Crystalline CaCO3 Research Articles

Micro/nano-structured titanium surfaces modified by NaOH–CaCl2-heat-water treatment: Biomimetic calcium phosphate deposition and hMSCs behavior

The unexplored effect of chemical treatment of laser micro/nanostructured titanium surfaces deserves attention due to broadening our knowledge of surface enhancement of biomimetic synthesis of hydroxyapatite and osseointegration of titanium implants. In this study, NaOH–CaCl2-heat-water treatment of titanium is revisited and used to modify porous laser micro/nanostructured oxidic and flat titanium surfaces which are characterized by XRD, electron microscopy, zeta potential and FTIR and Raman spectroscopy. These surfaces are also assessed for their ability to induce biomimetic Ca phosphate deposition from a simulated body fluid (SBF) and to grow human Mesenchymal stem cells (hMSCs). The treatment of titanium surfaces is shown to involve unreported formation of crystalline CaCO3 and the related interpretation of physicochemical changes of the treated titanium surface in soaked SBF raises doubts about the specific role of an intermediary CaTiO3 in the biomimetic formation of apatite on titanium substrates. We show that the biomimetic formation of Ca phosphate in Tas SBF solution occurs both on the surface and in the bulk solution, it is enhanced on the structured surfaces and is affected by a Ca--O(Ti) layer originating on the pristine and chemical treated flat and micro/nanostructured topographies with different delays. These findings are confronted with the pilot results of in vitro analyses showing that the cell growth, shape and osteogenic differentiation of hMSCs are impeded on the surfaces modified by the NaOH–CaCl2-heat-water treatment.

X-ray Total Scattering Study of Phases Formed from Cement Phases Carbonation

Carbonation in cement binders has to be thoroughly understood because it affects phase assemblage, binder microstructure and durability performance of concretes. This is still not the case as the reaction products can be crystalline, nanocrystalline and amorphous. The characterisation of the last two types of components are quite challenging. Here, carbonation reactions have been studied in alite-, belite- and ye’elimite-containing pastes, in controlled conditions (3% CO2 and RH = 65%). Pair distribution function (PDF) jointly with Rietveld and thermal analyses have been applied to prove that ettringite decomposed to yield crystalline aragonite, bassanite and nano-gibbsite without any formation of amorphous calcium carbonate. The particle size of gibbsite under these conditions was found to be larger (~5 nm) than that coming from the direct hydration of ye’elimite with anhydrite (~3 nm). Moreover, the carbonation of mixtures of C-S-H gel and portlandite, from alite and belite hydration, led to the formation of the three crystalline CaCO3 polymorphs (calcite, aragonite and vaterite), amorphous silica gel and amorphous calcium carbonate. In addition to their PDF profiles, the thermal analyses traces are thoroughly analysed and discussed.

Bivalve shells (Corbula trigona) as a new adsorbent for the defluoridation of groundwater by adsorption-precipitation

Defluoridation of groundwater was performed in a batch reactor using bivalve shell powder (BSP) as adsorbent. The physicochemical characteristics of BSP, studied by Fourier Transform Infrared, X-ray Diffraction and Inductively Coupled Plasma-Optical Emission Spectrometry after dissolution, have shown that BSP was mainly composed of crystalline CaCO3 (∼97.8%). The effects of pH, initial fluoride concentration, adsorbent dose and contact time on the adsorption capacity of BSP were investigated. For an initial fluoride concentration of 2.2 mg/L and with 16 g/L of BSP, after 8 hours of treatment, 27.3% were eliminated at pH 7.5 versus 68% at pH 3, highlighting the efficiency of the adsorption process. The difference in adsorption capacity as a function of pH was correlated to the pHpzc of the BSP, which was equal to 8.2. Thus, at pH below pHpzc, electrostatic attraction between the fluoride anions and the positively charged adsorbent could justify the adsorption mechanism. Fittings of experimental data have evidenced that the adsorption kinetics were of pseudo-second order whereas the adsorption isotherms were of Langmuir type. The chemical precipitation of calcium fluoride was also revealed to occur upon release of Ca2+ from partial dissolution of CaCO3 in acidic conditions.

