Molten Barium Research Articles

Locating anionic hydrogen in Ba3(Yb,Lu)2O5H2: A combined approach of X-ray diffraction, crystal chemistry, and DFT calculations

By a combination of x-ray diffraction, structural chemistry, and DFT calculations, the presence and location of anionic hydrogen in the two new, layered lanthanide oxyhydrides, Ba3Ln2O5H2 (Ln ​= ​Yb, Lu) is inferred. Single crystals of the compounds have been synthesized from a molten barium flux with the addition of small amounts of BaH2. These phases crystallize in space group I4/mmm (#139, Z ​= ​2) with lattice parameters a ​= ​4.3336(2) Å and c ​= ​22.7197(6) Å, and a ​= ​4.3291(1) Å and c ​= ​22.597(1) Å, respectively. The Ba3Ln2O5H2 phases comprise two different structural moieties: a perovskite double layer of stoichiometry Ba2Ln2O5H− formed by corner-connected LnO5 tetragonal bi-pyramids with a terminating hydrogen anion, and a puckered rocksalt-type (BaH)+ layer that is stretched along the c-axis. DFT calculations were used to arrive at hydrogen positions that minimize energy and are consistent with structural chemistry principles. Furthermore, the calculations show that the valence band edge is dominated by oxygen 2p orbitals with hydrogen 1s states admixed. The conduction band is formed by barium 5d-orbitals and Lu (Yb) 5d-orbitals. These are characteristics of materials with anionic H−. These new phases are isostructural with the Ba3Ln2O5Cl2 (Ln ​= ​Gd–Lu) family of compounds with the chlorine atom in the same apical position as the hydrogen atom. Steric effects limit the size of the lanthanide ion for Ba3Ln2O5H2.

Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers

In this article, the suitability of the etchants NaOH/KOH and Ba(OH)2 for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with a MgO‐assisted “drop method” is compared. Defect selectivity for the new etchant Ba(OH)2 is confirmed by the local TEM analysis. Temperature dependence (420–500 °C) of etch pit sizes of a‐, mixed‐, and c‐type dislocations for both etchants are investigated by statistical evaluation of scanning electron microscopy (SEM) images. Additionally, the etch pit shape is analyzed for samples etched at 460 °C by atomic force microscopy (AFM) measurements. While a‐ and mixed‐type dislocations result in pits of comparable size and shape for both etchants, c‐type dislocations are already strongly etched with NaOH/KOH at low temperatures leading to over‐etching and MgO precipitation. Ba(OH)2, in contrast, generates smaller c‐type etch pits at low and medium etching temperatures and no MgO precipitates and is therefore preferable for drop etching.

Experimental study on liquid seal and crystal surface morphology of barium hydroxide octahydrate

Molten barium hydroxide (BHO) with strong alkalinity will absorb CO2 in the air and denaturing part of BHO, so it is very important to treat it with liquid seal. In this paper, the effects of liquid seals with different cooling methods and white suspended substances on the phase change process of BHO were compared for phase change experiments, so as to study the influencing factors of powdery expansion of BHO and the crystal crystallization mode. The experimental results show that the probability of powdery expansion of BHO increases with the decrease of cooling rate. Liquid paraffin and high temperature silicone oil can play the role of air insulation, but will make BHO supercooling and powder expansion probability increase, some white powder suspended between molten BHO and liquid sealing material (BaCO3 attached to tiny bubbles) has a certain promoting effect on nucleating crystallization of BHO, and the supercooling degree of BHO without white powder will increase again, the surface of the BHO crystal shows a tight structure around the loose and porous center, known as a branch cavity structure, which becomes apparent as the cooling rate increases. This experiment provides a reference for the study of phase change materials in the field of phase change energy storage.

Molten barium titanate: a high-pressure liquid silicate analogue

The structure of molten BaTiO3 has been measured using laser heating, aerodynamic levitation and a combination of neutron diffraction with Ti isotope substitution, x-ray diffraction and spectroscopy. All measurements indicate a Ti–O coordination of nTiO = 4.4(2), far lower than the perovskite or hexagonal crystalline forms. However, nTiO > 4 suggests structural analogy with molten silicates at high pressures. We introduce methodology for ascertaining such analogies and demonstrate similarity with molten CaSiO3 at upper mantle pressures circa 5 GPa. Although some topological differences exist, we propose that planetary melt analogues provide rich insight into important processes relevant to hot exoplanets and Earth’s early history.

Synthesis and Crystal Structure of the Layered Lanthanide Oxychlorides Ba3Ln2O5Cl2.

