Atypical methods for characterization of used photovoltaic panels during their pre- and Post-Thermal treatment assessment

The study presents an innovative approach to the analysis of waste silicon photovoltaic panels prior and after thermal treatment. Using laser-induced breakdown spectroscopy (LIBS), the elemental composition of multilayered panel backsheets was determined, identifying a TiO2-containing coating laminate, a polyvinylidene fluoride (PVDF) layer, and an ethylene vinyl acetate (EVA) encapsulant, while also estimating their thickness. Identifying the fluorine-containing layers allowed their selective removal and safe processing of the used panels. Thermal processing parameters such as temperature (400-550 °C), time (5 - 60 min) and orientation of the busbar relative to the heat source were optimized based on contact angle measurements and CIELAB color space analysis, techniques used to detect organic residues in recovered glass and silicone. The decomposition process was examined by thermal analysis coupled with mass spectroscopy, which revealed that there were no volatile fluorine compounds in the gases released, although fluorine was detected on the recovered glass surface by SEM - EDS examination. After the PVDF layer was removed, fluorine compounds were not found in volatile gases or on the surface of recovered inorganic materials. The study indicated that the orientation of the busbars facilitates the decomposition of organic matter. Methods for reusing recovered secondary materials were also provided, suggesting the potential applications and benefits of recycling components from silicon photovoltaic panels.

The Effect of Biological Corrosion on the Hydration Processes of Synthetic Tricalcium Aluminate (C3A)

This paper presents a study related to the biological degradation of a tricalcium aluminate (C₃A) phase treated with reactive media from the agricultural industry. During one month of setting and hardening, synthetic C₃A was subjected to corrosion in corn silage, pig slurry and chicken manure. The hardening process of the C₃A phase in water was used as a reference sample. The phase composition and microstructure of the hydrating tricalcium aluminate slurries were characterised by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), scanning microscopy (SEM, EDS) and infrared spectroscopy (FT-IR). In the samples studied, it was observed that the qualitative and quantitative phase composition of the synthetic tricalcium aluminate preparations changed depending on the corrosion exposure conditions. The main crystalline phases formed by the hydration of the examined samples in water as well as in corrosive media were the catoite (Ca₃Al₂(OH)₁₂) and hydrocalumite (Ca₂Al(OH)₇·3H₂O) phases. Detailed analysis showed the occurrence of secondary crystallisation in hydrating samples and the phases were mainly calcium carbonates (CaCO₃) with different crystallite sizes. In the phase composition of the C₃A pastes, varying amounts of aluminium hydroxides (Al(OH)₃) were also present. The crystalline phases formed as a result of secondary crystallisation represented biological corrosion products, probably resulting from the reaction of hydrates with secondary products resulting from the metabolic processes of anaerobic bacterial respiration (from living matter) associated with the presence of bacteria in the reaction medium. The results obtained contribute towards the development of fast-acting and bio-corrosion-resistant special cements for use in bioenergetics.

Studies on Cement Pastes Exposed to Water and Solutions of Biological Waste

The paper presents studies on the early stages of biological corrosion of ordinary Portland cements (OPC) subjected to the reactive media from the agricultural industry. For ten months, cement pastes of CEM I type with various chemical compositions were exposed to pig slurry, and water was used as a reference. The phase composition and structure of hydrating cement pastes were characterized by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), and infrared spectroscopy (FT-IR). The mechanical strength of the cement pastes was examined. A 10 to 16% decrease in the mechanical strength of the samples subjected to pig slurry was observed. The results indicated the presence of thaumasite (C₃S·CO₂·SO₃·15H₂O) as a biological corrosion product, likely formed by the reaction of cement components with living matter resulting from the presence of bacteria in pig slurry. Apart from thaumasite, portlandite (Ca(OH)₂)—the product of hydration—as well as ettringite (C₃A·3CaSO₄·32H₂O) were also observed. The study showed the increase in the calcium carbonate (CaCO₃) phase. The occurrence of unreacted phases of cement clinker, i.e., dicalcium silicate (C₂S) and tricalcium aluminate (C₃A), in the samples was confirmed. The presence of thaumasite phase and the exposure condition-dependent disappearance of CSH phase (calcium silicate hydrate), resulting from the hydration of the cements, were demonstrated.

Spin relaxation by transient monopolar and bipolar optical orientation

We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the case of the material chosen, n-InSb, the increase was from 14 to 38 ps.