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Title: Fiber Optical Micro-detectors for Oxygen Sensing in Power Plants

Abstract

A reflection mode fiber optic oxygen sensor that can operate at high temperatures for power plant applications is being developed. The sensor is based on the {sup 3}O{sub 2} quenching of the red emission from hexanuclear molybdenum chloride clusters. Previously we described a particle-in-binder approach to immobilizing the potassium salt of a molybdenum cluster, K{sub 2}Mo{sub 6}Cl{sub 14}, at the tips of optical fibers. Compared to previous methods, the particle-in-binder approach affords fibers with greatly improved mechanical properties. We have extensively characterized two fiber sensors at high temperature. We obtain quenching ratios between pure nitrogen and 21% oxygen as high as 3.9 x at 70 C. For the first sensor at 60 C we obtained a {+-} 1% variation in the quenching ratio over 6 cycles of measurement, and monitored the device performance over 23 days. We were able to operate the second sensor continuously for 14 hours at 70 C, and the sensor quenching ratio was stable to 5% over that time period. These are promising results for a high temperature fiber optical oxygen sensor based on molybdenum chloride clusters.

Authors:
; ; ;
Publication Date:
Research Org.:
Michigan State Univ., East Lansing, MI (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
876615
DOE Contract Number:
FC26-02NT41582
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; 20 FOSSIL-FUELED POWER PLANTS; FIBER OPTICS; MONITORS; MOLYBDENUM CHLORIDES; OXYGEN; MONITORING; PERFORMANCE; POWER PLANTS; ON-LINE MEASUREMENT SYSTEMS

Citation Formats

Gregory L. Baker, Ruby N. Ghosh, D.J. Osborn III, and Po Zhang. Fiber Optical Micro-detectors for Oxygen Sensing in Power Plants. United States: N. p., 2006. Web. doi:10.2172/876615.
Gregory L. Baker, Ruby N. Ghosh, D.J. Osborn III, & Po Zhang. Fiber Optical Micro-detectors for Oxygen Sensing in Power Plants. United States. doi:10.2172/876615.
Gregory L. Baker, Ruby N. Ghosh, D.J. Osborn III, and Po Zhang. Sun . "Fiber Optical Micro-detectors for Oxygen Sensing in Power Plants". United States. doi:10.2172/876615. https://www.osti.gov/servlets/purl/876615.
@article{osti_876615,
title = {Fiber Optical Micro-detectors for Oxygen Sensing in Power Plants},
author = {Gregory L. Baker and Ruby N. Ghosh and D.J. Osborn III and Po Zhang},
abstractNote = {A reflection mode fiber optic oxygen sensor that can operate at high temperatures for power plant applications is being developed. The sensor is based on the {sup 3}O{sub 2} quenching of the red emission from hexanuclear molybdenum chloride clusters. Previously we described a particle-in-binder approach to immobilizing the potassium salt of a molybdenum cluster, K{sub 2}Mo{sub 6}Cl{sub 14}, at the tips of optical fibers. Compared to previous methods, the particle-in-binder approach affords fibers with greatly improved mechanical properties. We have extensively characterized two fiber sensors at high temperature. We obtain quenching ratios between pure nitrogen and 21% oxygen as high as 3.9 x at 70 C. For the first sensor at 60 C we obtained a {+-} 1% variation in the quenching ratio over 6 cycles of measurement, and monitored the device performance over 23 days. We were able to operate the second sensor continuously for 14 hours at 70 C, and the sensor quenching ratio was stable to 5% over that time period. These are promising results for a high temperature fiber optical oxygen sensor based on molybdenum chloride clusters.},
doi = {10.2172/876615},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Technical Report:

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  • In this report, initial results pertaining to the synthesis molybdenum clusters and characterization using absorption, optical microscopy, and x-ray powder diffraction are discussed. The synthesis was performed according to literature [1], but results from x-ray powder diffraction indicate that the synthesis did not give the desired compound. The absorption and optical microscopy indicate that the compound synthesized has properties similar to the desired Mo{sub 6}Cl{sub 12} clusters [2,3], so it is unclear as of yet what happened. The sample cell for performing high temperature spectroscopy on thin films of the molybdenum clusters at elevated temperature in a controlled gas environmentmore » was designed and an initial prototype was built.« less
  • More Mo{sub 6}Cl{sub 12} has been synthesized. We have found that previous ambiguous x-ray powder diffraction results are due to disruption of long-range order in the crystals during the heating stage of the synthesis. The quartz cell heaters have been redesigned and are able to heat the substrate. Initial films have been fabricated and are currently under investigation to determine optimal deposition conditions.
  • Mo{sub 6}Cl{sub 12}, a cluster compound whose luminescence depends on the ambient concentration of oxygen, is the basis for a real-time oxygen sensor for combustion applications. Previously, the properties of Mo{sub 6}Cl{sub 12} have largely been studied at room temperature; these studies have now been extended to 200 C. Optical microscopy shows that Mo{sub 6}Cl{sub 12} undergoes a steady change in color as it is heated from room temperature to 200 C, changing from canary yellow to crimson and then back to canary yellow. Concurrent thermal gravimetric analyses show a small weight loss for Mo{sub 6}Cl{sub 12} that is consistentmore » with loss of water or HCl from the clusters. These changes are reversible. Absorption and fluorescence emission spectroscopy of Mo{sub 6}Cl{sub 12} heated to 200 C for two hours shows no change in the photophysical parameters compared to the control sample that was not heat cycled.« less
  • A reflection mode fiber optic oxygen sensor that can operate at high temperatures for power plant applications is being developed. The sensor is based on the {sup 3}O{sub 2} quenching of the red emission from hexanuclear molybdenum chloride clusters. The luminescence of Mo{sub 6}Cl{sub 12} immobilized in a sol-gel matrix was measured as a function of heater temperature up to 200 C, in an inert environment. While the luminescence decreased with temperature, the integrated intensity at 200 C should be sufficient to enable detection of the luminescence in a fiber geometry. Previously we found that aging Mo{sub 6}Cl{sub 12} atmore » temperatures above 250 C converts the canary yellow Mo{sub 6}Cl{sub 12} to a non-luminescent gray solid. Optical and thermal aging experiments show that the alkali metal salts of Mo{sub 6}Cl{sub 12} have higher thermal stabilities and remain luminescent after aging at 280 C.« less
  • A reflection mode fiber optic oxygen sensor that can operate at high temperatures for power plant applications is being developed. The sensor is based on the {sup 3}O{sub 2} quenching of the red emission from hexanuclear molybdenum chloride clusters. Alkali salts of Mo{sub 6}Cl{sub 12} were synthesized and heated to 280 C for one hour in air. Optical measurements of the thermally treated material confirm the potential of the salts as lumophores in high temperature fiber optic sensors. In addition sol-gel films containing Mo{sub 6}Cl{sub 12} were dip coated on quartz substrates and heated at 200 C for one hour.more » Conditions were developed for successfully immobilizing monomeric complexes that are compatible with sol-gel processing.« less