SEARCH · Engineering Papers
Results for “HYDROXIDES”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Local environment and composition of magnesium gallium layered double hydroxides determined from solid-state {sup 1}H and {sup 71}Ga NMR spectroscopy
Ordering of gallium(III) in a series of magnesium gallium (MgGa) layered double hydroxides (LDHs), [Mg{sub 1−x}Ga{sub x}(OH){sub 2}(NO{sub 3}){sub x}·yH{sub 2}O] was investigated using solid-state {sup 1}H and {sup 71}Ga NMR spectroscopy as well as powder X-ray diffraction. Three different proton environments from Mg{sub 3}-OH, Mg{sub 2}Ga-OH and intergallery water molecules were assigned and quantified using ({sup 1}H,{sup 71}Ga) HETCOR and {sup 1}H MAS NMR. A single {sup 71}Ga site originating from the unique Ga site in the MgGa LDH's was observed in {sup 71}Ga MAS and 3QMAS NMR spectra. Both {sup 1}H MAS NMR spectra recorded at 21.1 T (900 MHz) and elemental analysis show that the synthesized MgGa LDH's had a lower Mg:Ga ratio than that of the starting reactant solution. The origin of this is the formation of soluble [Ga(OH){sub 4}]{sup −} complexes formed during synthesis, and not due to formation of insoluble gallium (oxy)hydroxides. No sign of Ga-O-Ga connectivities or defects were detected for the MgGa LDH's. - Graphical abstract: Two types of hydroxides groups are observed in magnesium gallium layered double hydroxides revealing an ordering of Ga in the cation layer. - Highlights: • Ga is ordered in our magnesium gallium layered double hydroxides. • Ga depletion due to formation of soluble Ga complexes during synthesis. • No sign of Ga rich regions in magnesium gallium LDHs. • Solid state {sup 1}H and {sup 71}Ga give detailed insight into the structure.
Lithium hydroxide, LiOH, at elevated densities
We discuss the high-pressure phases of crystalline lithium hydroxide, LiOH. Using first-principles calculations, and assisted by evolutionary structure searches, we reproduce the experimentally known phase transition under pressure, but we suggest that the high-pressure phase LiOH-III be assigned to a new hydrogen-bonded tetragonal structure type that is unique amongst alkali hydroxides. LiOH is at the intersection of both ionic and hydrogen bonding, and we examine the various ensuing structural features and their energetic driving mechanisms. At P = 17 GPa, we predict another phase transition to a new phase, Pbcm-LiOH-IV, which we find to be stable over a wide pressure range. Eventually, at extremely high pressures of 1100 GPa, the ground state of LiOH is predicted to become a polymeric structure with an unusual graphitic oxygen-hydrogen net. However, because of its ionic character, the anticipated metallization of LiOH is much delayed; in fact, its electronic band gap increases monotonically into the TPa pressure range.
Operando formation of an ultra-low friction boundary film from synthetic magnesium silicon hydroxide additive
Explore the source record for details and available documents.
Vibrational dynamics of aqueous hydroxide solutions probed using broadband 2DIR spectroscopy
We employed ultrafast transient absorption and broadband 2DIR spectroscopy to study the vibrational dynamics of aqueous hydroxide solutions by exciting the O–H stretch vibrations of the strongly hydrogen-bonded hydroxide solvation shell water and probing the continuum absorption of the solvated ion between 1500 and 3800 cm{sup −1}. We observe rapid vibrational relaxation processes on 150–250 fs time scales across the entire probed spectral region as well as slower vibrational dynamics on 1–2 ps time scales. Furthermore, the O–H stretch excitation loses its frequency memory in 180 fs, and vibrational energy exchange between bulk-like water vibrations and hydroxide-associated water vibrations occurs in ∼200 fs. The fast dynamics in this system originate in strong nonlinear coupling between intra- and intermolecular vibrations and are explained in terms of non-adiabatic vibrational relaxation. These measurements indicate that the vibrational dynamics of the aqueous hydroxide complex are faster than the time scales reported for long-range transport of protons in aqueous hydroxide solutions.
