This project addresses the development of an inlinesensor for measuring mixing quality in chlorine dioxide pulpbleaching. The sensor is based on a proprietary, integratedoptical interferometer. The interferometer's unique designminimizes thermomechanical noise to provide a highly stableplatform capable of detecting low concentrations of specificchemicals in fluid environments with high spatial resolution. Theapproach relies on the detection of small refractive index changesin a thin surface film. Specificity for chlorine dioxide isachieved by using a surface film that is reactive or interactivewith chlorine dioxide. A mixing sensor based on this approach hasseveral key advantages: (1) it allows real-time, continuous,in-situ monitoring; (2) it has a broad dynamic range, yet iscapable of sensitivities down to the ppb level; (3) it can be fullyreversible; and (4) it permits spatial resolution well below 1millimeter. The resulting product will be suitable for assessingboth macroscopic and microscopic mixing, and it will permitautomated feedback control of pulp mixers. Moreover, developmentof sensors for other bleaching chemicals (e.g., ozone, hydrogenperoxide) would be a direct extension of this effort. In Phase I,a preliminary selection of candidate waveguide coatings will bemade and they will be screened and optimized for their response toaqueous solutions of chlorine dioxide.Anticipated Results/Potential Commercial Applications as described by the awardee:Pulp bleaching consumes large quantities ofchemicals that are both energy intensive and environmentallyhazardous. Development of the planned sensor would provide a toolfor reducing chemical consumption while maintaining or improvingproduct quality. This development would cut costs, minimize energyconsumption, and reduce environmental impact.
