Decay Process of Serpentinite: The Case of the San Giovanni Baptistery (Florence, Italy) Pavement

Serpentinite is a low-grade metamorphic rock derived from the transformation of ultramafic rocks. Mainly because of its aesthetic characteristics it has been widely used as a building and ornamental stone. “Verde di Prato” is the most common local name used in Tuscany to refer to this type of rock, historically quarried in this area and used for many centuries in a large number of monuments of this region. In this paper, we report the results of a study carried out on the serpentinite from the pavement of the Florence baptistery, to properly characterize it from a physical point of view, describe the rock conservation state, and understand the phenomena responsible for its decay. The studied rock displays numerous forms of decay including fractures, loss of material, erosion, discolouration and efflorescence. X-ray diffractometer analyses of the efflorescence revealed the presence of numerous salts whose formation can be imputed to multiple, possibly concomitant, causes such as the high relative humidity and the variation of inside temperature, the presence of concrete and/or cementitious mortars in the subsoil, atmospheric pollution and the burial ground existing close the baptistery.

Investigation of boron distribution and material migration on the W7-X divertor by picosecond LIBS

One set of horizontal target elements of the Test Divertor Units (TDU), retrieved from the Wendelstein 7-X (W7-X) vessel after the end of second divertor Operation Phase (OP1.2B) in Hydrogen (H), were investigated by picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS). The Boron (B) distribution, H pattern and the material erosion/deposition pattern on these target elements were analyzed with high depth resolution and mapped in the poloidal direction of W7-X. From the spectroscopic analysis, B, H, Carbon (C) and Molybdenum (Mo) were clearly identified. A non-uniformly distributed B pattern on these divertor target elements was determined by the combination of B layer deposition during the three boronizations and W7-X plasma operation with multiple erosion and deposition steps of B. Like the TDU, the analyzed target elements are made of fine grain graphite, but have two marker layers which allow us to determine the material migration via the ps-LIBS technique. Two net erosion zones including one main erosion zone with a peak erosion depth of 6.5 μm and one weak erosion with a peak erosion of 1.3 μm were determined. Between two net erosion zones, a net deposition zone with width of 135 mm and a thickness up to 3.5 μm at the peak deposition location was determined by the ps-LIBS technique. The B distributions are correlated with the erosion/deposition pattern and the operational time in standard magnetic configuration of W7-X in the phases after the boronizations. The thickness of the containing B layer on these target elements also correlates with the erosion/deposition depth, in which the thickness of the containing B layer varies spatially in poloidal direction between 0.1 μm and 6 μm. Complementary, Focused Ion Beam combined with Scanning Electron Microscopy (FIB-SEM) was employed also to verify and investigate the deposition layer thicknesses at typical net erosion and net deposition zones as well as to identify the three boronizations in depth.

Calibration-free laser-based spectroscopic study of Sn-based alloys

The elemental quantification of liquid metal divertor (LMD) surface is important for understanding the material erosion, migration, re-deposition, and fuel retention in Plasma-Facing Components (PFCs). Currently, LMD are attractive candidates for the short- and long-term operation of fusion devices like DEMO. Liquid metals can provide self-cooling, self-replenishing plasma-facing surfaces requiring very little upkeep. In a previous work, we studied Li and LiSn layers deposited on attachment screws in the COMPASS tokamak by means of CF-LIBS. Several problems were encountered related to the detection of Sn in LiSn. Thus, in the present work, we are optimizing the experimental conditions for the detection of Sn I-II and Pb I-II in Pb-containing Sn-based alloys, performing the quantification of Pb in traces and in bulk quantities using Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) approach.

Theoretical Modeling for Predicting Material Removal Rate through Interelectrode Gap

In EDM, the thermal energy of the discharge causing material erosion which is supplied by the power source unit as electrical input. The discharge energy may be recognized by the current and voltage pulses on time transient discharge characteristic curve (V-I curve) during machining. However, the plasma resistance is very short for a smaller interelectrode gap in micro-EDM compared to the impedance of the circuit. Hence, direct probe-based measurement of current and voltage pulses may include the voltage drop across the stray impedance which causes variation in its exact value. Here, a modeling-based approach may help to analyze the energy interaction with the interelectrode gap. This article presents a theoretical modeling approach to predict the interelectrode gap based on gap voltage, gap current, and plasma characteristics. Initially, a simplified two-dimensional heat conduction equation (cylindrical form) was studied to understand the asymmetry of heat flow in Gaussian distribution. A numerical analysis of a single discharge pulse was considered by applying some basic assumptions. A numerical model has been developed to predict gap distance and MRR considering gap voltage, gap current, and plasma properties. The predicted model was validated against previously reported data from the literature. Later on, the impact of gap voltage on gap distance, plasma resistance, and material erosion rate was analyzed and discussed briefly.

Supplemental Material: Erosion of the Himalaya-Karakoram recorded by Indus Fan deposits since the Oligocene

Analytical methods, age controls, data tables, and additional figures.<br>

Supplemental Material: Erosion of the Himalaya-Karakoram recorded by Indus Fan deposits since the Oligocene

Analytical methods, age controls, data tables, and additional figures.<br>

Effect of simultaneous N2 collisions on atomic oxygen-induced polyimide erosion in sub-low Earth orbit: comparison of laboratory and SLATS data

The role of N2 in the upper atmosphere on the atomic oxygen (AO)-induced erosion of polyimide in low Earth orbit (LEO) and sub-LEO is investigated through ground-based experiments and flight data. The experiment is performed by adding an Ar beam at the same collision energy as an undecomposed O2 component in the AO beam formed by laser detonation to simulate the physical effect of simultaneous N2 collision in sub-LEO. The Ar beam is added by the dual-pulsed supersonic valve-equipped laser-detonation system developed at Kobe University. The experimental results indicate that the erosion of polyimide in the laser-detonation system is promoted by the presence of O2 and Ar in the beam, corresponding to N2 in the sub-LEO. On-ground experimental results are compared with in-orbit AO measurements. Previous space shuttle, international space station-based exposure experiments, as well as the world’s first real-time sub-LEO material erosion data aboard a super low altitude test satellite (SLATS) orbiting at an altitude of 216.8 km are presented. The SLATS data suggests the presence of an acceleration effect by N2 collision on AO-induced polyimide erosion, as predicted by ground-based experiments.