A system based on Raman spectroscopy has been developed for closed-loop control during the manufacture of titanium dioxide (TiO<sub>2</sub>). Spectra were obtained in the 50 to 700 cm<sup>-1</sup> range using excitation at ~532 nm and a fixed transmission-grating spectrograph coupled to a CCD detector. Quantitation has been achieved by linear interpolation based on the integrated intensity of phonons at 142 and 610 cm<sup>-1</sup> due to anatase and rutile phases, respectively. The spectroscopic instrumentation has been integrated with a powder sampling system and installed on four full-scale manufacturing plants. Fiber coupling (up to 100 m) has been employed, and each spectrometer system is multiplexed to three sampling heads. Spectra are corrected for changes in sample temperature, and the systems are designed to be fully automatic and require no user intervention.
Ian M. Clegg, Neil J. Everall, Bert King, Hugh Melvin, and Colin Norton, "On-Line Analysis Using Raman Spectroscopy for Process Control during the Manufacture of Titanium Dioxide," Appl. Spectrosc. 55, 1138-1150 (2001)