Alkaline Earth Carbonates Research Articles

Corrosion resistance of borophosphate enamels in molten zinc

Abstract A study has been conducted of the resistance to corrosion in molten zinc of borophosphate enamels. The melting temperature of the enamels was adjusted by adding the carbonates of alkali metals and alkaline earth metals. Scanning electron microscopy was used to examine solidified interfaces between the enamels and the molten zinc. At low magnification (× 30) no evidence of components from the B2O3-P2O5 enamels was detected by electron probe in the industrially pure zinc near the interface with the enamel, but elemental Zn was found in the initially zinc free B2O3-P2O5 enamels. When the interface was examined at a magnification of 1000 times, it was confirmed by electron probe that no phosphorus from the borophosphate enamel was present in the zinc matrix at a position 60 μm from the interface. The results show that the borophosphate enamels are extremely resistant to corrosion in molten zinc.

Potentiometric investigation of oxide solubilities in molten KCl–NaCl eutectic.: The effect of surface area of solid particles on the solubilities

The sequential additions method (SAM) was used to determine solubility and disassociation characteristics of metal oxides MeO (CaO, PbO, ZnO, CdO) and carbonates (CaCO 3, SrCO 3, BaCO 3) in molten KCl–NaCl eutectic at 700 °C. A membrane oxide-reversible electrode Pt(O 2)/YSZ) was used to detect oxide ion concentrations. The oxides (MeO) were found to be weak bases in unsaturated solutions, their dissociation constants (p K) were found to be 3.27±0.2 (CaO), 3.50±0.1 (PbO), 6.1±0.2 (ZnO) 5.3±0.2 (CdO). All the emf−(−log m MeO) plots in the vicinity of the saturation point include bends to the concentration axis. These were explained by the partial dissolution of MeO powders resulting in a decrease of their particle sizes and a corresponding rise of the molar surface areas (MSA). Calculations performed give surface energies of MeO solid/KCl–NaCl systems of the order of 30–50 J m −2. This allowed us to estimate MSAs of the MeO particles formed in MeO solubility determinations in molten KCl–NaCl by isothermal saturation and potentiometric titration methods. The solubilities of the alkaline earth carbonates were determined in a CO 2 atmosphere. Under these conditions solubility products of the carbonates were achieved before oxide precipitation. The alkaline earth carbonates were found to be appreciably soluble in the KCl–NaCl eutectic at 700 °C. Their solubility products determined by SAM were equal to p P BrCO 3 =0.36±0.3, p P SrCO 3 =2.04±0.2, p P CaCO 3 =2.04±0.2 (in a CO 2 atmosphere). Under these conditions the particle size effect was imperceptible.

Conceptual model of the controls on natural water chemistry at Yucca Mountain, Nevada

The natural waters associated with Yucca Mountain include precipitation (rain and melted snow), ephemeral surface waters, soil waters, vadose zone pore waters, perched waters and saturated zone ground waters. Using precipitation compositions as a starting point, chemical and isotopic data for the other water types are evaluated to identify significant processes that may control their compositions. The ratios of Cl − to each of the other major constituents in precipitation waters are used to evaluate gains or losses of major ions in the other waters. Evapotranspiration of precipitation waters in the soil zone appears to be a very important process in the control of vadose zone pore waters, perched waters and saturated zone ground water compositions. In the desert climate associated with the Yucca Mountain site, this process leads to the precipitation of salts and silica in the soil zone. Surface waters sampled near the site have preferentially dissolved soil zone chlorides, sulfates, carbonates, and silica. Pore waters extracted from bedded tuffs of the upper Paint Brush Tuff in Yucca Mountain have ratios of Ca, Na, HCO 3 and SO 4 to Cl that are all lower than those found in precipitation. The lower ratios likely reflect precipitation of alkaline earth carbonates and possibly sulfates in the soil zone. Pore waters extracted from the Calico Hills Tuff also appear to reflect the precipitation of alkaline earth sulfates in the soil zone. Alternatively, the low SO 4 to Cl ratios observed in these waters reflect variations in precipitation compositions with time. Perched waters are more dilute than vadose zone pore waters but appear to have gained their solutes by similar mechanisms. For perched waters, sulfates were dissolved in the soil zone in addition to carbonates and chlorides. The dissolution of the less soluble phases (i.e. alkaline earth carbonates and sulfates) in the soil zone implies perched waters were infiltrated under wetter climatic conditions. Saturated zone waters originated by processes similar to those that formed the perched waters except that the former were subject to more extensive ion exchange reactions. Ground waters in the shallow saturated zone beneath Yucca Mountain appear to include a significant component that was locally infiltrated. Deeper saturated zone waters likely infiltrated further upgradient in the direction of Pahute Mesa.

