Dewar Flask Glass Composition for Helium Permeation Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional dewar flasks made of glass for photoluminescence measurements suffer from rapid helium gas permeation, leading to frequent vacuum evacuations, increasing operator burden and costs due to decreased heat-insulating effectiveness at low temperatures.
Innovation Solution
A dewar flask made of glass with an SiO2 content of 65-75% by weight and an average thermal expansion rate of 25-55 × 10^-7/°C, reducing helium permeation and the need for frequent evacuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional dewar flask made of glass is used to hold liquid helium for photoluminescence measurements, then the measurement can be performed, but helium gas rapidly permeates through the glass wall causing the vacuum degree to decrease and requiring frequent evacuations
Solution Approach 1:
The patent changes the chemical composition parameters of the glass material, specifically setting SiO2 content to 65-75% by weight and B2O3 content to 10-30% by weight, which fundamentally alters the glass structure to reduce helium permeation. This parameter optimization resolves the contradiction by maintaining vacuum reliability while minimizing evacuation frequency.
Solution Approach 2:
The patent creates a composite glass material combining specific ratios of SiO2, B2O3, and other oxides (Al2O3, Na2O, K2O, CaO, MgO) to achieve both low helium permeation and appropriate thermal expansion properties. This composite approach allows simultaneous optimization of multiple properties to resolve the vacuum maintenance contradiction.
2Reliability
If glass with high SiO2 content is used to reduce helium permeation, then vacuum maintenance improves, but the glass becomes more difficult to process into a dewar flask
Solution Approach 1:
The patent optimizes SiO2 content to 65-75% rather than using higher values, which would provide even better helium resistance but make processing prohibitively difficult. This parameter range represents the optimal balance point where sufficient helium resistance is achieved while the glass remains processable into dewar flask forms.
Solution Approach 2:
By incorporating B2O3 (10-30% by weight) and other modifying oxides into the glass composition, the patent creates a composite material that lowers the melting point and improves viscosity characteristics, making high-SiO2 glass easier to process while maintaining low helium permeation properties.
3Strength
If glass with low thermal expansion rate is used to improve durability at low temperatures, then the dewar flask becomes more durable, but helium permeation increases
Solution Approach 1:
The patent creates a multi-component glass composite where SiO2 provides structural integrity and low thermal expansion, while B2O3 and other oxides modify the network structure to reduce helium permeation pathways. The synergistic interaction between components resolves the contradiction between durability and helium resistance.
Solution Approach 2:
The patent optimizes the thermal expansion rate to a specific range (25-55 × 10^-7/°C) rather than minimizing it, which balances thermal durability with helium permeation resistance. This parameter optimization ensures the glass can withstand thermal cycling while maintaining vacuum integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly reduces the operator burden and cost associated with evacuations while maintaining the dewar flask's durability and heat-insulating properties, allowing for more frequent and reliable impurity concentration measurements in silicon.
Implementation Method 1
helium gas has the property of permeating through glass. Thus, in a case where the liquid helium is held in the conventional measurement-use dewer flask to carry out the concentration measurement, helium gas from the liquid helium rapidly permeates through a glass wall of the dewar flask
Implementation Method 2
a heat-insulating effect of a heat-insulating layer which is constituted by the vacuum layer is decreased
Implementation Method 3
the entire sample is immersed into the liquid helium... it becomes impossible to maintain the sample at a measurement temperature (approximately 4K)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A significant reduction in the burden on an evacuation operator and a significant reduction in evacuation cost are achieved when the concentration of impurities included in silicon are measured in liquid helium by a photoluminescence method. A glass which serves as a material for forming an inner cylinder Dewar flask (2) has an SiOz content of 65% by weight to 75% by weight, and has an average thermal expansion rate of 25 × 10-7/°C to 55 × 10-7/°C when the temperature of the glass is 20°C to 300°C. (Fig. 2)