Chromium Fluoride Research Articles

Formation and Mechano-Chemical Properties of Chromium Fluorides Originated from the Deposition of Carbon-Chromium Nanocomposite Coatings in the Reactive Atmosphere (Ar + CF4) during Magnetron Sputtering

The literature analysis did not indicate any studies on fluorination tests of carbon nanocomposite coatings doped with transition metals in a form of nanocrystalline metal carbide in amorphous carbon matrix (nc-MeC/a-C). As a model coating to investigate the effect of fluorination in a tetrafluoromethane (CF4) atmosphere, a nanocomposite carbon coating doped with chromium-forming nanocrystals of chromium carbides in a-C matrix (nc-CrC/a-C) produced by magnetron sputtering from graphite targets and using a Pulse-DC type medium frequency power supply was chosen. After the deposition of the gradient chromium carbonitride (CrCN) adhesive sublayer, the fluorination of the main coating was conducted in a reactive mode in an (Ar + CF4) atmosphere at various CF4 content. It was observed that the presence of CF4 in the atmosphere resulted in a reduced amount of chromium carbides formed in favor of chromium fluorides. Thus far, this is an observation that seems unnoticed by the carbon coatings researchers. Fluorine was assumed to bond much more readily to carbon than to chromium, due to the stability of tetrafluoromethane (CF4). The opposite seems to be true. The mechanical properties (nano-hardness and Young’s modulus) and tribological properties in the ‘pin-on-disc’ friction pair are presented, along with the analysis of bonds occurring between chromium, carbon, and fluorine by means of X-ray photoelectron spectroscopy (XPS).

Electrochemical Behavior of Chromium Difluoride in Molten Lithium and Beryllium Fluoride Mixtures

The interaction between CrF2 and a molten binary LiF-BeF2 mixture has been studied using the electrochemical methods. The polarization of the chromium electrode relative to the dynamic beryllium electrode was measured. The obtained voltammetry data elucidates that under the experimental conditions, chromium is observed exclusively in one valence form. According to the cathode polarization dependences, it is established that the reduction of chromium ions in the metal occurs by a two-electron electrode reaction. The equilibrium concentrations of chromium were experimentally measured at the temperatures of 923, 973, and 1023 K at different chromium fluoride concentrations in the melt. The oxidation degree of chromium, dissolved in the melt, was calculated according to the concentration dependences of the equilibrium potentials. A thermodynamic analysis of the chromium difluoride dissolution in a molten mixture of lithium and beryllium fluorides was performed. The formation of dilute solutions of chromium difluoride is accompanied by slight deviations of the salt system from Raoult’s laws.

Composition and growth mechanism of nanoporous anodic fluoride films on stainless steel

Anodizing of 304L stainless steel performed in ethylene glycol solution containing 0.1 M NH4F and 0.1 M H2O at constant voltage under static conditions at 5 °C results in the formation of porous anodic films. Several analysis techniques revealed a rather complex composition of the anodic layer for stainless steel compared to that reported in the literature for iron in the same anodizing conditions. Contrary to what might be expected, the anodic layers consist mainly of iron and chromium fluorides rather than oxides. Furthermore, the multilayer fitting of the Rutherford Backscattered spectroscopy shows a decreasing content of chromium and nickel fluorides from the outermost layer to the innermost layer at the metal/film interface, which is composed only of iron fluoride. Film-assisted dissolution mechanisms and the Gibbs-free energy appear to be responsible for the cation distribution and compounds formed throughout the anodic film. In addition, the thickness and final composition of the anodic layer appear to be dependent on the cleaning process carried out after the anodizing.Graphical abstract

New Homometallic Octanuclear Chromium(III) Rings

Four new {Cr8} rings have been synthesized and characterized; they are all based on the classic [CrF(O2CtBu)2]8 ring 1. Three routes have been studied. The first is direct synthesis, by reacting hydrated chromium(III) fluorides with the acid; this has been used to produce LS[CrF(O2CEt)2]8 3. The second route uses 3 as a precursor and substitute with an incoming carboxylate. This has been used to make [CrF(O2CCCl3)2]8 4 and [CrF(O2CC6F5)2]8 5. The third route uses LSN-ethyl-D-glucamine (H5Etglu) as a template and produces chiral rings [Cr8F4(Etglu)(O2CtBu)15] 6. The single crystal X-ray structures of these new compounds are reported.

