Reaction Of CaCO3 Research Articles

Use of carbonated recycled cement paste powder as a new supplementary cementitious material: A critical review

This paper focused on reviewing and decoupling analysis the effects of carbonated recycled cement paste powder (RCPP) as a new supplementary cementitious material (SCM) on the mechanical properties, rheology, durability, and carbon sequestration capacity of cement-based materials according to the results in previous studies. The results suggest that that carbonated RCPP serves as an excellent SCM in enhancing the compressive strength of cement paste, mainly through increasing the filler effect and the chemical reaction of CaCO3 with C3A. Extensive cement replacement with carbonated RCPP does not significantly reduce strength. However, when considering rheology and durability, particularly concerning steel corrosion, a 20-30% cement replacement results in significant performance degradation due to the water absorption and the pozzolanic effect of silica gel, respectively. Furthermore, an increase in the carbonation products content (carbonation degree) can enhance the strength, but adversely affect rheological properties and corrosion resistance of reinforcement of cement-based material. Addressing this contradiction to synergistically enhance the various properties of cement-based material containing carbonated RCPP is the focus of future efforts.

Oxygen isotope fractionation during amorphous to crystalline calcium carbonate transformation at varying relative humidity and temperature

Crystalline calcium carbonate isotope compositions have been widely used to reconstruct past environments. However, if their isotopic compositions are modified because of crystallization from an amorphous precursor, their reliability as paleo-geochemical proxies can be compromised. This study explored the changes in the oxygen isotope compositions during the transformation of amorphous calcium carbonate (ACC) into crystalline carbonate under different conditions of relative humidity (RH of 33–95 %), temperature (T of 5 °C and 20 °C) and in the presence/absence of atmospheric CO2. The data showed that at low RH and T (e.g., RH ≤ 45 % and 5 °C) when a complete ACC-crystalline carbonate transformation did not take place then the original ACC δ18O values (δ18OCaCO3 = −15.9 ± 1.0 ‰, VPDB) were preserved throughout the experimental runtime (up to 144 days). In contrast, in fully crystallized CaCO3 (e.g., at RH ≥ 60 %) the δ18OCaCO3 values increased rapidly over the first few days, followed by a slower and gradual increase. By the end of the experiments (i.e., after 103–144 days) the crystalline δ18OCaCO3 values ranged from −10.4 ‰ to −8.1 ‰ in the presence of atmospheric CO2 and from −12.6 ‰ to −9.5 ‰ in the CO2-free experiments. These changes in oxygen isotope compositions of the CaCO3 reaction products (calcite and/or vaterite) were mainly driven by exchange with H2O from the hydrated ACC i.e. the synthesis fluid. In CO2-present experiments, oxygen isotope fractionation factors between the CaCO3 reaction products and the synthesis fluid (18αc–w) approached or exceeded oxygen isotope equilibrium values. This could be explained by a decrease in the initially high pH of the aqueous fluid released from ACC dissolution during CO2 hydration/hydroxylation, which would have increased the oxygen isotope exchange kinetics between H2O and dissolved inorganic carbon (DIC). In some experiments, the hydration/hydroxylation of 18O-enriched CO2, due to isotopic salt-effects, might have also resulted in 18O-enriched calcium carbonates and calculated fractionation factors that exceeded equilibrium values. In the CO2-free experiments, isotopic equilibrium between the crystalline phase and the synthesis fluid was not reached. This oxygen isotope disequilibrium suggests that without the pH lowering effect of the hydroxylation/hydration of CO2, the CO32− released during ACC/calcite dissolution-reprecipitation may have not isotopically equilibrated with the high pH synthesis fluid due to the long equilibration times required to reach isotope equilibrium at high pH values, leading to the self-buffering of δ18OCaCO3 values. The results suggest that the oxygen isotopic compositions of natural carbonates formed from ACC transformation in air and at low water/solid ratio (e.g., biominerals or carbonates formed in caves) are complex and cannot be used as simple proxies if the reaction kinetics (RH/CO2/T) and H2O sources are not known and quantified.