In Situ Generation of Strong Bases from Alkaline and Alkaline–Earth Carbonates

Strong bases from alkaline and alkaline-earth metal carbonates were generated in situ by adding a small amount of acetic acid at reflux in toluene under water-free conditions. Their basic strength reached superbasicity thus changing the color of 4-chloroaniline (H−=26.5). The high conversion of ethyl acetate in its self-condensation over decomposed carbonates, which require strong basicity to abstract protons from ethyl acetate (pKa=25), also confirmed the formation of strong bases. Adding acetic acid during the reaction indicated that metal oxides—decomposed materials from carbonates—were responsible for their high catalytic activity. The lack of sufficient coordination of in situ generated metal oxides was considered to be a plausible cause for their strong basicity.

Structurally modulated magnetic properties in the A(3)MnRu(2)O(9) phases (A = Ba, Ca): the role of metal-metal bonding in perovskite-related oxides.

Ca(3)MnRu(2)O(9) and Ba(3)MnRu(2)O(9) were synthesized from transition metal dioxides and alkaline earth metal carbonates at 1100-1300 degrees C. Ca(3)MnRu(2)O(9) adopts the prototypical GdFeO(3)-type perovskite structure with Mn and Ru statistically disordered over the single metal atom site. The susceptibility shows Curie-Weiss behavior above 240 K with mu(eff) = 3.14 micro(B)/metal atom, which is in excellent agreement with the expected spin-only moment of 3.20 micro(B). Below 150 K, the compound shows spin-glass-like short-range ferrimagnetic correlations. The high-temperature region of the electrical resistivity reveals a small activation energy of 17(1) meV whereas the low-temperature region is nonlinear and does not fit a variable range hopping model. Ba(3)MnRu(2)O(9) crystallizes in the 9-layer BaRuO(3)-type structure containing M(3)O(12) face-shared trioctahedral clusters in which Mn and Ru are statistically disordered. Ba(3)MnRu(2)O(9) shows nonlinear reciprocal susceptibility at all temperatures and is described by a variable-spin cluster model with an S = (1)/(2) ground state with thermally populated excited states. The low spin value of this system (S = (1)/(2)) is attributed to direct metal-metal bonding. Below 30 K, the compound shows short-range magnetic correlations and spin-glass-like behavior. The high-temperature region of the electrical resistivity indicates a small activation energy of 8.8(1) meV whereas the low-temperature region is nonlinear. The importance of metal-metal bonding and the relationships to other related compounds are discussed.

Physico-chemical studies on the thermolysis of strontium and barium ferrimaleates

The thermolysis of strontium and barium tris(maleato)ferrates(III), M3 [Fe(C2 H2 C2 O4 )3 ]2 ·x H2 O has been investigated from ambient temperature to 800 °C using simultaneous TG-DTG-DTA, XRD, Mossbauer and IR spectroscopic techniques. After dehydration the anhydrous complexes undergo decomposition to yield an iron(II)maleate/oxalate intermediate in the temperature range of 240-280 °C. An oxidative decomposition of iron(II) species leads to the formation of α-Fe2 O3 and respective alkaline earth metal carbonate in the successive stages. Finally at 540-590 °C, a solid state reaction occurs between α-Fe2 O3 and strontium/barium carbonate resulting in the formation of SrFeO2.5 and BaFe2 O4 , respectively.