Larval calcification and growth of veligers to early pediveliger of the queen conch Strombus gigas in mesocosm and laboratory conditions

The goals of this study were to evaluate growth, development, and calcification process of veligers of Strombus gigas grown in natural conditions in mesocosm versus laboratory conditions. In this study, larvae bred in mesocosm conditions had a good growth rate (33.3±12.40 μm.day−1) when fed with natural phytoplankton in natural flowing seawater versus a lower growth rate of 8.8±5.20 μm.day−1 for larvae reared in laboratory conditions and fed with a monoalgal diet of Nannochloropsis oculata. Physicochemical parameters did not explain the difference on larval growth in both culture systems according to the principal component analysis done. Raman microspectrometry carried out on conch larvae grown in mesocosm and lab conditions allowed us to emphasize the biosynthesis of calcium carbonate species and their structure type evolution (amorphous, aragonite, or calcite structure) as a function of the breeding time by detecting and identifying in the spectra the characteristic Raman bands of CO3 chemical groups and lattice vibrations. This analytical method seems to indicate that crystalline CaCO3 structures are not detected in the recorded spectra on larvae reared in laboratory conditions during the early stages of the shell construction of 1 to 8 days. For this reason, light and current flow have also been considered in the discussion that can help to explain the differences found in this study. Contrarily, the Raman spectra acquired on larvae grown in mesocosms exhibit characteristic bands of aragonite (CO3 double peak at 697–701 cm−1 and lattice vibrations at 170 and 220 cm−1) from the third day of breeding. The best shell growth and shell calcification pointed out in larvae grown in mesocosm compared to laboratory conditions are probably due to the nutrient amounts present in the food available in mesocosm.

Salvando el planeta con biotecnología apropiada: 5. Un plan de acción

We evaluate suggestions to harness the ability of calcifying organisms (molluscs, crustacea, corals and coccolithophore algae) to remove permanently CO2 from the atmosphere into solid (crystalline) CaCO3 for atmosphere remediation. Here, we compare this blue carbon with artificial/industrial Carbon dioxide Capture & Storage (CCS) solutions. An industrial CCS facility delivers, at some cost, captured CO2, nothing more. But aquaculture enterprises cultivating shell to capture and store atmospheric CO2 also produce nutritious food and perform many ecosystem services like water filtration, biodeposition, denitrification, reef building, enhanced biodiversity, shoreline stabilisation and wave management. We estimate that a mussel farm sequesters three times as much carbon as terrestrial ecosystems retain. Blue carbon farming does not need irrigation or fertiliser, nor conflict with the use of scarce agricultural land. Blue carbon farming can be combined with restoration and conservation of overfished fisheries and usually involves so little intervention that there is no inevitable conflict with other activities. We calculate that this paradigm shift (from ‘shellfish as food’ to ‘shellfish for carbon sequestration’) makes bivalve mollusc farming and microalgal farming enterprises, viable, profitable, and sustainable, alternatives to all CCUS industrial technologies and terrestrial biotechnologies in use today.

Improvement of desulfurization efficiency of Al-rich ladle furnace refining slag with an aqueous carbonation method by hydrothermal or ultrasound pretreatment.

Ladle furnace (LF) slag is a type of steel slag, which has limited applications due to its high S content. Aqueous carbonation is a prospective method for desulfurization of the LF slag. However, the Al-rich LF raw slag has very low desulfurization efficiency with carbonation method. This study investigated the improvement of desulfurization efficiency of the Al-rich LF slag with carbonation method by hydrothermal (HP) or ultrasound pretreatment (UP). The results showed that C3AHX was formed in pretreated slags because of C12A7 hydration, which could remove part of S. After carbonation, most of the C3AHX in pretreated slags produced crystalline CaCO3 bonded by amorphous Al(OH)3 (the other reaction product) in 10min. In the carbonation process, S removal was mainly determined by carbonation efficiency. The S content was reduced to about 0.40% for the pretreated slags from 1.04% in the raw slag. By contrast, the S content was reduced to only 0.93% for slag without pretreatment under the same carbonation conditions. The possible reason of the improvement of desulfurization efficiency by HP or UP was the formation of thin plate-like C3AHx, which increased the surface area available for carbonation reaction. The UP slag presented slightly lower S content than the HP slag because high ultrasound energy increased the reactivity of Ca2SiO4.