High-performance and low-cost electrochemical reactor for limestone decarbonation applied to clinker production – A validation at laboratory scale

Limestone decarbonation to obtain CaO (calcium oxide) and produce cement is an industrial activity with enormous CO2 emissions (CaCO3(s)→CaO(s)+CO2(g)), due to the intrinsic calcination reaction of CaCO3 (calcium carbonate), in addition to the use of fossil fuels. One of the most recent ideas to reduce CO2 emissions in this process has been the electrochemical decarbonation of limestone where Ca(OH)2 (calcium hydroxide) is obtained as an intermediate product that is then used as CaO precursor in clinker synthesis.This study shows the design of a low-cost electrochemical reactor and the optimization of the parameters to produce Ca(OH)2 with high purity and yield from the decarbonation processes of pure CaCO3 and limestone used in the cement industry. In addition, the remaining limestone sludge and electrolytic solutions were analyzed, and it was found that the sludge can be used as a correction material in clinker preparation, and it is also possible to reuse the electrolytic solution twice. Finally, the main finding is the proposal of a new clinker synthesis, which results in a cement with comparable characteristics to those of ordinary Portland cement, using Ca(OH)2 obtained from the electrochemical decarbonation of CaCO3, achieving a reduction in CO2 emissions of approximately 90% compared to the conventional method.

Metabolic flux analysis of coenzyme Q10 synthesized by Rhodobacter sphaeroides under the influence of different pH regulators

Coenzyme Q10 (CoQ10) is crucial for human beings, especially in the fields of biology and medicine. The aim of this experiment was to investigate the conditions for increasing CoQ10 production. At present, microbial fermentation is the main production method of CoQ10, and the production process of microbial CoQ10 metabolism control fermentation is very critical. Metabolic flux is one of the most important determinants of cell physiology in metabolic engineering. Metabolic flux analysis (MFA) is used to estimate the intracellular flux in metabolic networks. In this experiment, Rhodobacter sphaeroides was used as the research object to analyze the effects of aqueous ammonia (NH3·H2O) and calcium carbonate (CaCO3) on the metabolic flux of CoQ10. When CaCO3 was used to adjust the pH, the yield of CoQ10 was 274.43 mg·L−1 (8.71 mg·g−1 DCW), which was higher than that of NH3·H2O adjustment. The results indicated that when CaCO3 was used to adjust pH, more glucose-6-phosphate (G6P) entered the pentose phosphate (HMP) pathway and produced more NADPH, which enhanced the synthesis of CoQ10. At the chorismic acid node, more metabolic fluxes were involved in the synthesis of p-hydroxybenzoic acid (pHBA; the synthetic precursor of CoQ10), enhancing the anabolic flow of CoQ10. In addition, Ca2+ produced by the reaction of CaCO3 with organic acids promotes the synthesis of CoQ10. In summary, the use of CaCO3 adjustment is more favorable for the synthesis of CoQ10 by R. sphaeroides than NH3·H2O adjustment. The migration of metabolic flux caused by the perturbation of culture conditions was analyzed to compare the changes in the distribution of intracellular metabolic fluxes for the synthesis of CoQ10. Thus, the main nodes of the metabolic network were identified as G6P and chorismic acid. This provides a theoretical basis for the modification of genes related to the CoQ10 synthesis pathway.

A viable mechanism to form boron-bearing diamonds in deep Earth

Boron is considered extremely depleted inside Earth’s mantle. It is therefore a great challenge to elucidate the prevalence of boron impurity seen in sublithospheric diamonds, especially in identifying the boron source and the mechanism for its incorporation into these enigmatic diamonds. Here, we unveil a pathway for the crystallization of boron-bearing diamonds via redox reactions of carbonates and borides at pressure–temperature conditions relevant to the Earth’s lower mantle. We present computational results along with pertinent experimental evidence for a genesis of boron-bearing diamonds via the redox reaction of CaCO3 and FeB at 22.5 GPa and 2100 K, corresponding to the geological conditions at the top of the lower mantle. The present findings offer a viable mechanism for the formation of boron-bearing diamonds deep inside the Earth’s mantle.

