup
A capacitance manometer using sapphire diaphragm developed by Temson Inc. is employed for present experiment.1) Two thin sapphire plates with vacuum deposited Cr electrode are hot-pressed under high-vacuum forming a capacitor with tiny volume (Fig. 1). This diaphragm of capacitor is set in a crucible made by Alloy 42 as thermal expansion matching metal for sapphire (Fig. 2).
Two sapphire manometers of almost the same characteristics are located at each chamber of measuring and reference, respectively. Each manometer is separated by a valve from an ultra-high vacuum system forming a vacuum chamber with small volume. The measuring chamber has a sample holder with cooling jacket for recovery of the sample, and as working also a loading port of the sample. These two manometers are set in a temperature-controlled housing heated by a blower and heater unit (Fig. 3). Temperature of crucible is detected by a thermocouple (CA).
3. Results and Discussion
For calibration of the apparatus, a commercial Pyrene (Wako Pure Chemical Industries, Ltd.) is used without further purification. Obtained vapor pressure at 160 degrees is 313 Pa, which is about two-times larger than the reported value (133.3 Pa).4) Usually, a commercial reagent includes some kind of solvent, obtained vapor pressure is summation of both vapor pressure of Pyrene and gaseous residues in Pyrene crystal. Some kind of degas processing for gaseous residues will be needed using the apparatus.
References
1) Method and Apparatus for a direct bonded pressure sensor. I.P.N; WO 01/50104 A2,
Rosemount Inc. MN. USA, 6 January 2000
2) M. Aizawa et al. Japanese patent; No.3681728, 5 May 2005
3) T. Hiraga et al., Japanese patent; 2007-275766
4) T. E. Jordan: “Vapor Pressure of Organic Compounds” Interscience(1954)