The Fusion of Difficult Materials Including Chromite, Cassiterite and Reduced Sulphur

Abstract

The practice of adding alkali metal nitrates such as sodium nitrate to borate Ñuxes and pre-oxidizing samples at low temperature has been taken a logical step further by the synthesis of sodium borate Ñuxes via the use of intimate mixtures of sodium nitrate and boric acid. The process of low-temperature pre-Ðring/decomposition followed by melting at normal high temperature gives enormous oxidative power yet does not give rise to crucible attack and provides a convenient route to produce Ñuxes from cheap and highly pure starting materials. An improvement in the efficacy of attack for a number of sample types has been observed, allowing for much smaller dilution ratios than have hitherto been achieved for chromite and cassiterite samples, for instance. Further, the inherent ease of formulation allows for the Ðnal stoichiometry to be achieved in stages whereby a liner can be made in a platinum crucible consisting of all of the boric oxide and a small amount of the sodium oxide. The remaining sodium oxide is added in the form of sodium peroxide mixed with the sample, which is sintered at a low temperature followed by safe decomposition and fusion at normal temperature. The use of pure alumina crucibles is shown to be possible for samples of such a nature that attack on platinum ware is to be feared and has allowed the use of sodium peroxide for the fusion of ferro-chrome and ferro-niobium. The complete retention of pyritic sulphur in the above methods and with lithium carbonate-tetraborate Ñuxes has been chemically proven.

XRF analysis of chromite‐rich samples—another look at powder briquettes

“…The selection of any analytical procedure has to be based on the requirements for, and applications of, the results. Producing glass disks with high dilution factors might create results without textural and mineralogical effects; however, by weighing errors an increased chance of not having a representative sample and high dilution (0.25 g sample in 10 g flux) 30 will in all likelihood make such an approach unsuitable if the emphasis of the investigation is to include minor and trace elements. Where speed of sample preparation and cost savings are of prime importance, like in a process control environment where trends are of more importance than accurate concentration values, micronizing chromitite samples and the preparation of powder briquettes appear to be a viable alternative to the production of glass disks.…”

Analysis of corrosion residues by WDXRF

“…Several studies on the characterization of non-oxide materials have been found in the literature. Sear [1] studied the optimal sample preparation for adequate recovery of the analytes in materials with high contents of sulfides. Schwartz et al [2] studied the sample preparation for the analysis of ferrosilicon and silicon carbide by X-ray fluorescence spectrometry, and Gómez et al [3] developed a methodology to control ferroalloys by means of instrumental techniques.…”

A thermogravimetric analysis study of volatilization of flux mixtures used in XRF sample preparation

“…Even after 45 years of using fused beads for XRF analysis, certain matrices still prove to be problematic. Although a number of reports on fusion methods for chromite-, sulphide-and cassiterite-rich materials have been published, 6,7 routine methods for these are still eluding analytical chemists. Lengthy fusion steps at temperatures in excess of 1100°C are often stipulated 6,8 for refractory materials and ores.…”