413 research outputs found
Evaluation of the effects of sodium laurate on calcium carbonate precipitation: Characterization and optimization studies
No full textThe effects of using sodium laurate as an additive on the calcium carbonate precipitation process and on the product characteristics were investigated experimentally through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), particle size, and Brunauer, Emmett, and Teller (BET) analysis. The characterization results showed that the addition of sodium laurate to the crystallization media contributed to the formation of the vaterite form of calcium carbonate. The average particle size changed from 32 mu m to 14 mu m with increasing sodium laurate concentration. The SEM results suggested that the presence of sodium laurate had a strong influence on the calcium carbonate morphology and the crystals transformed from cubic to ellipsoidal shape. This study also emphasized the application of a statistical tool, response surface methodology (RSM) based on Box-Behnken design (BBD), to determine the optimal conditions for the production of calcium carbonate crystals with high specific surface area. The precipitation process was performed using different combinations of additive concentration, pH, and temperature, which are the main parameters affecting this process. The effects of these parameters on the responses, i.e., average particle size, surface area, and the relative fraction of vaterite, were investigated. Second-order polynomial equations were developed for the particle size, specific surface area and vaterite composition to correlate the parameters. The maximum specific surface area (12.430 mg/g) was obtained under the optimal conditions of 50 ppm additive concentration, pH 8.5, and 40 degrees C
An in vitro evaluation of the effects of Urtica dioica and Fructus Urtica Piluliferae extracts on the crystallization of calcium oxalate
No full textThis study investigated crystallization of calcium oxalate in the presence of Urtica dioica and Fructus Urtica Piluliferae extracts. To evaluate the structures, morphologies and phase transformations of the crystals, X-ray diffraction, Raman and Fourier-transform infrared spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used. The results showed that both additives exerted significant effects on the crystallization process. When Fructus Urtica Piluliferae was used as an additive, the products were a mixture of the monohydrate and dihydrate forms of calcium oxalate. Both SEM and TEM confirmed that the crystals contain different morphologies including hexagonal prismatic and tetragonal bipyramidal forms. The addition of Urtica dioica to the crystallization medium led to the formation of the monohydrate form being efficiently inhibited with only the dihydrate crystals of calcium oxalate being formed over 30 days. A change in the morphology of the crystals from hexagonal prismatic to round nanocrystals was detected in the Urtica dioica medium. Moreover, zeta potential measurements showed that the surface of the crystals became more negative when compared with those prepared from the pure medium with the value increasing from -3.2 +/- 0.5 to -40 +/- 4.6 mV. This study demonstrated the modification of the structure and morphology of calcium oxalate crystals as well as the inhibition of its monohydrate form were possible using Urtica dioica and Fructus Urtica Piluliferae
THE PHYSICOCHEMICAL CHARACTERIZATION AND KINETIC PARAMETER_x000D_ ASSESSMENT OF HYDROXYAPATITE CRYSTALS
No full textThe crystallization of hydroxyapatite (HAP) was analyzed in a batch system in pure medium and in the presence of butyricacid as an additive. The experiments were conducted at different additive concentrations and the influences of the additive wereinvestigated. Firstly, the crystals obtained were characterized by X-ray diffraction, Brunauer–Emmett–Teller, transmissionelectron microscopy, zeta potential measurement, Fourier transform infrared spectroscopy, and thermogravimetric analysis.The structure, surface areas, morphology, surface potential charges, functional groups and thermal decomposition behavior ofthe crystals were determined. In the next step, thermal decomposition kinetic profiles were modeled using the distributedactivation energy model (DAEM), Flynn-Wall-Ozawa (FWO) and Friedman models. All the models used provided accuratefits of the TGA data with acceptably high values. The value for the crystals obtained from the butyric acid containingmedium was about 589 kJ/mol higher than that found for the crystals from the pure medium (538 kJ/mol). According to theresults of the characterization and kinetic analysis, butyric acid could be employed as an additive for the production of HAPcrystals with the desired quality and physical properties
Experimental investigations on the effects of asparagine and serine on the polymorphism of calcium carbonate