Early release of H2O during subduction of carbonated ultramafic lithologies

To investigate the effect of carbon-bearing phases on the release of fluids in subducted serpentinites, we performed high-pressure multi-anvil experiments on representative ophicarbonate assemblages over a pressure range from 2.5 GPa to 5 GPa and from 450 °C to 900 °C, across the antigorite-out reaction. Parallel experiments were performed on carbonate-free serpentinites. In all experiments, we monitored and/or controlled the oxygen fugacity. The addition of 20 wt. % CaCO3 to a serpentinite assemblage at 2.5 GPa is found to decrease the onset of the serpentine dehydration by over 100 °C, in comparison to carbonate-free assemblages. Similarly, the final disappearance of serpentine is also affected by the presence of CaCO3. For a bulk CaCO3 content of 20 wt. %, this causes a decrease in maximum stability of antigorite by 50 °C. For a bulk CaCO3 content exceeding 25 wt. %, this difference can be as high as 100 °C in warm and 150 °C in cold subduction zones, causing antigorite to be completely dehydrated at 500 °C. This results from the reaction of CaCO3 with serpentine to form clinopyroxene and Mg-rich carbonates. This reaction, however, causes no discernible decrease in the proportion of carbonate, indicating that the amount of released carbon is insignificant. Whilst CaCO3, therefore, influences serpentine stability, there is no significant effect of hydrous phases on the carbonate stability. On the other hand, a MgCO3-bearing system shows no significant effects on the serpentinite stability field. Further experiments and oxygen fugacity calculations indicate that graphite is not stable in typical magnetite-bearing serpentinites. The reduction of carbonates to graphite would require oxygen fugacities that are 1–2 log units below those of magnetite-bearing serpentinites. This confirms earlier studies and indicates that reduction of carbonates can only occur through the infiltration of external H2-rich fluids.

Kinetic investigation and numerical modelling of CaCO3/Al2O3 reactor for high-temperature thermal energy storage application

This study conducts kinetic analyses of the carbonation reaction of CaCO3 (doped with Al2O3) as well as parametric analyses of the performance of a thermochemical reactor, which can act as a thermal battery. Kinetic measurements of CO2 release and absorption were carried out using thermogravimetric analysis (TGA) at 815, 830 and 845 °C on a CaCO3/Al2O3 sample that had been previously cycled over 500 times. The rapid reaction kinetics revealed that the Avrami nucleation growth model with exponent 3 fits well to explain the carbonation reaction. The numerical study considered a cylindrical reactor with a height and diameter of 100 mm. According to numerical analysis, at an applied CO2 pressure of 1 bar, increasing the thermal conductivity of the reactor bed from 1.33 to 5 W/m.K increases the rate of carbonation reaction by 74%. When the applied CO2 pressure is increased from 1 to 2 bar, the performance of the reactor bed with thermal conductivity of 1.33 W/m.K improves by 42%; however, when the applied CO2 pressure is increased from 2 to 3 bar, the performance improves by only 18%. Additionally, when the boundary temperature of the reactor was lowered by 30 °C, performance was enhanced by 43% at an applied CO2 pressure of 1 bar. This study also examined the effect of using a graphite fin as a heat extraction system. The graphite fin allowed for more rapid heat extraction and increased the carbonation reaction by 44% in the reactor bed with poor thermal conductivity (1.33 W/m.K) but had no effect in the reactor with modest thermal conductivity of (5 W/m.K) due to its ability to already transfer heat effectively to the reactor shell.

CaCO3 -Encapuslated Microspheres for Enhanced Transhepatic Arterial Embolization Treatment of Hepatocellular Carcinoma.