Monitoring a Mechanochemical Reaction Reveals the Formation of a New ACC Defect Variant Containing the HCO3– Anion Encapsulated by an Amorphous Matrix

Amorphous calcium carbonate (ACC) is an important precursor in the biomineralization of crystalline CaCO3. In nature, it serves as a storage material or as a permanent structural element, whose lifetime is regulated by an organic matrix. The relevance of ACC in materials science is primarily related to our understanding of CaCO3 crystallization pathways and CaCO3/(bio)polymer nanocomposites. ACC can be synthesized by liquid–liquid phase separation, and it is typically stabilized with macromolecules. We have prepared ACC by milling calcite in a planetary ball mill. Phosphate “impurities” were added in the form of monetite (CaHPO4) to substitute the carbonate anions, thereby stabilizing ACC by substitutional disorder. The phosphate anions do not simply replace the carbonate anions. They undergo shear-driven acid/base and condensation reactions, where stoichiometric (10%) phosphate contents are required for the amorphization to be complete. The phosphate anions generate a strained network that hinders ACC recrystallization kinetically. The amorphization reaction and the structure of BM-ACC were studied by quantitative Fourier transform infrared spectroscopy and solid state 31P, 13C, and 1H magic angle spinning nuclear magnetic resonance spectroscopy, which are highly sensitive to symmetry changes of the local environment. In the first—and fast—reaction step, the CO32– anions are protonated by the HPO42– groups. The formation of unprecedented hydrogen carbonate (HCO3–) and orthophosphate anions appears to be the driving force of the reaction, because the phosphate group has a higher Coulomb energy and the tetrahedral PO43– unit can fill space more efficiently. In a competing second—and slow—reaction step, pyrophosphate anions are formed in a condensation reaction. No pyrophosphates are formed at higher carbonate contents. High strain leads to such a large energy barrier that any reaction is suppressed. Our findings aid in the understanding of the mechanochemical amorphization of calcium carbonate and emphasize the effect of impurities for the stabilization of the amorphous phases in general. Our approach allowed the synthesis of new amorphous alkaline earth defect variants containing the unique HCO3– anion. Our approach outlines a general strategy to obtain new amorphous solids for a variety of carbonate/phosphate systems that offer promise as biomaterials for bone regeneration.

Recycling drinking water treatment sludge into eco-concrete blocks with CO2 curing: Durability and leachability

Drinking water treatment sludge (DWTS) can be recycled into low-strength concrete blocks for construction use. The sodium sulfate resistance and leaching behaviours of the DWTS-derived blocks are investigated in this study. The experimental results show that the addition of DWTS degrades the sodium sulfate resistance of the concrete blocks, however CO2 curing compensates for such property, especially in the case of blocks incorporating 30% DWTS. The improvement can be attributed to the formation of crystalline CaCO3 during CO2 curing for microstructure refinement evidenced by X-ray Computed Tomography and Scanning Electron Microscopy. Leaching analyses show that Cu and Al concentrations increased with increasing DWTS content, and CO2 curing adversely increased the leachability of metals due to the decrease of pH, especially at early leaching stage. Nevertheless, the total leaching concentrations of Cu and Al after 60-day test is far below the prescribed limitations, regardless of samples subject to air curing or CO2 curing. In summary, sludge-derived blocks exposed to CO2 curing are safe and behave well in aggressive environments. Therefore, this study showcases a green technology that successfully recycling DWTS into value-added and durable concrete blocks with low environmental impacts.

