Ultramarine, Lazurite and Sodalite Studied by Positron Annihilation and EPR Methods

Abstract

Studies of positron annihilation accompanied by EPR technique were undertaken for sodalite and lazurite and their synthetic counterparts (synthetic sodalite and ultramarines). Results of measurements performed by two techniques of positron annihilation spectroscopy (angular correlation of annihilation radiation, ACAR, and positron annihilation lifetime) revealed the undoubted influence of free radicałs on positron annihilation mechanism but both inhibition of positronium formation by them and the effect of filling cages ought to be taken into account. The distinct differences between ACAR curves for sodalites, lazurites and ultramarines probably reflect the presence of different radicals in their cages and chemical heterogeneity as well as the disorder in Al, Si-site ordering in case of ultramarines. Comparison of the results of ACAR measurements with the ones of the EPR studies indicates that there is correspondence between them. Similarly to three families of the ACAR curves, different likes of EPR lines were obtained for three groups of samples; sodalites, lazurites and ultramarines. It is possible that the annihilation of positrons takes place mainly with unpaired electrons recorded by the EPR technique.PACS numbers: 61.90.+d, 71.60.+z, 76.30.-v, 78.70.-g (29) 30 A. Baranowski et al.

Sulfur K-edge XANES of lazurite: Toward determining the provenance of lapis lazuli

“…Sensitive to the formal oxidation state and coordination chemistry of sulfur 39 , sulfur K-edge XANES is ideal for probing the sulfur chemistry of lazurite and has been previously employed in lazurite studies by Tauson et al 40 , Fleet et al 41,42 , and Goettlicher et al 14 . Because of the sensitivity of XANES to transitions from all of the present sulfur species, resultant data strongly complements recent multi-technique studies of lapis lazuli and ultramarine [15][16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][37][38]40 . The technique is also particularly attractive for use in the field of cultural heritage as it is non-destructive and requires little to no sampling; however, it requires a helium (or vacuum) chamber with fixed incident beam and detector geometries, limiting the size/shape of objects that can be examined in-situ.…”

“…Here we examine the provenance of lapis lazuli-prior to studying processed materials such as pigments-by focusing specifically on the sulfur speciation within lazurite. Although the mechanism is not well understood, the variation in the color of lazurite is thought to arise from altered ratios of the sulfur species, with the blue color attributed to the trisulfur radical (S3 .-) and deviations from blue a result of disulfur (S2 .-) and tetrasulfur (S4 .-) radical species respectively contributing yellow and red to the overall color of lazurite [26][27][28][29][30][31][32][33][34][35][36][37][38] . While many researchers have demonstrated via a variety of measurements the existence and stabilized presence of the disulfur and trisulfur species within the lazurite structure, the actual occurrence of a tetrasulfur radical is less understood 35 .…”

Structural, Optical, and Magnetic Properties of Ultramarine Pigments: A DFT Insight

“…The properties of S 3 – radicals inside UM have been studied by spectroscopic techniques, mainly electron paramagnetic resonance (EPR), ,,− Raman, ,,,,− and ultraviolet–visible (UV–vis) spectroscopy. ,,,,, Other techniques are also occasionally used, such as positron annihilation, infrared, nuclear magnetic resonance, ,, X-ray photoelectron, ,, and recently X-ray absorption spectroscopy (XAS). ,, …”

Annihilation of o-Positronium in the Vicinity of the Critical Mixing Point

“…Positron annihilation measurements are a suitable experimental technique for investigation of solid minerals [22], polymers [23], as well as for investigation of clathrate-like structures in diluted aqueous mixtures of non-electrolytes [24][25][26].…”