scholarly journals Synthesis of Calcium Orthophosphates by Chemical Precipitation in Aqueous Solutions: The Effect of the Acidity, Ca/P Molar Ratio, and Temperature on the Phase Composition and Solubility of Precipitates

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1009
Author(s):  
Mykola V. Nikolenko ◽  
Kateryna V. Vasylenko ◽  
Victoria D. Myrhorodska ◽  
Andrii Kostyniuk ◽  
Blaž Likozar
Keyword(s):  
Solid Phase ◽  
Chemical Precipitation ◽  
Molar Ratio ◽  
Key Factors ◽  
Correlation Dependence ◽  
Molar Ratios ◽  
Calcium Orthophosphates ◽  
Calcium Cations ◽  
Solubility Isotherms ◽  
Solubility Products

Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases into less soluble precipitates of the phosphates. It was proposed to compare calcium orthophosphates solubility products with calcium cations quantities in their formulas. It was found that there was a linear correlation between calcium orthophosphates specific solubility products and their molar ratios Ca/P if hydroxyapatite and its Ca-deficient forms were excluded from consideration. It was concluded that the relatively large deviations of their solubility products from the found correlation should be thought of as erroneous data. That is why solubility products were changed in accordance with correlation dependence: pKS for hydroxyapatite was 155, pKS for Ca-deficient hydroxyapatites was 114–155. The solubility isotherms, which were calculated on the basis of the corrected pKS values, coincided with the experimental data on solid-phase titration by Pan and Darvell.

scholarly journals Synthesis of calcium orthophosphates by chemical precipitation: re-evaluation of the solubility products of hydroxyapatites

2020 ◽  
pp. 124-133
Author(s):  
M.V. Nikolenko ◽  
◽  
K.V. Vasylenko ◽  
V.D. Myrhorodska ◽  
I.M. Ryshchenko ◽  
...  
Keyword(s):  
Crystal Lattice ◽  
Tricalcium Phosphate ◽  
Chemical Precipitation ◽  
Degree Of Crystallinity ◽  
Molar Ratio ◽  
Chemical Thermodynamics ◽  
Stable Form ◽  
Hydrogen Phosphate ◽  
Calcium Orthophosphates ◽  
Solubility Products

For the first time, a linear correlation was found between the specific solubility products of calcium orthophosphates and their molar ratio Ca/P (the correlation coefficient being R2=0.9742). Nevertheless, the values of solubility products of tricalcium phosphate (pKS=26–29), hydroxyapatite (pKS=116.8) and its Ca-deficient forms (pKS~85) cannot be correlated. We proposed to adjust these values of solubility products in accordance with the obtained correlation dependence as follows: pKS is 40, 155 and 114–155 for tricalcium phosphate, hydroxyapatite and Ca-deficient hydroxyapatite, respectively. The calculated solubility diagrams (isotherms) with adjusted solubility products agree reasonably well with the known experimental data, which could not be explained and were not accepted by the scientific community up to the present day. Based on well-known ideas of chemical thermodynamics, we suggested an explanation of the correlation between the specific solubility products of calcium orthophosphates and their molar ratios Ca/P. The developed model of dissolution process is based on a comparison between crystal lattice energy and hydration energy of calcium ions. The experiments on chemical precipitation of orthophosphates were performed at pH 4–10 and at a constant molar ratio Ca/P=1.5; their results showed that only one single metastable form, calcium hydrogen phosphate, is precipitated within the entire pH range at the temperature of 200С. The obtained sediments were isothermally exposed at the temperature of 2500С in a mother solution for 6 hours; such a treatment resulted in a full dehydration of calcium hydrogen phosphate and its partial transformation into a more stable form (hydroxyapatite). The mass fraction of hydroxyapatite increases from 14% to 70% and the degree of crystallinity decreases from 20% to 5% with increasing the value of solution pH. It was concluded that the rate of phase transition from CaHPO4 to Ca10(PO4)6(OH)2 in influenced by the concentration of hydroxide ions that are incorporated into a crystal lattice of hydroxyapatite.

