Ultrasonic-assisted eggshell extract-mediated polymorphic transformation of calcium carbonate

This study aimed to evaluate the combined effects of eggshell extract and ultrasonic irradiation on the polymorphic transformation of calcium carbonate (CaCO₃). In this context, XRD, Raman spectroscopy, SEM, AFM, TGA-FTIR, BET, and zeta potential analysis were used to identify and characterize the different polymorphs of CaCO₃ obtained in the absence and presence of eggshell extract in the media with and without ultrasonic irradiation. The morphology and polymorphic nature of the CaCO₃ crystals were observed to change, which indicated that the eggshell extract and ultrasonication influenced the structure and crystallization of CaCO₃. The structural analysis results indicated that the addition of eggshell extract to the media resulted in the full transformation of calcite to the vaterite polymorph. The results also showed that ultrasonic irradiation had a more significant influence on the BET specific surface area of the crystals compared to the eggshell extract media. Furthermore, a Box–Behnken design with response surface methodology was employed to determine the optimal operating conditions for CaCO₃ crystallization. The effects of stirring rate, extract concentration, and ultrasonic power on the BET surface area were investigated. The results show that the data sufficiently fit the second-order polynomial model. Understanding the eggshell extract-mediated polymorphic transformation with ultrasonic irradiation obtained in this study makes it possible to control the polymorphic formation and modify the product characteristics.     

Ultrasonic-assisted production of precipitated calcium carbonate particles from desulfurization gypsum

This study aimed to investigate the effect of ultrasonic application on the production of precipitated calcium carbonate (PCC) particles from desulfurization gypsum via direct mineral carbonation method using conventional and venturi tube reactors in the presence of different alkali sources (NaOH, KOH and NH₄OH). The venturi tube was designed to determine the effect of ultrasonication on PCC production. Ultrasonic application was performed three times (before, during, and after PCC production) to evaluate its exact effect on the properties of the PCC particles. Scanning electron microscope (SEM), X-ray diffraction (XRD), Atomic force microscope (AFM), specific surface area (SSA), Fourier transform infrared spectrometry (FTIR), and particle size analyses were performed. Results revealed the strong influence of the reactor types on the nucleation rate of PCC particles. The presence of Na⁺ or K⁺ ions in the production resulted in producing PCC particles containing only calcite crystals, while a mixture of vaterite and calcite crystals was observed if NH₄⁺ ions were present. The use of ultrasonic power during PCC production resulted in producing cubic calcite rather than vaterite crystals in the presence of all ions. It was determined that ultrasonic power should be conducted in the venturi tube before PCC production to obtain PCC particles with superior properties (uniform particle size, nanosized crystals, and high SSA value). The resulting PCC particles in this study can be suitably used in paint, paper, and plastic industries according to the ASTM standards.     

Effect of amplitude and frequency of ultrasonic irradiation on morphological characteristics control of calcium carbonate

We have previously reported on the morphological control of calcium carbonate by changing synthetic conditions such as temperature, pH and degree of supersaturation in liquid reaction. The present study reports the effect of amplitude and frequency of ultrasonic irradiation on the particle size of calcium carbonate using a horn type ultrasonic apparatus at two different frequencies. The calcium carbonate precipitated by mechanical stirring had a particle size of about 20 μm. By contrast, the particle size of vaterite formed under ultrasonic irradiation was about 2 μm, with a specific surface area of 25–30 m²/g. The major polymorph of calcium carbonate formed by ultrasonic irradiation was vaterite with some calcite present. For 40 kHz ultrasonic irradiation, the specific surface area of the calcium carbonate increased with increasing amplitude. The particle size of vaterite formed at this frequency was about 2 μm, and its distribution was sharper than that obtained at 20 kHz. The mode diameter of the synthesized vaterite was found to decrease with increasing amplitude at 40 kHz.     

碳酸钙在溶液中的演化机理

以EDTA作为添加剂,在CaCl₂/NaCO₃混合液中采用共沉淀法制备了碳酸钙,并探讨它在母液中的演化机理. 热力学和动力学计 算表明虽然形成无定形碳酸钙(ACC)的驱动力小于方解石和球霰石,但在共沉淀反应的初始阶段ACC的形核速率高于方解石和球霰石. 随着陈化时间的延长,最新生成的碳酸钙成为球霰石和方解石异相形核的活性点. 通过SEM发现ACC和球霰石在母液中通过溶解-再结晶机理转化成方解石. 此外,EDTA添加剂不仅提高了ACC和球霰石的稳定性,而且有助于碳酸钙在母液中陈化7天后转化成长棒状、菱形的方解石晶体. 如果将碳酸钙放置在空气介质中,ACC和球霰石也可以通过溶解-再结晶反应转化成方解石,但其转化速率低于溶液介质.     

