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Abstract

Emanation coefficients for radon (222Rn) and thoron (220Rn) were measured from fully metamict samarskite collected from Centennial Cone after 1 h and 24 h annealing in argon from 473 to 1373 K. For the 1 h annealing run, 222Rn emanation coefficients ranged from 5 × 10-6 to 2.1 × 10-5 %, while 220Rn coefficients varied from 6.3 × 10-3 to 2 × 10-2 %. For the 24 h annealing run, 222Rn coefficients ranged from 5.8 × 10-6 to 2.3 × 10-5 %, while 220Rn coefficients varied from 4.1 × 10-3 to 1.5 × 10-2 %. The 222Rn and 220Rn emanation coefficients vs. annealing temperature data can be described by an exponentially decreasing sinusoidal function. Both 222Rn and 220Rn emanation coefficient values after annealing considerably exceeded those measured from an unheated powder reference sample and from the original samarskite sample.

Abstract

Carboxylation and decarboxylation are two fundamental classes of reactions that impact the cycling of carbon in and on Earth’s crust. These reactions play important roles in both long-term (primarily abiotic) and short-term (primarily biotic) carbon cycling. Long-term cycling is important in the subsurface and at subduction zones where organic carbon is decomposed and outgassed or recycled back to the mantle. Short-term reactions are driven by biology and have the ability to rapidly convert CO2 to biomass and vice versa. For instance, carboxylation is a critical reaction in primary production and metabolic pathways like photosynthesis in which sunlight provides energy to drive carbon fixation, whereas decarboxylation is a critical reaction in metabolic pathways like respiration and the tricarboxylic acid cycle. Early life and prebiotic chemistry on Earth likely relied heavily upon the abiotic synthesis of carboxylic acids. Over time, life has diversified (de)carboxylation reactions and incorporated them into many facets of cellular metabolism. Here we present a broad overview of the importance of carboxylation and decarboxylation reactions from both abiotic and biotic perspectives to highlight the importance of these reactions and compounds to planetary evolution.

Abstract

The copper-rich intermetallic compounds CaCu9Mg2 and SrCu9Mg2 were synthesized by induction melting of the elements and subsequent annealing in a muffle furnace. CaCu9Mg2 and SrCu9Mg2 crystallize with the TbCu9Mg2 type structure, space group P 63/mmc, which is a ternary ordered variant of CeNi3. The polycrystalline samples were characterized through their X-ray powder patterns. The CaCu9Mg2 structure was refined from single-crystal X-ray diffraction data. a = 504.13(9), c = 1622.5(3) pm, wR2 = 0.0635, 302 F2 values and 19 variables. The two striking coordination polyhedra in the CaCu9Mg2 structure are Ca@Cu18Mg2 and Mg@Cu12Mg3Ca. These polyhedra condense to layers which are stacked in ABA′B′ sequence. The X-ray data give no hint for Ca/Mg mixing.