Formation Of Calcium Carbonate Polymorphs Research Articles

Nested Formation of Calcium Carbonate Polymorphs in a Bacterial Surface Membrane with a Graded Nanoconfinement: An Evolutionary Strategy to Ensure Bacterial Survival.

It is the intention of this study to elucidate the nested formation of calcium carbonate polymorphs or polyamorphs in the different nanosized compartments. With these observations, it can be concluded how the bacteria can survive in a harsh environment with high calcium carbonate supersaturation. The mechanisms of calcium carbonate precipitation at the surface membrane and at the underlying cell wall membrane of the thermophilic soil bacterium Geobacillus stearothermophilus DSM 13240 have been revealed by high-resolution transmission electron microscopy and atomic force microscopy. In this Gram-positive bacterium, nanopores in the surface layer (S-layer) and in the supporting cell wall polymers are nucleation sites for metastable calcium carbonate polymorphs and polyamorphs. In order to observe the different metastable forms, various reaction times and a low reaction temperature (4 °C) have been chosen. Calcium carbonate polymorphs nucleate in the confinement of nanosized pores (⌀ 3–5 nm) of the S-layer. The hydrous crystalline calcium carbonate (ikaite) is formed initially with [110] as the favored growth direction. It transforms into the anhydrous metastable vaterite by a solid-state transition. In a following reaction step, calcite is precipitated, caused by dissolution of vaterite in the aqueous solution. In the larger pores of the cell wall (⌀ 20–50 nm), hydrated amorphous calcium carbonate is grown, which transforms into metastable monohydrocalcite, aragonite, or calcite. Due to the sequence of reaction steps via various metastable phases, the bacteria gain time for chipping the partially mineralized S-layer, and forming a fresh S-layer (characteristic growth time about 20 min). Thus, the bacteria can survive in solutions with high calcium carbonate supersaturation under the conditions of forced biomineralization.

Carbonation rate and microstructural alterations of class G cement under geological storage conditions

Cementitious grouts are a vital component for the economically-viable implementation of the geological storage of CO2 in providing an engineered long-term seal. In this study a class G cement was carbonated at 80 bar, at either 60 °C or 120 °C, whilst immersed in a synthetic brine for durations of up to 5 months. X-ray computed tomography was used to evaluate the advancement of carbonation depth, whilst SEM/EDXA and XRD were used to characterise microstructural alteration of the cement phases. The microstructure of the ‘main carbonation front’ was found to be representative of the governing reactive transport mechanism. An ill-defined ‘main carbonation front’ during carbonation at 80 bar/60 °C showed a carbonation mechanism controlled by the rate or precipitation/dissolution reactions; diffusion in that case was not the controlling factor. The faster local supersaturation conditions in the pores at 60 °C (with respect to Ca2+ and HCO3−) created a dynamic system of aragonite precipitation from the carbonated to the inner regions of the cement. At 80 bar/120 °C a clearly defined ‘main carbonation front’ with higher compositional density than at 60 °C, was correlated with the fast reactions and diffusion limited evolution of the ‘main carbonation front’. Calcite, as the main result of those fast reactions at 120 °C, filled ubiquitously previously unmineralized voids, creating a system less prone to compositional alterations by chemical changes due to the CO2 plume. This study showed, that the formation of calcium carbonate polymorphs depends on the kinetics of carbonation reactions for a class G cement that is determined by temperature and time. The findings of the current paper can be further used for the understanding of reaction processes within the cements of the CO2 injection wells and assess their long-term chemical stability.

A parametric study of layer-by-layer deposition of CaCO3 on glass surfaces towards fabricating carbonate reservoirs on microfluidic chips

Recently, geomaterial-functionalized microfluidic chips have been receiving increased attention as they facilitate material representation to mimic surface mineralogy in addition to direct visualization and quantification of multiphase flow and transport processes in a porous media. In particular, calcite-coated glass surfaces have been used to mimic the solid-fluid interactions involved in carbonate reservoirs. The coating procedure usually involves the deposition of calcium carbonate layers on a functionalized glass surface. Depending upon experimental conditions, the deposited calcium carbonate could be one or more of the three polymorphs: calcite, vaterite, and aragonite. Hence, it is essential to analyze and control the formation of the desired calcium carbonate polymorph. In this study, we transformed glass surfaces into carbonate surfaces by growing calcium carbonate particles in-situ using a layer-by-layer deposition procedure. The influences of process parameters involved in the deposition procedure on the formation of calcium carbonate polymorphs were analyzed. The parameters evaluated were: initial glass surface cleaning phase – DI water, plasma, piranha and NaOH as substrate cleaners; surface functionalization phase – DI water and chloroform as silane solvents; and calcite crystals growth phase – effect of number of coating cycles and concentration of CaCl2 and Na2CO3 solutions on the coating. After CaCO3 deposition, strategies to transform kinetically favorable vaterite to thermodynamically stable calcite are discussed. Coating uniformity, morphology, elemental atomic percentage of coating, and the CaCO3 polymorphs were examined by optical microscopy, Scanning Electron Microscopy (SEM), SEM Energy Dispersive X-Ray Spectroscopy (SEM EDS), and Raman spectroscopy, respectively.

