Optimized Sealing Process and Real-Time Monitoring of Glass-to-Metal Seal Structures

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 (α_metal) 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.......

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.......

Materials

Name	Company	Catalog Number	Comments
ABAQUS	Dassault SIMULA	ABAQUS6.14-5	The software to carry out numerical simulation.
Fiber Bragg grating sensors	Femto Fiber Tec	FFT.FBG.S.00.02 Single	apodized FBG
Fusion splicer	Furukawa Information Technologies and Telecommunications	S123M12	FITEL's line of fusion splicers provides an excellent solution for both field and factory splicing applications。
Glass powder	Shenzhen Sialom Advanced Materials Co.,Ltd	LC-1	A kind of low melting-point glass powder (380℃).
Graphite mold	Machining workshop of Tsinghua University	Graphite	The mold to locate each part of the metal-to-glass structure.
Heating furnace	Tianjin Zhonghuan Electric Furnace Technology Co., Ltd	SK-G08123-L	vertical tubular furnace
Kovar conductor	Shenzhen Thaistone Technology Co., Ltd	4J29	A common material used for the electrical penetration in the metal-to-glass seal structure
Optical interrogator	Wuhan Gaussian Optics CO.,LTD	OPM-T400	FBG spectrum analysis modules
Pro/Engineer	Parametric Technology Corporation	PROE5.0	The software to establish the 3D geometry.
Steel shell	Beijing Xiongchuan Technology Co., Ltd	316 stainless steel	A kind of austenitic stainless steel