Lithium tetraborate flux

Lithium tetraborate [1303-94-2], is used as a flux in ceramics and in x-ray fluorescence spectroscopy. The salt has also been proposed for... 

Probably the most common fluxes are sodium carbonate (Na2C03), lithium tetraborate (Li2B407), and lithium metaborate (LiB02). Fluxes maybe used by themselves or in combination with other compounds, such as oxidizing agents (nitrates, chlorates, and peroxides). Applications include silicates and silica-based samples and metal oxides. 

Melting of samples is necessary for performing the analysis of ceramics and glass materials by means of x-ray fluorescence (XRF). Lithium tetraborate is added as flux for lowering the melting temperature. The homogeneous disks that form can be considered a solid solution of the sample compounds in the binder. 

Most fusions use lithium tetraborate (Li2B407, m.p. 930°C), lithium metaborate (LiB02, m.p. 845°C), or a mixture of the two. A nonwetting agent such as KT can be added to prevent the flux from sticking to the crucible. For example, 0.2 g of cement might be fused with 2 g of Li2B407 and 30 mg of KI. 

The introduction of atomic absorption spectroscopy has resulted in major advances in the rapid analysis of many elements. Initially, atomic absorption was applied only to aqueous systems or to materials that could be readily solubilized. There are methods to analyze major elements in such complex materials as silicates and vitreous siliceous coal ashes (1-5). More recently, lithium metaborate has been reported to be a good fluxing agent (6) and has also been used in conjunction with atomic absorption analysis in silicate analysis (7). This paper describes a lithium tetraborate-atomic absorption analytical technique which is being used to analyze coal ash. 

In the form of a solid solution (or pearls) by dilution in a flux powder based on a mixture of lithium metaborate and lithium tetraborate (analysis of major elements)... 

ABSTRACT A rapid and precise X-ray fluorescence method has been developed for the multielement analysis of gypsum and gypsum products. Gypsum specimens are calcined at IOOO°C and then fused with sodium tetraborate flux into flat and transparent disks. The choice of a suitable flux system for the specimen preparation is critical because of a rapid decomposition of anhydrite. CaSO,. in lithium ba fluxes at temperatures above 95O C. This decomposition causes not only visible imperfections in the didi surface but also alters considerably the concentrations of the major elements, calcium and sulfur. The procedure used for a fast setup of ten element analysis of gypsum on the Philips PW-1400 spectrometer utilizing synthetic standards and off-line calculated alpha coefficients is presented. Calibrations carried out with chemically analyzed specimens and their mixtures are compared lo those performed with synthetic standards prepared by blending pure chemicals and anhydrite into the flux. 

The most popular and elegant specimen preparation technique introduced by Claisse 17] is based on fusion of solid specimens with lithium tetraborate. The method was used with great success in our laboratory for the rapid quantitative X-ray fluorescence analysis of silicates, bricks, refractories, limes, iron, and manganese ores. The use of lithium tetraborate and lithium fluoride flux systems was therefore examined first. 

A small amount, 2.5 to 3.0 g of representative gypsum specimen, was calcined for 1 h at 1000°C in a platinum crucible, and the loss on ignition was recorded. A portion of 1.0000 g of the calcined specimen was mixed with 6.000 g of dense lithium tetraborate (Spectroflux 100 , Johnson and Matthey Co.) and 0.3000 g of lithium fluoride. Approximately 3 mg of lithium bromide was added to the mixture as a release (nonsticking) agent. Fusions were carried out on a propane flame, using a Claisse fluxer (2] equipped with crucibles and molds made from 95% platinum-5% gold alloy. The volume of molten flux was adequate to fill the 32-mm diameter mold to a sufficient height and produce a disk approximately 4 mm thick. 

