Chromium Phosphate Research Articles

Studies on phase formation temperature and photocatalytic properties of nano-sized solid solution of nickel molybdate and chromium–phosphate (NixCr1−xMoxP1−xO4)

The nano-sized Ni x Cr 1− x Mo x P 1− x O 4 was synthesized by CSD method and photocatalytic activity was investigated. The average particle size of Ni x Cr 1− x Mo x P 1− x O 4 ( x = 0.1) was found to be 55 ± 10 nm and it has effective surface area is ∼72.85 m 2 /g. It is showed the highest photocatalytic activity compared other mixed oxides due to small particle size and high surface area. The photocatalytic activity of various proportions of nickel–chromium–molybdenum–phosphorous (Ni x Cr 1− x Mo x P 1− x O 4 ) oxides in the oxidation of thymol blue at pH 8.001 under both UV and visible light has been examined. The nano-size different compositions of Ni x Cr 1− x Mo x P 1− x O 4 (where x = 0.1, 0.2, 0.3 and 0.4) photocatalyst were prepared by chemical solution decomposition (CSD) method and characterized with X-ray diffraction (XRD), UV–vis spectroscopy, Transmission Electron microscopy (TEM), specific surface area (Brunauer–Emmett–Teller (BET)), X-ray photoelectron spectroscopy (XPS) and ICP analysis. The variations of phase separation temperature with respect to the amount of different constituents have been studied. The average particle size of Ni x Cr 1− x Mo x P 1− x O 4 ( x = 0.1) was found to be 55 ± 10 nm measured from Transmission Electron microscopy (TEM) and specific surface area (BET) is found to be ∼72.85 m 2 /g.

Features of the local structural disorder in Li2O–CaF2–P2O5 glass–ceramics with Cr2O3 as nucleating agent

Abstract Li 2 O–CaF 2 –P 2 O 5 glasses mixed with different concentrations of Cr 2 O 3 (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy (EDS), differential thermal analysis and conventional spectroscopic techniques. The X-ray diffraction and scanning electron microscopic studies reveal the presence of lithium phosphate, calcium phosphate and chromium phosphate (complexes of Cr 3+ , Cr 5+ and Cr 6+ ions) crystal phases. The study on DTA suggests that the crystallization is predominantly due to the surface crystallization when the concentration of nucleating agent Cr 2 O 3 is around 0.8 mol%. The IR and Raman spectral studies of these samples indicate that the sample crystallized with 0.8 mol% Cr 2 O 3 is more compact and possesses high rigidity due to the presence of chromium ions largely in tetrahedral positions.

Obtaining of chromium(III) phosphates(V) in the solid-state and their thermal stability

As a result of solid-state reactions four chromium(III) phosphates(V) have been obtained, i.e. Cr(PO3)3, Cr4(P2O7)3, Cr2P4O13 and CrPO4. Cr2P4O13 has been obtained as a result of a solid-state reaction between Cr2O3 and (NH4)2HPO4 as well as between CrPO4 and Cr(PO3)3 mixed at a molar ratio of 1:1 or between Cr4(P2O7)3 and Cr(PO3)3 mixed at a molar ratio of 1:2. Melting temperatures and the products of thermal decomposition have been determined for the obtained chromium(III) phosphates(V).

Phase Evolution of Aluminum-Chromium-Phosphate Binders during Heat-Treatment

Aluminum phosphate is one of the best inorganic binders, and the addition of chromium oxide can improve the properties of the binder. In this work, the phase evolutions in chromium phosphate system and aluminum-chromium-phosphate system during heat-treatment were investigated. The initial binder solutions were prepared by dissolving Al(OH)3 and Cr2O3 in aqueous H3PO4 solution. The binder solutions consolidated at 100°C. The as-consolidated products were heated at different temperature. The experimental results showed the phase evolution of the consolidated products as: amorphous phase in 300~800°C, Cr(PO3)3 and Cr4(P2O7)3 in 900~1200°C for chromium phosphate system binder; amorphous phase in 300~1000°C, Cr(PO3)3 and AlPO4 in 1100°C, Cr4(P2O7)3 and AlPO4 in 1200°C for aluminumchromium- phosphate system binder. The addition of chromium oxide demonstrates to strengthen amorphous network, which further improves the thermal stability.

