CaCo3 crystallization control by poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer and O-(hydroxy isopropyl) chitosan

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) ((EO)₂₀-(PO)₇₂-(EO)₂₀) and O-(hydroxy isopropyl) chitosan (HPCHS) were employed as control agents of calcium carbonate crystal growth. The effect of the concentrations of polymers, [Ca²⁺] and [CO₃²⁻], the ratios of [Ca²⁺]-[CO₃²⁻] and the initial pH of the solutions were investigated. The obtained CaCO₃ particles were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The particles are mainly calcite with various morphologies; their size and morphologies are influenced by the polymer content. For (EO)₂₀-(PO)₇₂-(EO)₂₀ systems, the initial pH has a notable influence; but in the HPCHS solution pH shows little influence. The ratio of [Ca²⁺]-[CO₃²⁻] clearly affects the CaCO₃ particle size and aggregation degree. HPCHS showed more significant influence on CaCO₃ crystallization than (EO)₂₀-(PO)₇₂-(EO)₂₀. The mechanisms of the CaCO₃ crystallization as controlled by (EO)₂₀-(PO)₇₂-(EO)₂₀ and HPCHS are proposed and demonstrated by the molecular dynamics simulations.     

Study on crystallization of calcium carbonate from calcium sulfate and ammonium carbonate in the presence of magnesium ions

Batch reactive crystallization of calcium carbonate (CaCO₃) from ammonium carbonate ((NH₄)₂CO₃) and calcium sulfate (CaSO₄) was investigated in the presence of magnesium (Mg²⁺) ions. It was observed that Mg²⁺ ions partly inhibited the conversion of CaSO₄ into CaCO₃. When the content of Mg²⁺ was less than 2%, the reduction in conversion rate of CaSO₄ was less than 2%, and the effect of Mg²⁺ ions could be ignored. Effect of impurity on crystallization kinetics of CaCO₃, including the growth rate and nucleation rate, was investigated. The results revealed that when Mg²⁺ ions content was less than 1%, Mg²⁺ could promote the growth of CaCO₃ and inhibit the nucleation process, which was favorable for the filtration of CaCO₃.When the content of Mg²⁺ ions was greater than 1%, Mg²⁺ inhibited the growth of CaCO₃, which resulted in explosion nucleation and led to a large number of particles in the solution, which was unfavorable for the filtration of CaCO₃. Based on the Bransom model, the particle size distribution equations of CaCO₃ were established. X‐ray diffraction patterns and scanning electron microscopy images exhibited the existence of spherical vaterite of CaCO₃ due to the reaction of CaSO₄ with (NH₄)₂CO₃ under the effect of Mg²⁺ ions, which was inconsistent with the results reported in the literatures.     

Nucleation-growth process of scale electrodeposition – influence of the magnesium ions

Electrodeposition of CaCO₃ was studied under the influence of magnesium ions present in a carbonically pure water. The investigation was performed using electrochemical, gravimetric and optical methods. The chronoamperometric measurements confirmed the inhibiting property of Mg²⁺ when its concentration is higher than 120 mg L⁻¹ in a solution containing 160 mg L⁻¹ of Ca²⁺. The optical technique led the nucleation-growth process to be accessed by means of an optical microscope positioned behind a transparent electrode. The increase of Mg²⁺ concentration changed drastically the calcite morphology. At 360 mg L⁻¹ of Mg²⁺, the calcite morphology was optically amorphous but the Raman spectrum confirmed its structure. The crystal growth was recorded in situ and the image analysis software characterised the nucleation process as well as the growth rate of the crystals. It allowed the influence of the Mg²⁺ ions on the crystallisation process of CaCO₃ to be quantified.     

The effect of B2O3 on the luminescent properties of Eu ion-doped aluminoborosilicate glasses

A series of Eu ion-doped aluminoborosilicate glasses was prepared by melt-quenching method and characterized by spectroscopic techniques, including Fourier transform infrared (FTIR), absorption, photoluminescence (PL), and electron paramagnetic resonance (EPR). The FTIR spectra showed that various glass structures formed when Al₂O₃ was partially replaced by B₂O₃. The PL characterization revealed that the emission intensity of Eu²⁺ ions firstly increased and then decreased with an increasing amount of Al₂O₃ replaced by B₂O₃. Meanwhile, the emission intensity ratio of [Eu²⁺]/[Eu³⁺] also followed the same trend. The EPR spectra confirmed the concentration variation of Eu²⁺ ions in the glass samples, which agreed well with the PL results. The possible mechanism of the effect of the glass network structure on the reduction behavior of Eu ions is discussed.     