Because of the suspected decomposition of anhydrite, CaSO4, in lithium-based tetraborate flux systems at elevated temperatures, it was decided to study their behavior by means of thennal analysis (TGA, DTA). Thermal scans were performed on the Mettler TA-2 thermoanalyzer equipped with a DTA-20 macroholder. Platinum crucibles were filled with 200 mg of specimen flux mixtures and balanced by equal portions of alumina as the reference material. All specimens were heated at a rate of 10 C/min in an oxidation atmosphere (stream of air). 

When lithium tetraborate and lithium fluoride are used as a flux, or when... 

Like cements, the composition of clay is established by either XRF or AAS/ICP-AES. However, it is necessary to modify the method of preparation of the fused bead by using a mixture of lithium tetraborate and lithium metaborate as the flux rather than lithium tetraborate alone. 

Chrome-bearing refractories are particularly difficult to fuse, and, although not entirely satisfactory, a flux mixture of 10 parts of lithium metaborate and 12.5 parts of lithium tetraborate to one part of sample is generally used for chrome-magnesite, chrome-magnesia—zirconia and chrome ore samples, but not metallvugical chrome ore, which requires further dilution in MgO. 

The reduced materials (category (f)) require special fusion conditions because dissolution produces an exothermic reaction that can destroy the platinum alloy fusion vessels. For example, the flux used for sihceous materials is reconstituted as lithium tetraborate and hthium carbonate. A SiC or other reduced sample is mixed with lithium carbonate and sintered on top of a protective layer of lithium tetraborate that has been fused and spread over the dish. The weight of the reduced sample therefore needs to be adjusted to maintain the flux to a (oxidized) sample ratio at 5 1. If samples lie in category (c), lithium tetraborate is replaced by boric oxide, which together with the lithium carbonate will ultimately give the appropriate lithium tetraborate/sample ratio (ignited basis). 

Inorganic substances that do not dissolve in acid can usually be dissolved by a hot, molten inorganic flux, examples of which are lithium tetraborate ( 26407) and sodium hydroxide (NaOH). Mix the finely powdered unknown with a mass of solid flux that is 2 to 20 times the mass of the unknown. Fuse (melt) the mixture in a platinum-gold alloy crucible at 300° to 1 200°C in a furnace or over a burner. When the sample is homogeneous, carefully pour the molten flux into a beaker containing 10 wt% aqueous HNO to dissolve the product. 

A fourth method involves the dilution of the sample into a matrix so that the major constituents are the same for both standards and samples. Fusion fluxes often used for this purpose include borax, boric acid, lithium tetraborate and sodium tetraborate (Plowman, 1971 Matsumura et al., 1973 Chandola and Mobile, 1976). Dilution into a dry powder mixture is also effective. Lytle and Heady (1959) recommended LiCOj as a suitable diluent. For both the thin sample and the dilution techniques, detectability is sacrificed for improved accuracy. Consequently, these methods are mainly applied to rare earth determinations at the major and minor constituent levels. 

The advantages of using sodium tetraborate for the fusions outweigh the loss of sodium as an analyzed element. Times required for the fusion and swirling of the flux on flame (Table 1) were quite short. The use of lithium fluoride and lithium bromide was eliminated completely. The disks prepared from sodium tetraborate release easily from the molds each time, without any sign of sticking, cracking, or crystallization. 

After reaching the upper temperature set limit, the temperature was held constant (isothermal hold) for several hours. The weight-loss curves (TG) are shown in Fig. 1. The weight losses recorded on lithium and sodium fluxes alone (Spec-troflux 100 and 200) caused by thermal decomposition above i000°C were negligible. Similar results were obtained with mixtures of anhydrite and sodium tetraborate. The latter showed a weight loss of less than 0.1% when heated at lOOO C for 1 h. 

Boric acid Copper oxide (ic) Lithium chloride Lithium fluoride Potassium tetraborate Tributyl borate Zirconium potassium hexafluoride welding flux, gaseous Trimethyl borate welding fluxes, special Zirconium welding gas Oxygen... 

---