Why to synthesize vaterite polymorph of calcium carbonate on the cellulose matrix via sonochemistry process?

Vaterite is an important biomedical material due to its features such as high specific surface area, high solubility, high dispersion, and small specific gravity. The purposes of this article were to explore the growth mechanism of vaterite on the cellulose matrix via sonochmistry process. In the work reported herein, the influences of experimental parameters on the polymorph of calcium carbonate were investigated in detail. The calcium carbonate crystals on the cellulose matrix were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Experimental results revealed that all the reactants, solvent, and synthesis method played an important role in the polymorph of calcium carbonate. The pure phase of vaterite polymorph was obtained using Na₂CO₃ as reactant in ethylene glycol on the cellulose matrix via sonochmistry process. Based on the experimental results, one can conclude that the synthesis of vaterite polymorph is a system process.     

A preliminary assessment of microstructural and compositional characteristics of two variants of precarbonated and postcarbonated concrete mixes

The hydration, precarbonation, and postcarbonation microstructural and compositional attributes of 2 variants of concrete were studied using scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction techniques. Results obtained showed presence of large number of diffraction peaks indicative of SiO₂ as major phase. Higher pH, alkalinity, and absence of effects of carbonation were suggested from the presence of portlandite peaks. Evidence of effect of carbonation was studied through the analysis of the experimental diffraction peaks obtained postexposure to accelerated carbonation in a controlled environment. Presence of all the 3 polymorphs of calcium carbonate (CaCO₃) such as aragonite, vaterite, and calcite depending upon the moisture content and the material constituting the concrete sample were envisaged signifying carbonation. Precipitation of these CaCO₃ crystals was responsible for depletion of CH as well as calcium–silicate–hydrate, ettringite with the progress of carbonation as suggested by their absence in the X‐ray diffraction diffractograms of the carbonated samples. The crystal structure of the newly formed minerals in both the variants of concrete sample was highly controlled by the stages of carbonation, with development of amorphous CaCO₃ (amalgamated with that of calcium hydrates) in early stages of carbonation as well as fully developed rhombohedral CaCO₃ crystals in later stages.     

Compare study CaCO3 crystals on the cellulose substrate by microwave-assisted method and ultrasound agitation method

The purposes of this article were to investigate the influences of synthesis strategy on the CaCO₃ crystals on the cellulose substrate. In this study, CaCO₃ crystals were synthesized using cellulose as matrix by the microwave-assisted method and ultrasound agitation method, respectively. The CaCO₃ crystals on the cellulose substrate were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Experimental results demonstrated that the synthesis strategy had a dramatically influences on the phase, microstructure, morphology, thermal stability, and biological activity of the CaCO₃ crystals. The pure phase of vaterite spheres with the diameter of about 320–600 nm were obtained by ultrasound agitation method, meanwhile, the mixed phases of calcite and vaterite with the diameter of about 0.82–1.24 μm were observed by microwave-assisted method. In view of experimental results, one can conclude that the ultrasound agitation method do more favors to the synthesis of CaCO₃ crystals with uniform morphology and size, compared with microwave-assisted method. Furthermore, cytotoxicity experiments indicated that the CaCO₃ crystals on the cellulose substrate had good biocompatibility and could be a candidate for the biomedical applications.     

Group Theoretical Analysis of the v 1 (CO 3 2-) Vibration in Crystalline Calcium Carbonate

A group theoretical analysis, based on the correlation method, is presented for the symmetric stretch vibration of the carbonate ion in three crystalline forms of calcium carbonate: calcite, aragonite and vaterite. Numbers of Raman and infrared active components are calculated and compared with experimental data, including those from a recent Raman study of vaterite. It is shown that the splitting observed for v _l in vaterite is compatible with two of the proposed crystal structures for this compound.     

Bio-vaterite formation by glycoproteins from freshwater pearls

A 48 kDa acidic and putative calcium-binding glycoprotein was isolated from pearls of the freshwater mussel Hyriopsis cumingii. This protein was compared with a related 46 kDa polypeptide, obtained from the nacreous shell of the same species. Separation by two-dimensional gel electrophoresis revealed that the difference in molecular weight is due to the higher extent of glycosylation of the 48 kDa protein existing in pearls. Evidence is presented that the sugar moieties of the protein contribute to crystal growth, starting with the nucleation step. In in vitro precipitation experiments, the 48 kDa glycoprotein of pearls directed the formation of round-shaped vaterite crystals while the 46 kDa glycoprotein of shells promoted formation of small irregular calcite particles. Furthermore, both proteins, 48 kDa/46 kDa, comprised carbonic anhydrase activity that has been implicated in CaCO₃ formation. Thus, a function of the isolated glycoproteins in biomineralization is proposed together with the mechanism by which they can stabilize different calcium carbonate polymorphs.     