Investigation on the dehydrofluorination of 2H,3H-decafluoropentane

Studies were conducted on the vapor-phase dehydrofluorination of 2H,3H-decafluoropentane. It was found that 2H,3H-decafluoropentane could be dehydrofluorinated to give Z-1,1,1,2,4,4,5,5,5-nonafluoro-2-pentene and Z-1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene over chromium fluoride or aluminum fluoride catalysts. With stoichiometric calculation, Z-isomer was the main product in the dehydrofluorination owing to its lower relative energy, which was consistent with the experimental result. Consequently, the reaction mechanisms of selective dehydrofluorination of 2H, 3H-decafluoropentane were proposed.

Enthalpies of Formation of Chromium Fluorides. II. Higher Fluorides CrF4, CrF5, and CrF6

Enthalpies of Formation of Chromium Fluorides. II. Higher Fluorides CrF4, CrF5, and CrF6

Enthalpies of Formation of Chromium Fluorides I. Lower Fluorides CrF, CrF2, and CrF3

Enthalpies of Formation of Chromium Fluorides I. Lower Fluorides CrF, CrF2, and CrF3

The Synthesis and Characterisation of a Molecular Sea-Serpent: Studies of a {Cr24 Cu7 } Chain.

A finite chain of thirty‐one paramagnetic centers is reported, synthesized by reaction of hydrated chromium fluoride, copper carbonate and pivalic acid in the presence of 1,4,7,10‐tetrazacyclododecane (cyclen). Magnetic studies show predominantly anti‐ferromagnetic exchange leading to a high density of low‐lying spin states and large saturation field.

The Synthesis and Characterisation of a Molecular Sea‐Serpent: Studies of a {Cr24Cu7} Chain

AbstractA finite chain of thirty‐one paramagnetic centers is reported, synthesized by reaction of hydrated chromium fluoride, copper carbonate and pivalic acid in the presence of 1,4,7,10‐tetrazacyclododecane (cyclen). Magnetic studies show predominantly anti‐ferromagnetic exchange leading to a high density of low‐lying spin states and large saturation field.

High surface area chromium(III) fluoride – Preparation and some properties

Reaction of hydrated hydrazinium fluorochromate(III), [N2H6][CrF5]·H2O, with fluorine (F2) in anhydrous hydrogen fluoride (aHF) medium at room temperature yields completely amorphous CrF3-based materials with exceptionally high specific surface areas of 180–420 m2 g−1 (HS-CrF3). The stepwise reaction starts with the oxidative decomposition of the cationic part of the precursor with F2 that gives a CrF3 intermediate with low surface area. In the following step, part of Cr3+ is oxidized to Cr>3+, and in the presence of residual H2O/[H3O]+ species Cr>3+ fluoride oxides are formed. Formation of volatile chromium compounds, mainly CrO2F2, is apparently the key step in HS-CrF3 formation. Removal of these components from the final product reduces the oxygen content, and generates microporosity. The HS-CrF3 materials are completely amorphous with a bulk composition that is close to stoichiometric CrF3. Small amounts of Cr>3+ and oxygen in the final product very likely originate from the retained non-volatile CrOF3. The HS-CrF3 materials are Lewis acids and exhibit a high reactivity towards chlorofluorocarbons (CFCs) evidenced by substantial F/Cl exchange between CFCs and the solid fluoride. High reactivity of these new materials can be ascribed to their nanoscopic nature, exceptionally high surface area, and low levels of impurities. As such, they represent an interesting new class of benchmark fluoride materials applicable in fluorocarbon chemistry.

Two-site fluctuations and multipolar intersite exchange interactions in strongly correlated systems

An approach is proposed for evaluating dipolar and multipolar intersite interactions in strongly correlated materials. This approach is based on the single-site dynamical mean-field theory (DMFT) in conjunction with the atomic approximation for the local self-energy. Starting from the local-moment paramagnetic state described by DMFT, we derive intersite interactions by considering the response of the DMFT grand potential to small fluctuations of atomic configurations on two neighboring sites. The present method is validated by applying it to one-band and two-band ${e}_{g}$ Hubbard models on the simple-cubic $3d$ lattice. It is also applied to study the spin-orbital order in the parent cubic structure of ternary chromium fluoride ${\mathrm{KCrF}}_{3}$. We obtain the onset of a G-type antiferro-orbital order at a significantly lower temperature compared to that in real distorted ${\mathrm{KCrF}}_{3}$. In contrast, its layered A-type antiferromagnetic order and N\'eel temperature are rather well reproduced. The calculated full Kugel-Khomskii Hamiltonian contains spin-orbital coupling terms inducing a misalignment in the antiferro-orbital order upon the onset of antiferromagnetism.

Polyfluorides and Neat Fluorine as Host Material in Matrix-Isolation Experiments.