scholarly journals Comprehensive characterization of humic-like substances in smoke PM<sub>2.5</sub> emitted from the combustion of biomass materials and fossil fuels

2016 ◽  
Vol 16 (20) ◽  
pp. 13321-13340 ◽  
Author(s):  
Xingjun Fan ◽  
Siye Wei ◽  
Mengbo Zhu ◽  
Jianzhong Song ◽  
Ping'an Peng
Keyword(s):  
Coal Combustion ◽  
Fossil Fuels ◽  
Solid Phase ◽  
Water Soluble ◽  
Total Carbon ◽  
Atmospheric Environment ◽  
Molar Ratio ◽  
Resonance Spectroscopy ◽  
Molar Ratios ◽  
Biomass Materials

Abstract. Humic-like substances (HULIS) in smoke fine particulate matter (PM2.5) emitted from the combustion of biomass materials (rice straw, corn straw, and pine branch) and fossil fuels (lignite coal and diesel fuel) were comprehensively studied in this work. The HULIS fractions were first isolated with a one-step solid-phase extraction method, and were then investigated with a series of analytical techniques: elemental analysis, total organic carbon analysis, UV–vis (ultraviolet–visible) spectroscopy, excitation–emission matrix (EEM) fluorescence spectroscopy, Fourier transform infrared spectroscopy, and 1H-nuclear magnetic resonance spectroscopy. The results show that HULIS account for 11.2–23.4 and 5.3 % of PM2.5 emitted from biomass burning (BB) and coal combustion, respectively. In addition, contributions of HULIS-C to total carbon and water-soluble carbon in smoke PM2.5 emitted from BB are 8.0–21.7 and 56.9–66.1 %, respectively. The corresponding contributions in smoke PM2.5 from coal combustion are 5.2 and 45.5 %, respectively. These results suggest that BB and coal combustion are both important sources of HULIS in atmospheric aerosols. However, HULIS in diesel soot only accounted for  ∼  0.8 % of the soot particles, suggesting that vehicular exhaust may not be a significant primary source of HULIS. Primary HULIS and atmospheric HULIS display many similar chemical characteristics, as indicated by the instrumental analytical characterization, while some distinct features were also apparent. A high spectral absorbance in the UV–vis spectra, a distinct band at λex∕λem ≈  280∕350 nm in EEM spectra, lower H ∕ C and O ∕ C molar ratios, and a high content of [Ar–H] were observed for primary HULIS. These results suggest that primary HULIS contain more aromatic structures, and have a lower content of aliphatic and oxygen-containing groups than atmospheric HULIS. Among the four primary sources of HULIS, HULIS from BB had the highest O ∕ C molar ratios (0.43–0.54) and [H–C–O] content (10–19 %), indicating that HULIS from this source mainly consisted of carbohydrate- and phenolic-like structures. HULIS from coal combustion had a lower O ∕ C molar ratio (0.27) and a higher content of [Ar–H] (31 %), suggesting that aromatic compounds were extremely abundant in HULIS from this source. Moreover, the absorption Ångström exponents of primary HULIS from BB and coal combustion were 6.7–8.2 and 13.6, respectively. The mass absorption efficiencies of primary HULIS from BB and coal combustion at 365 nm (MAE365) were 0.97–2.09 and 0.63 m2 gC−1, respectively. Noticeably higher MAE365 values for primary HULIS from BB than coal combustion indicate that the former has a stronger contribution to the light-absorbing properties of aerosols in the atmospheric environment.