Investigation of calcium carbonate precipitated in the presence of alkanols

The influence of myristyl alcohol (CH₃(CH₂)₁₃OH), cetyl alcohol (CH₃(CH₂)₁₅OH) and behenyl alcohol (CH₃(CH₂)₂₁OH) on the structure, morphology, size and surface properties of calcium carbonate (CaCO₃) has been investigated. Changes in the nature of the washing solvent, in the C_nOH/Ca²⁺ and CO₃²⁻/Ca²⁺ molar ratios and in temperature have been also evaluated. The sole polymorph produced was rhombohedral calcite. At room temperature, while microspheres composed of submicrocubes were produced at a high molar ratio CO₃²⁻/Ca²⁺ and low CH₃(CH₂)₁₅OH concentration, a stoichiometric molar ratio CO₃²⁻/Ca²⁺ and high CH₃(CH₂)₁₅OH concentration induced the formation of microcubes and microboxes. In the presence of this alkanol (12 % molar) a significant enhancement of the water contact angle (ca. 40 °) resulted in a sample obtained with a stoichiometric CO₃²⁻/Ca²⁺ ratio. These results emphasize the key role played by the three non‐ionic surfactants in the formation of materials with variable crystal shape and wettability and thus technological interest for a range of applications.     

Isomorphous substitution and luminescence properties of haloapatites synthesized by the low-temperature method

Single-phase polycrystalline fluorapatites of the Ca_{10 − x} Me _x (PO₄)₆F₂:Eu³⁺ (Me = Pb, Mg) composition are obtained by deposition from aqueous solutions. The effect of modifier ions (Pb²⁺, Mg²⁺) with significantly different ionic radii on the structure and spectral luminescence properties of the fluorapatites are studied. It is established that Pb²⁺ and Mg²⁺ ions affect the preferred location of Eu³⁺ ions in the structure of Ca_{10 − x} Me _x (PO₄)₆F₂ crystals.     

Controllable mineralization of calcium carbonate on regenerated cellulose fibers

Gel–forming fibers (GF fibers) can serve as nucleation sites to prepare calcium carbonate (CaCO₃) because they can adsorb large amounts of Ca²⁺ due to their porous structure. In this paper, mineralization behavior of CaCO₃ on GF fibers in ethanol–water mixed solvents without any additives has been investigated. The results showed that some crystals covered the fibers, while others were embedded in fibers. Twin–sphere based vaterite, zonary and rodlike calcite with large aspect ratio could be prepared successfully. The effect of ethanol content inside GF fibers, concentration of Ca²⁺ and CO₃^2‐, mineralization time, miscibility between alcohol and water, and temperature were studied. Lastly, a possible mineralization mode was suggested. This work could provide a new method to prepare inorganic/polymer hybrid materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ba2.2Ca0.8Mg4F14, a new “solid solution stabilized” matrix for an intense blue phosphor

Barium calcium magnesium fluoride (Ba₂(Ba_xCa_1‐x)Mg₄F₁₄, x=0.19‐0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba_2.200(2)Ca_0.800(2)Mg₄F₁₄were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203(8) and c = 7.4365(5) Å [tetragonal, space group P4₂/mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF₆ octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off‐center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca²⁺and Ba²⁺. The structure is isotypic with Pb₃Nb₄O₁₂F₂ but has a different coordination around Ba/Ca and Pb, respectively. Doped with ∼1% Eu(II), the compound shows intense blue luminescence under UV activation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photochemical reduction of iron trichloride in ethyl acetate: synthesis,Mössbauer spectra and the crystal structure at 80 K of hexakis(ethyl acetate)iron(II) bis-tetrachloroironate(III)

FeCl₃ in ethyl acetate under the influence of sunlight, undergoes partial reduction yields the [Fe(CH₃CO₂Et)₆](FeCl₄)₂ salt. The Mössbauer spectra showed that the iron atoms are at +2 and +3 oxidation states. The crystal structure determined by X-ray diffraction methods at 80 K and refined by full-matrix least-squares techniques toR=0.028 for 2410 independent non-zero reflections is in good agreement with the Mössbauer results. The [Fe(CH₃CO₂Et)₆]²⁺ cations occupy centers of symmetry and the Fe²⁺ ions are octahedrally coordinated by six carbonyl oxygen atoms of six ethyl acetate molecules.     