Properties and microstructure of concrete blocks incorporating drinking water treatment sludge exposed to early-age carbonation curing

In recent decades, industrial by-products have gained significant attention for their potential as components of more environmentally friendly construction materials. In this context, this paper presents the manufacture of concrete blocks (CB), in which sand was replaced with oven-dried drinking water treatment sludge (DWTS). In addition, CB with DWTS contents ranging from 0% to 30% by weight were exposed to early-age carbonation curing. Experiments were conducted to determine the compressive strength, splitting tensile strength, and water capillary absorption of CB subjected to normal or early-age carbonation curing. The results indicated that DWTS degraded durability and mechanical properties of CB because of the high-water absorption and high organic content of DWTS. However, early-age carbonation curing was found to improve the overall performance of CB with DWTS, such that the carbonated CB mixtures satisfied the strength requirement of load-bearing blocks. The pH values of CB after carbonation curing increased with increasing content of DWTS. Microstructural analyses showed that the addition of DWTS into CB caused the formation of ettringites because of the presence of alum and gypsum in DWTS, and early-age carbonation curing decomposed these ettringite into calcium carbonates. The results also showed that the production of crystalline CaCO3 under carbonation had a filling effect that refined the pore sizes. Thus, the findings of this study indicate that utilisation of DWTS in CB offers significant environmental and health benefits via increased greenhouse gas absorption, as well as reduced DWTS disposal in landfills and unsustainable sand extraction.

Una ampliación biotecnológica del cultivo de moluscos bivalvos podría eliminar permanentemente el dióxido de carbono de la atmósfera.

To combat climate change, proposals have been made to develop methods that would pull carbon dioxide out of Earth’s atmosphere. One recommended approach is to remove CO2 from the atmosphere with activities such as reforestation and changing forest management and agricultural practices to enhance soil carbon storage. However, it is also noted that such activities would limit land for food production and negatively affect biodiversity. Furthermore, decay of dead wood and fallen leaves in natural forests releases huge quantities of CO2 and other greenhouse gases back into the atmosphere. The only other carbon-sequestration technique that is widely considered is the application of CO2 capture processes to flue gases of power plants, which are responsible for about 80% of the worldwide CO2 emission from large stationary sources. Hydrate-based processing is a promising technology for CO2 capture as it results in high CO2 recovery, but its high cost prevents this technology having much impact. In this note I suggest that the ability of marine organisms (shellfish and coccolithophore algae) to remove permanently CO2 from the atmosphere into solid (crystalline) CaCO3 should be harnessed. I suggest that if the level of finance and effort that are readily anticipated for forest management and flue gas treatments were to be applied to expansion of shellfish cultivation around the world, significant amounts of carbon dioxide could be permanently removed from the atmosphere within the timescale that is currently envisaged for carbon capture by afforestation.

The effects of carbonation and hydration on the mineralogy and microstructure of basic oxygen furnace slag products

Basic oxygen furnace slag (BOFS) is one of many alkaline industrial residues. However, BOFS has a low utilization value, and it also may have environmental issues in the practical application. This paper performs a long-term study on the evolution of pH and compressive strength during the combined-curing through carbonation and subsequent hydration of BOFS. Results showed that the combined-curing is a promising and environmentally beneficial way to dispose and utilize BOFS, because it 1) permanently stores carbon dioxide, 2) makes full use of the activity of the minerals in BOFS, and 3) enhances the properties of building materials by improving the compressive strength, reducing the pH, and reducing the true density, without causing concerns on the properties of expansion and fracture. The pore structure was improved by the formed poorly crystalline calcium carbonate (CaCO3), crystalline CaCO3, and monocarboaluminate during the combined-curing process. The pH of the liquid phase initially decreased with the carbonation degree. After the CaCO3-coating was separated from the surface of basic phases, the late-age hydration of un-carbonated basic phases led to a rebound of pH. Rietveld refinement and the evolution of pH showed that the hydration rate decreased as the carbonation degree increased due to the absence of calcium hydroxide. Thus, the physico-chemical mechanism involved in the strength gain, and the alteration of the pH was explained through the composition and structure analysis. The above findings could be meaningful for the steel slag recycling, CO2 utilization and sequestration.

