Topographic Analysis of Calcite (104) Cleavage Surface Dissolution in Ethanol–Water Solutions

The interaction of organic molecules with calcite surfaces plays a key role in many geochemical, industrial and biomineralization processes, and exploring the influences of organic molecules on calcite reactions is crucial for a fundamental understanding of the reaction mechanisms. Here, we used digital hologram microscopy to explore the in situ evolution of the calcite (104) surfaces when dissolved in ethanol–water solutions, and total organic carbon analysis was applied to confirm the adsorption of ethanol by calcite. The results showed that the bulk dissolution rate of calcite decreases as the volume fraction of ethanol increases, and the topographic features of etch pits were also altered by the presence of ethanol. When exposed to too much ethanol, the etch pits’ growth was inhibited and their shapes tended to change from rhombuses in ultrapure water to triangles. Our results provide insights into the interaction between adsorbed ethanol and evolving calcite crystal, which highlights the dissolution regulation of calcite by organic molecules that could benefit a broad range of fields.

Eleomelanite, (K2Pb)Cu4O2(SO4)4, a new mineral species from the Tolbachik Volcano, Kamchatka, Russia

ABSTRACT The new mineral eleomelanite, (K2Pb)Cu4O2(SO4)4, was found in the Arsenatnaya fumarole on the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia. It is associated with euchlorine, fedotovite, wulffite, chalcocyanite, dolerophanite, dravertite, hermannjahnite, alumoklyuchevskite, klyuchevskite, piypite, cryptochalcite, cesiodymite, anglesite, langbeinite, calciolangbeinite, metathénardite, belomarinaite, aphthitalite, krasheninnikovite, steklite, anhydrite, hematite, tenorite, sanidine, sylvite, halite, lammerite, urusovite, and gold. Eleomelanite occurs as interrupted crusts up to 6 mm across and up to 0.3 mm thick consisting of equant, prismatic, or tabular crystals or grains up to 0.3 mm. It is translucent and black. The luster is oleaginous on crystal faces and vitreous on a cleavage surface. Dcalc is 3.790 g/cm3. Eleomelanite is optically biaxial (–), α 1.646(3), β 1.715(6), γ 1.734(6), 2Vmeas. = 60(15)°. The chemical composition (wt.%, electron-microprobe) is K2O 9.62, Rb2O 0.49, Cs2O 0.24, CaO 1.23, CuO 35.28, PbO 19.25, SO3 34.78, total 100.89. The empirical formula calculated based on 18 O apfu is (K1.88Pb0.79Ca0.20Rb0.05Cs0.02)Σ2.94Cu4.07S3.99O18. Eleomelanite is monoclinic, P21/n, a 9.3986(3), b 4.8911(1), c 18.2293(5) Å, β 104.409(3)°, V 811.63(4) Å3, and Z = 2. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.38(44)(101), 3.699(78)(112), , 3.173(40)(211), 2.915(35)(114), 2.838(35)(204), , and . The crystal structure was solved using single-crystal XRD data, R1 = 4.78%. It is based on heteropolyhedral Cu–S–O chains composed of Cu-centered polyhedra with [4+1+1] Cu2+ coordination and SO4 tetrahedra. Adjacent Cu–S–O chains are connected via chains of (K,Pb)O8 and KO10 polyhedra. Eleomelanite belongs to a novel structure type but has common structural features with klyuchevskite, alumoklyuchevskite, wulffite, parawulffite, and piypite. The name is derived from the Greek ελαιν (eleon), oil, and μλας (melas), black, due to its black color and oleaginous luster on crystal faces that are uncommon for sulfate minerals.

Revealing the intrinsic superconducting gap anisotropy in surface-neutralized BaFe2(As0.7P0.3)2

Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. Extensive results have been obtained including band structure, gap anisotropy, etc. However, the complicacy of 122 caused by its charge-non-neutral cleavage surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe2(As0.7P0.3)2, the surface-induced spectral broadening is strongly suppressed, while the coherent spectra that reflects the intrinsic bulk electronic state recovers. This raises the accuracy of the gap measurement and gap fitting to an unpreceded level. The results clearly distinguish two pairing channels originated respectively from the inner and outer Fermi pockets. While the gap anisotropy on the outer hole/electron pockets can be well fitted using an s± gap function, the gap magnitude on the inner hole/electron pockets show a clear deviation. Our results provide quantitative constraints for refining theoretical models and demonstrate an experimental method for revealing the intrinsic electronic properties of 122 in future studies.