Evaluation of layered zinc hydroxide nitrate and zinc/nickel double hydroxide salts in the removal of chromate ions from solutions
Layered zinc hydroxide nitrate (ZnHN) and Zn/Ni layered double hydroxide salts were synthesized and used to remove chromate ions from solutions at pH 8.0. The materials were characterized by many instrumental techniques before and after chromate ion removal. ZnHN decomposed after contact with the chromate solution, whereas the layered structure of Zn/Ni hydroxide nitrate (Zn/NiHN) and Zn/Ni hydroxide acetate (Zn/NiHA) remained their layers intact after the topotactic anionic exchange reaction, only changing the basal distances. ZnHN, Zn/NiHN, and Zn/NiHA removed 210.1, 144.8, and 170.1 mg of CrO{sub 4}{sup 2−}/g of material, respectively. Although the removal values obtained for Zn/NiHN and Zn/NiHA were smaller than the values predicted for the ideal formulas of the solids (194.3 and 192.4 mg of CrO{sub 4}{sup 2−}/g of material, respectively), the measured capacities were higher than the values achieved with many materials reported in the literature. Kinetic experiments showed the removal reaction was fast. To facilitate the solid/liquid separation process after chromium removal, Zn/Ni layered double hydroxide salts with magnetic supports were also synthesized, and their ability to remove chromate was evaluated. - Highlights: • Zinc hydroxide nitrate and Zn/Ni hydroxide nitrate or acetate were synthesized. • The interlayer anions were replaced by chromate anions at pH=8.0. • Only Zn/Ni hydroxide nitrate or acetate have the structure preserved after exchange. • Fast exchange reaction and high capacity of chromate removal were observed. • Magnetic materials were obtained to facilitate the solids removal the from solutions.
Spectral Induced Polarization Signatures of Hydroxide Adsorption and Mineral Precipitation in Porous Media
The spectral induced polarization (SIP) technique is a promising approach for delineating subsurface physical and chemical property changes in a minimally invasive manner. To facilitate the understanding of position and chemical properties of reaction fronts that involve mineral precipitation in porous media, we investigated spatiotemporal variations in complex conductivity during evolution of urea hydrolysis and calcite precipitation reaction fronts within a silica gel column. The real and imaginary parts of complex conductivity were shown to be sensitive to changes in both solution chemistry and calcium carbonate precipitation. Distinct changes in imaginary conductivity coincided with increased hydroxide ion concentration during urea hydrolysis. In a separate experiment focused on the effect of hydroxide concentration on interfacial polarization of silica gel and well-sorted sand, we found a significant dependence of the polarization response on pH changes of the solution. We propose a conceptual model describing hydroxide ion adsorption behavior in silica gel and its control on interfacial polarizability. Our results demonstrate the utility of SIP for noninvasive monitoring of reaction fronts, and indicate its potential for quantifying geochemical processes that control the polarization responses of porous media at larger spatial scales in the natural environment.
Nickel hydroxide electrode. 3: Thermogravimetric investigations of nickel (II) hydroxides
Water contained in Ni hydroxide influences its electrochemical reactivity. The water content of alpha and beta Ni hydroxides is different with respect to the amount and bond strength. Thermogravimetric experiments show that the water of the beta Ni hydroxides exceeding the stoichiometric composition is completely removed at 160 deg. The water contained in the interlayers of the beta hydroxide, however, is removed only at higher temperatures, together with the water originating from the decomposition of the hydroxide. These differences are attributed to the formation of II bonds within the interlayers and between interlayers and adjacent main layers. An attempt is made to explain the relations between water content and the oxidizability of the Ni hydroxides.
Hydroxide-ion transport and stability of diblock copolymers with a polydiallyldimethyl ammonium hydroxide block
Base-stable amphiphilic diblock copolymers with a polydiallyl dimethyl ammonium hydroxide block were synthesized and characterized to quantify hydroxide-ion transport in the hydrated state; polystyrene was the hydrophobic block. The challenge of synthesizing a copolymer comprising blocks with very different solubility behaviors was addressed by a combination of reversible addition fragmentation chain transfer polymerization and ion metathesis. Both monomers used in the polymerization are commercially available on industrial scales. Hydroxide-ion conductivities of 0.8 mS/cm were achieved in hot-pressed membranes immersed in water at room temperature despite relatively low water uptake (4.2 water molecules per hydroxide ion). Finally, the stability of the polydimethyl ammonium hydroxide chains was investigated in 2 M NaOD at 60 °C.1H NMR spectroscopy studies showed no detectable degradation after 2000 hours.
