Technological Sciences
CHENG Yongjun
Cheng Yongjun, was born in Huining, Gansu province on April 18, 1975. He graduted from Northwest Polytechnical University in 1998. Since 1998, he has been working in Lanzhou Institute of Physics. In 2008, he become a senior engineer. Now he is deputy director of the Laboratory of vacuum metrology, Lanzhou Institute of Physics, and deputy director of vacuum metrology centre, Science technology industry. At present, he was elected as a member of vacuum metrology professional institute, Chinese Society for Measurement, and he also become a metrology examinator.
His research was mainly focus on the the area of vacuum metrology. He has developed many vacuum metrology standards, such as the first UHV/XHV standard apparatus, pressure leak standard apparatus with constant pressure method, very low range gas flow measurement standard apparatus, and a new generation static expansion vacuum primary standard apparatus. With these standard apparatus development, the system of vacuum value transmission will further be improved. Now he has obtained 15 national invention patent authorization, published about 60 scientific research papers, and obtained Scientific and Technological Progress Award, first class, Technology Invention Award, second class.
Applications of non evaporable getter in extension the lower limit of vacuum standard
Due to the outgassing effect of inner surface of calibration chamber, the extension of lower limit of vacuum standard is limited. In order to reduce the impact of the outgassing effect , the popular measures are to polish the inner surface of the vacuum chamber and the use of high temperature bakeout. But the two methods do not completely eliminate the impact of the outgassing effect. Therefore, the extension of lower limit for vacuum standard continues to be a challenging work.
Non Evaporable Getter (NEG) have two remarkable characteristics , one is the large pumping speeds for active gases, especially for H2 at ambient temperature and the other is no pumping speed for inert gases. So in static expansion vacuum standard, NEG can eliminate the outgassing influence and maintain ultra-high vacuum background without changing gas quantity in the calibration chamber when inert gas is used as test gas, which makes the standard pressure accurately calculable by Boyle-law.The lower limit of the static expansion vacuum standard can be extended to 10-7Pa by using the NEG when an inert gas is used as the test gas. This method provides a new idea for the investigation of the static expansion vacuum standard.
In UHV/XHV standard, because NEG has no pumping speed for inert gas, it not only maintains the XHV background, but also not changes the effective pumping speed to the XHV calibration chamber when inert gas is used as a test gas, thereby enabling the standard pressure to be accurately calculated by dynamic flow method. The lower limit of the UHV/XHV standard can be extended to 10-10 Pa by using the NEG when an inert gas is used as the test gas.