XRD application support cement whitepaper

Introduction

The XRD application support cement is part of Malvern Panalytical’s solution for the automated quantitative phase analysis of all types of (blended) cements, its raw materials and intermediate products such as clinker and hotmeal. Once set-up there is no user interaction required and the analyses are performed fully automatically. The methods are based on direct phase probing with X-ray diffraction (XRD) and phase analysis with Malvern Panalytical’s HighScore Plus and/or RoboRiet software.

Description of the solution

Malvern Panalytical supports mineralogical quantification methods for every type of material that is typical in the cement making process. These materials range from raw materials, intermediate compounds like hotmeal or clinker, and every type of (blended) cement. The control files for quantification contain the typical clinker and cement phases. The lists of phases are based on the EN 197-1, ASTM C150, ASTM C595 and ASTM C1157 classification norms. Additional compounds of interest can be selected on demand and Malvern Panalytical will then provide methods for the phase quantification of the chosen compounds.

The methods run with Malvern Panalytical’s HighScore Plus or RoboRiet software. The methods yield phase quantification results using Rietveld and/or Partial Least Squares Regression analyses. The results are in absolute wt-% and are written to exportable and customizable outputs compatible with Excel and most common LIMS systems. In addition, statistical analyses can be performed with a clustering technique allowing pass/fail or classification analyses. 

Quantification accuracy with XRD may be influenced by the stability of the phase, sensitivity of the phase to sample preparation (grinding in particular) and significant changes in mineralogy of the additives. For this reason, Malvern Panalytical only guarantees repeatability targets for the analytical precision of the methods.  

The analytical accuracy of Malvern Panalytical’s Aeris Cement Edition (600 and 300 Watt) XRD instruments is guaranteed using Si reference samples. The instrument tests are performed at the factory, during on-site installation and/or during maintenance.

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Introduction

The XRD application support cement is part of Malvern Panalytical’s solution for the automated quantitative phase analysis of all types of (blended) cements, its raw materials and intermediate products such as clinker and hotmeal. Once set-up there is no user interaction required and the analyses are performed fully automatically. The methods are based on direct phase probing with X-ray diffraction (XRD) and phase analysis with Malvern Panalytical’s HighScore Plus and/or RoboRiet software.

Description of the solution

Malvern Panalytical supports mineralogical quantification methods for every type of material that is typical in the cement making process. These materials range from raw materials, intermediate compounds like hotmeal or clinker, and every type of (blended) cement. The control files for quantification contain the typical clinker and cement phases. The lists of phases are based on the EN 197-1, ASTM C150, ASTM C595 and ASTM C1157 classification norms. Additional compounds of interest can be selected on demand and Malvern Panalytical will then provide methods for the phase quantification of the chosen compounds.

The methods run with Malvern Panalytical’s HighScore Plus or RoboRiet software. The methods yield phase quantification results using Rietveld and/or Partial Least Squares Regression analyses. The results are in absolute wt-% and are written to exportable and customizable outputs compatible with Excel and most common LIMS systems. In addition, statistical analyses can be performed with a clustering technique allowing pass/fail or classification analyses.

Quantification accuracy with XRD may be influenced by the stability of the phase, sensitivity of the phase to sample preparation (grinding in particular) and significant changes in mineralogy of the additives. For this reason, Malvern Panalytical only guarantees repeatability targets for the analytical precision of the methods. 

The analytical accuracy of Malvern Panalytical’s Aeris Cement Edition (600 and 300 Watt) XRD instruments is guaranteed using Si reference samples. The instrument tests are performed at the factory, during on-site installation and/or during maintenance.

Quantification and statistical methods with HighScore Plus and RoboRiet 

  • Rietveld analysis is a standardless method that yields the amount of all expected crystalline and amorphous phases. The results are expressed in absolute wt-%. The analysis is performed by comparing the measured diffraction profile to a calculated one that is based on expected phases.
  • Partial Least Squares Regression (PLSR) provides an easy to use method that yields the value of one single process parameter. The method compares the diffraction signal of an unknown sample with diffraction signals from standards with varying process parameter. The result of the PLSR analysis is the value of the process parameters of the unknown sample. An example is the quantification of fly-ash, slag or pozzolan additives in the cement.
  • Cluster analysis is a statistical method that is able to cluster samples into groups of similar materials. The groups can be used to easily identify similar or dissimilar materials, pass/fail samples and outliers. Similar diffraction signals are clustered into a group. Any new diffraction signal can be compared to existing clusters and therefore the material can be classified as either belonging to a certain cluster or as an outlier.

