Particle-Bound Mercury Characterization in the Central Italian Herbarium of the Natural History Museum of the University of Florence (Italy)

Museums air quality can be negatively affected by treatments with heavy metals compounds employed to prevent pest infestations. Among these, the past use of mercury dichloride (HgCl2) on herbaria artifacts currently produces high levels of indoor atmospheric gaseous mercury (Hg0) and possibly of particulate bound Hg (PBM), i.e., the particulate matter containing Hg. This study evaluates the PBM pollution in the Central Italian Herbarium (Natural History Museum of the University of Florence, Italy), characterizing the size range and chemical speciation with SEM-EDS microanalysis. The analysis of the total Hg concentration in the samples allowed to calculate the workers exposure risk to this pollutant. PBM is almost totally classifiable as fine particulate with a significant dimensional increase in a period of scarce attendance of the Herbarium rooms. The microanalysis indicates that Hg is essentially bound to S, highlighting the change of Hg speciation from the original association with Cl. The average Hg concentration reveals a potential health risk for workers as result of multiple Hg exposure pathways, mainly by ingestion. The study provides information for characterizing PBM pollution that could affect a workplace atmosphere and a useful basis to evaluate and correctly design solution strategies to reduce the contamination levels and protect workers’ health.

Microstructure of Rhenium Doped Ni-Cr Deposits Produced by Laser Cladding

The addition of Rhenium up to 6% to Ni-Cr alloys can dramatically improve the corrosion and oxide resistance of deposited coatings at high operating temperatures. Ni-Cr+Re layers can be successfully produced using conventional powder metallurgy, high rate solidification (HRS), or magnetron sputtering methods. However, in industrial applications, high-performance deposition methods are needed, e.g., laser cladding. Laser cladding has several advantages, e.g., metallurgical bonding, narrow heat-affected zone (HAZ), low dilution, and slight thermal damage to the substrate. In this paper, a powder Ni-Cr composite with 1% (wt.) of Rhenium was produced, then deposited onto a steel substrate (16Mo3) by laser cladding to assess the micro and macrostructural properties of the obtained layers. Besides the macro and microscopic observations, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) microanalysis of the deposit and HAZ as well as microhardness measurements have been conducted. The microstructure observations revealed four subareas of HAZ gradually changing from the fusion line towards the base material. Maximum hardness occurred in the HAZ, mainly in areas closer to the clad/substrate interface, reaching up to 350–400 HV. No sudden changes in the composition of the deposit and the area of fusion line were observed.

Mineral diagnostics: SEM-EDS Monte Carlo strategy for optimised measurements of ultrathin fragments in Cultural Heritage studies

The availability of minute quantities of sampling material is often an issue in the context of cultural heritage and archaeology due, for instance, to the value of the sample, its uniqueness or the small amount of residual material which testify the original form of the art to be restored. In this context, electron-excited energy-dispersive X-ray spectrometry (EDS) performed in a scanning electron microscope (SEM) has proven to be a primary methodology for analysing minute quantities of material thanks to its morphological and micro-analytical capability. However, when dealing with micro- and sub-micrometre specimens, as can be the case in ultrathin glass and metal fragments, several effects resulting from the physics and operational settings of the measurement must be considered to avoid quantification errors. In this paper, a detailed study of the effects of micro- and nanometric-sized glass and gold-alloy fragments on SEM-EDS microanalysis is presented. Monte Carlo simulations of different kinds of elongated glass fragment, with a square section and a thickness of 0.1 to 10 µm, and of some gold alloys demonstrated a strong influence in terms of the fragment size and operational conditions (beam energy, detector position, etc.). This work can be used to devise an appropriate and optimised measurement strategy.

Particulate bound mercury pollution in the Central Italian Herbarium (Firenze, Italy)

