The Effect of Chemical Combination on the K X-ray Spectra of Silicon

Koffman, Donald M.; Moll, Sheldon H.

doi:10.1007/978-1-4684-7633-0_29

Cited by 5 publications

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“…Special attention has been paid to the coordination of aluminium and silicon in silicate minerals by several authors, e.g. Baun & Fischer 1964, Koffman & Moll 1965and Läuger 1968. Recently Dodd & Glenn (1968, 1969 combined the X-ray ÅT/?-spectrum with the so-called molecular orbital (MO) theory in order to explain the differences between the spectral lines from various aluminosilicates.…”

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confidence: 99%

The aluminium Kβ-band structure of andalusite, sillimanite and kyanite

Siivola¹

1971

Bull Geol Soc Finland

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The paper describes the results obtained from the x-ray Kß-band spectra of Al for andalusite, sillimanite and kyanite. The fine structure of the aluminium Kß-band is correlated with the crystal structure of these minerals. It is considered that the difference between the energies of the Kß-and .KTjS'-lines depends on the distance between the aluminium and oxygen atoms. The energy differences between the Al and O atoms in andalusite, sillimanite and kyanite have been determined. The energy differences show a linear correlation to the known interatomic distances.

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Section: Introductionmentioning

confidence: 99%

The aluminium Kβ-band structure of andalusite, sillimanite and kyanite

Siivola¹

1971

Bull Geol Soc Finland

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“…Since 1959, systematic shifts in both Al Kα and Kβ positions resulting from different bonding environments in Al-bearing phases have been recognized [2,3,4]. There is a clear Si Kα peak shift between Si metal and silicates and Kβ peak shifts between most phases [5]. There is little published on Mg Kα, whereas Mg Kβ shifts are more obvious [6].…”

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Al and Mg Kα Shifts in Common Silicate and Oxide Minerals: Relevance to Achieving the Goal of 1% Accuracy in EPMA

Fournelle¹

2006

Microsc Microanal

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During the early years (1920s) of x-ray spectroscopy, Lindh and Lunquist [1] demonstrated the existence of shifts in P, S and Cl Kβ peaks. These were characterized as resulting from differences in the electronic bonding, i.e., differences in the valence state. Since 1959, systematic shifts in both Al Kα and Kβ positions resulting from different bonding environments in Al-bearing phases have been recognized [2,3,4]. There is a clear Si Kα peak shift between Si metal and silicates and Kβ peak shifts between most phases [5]. There is little published on Mg Kα, whereas Mg Kβ shifts are more obvious [6]. Many of these studies from 3-4 decades ago utilized the electron microprobe as an explicit tool for studying bonding of various silicates and oxides.In 2003, during the course of troubleshooting some issues with accuracy of EPMA analyses of common alumino-silicate minerals in our lab [7], four facts emerged: 1) ROM automated peaking routines could return faulty peak center positions a significant number of times (not at the center of the peak, defined by fitting a curve to the upper ~90% of the peak and bisecting it), 2) the Al and Si Kα peak centers on TAP (99.5% of max counts) are ~5 sin theta units wide for feldspars, whereas wider (~12 units) on garnet, 3) there are systematic shifts in Al Kα peak positions for many common minerals, and 4) proper stage height (Z) is critical (i.e. Rowland circle focus), as a >2 micron error will act like a peak shift. The combination of subtle to not-so-subtle peak shifts between standard and unknown, exacerbated by ROM peak choices that were slightly off peak, lead to errors. One result was a modification of the software to include explicit operator controlled precise apex peaking during calibration [8].Mg Kα peak shifts: eight silicate and oxide minerals were evaluated for peak shifts relative to an Mg-Al alloy (later MgO was used as the reference, and the determined offset from Mg metal added). See Table 1. The maximum relative shift was on the order of 10 sin theta units, with spinels (Crspinel and MgAl 2 O 4 ) shifted 4-5 units below Mg metal, and the pyrope garnet (Mg 3 Al 2 Si 3 O 12 ) shifted over 13 units below Mg metal. Forsteritic olivine, enstatite and diopside were intermediate, shifted 8-9 units below Mg metal. These peaks are not very narrow, ~8-12 sin theta units wide, and one might first think that peak shifts would not be critical. Figure 1 shows the relative offset between pyrope and chromite peaks, and demonstrates that there is ~8 unit shift between the Cr-spinel and the pyrope peaks. When counts from both standards are acquired at the two different peak positions, there are 3-4% errors. Incorrect ROM peaking has been found to yield this range of error. (Table 2).Al Kα peak shifts: 14 silicate and oxide minerals were evaluated, relative to an Al-Fe alloy. Results are similar to those reported in 2004 [7] and to a recently discovered earlier study by Lauger cited by Weich [9], and we expanded our list to include 5 garnets (4 natural plus synthetic YAG) ( Tab...

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