At the heart of the analysis part of the methods are Malvern Panalytical’s HighScore Plus or RoboRiet software packages.

HighScore Plus is the most advanced software suite to provide complete information on the sample and the underlying processes using qualitative, quantitative and statistical analysis on XRD data. For quantitative analysis it uses advanced methods like Rietveld and Partial Least Squares Regression (PLSR), while for statistical analysis it uses an integrated module called cluster analysis.

RoboRiet from Malvern Panalytical is a special ‘execution-only’ implementation of the Rietveld method for crystalline and amorphous phase quantification. It is designed for ‘push-button’ operation at production sites with minimal installation requirements. The RoboRiet program for automatic quantification is pre-installed on the Aeris Cement Edition systems.

Quantification accuracy of phases in cement

The accuracy of quantification methods depends on a number of factors. One of the main factors is sample preparation. Overgrinding can destroy the crystals in a given phase and render them partially amorphous (1). This is particularly true for ‘soft’ phases like free lime, calcite and the sulphates (gypsum, bassanite and anhydrite). The best results are obtained with full XRD and XRF analyses and sample preparation methods, optimized for each technique individually. In practice sample preparation is optimized to serve both XRD and XRF. Ideally, the XRD sample should be ground at lower rpm and shorter time compared to XRF. If available at customer site, we recommend that the result is crosschecked with other techniques such as titration and DSC/TG. This crosscheck only needs to be done once at the outset or subsequently whenever the sample preparation strategy or equipment is changed. Further, it is important for any process control application that the sample preparation is reproducible.

Another factor that is important to consider is the number of sources of additives like fly-ash, slag and pozzolan. Additives coming from different sources have different characteristics in their diffraction signal. Applying a method for an additive coming from one source to an additive coming from another source may render the results inaccurate.

The last factor that is of importance is the hydration of free lime. Free lime converts to portlandite when exposed to moisture. It is thus recommended that samples be measured immediately after preparation without any delay. If this conversion inadvertently happens, XRD will underreport the free lime content.

Repeatability targets

Malvern Panalytical guarantees the performance of the methods by specifying the repeatability targets. Reproducibility is not taken into account as it highly depends on the quality of the sample preparation. Typical repeatability values are listed in Table 1. The repeatability tests are performed by applying the methods on the same sample at least 10 times. Values for the repeatability of each phase are given in 1σ. Following (2), 1σ guarantees that 68.3% of the measurements are within the specified repeatability. 

Criteria for repeatability measurements

Repeatability measurements require a good scan quality. Typical measurement conditions at the Aeris are for clinker a range 10 - 65°ϑ in 5:30 min, for cements a range 10 - 65°ϑ in 10:00 min and for raw materials a range 8 - 65°ϑ in 5:45 min for the Aeris Cement Edition equipped with 600 Watt X-ray generator. With a 300 W generator, the measurement times must be doubled. Generally, longer measurement times improve the repeatability.

The most intense peak should have an intensity of at least around 10.000 counts. For lower intensities the measurement time should be increased. The scan should not show very strong preferred orientation effects. The sample surface must be at the same height as the metal ring surface. The refined value for the sample displacement must be lower than 0.15 mm. Too energetic milling conditions are indicated by a peak broadening (larger W parameter determined by Rietveld refinement). The W parameter for alite (C3S) should not be larger than 0.025.

A good sample preparation is also required for raw materials. Minerals like gypsum, hemihydrate, anhydrite or calcite are very sensitive to preparation conditions. Too weak milling result in bad particle statistics with strong preferred orientation effects. Too energetic milling destroys the minerals and produces amorphous material. Both have a negative influence on repeatability values. 

For more information see the “Aeris Cement Edition sample preparation: Standard Operating Procedure”. An improper sample preparation can affect the repeatability targets in Table 1.

Table 1: Repeatability of the Rietveld based quantification of phases in clinker, various types of cement, raw mix and gypsum. The values are in wt-% at 1σ

Clinker
General file/
Customer-specific file
1)

CEM ICEM-II/A-L

Slag cement
CEM III A/
CEM III B
2)

Limestone, Rawmix3)

