Biomechanical design of a new proximal humerus fracture plate using alternative materials.

Comminuted proximal humerus fractures are often repaired by metal plates, but potentially still experience bone refracture, bone "stress shielding," screw perforation, delayed healing, and so forth. This "proof of principle" investigation is the initial step towards the design of a new plate using alternative materials to address some of these problems. Finite element modeling was used to create design graphs for bone stress, plate stress, screw stress, and interfragmentary motion via three different fixations (no, 1, or 2 "kickstand" [KS] screws across the fracture) using a wide range of plate elastic moduli (E = 5-200 GPa).

Scaling high-speed counter-current chromatography for preparative neodymium purification: Insights and challenges.

Efficient rare earth element (REE) separations are becoming increasingly important to technologies ranging from renewable energy and high-performance magnets to applied radioisotope separations. These separations are made challenging by the extremely similar chemical and physical characteristics of the individual elements, which almost always occupy the 3+ oxidation state under ambient conditions. Herein, we discuss the development of a novel REE separation aimed at obtaining purified samples of neodymium (Nd) on a multi-milligram scale using high-speed counter-current chromatography (HSCCC).

Separation of rare earth element radioisotopes by reverse-phase high-speed counter-current chromatography.

Analytical scale purification of rare earth element (REE) radioisotopes is typically accomplished using cation-exchange resins (e.g. AG 50W-X8) and high-performance liquid chromatography (HPLC).

Rare earth element separations by high-speed counter-current chromatography.

Following the initial development of High-Speed Counter-Current Chromatography (HSCCC) in the 1960s, several studies have explored its applicability in the separation of rare earth elements (REEs). More recently, however, HSCCC publications have transitioned towards the separation of natural products or pharmaceuticals, leaving the application for REEs largely unexplored from a practical standpoint. Herein, we expand upon prior work in this field by evaluating the suitability of HSCCC to separation of a subset of non-radioactive REEs (Nd, Sm, Eu, Tb, and Y) at 10 mol levels using di-(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane as the stationary phase and hydrochloric acid as the mobile phase.

Cluster defects in gibbsite nanoplates grown at acidic to neutral pH.

Gibbsite [α-Al(OH)] is the solubility limiting phase for aluminum across a wide pH range, and it is a common mineral phase with many industrial applications. The growth mechanism of this layered-structure material, however, remains incompletely understood. Synthesis of gibbsite at low to circumneutral pH yields nanoplates with substantial interlayer disorder.

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species.

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH)) or dimeric (AlO(OH)) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space.

The controlling role of atmosphere in dawsonite gibbsite precipitation from tetrahedral aluminate species.

In highly alkaline solution, aluminum speciates as the tetrahedrally coordinated aluminate monomer, Al(OH) and/or dimer AlO(OH), yet precipitates as octahedrally coordinated gibbsite (Al(OH)). This tetrahedral to octahedral transformation governs Al precipitation, which is crucial to worldwide aluminum (Al) production, and to the retrieval and processing of Al-containing caustic high-level radioactive wastes. Despite its significance, the transformation pathway remains unknown.

Prediction of Solution Behavior via Calorimetric Measurements Allows for Detailed Elucidation of Polyoxometalate Transformation.

The solution behavior of a polyoxometalate cluster, LiNa-UPp (LiNa[(UOO)(PO)]) that consists of 24 uranyl ions, peroxide groups, and 12 pyrophosphate linkers, was successfully predicted based on new thermodynamic results using a calorimetric method recently described for uranyl peroxide nanoclusters (UPCs), molybdenum blues, and molybdenum browns. The breakdown of LiNa-UPp and formation of U (Li[UOOOH]) was monitored via Raman spectroscopy using a custom heating apparatus. A combination of analytical techniques confirmed the simultaneous existence of UPp and U midway through the conversion process and U as the single end product.

Mechanisms of Al Dimerization in Alkaline Solutions.

The molecular speciation of aluminum (Al) in alkaline solutions is fundamental to its precipitation chemistry within a number of industrial applications that include ore refinement and industrial processing of Al wastes. Under these conditions, Al is predominantly Al(OH), while at high [Al] dimeric species are also known to form. To date, the mechanism of dimer formation remains unclear and is likely influenced by complex ion···ion interactions.

Influence of soluble oligomeric aluminum on precipitation in the Al-KOH-HO system.

The role of oligomeric aluminate species in the precipitation of aluminum (Al) phases such as gibbsite (α-Al(OH)) from aqueous hydroxide solutions remains unclear and difficult to probe directly, despite its importance for developing accurate predictions of Al solubility in highly alkaline systems. Precipitation in this system entails a transition from predominantly tetrahedrally coordinated aluminate (Al(OH)) species in solution to octahedrally coordinated Al in gibbsite. Here we report a quantitative study of dissolved Al in the Al-KOH-HO system using a combination of molecular spectroscopies.

Inference of principal species in caustic aluminate solutions through solid-state spectroscopic characterization.

Tetrahedrally coordinated aluminate Al(OH) and dialuminate AlO(OH) anions are considered to be major species in aluminum-rich alkaline solutions. However, their relative abundance remains difficult to spectroscopically quantify due to local structure similarities and poorly understood effects arising from extent of polymerization and counter-cations. To help unravel these relationships here we report detailed characterization of three solid-phase analogues as structurally and compositionally well-defined reference materials.

Solid-State Recrystallization Pathways of Sodium Aluminate Hydroxy Hydrates.

Crystallization of Al-bearing solid phases from highly alkaline NaO:AlO:HO solutions commonly necessitates an Al coordination change from tetrahedral to octahedral, but intermediate coordination states are often difficult to isolate. Here, a similar Al coordination change process is examined during the solid-state recrystallization of monosodium aluminate hydrate (MSA) to nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While the MSA structure contains solely oxolated tetrahedral Al, the NSA structure is a molecular aluminate salt solely based upon monomeric octahedral Al.

Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters.

Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO)(O)(PO)] ({UPp}), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral () molecular symmetry. One-dimensional P NMR experiments provide direct evidence that both K and Rb ions trigger an -to- conformational change within {UPp}.

Ion-ion interactions enhance aluminum solubility in alkaline suspensions of nano-gibbsite (α-Al(OH)) with sodium nitrite/nitrate.

Despite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion-ion and ion-solvent interactions. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S.

Neptunyl Peroxide Chemistry: Synthesis and Spectroscopic Characterization of a Neptunyl Triperoxide Compound, Ca[NpO(O)]·9HO.

Little is known about the crystal chemistry of neptunyl peroxide compounds compared to uranyl peroxide compounds, for which dozens of structures have been described. Uranyl peroxides are formed over a broad range of pH and solution conditions, but neptunyl peroxide chemistry is complicated by the ability of HO to act as an oxidizing or reducing agent for Np, depending on the conditions present. The combination of Np(V) in 1 M HCl, HO, and CaCl under alkaline conditions leads to the immediate crystallization of a neptunyl triperoxide monomer, Ca[NpO(O)]·9HO, which is the first Np(VI)-based peroxide compound to be characterized in the solid state and is isostructural to Ca[UO(O)]·9HO.

Uranyl-Peroxide Capsule Self-Assembly in Slow Motion.

Uranyl-peroxide capsules are the newest family of polyoxometalates. Although discovered 13 years previously with over 70 topologies reported, there is a lack in the fundamental understanding of assembly mechanisms, particularly the role of the alkali counterions. Herein, the reaction pathway and assembly of uranyl peroxide capsules is reported by tracking the conversion from K uranyl triperoxide monomer to the K uranyl-peroxide U capsule by means of small-angle X-ray scattering and Raman spectroscopy.

Energetic Trends in Monomer Building Blocks for Uranyl Peroxide Clusters.

The uranyl triperoxide anionic monomer is a fundamental building block for uranyl peroxide polyoxometalate capsules. The reaction pathway from the monomer to the capsule can be greatly altered by the counterion: both the reaction rate and the resulting capsule structure. We synthesized and characterized uranyl triperoxides MgUO(O)·13HO (MgUT), CaUO(O)·9HO (CaUT), SrUO(O)·9HO (SrUT), and KUO(O)·3HO (KUT) and compared their thermodynamic stabilities.

Al Pulsed Field Gradient, Diffusion-NMR Spectroscopy of Solvation Dynamics and Ion Pairing in Alkaline Aluminate Solutions.

Pulsed field gradient nuclear magnetic resonance (PFG-NMR) measurements were successfully applied to the Al ( I = 5/2) nucleus in concentrated electrolytes to investigate the diffusion of aluminate ions [Al(OH)] in simulant high-level nuclear waste (3 M NaOH) between 25 and 85 °C. The temperature-dependent diffusion coefficients obtained from H, Na, and Al PFG-NMR were well fit by a Vogel-Fulcher-Tammann model and a power law equation. Comparison of Al diffusion coefficients of 0.

In Situ Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite.

Aluminum hydroxide (Al(OH), gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral ( T ) coordination in solution to octahedral ( O ) in the solid. We explored dissolution of Al(OH) that was used to produce variably saturated aluminate (Al(OH))-containing solutions under alkaline conditions (pH >13) with in situ Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations.

Complexity of Uranyl Peroxide Cluster Speciation from Alkali-Directed Oxidative Dissolution of Uranium Dioxide.

Solid UO dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, with a focus on the role of alkali metals. UO powders were dissolved in solutions containing XOH (X = Li, Na, K) and 30% HO. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements of solutions revealed linear trends of uranium versus alkali concentration in solutions resulting from oxidative dissolution of UO, with X:U molar ratios of 1.

Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation.

The characterization of prenucleation species is essential to understand crystallization mechanisms across many chemical systems and often involves the use of vibrational spectroscopy. Nowhere is this more evident than in the development of "green" aluminum processing technologies, where detailed understanding of the speciation of aluminum and its polynuclear analogues in highly alkaline, low water solutions is elusive. The aluminate anion Al(OH) predominates in alkaline conditions, yet equilibrium with dimeric species, either μ-oxo AlO(OH) or di-μ-hydroxo Al(OH), can be assumed.

Boehmite and Gibbsite Nanoplates for the Synthesis of Advanced Alumina Products.

Boehmite (-AlOOH) and gibbsite (-Al-(OH)) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications. Developing the ability to understand and predict the properties and characteristics of these materials, on the basis of their natural growth or synthesis pathways, is an important fundamental science enterprise with wide-ranging impacts. The present study describes bulk and surface characteristics of these novel materials in comprehensive detail, using a collectively sophisticated set of experimental capabilities, including a range of conventional laboratory solids analyses and national user facility analyses such as synchrotron X-ray absorption and scattering spectroscopies as well as small-angle neutron scattering.

The Propensity of Uranium-Peroxide Systems to Preserve Nanosized Assemblies.

Understanding the stability fields and decomposition products of various metal- and actinide-oxide nanoclusters is essential for their development into useful materials for industrial processes. Herein, we explore the spontaneous transformation of the sulfate-centered, phosphate functionalized uranyl peroxide nanocluster {UP} to {U} under aqueous ambient conditions using time-resolved small-angle X-ray scattering, Raman, and P NMR spectroscopy. We show that the unusual μ-η:η bridging mode of peroxide between uranyl ions observed in {UP} may lead to its rapid breakdown in solution as evidenced by liberation of phosphate groups that were originally present as an integral part of its cage structure.