Tungsten Cathode with Stabilizing Oxides for High-Load Discharge Lamps
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Solution Overview
Problem
High-load and high-intensity discharge lamps, such as xenon short arc lamps, require cathode materials that can withstand high heat loads without evaporating, as existing thorium-free materials like barium and metal oxides have short lifetimes due to evaporation under extreme conditions.
Innovation Solution
A cathode material composed of a tungsten base with coexisting substances like lanthanum oxide and stabilizing oxides (titanium, zirconium, hafnium, niobium, or tantalum) is used, where the conversion grain size is 15 μm or greater, suppressing tungsten oxide production and maintaining electron emission stability under high heat loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If barium oxide is used as an electron emitting material in a cathode, then the lamp can operate with relatively low input power, but the cathode cannot withstand high heat loads and barium evaporates prematurely, limiting the lamp to low-power applications
Solution Approach 1:
The invention uses a composite cathode material consisting of a metal base (mainly tungsten) containing multiple metal oxides: lanthanum oxide (electron emitting material), and stabilizing oxides (titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, or tantalum oxide). This composite structure combines the electron-emitting properties of lanthanum oxide with the heat-resistant stabilizing properties of the other metal oxides, enabling the cathode to withstand high heat loads while maintaining electron emission capability.
2Power
If metal oxides like lanthanum oxide are used as electron emitting materials in high-power discharge lamps, then the cathode can handle higher input power, but the metal oxide evaporates at an early stage due to high heat load, resulting in short lifetime
Solution Approach 1:
The stabilizing metal oxides (titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, or tantalum oxide) act as intermediary substances that protect the lanthanum oxide electron emitting material from direct evaporation. These stabilizing oxides have high melting points and form a protective matrix that retards the evaporation of lanthanum oxide under high heat load conditions, thereby extending cathode lifetime while maintaining high-power operation capability.
3Reliability
If thoriated-tungsten material is used as a cathode, then high arc stability and long lifetime are achieved, but thorium is a radioactive material creating environmental load
Solution Approach 1:
The invention extracts and removes the radioactive thorium component from the cathode material while retaining the essential functional properties. By using lanthanum oxide as the electron emitting material and stabilizing metal oxides as the matrix, the cathode achieves comparable arc stability and lifetime to thoriated-tungsten without the radioactive environmental hazards, thus eliminating the harmful thorium substance while preserving performance.
4Stability of the object's composition
If the conversion grain size of coexisting substances in the cathode is smaller than 15 μm, then the electron emitting material can be more uniformly distributed, but the tungsten oxide production increases and electron emission stability decreases under high heat loads
Solution Approach 1:
The invention specifies a minimum conversion grain size of 15 μm for the coexisting substances (lanthanum oxide and stabilizing metal oxides) in the cathode material. This parameter change in grain size prevents excessive tungsten oxide production that occurs with finer grains under high heat load conditions, thereby maintaining electron emission stability. The larger grain size reduces the surface area-to-volume ratio, limiting oxidation reactions while preserving uniform electron emission.
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
This configuration enhances arc stability and extends the lifetime of high-load and high-intensity discharge lamps by stabilizing electron emission and preventing premature depletion of the electron emitting material, matching the performance of thoriated-tungsten cathodes.
Implementation Method 1
a cathode (2), which is made from a metal base (31) having a high melting point
Data Source
AI summary
The present high-load and high-intensity discharge lamp includes a cathode made of a material which does not (substantially) include thorium but can be used as a cathode material of high heat load, so that a long lifetime and high stability corresponding to those of thoriated-tungsten can be realized. Specifically, the cathode is made of a metal base having a high melting point which mainly consists of tungsten and includes a coexisting substance in which an oxide of at least one kind of metal selected from lanthanum, cerium, yttrium, scandium, and gadolinium and an oxide of at least one kind of metal selected from titanium, zirconium, hafnium, niobium, and tantalum are coexistent. The conversion grain size of the coexisting substance is 15 μm or greater, and the plurality of coexisting substances are present in the metal base with a high melting point.