Enhanced biomass and lipid production of Neochloris oleoabundans under high light conditions by anisotropic nature of light-splitting CaCO3 crystal

The aim of this work was to study the anisotropic effect of crystalline CaCO3 nanoparticles (CN)-driven multiple refraction/scattering from the CN-coated agglomerated cells on the rate of photosynthesis and the product yield under high light conditions in the freshwater microalgae Neochloris oleoabundans. The CN-coating via biomineralization significantly improved the biomass and lipid production of N. oleoabundans during second stage of autotrophic induction by sustaining relatively high rate of photosynthesis at high irradiance using the multiple-splitting effect of the anisotropic polymorphism. The CN were successfully produced, adsorbed and grown on the external cells under conditions of mild alkalinity (pH 7.5–8.0), mild CaCl2 concentration (0.05 M) and under nitrogen starvation with strong light (400 µE m−2 s−1). Consequently, lipid content and productivity of N. oleoabundans cells cultured with 0.05 M CaCl2 increased by 18.4% and 31.5%, respectively, compared to the cells cultured with 0.05 M CaCl2 and acetazolamide to inhibit calcification.

Amazonia versus Pontocaspis: a key to understanding the mineral composition of mysid statoliths (Crustacea: Mysida)

We have determined the mineral composition of statoliths in 169 species or subspecies (256 populations) of the family Mysidae on a worldwide scale. Including previously published data, the crystallographic characteristics are now known for 296 extant species or subspecies: fluorite (CaF2) in 79%, vaterite (a metastable form of crystalline CaCO3) in 16%, and non-crystalline (organic) components in 5%, the latter exclusively and throughout in the subfamilies Boreomysinae and Rhopalophthalminae. Within the subfamily Mysinae vaterite or fluorite were found in three tribes, whereas other three tribes have fluorite only. The exclusive presence of fluorite was confirmed for the remaining seven subfamilies. Hotspots of vaterite were found in Amazonia and the Pontocaspis, in each case with reduced frequencies in main and tributary basins of the Atlantic and N-Indian Ocean. Vaterite is completely absent in the remaining aquatic regions of the world. In accordance with previous findings, fluorite occurred mainly in seawater, vaterite mostly in brackish to freshwater. Only vaterite was found in electrolyte-poor Black Water of Amazonia, which clearly cannot support the high fluorine demand for renewal of otherwise large fluorite statoliths upon each moult. Vaterite prevails in Diamysini, distributed over most of the area once occupied by the Tethyan Sea. It also prevails in Paramysini with main occurrence in the Pontocaspis, where fossil calcareous statoliths in the stable form of calcite are known from Miocene sediments of the brackish Paratethys. Four Recent genera from three tribes are heterogeneous in that they comprise both vaterite- and fluorite-precipitating species. Previous hypotheses are expanded to cover greater geographic and time scales, proposing that fluorite-bearing marine ancestors penetrated freshwaters in Tethyan and Paratethyan basins, where they developed precipitation of vaterite. This gave their successors predispositions for shifting into separate evolutionary lines from fluorite to vaterite precipitation and vice versa.

Facile synthesis of CaCO3 and investigation on structural and optical properties of high purity crystalline calcite

Crystalline calcium carbonate (CaCO3) is an inorganic substance readily available and able to be produced artificially. The widespread applications to industries especially as a filler has increased the need for further research on its properties and behavior. Crystalline CaCO3 may also provide a route to hydroxyapatite with biomedical applications. The physicochemical properties of CaCO3 can be manipulated via different preparation methods. This study focusses on a precipitation method to synthesize CaCO3. Calcium chloride (CaCl2) and ammonium carbonate (NH4CO3) were used for the synthesis in different concentrations ranging from 0.05 M to 1.0 M. Elemental and particle analysis were done to describe the resulting products structurally and phase identification. Elemental analysis was undertaken by X-Ray diffraction (XRD), Fourier transform infrared Spectroscopy (FT-IR), Raman Spectroscopy and Energy Dispersive X-Ray Analysis (ED-X). From elemental analysis, it was confirmed that the resulting product was calcite micro-particles. Further analysis was done on particle and crystallite sizes by Nano-Particle Sizer, XRD and FE-SEM micrograph. It was deduced from the aforementioned analysis, the smallest crystallite size measured by Scherrer equation is 85.71 nm obtained by precipitation CaCO3 at 0.5 M concentration. This also tallied with the smallest particle size measured by FESEM micrograph showing the smallest margin of particles with size 783 nm. Optical characteristic of CaCO3 was described by ultra-violet spectroscopy (UV–vis) showing UV was absorbed in UV-C range. This study is also informative by presenting calculated absorption coefficient 0.1154 M−1cm−1. Recent studies on CaCO3 precipitation method have rarely reported its absorption coefficient: hence this information is useful. It was concluded that the optimal concentration for CaCO3 precipitation is within the range of 0.1 M–0.5 M. Synthesized CaCO3 crystalline are all ≤1000 nm. This study has demonstrated that the precipitation method is able to produce calcite in the micrometer range and is suitable for further study on biosensor technology or drug delivery system application.