CdCu{sub 3}(OH){sub 6}Cl{sub 2}: A new layered hydroxide chloride
A new transition metal hydroxide chloride containing kagome layers of magnetic ions, CdCu{sub 3}(OH){sub 6}Cl{sub 2}, has been synthesized and structurally characterized. The actual low symmetry P2{sub 1}/n structure can be derived from the ideal trigonal one with a change in cation distribution and coherent distortions of the anion framework. The result is a fundamentally different Cu{sup 2+} kagome framework than found in the related Herbertsmithite and Kapellasite minerals. Magnetization measurements show no transition to long range magnetic order above T=2 K, despite strong antiferromagnetic interactions with a Weiss temperature of {theta}{sub w}=-150 K. Furthermore, we show that the structure of CdCu{sub 3}(OH){sub 6}Cl{sub 2} and related hydroxide chlorides can be rationalized on the basis of [(OH){sub 3}Cl]{sup 4-} pseudopolyatomic anions that pack and rotate, in much the same way as do traditional polyatomic anions. This opens the door to rational design of new and useful hydroxide chloride materials. - Graphical Abstract: The [(OH){sub 3}Cl]{sup 4-} pseudopolyatomic anion and the kagome lattice of CdCu{sub 3}[(OH){sub 3}Cl]{sub 2}. Highlights: Black-Right-Pointing-Pointer A new understanding of hydroxide chlorides, based on the polyatomic anion [(OH){sub 3}Cl]{sup 4-}. Black-Right-Pointing-Pointer Synthesis and structure of a new layered hydroxide chloride, CdCu{sub 3}(OH){sub 6}Cl{sub 2}, are reported. Black-Right-Pointing-Pointer A new compound is reported with kagome layers of Cu{sup 2+}.
Nitrate and Nitrite Incompatibility with Hydroxide Ions in Concentrated NaOH Solutions: Implications for Hydroxide and Gibbsite Reactivity in Alkaline Nuclear Waste
Electrolyte solutions in alkaline nuclear waste contain aluminate, hydroxide, nitrate and nitrite with sodium as the predominant counterion. The salts of these ions are highly soluble, so the liquids are highly concentrated. This study found that there is a substantial incompatibility between the hydroxide and nitrate and/or nitrate ions. This was determined by the observations that adding just one molal of NaNO2 or NaNO3 to saturated NaOH solution precipitation of 12 moles of NaOH·H2O salt, whereas the common ion effect would have expected only about 1 mole to precipitate. Further analysis indicates that the presence of nitrate and nitrite drastically increases the reactivity of sodium hydroxide ions in solution, which likely influences the reactivity of other hydroxide-mediated reactions. This enhanced reactivity is likely because it disrupts large Na+-OH- ion networks because nitrate and nitrite do not fit in those ion networks similarly to how some ions cannot substitute into a foreign crystal lattice. In contrast, the aluminate ion did not have the same large incompatibility with hydroxide.
Contribution to the knowledge of nickel hydroxide electrodes. 5. Analysis and electrochemical behavior of cadmium nickel hydroxides
Electrochemical experiments performed at sintered and bulk electrodes show that beta nickel hydroxide contains an electrochemically inactive proportion of cadmium hydroxide of up to 10%. The electrochemically ineffective cadmium hydroxide is homogeneously dissolved in beta nickel hydroxide.
Hydrogenolysis of Dinuclear PCN R Ligated Pd II μ‐Hydroxides and Their Mononuclear Pd II Hydroxide Analogues
Abstract The hydrogenolysis of mono‐ and dinuclear Pd II hydroxides was investigated both experimentally and computationally. It was found that the dinuclear μ‐hydroxide complexes {[(PCN R )Pd] 2 (μ‐OH)}(OTf) (PCN H =1‐[3‐[(di‐ tert ‐butylphosphino)methyl]phenyl]‐1 H ‐pyrazole; PCN Me =1‐[3‐[(di‐ tert ‐butylphosphino)methyl]phenyl]‐5‐methyl‐1 H ‐pyrazole) react with H 2 to form the analogous dinuclear hydride species {[(PCN R )Pd] 2 (μ‐H)}(OTf). The dinuclear μ‐hydride complexes were fully characterized, and are rare examples of structurally characterized unsupported singly bridged μ‐H Pd II dimers. The {[(PCN Me )Pd] 2 (μ‐OH)}(OTf) hydrogenolysis mechanism was investigated through experiments and computations. The hydrogenolysis of the mononuclear complex (PCN H )Pd‐OH resulted in a mixed ligand dinuclear species [(PCN H )Pd](μ‐H)[(PCC)Pd] (PCC=a dianionic version of PCN H bound through phosphorus P, aryl C, and pyrazole C atoms) generated from initial ligand “rollover” C−H activation. Further exposure to H 2 yields the bisphosphine Pd 0 complex Pd[(H)PCN H ] 2 . When the ligand was protected at the pyrazole 5‐position in the (PCN Me )Pd−OH complex, no hydride formed under the same conditions; the reaction proceeded directly to the bisphosphine Pd 0 complex Pd[(H)PCN Me ] 2 . Reaction mechanisms for the hydrogenolysis of the monomeric and dimeric hydroxides are proposed.
