Elemental Analysis of Glass and Raw Materials

Scope

The analysis of glass and raw materials is demonstrated in the manufacturing of soda-lime glass using the NEX CG II. This system is an indirect excitation EDXRF analyzer that uses secondary targets rather than tube filters. Its Cartesian Geometry optical kernel provides monochromatic excitation and removes background, supporting ultra-low detection limits. NEX CG II runs Rigaku RPF-SQX Fundamental Parameters (FP) software with Matching Library.

The FP approach with Matching Library was used for the measurements of finished glass and compositional analysis of the raw materials, dolomite and limestone. Semiquant FP with no Matching Library is also shown, ideal for screening contaminant elements for measuring the purity of the raw materials, sand and soda ash.

Background

Soda-lime glass makes up 90% of the global glass production and is used to make windows, glassware, and bottles. Common raw materials include sodium carbonate (soda ash), calcium carbonate (limestone), calcium oxide (lime), dolomite, alumina, slags, and sand (silica). Raw materials must be screened and mixed properly to give the desired glass properties for the finished products. Metal oxides such as CrO₃ and Fe₂O₃ impart color to the glass and so must also be closely monitored during production. The final glass composition is then monitored to ensure the highest quality product. The Rigaku NEX CG II meets these measurement needs in a simple-to-use benchtop system, designed for the at-line non-technical QC technician and the advanced technical user alike.

Rigaku RPF-SQX Fundamental Parameters (FP)

Rigaku RPF-SQX FP software estimates elemental concentration based on XRF theory called Fundamental Parameters (FP). Rigaku Profile Fitting (RPF) automatically deconvolutes spectral peaks and models the sample matrix using fundamental XRF equations to provide semi-quantitative measurements of elemental concentrations without needing any known standards, called semi-quantitative or semi-quant analysis.

Rigaku User-defined Matching Library

The user can easily tune the FP results using Matching Libraries by measuring one or more samples of the actual sample material with known elemental assay values from a referee technique such as WDXRF or ICP. Rigaku’s Matching Library adjusts the theoretical FP adjusted intensities to match the measured intensities of the material at a known concentration. In this way, the XRF is tuned to the actual material and reference numbers, allowing NEX CG II to reliably model variations in elemental and oxide composition. As a result, it ensures optimum accuracy and reliable, high-quality data without the need for a large suite of standards.

Results — Finished Glass

The Rigaku FP Metal template was used as the basis of the application method with no balance component. A 1-point Matching Library was made for the critical oxides SiO₂, Al₂O₃, CaO, MgO, Fe₂O₃, SO₃, Na₂O, K₂O, and TiO₂, while the other oxides were measured by semi-quant FP. WDXRF values are included as reference assays to demonstrate traceability of results, not a comparison of techniques.

Stat. Err. (statistical error) is the precision of the measurement.

Results — Raw Materials (Composition of Dolomite and Limestone)

The Rigaku FP Oxide Powder template was used as the basis of the application method with the balance component set to oxygen. A separate 1-point Matching Library was made for dolomite and limestone for the critical oxides SiO₂, Al₂O₃, CaO, MgO, and Fe₂O₃, while the other oxides were measured by semi-quant FP. WDXRF values are included as reference assays to demonstrate traceability of results, not a comparison of techniques.

ND means not detected.

Results — Raw Materials (Purity of Sand and Soda Ash)

The Rigaku FP Oxide Powder template was used as the basis of the application method, with the balance component set to oxygen. Purity cannot be measured directly due to the self-absorption of the pure oxide component. Rigaku Semi-quant was used with the main oxide set as the balance component, and in this way, the impurities are measured with reliable accuracy. The purity analysis of sand (silica) and soda ash (sodium carbonate) is shown here.

Conclusion

The Rigaku NEX CG II yields excellent performance for the elemental analysis of raw materials and final characterization of finished glass. Using indirect excitation with secondary targets in Cartesian Geometry, NEX CG II achieves near-complete background removal, allowing for ultra-low detection limits and exceptional quality of data. If desired, FP semi-quantification can be improved with Matching Libraries based on one or more assayed type standards of the particular material type, as shown in the glass and raw materials analyses.

RPF-SQX FP software is powerful and flexible, yet simple and intuitive to operate. These features make the NEX CG II ideal for at-line screening and characterization of glass and raw materials without the burden of large standard suites.

For facilities that also use WDXRF, the NEX CG II can complement lab workflows by handling routine at-line screening and material intake. And, for smaller operations, the NEX CG II stands on its own as a compact, cost-effective solution for product QA/QC, the quality laboratory, and R&D.