Natural carbonation-induced phase and molecular evolution of alkali-activated slag: Effect of activator composition and curing temperature

In this work, the evolution of reacted phase assemblage and molecular structure of alkali-activated slag (AAS) exposed to atmospheric natural carbonation is studied. The hardened AAS pastes with various activator types (i.e., sodium hydroxide, sodium carbonate, sodium sulfate, potassium hydroxide, and potassium carbonate solutions) and cured under two temperature conditions (20 °C and 80 °C) are evaluated. The results show that natural carbonation leads to a strong decalcification and silicate polymerization of calcium-aluminosilicate-hydrate (C-A-S-H) and precipitation of various calcium carbonate polymorphs depending on activator composition. The sulfate-activated slag shows the poorest carbonation resistance likely due to its limited CO2 absorption capacity, manifested with the formation of calcium carbonate polymorphs, gypsum, gibbsite, and calcium-deficit aluminosilicate gels. While high-temperature curing tends to increase the crystallinity level of C-A-S-H, it has little effect on its carbonation resistance in terms of phase and molecular stability.

Kalsiyum Karbonat Polimorflarının Oluşumuna Yaşlandırma Süresinin Etkisi

Bu çalışmada, yaşlandırma süresinin, başlangıç reaktan konsantrasyonunun, reaktan besleme hızınınve katkı maddesinin kalsiyum karbonat kristalizasyonuna etkisi ıslak çöktürme yöntemi ile incelenmiştir.Kristalizasyon deneylerinde çöken faza belirlenen sürelerde yaşlandırma işlemi uygulanmış ve elde edilen kristallerFourier Dönüşümlü Kızılötesi Spektroskopi (FT-IR) ve X-Işınları Toz Difraksiyon (XRD) metotları ile karakterizeedilmiştir. CaCO3 kristallerinin polimorflarının oluşumunda yaşlandırma süresinin ve kullanılan polimerik katkımaddesinin etkili olduğu görülmüştür.

Influence of the Type of Cement on the Formation of Calcium Carbonate Polymorphs due to Carbonation of Cement Materials

The objective of this study was to examine the influence of the type of cement on the formation of calcium carbonate CaCO3 polymorphs after carbonation of cement materials. Thermogravimetric analysis and X-ray diffraction were used to follow mineralogical changes of CEM I and CEM II mortars and pastes which were submitted to an accelerated carbonation at 20% CO2, 20°C and 65% relative humidity. The results indicated that aragonite and vaterite are formed from the carbonation of CEM II materials while these metastable polymorphs are not present in carbonated CEM I materials. It is likely that aragonite and vaterite are formed only at an advanced level of carbonation when pH is smaller than 9, which is the case of CEM I mortar and paste.

In vitro growth of calcium carbonate crystals on bivalve shells: Application of two methods of synthesis

The classic ammonium carbonate vapor diffusion method (VDM) and the coprecipitation method (CM) in its modified form were applied for in vitro growth of calcium carbonate crystals on glass substrate and on calcitic and aragonitic shell layers of blue mussel Mytilus edulis (L.) and Iceland scallop Chlamys islandica (M.). The experiments were carried out using large volumes of growth medium (250ml and 1000ml). Crystallization using the VDM is relatively slow, but faster with the CM. The formation of calcium carbonate polymorphs is strongly influenced by the mineralogical phase in the uppermost layer of the shell substrate bathed in the experimental solution, even if magnesium ions are added to solution with the CM. The morphology of calcium carbonate crystals clearly differs between methods, and is influenced by the type of substrate. The effect of biomacromolecules released from the shell substrate on morphology and organization of calcium carbonate crystals is clearly observed with both methods of crystallization.

Formation of Calcium Carbonate Polymorphs Induced by Living Microalgae

Calcium carbonate (CaCO3) occurs in the three polymorphs calcite, aragonite and vaterite. The formation of these crystals in inorganic solutions is influenced by parameters like pH, temperature or impurities. Living freshwater microalgae can also induce the formation of CaCO3 when they live in a suitable environment containing saturated amounts of Ca2+. Through this biologically induced biomineralization only the formation of the polymorph calcite has been reported yet. We investigated the precipitates which have been formed in solutions containing the freshwater microalgae Scenedesmus obliquus and different zinc amounts (0, 3.27 and 6.53 mg Zn2+/l) by XRD and SEM. As references precipitates from the same solutions but without algae were investigated. We could show that the presence of living microalgae has a great influence on the precipitation of calcium carbonate crystals. In algae-containing media without or with a low zinc amount always calcite and aragonite are formed. In the corresponding medium with 6.53 mg Zn2+/l pure aragonite crystals were built. In contrast, in the inorganic, algae-free solutions without zinc, pure calcite is precipitated. Both inorganic solutions with zinc show major calcite precipitation and weak aragonite precipitation. Thus the algae cells advance significantly the formation of aragonite, which is enhanced by the presence of zinc cations in the media. Possible mechanisms are discussed.