Transcatheter arterial embolization (TAE) is an extensively applied treatment method for hepatocellular carcinoma (HCC). However, the worsened tumor microenvironment (TME, e.g., reduced pH post-TAE) may result in unsatisfactory therapeutic outcome. Herein, a new kind of embolic agent, calcium carbonate encapsulated alginate microspheres (CaCO3 -ALG MSs) are synthesized. Such CaCO3 -ALG MSs are able to neutralize the tumor pH owing to the reaction of CaCO3 with protons, which would not affect the overall morphology of microspheres after decomposition of CaCO3 . TAE treatment with CaCO3 -ALG MSs is then conducted in an orthotopic rat liver cancer model. 18 F-Fluorodeoxyglucose micropositron emission tomography/computed tomography imaging is conducted post-TAE and discovered that intra-arterial injection of CaCO3 -ALG MSs shows obvious enhanced therapeutic outcome compared to the same treatment with bare ALG MSs or the clinically used lipiodol. Further studies including analysis of immune cells in tumors, cytokine assays, and bioinformatics analysis all verify the reverse of immunosuppressive TME toward a more immunosupportive one after TAE with CaCO3 -ALG MSs. The research not only presents a new CaCO3 -containing embolic agent for enhanced TAE treatment of HCC but also highlights a clinically meaningful approach to improve cancer treatment via tumor pH neutralization.

Heterogeneous Reaction of CaCO3 With NO2 at Different Relative Humidities: Kinetics, Mechanisms, and Impacts on Aerosol Hygroscopicity

AbstractHeterogeneous reaction of NO2 with CaCO3, an abundant and reactive component in mineral dust aerosol, was investigated in this work at different relative humidifies (RH, up to 80%), using a fixed‐bed reactor. Ion chromatograph and a vapor sorption analyzer were employed to measure changes in particulate nitrate and water with reaction time (up to 24 h). When NO2 concentration was ∼10 ppmv (∼2.5 × 1014 molecule cm−3), CaCO3 showed very low reactivity toward NO2 at <1% RH, and γ(NO2) was estimated to be <2 × 10−8; consequently, no significant change in hygroscopicity of CaCO3 particles was observed after reaction with NO2 for 24 h at <1% RH, as the amount of nitrate formed was very limited. Heterogeneous reactivity was significantly enhanced at elevated RH (20%–80%), and during the reaction CaCO3 was covered with a deliquesced layer resulting from water uptake by formed nitrate; in addition, the average γ(NO2) was determined to be (1.21 ± 0.45) × 10−7, independent of RH (20%–80%) and reaction time (3–24 h). After reaction with 10 ppmv NO2 for 24 h at elevated RH (20%–80%), the mass of particulate water associated with reacted CaCO3 at 90% RH was equal to ∼45% of the mass of unreacted CaCO3, suggesting that heterogeneous reaction of CaCO3 with NO2 at 20%–80% RH could substantially increase its hygroscopicity. Overall, our laboratory study suggested that heterogeneous reaction with NO2 may significantly impact composition and hygroscopicity of CaCO3 particles.

Heterogeneous reaction of CaCO3 with NO2 at different relative humidities: kinetics, mechanisms, and impacts on aerosol hygroscopicity

Heterogeneous reaction of CaCO3 with NO2 at different relative humidities: kinetics, mechanisms, and impacts on aerosol hygroscopicity

A Ca-Cu Chemical Loop Process for CO2 Capture in Steel Mills: System Performance Analysis

The conceptual design and modelling of the Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH) process for the conversion of blast furnace gas (BFG) into H2-rich stream and CO2-rich stream at a large scale is discussed in this work. High temperature reactors packed with CaO- and Cu-based materials are used to remove CO2 from the gaseous phase and simultaneously shifting the WGS equilibrium towards H2-rich products. The incorporation of a Cu/CuO chemical loop to such sorption process allows an efficient regeneration of the CO2 sorbent. In this case, the heat needed for the calcination of the CaCO3 is supplied in situ by the exothermic reduction of CuO to Cu with a gaseous fuel (e.g. CH4, CO or H2). The Cu-based solid is firstly converted to CuO(s) during the oxidation step with air and later reduced during the regeneration step, which involves the combination of the endothermic reaction of CaCO3(s) calcination and the exothermic gas-solid reduction of CuO(s) to Cu(s) using a gaseous fuel (typically BFG or natural gas producing a highly concentrated stream of CO2 and H2O(v)). In this paper, the three reaction stages of the CASOH process are modelled with a new 1-D reactor model that integrates state of the art kinetic information on the gas solid reactions, predicting the molar composition of the product gases (dry basis) at the outlet of the packed-bed reactor and maximum temperature achieved in each stage. The 1-D reactor modelling results confirm that process allows the conversion of up to 99% of the inlet CO to H2 at intermediate temperatures (about 650 °C), because of the efficient and continuous removal of CO2 from the gas phase. The high pressure (10 bar) during the Cu-oxidation step causes a very low leakage of CO2 (1.1 vol. %) due to the partial calcination of CaCO3, i.e. only 8 wt. % of the CaCO3 is calcined in this stage. Finally, the feed of BFG as reducing gas during the regeneration stage leads to a maximum temperature of 850 °C in the bed, which allows the complete calcination of the sorbent and gives as a result a CO2-rich stream ready for purification and subsequent use or storage.