No full textThe present study investigated the effects of the amino acids asparagine and serine, as additives, on the polymorphic transformation of calcium carbonate (CaCO3) within the concentration range of 25-100 ppm at 30 degrees C and pH 12. The structural composition and morphology of the samples prepared with and without additives were evaluated experimentally through X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis. The XRD results showed that the calcite composition of CaCO3 samples prepared with asparagine and serine reduced with increasing concentrations of both additives. SEM images showed that CaCO3 prepared with asparagine and serine had three coexisting crystal forms: cubic-shaped calcite, spherical shaped vaterite, and needle-like aragonite crystals. Moreover, the addition of both additives separately was found to increase the average particle size and Brunauer-Emmett-Teller (BET) specific surface area of the crystals. Higher concentrations of serine and asparagine individually in the crystallization media resulted in a more negative zeta potential. Meanwhile, the thermal behavior, kinetics, and thermodynamics of the CaCO3 crystals were simultaneously evaluated by means of by thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) and mass spectrometry (MS). The master plots method combined with the Friedman method revealed that the decomposition of CaCO3 prepared in pure media followed the contracting volume mechanism, R-3. Positive values of Delta H and Delta G were obtained for CaCO3 decomposition. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved
Effect of L-alanyl-glycine dipeptide on calcium oxalate crystallization in artificial urine
No full textPathological crystallization of calcium oxalate (CaOx), the most common constituent of kidney stones, has attracted much attention due to recent surge in reported natural and synthetic additives effectively inhibiting its nucleation and growth. The aim of this study is to investigate the effect of L-alanyl-glycine (Ala-Gly), a dipeptide commonly found in human urine, on CaOx crystallization and its phase transformation in the presence of an artificial urine media. The nucleated CaOx crystals are characterized by XRD, FTIR, SEM, and dynamic light scattering in terms of changes in their crystalline form, morphology, and size. XRD and FTIR results revealed that Ala-Gly inhibited the formation of the thermodynamically most stable phase of CaOx, calcium oxalate monohydrate (COM) crystals. SEM images revealed that hexagonal plate-shaped COM crystals are transformed into the smaller tetragonal bipyramidal calcium oxalate dihydrate (COD) crystals with increasing additive concentrations. At 125 ppm Ala-Gly concentration more pronounced aggregation of CaOx crystals is observed accompanied with higher negative zeta potential value of -27.1 +/- 2.9 mV. Moreover, the phase transformation from COM to COD is also confirmed through thermogravimetric analysis. Consequently, these results suggest that Ala-Gly has a profound effect on preventing the formation of COM crystals and helping to stabilize the COD crystals, a CaOx phase that is reported to have a lower tendency to stick to kidney cells thus decreasing the risk of stone formation. The reported suppression of COM in the presence of Ala-Gly might be significant to clinicians in their attempt to develop a long-term effective treatment for kidney stones
Elucidating the role of hyaluronic acid in the structure and morphology of calcium oxalate crystals
No full textRecent surge in reports describing new additives that inhibiting the growth and nucleation of calcium oxalate (CaOx), the most common component of renal calculi or kidney stones, have rekindled interest in CaOx crystallization. In this in vitro study, the effect of hyaluronic acid (HA), a protein commonly found in urine, on the morphology and phase of the CaOx crystals is investigated. CaOx crystals were crystallized at pH 5.8 and 37 degrees C with a [Ca2+]:[C2O42-] ratio of 20:1, which is close to physiological conditions, in aqueous solution and artificial urine media. The obtained crystals were characterized structurally, morphologically and in terms of their surface charge. The crystals precipitated in aqueous solution without the HA additive were pure phase calcium oxalate monohydrate (COM) crystals with typical hexagonal morphology. The addition of HA partially promotes the transformation of COM into calcium oxalate dihydrate (COD) in aqueous solution. However, the only solid phase to form in artificial urine media with and without HA was identified as COD with tetragonal bipyramidal morphology. The results of this investigation will contribute to the understanding of the role HA plays on the morphology, structure, and thermal characteristics of CaOx and ultimately facilitate the development of effective treatments for kidney stones. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved
Characteristics and Thermal Kinetics of Hydroxyapatite Crystals Doped with Tricarballylic Acid
No full textHydroxyapatite (HAP) has attracted interest in many fields, e.g., catalysis, water treatment processes, and pharmaceutical industries. HAP crystallization was performed within a batch-type crystallizer both with and without tricarballylic acid used as additive. The crystals produced in pure media and in the presence of tricarballylic acid were characterized and their thermal degradation was then accomplished in a thermal analyzer in an inert atmosphere. Experimental data was used to calculate the activation energies based on the Kissinger, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink kinetic models. The results revealed that tricarballylic acid was adsorbed onto the crystal surface, with significant effects on crystal morphology, thermal degradation behavior, and average activation energy
