Design And Fabrication Of Functionally Graded Material For Sealing High-pressure Gas Discharge Lamps

High-pressure gas discharge lamp (HGDL) has promising market due to highluminous efficiency, long life and good colorimetric characteristic. The part of sealing isimportant for HGDL and needs high temperature resistant, corrosion-resistant, highpressure-resistant and high airtight. The conventional sealing of HGDL is usually of thesandwich type between a thin Mo foil and a fused silica envelope. Due to the difference inthermal expansion between Mo and silica, high residual stress develops during sealingand operation, which often results in crack and delamination. In this study, the Mo/SiO₂FGM is fabricated to apply into sealing for relaxing residual stress.The dense samples were obtained by spark plasma sintering(SPS). The mechanismof sintering fused quartz powder was studied. The result indicates that fused quartz issintered by exterior fused. The size of mould and pressure of sintering affect thesintering behavior. The appropriate sintering condition is as below:1150℃～1200℃,20MPa,5min. The relative density of the obtained fused quartz reaches 95.8%～99.7% (relates to the size of mould).The sintering behavior of pure Mo and additive Ni, Cu in Mo alloy sintered bySPS was studied. The experimental results illustrate that the relative density of pureMo sintered at 1200℃is only 80.1%. The powders Ni and Cu can promote thedensity of sintered Mo. In the processing of sintering, Cu powder melts and Ni,dissolves in liquid Cu. The relative density of Mo alloy is 99.1% when the content ofadditive Ni is 3% and Cu is 2%.The Mo/SiO₂ composites with different Mo content were fabricated by SPS at thecondition of 1200℃-20MPa-5min. The relative density, electrical property,mechanical property and thermal property were measured and the microstructure wasobserved. The relative density is promoted because Mo particles fill into the holes offused quartz. With the increasing Mo content, the Mo powders disperse into the fusedquartz to form percolation structure, which leads to the conducting of the composite.The critical mass fraction for the Mo powder with a size of d₅₀=5μm and d₅₀=10μmis 35%～40% and 40%～45%, respectively.The finite element method is employed to calculate residual thermal stress and designthe structure. The result indicates that graded composites can effectively reduce theresidual thermal stress. The relaxation effect is up to 60% when the amount of layers between 50%Mo-SiO₂/SiO₂ is four. With the design and optimization, the50%Mo-SiO₂/SiO₂ FGM (six layers) was fabricated with the powder stacking-method bySPS.