Kinetic Study of CaCO3 Precipitation Accelerated by High Voltage Impulse

Objectives : Determination of reaction order (n) and rate constants (k) of the CaCO<sub>3</sub> scale formation reaction that was accelerated by the HVI (high voltage impulse) induction.Methods : HVI was inducted to the synthetic solution containing 2.5 mM of Ca<sup>2+</sup> ion at different temperatures of 25, 40, 60℃. The concentration of Ca<sup>2+</sup> ion has been monitored as voltages of the HVI increased from 0 to 5, 10, 15 kV. Reaction order and the rate constants of the CaCO<sub>3</sub> formation reaction were determined with the experimental dataset of Ca<sup>2+</sup> concentration vs. time plots.Results and Discussion : The CaCO<sub>3</sub> formation was determined to follow two-molecules 2<sup>nd</sup> order reaction. The reaction rate constant, k increased as temperature and the applied voltages of HVI increased. The rate constant, k at 25℃ and 15 kV of HVI was 8.2×10<sup>-3</sup> L/(mmol･hr), which was 2.7 times greater than the k of the control at 25℃, 3.0×10<sup>-3</sup> L/(mmol･hr).Conclusions : The reaction of CaCO<sub>3</sub> formation was accelerated by HVI as the applied voltages of HVI increased, indicating that the HVI could be used as an alternative desalting technology for scale control.

Thermodynamic evaluation and experimental investigation of CaO-assisted Fe-based chemical looping reforming process for syngas production

Many works have focused on the reactivity and valence transition of Fe-based oxygen carriers in chemical looping partial oxidation reforming process. However, the reforming performance and impacts of operating factors are unclear with the co-feeding of CaO being CO2 carrier to realize simultaneous CO2 capture and utilization. In this work, thermodynamic equilibrium calculation, reactivity test and material characterization are carried out to optimize the process characteristics. The impacts of feeding conditions (Fe/Al weight ratio, methane amount, Ca/Fe mole ratio and packing manner) on the reforming reactivity are obtained to reveal the interaction between CaO and Fe2O3. The gas product distribution indicates that the carbon deposition and oxidation degree is closely related to CH4 amount. The spatial configuration between CaCO3 and Fe2O3 reforming is essential to obtain the desirable reforming products. The difference of FeO existence on the theoretical and experimental phase components illustrates that reaction degree is affected by the reduction agent amount. By comparing the methane temperature-programmed reaction of CaCO3, Fe2O3 and their mixture, it is suggested that the existence of CaCO3 is beneficial for accelerating iron-based methane reforming. This study provides a way to improve reaction degree and optimize process characteristic for chemical looping reforming process.

Modeling and Investigating the Production of Carbon Dioxide Gas Using HSC Software in the Tile Industry

Background: The study of the production and emission of greenhouse gases, including CO2 in the atmosphere, is one of the most important environmental issues and concerns of the international community. This study was conducted to investigate the effect of temperature and furnace fuel concentration changes on CO2 and CO production.
 Methods: In this study, using HSC Chemistry 6 software, the existing reactions for fuels used in the furnace, including CaCO3, MgCO3, Fe2O3, and Fe3O4, were simulated. The concentrations of carbon dioxide and carbon monoxide produced at different temperatures were investigated.
 Results: In the CaCO3 reaction, the temperature has a direct effect on carbon dioxide production but no effect on carbon monoxide production. In the MgCO3 reaction, the temperature has little effect on the production of both, and for the rest of the reactions, the effect of temperature depends on the molar composition and reaction conditions.
 Conclusion: In general, the results show that temperature affects the production of carbon dioxide and monoxide, so the emission of these gases to the environment can be reduced by adjusting the temperature of the furnace reactors.

