Aqueous Feedstock Research Articles

Defect evolution and mitigation in metal extrusion additive manufacturing: From deposition to sintering

Material extrusion additive manufacturing of metals has found widespread application and is typically thought of as a facile technique to create metal components. This can be undertaken without the need for energy sources typically used in direct energy deposition and powder bed fusion processes. Despite recent advances in achieving net shape and improvements to material/component integrity, these processes are characterized by performance limiting defects which often emerge as a result of deposition strategy and are retained post sintering. Although the debinding and sintering steps have been investigated for metal injection molding technology, quantitative studies of defect evolution are lacking. This work proposes an approach to study the pore evolution behavior from deposition to sintering through X-ray Computed Tomography (XCT) image processing. Quantitative results of pore shrinking, partial and full closure through backtracking of individual pores from the sintered to the green state are presented. It is shown that where pores are larger than 4 × 10-6 mm3, equals to the D90 of the feedstock metal particles, these cannot be fully closed upon sintering and will survive to limit the performance of the final part. The average pore shrinkage is by a factor of 5.6 and partial closure happens in pores with minimum Feret diameter of 33 μm, equals to 160% of the D90 powder particle, or less. The utilization of overfill as a proposed technique in the literature for the elimination of macro pores is investigated, yielding disparate and unsatisfactory results. This discrepancy can be attributed to the insufficient formation of micro-channels within the pore structure during the deposition process of the aqueous feedstock, leading to regions of weak grain bonding. To evaluate the contribution of these to undermining material integrity, tensile tests of linear and circular deposition strategies are undertaken. Experiments show that track interface length plays a major role in determining elongation to failure and tensile strength. It is concluded that the limitation to the mechanical properties of metal paste extrusion components originates from the emergence of defects and their characteristics after the completion of the processing, as opposed to being influenced by the metallurgy prior or post sintering.

Pyrene‐Derived Carbon Nanomembranes Selectively Pass Metal Ions in Water

AbstractDespite the potential environmental benefits, the use of membranes for extracting, reclaiming, and purifying alkali metals from aqueous feedstocks remains challenging due to low inter‐cation selectivity. Two‐dimensional materials equipped with nanoscale pores have revealed intriguing performance in ion separation, but their practical implementation is bottlenecked by the perforation procedures. This work presents electrodialysis experiments with intrinsically porous carbon nanomembranes (CNMs) that are featured by a high areal density of sub‐nanometer channels. The free‐standing membranes prepared from pyrene are shown to have great mechanical strength and a narrow pore size distribution enabling selective passage of metal ions. CNMs can sieve hydrated cations following the order K+ > Na+ > Li+ > Ca2+ > Mg2+, while the K+/Mg2+, Na+/Mg2+, Li+/Mg2+ selectivity amounts to 220, 86, and 13 respectively. It is found that the ion transport selectivity is attributed to the combined effect of the small pore dimensions and electrostatic exclusion induced by surface charges. It has been also observed that the membrane thickness in the range from 3 to 6.5 nm has little impact on the ion transport which suggests interesting implications for ion batteries and other energy conversion systems.

Bridging Hydrometallurgy and Biochemistry: A Protein-Based Process for Recovery and Separation of Rare Earth Elements.

The extraction and subsequent separation of individual rare earth elements (REEs) from REE-bearing feedstocks represent a challenging yet essential task for the growth and sustainability of renewable energy technologies. As an important step toward overcoming the technical and environmental limitations of current REE processing methods, we demonstrate a biobased, all-aqueous REE extraction and separation scheme using the REE-selective lanmodulin protein. Lanmodulin was conjugated onto porous support materials using thiol-maleimide chemistry to enable tandem REE purification and separation under flow-through conditions. Immobilized lanmodulin maintains the attractive properties of the soluble protein, including remarkable REE selectivity, the ability to bind REEs at low pH, and high stability over numerous low-pH adsorption/desorption cycles. We further demonstrate the ability of immobilized lanmodulin to achieve high-purity separation of the clean-energy-critical REE pair Nd/Dy and to transform a low-grade leachate (0.043 mol % REEs) into separate heavy and light REE fractions (88 mol % purity of total REEs) in a single column run while using ∼90% of the column capacity. This ability to achieve, for the first time, tandem extraction and grouped separation of REEs from very complex aqueous feedstock solutions without requiring organic solvents establishes this lanmodulin-based approach as an important advance for sustainable hydrometallurgy.

