SYNTHESIS OF CALCIUM FLUORIDE BY DRY METHOD FROM CALCIUM CARBONATE  AND AMMONIUM FLUORIDE

The proposed scheme for producing CaF2 according to the “dry” method is based on the following stages: hydrolysis of hydrofluoric acid to produce white carbon black and a 12-18% NH4F solution and subsequent production of CaF2 from CaCO3 at a temperature of 200-400 °C in a fluidized bed or drum furnace in a continuous mode, while ammonia from the exhaust gas is sent to the stage of hydrolysis of hydrofluoric acid. In the article the features of synthetic calcium fluoride obtaining by the "dry" method from calcium carbonate and ammonium fluoride are studied. It is shown that the heating of the mixture proceeds with a step-by-step decomposition of ammonium fluoride, and decomposition products interact with calcium carbonate forming a synthetic calcium fluoride. These factors determine the behavior of a solid mixture of calcium carbonate and ammonium fluoride under heating, which allows us to evaluate the kinetic factors of the interaction of reagents and products and of their thermal transformation. Conditions of receiving synthetic calcium fluoride from the waste products of phosphoric acid and synthetic calcium carbonate by “dry” method are determined. The calcium fluoride can be recognized as a basic product in solving the problem of the waste catalyst hydrofluoric acid utilization. In the article, the features of synthetic calcium fluoride obtaining by the “dry” method from calcium carbonate and ammonium fluoride are studied. A synchronous thermal analysis of this mixture was carried out with the analysis of exhaust gases by the IR-Fourier method at samplesheating rates of 1.5 ; 5; 10 °С /min in an air atmosphere. It was shown that heating of this mixture proceeds with stepwise decomposition of ammonium fluoride, the products of which interact with calcium carbonate, form synthetic calcium fluoride. In the first stage, the reactions of calcium carbonate with ammonium fluoride and hydrogen fluoride occur in the kinetic region (Еа = 94.22 kJ/mol), and in the second, the reaction of interaction of CaCO3 and HF (Еа = 30.09 kJ/mol) is limited diffusion of HF to the CaCO3 core in the temperature range of 250-300 °С. These factors determine the behavior a solid mixture of calcium carbonate and ammonium fluoride under heating conditions, which allows us to evaluate the kinetic laws of the process of interaction of reagents and products of their thermal transformation. The conditions for obtaining by “dry” method of synthetic calcium fluoride from waste products of phosphoric acid and synthetic calcium carbonate have been identified, and calcium fluoride can be recognized as the base product in solving the problem of disposal of waste hydrofluoric acid.

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EINE CHEMISCHE METHODE ZUR BESTIMMUNG VON 16-EPI-ÖSTRIOL IM URIN DES MENSCHEN

Acta Endocrinologica ◽

10.1530/acta.0.0440047 ◽

1963 ◽

Vol 44 (1) ◽

pp. 47-66 ◽

Cited By ~ 2

Author(s):

W. Nocke ◽

H. Breuer

Keyword(s):

Melting Point ◽

Phosphoric Acid ◽

Aqueous Alkali ◽

Percentage Error ◽

Organic Layer ◽

Maximum Percentage ◽

Chemical Determination ◽

Routine Assay ◽

Hydrolysis Of

ABSTRACT A method for the chemical determination of 16-epi-oestriol in the urine of nonpregnant women with a qualitative sensitivity of less than 0.5 μg/24 h is described. The separation of 16-epi-oestriol and oestriol is accomplished by converting 16-epi-oestriol into its acetonide, a reaction which is stereoselective for cis-glycols and therefore not undergone by oestriol as a trans-glycol. Following partition between chloroform and aqueous alkali, the acetonide of 16-epi-oestriol is completely separated with the organic layer whereas oestriol as a strong phenol remains in the alkaline phase. 16-epi-oestriol is chromatographed on alumina as the acetonide and determined as a Kober chromogen. This procedure can easily be incorporated into the method of Brown et al. (1957 b) thus making possible the simultaneous routine assay of oestradiol-17β, oestrone, oestriol and 16-epi-oestriol from one sample of urine. The specificity of the method was established by separation of 16-epi-oestriol from nonpregnancy urine as the acetonide, hydrolysis of the acetonide by phosphoric acid, isolation of the free compound by microsublimation and identification by micro melting point, colour reactions and chromatography. The accuracy of the method is given by a mean recovery of 64% for pure crystalline 16-epi-oestriol when added to hydrolysed urine in 5–10 μg amounts. The precision is given by s = 0.24 μg/24 h. For the duplicate determination of 16-epi-oestriol the qualitative sensitivity is 0.44 μg/24 h, the maximum percentage error being ± 100% The quantitative sensitivity (±25% error) is 1.7 μg/24 h.