Al3Ti/ADC12 Composite Synthesized by Ultrasonic Chemistry in Situ Reaction

Al3Ti/ADC12 composite was synthesized in situ using Al-fluoride potassium titanate (K2TiF6) as the reaction system and an ultrasonic assisted direct melt reaction. Results indicate ultrasonic chemistry reactions are both accelerated and more complete compared to traditional in situ reactions. Al3Ti reinforced particles with a regular shape and size of 1-2 μm were well distributed and as-cast microstructures of composites were superior. Composite particles under ultrasonic assistance were also refined to a greater extent. Tensile strength and elongation rate of the composites reached 255 MPa and 2.2%, an increase of 19.1% and 37.5% respectively to those without ultrasonic aid. Cleavage surface of the composite declined and the number of dimples increased while dimples became smaller and deeper, showing obvious ductile fracture.

Материалы на основе твердых растворов теллуридов висмута и сурьмы, полученные методами быстрой кристаллизации расплава

Abstractp -type Bi_0.5Sb_1.5Te_3 solid solutions prepared by hot pressing and the extrusion of powders prepared by rapid melt crystallization methods such as melt spinning and melt crystallization in a liquid are investigated. The morphology of the powders, the sample cleavage surface, and their microstructure are investigated using optical microscopy, scanning electron microscopy, and scanning tunneling microscopy. The mechanical properties of the samples are investigated by room-temperature compression tests. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the materials are measured in the temperature range of 100–600 K. The highest limiting compressive strength σ_B = 145 MPa at 300 K and maximal thermoelectric efficiency ( ZT )_max = 1.34 at 370 K are found for materials extruded from granules prepared by melt crystallization in water and ground in a ball mill.

Soil Particle Surface Charge

Structural charge arises on the surfaces of soil mineral particles in which either cation vacancies or isomorphic substitutions of cations by cations of lower valence occur. The principal minerals bearing structural charge are therefore the micas (Section 2.2), the 2:1 clay minerals (Section 2.3), or the Mn(IV) oxide, birnessite (Section 2.4). These three classes of mineral are all layer type and the cleavage surface on which their structural charge is manifest is a plane of O ions. The plane of O ions on the cleavage surface of a layer-type aluminosilicate is called a siloxane surface.This plane is characterized by hexagonal symmetry in the configuration of its constituent O ions, as shown at the top of Fig. 2.3 and, more explicitly, on the right side of Fig. 2.4, where a portion of the siloxane surface of the micas is depicted. Reactive molecular units on the surfaces of soil particles are termed surface functional groups. The functional group associated with the siloxane surface is the roughly hexagonal (strictly speaking, ditrigonalbecause the hexagonal symmetry is distorted when the tetrahedral sheet is fused to an octahedral sheet to form a layer) cavity formed by six corner-sharing silica tetrahedra. This cavity has a diameter of about 0.26 nm. The reactivity of the siloxane cavity depends on the nature of the electronic charge distribution in the layer structure. If there are no nearby isomorphic cations substitutions to create a negative charge, the O ions bordering the siloxane cavity function as an electron cloud donor that can bind molecules weakly through the van der Waals interaction. These interactions are akin to those underlying the hydrophobic interaction, discussed in Section 3.5, because the O in the siloxane surface can form only very weak hydrogen bonds with water molecules. Therefore, uncharged patches on siloxane surfaces may be considered hydrophobic regions to a certain degree, with, accordingly, an attraction for hydrophobic organic molecules. However, if isomorphic substitution of Al3+ by either Fe2+ or Mg2+ occurs in the octahedral sheet, the resulting structural charge is manifest on the siloxane cavities, as discussed in Section 2.3.

Electronic and structural properties of bulk arsenopyrite and its cleavage surfaces – a DFT study

We have investigated the structural and electronic properties of arsenopyrite and its cleavage surface formation using a density functional/plane waves method. QTAIM and ELF were applied for investigating the nature of the bonding in arsenopyrite.