CO2-Responsive Switchable Solvents to Induce Self-Assembled Crystallization and Phase Control of CaCO3

We propose a novel and cyclic synthetic approach for controlling crystal polymorphs of CaCO3 by using green CO2-responsive switchable solvents which acted as both the CO2 capturer for the carbonate source and the polymorphisms director. Five solvents were employed, and various reaction conditions such as calcium resources, calcium concentration, reaction temperature, and reaction time were investigated. Results show that this developed framework permits producing any crystalline CaCO3 phases including metastable vaterite and aragonite in pure phases by selecting a suitable solvent and adjustment of the reaction conditions. Furtherly, the mechanism study demonstrates that the solvents attach on the surface of the primary nanoparticles to selectively control and direct the growth of any specific polymorph phases. Eventually, the nuclei are self-assembled into an oriented geometry, allowing the growth and stability of specific crystals; as such, spherical vaterite, rods, and shuttle-like aragonite crystals can be obtained. This new configuration would be an appropriate and an efficient method to apply to large-scale production, therefore, a promising process attributed to complete solvent recovery and regeneration of the initial reactants, thus being an environmentally risk-free route.

Study of Durability of Concrete with Fly Ash as Fine Aggregate under Alternative Interactions of Freeze‐Thaw and Carbonation

To study the durability of concrete with fly ash as fine aggregate subjected to alternative attacks of freeze‐thaw and carbonation, the appearance, mass loss, relative dynamic modulus of elasticity, relative compressive strength, and carbonation depth of the concrete are investigated using cyclic tests under single carbonation, single freeze‐thaw, and alternation of freeze‐thaw and carbonation. In addition, microstructural analysis techniques including scanning electron microscope and X‐ray diffraction are adopted to reveal the deterioration mechanism of alternating freeze‐thaw and carbonation. Results show that carbonation is beneficial for refining the pore structure and increasing concrete strength in the initial alternative cycle, which delays the damage from freeze‐thaw cycles. Damage from freeze‐thaw causes crack propagation in concrete, which leads to carbonation intensification. Compared with other test modes, concrete under alternative freeze‐thaw and carbonation causes the greatest degree of deterioration during the initial freeze‐thaw cycles. The carbonation depth under alternative freeze‐thaw and carbonation is positively correlated with the carbonation time and the water‐to‐cement ratio. However, as the reactant is continuously consumed due to the expansion of crystalline ice and CaCO3, alternative cycles result in the appearance of many more new cracks in the concrete.

Crystallization kinetics of amorphous calcium carbonate in confinement.

Phase transformations of carbonates are relevant to a wide range of biological, environmental, and industrial processes. Over the past decade, it emerged that crystallization pathways in these systems can be quite complex. Metastable intermediates such as amorphous calcium carbonate (ACC) were found to greatly impact composition, structure, and properties of more stable phases. However, it has been challenging to create predictive models. Rapid transformation of ACC in bulk has been one obstacle in the determination of nucleation rates. Herein, it is reported that confinement in microfluidic droplets allows separating in time the precipitation of ACC and subsequent nucleation and growth of crystalline CaCO3. An upper limit of 1.2 cm-3 s-1 was determined for the steady-state crystal nucleation rate in the presence of ACC at ambient conditions. This rate has implications for the formation of calcium carbonate in biomineralization, bio-inspired syntheses, and carbon sequestration.

