Ray Collier Hughes

Excitation in radio-frequency discharges

Abstract The possibility of using a radio-frequency, flame-like discharge as an excitation source for spectroscopy, discussed in an earlier publication, has been investigated. Both a triode driven oscillator of 250 W output at 30 Mc, and a magnetron powered unit of 2 kW output at 2450 Mc were employed. The RF-excited spectra, between 2000 and 10,000 A, of air, N 2 , O 2 , He and H 2 have been examined. Helium and H 2 , producing simple spectra, provide advantageous discharge sustaining atmospheres for excitation of line and band spectra of many chemical species. The neutral-gas temperature of the discharge in He and H 2 of approximately 3000°K limits the ability of the discharge in melting, volatilizing and dissociating samples, and imposes pronounced preferential excitation effects. However, a much higher electron temperature permits excitation of vapor species requiring high excitation energies. Techniques are described for the introduction of solid and liquid samples into the discharge. Spectra of some seventy-five elements were excited and their emissions are discussed. The application of RF excitation to quantitative analysis is illustrated by the analysis of tin-lead solders, within the range of 30–55% tin, for major constituents. The RF discharge at atmospheric pressure in He or H 2 appears to be a valuable technique, widely applicable for spectroscopic investigations.

Chemical Reactions in Barium Oxide on Tungsten Emitters

When barium carbonate is heated in vacuum in contact with tungsten, the following reactions may occur in sequence as progressively higher temperatures are reached: (1) WO3+BaCO3⇄BaWO4+CO2. (2) 3BaCO3+W⇄Ba3WO6+3CO. (3) BaCO3⇄BaO+CO2. (4) 6BaO+W⇄Ba3WO6+3Ba.At a temperature of approximately 600°C, reaction (2) begins to occur with appreciable speed. Reaction (3) proceeds at 800–900°C. Reactions (2) and (3) may be made to proceed simultaneously, the preponderance of one over the other depending upon state of subdivision and intimacy of admixture of the reactants. Under favorable conditions, reaction (2) may be driven to completion with almost total absence of reaction (3). Reaction (4) progresses with appreciable speed at temperatures over approximately 1000°C.Activated cathodes of BaO on W will have an interface of Ba3WO6 formed by reactions (2) or (4), or both, unless unusual precautions are taken to avoid this. The end result of heating the cathode is the conversion of the entire thickness of the oxide coa...

Bariated Tungsten Emitters

Thermionic emitters consisting of barium oxide dispersed throughout a body of porous tungsten can be successfully made if suitable compounds of barium are employed as the source of the oxide. Compounds such as the carbonate, which can oxidize tungsten and react to form Ba3WO6: 3BaCO3+W→Ba3WO6+3CO, are unsuitable. However, if by various means, BaO is dispersed in tungsten, reaction occurs at operating temperature of the cathode to slowly generate free barium: 6BaO+W→Ba3WO6+3Ba, which diffuses to the surface and lowers the work function.Cathodes consisting of approximately 5 percent of BaO in W are capable of supplying continuous emission in excess of 100 amp/cm2, give equivalent dc and pulsed emission, and are highly resistant to damage by arcing, temporary poor vacuum, ion bombardment, and high temperatures.Emission current of approximately 8 amp/cm2 was obtained at an operating temperature of 1000°C from a typical cathode of this type. The life of this cathode, at 1100°C, was in excess of 650 hours. Cons...