Phase diagram of the system CaSO4—K2SO4—KNO3—Ca(NO3)2—H2O

2014 ◽  
Vol 7 (1) ◽  
pp. 20-24 ◽  
Author(s):  
Jana Jurišová ◽  
Vladimír Danielik ◽  
Pavel Fellner ◽  
Marek Lencsés ◽  
Milan Králik
Keyword(s):  
Phase Diagram ◽  
Quantitative Determination ◽  
Solid Phase ◽  
Calcium Nitrate ◽  
Primary Crystallization ◽  
Potassium Nitrate ◽  
Molar Ratio ◽  
Calcium Cations ◽  
Lower Ratio

Abstract Potassium nitrate as a fertilizer suitable for greenhouse and hydroponic applications can be prepared by the reaction of potassium sulphate with calcium nitrate. However, it may happen that simultaneously with the precipitation of gypsum (CaSO4·2H2O) also two other binary salts, viz. syngenite (K2SO4·CaSO4·H2O) and görgeyite (K2SO4·5CaSO4·H2O) can crystallize. This would lower the yield of KNO3. For minimization of potassium loss we have to determine the conditions under which syngenite and görgeyite crystallize. As a useful tool for the quantitative determination of specific hydrates, simultaneous DTA/TG technique appeared. Each hydrate decomposes at a certain temperature. The loss of water at dehydration can be used for a quantitative determination of the amount of the hydrate in the precipitating solid phase. Based on the experimental data several conclusions can be drawn: (i) excess of calcium cations lowers the concentration of sulphate ions in the liquid phase together with lowering of contents of syngenite and görgeyite in the solid phase; (ii) higher content of water results in a higher solubility of sulphate ions; (iii) joint crystallization of syngenite and gypsum occurs in the composition area interesting from the point of KNO3 production; (iv) area of the primary crystallization of görgeyite does not exist in the phase diagram at 80 °C. However, görgeyite crystallizes at the molar ratio Ca(NO3)2:K2SO4 = 1:1 by ternary crystallization; (v) area of crystallization of pure gypsum is shifted to lower ratio Ca(NO3)2:K2SO4 by the addition of water to the system.

Effect of Experimental Conditions on the Chemical Composition of Hydroxyapatite Synthesized by Chemical Precipitation

MRS Advances ◽  
2017 ◽  
Vol 2 (61) ◽  
pp. 3851-3857 ◽  
Author(s):  
Jorge López-Cuevas ◽  
Juan C. Rendón-Angeles ◽  
José L. Rodríguez-Galicia ◽  
Carlos A. Gutiérrez-Chavarría
Keyword(s):  
Particle Size ◽  
Chemical Composition ◽  
Room Temperature ◽  
Ambient Air ◽  
Chemical Precipitation ◽  
Molar Ratio ◽  
Experimental Conditions ◽  
Molar Ratios ◽  
Pure Phase ◽  
Suspension Ph

ABSTRACTHydroxyapatite [HAp, Ca5(PO4)3(OH)] was synthesized by chemical precipitation, using H3PO4 and Ca(OH)2 as chemical precursors. The precursors were slowly mixed in suitable proportions aiming to obtain Ca/P molar ratios of 1.5, 1.67 or 2.0 in the reacting suspension. This was followed by 21.5 h of aging. Both reaction and aging stages were carried out under an atmosphere of still ambient air and under continuous stirring, either at room temperature, 60 or 90 °C. The precipitates were characterized by ICP-AES and XRD. The results suggested that the most suitable Ca/P molar ratio for the production of pure phase HAp is Ca/P = 1.67, as long as the initial Ca(OH)2 particle size and/or the suspension pH are carefully controlled, especially when the synthesis is carried out above room temperature.

scholarly journals Photocatalytic Reduction of CO2 to Methanol Using a Copper-Zirconia Imidazolate Framework

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 346
Author(s):  
Sonam Goyal ◽  
Maizatul Shima Shaharun ◽  
Ganaga Suriya Jayabal ◽  
Chong Fai Kait ◽  
Bawadi Abdullah ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Catalyst Support ◽  
Oxidation Potential ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molar Ratios ◽  
Optimum Parameters ◽  
Reduction Of Co2 ◽  
Enhanced Yield