Influence of biodegradation on the tensile and wear resistance properties of bio-derived CaCO3/epoxy composites

This research work investigated the influence of palm kernel shell-derived calcium carbonate (CaCO3) fillers and biodegradation on the tensile and wear properties of epoxy composites. CaCO3 fillers were obtained from pulverised charred palm kernel shell (CPKS) particles. The composites contained between 2 wt.% and 20 wt.% of CaCO3 fillers. The samples were characterised for microstructural examination, phase analysis, tensile, and wear properties. The results revealed that the composite samples possessed enhanced properties compared with the neat matrix due to the presence of CaCO3 fillers. No particle debonding was observed on the fracture surfaces of the composite samples, which suggested that a strong interface existed between the fillers and the matrix. This could be attributed to the elimination of amorphous content from the CPKS particles during the pyrolysis process, which yielded highly crystalline CaCO3. This was strongly supported by the XRD results. Furthermore, the effect of biodegradation on the composite properties was studied on the samples interred for 90 days in natural soil. Degradation increased as the fraction of CaCO3 fillers increased due to the microbial degradation of CaCO3 fillers and the investigated properties deteriorated as compared with samples that were not buried. It was concluded that bio-derived CaCO3 fillers could function as reinforcement particles in an epoxy matrix and enhance its degradation when added in large quantities to the matrix.

Mechanochemical Access to Defect-Stabilized Amorphous Calcium Carbonate

Amorphous calcium carbonate (ACC) is an important precursor in the biomineralization of crystalline CaCO3. The lifetime of transient ACC in nature is regulated by an organic matrix, to use it as an intermediate storage buffer or as a permanent structural element. The relevance of ACC in material science is related to our understanding of CaCO3 crystallization pathways. ACC can be obtained by liquid–liquid phase separation, and it is typically stabilized with the help of macromolecules. We have prepared ACC by milling calcite in a planetary ball mill. The ball-milled amorphous calcium carbonate (BM-ACC) was stabilized with small amounts of Na2CO3. The addition of foreign ions in form of Na2CO3 is crucial to achieve complete amorphization. Their incorporation generates defects that hinder recrystallization kinetically. In contrast to wet-chemically prepared ACC, the solvent-free approach makes BM-ACC an anhydrous modification. The amorphization process was monitored by quantitative Fourier transform infrare...

Influence of carbonate and nickel(II) concentration on the synthesis of calcium phosphates

Two sets of Ni-substituted calcium phosphate were synthesized by precipitation method at pH = 7 and at two different concentrations of ion carbonate (CO32-) in solution and Ni(II) concentrations lower than 15%. The produced solids were characterized by chemical analysis, infrared spectroscopy, x-ray powder diffraction and scanning electron microscopy. The solid samples obtained at low concentration of CO32- (5%) and Ni(II) concentrations 5%, 10% and 15% were synthesized at 25 and 37 °C. All solids showed the presence of a stable and crystalline brushite (CaHPO4·2H2O). The samples synthesized in presence of high levels of carbonate (50%) and Ni(II) concentration 5% at 25, 37 and 100 °C vary with temperature. Those obtained at the lower temperatures (25 and 37 °C) showed coexistence of two phases: a crystalline CaCO3 and carbonate apatite with low crystallinity. At 100 °C, only carbonate apatite could be recognized. Data supported the carbonate substitution by OH- (position A) and PO43- (position B) in the hydroxyapatite structure. The comparison of the chemical analysis results of both systems studied (Ni,Ca) apatite and (Ni,Ca) carbonate apatite evidences a rise of Ni(II) incorporation in the apatite lattice, with simultaneous inclusion of CO32- and temperature increase. The obtained results suggest that brushite kidney stones development may be induced by the presence of traces of Ni(II) and simultaneous decrease of carbonate levels in the biological fluids.