Effect of mo powder surface condition on fabrication of Mo-SiO₂ functionally graded materials with slipcasting method

The conventional high intensity discharge lamps are made of Mo foil-sealing method, in which the Mo-metal of 30 μm thick is sandwiched by the fused silica envelope. The conventional high intensity discharge lamps therefore requires cooling system to reduce the thermal stress between Mo and fused silica during the switching operation and a long sealing zone is usually required to complete hermeticity, especially in high power devices, so that the production of compact high intensity discharge lamps has been a Herculean task. We show the invention of the new type of hermetically-sealed high intensity discharge lamps, made of Mo-SiO₂ functionally graded material (FGM) as an electrode and a sealing component. In the case of high intensity discharge lamps with Mo-SiO₂ FGM (FGM-Lamp), the thermal expansion coefficient between Mo and SiO₂ is functionally graded so that it tolerates a large numbers of heating cycles, with no cooling system are required. Furthermore lamps survive without breakage. The W electrode is totally separated from the lamp envelope by the FGM, so that no leakage of the luminous elements or gases takes place, when a large gas pressure exists inside a lamp. In this paper, effects of Mo powder surface conditions on the fabrication of Mo-SiO ₂ FGM have been investigated. Mo-SiO₂ FGM with as-received Mo powder revealed that the Mo particles were homogenously distributed, which resulted in no microscopic compositional gradient. In contrast. Mo-SiO ₂ FGM with pre-treated Mo powder provided a uniform gradient from the conductive part (Mo-rich phase) to the sealing part (amorphous silica).