José Luis Ruvalcaba-Sil

Bio: José Luis Ruvalcaba-Sil is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Raman spectroscopy & Painting. The author has an hindex of 15, co-authored 69 publications receiving 600 citations. Previous affiliations of José Luis Ruvalcaba-Sil include University of Delaware & Université de Namur.

Boletín de la Sociedad Geológica Mexicana

Abstract: Resumen en: Palaeometry involves the combined use of different non-destructive analytical techniques on the study of fossil and subfossil materials. This work report...

Differential PIXE analysis of Mesoamerican jewelry items

Abstract: Gold jewelry items of Mesoamerican origin (from Peru, Colombia, Mexico, etc,…) are usually cast in Tumbaga: a man-made gold-copper-silver alloy containing a large proportion of copper. In order to give the objects a colour close to that of pure gold, ancient Mesoamerican goldsmiths experimented with a procedure to eliminate less noble metals (like copper and silver) from the surface. RBS may be used to identify a possible enrichment in gold in the most external layer of the items but due to the low capability of this technique to separate scattered particles on gold and silver and due to the low Rutherford cross section for α-particles on copper by comparison with those on gold, the determination of the exact depth depletion of copper cannot be easily reached. Differential PIXE is an appropriate method to achieve this goal. It takes the relative X-ray intensities of Cu and Au lines into account. By varying the incident proton energy, this ratio is modified in a completely different way if the sample is homogeneous or exhibits a layered or depth profile structure.

Surface-enhanced Raman spectroscopy spectra of Mexican dyestuffs

Abstract: Dyes were used in Mexico since early pre-Hispanic periods for coloring of fibers, codex writing, and mural paintings, among other purposes. From the wide variety of Mexican dyes, only a handful has been studied at length. Moreover, few studies had been devoted to the identification of these substances in artistic or historical objects, in part, because of the lack of a suitable technique that complies with the nondestructive or microdestructive requirements that involves working with such objects. Surface-enhanced Raman spectroscopy (SERS) may provide the tool needed to identify the more than 20 dyes that can be found in Mexico and the first step would be acquiring their SERS spectra in laboratory conditions. To fulfill that goal, carminic acid, cochineal (Dactylopius coccus), achiote (Bixa orellana), muitle (Justicia spicigera), zacatlaxcalli (Cuscuta sp.), brazilwood (Caesalpinia echinata), and cempazuchitl (Tagetes erecta) SERS spectra were recorded in aqueous solution and directly on dyed wool fibers, using silver colloids as SERS substrate. Ag nanoparticles were prepared by chemical reduction with sodium citrate and characterized by UV–Vis spectroscopy and high resolution transmission electronic microscopy. Pure carminic acid was used for control SERS spectra and then samples of cochineal, achiote, muitle, zacatlaxcalli, brazilwood, and cempazuchitl were tested. Samples were prepared either by extraction from their natural sources or by dyeing the fibers; in both cases traditional recipes were followed. The acquired spectra may serve in future research as comparative references for the identification of the dyes present in cultural artifacts, and in the case of cempazuchitl, muitle, and zacatlaxcalli, these are probably the first reported Raman spectra of such plants. Copyright © 2012 John Wiley & Sons, Ltd.

PIXE and Ionoluminescence for Mesoamerican Jadeite Characterization

Abstract: Greenstones were highly appreciated in pre-Hispanic Mesoamerica. Most of the finest green artefacts were worked in jadeite and other minerals such as serpentine and nephrite. Jadeite is perhaps the most precious stone of the jade family in ancient Mesoamerica, and it was widely used and traded since the Preclassic Horizon (1500 B.C.). The main beds are located in the Maya region, in the Motagua area of Guatemala. In this work, three pieces of a necklace of greenstones from an offering discovered in an extensive excavation carried out in the palatial structure of Xalla, at Teotihuacan site, in the central highlands of Mexico, were studied using external beam PIXE. The aim of this study is to determine the elemental composition of the greenstones and to establish the sourcing, trade and relationship between these regions. The offering corresponds to the early Miccaotli period (around 155 A.D.). The necklace is composed by eleven round pieces of green colors ranging from light to dark green. The analysis of three pieces was compared with several samples from Manzanal sources of Motagua. Green luminescence of high intensity was observed in the archaeological pieces but only in one case the luminescence was blue-violet. When comparing with the mineral samples of other green minerals, only the jadeite presented the green and violet luminescence. The corresponding spectra were obtained by proton induced luminescence in vacuum on the mineral samples. The comparison of the elemental composition of the archaeological items and the known mineral samples indicates that only one archaeological piece is related to the Manzanal source. The luminiscence spectra, corresponding mainly to Mn 2+ , Ce 3+ and Al 3+ emissions, are discussed. No correlation was observed among light emission color and jadeite sources.