Calcium carbonate synthesis from waste concrete for carbon dioxide capture: From laboratory to pilot scale

This research article explains the synthesis and scale-up of calcium carbonate (CaCO3) from waste concrete as calcium-rich material by an inorganic carbonation process. The operating parameters include S/L ratio, HCl concentration, contact time, and extraction pH were investigated. The calcium hydroxide (Ca(OH)2) was synthesized by reaction between calcium chloride (CaCl2) and sodium hydroxide (NaOH), which induced the spontaneous reaction of CaCO3 without additional energy consumption. The productivity of CaCO3 was 1 kg/d in the laboratory scale experiment, and the CaCO3 productivity was scale-up to 20 kg/d through pilot scale process by same way as the laboratory scale. The approximately 4800 g of CaCO3 was produced and 2112 g of CO2 was captured per each cycle operation. Consequently, considered power consumption, the estimated amount of reduced CO2 was 465 g of CO2 in the pilot-scale reactor per cycle and produced CaCO3 with a purity of 99.0 %.

The Effect of Mechanochemical on The Formation of Calcium Titanate (CaTiO3) Prepared by High Energy Milling

Single-phase calcium titanate (CaTiO3) was successfully synthesized by mechanical milling and the solid-state reaction of CaCO3 and TiO2. The speed of high energy ball milling was 700 rpm with the ball and jar were made from stainless steel. The milling time and ball to powder ratio was 10 h and 50 h, respectively. After milling for 10 h, the mixed powder of CaCO3 and TiO2 experienced heavy milling, which indicated by the average particle size before and after milling was > 1 µm and 85.56 ± 35.62 nm, respectively. Furthermore, the XRD pattern of milled powder revealed the disappearance of CaCO3 peaks and a considerable reduction of TiO2 peaks after milling for 10 h. Moreover, the presence of CaTiO3 peaks in the milled powder was noticeably detected in the XRD pattern, showing the mechanical alloying of CaCO3 and TiO2 was occurred. The milled powder was calcined at 800, 900 and 1000°C for 2 h. The results showed the formation of a single phase of CaTiO3 after calcination at any temperatures. However, the samples indicated the presence of Fe2O3, which from the milling media. The presence of impurities after milling is inevitable due to friction between ball and jar. Further study is needed to obtain the optimum condition of mechanical milling to minimize the contamination.

Calcium phosphate powders synthesized from CaCO3 and CaO of natural origin using mechanical activation in different media combined with solid-state interaction.

The highly pure and crystalline calcium carbonate (CaCO3) and calcium oxide (CaO) with small amounts of As, Cd, Hg, and Pb were prepared by calcinating shells of a golden apple snail. Solid-state reaction and mechanical activation between the CaCO3 and CaO from calcined golden apple snail shells and dibasic calcium phosphate dihydrate (CaHPO4•2H2O, DCPD) were performed to develop calcium phosphate powders. The effects of the milling media used on the mechanical activation were examined. A solid-state reaction of manually mixed CaCO3 or CaO with DCPD powders at a temperature of 1100°C produced mostly β-tricalcium phosphate (β-TCP). Hydroxyapatite (HAp) with a small quantity of β-TCP could be produced from a mixed CaCO3+DCPD powder using dry and wet mechanical activations with distilled water, alcohol and acetone and from a mixed CaO+DCPD powder using dry mechanical activation combined with a solid-state reaction at a temperature of 1100°C. A phase change of milled powders to β-TCP was clearly observed from a wet mechanical activation of CaO+DCPD powder with distilled water or alcohol in a solid-state reaction. The thermal instability of HAp powders from a combined mechanical activation with solid-state reaction of CaCO3 or CaO and DCPD powders could result from two factors. The first is that the pollution was released from the balls and pot mill materials during the mechanical process. Another factor is a reduced level of calcium in the CaO+DCPD mixed powder due to a reaction between CaO and water or alcohol during mechanical milling.