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Calcium pyrophosphate powder synthesized from phosphoric acid and calcium carbonate

Materials Science ◽

10.31044/1684-579x-2020-0-11-42-48 ◽

2020 ◽

pp. 42-48

Author(s):

Tatiana Safronova ◽

◽

Tatiana Shatalova ◽

Snezhana Tikhonova ◽

Yaroslav Filippov ◽

...

Keyword(s):

Calcium Carbonate ◽

Phosphoric Acid ◽

Functional Materials ◽

Bone Defects ◽

Thermal Conversion ◽

Calcium Pyrophosphate ◽

Molar Ratio

Powders of calcium pyrophosphate Ca2P2O7 in the form of γ- и β-modifications have been produced as a result of thermal conversion of brushite CaHPO4∙2H2O synthesized from phosphoric acid H3PO4 and calcium carbonate CaCO3 at the molar ratio P / Ca = 1.1. The resulting powders can be used for production of various functional materials including biocompatible and bioresorbable ones for the treatment of bone defects.

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Preparation of hydroxyapatite by aqueous precipitation from calcium carbonate and phosphoric acid

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1113/1/012013 ◽

2021 ◽

Vol 1113 (1) ◽

pp. 012013

Author(s):

Byeong Woo Lee

Keyword(s):

Calcium Carbonate ◽

Phosphoric Acid

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Four chemical methods of porcelain conditioning and their influence over bond strength and surface integrity

Dental Press Journal of Orthodontics ◽

10.1590/2176-9451.20.4.051-056.oar ◽

2015 ◽

Vol 20 (4) ◽

pp. 51-56 ◽

Cited By ~ 5

Author(s):

João Paulo Fragomeni Stella ◽

Andrea Becker Oliveira ◽

Lincoln Issamu Nojima ◽

Mariana Marquezan

Keyword(s):

Phosphoric Acid ◽

Bond Strength ◽

Surface Integrity ◽

Hydrofluoric Acid ◽

Shear Bond Strength ◽

Testing Machine ◽

Acid Etching ◽

Ceramic Surface ◽

Surface Conditioning ◽

Phosphoric Acid Etching

OBJECTIVE: To assess four different chemical surface conditioning methods for ceramic material before bracket bonding, and their impact on shear bond strength and surface integrity at debonding.METHODS: Four experimental groups (n = 13) were set up according to the ceramic conditioning method: G1 = 37% phosphoric acid etching followed by silane application; G2 = 37% liquid phosphoric acid etching, no rinsing, followed by silane application; G3 = 10% hydrofluoric acid etching alone; and G4 = 10% hydrofluoric acid etching followed by silane application. After surface conditioning, metal brackets were bonded to porcelain by means of the Transbond XP system (3M Unitek). Samples were submitted to shear bond strength tests in a universal testing machine and the surfaces were later assessed with a microscope under 8 X magnification. ANOVA/Tukey tests were performed to establish the difference between groups (α= 5%).RESULTS: The highest shear bond strength values were found in groups G3 and G4 (22.01 ± 2.15 MPa and 22.83 ± 3.32 Mpa, respectively), followed by G1 (16.42 ± 3.61 MPa) and G2 (9.29 ± 1.95 MPa). As regards surface evaluation after bracket debonding, the use of liquid phosphoric acid followed by silane application (G2) produced the least damage to porcelain. When hydrofluoric acid and silane were applied, the risk of ceramic fracture increased.CONCLUSIONS: Acceptable levels of bond strength for clinical use were reached by all methods tested; however, liquid phosphoric acid etching followed by silane application (G2) resulted in the least damage to the ceramic surface.

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One Step Microwave-Assisted Synthesis of Fluorinated Titania Photocatalyst

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.670.177 ◽

2015 ◽

Vol 670 ◽

pp. 177-182

Author(s):

Alexey A. Sadovnikov ◽

Alexander E. Baranchikov ◽

Vladimir Kozik ◽

Lyudmila P. Borilo ◽

Sergey A. Kozyukhin ◽

...

Keyword(s):

Ammonium Fluoride ◽

Organic Dye ◽

Microwave Assisted Synthesis ◽

Dye Sensitized ◽

Microwave Assisted ◽

One Step ◽

Nanocrystalline Titanium ◽

Nanocrystalline Titanium Dioxide ◽

Titania Photocatalyst ◽

Hydrolysis Of

Microwave-assisted high temperature hydrolysis of titanium oxysulfate, in the presence of ammonium fluoride, allows synthesizing nanocrystalline titanium dioxide photocatalysts possessing photocatalytic activity as high as the commercial photocatalyst Evonik Aeroxide® TiO2 P 25. Dye-sensitized reactions play an important role in organic dye discoloration in the presence of fluorinated titania.

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