The use of neat fluorine in matrix isolation is reported, as well as the formation of polyfluoride monoanions under cryogenic conditions. Purification procedures and spectroscopic data of fluorine are described, and matrix shifts of selected molecules and impurities in solid fluorine are compared to those of common matrix gases (Ar, Kr, N2 , Ne). The reaction of neat fluorine and IR-laser ablated metal atoms to yield fluorides of chromium (CrF5 ), palladium (PdF2 ), gold (AuF5 ), and praseodymium (PrF4 ) has been investigated. The fluorides have been characterized in solid fluorine by IR spectroscopy at 5 K. Also the fluorination of Kr and the photo-dismutation of XeO4 have been studied by using IR spectroscopy in neat fluorine. Formation of the [F5 ](-) ion was obtained by IR-laser ablation of platinum in the presence of fluorine and proven in a Ne matrix at 5 K by two characteristic vibrational bands of [F5 ](-) at $\tilde \nu $=850.7 and 1805.0 cm(-1) and its photo-behavior.

Electrochemical and quantum-chemical studies of chromium(III,II) fluoride complexes in alkali chloride melts

The standard rate constants (ks) of charge transfer on a glass carbon electrode were determined for the Cr(III)/Cr(II) redox pair in the NaCl-KCl-K3CrF6, KCl-K3CrF6, and CsCl-K3CrF6 systems at 973–1173 K by cyclic voltammetry. The ks constant was found to increase at elevated temperatures and the following nonmonotonic dependence of ks on the nature of the outer-spheric cation was found: ks (CsCl) > ks (NaCl-KCl) > ks (KCl). On the basis of quantum-chemical data for the M3CrF6 + 18MCl (M = Na, K) model systems, it was shown that the complex chromium particles with four or five outer-spheric sodium or potassium cations had maximum thermodynamic stability. Quantum-chemical calculations were performed to interpret the experimental data on the effect of the second coordination sphere of the complexes on the standard charge transfer rate constants.

Biosorption and biotransformation of chromium by Serratia sp. isolated from tannery effluent

A bacterium isolated from soil and sediment of a leather tanning mill's effluent was identified as Serratia sp. by the analysis of 16S rDNA. Scanning electron microscopy–energy dispersive X-ray analysis (SEM-EDX) and transmission electron microscopy (TEM) were used to assess morphological changes and confirm chromium biosorption in Serratia sp. both in a shake-flask culture containing chromium and in a tannery wastewater. The SEMEDX and the elemental analysis of the chromate-containing samples confirmed the binding of chromium with the bacterial biomass. The TEM exhibited chromium accumulation throughout the bacterial cell, with some granular deposits in the cell periphery and in the cytoplasm. X-ray diffraction analysis (XRD) was used to quantify the chromium and to determine the chemical nature of the metal–microbe interaction. The XRD data showed the crystalline character of the precipitates, which consisted of mainly calcium chromium oxide, chromium fluoride phosphate and related organo-Cr(III) complex crystals. The XRD data also revealed a strong involvement of cellular carboxyl and phosphate groups in chromium binding by the bacterial biomass. The results of the study indicated that a combined mechanism of ion-exchange, complexation, croprecipitation and immobilization was involved in the biosorption of chromium by bacterial cells in contaminated environments.

New role of chromium fluoride: Its catalytic action on the synthesis of hydroxymethylfurfural in ionic liquid using raw plant biomass and characterization of biomass hydrolysis

A simple two-step process was conducted to scrutinize new catalytic action of chromium fluoride (CrF 3) by evaluating its effect on the yield of hydroxylmethylfurfural (HMF) in ionic liquid (1-octyl-3-methylimidazolium chloride) using raw tapioca root biomass with high starch, and hydrolysis efficiency of the biomass extract was characterized by FT-IR spectrometry and FESEM image analysis. The FT-IR absorbance bands confirmed the presence of starch and other soluble sugars in the acidic biomass extract by presenting its frequency signals in the 950–1200 cm −1 regions. FESEM image showed that the efficiency of the biomass hydrolysis is time-dependent. The concentration of CrF 3 significantly affected the yield of HMF. Its highest yield (52.6 ± 4.8 dwt%) was achieved at 1% CrF 3, but over 1% CrF 3 its yields began to decline. The combined addition of CrF 3 and CrBr 3 showed ca. 1.3-fold higher yield than CrF 3 alone. The reaction rates of HMF synthesis were considerably influenced by the stoichiometry ratio of CrF 3 to biomass. The highest reaction rate (0.41 g/g biomass/h) occurred at 0.2 ratio value.