Aqueous phase reforming of the residual waters derived from lignin-rich hydrothermal liquefaction: investigation of representative organic compounds and actual biorefinery streams

Abstract Secondary streams in biorefineries need to be valorized to improve the economic and environmental sustainability of the plants. Representative model compounds of the water fraction from the hydrothermal liquefaction (HTL) of biomass were subjected to aqueous phase reforming (APR) to produce hydrogen. Carboxylic and bicarboxylic acids, hydroxyacids, alcohols, cycloketones and aromatics were identified as model compounds and tested for APR. The tests were performed with a Pt/C catalyst and the influence of the carbon concentration (0.3–1.8 wt. C%) was investigated. Typically, the increase of the concentration negatively affected the conversion of the feed toward gaseous products, without influencing the selectivity toward hydrogen production. A synthetic ternary mixture (glycolic acid, acetic acid, lactic acid) was subjected to APR to evaluate any differences in performance compared to the tests with single compounds. Indeed, glycolic acid reacted faster in the mixture than in the corresponding single compound test, while acetic acid remained almost unconverted. The influence of the reaction time, temperature and carbon concentration was also evaluated. Finally, residual water resulting from the HTL of a lignin-rich stream originating from an industrial-scale lignocellulosic ethanol process was tested for the first time, after a thorough characterization. In this framework, the stability of the catalyst was studied and found to be correlated to the presence of aromatics in the aqueous feedstock. For this reason, the influence of an extraction procedure for the selective removal of these compounds was explored, leading to an improvement in the APR performance.

Electrochemical Liquid Phase Epitaxy (ec-LPE): A New Methodology for the Synthesis of Crystalline Group IV Semiconductor Epifilms.

Deposition of epitaxial germanium (Ge) thin films on silicon (Si) wafers has been achieved over large areas with aqueous feedstock solutions using electrochemical liquid phase epitaxy (ec-LPE) at low temperatures (T ≤ 90 °C). The ec-LPE method uniquely blends the simplicity and control of traditional electrodeposition with the material quality of melt growth. A new electrochemical cell design based on the compression of a liquid metal electrode into a thin cavity that enables ec-LPE is described. The epitaxial nature, low strain character, and crystallographic defect content of the resultant solid Ge films were analyzed by electron backscatter diffraction, scanning transmission electron microscopy, high resolution X-ray diffraction, and electron channeling contrast imaging. The results here show the first step toward a manufacturing infrastructure for traditional crystalline inorganic semiconductor epifilms that does not require high temperature, gaseous precursors, or complex apparatus.

Pb2PdO2(OH)2 and Pb2PdO(OH)4(H2O): Synthesis and Crystal Growth at Ambient Conditions

AbstractNew Pb2PdO2(OH)2 and Pb2PdO(OH)4(H2O) were synthesized at ambient conditions from respective KOH alkaline and metal nitrate aqueous feed stocks in high purity and as coarse crystals. The constitutions of the two lead palladates were determined by combined powder neutron and single‐crystal X‐ray diffraction studies. Both crystal structures exhibit a distinct pseudo symmetry, and settling the true lattice symmetry [Pb2PdO2(OH)2: a = 5.9512(3) Å, b = 5.9479(3) Å, c = 7.9480(2) Å, α = 90.256(4)°, β = 90.392(4)°, γ = 119.694(1)°; Pb2PdO(OH)4(H2O): a = 10.706(2) Å, b = 10.32(1) Å, c = 5.7813(3) Å, α = β = γ = 90°] required to employ high resolution synchrotron powder diffraction data. The combined use of neutron and X‐ray diffraction measurement has enabled solving the crystal structure of Pb2PdO2(OH)2 including hydrogen positions. For Pb2PdO(OH)4(H2O) only a high symmetry, heavy atoms (Pb, Pd, O) average structure was determined, since the background in the neutron data was strongly enhanced due to the high amount of incoherently scattering hydrogen atoms and considerable disorder present. The crystal structures feature unprecedent connectivities, however, as expected square‐planar coordination of palladium(II) and typical crooked surroundings of lead(II) with the 6s2 lone pair acting as a virtual ligand.

Simultaneous production of high-quality water and electrical power from aqueous feedstock’s and waste heat by high-pressure membrane distillation

A new membrane distillation (MD) concept (MemPower) has been developed for the simultaneous production of high-quality water from various aqueous feedstocks with cogeneration of mechanical power (electricity). Driven by low-grade heat (waste, solar, geothermal, etc.) a pressurized distillate can be produced by operating TNO’s Memstill® process at high hydraulic pressures. These pressures are theoretically limited by the liquid entry pressure (LEP) of the membrane. The proof of principle has been shown and is based on the transport of water vapor against a hydraulic pressure gradient. Various commercially available membranes have been evaluated in order to obtain high yields in water flux and power densities. Power densities have been measured which are sufficient to drive the pumps in MD. This allows standalone Memstill® units without electricity consumption to be possible, which are fully driven by waste heat. The application of new incompressible hydrophobic membranes, combining a high permeance with a high LEP, will allow for much higher power densities.