Gypsum
Alite C3S0.4 / 0.2 0.40.40.4
    Alite M1   1.6 / 1.6
    Alite M3   1.6 / 1.6
Belite C2S0.4 / 0.2 0.30.30.4
    Belite β    0.4 / 0.2 0.30.3
    Belite α    0.2 / 0.1 0.10.1
    Belite γ    0.2 / 0.1 0.10.1
Ferrite0.2 / 0.1 0.20.20.2
Aluminate cub.0.2 / 0.1 0.20.20.2
Aluminate ortho0.2 / 0.1 0.20.20.2
Free Lime0.10.10.10.1
Portlandite0.10.10.10.1
Periclase0.10.10.10.1
Arcanite0.10.10.10.1
Aphthitalite0.10.10.10.1
Calciolangbeinite0.10.10.10.1
Gypsum0.20.20.20.2
Hemihydrate0.20.20.20.2
Anhydrite0.20.20.20.2
Calcite0.20.20.20.20.2
Quartz0.10.10.10.10.1
Dolomite0.10.1
Mica0.10.1
Hematite0.1
Plagioclase0.1
Orthoclase0.1
Slag0.7 / 0.4 
1) Standard deviation for a general file designed for large compositional variance (for example, alite 40 – 75%, belite 10 – 50 %) and for customer-specific, fine-tuned files with smaller compositional variance.
2) The repeatability for slag and other amorphous components depends strongly on the amount. Higher amounts of amorphous material can be given with higher accuracy and better repeatability than low amounts.
3) In natural gypsum and limestone, additional phases can be present, for example clinochlore, kaolinite, amphiboles, pyroxenes or others.

Scope of supply

The Aeris Cement Edition is supplied with a pre-installed set of files for automatic quantification: clinker, CEM-I, limestone-cement, gypsum, limestone, rawmeal and hotmeal (XRD Cement Solutions Basic Pack, 9430 020 81001). The files are designed for an optimized sample preparation (automatic swing-disk mill, 750 rpm, 30 sec milling, 100 kN pressing in steel rings for 30 sec). For more details see the “Aeris Cement sample preparation: Standard Operating Procedure”. A different sample preparation, especially if a sample should be used both for XRF and XRD, requires a fine-tuning of the files. Additional phases can be included in the files upon request.

Quantification files for additional materials like slag cements, fly-ash cements, other blended cements, pure slag, pure fly-ash, other raw materials can be ordered in the Premium Pack (9430 020 81011). 

Output of the results is in a pie chart on the AERIS touch screen and in a TXT file on the system, which can be exported. Additional output options are the data transfer to a LIMS in file format compatible with FLSmidth and Thyssen-Krupp Industrial Solutions (Polysius) based automation and a table in Excel file format to a separate computer or network. Other file formats must be ordered separately.

The accuracy of the pre-installed CEM-I file is demonstrated by measurement and quantification of the VDZ100 standard sample of the organization of the German Cement Industry, VDZ (Table 2). 

Table 2. Measurement of the VDZ100 sample on the Aeris (sample preparation according to SOP, 10 measurements, with standard deviation 1σ)
Reference from VDZ100Aeris measurement Value (std. dev.)
Alite59 ±0.659.20 (0.08)
  Alite M3  23.14 (0.63)
  Alite M1  36.06 (0.60)
Belite sum14.1 ±0.514.06 (0.07)
  Belite beta  13.49 (0.07)
  Belite alpha  0.26 (0.01)
  Belite gamma  0.31 (0.01)
Ferrite6.9 ±0.56.66 (0.05)
C3A sum8.3 ±0.38.47 (0.03)
  C3A cubic5.9 ±0.3  6.03 (0.04)
  C3A ortho.2.3 ±0.3  2.44 (0.03)
Free Lime0.3 ±0.10.15 (0.02)
Portlandite2.0 ±0.31.72 (0.02)
Periclase0.1 ±0.10.12 (0.03)
Arcanite0.3 ±0.10.20 (0.04)
Aphthitalite0.2 ±0.10.17 (0.03)
Calciolangbeiniteb.d.l.
Gypsum0.2 ±0.10.32 (0.04)
Bassanite1.8 ±0.31.64 (0.05)
Anhydrite2.6 ±0.32.69 (0.03)
Calcite4.4 ±0.44.50 (0.07)
Quartz0.2 ±0.10.11 (0.03)

References

(1) Witzke, T. & Füllmann, T. (2015): Influence of sample preparation of clinker on Rietveld quantification results and crystallite size. IBAUSIL, 16th-18th September, Weimar, Volume 1, 465-472

(2) Wheeler, D.J. and Chambers, D.S. Understanding Statistical Process Control. s.l. : SPC Press, 1992.

Edition notice

Second Edition, 2020

Acknowledgements

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Copyright 2020, Malvern Panalytical, Almelo, The Netherlands. All rights reserved worldwide. No part of this document may be copied, distributed, transmitted, stored in a retrieval system or translated into any human or computer language, in any form or by any other means, electronic, mechanical, magnetic, manual or otherwise, or disclosed to third parties without the express written permission of Malvern Panalytical.

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