Enhancement of desorption amount of carbon dioxide gas from monoethanolamine solution using ultrasound and calcium chloride

Ultrasound can desorb CO2 from dissolved CO2 gas [CO2(aq)] in a low-concentration monoethanolamine (MEA) solution (0.2 M) at a low temperature (25 °C). However, it is difficult to desorb CO2 using ultrasound at pH >8.2 because CO2 mainly exists as HCO3− and not as CO2(aq). We investigated the increment of the CO2 gas desorption ratio on the synthesis reaction of CaCO3 by the shift in the CO2 equilibrium in the direction of the increase of CO2(aq) by the decrease of pH from 8.2 with an increase in the H+ concentration in the MEA solution. Results indicated that a high Ca recovery ratio of 93.1% was observed by CaCl2 addition and ultrasound irradiation. Compared with the desorption ratio of CO2 gas using ultrasound irradiation without the addition of CaCl2, the CO2 gas desorption ratio increases from 2.2% to 9.8% using ultrasound with a low concentration of CaCl2 (Ca/MEA molar ratio 0.026).

Investigation on the stability, electronic, optical, and mechanical properties of novel calcium carbonate hydrates via first‐principles calculations

AbstractCalcium carbonate (CaCO3) is an inorganic compound which is widely used in industry, chemistry, construction, ocean acidification, and biomineralization due to its rich constituent on earth and excellent performance, in which calcium carbonate hydrates are important systems. In Zou et al's work (Science, 2019, 363, 396‐400), they found a novel calcium carbonate hemihydrate phase, but the structural stability, optical, and mechanical properties have not been studied. In this work, the stability, electronic, optical, and mechanical properties of novel calcium carbonate hydrates were investigated by using the first‐principles calculations using density functional theory. CaCO3·xH2O (x = 1/2, 1 and 6) are determined dynamically stable phases by phonon spectrum, but the Gibbs energy of reaction of CaCO3·1/2H2O is higher than other calcium carbonate hydrates. That is why CaCO3·1/2H2O is hard to synthesize in the experiments. In addition, the optical and mechanical properties of CaCO3·xH2O (x = 1/2, 1 and 6) are expounded in detail. It shows that the CaCO3·1/2H2O has the largest bulk modulus, shear modulus, and Young's modulus with the values 60.51 GPa, 36.56 GPa, and 91.28 GPa. This work will provide guidance for experiments and its applications, such as biomineralization, geology, and industrial processes.

Breyite inclusions in diamond: experimental evidence for possible dual origin

Abstract. Inclusions of breyite (previously known as walstromite-structured CaSiO3) in diamond are usually interpreted as retrogressed CaSiO3 perovskite trapped in the transition zone or the lower mantle. However, the thermodynamic stability field of breyite does not preclude its crystallization together with diamond under upper-mantle conditions (6–10 GPa). The possibility of breyite forming in subducted sedimentary material through the reaction CaCO3 + SiO2 = CaSiO3 + C + O2 was experimentally evaluated in the CaO–SiO2–C–O2 ± H2O system at 6–10 GPa, 900–1500 ∘C and oxygen fugacity 0.5–1.0 log units below the Fe–FeO (IW) buffer. One experimental series was conducted in the anhydrous subsystem and aimed at determining the melting temperature of the aragonite–coesite (or stishovite) assemblage. It was found that melting occurs at a lower temperature (∼1500 ∘C) than the decarbonation reaction, which indicates that breyite cannot be formed from aragonite and silica under anhydrous conditions and an oxygen fugacity above IW – 1. In the second experimental series, we investigated partial melting of an aragonite–coesite mixture under hydrous conditions at the same pressures and redox conditions. The melting temperature in the presence of water decreased strongly (to 900–1200 ∘C), and the melt had a hydrous silicate composition. The reduction of melt resulted in graphite crystallization in equilibrium with titanite-structured CaSi2O5 and breyite at ∼1000 ∘C. The maximum pressure of possible breyite formation is limited by the reaction CaSiO3 + SiO2 = CaSi2O5 at ∼8 GPa. Based on the experimental results, it is concluded that breyite inclusions found in natural diamond may be formed from an aragonite–coesite assemblage or carbonate melt at 6–8 GPa via reduction at high water activity.