Effect of boron oxide addition on the Nd environment in a Nd-rich soda-lime aluminoborosilicate glass

The environment of Nd³⁺ ions has been studied using optical absorption spectroscopy and EXAFS at the Nd L₃-edge, in a series of soda lime aluminoborosilicate glasses with increasing B₂O₃ content. The proportion of BO₄ units has been determined by ¹¹B MAS NMR in an equivalent glass series with La³⁺ ions replacing the majority of Nd³⁺ ions, and complementary information has been obtained by measuring the Nd³⁺ decay fluorescence times in these latter glasses. In these glasses with low Al₂O₃ content, the R′ ratio, with R′ = [Na₂O^exc] / [B₂O₃] and [Na₂O^exc] = [Na₂O] − [Al₂O₃] − [ZrO₂], plays a key role in controlling the structural organization and crystallization resistance, in a similar way as the R ratio in the Dell and Bray model of sodium borosilicate glasses. At R′ > 0.5, the Nd³⁺ ions are located in a mixed silicate-borate environment and, by slow cooling of the melt, they tend to crystallize within a silicate apatite phase close to the Ca₂Nd₈(SiO₄)₆O₂ composition. At R′ < 0.5, the structural results are compatible with Nd³⁺ ions located in a borate-type environment (not excluding Si neighbors), and, by slow cooling of the melt, they segregate with Ca²⁺ ions within a Si-depleted separated borosilicate phase.     

Investigation of the crystallization features,atomic structure,and microstructure of chromium-doped monticellite

A series of Cr⁴⁺:CaMgSiO₄ single crystals is grown using floating zone melting, and their microstructure, composition, and crystal structure are investigated. It is shown that regions with inclusions of second phases, such as forsterite, akermanite, MgO, and Ca₄Mg₂Si₃O₁₂, can form over the length of the sample. The composition of the single-phase regions of the single crystals varies from the stoichiometric monticellite CaMgSiO₄ to the solid solution Ca_{(1 ? x)}Mg_{(1 + x)}SiO₄(x = 0.22). The Cr:(Ca_0.88Mg_0.12)MgSiO₄ crystal is studied using X-ray diffraction. It is revealed that, in this case, the olivine-like orthorhombic crystal lattice is distorted to the monoclinic lattice with the parameters a = 6.3574(5) Å, b = 4.8164(4) Å, c = 11.0387(8) Å, β = 90.30(1)^o, Z = 4, V = 337.98 ų, and space group P2₁/c. In the monoclinic lattice, the M(1) position of the initial olivine structure is split into two nonequivalent positions with the center of symmetry, which are occupied only by Mg²⁺ cations with the average length of the Mg-O bond R _av = 2.128 Å. The overstoichiometric Mg²⁺ cations partially replace Ca²⁺ cations (in the M(2) position of the orthorhombic prastructure) with the average bond length of 2.347 Å in the [(Ca,Mg)-O₆] octahedron. The average distance in SiO₄ distorted tetrahedra is 1.541 Å.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Phase and morphology evolution of vaterite crystals in water/ethanol binary solvent

Keeping stability is important for metastable vaterite to be applied. In this work, crystal evolution of vaterite in water/ethanol binary solvent (WEBS) was investigated. Phase identification was confirmed by XRD measurement. It is found that the stability of vaterite is sensitive to the concentration of surplus CO₃^2‐ and the ethanol mole fraction in WEBS. The vaterite phase would transform to either aragonite or calcite decided by the surplus CO₃^2‐ ions or Ca²⁺ ions, respectively. SEM observation shows that the polymorph evolution also induced the morphology change. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and defect crystal structure of CdF2 and nonstoichiometric Cd1?xRxF2+x phases (R = rare earth and In). Part 3. Crystal structure of as-grown Cd0.90R0.10F2.10 (R = Sm-Lu, Y) single crystals

