Searching for the fundamentals of rehydroxylation dating of archaeological ceramics via NMR and IR microscopy

Determining absolute ages of archaeological ceramics is crucial for understanding past societies and reconstructing their accurate chronologies. The amount of OH hydroxyl chemically combined with ceramic material has been claimed to provide an ‘internal clock’ that can be read via RHX dating to determine the elapsed time since it was fired. The hydroxylation reaction, controlled by the slow diffusion of water molecules within the structure of clay minerals, has been described by a quartic root (time)^1/4 power law dependence. However, previous attempts of RHX dating by gravimetric methods have not been successful, since the mass gain due to OH hydroxylation or H₂O hydration could not be distinguished. We carried out a preliminary study of RHX dating via Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopy of three pure clay minerals, beidellite, illite and muscovite, as analogues for components of archaeological materials. Our study of RHX kinetics via IR microscopy gives important evidence regarding the quartic root time power law dependence. Furthermore, NMR allows us to study the structural as well as dynamic features of clays. Through observing the H/D exchange, we obtain access to the relevant activation energies and diffusion coefficients. We show that IR and NMR methods hold significant potential to refine the RHX dating method by understanding the elementary processes of mass transfer and hydroxylation in pure clays.     

Investigation of crystal growth of borax in single and dual impeller batch cooling crystallizer

Abstract

The purpose of this work was to investigate and compare the influence of fluid flow in a single and dual impeller batch cooling crystallizer on crystal growth kinetics of borax decahydrate. Examinations were conducted in a crystallizer of 15?dm³ stirred by a single pitched blade turbine and straight blade turbine as well as their dual configurations. Kinetics parameters of crystal growth determined at applied mixing conditions were correlated with hydrodynamic conditions. In this paper, hydrodynamics was characterized by mixing time, which was experimentally determined, and by fluid flow patterns, which were simulated by the means of computational fluid dynamic (CFD). It was found that although the crystal growth in all systems investigated was controlled by the integration mechanism, the crystal growth rate constant changed significantly with impeller configuration. Regarding the characteristics of the final product, a dependence of the crystal size distribution on the fluid flow pattern was noticed while the number of impellers did not affect the product properties. On the other hand, mixing efficiency differed significantly with the type and number of impellers.     

Structural and physical properties of the U9Fe7Ge24 uranium germanide

A new ternary compound, U₉Fe₇Ge₂₄, was synthesized by arc-melting the elements, followed by annealing at 900 °C. This compound was characterized by single crystal and powder X-ray diffraction, magnetization, specific heat and electrical transport measurements. It crystallizes in an original tetragonal structure type (space group I4/mmm), with lattice parameters a = 12.3789(2) Å and c = 18.2881(3) Å. Three uranium, eighth germanium, and three iron crystallographic sites exist in this structure, with the atoms making a stacking of infinite chains along the a and b axis. From their interatomic distances strong interactions between the uranium and germanium atoms can be predicted. The magnetic and specific heat measurements down to 2 K do not show any magnetic transition. The Curie–Weiss behaviour with a negative paramagnetic Curie temperature θp = ?94 K and reduced effective magnetic moment of μ_eff = 2.13 μ_B/U indicate that the compound is rather far from onset of magnetism, presumably due to a strong hybridisation of the 5f and ligand states. The electrical transport measurements show a metallic behaviour.     

The crystallization behavior of amorphous Fe–Sn–B ribbons

Amorphous Fe_(95?x)Sn₅B_x ribbons (x = 15, 17, 20) were prepared for the first time by planar-flow casting. Their thermodynamic stability and kinetics of crystallization were studied by differential thermal analysis, differential scanning calorimetry and magnetometry (thermobalance with permanent magnet). Formation of crystalline phases and their morphology were analyzed by X-ray diffraction and transmission electron microscopy. The results indicate the existence of critical composition for the transformation kinetics. The relation between the magnetic state of the material and the kinetics of crystallization was analyzed.