Mandelik Asit ve Propan-1,2,3-Trikarboksilik Asitin Kalsiyum Oksalat Monohidrat Kristalizasyonuna Etkisi
No full textThe effects of mandelic and propane-1,2,3-tricarboxylic acids as additives on calcium oxalate monohydrate (COM) crystals were investi-gated in this study. The physicochemical properties of the COM crystals prepared with and without these additives were characterized us-ing X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta po-tential analysis. The XRD and SEM results showed that the crystals prepared in pure medium were monohydrates and consisted primarily of hexagonal crystals, respectively. The additives mandelic acid and propane-1,2,3-tricarboxylic acid in the crystallization media signifi-cantly changed the size and morphology of the COM crystals, the effects of which were more pronounced with higher concentrations of the additives. The results of FTIR suggested that both carboxylic acids were adsorbed onto the surface of the COM crystals. The zeta po-tential analysis showed a negative charge on the surface of the COM crystals in the mandelic acid medium, while the surface became more positive in the medium containing increasing concentrations of propane-1,2,3-tricarboxylic acid. In addition, an analysis was conducted to evaluate the thermal characteristics of the COM crystals prepared with and without the additives. The data obtained were used to calculate the kinetic parameters, such as the activation energy and pre-exponential factor, using the Coats-Redfern method. The calculated activation energies for stages I, II, and III in pure medium were 98.76, 270.69, 258.55 kJ/mol, respectively, which were lower than that of COM crys-tals prepared in the two media containing the additives
An experimental investigation and kinetic‐modeling study of the phase transformation behavior of glycine in various carboxylic acids
No full textIn this study, the phase transformation behavior from beta-glycine (Gly) to alpha-Gly was examined in the presence of three different carboxylic acid additives (acetic, tartaric, and citric acid) at three different concentrations. Initially, the structure, morphology, shape parameters, surface functional groups, and elemental properties of the crystals prepared from the additive-containing and nonadditive media were investigated. The characterization results showed that when compared with the pure medium, both the duration of the phase transformation and physicochemical properties of the alpha-Gly crystals were altered in the presence of the three carboxylic acid additives studied. Subsequently, the experimental data obtained from the thermogravimetric analysis of the alpha-Gly samples obtained from the additive containing and nonadditive media were modeled using a simplified DAEM kinetic model. On the basis of the data obtained from the distributed activation energy model, the average activation energy for the Gly crystals obtained from the pure medium was calculated to be 90.8 kJ/mol. The value for the crystals obtained from the acetic acid-containing medium was 104.0 higher than that found for the crystals from the pure medium and other two other additives studied. Besides kinetic analysis, thermogravimetric analysis/Fourier-transform infrared spectroscopy and elemental analysis confirmed that the carboxylic acid was adsorbed on the crystal's surface. The amount of acetic, tartaric, and citric acid adsorbed was 2.97, 2.38, and 1.72 mg/g, respectively
The characterization and polymorphism of α-Glycine in the presence of butyric acid
No full textThe present study aims to investigate the effect of butyric acid used as an additive and its concentration ranging between 50 ppm and 250 ppm during the polymorphic phase transformation of beta-glycine to alpha-glycine. Analysis includes a continuous measurement of the ultrasonic velocity and periodically the X-ray diffraction (XRD) pattern. Morphological characterization shows that the alpha-glycine crystals obtained in pure media are smooth, prismatic shapes, and that butyric acid plays a major role in crystal shape change. SEM imaging and morphology analysis indicates that the presence of butyric acid to media results in shorter, rounded and aggregated crystals. Further analyses of Fourier Transform Infrared Spectroscopy (FTIR), zeta potential measurements, and elemental analysis reveals that butyric acid adsorbs on the crystals' surface and changes both the surface charge and the elemental composition of the crystals obtained. In addition, thermal decomposition behaviors of the crystals are investigated and the obtained data is modeled using the thermal decomposition kinetic models of FWO, KAS, and Tang. Based on the data of the FWO kinetic model, the average activation energy of the crystals obtained in butyric acid media is calculated as 118.8 +/- 17.0 kJ/mol, which is higher than that of crystals obtained in pure media. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved
- …
