THE USE OF ZONE CONTROL CHARTS IN QUANTITATIVE X-RAY POWDER PHASE ANALYSIS TO INSURE QUALITY CONTROL. Jeffery N. Dann and Harry O. Fassett, Osram Sylvania Inc. Tonawanda PA 18848-0504

Statistical Process Control (SPC) charts, or Shewhart Charts are used to monitor reference or control samples, to insure that the calculated phase analyses of unknown samples are not in error due to equipment or sample preparation variability.

As long as the calculated amounts of phases present in the control samples do not vary from the historic mean values by more than three standard deviations, the calculated amounts of phases in unknown samples are assumed to be correct.

Zone Control Charts make the plotting of data points less difficult for X-ray Diffraction operators than the standard control charts. Examples will include determination of Ba₅Si₈0₂₁ in BaSi₂0₅,Sb₄0₅Cl₂ in Sb₂0₃, and Y₃Ta0₇ in YTa0₄.