Quantitative Phase Analysis

Methodologies

Quantitative Phase Analysis Overview

Quantitative phase analysis can be used to measure not only the type of compounds but also the amount present in a solid or powder system. Diffraction analysis has advantages over ordinary chemical analysis in that the diffraction method will reveal the presence of compounds whereas chemical analysis can only provide elemental information. Quantitative phase analysis can be used for plasma spray process development and quality control testing of coatings. Quantitative analysis can by used to determine trace silica in ceramics and minerals, and provide quality control of austenite content in heat-treated steel components.

Lambda’s quantitative phase analysis is based upon the rigorous Reference Intensity Ratio (RIR) method. Procedures developed for specific systems of phases are "calibrated" by either calculation of the material dependent structure factor portion of the RIR, or by direct measurement using mixtures of known powder components. All procedures developed at Lambda are tested using known mixtures before application. Systems of ceramic, alloy or mineral components may be analyzed in either solid or powdered form. Complete facilities for sample preparation, sectioning, polishing, pulverizing, and sizing are available.

Lambda has developed unique quantification software allowing complex diffraction patterns to be analyzed. A variety of algorithms are available for background subtraction, diffraction peak integration, and peak profile deconvolution in any combination. Once technique files controlling the software have been developed for a system of phases, the diffraction data analysis for subsequent samples is independent of any subjectivity on the part of the technician. Lambda employs three methodologies in quantitative analysis determination:

Internal Standard

The Internal Standard Method is the procedure of choice for analyzing powdered systems. A known quantity of a reference powder is added to the unknown. Any number of constituents in a mixture may be quantified independently. The mixture may contain amorphous (noncrystalline) components. The mass absorption coefficient of the mixture need not be known in advance. The Internal Standard Method is applied broadly to any mineral or materials systems for which the chemistry is unknown.

The External Standard Method may be applied to solid systems, such as alloys, plasma sprayed coatings, or oxide layers. This method allows the quantification of one or more components in a system that may contain an amorphous fraction. The mass absorption coefficient must, however, be known in advance, requiring either full elemental chemistry or prior knowledge of the chemistry, as in the case of plasma spray coatings or alloys.

Direct Comparison

This procedure requires no standards, but is only applicable to fully crystalline mixtures. All of the components in the system must be quantified for solution. The Direct Comparison Method is the common method used for retained austenite determination.

For further information regarding Quantitative Phase Analysis, see:

• Lambda Research Diffraction Note, No. 12.
• Lambda Research Diffraction Note, No. 13.
• Lambda Research Paper entitled "X-ray Diffraction Characterization of Crystallinity and Phase Composition in Plasma-Sprayed Hydroxylapatite Coatings".

Features

• Graphite monochromators provide virtual immunity to fluorescence from the sample for optimum detection limits and precision.
  
  
• All diffractometers at Lambda are calibrated to the NIST mica and silicon standards (SRM 675 and 640) and corrected for angular error using algorithms unique to Lambda Research's data collection software.
  
  
• The data collection and reduction software developed at Lambda can be tailored for specific applications allowing detection of extremely broad peaks and deconvolution of overlapping peaks.
  
  
• Rapid nondestructive analysis using the External Standard Technique.
  
  
• Percent crystallinity from the sum of the crystalline components.
  
  
• RIR determination for technique development.
  
  
• Reproducibility of data collection and analysis, and elimination of subjectivity.
  
  
• Speed, accuracy and reduced cost to support effective quality control testing.