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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Key procedures to optimize the sealing process and achieve real-time monitoring of the metal-to-glass seal (MTGS) structure are described in detail. The embedded fiber Bragg grating (FBG) sensor is designed to achieve online monitoring of temperature and high-level residual stress in the MTGS with simultaneous environmental pressure monitoring.

Abstract

Residual stress is an essential factor to keeping the hermeticity and robustness of a glass-to-metal seal structure. The purpose of this report is to demonstrate a novel protocol to characterize and measure residual stress in a glass-to-metal seal structure without destroying the insulation and hermeticity of sealing materials. In this research, a femto-laser inscribed fiber Bragg grating sensor is used. The glass-to-metal seal structure that is measured consists of a metal shell, sealing glass, and Kovar conductor. To make the measurements worthwhile, the specific heat treatment of metal-to-glass seal (MTGS) structure is explored to obtain the model with best hermeticity. Then, the FBG sensor is embedded into the path of sealing glass and becomes well-fused with the glass as the temperature cools to RT. The Bragg wavelength of FBG shifts with the residual stress generated in sealing the glass. To calculate the residual stress, the relationship between Bragg wavelength shift and strain is applied, and the finite element method is also used to make the results reliable. The online monitoring experiments of residual stress in sealing glass are carried out at different loads, such as high temperature and high pressure, to broaden functions of this protocol in harsh environments.

Introduction

Metal-to-glass sealing is a sophisticated technology that combines interdisciplinary knowledge (i.e., mechanics, materials, and electrical engineering) and is widely applied in aerospace1, nuclear energy2, and biomedical applications3. It has unique advantages such as higher temperature and pressure endurance compared with organic material sealing structures. According to the difference of coefficient of thermal expansion (CTE), MTGS can be divided into two types: matched seal and mismatched seal4. As for the matched seal, the CTE of metal (αmetal) and seali....

Protocol

1. Production of MTGS structure with good hermeticity

NOTE: The procedures for MTGS structure include the preparations for components of the combined structure, the heat treatment process, and examinations for the performance of MTGS samples. The complete MTGS structure consists of a steel shell, Kovar conductor, and sealing glass. See the diagram and dimensions shown in Figure 1 and Table 1, respectively.

  1. Pour the granulated glass pow.......

Representative Results

From the results of Figure 5, the standard heat treatment to produce the MTGS models with high pressure endurance is explored, and the models can satisfy the examinations (i.e., light transmissions, pressure endurance, SEM, etc.). Thus, the produced MTGS structure can be applied to keep hermeticity in harsh environments.

The FBG can be well-fused with MTGS structure, and the residual strain in sealing glass will be reflected by Bragg wavelength shift after the hea.......

Discussion

The critical steps for the stress measuring of sealing material of MTGS structure at high temperature and high pressure include 1) manufacturing of the MTGS models with the FBG sensor, of which the grating region is located at the middle of sealing glass; 2) heating of the whole model using a standard heat treatment process, and after the model cools to RT, the FBG sensor will becomes well-fused with MTGS model, and the residual stress can be measured by Bragg wavelength shift; 3) placing of the complete model into the f.......

Acknowledgements

This work has been supported by the National S&T Major Project of China (ZX069).

....

Materials

NameCompanyCatalog NumberComments
ABAQUSDassault SIMULAABAQUS6.14-5The software to carry out numerical simulation.
Fiber Bragg grating sensorsFemto Fiber TecFFT.FBG.S.00.02 Singleapodized FBG
Fusion splicerFurukawa Information Technologies and TelecommunicationsS123M12FITEL's line of fusion splicers provides an excellent solution for both field and factory splicing applications。
Glass powderShenzhen Sialom Advanced Materials Co.,LtdLC-1A kind of low melting-point glass powder (380℃).
Graphite moldMachining workshop of Tsinghua UniversityGraphiteThe mold to locate each part of the metal-to-glass structure.
Heating furnaceTianjin Zhonghuan Electric Furnace Technology Co., LtdSK-G08123-Lvertical tubular furnace
Kovar conductorShenzhen Thaistone Technology Co., Ltd4J29A common material used for the electrical penetration in the metal-to-glass seal structure
Optical interrogatorWuhan Gaussian Optics CO.,LTDOPM-T400FBG spectrum analysis modules
Pro/EngineerParametric Technology CorporationPROE5.0The software to establish the 3D geometry.
Steel shellBeijing Xiongchuan Technology Co., Ltd316 stainless steelA kind of austenitic stainless steel

References

  1. Alves, F. J., Baptista, A. M., Marques, A. T. Metal and ceramic matrix composites in aerospace engineering. Advanced Composite Materials for Aerospace Engineering. , 59-99 (2016).
  2. Dai, S., et al.

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Glass to metal SealReal time MonitoringTemperature MonitoringStress MonitoringFiber Bragg Grating SensorMetal to glass StructureGlass CylinderSteel ShellKovar ConductorHeat TreatmentResidual Stress MeasurementFBG SensorTemperature ControlMTGS Model

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