<p>The attention devoted to air quality is particularly important in workplaces, such as museums, where the health of visitors and workers must couple with the safeguard of collections. This especially holds for herbaria where, until the middle of the last century, the collections were protected using a solution of mercury dichloride (HgCl<sub>2</sub>) to prevent cryptogamic or animal infestations. The decomposition of HgCl<sub>2</sub> causes the Hg reduction through a reaction pathway that is still poorly known, and the consequent release of Hg<sup>0</sup> in the indoor atmosphere. Besides Hg<sup>0</sup>, Hg in air exists also as bound to particulate (PBM). In the museums’ atmosphere, this fraction may represent a non-negligible proportion of total atmospheric Hg and should be monitored.</p><p>This study aims to characterize the PBM in the <em>Central Italian Herbarium</em> of Firenze (University of Firenze, Italy), one of the largest herbaria worldwide. Here recent studies proved high levels of Hg<sup>0</sup>.</p><p>PBM sampling has been carried twice (2018 and 2020 soon after the lockdown period caused by the Covid-19), collecting the dust on a SEM-EDS stub from different surfaces (furniture, wall cornice, sample cabinet). Samples were roughly divided according to their deposition time between old (<em>OD</em>), almost-new (<em>AD</em>) and new dust (<em>ND</em>). The samples were analyzed using SEM-EDS to characterize the dimension and the chemical speciation of Hg particulate.</p><p>Hg-particles were detected in all the three types of dust collected in both the years: the mean dimension is 0.80±0.01 µm (3σ). The highest number of Hg-particles has been always reached in the <em>AD</em>, i.e. the dust collected directly on the packages containing herbarium specimens, with a strong increase in the 2020 sample. Additionally, the EDS microanalysis revealed that Hg-particles are now mainly associated with S (sometimes with O), suggesting the presence of sulphate or sulphide.</p><p>The above evidences show that PBM constitutes a fraction of Hg pollution in the <em>Herbarium</em> that cannot be ignored. The number of particles strongly increased in a period of low attendance of the <em>Herbarium</em> rooms and consequently cleaning, due to the COVID-19 pandemic: despite this, almost all are still classifiable as fine particulate (i.e. ECD< 2.5 µm) particularly harmful for human health. The presence of sulphate/sulphide indicated the change of Hg speciation with time and its reaction with S and O. These compounds, although less bioavailable than Hg<sup>0</sup>, still represent a risk for both herbarium workers and visitors.</p><p>The results of the present study offer preliminary information on the abatement system to be installed in the museum halls, which should be supplied with filters to retain very fine particles (< 1 µm).</p>

Considerations and Influencing Parameters in EDS Microanalysis of Biogenic Hydroxyapatite

Calcium phosphates (CPs) used as biomaterials have been intensively studied in recent years. In most studies, the determination of the chemical composition is mandatory. Due to the versatility and possibilities of performing qualitative and quantitative compositional analyses, energy dispersive spectrometry (EDS) is a widely used technique in this regard. The range of calcium phosphates is very diverse, the first method of approximating the type of compound being EDS microanalysis, by assessing the atomic Ca/P ratio. The value of this ratio can be influenced by several factors correlated with instrumental parameters and analysed samples. This article highlights the influence of the electron beam acceleration voltage (1 kV–30 kV) and of the particle size of calcium phosphate powders on the EDS analysis results. The characterised powders were obtained from bovine bones heat-treated at 1200 °C for 2 h, which have been ground and granulometrically sorted by mechanical vibration. The granulometric sorting generated three types of samples, with particle sizes < 20 μm, < 40 μm and < 100 μm, respectively. These were morphologically and dimensionally analysed by scanning electron microscopy (SEM) and compositionally by EDS, after the spectrometer was calibrated with a standard reference material (SRM) from NIST (National Institute of Standards and Technology). The results showed that the adjusting of acceleration voltage and of the powder particle size significantly influences the spectrum profile and the results of EDS analyses, which can lead to an erroneous primary identification of the analysed calcium phosphate type.

Metallographic Analysis of Stainless Steel Inner Shaft of Centrifugal Pump

The paper focuses on the metallographic analysis of the damaged inner shaft of a centrifugal pump with a magnetic clutch. This pump was used for the pumping of viscous suspensions. The damaged part of the centrifugal pump was made of stainless steel and transmitted power from the magnetic clutch to the impeller of the pump. The pump was overhauled by the Manufacturer after ten years of routine work. Slightly worn parts of the pump, including the inner stainless steel shaft, were replaced by the Manufacturer according to the preserved documentation. The overhauled pump failed after two days of running in the original conditions. The problematic is solved by an analysis of three used inner shafts with the aid of a metallographic analysis of the microstructure of the material, using light microscopy and scanning electron microscopy, and an EDS microanalysis of the chemical composition and hardness measurements.

Memristive Properties of PANI-Polysterene/PVDF-TrFE Interface

The article presents the results of an experimental study of the transport of charge carriers through semiconductor PANI-polystyrene/ ferroelectric PVDF-TrFE interface. Current-voltage characteristics of the structure under study have a typical form for memristors and may be explained by the movement of charge carriers in the internal switchable field of the crystal ferroelectric microregions located within a bulk volume of amorphous PVDF-TrFE matrix. This assumption is subject to XRD phase analysis, FTIR spectroscopy, and X-ray EDS microanalysis. A long-term (about 100 h) relaxation is detected for the resistance of the PANI-polysturene/PVDF-TrFE interface after the current-voltage characteristics measurement cycle that is associated with the processes of capture and release traps of charge carriers.