ChemInform Abstract: Mixed Valence Iron and Chromium Fluorides: Bronzes and Related Compounds. Chemistry, Structure and Magnetism

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Alkali metal cation complexation and solvent interactions by robust chromium(III) fluoride complexes

Interaction of robust chromium(III) fluoride complexes with sodium or lithium cations in solution lead to hypsochromic spectral shifts of increasing magnitude along the series: trans-[CrF 2(py) 4] +, mer-[CrF 3(terpy)], and fac-[CrF 3(Me 3tacn)]. Crystalline products isolated from solution exhibit μ 2-bridging by the fluoride ligands in a linear fashion between Na +-ions and chromium centres in catena-[Na(H 2O) 4(μ-F)- trans-{CrF(py) 4}](HCO 3) 2 and in the dimers [Li(H 2O) n (μ-F)- trans-{CrF(py) 4}] 2+ ( n = 3, 4). The uncharged chromium complexes fac-[CrF 3(Me 3tacn)] and mer-[CrF 3(terpy)] have been synthesized from mer-[CrF 3(py) 3] and shown to precipitate sodium salts from solution, of which 3[CrF 3(Me 3tacn)]·2Na(Bph 4)·solv and 6[CrF 3(terpy)]·4Na(Bph 4)·solv have been crystallographically characterized. In these clusters, the neutral fluoride complexes bring the Na + cation separation down to 3.610 Å and 3.369 Å, respectively, which is much closer than the inter-cation distance in NaCl and comparable to that of NaF. DFT calculations support the notion of a strong interaction between Na + ions and neutral chromium(III) fluoride complexes. The calculations reproduce the magnitude and the counter-intuitive sign of the spectral shifts induced by second sphere complexation in solution, which originates in a breakdown of the assumption of parameter transferability in ligand-field descriptions.

Passivation behavior of Type 304 stainless steel in a non-aqueous alkyl carbonate solution containing LiPF 6 salt

Passivation behavior of type 304 stainless steel in a non-aqueous alkyl carbonate solution containing LiPF 6 salt was studied using electrochemical polarization, X-ray photoelectron spectroscopy (XPS) and time of flight-secondary ion mass spectroscopy (ToF-SIMS). Cathodic polarization to 0 V vs. Li/Li + resulted in most but not complete reduction of the air-formed film from oxides to metal on the stainless steel, as confirmed by XPS. For complete elimination of the air-formed film, the surface of the stainless steel was scratched under anodic polarization conditions. At 3 V vs. Li/Li + where an anodic current peak appeared, only an indistinct layer was recognized on the newly scratched surface, according to ToF-SIMS analysis. Above 4 V vs. Li/Li +, substantial passive films were formed, which were composed of oxides and fluorides of iron and chromium. The origin of oxide was due to water contained in the non-aqueous alkyl carbonate solution, and that of fluorides were the result of the decomposition of electrolytic salt, LiPF 6, especially at higher potential. The resultant passive films were stable in the non-aqueous alkyl carbonate solution containing LiPF 6 salt.

Investigation of combined effect of chromium (VI) and sodium fluoride in experiments on rats

Investigation of combined effect of chromium (VI) and sodium fluoride in experiments on rats

Hydrolysis of iron and chromium fluorides: Mechanism and kinetics

Fluoride complexes of metallic ions are one of the main problems when processing industrial effluents with high content of fluoride anion. The most important case is derived from pickling treatment of stainless steel, which is performed with HNO 3/HF mixtures to remove oxides scale formed over the metal surface. Waste from this process, spent pickling liquor, must be treated for recovering metallic and acid content. Conventional treatments produce a final effluent with high quantity of fluoride complexes of iron and chromium. This work proposes a hydrolysis treatment of these solid metal fluorides by reacting them with a basic agent. Metal oxides are obtained, while fluoride is released to solution as a solved salt, which can be easily recovered as hydrofluoric acid. Solid iron and chromium fluorides, mainly K 2FeF 5(s) and CrF 3(s), obtained in the UCM treatment process, were employed in this work. Optimal hydrolysis operating conditions were obtained by means of a factorial design: media must be basic but pH cannot be higher than 9.5, temperature from 40 to 70 °C and alkali concentration (potassium hydroxide) below 1.1 mol L −1. Secondary reactions have been detected, which are probably due to fluoride adsorption onto obtained oxides surface. Mechanism of reaction consists of several stages, involving solid fluoride dissolution and complexes decomposition. Hydrolysis kinetics has been modeled with classical crystal dissolution kinetics, based on mass transfer phenomena.