使用EDXRF测定氟

Fluorite or fluorspar, a mineral composed of calcium and fluorine, is used in a number of industrial applications, namely in the production of aluminum, fluorine, fluorocarbons, and hydrofluoric acid. It also serves as flux in the manufacture of steels, lowering energy costs by reducing the melting temperature of the steel. The chemical formula of fluorite is CaF₂.

Since the purity of fluorite can vary greatly, analyzing the mineral rapidly and reliably is highly critical. Analytical techniques such as titration or ion chromatography are often used for determining fluorite, but these wet chemical methods require digestion of samples with acids. This, in turn, increases the time and cost of the analysis.

Conversely, X-ray fluorescence analysis (XRF) does not require sample digestion, making XRF the ideal analytical technique for grade control of industrial minerals. XRF analysis is straightforward, accurate, precise and rapid due to its simple sample preparation requirements. Energy dispersive X-ray fluorescence spectrometers (EDXRF) are the most commonly used instruments of the two major types of XRF spectrometer for product grade control.

然而，由于镁（Mg，Ka1 = 1.3KeV）和荧光（F，Kα1= 0.677KeV）吸收了低能量荧光，因此传统的EDXRF光谱仪对光元素的灵敏度非常差。

但是，带有XFLASH的EDXRF光谱仪S2 Ranger^®由于现代探测器技术，较薄的稳定入口窗和高功率直接激发的结合，LE探测器具有卓越的功能。使用Xflash的S2 Ranger对光元素，尤其是氟的分析^®本文讨论了LE探测器和AG目标X射线管。

Instrumentation

Xflash的S2游骑兵^®LE silicon drift detector (SDD) was used to perform the measurements. The system is an all-in-one benchtop system equipped with a user-friendly touchscreen interface, TouchControlTM (Figure 1). The XFlash^®LE silicon drift detector features an ultrathin, high transmission entrance window, which greatly optimizes the light element sensitivity.

Figure 1.S2 Ranger EDXRF光谱仪

The Ag target X-ray tube was used in place of the standard Pd target X-ray tube to eliminate overlays with tube lines, thereby providing optimum results for these elements. A typical spectrum of a sample containing calcium fluoride acquired with the Ag target X-ray tube is shown in Figure 2. The spectrum shows the clearly resolved F signal at 0.677keV, revealing the intensity increase with each standard.

Figure 2.Spectrum of a typical fluorspar sample in the low energy range of 0.45 to 0.85keV

实验程序

Sample Preparation

The experiment involved the preparation of samples as pressed pellets. For each preparation, 11g samples were milled with four grinding aid pellets from Polysius. A 40mm diameter pellet was produced using the automatic press APM from Polysius and an applied pressure of 150kN.

测量参数

The low energy and high energy lines were excited using two measurement regions. The detailed measurement parameters are summarized in Table 1. All measurements were carried out under vacuum. It took 4-5 minutes for the overall processing per sample which includes sample handling, evacuating the sample chamber and actual counting time for the measurement.

Table 1.Measurement parameters for the different elements

Elements	管电压[KV]	Tube current [µA]	筛选	Measurement time [s]
F，MG，SI	5	2000	没有任何	100
Ca	40	variable	500 µm Al	100

Calibration

Using a set of six in-house standards, calibration for Ca, F, SiO₂并进行了MG进行定量XRF测量。一种独立的分析技术已经验证了标准标准的化学组成。表2列出了不同标准的元素浓度。F，Mg和Ca的校准曲线分别显示在图3至5中。

表2。不同标准的元素浓度

	F [%]	Mg [%]	Si [%]	Ca [%]
Standard 1	27.84	1.80	7.26	41.38
Standard 2	22.78	2.34	9.30	39.00
Standard 3	47.45	0.03	0.64	50.20
Standard 4	47.16	0.06	0.71	50.47
Standard 5	36.70	0.75	7.90	43.15
Standard 6	41.37	0.59	4.13	46.88

Figure 3.Calibration curve for F

Figure 4.Calibration curve for Mg

Figure 5.Calibration curve for Ca

实验结果

具有标准的仪器的校准CA，F，SIO的校准₂and Mg was carried out. However, other compounds such as CaF₂or CaCO₃还确定了适当的过程控制。

It is possible to determine these compounds with minimal additional efforts. A muffle furnace is used to determine the loss on ignition (LOI) of the samples at 950°C. This content is automatically converted into the CO₃使用仪器软件浓缩。

The CaF₂concentration is estimated from the measured F concentration and the difference of Ca_total和CAF₂is used to calculate CaCO₃concentration. Table 3 summarizes the chemical composition for different samples.

Table 3.各种样品的化学组成

	Catotal [%]	F [%]	SiO2 [%]	Mg [%]	CAF2 [％]	CaCO3 [%]
样品	44.82	36.45	5.70	1.000	74.7	16.78
样品b	45.54	39.56	5.34	0.423	81.1	10.45
样品c	45.57	38.36	6.10	0.813	78.6	13.65
样品d	43.54	38.15	4.67	1.331	78.2	9.133

图6上以图形表示氟样品的氟的可重复性。红线表示测量的标准偏差。可以为每个元素定义仪器软件中的阈值，从而帮助用户确定“规范之外”样本。

Figure 6.显示F的样品B的可重复性

Conclusion

常规的EDXRF发现很难确定光元素，例如氟。但是，S2 Ranger可以非常准确，精确地确定这些光元素，这要归功于其直接激发技术，超薄高传输窗口和SDD的出色分辨率。

结果清楚地表明，配备Xflash LE的S2 Ranger的出色分析性能以及其在过程和质量控制方面的适用性。

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

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