Fluxers and Flux Mixtures

The borate fusion technique has the purpose of preparing near-homogenous or highly pure heterogenous samples for x-ray fluorescence (XRF) and inductively coupled plasma (ICP) analysis. Oxidized minerals are dissolved in a molten fusion flux product at a temperature of more than 1000 °C (1832 °F).

To encourage the molecules of the sample to dissolve in the molten borate flux, specialized furnaces are used. The furnaces have the function of increasing the temperature. In order for it to cool, the mixture is placed in a platinum mold. Usually, this method prepares fused discs, beads or heterogenous liquid fusions for ICP analysis.

Mixtures of lithium tetraborate (Li2B4O7) and lithium metaborate (LiBO2) are the main fusion flux products in raw form. However, protecting the platinum labware and achieving the highest possible purity of the samples are extremely important, so extra oxidizing ingredients and release agents are required for achieving those. This article post explores the fusion flux products available from XRF Scientific in more detail.

Fusion Flux Products: Borate Mixtures

Borates are chemical compounds, derivatives of the boric acid (BH3O3), which contain one or more boron atoms. These salts consist of lithium tetraborate and lithium metaborate, both of which can be used to dissolve oxidized materials at high temperatures.

There is a consensus in the scientific sphere that a tetraborate reacts well with base oxides, while a metaborate reacts well with acidic oxides. It is rare, however, for the two fusion flux products to be used in isolation. More often, mixtures of the two are used in the process of dissolving oxides into a eutectic mixture.

The range of fusion flux products available through XRF Scientific includes 100% lithium metaborate, which exhibits a high-reactivity with acidic oxides, such as silicon dioxide (SiO2). The lithium metaborate is ideal for wet chemistry application, although it is not typically used in XRF analyses.

Instead, lithium tetraborate of 100% purity is used for spectrochemical sample preparation, because it displays good reactivity with base oxides, such as calcium oxide (CaO) and magnesium oxide (MgO).

To determine the appropriate fusion flux products required in the preparation of samples, the acidity and basicity of the materials are of crucial importance. Borate fusion aims at altering the chemical properties of the sample, so that the neutrality of the homogenous disc or heterogenous solution is as high as possible. The prevalence towards borate mixtures of varying consistencies follows from its neutrality.

The fusion flux mixtures offered by XRF include:

  • Lithium tetraborate of 66%: lithium metaborate 34%. It is routinely used for fusion of geological samples, such as limestone and cement;
  • Lithium tetraborate of 50% and lithium metaborate of 50%. This is a general purpose fusion flux product with a relatively low melting point of 870 °C (1598 °F);
  • Lithium tetraborate of 35.3% and lithium metaborate 64.7%, an alkaline borate mixture for sample preparation of more acidic samples. However, it is generally considered a universal fusion flux product and is suitable for the preparation of iron ore, mineral sands, nickel, etc.

Fusion Flux Products: Non-Wetting Additives

The aforementioned mixtures can be augmented with extra compounds to improve the non-wetting and release characteristics of the fused material, or to oxidize sample compounds. XRF Scientific provides fusion flux mixtures with non-wetting lithium bromide (LiBr) or lithium iodide (LiI) at concentrations of up to 1.5%. Such concentrations reduce the risk of sample discs fusing to platinum labware and enable easy release after cooling. XRF also supplies lithium bromide assay separately at purity of up to 99.5%.

Alternative release agents are ammonium iodide anhydrous powder and ammonium iodide tablets.

Fusion Flux Products from XRF Scientific

XRF Scientific is a world leading manufacturer of borate flux products for XRF and ICP sample preparation. The company provides a sturdy method development service to ensure the formulations are optimized and to achieve quantitative results in the particular field.

How Does a Fusion Fluxer Work?

Fusion fluxers are sample preparation instruments for both X-ray fluorescence (XRF) and inductively coupled plasma (ICP) analysis. Both of the methods make it possible for researchers to assess the elemental composition of solid samples more precisely.

The XRF analysis also enables quality control of construction materials, such as iron and cement.  Moreover, the ICP spectroscopy is a versatile process that can serve multiple purposes. However, both XRF and ICP are methodologies requiring the samples to be of near-homogenous condition or of high-purity in order to ensure accuracy in the results.

Assessing samples without fusion flux preparation can lead to inaccuracy in the results. For instance, unfinished solid samples can exhibit surface variations that can intervene with an XRF spectrometer’s calibration.

The accuracy of the ICP results could also be affected by unprepared liquid samples that display irrelevant trace elements. Fusion fluxers reduce these margins of error by providing precise insights into sample XRF reactions and plasma ionization.

XRF Fusion Fluxer

A solid sample is first crushed, then it is weighed into a platinum crucible and dosed with an exact ratio of a lithium borate (Li2B4O7) fusion flux mixture. After that, it is transferred to the furnace chamber of the fusion fluxer, which typically consists of a thermally-resistant ceramic cradle. The cradle suspends the sample crucibles in the furnace chamber to guarantee a zero contamination.

To generate temperatures of up to 1250 °C (2282 °F), gas or electricity is used. Both can melt the sample and flux into a molten eutectic mixture, which is then rocked in a ceramic cradle - a technique that encourages the fusion process. After that, the molten mixture is mechanically poured into a platinum casting dish (mold), where the sample is, first, cooled, and then, hardened into a glass disc.

ICP Fusion Fluxer

The way in which samples are prepared through an ICP fusion fluxer is similar to the process described above, except that samples are prepared as heterogenous liquid mixtures, instead of as discs. The solid sample, which in the form of powder, is dosed with a lithium borate fusion mixture, and then placed within the ceramic cradle. The sample is dissolved in the fusion fluxer by heating and agitating it. After that, it is pouredput into a magnetically stirred beaker with acid solution.

Fusion Fluxers from XRF Scientific

XRF Scientific offers a large spectrum of fusion fluxers capable of preparing samples for XRF and ICP analysis. The products include:

  • Modutemp Shaking Fusion Furnace: a high-volume glass bead processing furnace with a continuous upper use limit of 1250 °C and a throughput of up to 30 beads per hour;
  • xrFuse 1: a compact electric fusion fluxer. It is used for specialized applications because of its smooth process and flexibility., The standard model is capable of preparing glass beads for XRF or ICP solutions;
  • xrFuse 2: a robust, automated fusion fluxer with a continuous upper use limit of 1200 °C (2192 °F) and an optional ICP solutions module;
  • xrFuse 6: a high throughput automated electric fusion fluxer that can produce up to 30 beads per hour with 12 distinct programmable recipes;

Phoenix II; an innovative gas-powered fusion fluxer with a continuous upper use limit of 1250 °C, and 20 programmable recipes for both XRF and ICP sample preparation.

This information has been sourced, reviewed and adapted from materials provided by XRF Scientific.

For more information on this source, please visit XRF Scientific.

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