How to Determine Carbon and Sulfur in Cement

Cement is a fundamental ingredient of many construction materials, such as concrete and mortar, acting as a hydraulic binder. Quality- and Process-Control demand rapid, accurate analysis of the elemental and phase composition of the material.

Combustion analysis is an easy-to-use, high-speed method to manage the limestone and gypsum/anhydrite addition in cements by accurately measuring carbon and sulfur.

This article demonstrates how the G4 ICARUS Series 2 combined with a high-frequency (HF) induction furnace makes determining carbon and sulfur levels simple, fast and reliable.

Measuring Principle

Combustion occurs within a sealed HF induction furnace under a flow of oxygen. While the sample, with the addition of a metallic accelerator, is heated by induction and combusts at temperatures over 2000 °C.

Sulfur compounds are then oxidized to SO2 and carbon to CO2. Subsequently, the total amount of carbon and sulfur elements are calculated in relation to the amount of these combustion gases, quantified using selective detection systems.

Combustion Without Compromises: G4 ICARUS

With its robust HF-furnace supplemented with ZoneProtect™, its novel vacuum-free automatic cleaning system, HighSense™ detectors and electronic flow- and pressure-control, adding the G4 ICARUS Series 2 is a smart decision for every industrial user who demands a reliable instrument even in extreme conditions.

The G4 ICARUS Series 2 has the capacity to rapidly measure both carbon and sulfur in cast iron and related materials with excellent accuracy – usually less than one minute.

How to Determine Carbon and Sulfur in Cement

Image Credit: Bruker AXS Inc.

Sample Preparation

For the best possible precision, the sample should be ground or crushed into a uniform powder before running the analysis. If necessary, it should be allowed to dry for at least 1 hour at 110 °C. No additional sample preparation is required.

Method Parameters

  • Accelerators:
    • Tungsten/Tin: ~1.5 g
    • High purity iron chips: ~0.7 g
  • Analysis time 1: 35 seconds (power Level: 4)
  • Analysis time 2: 25 seconds (power level: 0)
  • Baseline check before analysis: 5 seconds
  • Baseline check after analysis: 5 seconds
  • Crucible cool time: 10 seconds
  • Purge time: 5 seconds
  • Sample mass: ~0.2 g (weighed to 0.1 mg)
  • Start delay: 5 seconds 

Calibration 

The calibration of the analyzer is completed using reference materials with certified concentrations of carbon and sulfur. The analysis software supports multi-point calibration with multiple CRMs and single point calibration with one CRM. 

Procedure  

I. Determination of the Blank Value  

Conduct at least three analysis runs of the blank value by introducing the described number of accelerators into a preheated crucible and then analyze.1 

II. Measuring Reference Materials  

  • Select CRMs for calibration and identify them using the certified concentrations in the analysis software with designation.  
  • Weigh in the necessary amount of reference material into a preheated1 crucible, and carry the exact mass into the analysis software. Conceal the material with the desired amount of accelerator and run the analysis.  
  • For each reference material used, repeat step 2 at least three times. Calibrate the analyzer with the blank values recorded under I. and the results acquired with reference materials II. (for further details, refer to the user manual).  

III. Sample Measurement  

  • Weigh ~0.2 g of sample into a preheated1 crucible and transfer a precise amount of the sample mass to the analysis software. Conceal the sample using the described amount of accelerator and run the analysis.
  • Repeat step 1 until a suitable amount of repetitions has been achieved. 

How to Determine Carbon and Sulfur in Cement

Image Credit: Bruker AXS Inc.

Calibration Example  

The typical concentration levels for total carbon and total sulfur in cement fall in the range of: Carbon: 0.3 – 3% (1 – 11 %CO2) and Sulfur: 0.005 - 1.5% (0.01 – 4 %SO3). In the cement industry, the concentration level is often expressed in the form of %CO2 for carbon and %SO3 for sulfur. 