Textured films of chromium phosphate synthesized by low-temperature vapor diffusion catalysis

The application of kinetically controlled vapor diffusion catalysis to the synthesis of films of chromium phosphate produces a novel, nanostructured film morphology. The resulting material consists of a thin, flat backplane (3 μm thick) with needles of CrPO 4·6H 2O projecting from one surface of the film. The reaction process occurs at low temperature (25 °C) and mild pH.

Tripotassium Trichrome (III) Tetraphosphate K3Cr3(PO4)4: Synthèse, Étude Structurale, Caractérisation et Conductivité Ionique

The potassium chromium (III) phosphate K3Cr3(PO4)4 is prepared by a solid state reaction at 1173 K from a mixture of K2CO3, NH4H2PO4, and (NH4)Cr2O7. It is structurally characterized by single-crystal X-ray diffraction. It crystallizes in the Cmca (n°64) space group with a = 10.524(4) Åi, b = 20.466(6) Åi, c = 6.374(2) Åi, V = 1372.9(8) Åi3, Z = 4, R(F2) = 0.0452, and R W (F2) = 0.1184 for 790 reflections with I > 2σ(I). The structure consists of CrO6 octahedra and PO4 tetrahedra sharing corners and edges to form a two-dimensional framework. The K+ cations are located in the interlayer space. Conductivity measurement leads to σ = 47.32 10−5 Ω−1 m−1 at 729 K. K3Cr3(PO4)4 is a better ionic conductor than K3Cr3(AsO4)4 at the same temperature.

Synthesis of mesoporous chromium phosphate through an unconventional sol–gel route

Mesoporous chromium (III) phosphate has been synthesized first time using an unconventional sol–gel technique using inexpensive chromium source ammonium dichromate. In situ synthesized chromium (III), prepared through reduction of ammonium dichromate using ethanol and nitric acid, forms gel in presence of ammonium dihydrogen phosphate and urea at elevated temperature where tetradecyltrimethylammonium bromide (TTBr) is used as structure directing agent. High specific surface area of 384 m 2/g with narrow pore size distribution has been achieved after extracting the surfactants with ethanolic sodium acetate solution. EDS analysis shows that the Cr/P ratio is 1.05. The material was characterized by powder low angle X-ray diffraction (XRD), wide angle XRD, N 2 adsorption–desorption, HRTEM, FTIR, UV–visible and ESR spectroscopy. Wide-angle XRD patterns show the amorphous nature of the compound. UV–visible and ESR spectroscopic data shows the presence of octahedrally coordinated Cr 3+ solely.

NASICON-type Li2.5K0.16Na0.34Cr2(PO4)3

A new NASICON-type chromium(III) phosphate, K0.16Na0.34Li2.5Cr2(PO4)3, lithium sodium potassium dichrom­ate tris­(phosphate), has been prepared by solid-state reaction. It consists of CrO6 octa­hedra and PO4 tetra­hedra sharing corners to form a three-dimensional framework. The monovalent cations are located in the M1 (six-coordinate) and M2 (four-coordinate) sites of the framework. The M1 site is occupied by Na+ and K+ cations with 69 (3) and 31 (3)% occupancy, respectively. The Li+ ions, Li1 and Li2, are split over two M2 sites in general positions, with 60 (2) and 40 (2)% occupancy, respectively. Atom Li2 is disordered around a threefold inversion axis.

Investigation of phase formation temperature of nano-sized solid solution of copper/cobalt molybdate and chromium–phosphate (M 1xCr 1− xMo xP 1− xO 4) [M 1 = Co, Cu

A series of nano-sized metal–chromium–molybdenum–phosphorous (M 1 x Cr 1− x Mo x P 1− x O 4) [M 1 = Co, Cu] oxides solid solutions have been prepared having different percentage of the constituting transition metals from their precursors metal molybdates and chromium phosphate using organic complexing agent TEA (triethanolamine). The variations of phase separation temperature with respect to the amount of different constituents have been studied. The materials are efficient catalyst for reduction of p-nitrophenol to p-aminophenol by sodium borohydride.