Effect of polyacrylic acid and polyethylene glycol on the crystallization of calcium carbonates in the presence of magnesium ions

The effect of polyacrylic acid and polyethylene glycol on the crystallization of calcium carbonates in the presence of magnesium ions was studied. It was found that the presence of magnesium ions in solution and the treatment temperature (80°C) influence the formation of the final products of calcium carbonate crystallization. In binary mixtures, low-molecular-weight polyacrylic acid and polyethylene glycol affect synergistically, and such mixtures can be used for selectively influencing the formation of calcium carbonate polymorphs.

Influence of relative humidity on the carbonation of calcium hydroxide nanoparticles and the formation of calcium carbonate polymorphs

A consolidating product based on nanoparticles of slaked lime (Ca(OH) 2) dispersed in isopropyl alcohol was exposed under different relative humidities (RH), 33%, 54%, 75% and 90% during 7, 14, 21 and 28 days. The characterization of the calcium hydroxide nanoparticles and the formed calcium carbonate polymorphs have been performed by Micro Raman spectroscopy, Transmission Electron Microscopy (TEM), Environmental Scanning Electron Microscopy (ESEM) with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). Precipitation and transformation of calcium carbonate polymorphs strongly depend on the relative humidity (RH). Higher RH (75%–90% RH) gives rise to amorphous calcium carbonate and monohydrocalcite, calcite, aragonite and vaterite, faster carbonation and larger particles sizes with higher crystallinity compared to lower RH (33%–54% RH) that gives rise mainly to portlandite and vaterite, slower carbonation and smaller particle sizes with lower crystallinity.

Synthesis and characterization of calcite and aragonite in polyol liquids: Control over structure and morphology

An innovative precipitation process, achieved through the thermal decomposition of urea in polyols containing hydrated calcium salts, was used to prepare calcite and aragonite at elevated temperatures (120-180 degrees C). The effect of various experimental conditions, such as the media of different polyols (ethylene glycol, EG; diethylene glycol, DEG; and tetraethylene glycol, TEG), the temperature, the reaction time, and the addition of magnesium salts, on the structure, size, and morphology of the obtained solids is described. It was found that the formation of calcium carbonate polymorphs, i.e., calcite or aragonite, their morphology and their size was predominantly influenced by the type of polyols used, and by the diverse growing mechanisms occurring in the different polyol systems. Structurally and morphologically different calcite precipitates were formed in the DEG and TEG solvents via classical crystallization processes, while colloidal and nanostructured aragonite particles were assembled in the EG through a recently reaffirmed mechanism based on the role of nanoscale aggregation processes in the formation of carbonate solids. This study highlights the importance of the presence and concentration of magnesium ions in the inhibition of the crystal growth of nanosized aragonite, and in the stabilization of amorphous calcium carbonate (ACC) precipitates in polyol solutions.

Control of calcium carbonate polymorphism and morphology through biomimetic mineralization by means of nanotechnology.

In vitro biomimetic mineralization by means of nanotechnology allows the formation of calcium carbonate polymorphs at low temperatures (<25 degrees C) under a CO(2) atmosphere of 500-1500 ppm. A two-dimensional zinc-ion ordered array (zinc array), which acts as an active-site mimic of carbonic anhydrase, has been prepared by immersing the self-organized monolayer of 3-(2-imidazolin-1-y)propyltriethosilane on mica (ImSi substrate) into aqueous zinc solution. The zinc array mounted on the ImSi substrate catalyzed the conversion from CO(2) to HCO(3) (-), and accelerated the formation of calcium carbonate. In situ X-ray diffraction data of the formed calcium carbonate on the poly(L-aspartate)-coated chitin substrate (pAsp substrate), with calcium ion-recognition sites, demonstrated that the interaction between the zinc array and pAsp substrates formed both vaterite and calcite at low temperature (15 degrees C) and mainly vaterite at 25 degrees C; this interaction also controlled the morphology of calcium carbonate formed on pAsp substrate.

Factors controlling the transformation of natural ikaite from Shiowakka, Japan.

Ikaite (CaCO3·6H2O) transforms to calcite, aragonaite and/or vaterite, which are the polymorphs of calcium carbonate, at normal temperature and pressure. The presence of water promotes the transformation of natural ikaite to calcite in a room but the presence of magnesium ion in a solution reduces the transformation rate. The formation of calcium carbonate polymorphs through the transformation is influenced by temperature and magnesium ion concentration in a solution which contacts with ikaite, being analogous to those on the formation of calcium carbonate polymorphs from calcium bicarbonate solution. Rapid transformation of ikaite is favorable to the formation of vaterite, a metastable phase.