Biosynthesis and characterization of silver nanoparticles prepared from two novel natural precursors by facile thermal decomposition methods.

Abstract: In this work, two natural sources, including pomegranate peel extract and cochineal dye were employed for the synthesis of silver nanoparticles. The natural silver complex from pomegranate peel extract resulted in nano-sized structures through solution-phase method, but this method was not efficient for cochineal dye-silver precursor and the as-formed products were highly agglomerated. Therefore, an alternative facile solid-state approach was investigated as for both natural precursors and the results showed successful production of well-dispersed nanoparticles with narrow size distribution for cochineal dye-silver precursor. The products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray microanalysis (EDX), and Transmission Electron Microscopy (TEM).

Role of Polymerization in the Dissolution of Nepheline, Jadeite, and Albite Glasses: Toward Better Models for Aluminosilicate Dissolution

Abstract: Introduction: Dissolution and precipitation of feldspar is an important reaction in many environmental systems, as plagioclase feldspar is the most common mineral in the crust. However, the mechanism of dissolution of feldspar has remained in dispute despite twenty or more years of analysis of feldspar dissolution. We are pursuing an approach toward better understanding of feldspar dissolution by investigating reactivity of aluminosilicate glasses of variable composition. In particular, to investigate the effects of Al/Si ratio on plagioclase dissolution without complications of varying Na/Ca content or exsolution, three glasses with varying Al/Si ratio (albite, jadeite, nepheline) were synthesized. Glass powders were then prepared and dissolved at various values of pH in batch reactors under ambient conditions. Solution chemistry was analyzed by inductively coupled plasma -optical emission spectroscopy or -mass spectrometry. In addition, alteration of the glass surface was investigated using Xray photoelectron spectroscopy, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy. Dissolution results: Many similarities in dissolution behavior between plagioclase crystals and this suite of glasses were observed: 1) dissolution was slowest at near-neutral pH and increased under acid and basic conditions, 2) dissolution rate at all pH values increased with increasing Al/Si ratio, 3) the pH dependence of dissolution was higher for the phase with Al/Si = 1 than the phase with Al/Si = 0.3, 4) after acid leaching, the extent of Al-depletion of the altered surface increased with increasing bulk Al/Si ratio from Al/Si = 0.3 (albite) to 0.5 (jadeite), but then decreased in nepheline (Al/Si = 1.0), which dissolved stoichiometrically with respect to Al, and 5) little to no Al depletion of the surface of any glass occurred at pH > 7. However, in contrast with some observations for plagioclase dissolution, log(rate) increased almost linearly with Al content, and n, the slope of the log(rate)pH curve at low pH, varied smoothly from albite to jadeite to nepheline (n = 0.3, 0.6, 1.0 respectively). At high pH, the slope of this curve, m, did not differ between glasses (m = -0.4 + 0.1). Mechanistic interpretation: These results are consistent with an identical mechanism controlling dissolution of nepheline, albite, and jadeite glass, although no Si-rich layer can develop on nepheline because of the lack of Si-O-Si linkages. Such a conclusion is consistent with a transition state for these aluminosilicates at high pH consisting of a deprotonated Q3 hydroxyl group (where Qv refers to an x atom in a tetrahedral site with v bridging oxygens) or a five-coordinate Si site after nucleophilic attack by OH, and, at low pH, a protonated Q4OQ4. At low pH, we infer that Q4OQ4 Al linkages are ratelimiting because they are presumed to hydrolyze more slowly than Qv OQw Si (v,w < 3). According to this model, dissolution rate increases from albite to jadeite to nepheline because hydrolysis of Al-O-Si linkages becomes more energetically favorable as the number of Al atoms per Si tetrahedral increases, a phenomenon documented by geometry optimizations using ab initio methods (for example, Figure 1). However, a model wherein Q4OQ4 Si linkages are faster to hydrolyze than lower connectivity linkages between Si atoms (Qv OQw , v,w < 3) may also explain aspects of this data.