A set of novel photocatalysts, i.e., copper-zirconia imidazolate (CuZrIm) frameworks, were synthesized using different zirconia molar ratios (i.e., 0.5, 1, and 1.5 mmol). The photoreduction process of CO2 to methanol in a continuous-flow stirred photoreactor at pressure and temperature of 1 atm and 25 °C, respectively, was studied. The physicochemical properties of the synthesized catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The highest methanol activity of 818.59 µmol/L.g was recorded when the CuZrIm1 catalyst with Cu/Zr/Im/NH4OH molar ratio of 2:1:4:2 (mmol/mmol/mmol/M) was employed. The enhanced yield is attributed to the presence of Cu2+ oxidation state and the uniformly dispersed active metals. The response surface methodology (RSM) was used to optimize the reaction parameters. The predicted results agreed well with the experimental ones with the correlation coefficient (R2) of 0.99. The optimization results showed that the highest methanol activity of 1054 µmol/L.g was recorded when the optimum parameters were employed, i.e., stirring rate (540 rpm), intensity of light (275 W/m2) and photocatalyst loading (1.3 g/L). The redox potential value for the CuZrIm1 shows that the reduction potential is −1.70 V and the oxidation potential is +1.28 V for the photoreduction of CO2 to methanol. The current work has established the potential utilization of the imidazolate framework as catalyst support for the photoreduction of CO2 to methanol.

scholarly journals Lipozyme 435-Mediated Synthesis of Xylose Oleate in Methyl Ethyl Ketone

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3317
Author(s):  
Maria Carolina Pereira Gonçalves ◽  
Jéssica Cristina Amaral ◽  
Roberto Fernandez-Lafuente ◽  
Ruy de Sousa Junior ◽  
Paulo Waldir Tardioli
Keyword(s):  
Oleic Acid ◽  
Methyl Ethyl Ketone ◽  
Molar Ratio ◽  
Methyl Ethyl ◽  
Sugar Ester ◽  
Molar Ratios ◽  
Emulsion Capacity ◽  
Ping Pong ◽  
Commercial Sugar ◽  
Repeated Use

In this paper, we have performed the Lipozyme 435-catalyzed synthesis of xylose oleate in methyl ethyl ketone (MEK) from xylose and oleic acid. The effects of substrates’ molar ratios, reaction temperature, reaction time on esterification rates, and Lipozyme 435 reuse were studied. Results showed that an excess of oleic acid (xylose: oleic acid molar ratio of 1:5) significantly favored the reaction, yielding 98% of xylose conversion and 31% oleic acid conversion after 24 h-reaction (mainly to xylose mono- and dioleate, as confirmed by mass spectrometry). The highest Lipozyme 435 activities occurred between 55 and 70 °C. The predicted Ping Pong Bi Bi kinetic model fitted very well to the experimental data and there was no evidence of inhibitions in the range assessed. The reaction product was purified and presented an emulsion capacity close to that of a commercial sugar ester detergent. Finally, the repeated use of Lipozyme 435 showed a reduction in the reaction yields (by 48 and 19% in the xylose and oleic acid conversions, respectively), after ten 12 h-cycles.

Appearance, corrosion properties, and leach resistance of spruce and pine wood treated with Mea modified micronized copper preservative (MCu)

Holzforschung ◽  
2014 ◽  
Vol 68 (4) ◽  
pp. 477-486 ◽  
Author(s):  
Myung Jae Lee ◽  
Sedric Pankras ◽  
Paul Cooper
Keyword(s):  
Wood Species ◽  
Wood Preservative ◽  
Molar Ratio ◽  
Corrosion Properties ◽  
Pine Wood ◽  
Molar Ratios ◽  
Copper Leaching ◽  
Mold Resistance ◽  
Refractory Wood

Abstract Canadian refractory wood species treated with micronized copper (MCu) wood preservative become mottled and streaky in appearance. To overcome this issue, the MCu system was modified by adding small amounts of monoethanolamine (Mea). The modified systems were evaluated to clarify the role of Mea in terms of leaching, corrosion, and mold resistance of MCu systems. The mottled and streaky surface on treated spruce was prevented at Mea/Cu molar ratios between 0.7 and 1.5. Copper leaching remained modest and was only slightly higher than that of MCu alone up to a Mea/Cu molar ratio of 1.2. However, adding even a small amount of Mea to the MCu formulation increased fastener corrosion compared with MCu. Protonated Mea increased as more Mea was added and was identified as the main corrosion-causing electrolyte in the system.