Growth of single crystals belonging to a family of one-dimensional oxides: commensurate and incommensurate structures

Mixtures of alkaline earth carbonates together with nickel or copper oxide and iridium, ruthenium, platinum or rhodium metal in a carbonate flux at 1050–1150°C leads to the formation of black crystals. These crystals, whose habit is either hexagonal plates or hexagonal rods, belong to a family of perovskite related phases of general composition [A] x [(A′,B)O 3]. Preliminary diffraction experiments indicate that these crystals form with a composite structure, some commensurate and others incommensurate. The structures of the commensurate crystals were determined by single-crystal X-ray diffraction, while the structures of the incommensurate crystals are being investigated by powder diffraction. Several commensurate and incommensurate single crystals and their growth conditions are discussed in this paper.

Preparation of alkaline earth carbonates and oxides by the EDTA-gel process

The ethylene-diamine-tetra-acetic acid (EDTA)-gel process has been used to produce carbonates and oxides of the alkaline earth elements Ba, Sr and Ca and their solid solutions. These materials have a range of potential applications including electron emission and catalysis. Gels of composition Ba-EDTA, Sr-EDTA, [Ba0.5Sr0.5]-EDTA, [Ba0.5Sr0.45Ca0.05]-EDTA were prepared at pH 6 from aqueous solutions of the alkaline earth nitrates and EDTA and their thermal decomposition studied by TGA/DSC. The gels and the products derived from calcination of these gels at different temperatures have been characterised by FTIR, XRD and SEM, and shown to have high chemical homogeneity and fine particle size. Decomposition of the gels to the carbonate form occurred below 300°C with subsequent formation of the oxide occuring on heat treatment at temperatures ranging from approximately 800°C to > 1000°C depending upon gel composition. The process route is suitable for the production of particulate materials or porous coatings.

About the foamability of iron ‐ carbon alloys

The foamability of iron‐carbon alloys using the powder metallurgical process route was investigated. Pure iron and carbon powder with an addition of foaming agent were mixed and compacted. The foaming process started during heating the sample as soon as a temperature above the solidus temperature of the iron‐carbon alloy was reached. Result of the process is an iron foam with a porosity of up to 60%. It was investigated, how the foaming behaviour is influenced by the parameters of alloy composition and compaction process. Different foaming agents (alkaline earth metal carbonates and metal nitrides) as well as different carbon additions and compacting processes were tested.It can be seen that sort and amount of foaming agent have an unexpected low influence on the expansion process whereas an increasing carbon content supports the expansion significantly. The use of different compacting processes has only little influence on the expansion itself, but highly effects both the pore distribution and homogeneity. The poor effect of the foaming agent cannot be satisfactorily explained. Investigations of a possibly premature gas emission or of a not gas‐tight inclusion of the foaming agent do not show clear results. The support of the expansion by carbon additions can be attributed to the formation of CO‐gas by the Vacher‐Hamilton law during simultaneous formation of the liquid Fe‐FeC‐eutectic phase. The more inhomogeneous pore structure of iron foams caused by the use of hot‐or hot isostatically pressed semi‐finished products can be traced back to a higher internal gas pressure in the sample which results in a burst of the microstructure of the semi‐finished product.

Contributions of groundwater conditions to soil and water salinization

Salinization is the process whereby the concentration of dissolved salts in water and soil is increased due to natural or human-induced processes. Water is lost through one or any combination of four main mechanisms: evaporation, evapotranspiration, hydrolysis, and leakage between aquifers. Salinity increases from catchment divides to the valley floors and in the direction of groundwater flow. Salinization is explained by two main chemical models developed by the authors: weathering and deposition. These models are in agreement with the weathering and depositional geological processes that have formed soils and overburden in the catchments. Five soil-change processes in arid and semi-arid climates are associated with waterlogging and water. In all represented cases, groundwater is the main geological agent for transmitting, accumulating, and discharging salt. At a small catchment scale in South and Western Australia, water is lost through evapotranspiration and hydrolysis. Saline groundwater flows along the beds of the streams and is accumulated in paleochannels, which act as a salt repository, and finally discharges in lakes, where most of the saline groundwater is concentrated. In the hummocky terrains of the Northern Great Plains Region, Canada and USA, the localized recharge and discharge scenarios cause salinization to occur mainly in depressions, in conjunction with the formation of saline soils and seepages. On a regional scale within closed basins, this process can create playas or saline lakes. In the continental aquifers of the rift basins of Sudan, salinity increases along the groundwater flow path and forms a saline zone at the distal end. The saline zone in each rift forms a closed ridge, which coincides with the closed trough of the groundwater-level map. The saline body or bodies were formed by evaporation coupled with alkaline-earth carbonate precipitation and dissolution of capillary salts.