Single crystals of a new family of layered lanthanide oxychlorides, Ba3Ln2O5Cl2 (Ln = Gd-Lu), have been synthesized from a molten barium flux. This family crystallizes in the space group I4/mmm (No. 139; Z = 2) with lattice parameters a = 4.3384(1)-4.4541(1) Å and c = 24.5108(7)-24.8448(9) Å. Ba3Ln2O5Cl2 phases are built up of two different blocks: a perovskite double layer of stoichiometry Ba2Ln2O5 formed by corner-connected LnO5 tetragonal bipyramids and a puckered rock-salt-like interlayer of composition BaCl2. A complete structural study along with bond-valence-sum calculations shows that, for lanthanides larger than gadolinium, the structure becomes unstable. Density functional theory calculations show that the valence-band edge is dominated by oxygen orbitals, whereas the conduction band forms from Ba 5d orbitals. The synthesis of this family suggests a route to other potential multianion phases.

Ba2TeO: A new layered oxytelluride

Single crystals of the new semiconducting oxytelluride phase, Ba2TeO, were synthesized from barium oxide powder and elemental tellurium in a molten barium metal flux. Ba2TeO crystallizes in tetragonal symmetry with space group P4/nmm (#129), a=5.0337(1)Å, c=9.9437(4)Å, Z=2. The crystals were characterized by single crystal x-ray diffraction, heat capacity and optical measurements. The optical measurements along with electronic band structure calculations indicate semiconductor behavior with a band gap of 2.93eV. Resistivity measurements show that Ba2TeO is highly insulating.

STEP carbon capture – The barium advantage

We have recently introduced the theory of the Solar Thermal Electrochemical Process for carbon capture and utilization (STEP carbon). We have also provided experimental validation of that theory using electrolysis of molten lithium and eutectic alkali carbonates at high (∼50%) solar efficiency and high rate, and delineated the materials required to use STEP carbon to decrease atmospheric CO2 to preindustrial levels in ten years. In this communication an effective, alternative STEP carbon electrolyte is introduced. It is demonstrated thermodynamically that barium carbonate can provide more than an order of magnitude greater affinity for direct carbon dioxide absorption from the air than our prior lithium carbonate electrolyte. It is demonstrated experimentally that molten barium carbonate mixtures provide an effective medium for the direct electrolytic reduction of absorbed carbon dioxide at high rate and lower energy. The products of the electrolysis are graphite, which is readily stored as a valued added commodity for future generations, and oxygen. The electrolyte is not consumed in this carbon dioxide splitting process.

Copper-doped BaZrO 3 crucibles for YBCO single crystal growth

The corrosion resistance of BaZrO 3 to molten barium cuprates is controlled by secondary phases, and requires high chemical and phase purity, as well as high density for sustained flux containment. The high sintering temperatures required for solid-state derived powders is a significant obstacle inhibiting more widespread use of high density BaZrO 3. We have investigated the use of Cu 2+ doping to enable practical sintering temperatures whilst still producing corrosion resistant ceramics. Low levels of copper addition (0.2 wt.% CuO equiv.) produced densities of >97% theoretical using sintering temperatures as low as 1400 °C, as long as the dopant was added after all powder calcination steps, i.e. immediately before forming/sintering. Corrosion resistance at 0.2 wt.% CuO equiv. was equal to un-doped materials fabricated using the same powder processing method.

Study of the boron-oxygen units in crystalline and molten barium metaborate by high temperature Raman spectroscopy

The vibrational spectra of the boron-oxygen structural elements in single crystal β-BaB 2O 4 and BaB 2O 4 melts were studied by high temperature Raman spectral analysis. The experimental Raman peaks were assigned to the calculated normal vibrational modes of the free [B 3O 6] molecular unit. The observed vibrational mode splittings were found to be consistent with C 6 3 v symmetry for β-BaB 2O 4. Experimental vibrational spectra were compared with those of LiBO 2 and CsBO 2 in order to determine the temperature-dependent populations of chain, ring, and tetrahedral structural elements in the respective melts, and these in turn were shown to correlate with the degree of melt supercooling required for spontaneous crystallization to occur.

Viscosity and density of molten barium zirconate and related melts

Viscosity and density of molten ZrF 4 -BaF 2 mixtures have been measured using the oscillating cup method and the Archimedean method respectively. The viscosity had a marginal minimum around the composition BaF 2 .2ZrF 4 , and increased significantly towards the composition BaF 2 .ZrF 4 . The density of molten ZrF 4 -BaF 2 increased with the BaF 2 content, while the volume thermal expansion decreased. The effect of the valence of the counter cation on the viscosity was studied by substitution of the glass modifier BaF 2 with NaF or LaF 3 . The viscosity increased with the valence of the counter cation. These fragile glass-forming systems are more comparable to ionic glasses than typical network glasses. The physical properties of the molten fluorides are discussed in relation to complex formation and the ionic character of the melts

