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Target Material Characterization Apparatus Measurement Technique

Target Material Characterization Apparatus and Measurement Techniques Measurements of Diffusive, Effusive and Electrochemical transport Motivation.

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Target Material Characterization Apparatus Measurement Technique

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  1. Target Material Characterization Apparatusand Measurement TechniquesMeasurements of Diffusive, Effusive and Electrochemical transportMotivation • Direct measurements of the chemical interactions between the RIB species and target / ion source - fundamental limitation of the traditional ISOL technique - isolating the critical phenomena • Provide a matrix for initial investigations into the feasibility of developing new beams: D and ta must be within a reasonable range before investing time and resources • Provide a matrix for direct investigation of new-concept techniques such as electrochemical mass transport and other methods

  2. Target Material Characterization ApparatusMeasurement Technique • Introduce the stable analogue of the RIB species under investigation either as a gas or vapor into sample volume exposed to hot membrane. • Measure the time profile of the permeation and fit to solutions of Fick’s second law determining D ( D>10-9 cm2/s ) • Replace solid membrane with tube long, thin capillary tube with dimensions chosen so that Dcap>>Dsolid. Repeat diffusion measurements extracting ta from flow equations such as the Clausing relation

  3. Target Material Characterization ApparatusMeasurement Technique (con’t) • The permeation constant K=bD can also be measured from the saturation flow-rate. This allows determination of the solubility of the sample gas as a function of sample pressure. • This simplified configuration allows direct measurement of new techniques of mass transport such as: bulk or surface electrochemical (electrolytic) transport, electrochemical suppression (pumping) of unwanted isobars or vapors and the effects of physical or chemical carrier vapors.

  4. Determination of D from the measured time profile - solution to Fick’s second law

  5. Measurements of the diffusion coefficient:fitting the solution to the measured time profile Diffusion of 16O in ZrO2/Y2O3 (xYO=0.1) T=832 C Flow rate (arb. units) Time (min)

  6. T=915 C

  7. Measurement of mean surface adsorption timesta • Replace diffusive membrane with a long narrow capillary channel composed of the target or ion source material under investigation • Select channel dimensions to such that Dtube>> Dbulk and l>>r • Verify geometry using by flowing a mass range of the noble gases • Rapidly fill one side of capillary channel with a sample gas or vapor while monitoring RGA response • Mean surface adsorption times can be related to an effective diffusion coefficient, for example, in the molecular flow range:

  8. Example of surface adsorption time measurement Capillary time f=100 mm l=1 cm for O2 at 1000 C Measured delay time (min) Mean adsorption time (ms)

  9. A tool to investigate new methods of mass transport • Once the material has been characterized in terms of D and ta: the effect of alternative mass transport techniques can be investigated. • For example, the above measurements could be repeated with an electric field applied across the membrane and electrochemical transport investigated. An effective D could then be measured. • To investigate electrochemical surface migration, a potential could be set up along a capillary tube by passing a current through it.

  10. Ionic transport under an electrochemical potential gradient

  11. Conclusions • We have shown that the diffusive measurement technique gives reasonably accurate measurements of D for 16O and 18O in ZrO2/ Y2O3 (x=0.1) over a 400 C temperature range. • The successful diffusion measurements suggest determination of characteristic surface - particle adsorption times should also be readily achieved. • The electrical potential developed across the sample material shows the correct dependence on PO2 as predicted by the Nernst equation. • Repeating the 16O and 18O diffusion measurements with an external electrical potential across the material resulted in a ~103 mass transport enhancement over thermal pure diffusion. • Initial results of the F investigation (one experimental run) suggest fast electrochemical transport of F through ZrO2 / Y2O3. Data suggests Deff > 10-7 cm2/s when an electric field of ~3 V/mm is applied at 1005 C.

  12. Electrochemical transport through YSZ Conclusions • The electrical potential measured across the sample material showed the correct PO2 dependence as predicted by the Nernst equation • Repeating the 16O and 18O measurements with an external electrical potential across the materials resulted in an ~103 flow enhancement over thermal diffusion. The enhancement was increasing with increasing temperature. • Initial results of the F investigation (one experimental run) suggest fast electrochemical transport of F through ZrO2 / Y2O3 (x=0.1). Data suggests Deff> 10-7 cm2/s when an electric field of ~3 V/mm is applied at 1005 C

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