基于扩散放气模型的杜瓦真空寿命分析

Influence of Diffusion Out-Gassing on Life-Time of Dewar Vessels

杜瓦真空夹层材料会漏、放气,夹层材料的放气是影响真空寿命的主要因素。材料出气会缩短真空寿命,或者使器件性能下降。在杜瓦制作的排气工艺中,需要更高一些的烘烤温度,或者持续更长的烘烤时间。制定合适的排气工艺就需要了解放气率和温度、时间的函数关系。基于扩散理论,建立起材料的放气模型。使用出气模型分析杜瓦夹层材料放气特性,并借用Sofradir公司提供的数据作参考,对计算公式做标定。根据理论分析,杜瓦夹层材料的出气特性满足加速方程K=exp[(1/T1-1/T2)E/R]。根据Sofradir公司提供的数据计算得E/R=7007.72,即每提高10℃的温度,放气加速因子近似为2。应用扩散模型的分析结果,安排烘烤出气实验累积国产杜瓦产品的真空寿命数据。杜瓦置于80℃的恒定温度下持续15天的烘烤,四级质谱仪被用于分析两周内每天的气体变化情况。

The impacts of the leakage and out-gassing of vacuum insulation wails,made of a variety of materials,on the life-time of Dewar vessel were physically modeled, empirically approximated, and analytically calculated to compromise the baking temperature, backing time, and fabrication cost in industrial production. The out-gassing characteristics of the vacuum insulation wall materials were supposed to satisfy the out-gassing acceleration equation, K = exp[ （ 1/T1 - 1/T2） E/R ], where E / R was estimated to be 7007.72 by means of the data provided by the Dewar manufacturer Sofradir com- pany,that is,for an increase of 10℃ ,the out-gassing acceleration is approximately 2.0. The residue gases were monitored with four-pole mass spectroscopy in the process compromising test. We suggest that the compromised backing conditions of the Dewar vessel be a baking time of a good 15 days at 80℃.