Ion Exchange Sorption of Pb2+ Ions on CrPO4

The chromium(III) phosphate was observed to have a high affinity towards Pb2+ ion and the sorption capacities were found to be in the order: Pb2+ >Cu2+ >Cd2+ >Ni2+. Different characterization methods i.e. FTIR, SEM and EDX were employed to investigate the sorption mechanism of Pb2+ by chromium(III) phosphate, which showed that no new solid phases were present in the residue after sorption of Pb2+. The exchange between protons from the surface and Pb2+ from solutions was found to be responsible for Pb2+ sorption by chromium (III) phosphate.

Sorption of divalent metal ions on CrPO 4

The divalent metal ion sorption (Cu 2+, Cd 2+, Ni 2+, and Pb 2+) on chromium phosphate (CrPO 4) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb 3(PO 4) 2.

Study of the Chemical Conversion of Aluminum Alloys by Coupling CFDE and EQCM

The ability of the channel flow double electrode (CFDE) technique and electrochemical quartz crystal microbalance (EQCM) for studying in situ chromate phosphate conversion coating on 5182 aluminum alloys was explored. It was first demonstrated that aqueous Cr(VI) can be analyzed quantitatively with the CFDE technique by reduction into Cr(III) on a graphite electrode. Samples used for EQCM were quartz plated by physical vapor deposition using a 5182 alloy target, allowing thin layers of aluminum alloys with a similar chemical composition to be obtained. EQCM was adapted in order to account for the hydrodynamic conditions in an industrial process, by placing the quartz in a flow cell. In order to be able to control, and then study, the early stage of the coating, the aluminum electrode used for the CFDE technique was covered with a mask (a thin layer of varnish) that was removed in situ by a laser pulse. With EQCM the triggering of the coating was performed by injecting the required amount of hydrofluoric acid. Since the time duration of the transient responses was different in both techniques, we focused our discussion on the steady state. Measurements of the electroacoustic impedance of the aluminum-alloy-coated quartz in the conversion solution showed that the chromate phosphate film can be considered as acoustically thin, allowing the use of the Sauerbrey’s equation to calculate mass variations. Combining in the steady state the rate of mass variation measured by EQCM, and the rate of Cr(VI) reduction by CFDE as functions of the bath composition, it was possible to calculate a chemical yield for the film growth. The results in agreement with the literature indicate strong synergetic effect between chemical species present in the solution. © 2004 The Electrochemical Society. All rights reserved.

Thermochemical Study of Gaseous Salts of Oxygen-containing Acids: XIV. Barium and Chromium Phosphates

Gas-phase equilibria involving barium and chromium(II) phosphates were studied by high-temperature mass spectrometry. Standard enthalpies of formation and atomization of gaseous BaPO2, BaPO3, CrPO2, and CrPO3 were determined.

Cation-Exchange Properties of CrPO4

Alkali metal ion exchange (Li+, Na+ and K+) on chromium phosphate (CrPO4) was studied potentiometrically as a function of temperature and metal ion concentration. The shift in the potentiometric titration curves corresponding to the exchange of alkali metal cations increased with increasing pH and concentration of the metal ions, while the opposite results were obtained by increasing the temperature of the system. The affinity of the exchanger for alkali metal ions was also found to be in the order Li+ > Na+ > K+. The data were employed to evaluate the apparent deprotonation constants of CrPO4 and the corresponding thermodynamic parameters ΔH0, ΔS0 and ΔG0.

Effect of Phosphorus and Chromium Compounds on Thermooxidation of Polyvinyl Alcohol Fibres

It was shown that incorporation of chromium nitrate, diammonium hydrogenphosphate, and chromium phosphate enhances dehydration and cross-linking of the polymer. The pore volume in carbon fibre material can be regulated by adding inorganic salts.