The structures of as-grown Cd_0.90 R _0.10F_2.10 (R = Sm-Lu and Y) crystals are determined and related to the CaF₂ structure type. It is assumed that in all the crystals R ³⁺ and Cd²⁺ ions form clusters with the tetrahedral configuration of the [Cd₂ R ₂F₂₆] and [CdR ₃F₂₆] cations. The concentration of [Cd₂ R ₂F₂₆] cations in crystals with R = Er-Lu and Y is considerably higher that in crystals with R = Sm-Ho. The tendency to a decrease in the coordination number of R ³⁺ toward the end of the rare earth series manifests itself in the fact that the Yb³⁺ ions in Cd_0.90Yb_0.10F_2.10 occupy both tetrahedral (c.n. 10) and octahedral (c.n. 8) clusters. The Yb³⁺ ions in tetrahedral clusters are displaced from their basic positions by 0.15 Å along the 〈100〉 directions. In Cd_1−x R _x F_2+x the relaxation of the anion sublattice of the fluorite matrix around clusters is much more pronounced than in the Ca_1−x R _x F_2+x phases having similar geometry. __________ Translated from Kristallografiya, Vol. 50, No. 2, 2005, pp. 235–248. Original Russian Text Copyright ? 2005 by Sul’yanova, Shcherbakov, Molchanov, Simonov, Sobolev.     

Conductometric study of calcium carbonate prenucleation stage: underlining the role of CaCO3o ion pairs

Calcium carbonate crystallization process, especially the prenucleation stage, has increasingly been the subject of several works. In the present work, a simple method based on electrical conductivity modeling applied to the FCP (Fast Controlled Precipitation) method data is used to highlight the role of CaCO₃^o ion pairs on calcium carbonate prenucleation stage. A good agreement was obtained between the resistivity vs pH curves estimated by the McCleskey model equation and obtained experimentally in a FCP test. Results showed that the nucleation process begins with the formation of CaCO₃^o ion pairs as pre‐nuclei as soon as the calcite‐equilibrium pH is reached. Additionally CaCO₃^o content increases with pH to form aggregates, which depend on the saturation state of the solution. Basing on our thermodynamic data, these aggregates do not form amorphous calcium carbonate ACC as an intermediate phase. They lead to the formation of stable calcium carbonate nuclei which will further evolve to crystallize. Furthermore we demonstrate that in addition to their inhibitory effect on the Ca²⁺ and CO₃²⁻ association to form ion pairs, the two scale inhibitors sodium triphosphate (STP) and sodium polyacrylate (RPI) reduce ion pairs aggregation rate.     

Influence of valence and coordination of manganese ions on spectral and dielectric features of Na2SO4–B2O3–P2O5 glasses

Sodiumsulpho borophosphate glasses with composition (40 ? x)Na₂SO₄–30B₂O₃–30P₂O₅: xMnO with x ranging from 0 to 5.0 mol% were manufactures. Dielectric spectra have been studied over a wide frequency range of 10²–10⁵ Hz and in the temperature range within 30–250 °C. The valance states of manganese ions and their ligand coordination in the glass network have been investigated using optical absorption, luminescence and ESR spectroscopy. The analysis of the these results has indicated that the manganese ions exist both in Mn²⁺ as well as in Mn³⁺ states and occupy prevailingly octahedral positions and serve as modifiers similarly to Na⁺ ions The values of dielectric parameters (dielectric constant, ε′(ω), loss tan δ and ac conductivity, σ_ac) were found to increase with increasing MnO content. They play a role of modifiers similarly to Na⁺ ions, create bonding defects and free ions viz., [SO₄]^2?, [POO_1/2O₂]^2?, [POO_0/2O₃]^3–, Na⁺ and (NaSO₄)^?. The migration of these charge carriers would build up space charge polarization and may be responsible for the enhanced dielectric parameters. The ac conductivity also is enhanced with increasing MnO content. The mechanism responsible for such increase is well explained based on the modifying action of Mn²⁺ ions.     

Speciation of Fe(II) and Fe(III) effect on CaCO3 crystallization

The present work was carried out to investigate separately the effect of Fe²⁺ and Fe³⁺ on the precipitation kinetics and the microstructure of CaCO₃. For this an experimental procedure was proposed. Precipitation tests were made by using the dissolved‐CO₂ degassing method. Both air and nitrogen were employed to strip the CO₂ from a Ca(HCO₃)₂ solution initially rich in this gas. At anoxic medium, it was shown that iron (II) prolongs the nucleation step and decelerates the crystalline growth rate. X‐ray diffraction analysis shows that its presence inhibits calcite and promotes aragonite variety. By using air, the reaction medium is rich in oxygen and iron (II) is rapidly oxidized. Seeing the higher solution pH (> 6.5), iron hydroxide forms before the onset of CaCO₃ precipitation and plays a role of seed permitting to initiate CaCO₃ nucleation. So, contrary to the observed effect of iron (II), the presence of iron (III) accelerates the precipitation rate of CaCO₃. As for iron (II), iron (III) inhibits calcite formation but favored the vaterite variety instead of the aragonite one.     