Kinetics and mechanisms of the reverse Boudouard reaction over metal carbonates in connection with the reactions of solid carbon with the metal carbonates

The decomposition processes of alkali or alkaline earth carbonates with a large excess of carbon, and the reverse Boudouard reaction given by CO2/C→2CO over metal carbonates, were compared. The carbonates of Li+, Na+, K+, Cs+, Sr2+ and Ba2+ generated CO exclusively by an intermolecular redox reaction given by CO32-+C→2CO+O2-. The reverse Boudouard reaction over these metal carbonates at 700°C proceeded at a steady rate until just before the carbon was completely consumed, and in the cases of Li+, Sr2+ and Ba2+, the rates agreed with the initial rates of the intermolecular redox reaction. On the other hand, the rates over the carbonates of Na+, K+ and Cs+, the oxides of which undergo a disproportionation reaction to produce gas-phase metal and liquid-phase metal peroxide, were much higher than the initial rates of the intermolecular redox reaction. This discrepancy can be explained by the presence of a catalytic process on the metal-covered surface of the silica wool that was used for preventing the highly basic gas-phase metals from escaping.

Modeling the Thermal Decomposition of Solids on the Basis of Lattice Energy Changes: Part 1: Alkaline–Earth Carbonates

Decompositions of many solids are of the form: [Equation]As real examples of this reaction pattern, the decompositions of some alkaline-earth metal (Ca, Sr, Ba) carbonates [Equation] were selected for modeling. The crystal structures the reactants and the solid product oxides have been reported in the literature. Symmetry-controlled routes for transforming the reactant into the solid product oxide were devised as possible decomposition pathways. Lattice energies of the reactants, the conjectured transient intermediate structures, and the final products were then estimated by crystal modeling procedures, and profiles of energy changes during the proposed decomposition routes were constructed. Barriers in these energy profiles are compared with experimental values reported for the activation energies of the thermal decompositions.

Modeling the Thermal Decomposition of Solids on the Basis of Lattice Energy ChangesPart 1: Alkaline–Earth Carbonates

Decompositions of many solids are of the form: [Equation] As real examples of this reaction pattern, the decompositions of some alkaline-earth metal (Ca, Sr, Ba) carbonates [Equation] were selected for modeling. The crystal structures the reactants and the solid product oxides have been reported in the literature. Symmetry-controlled routes for transforming the reactant into the solid product oxide were devised as possible decomposition pathways. Lattice energies of the reactants, the conjectured transient intermediate structures, and the final products were then estimated by crystal modeling procedures, and profiles of energy changes during the proposed decomposition routes were constructed. Barriers in these energy profiles are compared with experimental values reported for the activation energies of the thermal decompositions.

Efficient Recovery of Carbon Dioxide from Flue Gases of Coal-Fired Power Plants by Cyclic Fixed-Bed Operations over K2CO3-on-Carbon

An efficient chemical absorption method capable of cyclic fixed-bed operations under moist conditions for the recovery of carbon dioxide from flue gases has been proposed employing K2CO3-on-carbon. Carbon dioxide was chemically absorbed by the reaction K2CO3 + CO2 + H2O ⇄ 2KHCO3 to form potassium hydrogencarbonate. Moisture, usually contained as high as 8−17% in flue gases, badly affects the capacity of conventional adsorbents such as zeolites, but the present technology has no concern with moisture; water is rather necessary in principle as shown in the equation above. Deliquescent potassium carbonate should be supported on an appropriate porous material to adapt for fixed-bed operations. After breakthrough of carbon dioxide, the entrapped carbon dioxide was released by the decomposition of hydrogencarbonate to shift the reaction in Eq.1 in reverse on flushing with steam, which could be condensed by cooling to afford carbon dioxide in high purity. Among various preparations of alkaline-earth carbonates (...