Hydrogen-bonded bent-core blue phase liquid crystal complexes containing various molar ratios of proton acceptors and donors

RSC Advances ◽  
2016 ◽  
Vol 6 (38) ◽  
pp. 32319-32327 ◽  
Author(s):  
Chun-Chieh Han ◽  
Yu-Chaing Chou ◽  
San-Yuan Chen ◽  
Hong-Cheu Lin
Keyword(s):  
Liquid Crystal ◽  
Chain Length ◽  
Alkyl Chain ◽  
Alkyl Chain Length ◽  
Chiral Center ◽  
Molar Ratio ◽  
Core Complex ◽  
Molar Ratios ◽  
Phase Liquid ◽  
Blue Phase

The molar ratio, alkyl chain length, lateral fluoro-substitution and the chiral center of H-bonded bent-core supramolecules would affect the BP ranges of BPLC complexes. H-bonded bent-core complex PIIIC9/AIIF* (3/7 mol mol−1) displayed the widest BPI range of ΔTBPI = 12 °C.

scholarly journals BrO/SO<sub>2</sub> molar ratios from scanning DOAS measurements in the NOVAC network

2013 ◽  
Vol 5 (2) ◽  
pp. 1845-1870 ◽  
Author(s):  
P. Lübcke ◽  
N. Bobrowski ◽  
S. Arellano ◽  
B. Galle ◽  
G. Garzón ◽  
...  
Keyword(s):  
Molar Ratio ◽  
Optical Absorption Spectroscopy ◽  
Short Term ◽  
Dynamic Changes ◽  
Volcanic System ◽  
Molar Ratios ◽  
Remote Sensing Technique ◽  
Field Campaigns ◽  
Term Field

Abstract. The molar ratio of BrO to SO2 is, like other halogen/sulphur ratios, a~possible precursor for dynamic changes in the shallow part of a volcanic system. While the predictive significance of the BrO/SO2 ratio has not been well constrained yet, it has the major advantage that this ratio can be readily measured using the remote-sensing technique Differential Optical Absorption Spectroscopy (DOAS) in the UV. While BrO/SO2 ratios have been measured during several short-term field campaigns this article presents an algorithm that can be used to obtain long-term time series of BrO/SO2 ratios from the scanning DOAS instruments of the Network for Observation of Volcanic and Atmospheric Change (NOVAC) or comparable networks. Parameters of the DOAS retrieval of both trace gases are given and the influence of co-adding spectra on the retrieval error will be investigated. Difficulties in the evaluation of spectroscopic data from monitoring instruments in volcanic environments and possible solutions are discussed. The new algorithm is demonstrated by evaluating data from the NOVAC scanning DOAS systems at Nevado del Ruiz, Colombia encompassing almost four years of measurements between November 2009 and end of June 2013. This dataset shows variations of the BrO/SO2 ratio several weeks prior to the eruption on 30 June 2012.

Structural characteristics of tetanolysin and its binding to lipid vesicles

1982 ◽  
Vol 152 (2) ◽  
pp. 888-892
Author(s):  
S Rottem ◽  
R M Cole ◽  
W H Habig ◽  
M F Barile ◽  
M C Hardegree
Keyword(s):  
Structural Characteristics ◽  
Lipid Vesicles ◽  
Molar Ratio ◽  
Molar Ratios ◽  
High Concentrations

Tetanolysin binding to lipid vesicles was found to depend on the molar ratio of cholesterol to phospholipid, being low in vesicles containing up to 20 mol% cholesterol and high in vesicles containing more than 33 mol%. High concentrations of purified tetanolysin preparations formed arc- and ring-shaped structures. The structures were not readily detectable in diluted preparations unless incubated with lipid vesicles containing high molar ratios of cholesterol to phospholipid. It is suggested that the toxin is concentrated on the vesicles to local concentrations high enough to form the arcs and rings.

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