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A high performance method for the accurate and precise determination of silicon isotopic compositions in bulk silicate rock samples using laser ablation MC-ICP-MS
摘要： MC-ICP-MS has become one of the most powerful analytical methods for Si isotopes in bulk liquid and solid samples in the past decade. Laser ablation provides direct sampling of solid samples, avoiding laborious chemical digestion procedures. As for powder bulk samples, the preparation of stable and homogeneous targets prior to measurements, and strategies to minimize potential matrix effects, are critical for accurate isotopic analysis. In this study, an accurate and precise method for Si isotope ratio measurements by fs-LA-MC-ICP-MS of bulk silicate rock samples was established. A new laser fusion sample preparation technique was developed to achieve fast and homogeneous fusion of silicate rock powders (including granite and granodiorite that contain abundant refractory minerals) into glasses. Compared to the pressed pellet technique, the measurement precision for fused glasses was improved ~5.7-fold. Matrix effects during Si isotopic analysis were observed when using non-matrix matched calibration protocols under normal dry-plasma instrument conditions with both ns- and fs-laser using a raster ablation mode. Matrix effects were eliminated by the addition of water vapor into the plasma, realizing accurate non-matrix matched calibration. In addition, fs-laser provided better measurement precisions, with the internal and external precisions being improved ~1.85 and ~2.4 fold compared to ns-laser at nearly equal signal intensities. Five well characterized silicate rock reference materials were analyzed using fs-LA-MC-ICP-MS calibrated against NBS-28 and BHVO-2G. Results obtained for =29Si and =30Si for these five reference materials were in agreement with previously reported values, confirming the accuracy of the proposed method.
关键词： matrix effects,Silicon isotopic analysis,water vapor addition,laser ablation MC-ICP-MS,silicate rock samples
更新于2025-09-23 15:21:01
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Direct mineralogical imaging of economic ore and rock samples with multi-modal nonlinear optical microscopy
摘要： Multi-modal nonlinear optical (NLO) microscopy, including stimulated Raman scattering (SRS) and second harmonic generation (SHG), was used to directly image mineralogical features of economic ore and rock samples. In SRS/SHG imaging, ore samples generally require minimal preparation and may be rapidly imaged, even in their wet state. 3D structural details, at submicron resolution, are revealed tens of microns deep within samples. Standard mineral imaging based on scanning electron microscopy (SEM), with elemental analysis via energy dispersive X-Ray spectroscopy, was used to independently validate the mineral composition of the samples. Spatially-resolved SRS from dominant Raman-resonant bands precisely maps the locations of specific minerals contained within the samples. SHG imaging reveals locally non-centrosymmetric structures, such as quartz grains. Competing absorption and nonlinear scattering processes, however, can reduce contrast in SRS imaging. Importantly, the correlation between standard electron microscopy and multi-modal NLO optical microscopy shows that the latter offers rapid image contrast based on the mineral content of the sample.
关键词： mineralogical imaging,second harmonic generation,stimulated Raman scattering,rock samples,nonlinear optical microscopy,economic ore
更新于2025-09-23 15:21:01
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Thermal/Mechanical Interaction in Laser Perforation Process: Numerical-Model Buildup and Parametric Study
摘要： In this paper, a generic thermal/mechanical interaction model was developed to predict the penetration rate and mechanical damage around perforation tunnels that resulted from the laser perforation of rock samples. The perforating process is driven by heat emitted by a laser beam directed at the surface of a sample. The temperature propagation, thermal expansion, and thermal/mechanical interaction were modeled by coupling heat conduction in solid media with the elastic/plastic constitutive mechanical response of rocks. The phase changes that occur during the melting and evaporating process were accounted for in the latent heat of fusion and of vaporization. The heating boundary was updated dynamically along with the evolution of perforation channels. The model was used to parametrically investigate the effects of material properties, stress ratio, and laser-beam characteristics on the penetration rate and mechanical damage.
关键词： mechanical damage,numerical model,laser perforation,rock samples,thermal/mechanical interaction,penetration rate
更新于2025-09-11 14:15:04