Validation of an alkali reaction, borate fusion, X-ray fluorescence method for silicon metal

Abstract

The value assignment of candidate Standard Reference Material ͑SRM®͒ 57b Silicon Metal provided an opportunity to develop an alkali reaction procedure as a precursor to borate fusion for the preparation of test specimens from the metal powder for X-ray fluorescence spectrometry ͑XRF͒. Suggested for this purpose by Blanchette in a 2002 Advances in X-ray Analysis article ͓ 45, 415-420 ͑2002͒ ͔, the alkali reaction uses LiOH · H 2 O to convert Si to Li 2 SiO 3 . Lithium silicate is fused with lithium borate flux without damage to platinum ware. Once specimens are fused and cast as beads, calibration standards are prepared to closely match the compositions of the specimens, allowing a linear calibration for each analyte. The XRF method yields results that are directly traceable to the mole through NIST SRM spectrometric solutions. The method was validated in two ways. First, the reaction was used on older SRMs for Si metal: SRM 57 and SRM 57a. Second, XRF results for candidate SRM 57b were compared to results obtained using prompt gamma-ray activation analysis ͑PGAA͒ and inductively coupled plasma optical emission spectrometry ͑ICPOES͒. Bias tests show the XRF results are accurate for the elements Al, S, Ca, Ti, Cr, Mn, Ni, Cu, and Zr. Levels of S, Ca, Cr, and Cu in candidate SRM 57b are near the limits of quantification of the borate fusion method. Iron results may be subject to a low bias. Phosphorus is not quantitatively retained during the alkali reaction and borate fusion. These elements, plus B, which cannot be determined after borate fusion, are listed in manufacturing specifications for Si metal.

Boron speciation in acid digests of metallurgical grade silicon reveals problem for accurate boron quantification by inductively coupled plasma – optical emission spectroscopy

“…The B concentration found by PGAA for NIST 57b in this study is approximately 5% higher than PGAA data quoted by Sieber et al, whereas our ICP-OES results obtained with the revised sample preparation protocol are in excellent agreement with Sieber's data. 18 It has to be mentioned though, that ICP-OES as well as PGAA results for NIST 57b reported in this study are based on a limited number of observations.…”

“…The B concentration for NIST 57b is only given as a reference value in the certicate and two different B concentrations are available in literature. 18 IPT 134 is not certied for its B content, does however contain a signicant amount of B measurable by ICP-OES. Whenever samples were not obtained as granulates or powders, they were crushed to a particle size of 1 mm at Elkem's central laboratory with a jaw crusher equipped with zircon oxide jaws (model BB 51, Retsch, Haan, Germany).…”

Atomic spectrometry update. Industrial analysis: metals, chemicals and advanced materials

“…Sieber, et al 28 described an XRF method for the determination of silicon metal and included impurities. A fused glass sample was made by reaction of the sample with LiOH to form Li 2 SiO 3 and followed by fluxing with lithium borate.…”

“…In the first, Sieber and co-workers validated an alkali reaction, borate fusion method of sample preparation followed by XRF measurement. 28 The authors used lithium hydroxide as a pre-treatment, which converts the silicon metal into lithium silicate and then fused this with lithium borate flux without any damage to platinum ware. Once the specimens were fused and cast as beads, calibration standards were prepared that matched as closely as possible the matrix of the sample.…”