Impacts of Surface Site Coordination on Arsenate Adsorption: Macroscopic Uptake and Binding Mechanisms on Aluminum Hydroxide Surfaces
Aluminum hydroxides play important roles in regulating the fate and transport of contaminants and nutrients in soils and aquatic systems. Like many metal oxides, these minerals display surface functional groups in a series of coordination states, each of which may differ in its affinity for adsorbates. The distribution of functional group types varies among distinct surfaces of aluminum hydroxides, and we thus hypothesize that the adsorption behavior and mechanisms will show a dependence on particle morphology. To test this hypothesis, we investigate arsenate adsorption on two aluminum hydroxide polymorphs with distinct particle morphologies, gibbsite [γ-Al(OH) 3 ] and bayerite [α-Al(OH) 3 ], at pH 4 and 7. Synthetic gibbsite platelets expose large (001) basal surfaces predicted to be terminated by doubly coordinated functional groups (>Al 2 OH). In contrast, synthetic bayerite microrods display mainly edge surfaces (parallel to the c axis) containing abundant singly coordinated functional groups (>AlOH 2 ). Macroscopic adsorption studies show that gibbsite adsorbs less arsenate per unit surface area than bayerite at both pH values and suggest that two surface complexes form on each material. Similar electrokinetic behavior is displayed at the same relative coverages of arsenate, suggesting that similar reactive surface groups (>AlOH 2 ) control the surface charging on both particles. EXAFS spectroscopy shows that there is no variation in arsenate surface speciation on a given mineral with surface coverage or pH. Whereas bidentate binuclear inner-sphere species are the dominant complexes present, the EXAFS result suggest that outer-sphere species also occur on both minerals, with a greater abundance on gibbsite. This binding mode likely involves adsorption to >Al 2 OH sites, which have a slow ligand exchange rate that inhibits inner-sphere binding. Lastly, these results demonstrate that adsorption mechanisms and capacity, even when normalized for specific surface area, vary with metal oxide particle morphology because of the distribution of distinct functional groups.
Aluminum Hydroxide Solubility in Sodium Hydroxide Solutions Containing Nitrite/Nitrate of Relevance to Hanford Tank Waste
The technical basis to support the One System River Protection Project Integrated Flowsheet assumption for diluting staged direct feed low-activity waste (DFLAW) from the Hanford waste tanks with raw river water must be assessed in light of the risk of aluminum hydroxide (gibbsite) precipitation prior to the subsequent transfer of tank contents into the low-activity waste pretreatment system (LAWPS) and/or the Tank Side Cesium Removal (TSCR) system from days to months after dilution. Aluminum solubility must be predicted as a function of the significant variables that influence gibbsite dissolution and precipitation. These variables include (i) other solution components that meaningfully affect the activity coefficient of either hydroxide or the aluminate ion, particularly nitrate and nitrite; and (ii) temperature. Based on a review of waste solubility data and the impact of dilution on solution stabilities with specific focus on aluminum hydroxide, data gaps associated with the impact of these variables on the prediction of gibbsite solubility with temperature were identified. An experimental program to aid in the prediction of gibbsite solubility in NaOH solutions containing a range of sodium nitrate and sodium nitrite concentrations up to the solubility limit at a range of temperatures has been conducted. The results of these investigations are summarized in this report.
Selective Covalent Basal Plane Modification as a Probe of Hydroxide Ion Conduction Pathways in Magnesium Aluminum Layered Double Hydroxides
Understanding ionic conduction in layered double hydroxides (LDHs) is a crucial step towards utilizing them as solid, hydroxide ion‐conducting electrolytes in energy conversion applications. We selectively modified the interlayer and external surfaces of MgAl LDHs with tris(hydroxymethyl)aminomethane (TRIS) ligands. By adjusting the concentration of the TRIS surface modifier, the LDH basal plane surfaces could be functionalized everywhere (internally and externally) or only externally. External modification resulted in loss of OH‐conductivity compared to pristine LDHs, confirming that external platelet surfaces are the primary ion conduction pathway.
Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides
The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.