Donald B. Dingwell

Amorphous carbonates are key phases in bio-geological processes. They also possess considerable unexplored potential for technological applications. We recovered a glass transition in biogenic amorphous calcium carbonate (ACC), extracted from...

Explosive volcanic eruptions are a major geo-hazard. Given the energetic nature of eruptive processes, direct observation is limited, making the study of deposits and pyroclast textures essential for understanding eruption dynamics. Experimental constraints therefore provide a vital contribution to improving hazard assessment. We performed tumbling experiments using pumice lapilli from the Laacher See eruption (Eifel, Germany) to investigate ash generation and pyroclast shape evolution. Before and after each experimental step, samples were sieved, and the volume and four morphological parameters (axial ratio, convexity, form factor, solidity) of 100 clasts were measured. Most shape change happened before the first 15 min (first experimental step) and produced up to 48 wt.% ash. We frame our analysis in terms of effective relaxation timescales, whereby pyroclasts display a decelerating rate of shape change towards a time-invariant morphology. This quantification of the susceptibility of porous pyroclasts to changes enhances our understanding of transport processes from clast generation to sedimentation.

Phosphorus is essential for extant and nascent life. However, phosphate’s low terrestrial abundance and the poor aqueous solubility of phosphorus-bearing minerals pose major hurdles for prebiotic chemistry. Here, we show that silicate-phosphate immiscibility in volcanic melts could have provided a widely available mechanism for the local enrichment of phosphate. Starting with a phosphorus-enriched Archean melt, we observe that rapid cooling results in the formation of immiscible glassy droplets with up to 21 weight % phosphorus pentoxide, which can be delivered to the surface by volcanic processes. In aqueous leaching, we detect millimolar phosphate concentrations, which enable the synthesis of phosphorylating agents such as polyphosphates and imidazole phosphate with up to 34% yield. These results demonstrate how volcanic processes can enrich phosphate to fuel prebiotic chemistry.

Environmental particulate deposits are the most severe factor causing high-temperature corrosion failure in advanced structural materials. Yet, the primary mechanisms of molten material corrosion under extreme conditions remain unclear, hindering the development and improvement of new crucial corrosion-resistant materials. “Ultra-high entropy” rare earth orthophosphates (REPOs) are one such promising class of materials. Here, we investigate the high-temperature structural state and properties of a wide range of substitutions involving 15 (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) rare earth elements in phosphates. Using stepwise stoichiometric compositional design, we aim to systematize our understanding of the corrosion resistance behavior of these complexes RE phosphates. We observe that high compositional complexity slows the reaction kinetics. Increasing rare-earth ionic radius, correlates positively with the chemical inertness of the synthesized material. This is overlain by phase state considerations whereby single-phase compositions exhibit the highest corrosion resistance. In summary, we infer that 1) the grade of complexity of rare earth mixtures; 2) the proportions of the individual rare earths and 3) the phase state of solid solution stoichiometries are the key factors in determining the corrosion resistance of these complex phosphate materials.