Electrical conductivity and thermal behavior of solid electrolytes based on alkali carbonates and sulfates

Both thermal stability and electrical conductivity of alkali ion conducting Na 2CO 3 and Na 2SO 4, were improved by adding alkaline earth carbonates and sulfates, respectively, as well as insulating materials like γ-Al 2O 3. The admixing of divalent compounds causes two effects. First a more or less extended solution can exist depending on the radius of the alkaline earth ion and is accompanied by an increase in electrical conductivity. Secondly, a phase mixture with an excess of dopant was observed that shows an enhancement in conductivity and mechanical stability. This phenomenon known as composite effect was observed in the following systems: Na 2CO 3-BaCO 3, Na 2CO 3-SrCO 3, Na 2SO 4-BaSO 4, Na 2SO 4-γ-Al 2O 3.

Synthesis of oxide perovskite solid solutions using the molten salt method

The molten salt method has in the past been employed to synthesize a large number of compounds at low temperatures. In this work we report the formation of solid solutions of BaTiO3–SrTiO3 and BaZrO3–SrZrO3 using a molten salt eutectic of NaOH–KOH as a solvent. Alkaline earth carbonates and titanium oxide were used as precursors for the titanate system, and alkaline earth carbonates and zirconium oxide were used as precursors for the zirconate system. It was found that both systems form solid solutions throughout the composition range. The implications of these results with regards to the applicability of the molten salt method as a tool to investigate low temperature phase equilibria are discussed.

High Temperature Corrosion of Type 316L Stainless Steel with Molten Carbonate. The Effect of Alkaline Earth Carbonate Addition

High Temperature Corrosion of Type 316L Stainless Steel with Molten Carbonate. The Effect of Alkaline Earth Carbonate Addition

Water action on Bi-based superconductor cuprates. I. Macroscopic and morphological features

After observation of the degradation of bismuth cuprate superconductor by moistened air we have examined the action of water alone, through different techniques, in order to distinguish the proper role of water and carbon dioxide. In air the degradation of both powders and crystal occurs with the formation of alkaline earth carbonates, followed by that of hydroxides. Under the action of water vapor action, products are developed close to crystal defects and steps. Calcium hydroxide appears first and then strontium hydroxide, which undergoes a further hydration. The role of water seems to be two-fold: a chemical reagent and a physical medium allowing reactions to occur and crystal to grow. As for air action, the resulting compound of bismuth cuprate superconductor degradation is Bi 2CuO 4.

Two types of luminescence from Pb 2+ in alkaline-earth carbonates with the aragonite structure

The luminescence of Pb 2+ as a dopant in alkaline-earth carbonates with the aragonite structure is investigated. An ultra-violet and a visible emission band have been observed, both originating from the same center. The former is ascribed to emission from the 3P 0,1 (6 s6 p) levels of the Pb 2+ ion, the latter to emission from a higher level which is probably charge-transfer in nature. The (co-)existence of both bands depends on the host-lattice.

A Sustainable Catalyst for the Partial Oxidation of Methane to Syngas: Ni/Ca1‐xSrxTiO3, Prepared In Situ from Perovskite Precursors

High activity and negligible coke formation in the course of the catalytic partial oxidation of CH4 to syngas are characteristics of the Ni/Ca4‐xSrxTiO3 catalyst, which is readily accessible by the citrate method from nickel nitrate, alkaline earth metal carbonates, and tetraisopropoxidotitanium. The properties and efficiency of the catalyst are normally only associated with catalysts that contain considerably more expensive metals such as Rh, Ir, and Ru.