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Application Note 19 Measurement of Calcium Fluoride Content in Fluorspar Application Note 20

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Application Note 19 Measurement of Calcium Fluoride Content in Fluorspar Application Note 20

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Fluorine

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39 views3 pages

Application Note 19 Measurement of Calcium Fluoride Content in Fluorspar Application Note 20

Uploaded by

hamid
Fluorine

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© All Rights Reserved
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NMR

Measurement of Calcium Fluoride


Content in Fluorspar

Summary
Application Note 20

• Fast, accurate and repeatable


• No sample preparation
• Simple linear calibration
• Esuitable
asiest, most reliable technique available;
for unskilled personnel

Application Method

The mineral fluorspar (or fluorite) is the most important The analytical technique is based on direct measurement of
source of fluorine. The purity (calcium fluoride content) of the the Nuclear Magnetic Resonance (NMR) signal of fluorine-19
mineral will determine its eventual use in the steel, aluminium which has 100% natural abundance. It is assumed that the

or chemical industries. The highest grade is used to produce measured NMR response is linearly proportional to the CaF2-
content of a material. The acquired NMR signal is normalised
hydrogen fluoride which is a precursor to many important
by the sample mass and then the CaF2 content (weight-%) is
compounds including pharmaceuticals and polymers, e.g.
calculated using an appropriate calibration curve.
polytetrafluoroethylene (PTFE), known by the commercial
name of Teflon. It is therefore important to determine the Calibration
fluorine content of fluorspar for commercial and quality It is possible to calibrate the MQC using only two samples
control purposes. if the reference values are known to be accurate. However,
initially it is recommended that the instrument is calibrated
Advantages of NMR by 3-6, preferably more, standards with known CaF2
Conventional wet chemical methods of calcium fluoride contents evenly spread over the range of interest. NMR is a
(CaF2) determination include measurement of fluoride by ion comparative technique therefore cannot be more accurate
selective electrode or ion chromatography, and calcium by than the reference technique against which it is being
complexometric titrimetry (ASTM E815). All of these methods compared; error is reduced by analysing more reference
are time-consuming operations, require skilled chemists and samples.
involve the use of potentially hazardous chemicals which
require disposal, all of which contribute to the cost of the
analysis.

The MQC benchtop Nuclear Magnetic Resonance (NMR)


analyser offers a simple, non-destructive and rapid method
for measurement of fluorine in fluorspar which may be used
for routine analysis in a production environment without any
requirement for additional chemicals and specialist operator
training.
NMR
Measurement of Calcium Fluoride Content in Fluorspar

Figure 1: NMR calibration for calcium fluoride in fluorspar Measurement


A tared sample tube is filled to a given height with the powder
sample, then weighed prior to NMR analysis. Measurement time is
80 seconds per sample.

Results
Table 1 shows a comparison of the predicted NMR values against
the given reference values. Deviations can be accounted for by
error in the reference values as well as fluorine from sources other
than calcium fluoride contributing to the NMR signal.
Table 2 shows that the repeatability (or precision) of the NMR
measurement of the same sample is excellent.

Table 1: NMR results predicted for calibration samples

Sample ID Given %CaF2 (wt.-%) Predicted %CaF2 (wt.-%) Difference %CaF2 (wt.-%)

FG1 81.9 83.5 +1.6


FG2 66.0 66.3 +0.3
FG3 11.3 12.6 +1.3
FG4 26.8 24.2 -2.6
FG5 47.7 45.1 -2.6
FG6 11.6 11.6 +0.0
FG7 10.7 12.5 +1.8
FG8 43.8 44.1 +0.3

Table 2: Measurement repeatability of the same fluorspar sample Conclusion

Repeat Measured CaF2 content, %


• A primary calibration can cover a concentration range
from 0 to 100%
1 37.1 • NMR is very stable over the long term and rarely needs
2 37.0 calibration adjustment
3 37.3 • NMR is insensitive to the air voids between grains of
4 37.1 powder
5 37.2
• Measurement precision is good compared to wet
6 37.0 chemical methods
7 37.0
• Sample measurement time is rapid
8
9
37.1
37.2
• The NMR technique is non-destructive so the same
sample may be measured several times before being
10 37.0 analysed by other techniques
Mean % 37.1
Std. Dev. % 0.1

2
Application Note 19
Complete Package
Oxford Instruments offers a package especially tailored to the measurement of fluorine in fluorspar.

• Oxford Instruments MQCF NMR Analyser


• 0.55 Tesla (22 MHz) high homogeneity magnet
• Probe for 26 mm diameter sample tubes (14 ml sample volume)
• Integrated system controller (no external PC required)
• Integrated flat-screen display

• MultiQuant software including RI Calibration, RI Analysis, and the EasyCal


‘Fluorine in Fluorspar' application which guides the user through the calibration and
analysis procedures

• Test/tuning samples
• Glass tubes
• User manual
• Method sheet
Optional items are:

• A precision balance
• A dry heater and aluminium block with holes for
sample conditioning at 40°C (optional)

visit www.oxford-instruments.com/mqc for more information or email: industrial@oxinst.com

This publication is the copyright of Oxford Instruments and provides outline information only which (unless agreed by the company in
writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation
relating to the products or services concerned. Oxford Instruments’ policy is one of continued improvement. The company reserves the
right to alter, without notice, the specification, design or conditions of supply of any product or service. Oxford Instruments acknowledges
all trademarks and registrations. © Oxford Instruments plc, 2014. All rights reserved. Ref:CaF2-04-14
2421

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