Characterization of Oxygen Systems in Molten Barium Hydroxide. Application to Oxidative Conversion of Methane

Characterization of Oxygen Systems in Molten Barium Hydroxide. Application to Oxidative Conversion of Methane

Oxidative Coupling of Methane in Molten Barium Hydroxide at 800°C

Molten barium hydroxide was used at 800°C as a catalyst for the oxidative coupling of methane. A mixture of methane and oxygen (CH4:O2=3:1), bubbled through the catalytic phase under atmospheric pressure, led to a methane conversion (X) of ca. 21% and a C2 selectivity (S) of ca. 33-38%. The effect of the acidity level (pO2-) of the molten phase was examined by imposing a water pressure P(H2O) (acidic medium) or by dehydration up to the precipitation of BaO (basic medium). Both X and S increase with increasing basicity. These results agree with the hypothesis of a peroxide intermediate as the catalyst, O2-2 species being stabilized in basic molten media.

Diffusion of Elements in Heat-Resisting Steels during Annealing in Molten Barium Chloride

Diffusion of Elements in Heat-Resisting Steels during Annealing in Molten Barium Chloride

Electrochemical characterization of oxygen systems in molten barium hydroxide at 500–700°C

The acidity—potential diagrams of molten Ba(OH) 2, calculated from thermochemical data at different temperatures between 500–700°C, allow the definition of the stability ranges of oxygen redox systems in this medium. Values calculated have then been compared with experimental results obtained from voltammetric studies at Pt and Ni electrodes. It is shown that the oxidation of oxide ions leads to peroxide ions, but is not followed, as in molten NaOH, by a second oxidation step of peroxide ions into superoxides. The solubility of BaO in molten Ba(OH) 2 has been estimated.

Acute Poisoning by a Barium Chloride Burn

A 62-year-old man sustained a barium chloride burn after his jackhammer penetrated a pocket of molten barium chloride. He subsequently developed signs of systemic barium poisoning including bigeminy and hypokalemia. Treatment consisted of early thorough debridement and intravenous potassium supplementation. Serum barium levels were determined. In a review of the literature these appeared to be the first toxic barium levels to be reported. The literature concerning barium poisoning and its complications is reviewed and related to the clinical presentation and treatment of this chemically burned patient.

The resistance of refractories to molten barium

Refractories processed from corundum, magnesia-alumina spinel, periclase, and calcium and barium zirconates exhibit good resistance to the action of molten barium up to 1600°C in the absence of BaO. Corundum and spinel react with barium oxide. The barium monoaluminate forming in the process reacts with the excess BaO to give a eutectic which melts at 1480°C so that the peak service temperature of refractories based on corundum and spinel is confined to 1400–1450°C if the barium melt contains BaO. Refractories based on calcium zirconate degenerate to barium zirconate in the presence of BaO and develop spalling so that this material cannot be recommended for use under the conditions discussed here. High-density refractories processed from pure magnesia and barium zirconate are stable to the action of molten barium and barium oxide up to 1600°C and thus are the most promising materials for the purpose discussed here.

Growth of Yttrium‐Iron Garnet from Molten Barium Borate

It has been found that yttrium‐iron garnet can be grown from solutions of yttrium‐iron garnet and molten BaO·xB2O3. This solvent possesses none of the undesirable properties of the usual solvents in that it is noncorrosive, nonvolatile, and has a specific gravity less than that of yttrium‐iron garnet. These properties make the solvent useful for the usual slow‐cooling growth methods and for controlled growth on seeds. The replacement of Ba with Na, K, Pb, Ca, and Sr will yield yttrium‐iron garnet as will the replacement of B2O3 with V2O5. A definite relation exists between the amount of B2O3 in the solvent and the amount of iron in the crystallized phase; namely, the percentage of iron in the crystallized phase is higher with increased B2O3 concentration in the solvent. The use of this type of phase equilibrium information makes possible an orderly method of selecting solvents for crystal growth.

The Free Energy Diagram of the Vanadium‐Oxygen System

A review of a number of earlier works permits the derivation of the free energy diagram of the system vanadium‐oxygen from composition down to beyond composition . It is shown that most of the earlier results agree fairly well if correctly interpreted. Results of some hydrogen reduction experiments are in accordance with the energy relations derived.The slope of the energy curve at low concentrations of oxygen has been determined by establishing equilibria between vanadium‐oxygen solutions and molten barium, magnesium, or calcium. The oxygen contents in vanadium thus obtained were determined by the vacuum fusion method. With these results the free energy curve for vanadium‐ oxygen has been completed. The results further suggest that the solubility of oxygen in vanadium is much lower than has been assumed hitherto, being possibly 0.25 per cent oxygen at 1000°C.