Feasibility study to probe the growth of chromate based conversion on Al by means of rotating ring disc electrode (RRDE) measurements

The use of a rotating ring disc electrode (RRDE) is introduced in this paper to study the formation of chromate–phosphate layers on rolled aluminium surfaces. A RRDE was developed containing an Al disc, which was converted with a chromate phosphate film, and a carbon ring, where the Cr 6+ reduction rate was measured in situ. The principle of the method is that Cr 6+ is transported from the bulk of the solution towards the disc and the ring electrode. At the disc electrode, a fraction of Cr 6+ is consumed during the conversion of the Al disc electrode. This leads to a decrease in ring current, which is directly related to the amount of Cr 6+ being reduced at the disc electrode. For proper operation of the RDDE system, an electrode with optimised geometrical characteristics is used. In order to be sure that the measured current on the ring is in relation with the Cr 6+ reduction rate occurring at the aluminium disc, a number of requirements need to be fulfilled. After showing that the RDDE system is indeed able to monitor in situ the Cr 6+ content during conversion, the amount of Cr 6+ reduced at the disc electrode is calculated from the recorded ring current time curves. The method allows (i) to follow the growth of a conversion layer quantitatively in situ and (ii) to study the influence of important process parameters such as fluoride content, chromate content of the conversion bath and influence of mass transport.

On the effect of copper and nitrate ions on the stainless steel corrosion in phosphoric acid

Investigations were carried out in a 3 M phosphoric acid at a temperature of 98 ° C. The dependence of the corrosion rate of steel on potential was investigated on cylindrical specimens rotated at a speed of 610 rpm. Sodium nitrate and copper phosphate were used as inhibitors of corrosion. Hydrogen was blown through the solution during the experiment. It appears from the figure that, compared to pure phosphoric acid (curve 1 ), nitrate ions accelerate the corrosion of steel in its active dissolution range (curve 2 ), but shift the boundary of this range in negative direction, which should facilitate passivation. As to copper (II) ions, they lower the critical current of passivation (curve 3 ), which also favors making steel passive. Such an effect may be associated with the shielding effect of metallic copper, which is deposited at the electrode in this potential range. In spite of its loose structure, the copper layer hinders the diffusion of soluble corrosion products into the bulk of solution and contributes to the formation of a surface protective layer built of iron, nickel, and chromium phosphates because of exceeding their solubility near the electrode.

The effect of a conversion layer and organic coating on the electrochemical behavior of 8006 and 8079 aluminum alloys

The corrosion behavior of bare and chromate–phosphate treated aluminum alloys 8006 and 8079, employed for the production of heat exchangers, was investigated in aqueous aerated 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS). Experimental results indicate that bare 8079 alloy is less sensitive to corrosion in NaCl containing environments than bare 8006 alloy. This behavior was attributed to the lower content of metallic segregates in the 8079 alloy. For the bare samples, the chromate–phosphate treatment improves the corrosion resistance of both alloys; nevertheless their behavior is still dominated by alloy composition. The application of a polymeric coating, ranging from 5 to 7 μm, provided improved protection for the foils investigated during this study. The reliability of these coatings is however dominated by the application procedure and curing.

The Use of Infrared Spectroscopic Ellipsometry for the Thickness Determination and Molecular Characterization of Thin Films on Aluminum

Like reflection-absorption Fourier transform infrared spectroscopy, infrared spectroscopic ellipsometry (IRSE) is a nondestructive infrared reflection technique, which allows a chemical characterization of thin films on metals. However, the stronger absorptions of inorganic compounds in the spectra obtained with both techniques feature optically induced peak shifts that can lead to erroneous interpretations of the spectra. Since IRSE measurements contain information concerning the film thickness, which also determines the magnitude of the peak shifts, they can be corrected more easily using IRSE. This is illustrated in the present paper, which discusses the joint chemical characterization and thickness determination of thin anodic oxide films and chromium phosphate conversion films on aluminum by means of IRSE. Though the spectra of the anodic oxide films and those from the chromium phosphate conversion films feature vibrations of different types (longitudinal and transversal optical modes), the procedure for the interpretation of the spectra is applicable in both cases. © 2001 The Electrochemical Society. All rights reserved.

Thin film analysis of chromium-phosphate conversion coatings on aluminium probed by ToF-SIMS and electron probe x-ray analysis

Time-of-flight SIMS was used to study chromium phosphate conversion layers on Al. During coating formation, fluorine is buried under a layer of CrPxOy as the layer thickens, yielding a duplex layer structure. Electron probe x-ray microanalysis was used to assess the variation in elemental composition of the coating. Preliminary results demonstrate a number of problems related to quantitative analysis of the coatings studied. Copyright @ 2000 John Wiley & Sons, Ltd.