PAA-assisted synthesis of CaCO3 microcrystals and affecting factors under microwave irradiation

In the present paper, we described a polyacrylic acid (PAA)-assisted microwave irradiation route for synthesis of Calcium carbonate (CaCO₃) microcrystals. CaCl₂·2H₂O and NaHCO₃ were used as the starting reactants. Researches showed that the presence of PAA could strongly affect the phase and morphology of CaCO₃ crystals. X-ray powder diffraction (XRD) analyses showed that the product prepared from the system with/without PAA corresponded to Vaterite/Calcite, respectively. Scanning electron microscopy (SEM) observations showed that the hierarchical CaCO₃ microcrystals were obtained in the presence of PAA. Some factors influencing the morphology of the as-synthesized CaCO₃ crystals were systematically investigated.     

Synthesis and characterization of polyester bionanocomposite membrane with ultrasonic irradiation process for gas permeation and antibacterial activity

Optically active bionanocomposite membranes composed of polyester (PE) and cellulose/silica bionanocomposite (BNCs) prepared with simple, green and inexpensive ultrasonic irradiation process. It is a novel method to enhance the gas separation performance. The novel optically active diol containing functional trifluoromethyl groups was prepared in four steps reaction and it was fully characterized by different techniques. Commercially available silica nanoparticles were modified with biodegradable nanocellulose through ultrasonic irradiation technique. Transmission electron microscopy (TEM) analyses showed that the cellulose/silica composites were well dispersed in the polymer matrix on a nanometer scale. The mechanical properties nanocomposite films were improved by the addition of cellulose/silica. Thermo gravimetric analysis (TGA) data indicated an increase thermal stability of the PE/BNCs in compared to the pure polymer. The results obtained from gas permeation experiments showed that adding cellulose/silica to the PE membrane structure increased the permeability of the membranes. The increase in the permeability of the gases was as follows: P_CH4 (38%) <P_N2 (58%) <P_CO2 (88%) <P_O2 (98%) Adding silica nanoparticles into the PE matrix, improved the separation performance of carbon dioxide/methane and carbon dioxide/nitrogen gases. Increasing the cellulose/silica mass fraction in the membrane increased the diffusion coefficients of gases considered in the current study. Further, antimicrobial test against pathogenic bacteria was carried out.     

Biomimetic nucleation and growth of hydrophobic vaterite nanoparticles with oleic acid in a methanol solution

Hydrophobic vaterite nanoparticles were prepared via crystallization of CaCO₃ with oleic acid in methanol by mimicking the process of biomineralization. The molar ratio of oleic acid to calcium ion was varied from 0.1 to 0.5. By changing the concentration of the oleic acid, CaCO₃ particles with different shapes and polymorphism were obtained. High concentration of the oleic acid gave stable vaterite crystals, the polymorph of which did not change when the composite was kept in water for more than one week. Fourier transform infrared spectroscopy (FT-IR) and TGA analysis of the obtained product indicated that the oleic acid was bound to the crystalline CaCO₃. The contact angle of the modified vaterite reached 122°. We have succeeded in crystallization of hydrophobic CaCO₃ nanoparticles in situ.     

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm³, had a specific surface area of 65 m²/g and a composition of CaCO₃•0.5H₂O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.     

Precipitation of calcium carbonate by ultrasonic irradiation

Supersaturated solution of calcium carbonate ([Ca²⁺]=1.2 mmol/L, [HCO₃⁻]=3.2 mmol/L, pH=8.8, T=30±0.5 °C), a scale forming component, was irradiated by an ultrasonic homogenizer (24 kHz, 15–250 W/cm²) to study the factors that affect its precipitation rate. The factors of (1) depth of horn immersion, (2) ultrasonic intensity and horn tip size and (3) cavitation, which can affect the precipitation rate were investigated in this study. Ultrasonic irradiation was observed to accelerate the precipitation of calcium carbonate and it was found that there exists an optimum range of horn immersion depth for maximizing the precipitation rate. The experimental data also established that the precipitation rate was proportional to ultrasonic intensity and diameter of horn tip. These findings were correlated to the effects of physical mixing, that arises due to ultrasonic irradiation. However, the effect of cavitation in accelerating the precipitation rate was found to be small. Thus it is forwarded that the physical mixing effect, especially macrostreaming is the main factor that accelerates the precipitation rate of calcium carbonate during ultrasonic treatment. Further, neither the morphology nor the size of the calcium carbonate crystals formed were found to be affected by the ultrasonic irradiation.     