Polymorphic composition and morphology of calcium carbonate as a function of ultrasonic irradiation

This paper reports on the precipitation of CaCO₃ polymorphs, having various crystal morphologies under different conditions. In particular, systems that were subject to ultrasonic irradiation were compared to the corresponding reference systems in the absence of such a treatment. The application of ultrasonic irradiation predominantly resulted in a change of particle size distribution and polymorphic composition of the precipitate, in comparison to the reference systems. Thus, it was found that the supersaturation and temperature influenced the size distribution, in both the reference and sonicated systems. A mixture of calcite, vaterite and aragonite was obtained in all reference systems, at 25 °C. At this temperature, the sonication caused the vaterite content to increase, while aragonite was not detected. In reference and sonicated systems at 80 °C, only aragonite precipitated. The results also indicate that the principle parameter responsible for the morphology of vaterite was the initial supersaturation: at higher supersaturation spherical vaterite particles precipitated, while at lower supersaturation hexagonal platelets were obtained. The morphological investigations also indicated different mechanisms of vaterite formation in the systems in which precipitation was initiated at higher supersaturation: spherulitic growth of vaterite was observed in sonicated systems, while the aggregation of primary particles was predominant in the reference systems. At lower supersaturation, the effect of c(Ca²⁺)/c(CO₃²⁻) on the morphology of hexagonal platelets of vaterite was observed as well. By varying the c(Ca²⁺)/c(CO₃²⁻), significant changes of the polymorphic composition were observed only in the sonicated systems, at 25 °C.     

Creation of calcite hollow microspheres with attached bundles of aragonite needles

Novel calcite hollow microspheres attached with bundles of aragonite needles have been synthesized via a simple precipitation reaction of aqueous solutions of CaClB_2B and NaB_2BCOB_3B in the presence of MgP^2+P ions at room temperature. The experimental results revealed that an appropriate molar ratio of [MgP^2+P]/[CaP^2+P], pH value of the solution and aging time are crucial for the formation of the unusual hierarchical CaCOB_3B superstructure. A possible growth mechanism is proposed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of strontium Di[bis(iminodiacetato)cobaltate(III)] pentahydrate,Sr[<Emphasis Type="Italic">cis</Emphasis>(N)-Co(<Emphasis Type="Italic">Ida</Emphasis>)<Subscript>2</Subscript>]<Subscript>2</Subscript> · 5H<Subscript>2</Subscript>O

Compound Sr[cis(N)-Co(Ida)₂]₂ · 5H₂O (I) is synthesized and its crystal structure is determined. The crystals are built of [Co(Ida)₂]^? anionic complexes, [Sr(H₂O)₃]²⁺ hydrated cations, and crystallization water molecules. Two independent anions are located on rotation axis 2 and have close structures. A distorted octahedral coordination of Co³⁺ atoms is formed by two N atoms and four O atoms of two Ida ^2? ligands [Co-N, 1.932(3) and 1.940(3) Å; Co-O, 1.879–1.899(3) Å]. [Sr(H₂O)₃]²⁺ cations randomly occupy half of the positions in the vicinity of centers of inversion. In addition to three water molecules, the environment of the Sr²⁺ atom includes five O atoms of five Ida ^2? ligands [Sr-O, 2.487(3)-2.889(5) Å]. Because of the disordering of [Sr(H₂O)₃]²⁺ cations, the structural function of the Ida ^2- ligands varies from tridentate chelate to pentadentate bridging chelate. Sr-O and hydrogen bonds connect structural elements into a three-dimensional framework. The structure of I is compared with that of a related compound Sr[CoEdta]₂·9H₂O (II). It is shown that the formation of N-H…O hydrogen bonds, which connect [Co(Ida)₂]^? anionic complexes in I into compact chains, is an important factor leading to the difference between packings I and II.