The analysis software is capable of converting and reporting the result expressed in these units on the fly, but reference material may only be specified in %C and %S. The conversion factors are: %C → %CO2: 3.6641 and %S → %SO3: 2.4969. 

The typical concentration range is useful information to consider when selecting appropriate reference material for calibration. Although all detectors are linearized, and an extrapolation of the calibration curve is possible, it is good laboratory practice that all samples fall within the calibrated range.

In this example, the reference materials shown in Table 1 have been used:

Table 1. Reference materials used for calibration. Source: Bruker AXS Inc.

Standard (lot#) Material Total carbon / % Total sulfur / %
AR 4006 (411B) ore 4.19 4.07
AR 4007 (1212E) ore 7.27 3.26
AR 4012 (52199) limestone 11.97 0.044
EZRM B 483-1 cast iron 2.46 0.103
Ag2SO(p.a.) pure substance n.a. 10.12 – 10.28
(98.5 - 100% purity)

 

The resulting calibration curves for carbon and sulfur (Fig. 1) with R2 = 0.9999 prove the excellent linearity, accuracy and reproducibility of the G4 ICARUS Series 2 detection system and the entire method.

Calibration curve for carbon (top) and sulfur (bottom)

Figure 1. Calibration curve for carbon (top) and sulfur (bottom). Image Credit: Bruker AXS Inc. 

Notes: 

1For optimal precision, ceramic crucibles shall be pre-heated in a muffle furnace at ≥1250 °C for a minimum of 15 minutes or ≥1000 °C for a minimum of 2 hours. To avoid contamination, crucibles must be handled with clean tongs and transferred to a desiccator for storage. 

How to Determine Carbon and Sulfur in Cement

Image Credit: Bruker AXS Inc.

Results  

The reproducibility of the G4 ICARUS Series 2 and the method outlined is demonstrated by a series of 10 repetitive measurements of real cement production samples

Table 2. Cement Sample 1. Source: Bruker AXS Inc.

Mass / g %CO2 %SO3
0.2022 8.504 2.964
0.2022 8.446 2.969
0.2026 8.468 2.976
0.2016 8.471 2.961
0.2029 8.435 2.991
0.2039 8.453 2.941
0.2018 8.501 2.984
0.2017 8.464 2.951
0.2028 8.416 2.951
0.2003 8.449 2.979
Mean 8.46 2.97
STD 0.03 0.02
%RSD 0.3 0.5

 

Table 3. Cement Sample 2. Source: Bruker AXS Inc.

Mass / g %CO2 %SO3
0.2001 2.213 3.213
0.2018 2.224 3.211
0.1997 2.253 3.213
0.2026 2.246 3.196
0.2016 2.261 3.223
0.2010 2.220 3.228
0.2001 2.217 3.171
0.2011 2.257 3.241
0.2010 2.246 3.218
0.2035 2.239 3.196
Mean 2.24 3.21
STD 0.02 0.02
%RSD 0.8 0.6

 

Table 4. Cement Sample 3. Source: Bruker AXS Inc.

Mass / g %CO2 %SO3
0.2037 9.248 1.750
0.1998 9.208 1.723
0.2003 9.245 1.753
0.2001 9.215 1.730
0.2038 9.281 1.725
0.2030 9.278 1.725
0.2028 9.186 1.710
0.2020 9.230 1.735
0.2012 9.230 1.718
0.2004 9.179 1.725
Mean 9.23 1.73
STD 0.03 0.01
%RSD 0.4 0.8

 

Summary  

The combination of HighSense™ detection systems with precise electronic flow control in the G4 ICARUS Series 2 delivers excellent and long-time stable analytical performance. The powerful HF-furnace equipped with the industry-leading ZoneProtect™ and its unique automatic cleaner ensures the lowest cost of ownership and high availability with little maintenance. 

The sample preparation for this method is straightforward and does not require any expert knowledge. 

The analytical performance, in combination with the speed of analysis and its ease of use, makes the G4 ICARUS Series 2 the ideal addition to XRF analysis for the quality control of cement and related products. 

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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