Physical Properties of Polypeptide Electrospun Nanofiber Cell Culture Scaffolds on a Wettable Substrate

Physical properties of poly(L-ornithine) (PLO), a polycation, poly(L-glutamic acid4-co-L-tyrosine) (PLEY), a polyanion, and electrospun fibers made of these polymers have been determined and compared. The polymers adopted random coil-like conformations in aqueous feedstocks at neutral pH and in dehydrated cast films and fibers on glass, and the fibers comprised numerous counterions, according to spectral analysis. Adsorption of model proteins and serum proteins onto hydrated and crosslinked fibers depended on the electrical charge of the proteins and the fibers. The surface charge density of the fibers will be comparable to, but less than, the charge density on the outer leaflet of the plasma membrane of usual eukaryotic cells. The present analysis thus advances understanding of cell behavior on electrospun fiber scaffolds, a topic of considerable current interest.

Simultaneous Aqueous‐Phase Reforming and KOH Carbonation to Produce COx‐Free Hydrogen in a Single Reactor

abstraction duringthe reforming process will help in displacing the equilibrium ofthe WGS reaction towards product formation, making this re-action more favorable than CO methanation. In addition themethanation of CO 2 , [9h] which also consumes H 2 , will be kineti-cally hindered when it is abstracted. It is practical to take ad-vantage of the unique aqueous-phase character of the reform-ing process by introducing KOH as a process modifier throughsimply switching the aqueous feedstock from ethylene glycolto a mixed solution of ethylene glycol and KOH without alter-ing the set-up of the reactor, as schematically illustrated inScheme 1. We found that by using this improved approachCO x -free H 2 could be successfully produced in a single reactor,even on an unpromoted non-precious-metal catalyst. Thesefeatures make the approach economical and very appealingfrom an environmental point of view.The employed non-precious-metal catalyst is a non-pyro-phoric (NP) Ni catalyst that has been described previously.

Continuous hydrothermal processing of nano-crystalline particulates for chemical-mechanical planarization

A wide range of nano-crystalline, single and multi-component oxide/oxyhydroxide particulates, which may be potentially useful as abrasives for chemical-mechanical planarization (CMP) processes, have been produced using a novel, flow-through hydrothermal technology previously developed at the Pacific Northwest National Laboratory. The process, termed rapid thermal decomposition of precursors in solution (RTDS), converts aqueous feed stock solutions containing metal salts and other thermally activated reactants into suspensions or slurries of nano-crystals (with diameters of generally less than 30 nm) by continuous flow through a heated, high pressure reaction pipe (typically, 200–400°C, 6000–8000 psi). Flow at pressure is maintained using a nozzle at the down-stream end of the reaction tube. Crystallite formation occurs during the solution’s brief residence time (<30 s) in the reaction pipe. Control over crystalline phase and, in some cases, particle morphology can be tailored by selecting the appropriate feed chemistry and processing conditions. Using bench-scale equipment, RTDS is capable of producing nano-crystalline particulate material at rates of up to ≈500 gm of solids per hour. The RTDS processing and characterization of nano-crystalline zirconium-, titanium-, and iron-based oxide and oxyhydroxide particulates are reviewed.

The modelling of equilibrium data for the liquid-liquid extraction of metals part III. An improved chemical model for the copper/LIX 64N system

New data are presented for the copper sulphate—sulphuric acid/LIX 64N—Escaid 100 solvent extraction system, and it is shown that these data do not exhibit the anomalous features of Robinson's (1971) results. The data are modelled using equations based on the thermodynamics of the Cu 2+, CuSO 4, H +, HSO 4 −, SO 4 2− aqueous system and the HR, (HR) n , CuR 2 organic sytem (where HR represents the active β-hydroxyoxime in LIX 64N). Although the values of the two aqueous and the two organic equilibrium constants cannot be held to have thermodynamic significance, the best models are capable of predicting the organic copper concentrations of the 86 data points at four different concentrations of LIX 64N (5–50 vol.%) from the aqueous phase analyses with average errors as low as 7%. Isotherms for desired aqueous feedstocks and desired concentrations of our batch of LIX 64N in Escaid 100 at 25–26°C can be calculated.