Combination of FTIR and SEM for Identifying Freshwater-Cultured Pearls from Different Quality

The freshwater-cultured pearl (Chamberlainia hainesiana species) is an organic gemstone mainly composed of calcium carbonate mineral including calcite, aragonite and vaterite phases. Generally, the quality of freshwater-cultured pearl is based on its luster. The high luster pearl is full of the aragonite phase without vaterite phase. On the other hand, the low luster pearl consists of aragonite and vaterite phases. These data could be proved by the Fourier Transform Infrared (FTIR) spectroscopy combined with the scanning electron microscopy (SEM). As the results, the high luster pearl similarly shows the FTIR spectrum of aragonite phase, and also, it shows the hexagonal shape of aragonite for the SEM image. On the other hand, the FTIR spectrum of low luster pearl has been pointed to the mixture component among aragonite and vaterite phases, and based on the SEM image; the irregular form is also interpreted to the mixture of aragonite and vaterite phases. This research concludes that the quality of freshwater-cultured pearls can be identified by the combination data of FTIR spectra and SEM images. These techniques are suitable for applied gemology.     

Raman spectroscopy of synthetic,geological and biological vaterite: a Raman spectroscopic study

Raman spectroscopy was used to study vaterite samples of biological, geological and synthetic origin. The Raman band positions and the full width at half‐maximum (FWHM) of the lattice modes and the internal modes of the carbonate ion of all specimens show no significant differences between vaterites of different origin. With increasing Mg concentrations, synthetic vaterite samples show increasing FWHM in the region of the lattice modes and the three ν₁ bands, whereas no change in luminescence was detected. In contrast, in situ measurements of vaterite areas in freshwater cultured pearls (FWCPs) by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) together with the Raman spectra obtained at the same points show that the luminescence intensity in biological samples is affected by the magnesium content. The Raman spectroscopic features of vaterite and parisite‐(Ce) are compared, and their similarities suggest that the structure of vaterite contains at least three crystallographically independent carbonate groups and similar carbonate group layers. A band at 263 cm⁻¹ is observed for the first time in this study, whereas it could be demonstrated that bands previously reported at 130 and 190 cm⁻¹ do not belong to vaterite. Copyright © 2009 John Wiley & Sons, Ltd.     

The Nanosecond Laser Flash Photolysis (LFP) Transient Spectra of Aqueous CCl4 Solution

Abstract

The Raman spectrum of polycrystalline vaterite is presented and compared to spectra of calcite and aragonite, the other two common CaCO₃ polymorphs; Raman spectroscopy easily distinguishes between these three polymorphs. An important feature of the Raman spectrum of vaterite is splitting of both the ν₁ and ν₄ peaks. The splitting of the ν1 peak implies two distinct site symmetries for the CO₃ ^?2 groups. A definitive crystal structure determination of vaterite is not yet available, but none of the three proposed structures for vaterite show such a feature.     

Ultrasonic assisted arsenate adsorption on solvothermally synthesized calcite modified by goethite, α-MnO2 and goethite/α-MnO2

A highly porous calcium carbonate (calcite; sorbent 1) was used as a support for modification with α-FeOOH (calcite/goethite; sorbent 2), α-MnO₂ (calcite/α-MnO₂; sorbent 3) and α-FeOOH/α-MnO₂ (calcite/goethite/α-MnO₂; sorbent 4) in order to obtain a cheap hybrid materials for simple and effective arsenate removal from aqueous solutions. The adsorption ability of synthesized adsorbents was studied as a function of functionalization methods, pH, contact time, temperature and ultrasonic treatment. Comparison of the adsorptive effectiveness of synthesized adsorbents for arsenate removal, under ultrasound treatment and classical stirring method, has shown better performance of the former one reaching maximum adsorption capacities of 1.73, 21.00, 10.36 and 41.94 mg g⁻¹, for sorbents 1–4, respectively. Visual MINTEQ equilibrium speciation modeling was used for prediction of pH and interfering ion influences on arsenate adsorption.     

Spectroscopic study of phase transitions in dolomite mineral

The process and the formation of new minerals upon heating carbonate rocks containing clay minerals together with dolomite are determined by thermal analysis, X‐ray diffraction (XRD), infrared and Raman spectroscopy. The dolomite–calcite–calcium oxide phase transition sequences were followed up to 947 °C in a naturally occurring dolomite sample. The spectral variations of the internal modes of the carbonate trigonal (ν₁, ν₂, ν₃ and ν₄) were used to probe the structural phase transitions. A new Raman mode emerged at 1090 cm⁻¹ in the ν₁ mode region, and infrared modes emerged at 713, 874, and 1420 cm⁻¹ in the ν₄, ν₂ and ν₃ regions at 750 °C, indicating the onset of the dolomite phase. The calcium oxide phase, (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 °C, was also characterized by the appearance of the infrared mode around 450 cm⁻¹. The minerals, which were formed upon heating the dolomite, were calcite, calcium oxide and diopside. Copyright © 2007 John Wiley & Sons, Ltd.     

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd₂O₃ in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn₃(PO₄)₂ · 4H₂O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd₂O₃ reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.