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Activation of dinitrogen (N2) by well-defined metal hydrides is of much interest and importance, but studies in this area have remained limited to date. We report here N2 activation and hydrogenati...

The reaction of dinuclear chromium hydride [(2,6-Me2Ph)2nacnacCr(µ-H)]2 ((2,6-Me2Ph)2nacnac = N,N′-bis(2,6-dimethylphenyl)-2,4-pentanediiminato) with trimethylsilyl-diazomethane did not yield the desired, known alkyl hydride [(2,6-Me2Ph)2nacnacCr]2(μ-H)(μ-CH2SiMe3). Rather, it resulted in an unexpected mixture of novel chromium complexes, which have been structurally characterized. They include macrocyclic dinitrogen complexes, namely [(2,6-Me2Ph)2nacnacCr(THF)(µ-N2)]3 (4) and [(2,6-Me2Ph)2nacnacCr(µ-N2)]4 (5). Other products containing various fragments of the diazo-reagent were [(2,6-Me2Ph)2nacnacCr]2(µ-N)(µ-H) (6), [(2,6-Me2Ph)2nacnacCr]2(µ-NSiMe3)(µ-H) (7) and [(2,6-Me2Ph)2nacnacCr]2(µ-N CH2)(µ-NH) (8). An analogous reaction of the sterically more encumbered [(2,6-iPr2Ph)2nacnacCr(µ-H)]2 ((2,6-Me2Ph)2nacnac = N,N′-bis(2,6-diisopropylphenyl)-2,4-pentanediiminato) produced [(2,6-iPr2Ph)2nacnacCr(µ-N)(µ-N(H)NC(H)SiMe3)]2 (9).

It is shown that, for the development of new chrome-plating technologies, it is necessary to proceed from the complicated Cr(III) chemistry. The analysis of the complexation processes of Cr(III) with hydroxycarboxylic acids in aqueous solutions is given. The results of investigations of deposition processes of chromium coatings from sulfate, oxalate–sulfate, and formate–glycine electrolytes are presented. Thin chromium films, as well as chromium films alloyed with cobalt, are obtained from formate–glycine electrolyte. With the use of atomic-force microscopy, it is shown that the formed chromium films are bright and possess a nanocrystalline structure and codeposition of chromium and cobalt leads to the formation of a more uniform structure.

Developing a functional Cr(III) electrolyte to replace carcinogenic and toxic Cr(VI) electroplating requires a deeper understanding of the deposition mechanisms. Hence, this study investigates and compares the growth of chromium on inert glassy carbon (GC) electrodes from low-concentration Cr(III) and Cr(VI) electrolytes, using a novel potentiodynamic deposition scheme. This allows the initial stages of deposition to be probed, which are crucial for determining the overall deposition mechanism. Scanning electron microscopy shows that, for both systems, micrometer-sized hexagonal chromium hydride crystals could be deposited on GC, thus serving to be the first reporting of such structures. In addition, by increasing the deposition time, the changes in a particle structure for both systems were tracked; therefore, possible areas of similarity as well as key differences could be identified, which, when addressed may provide a more viable, environmentally friendly trivalent electrolyte for chromium electroplating.

Four nanocomposites containing mixed phases of Co 3 Mo 3 N and Co 2 Mo 3 N doped with chromium have been prepared. A linear fit is found for relation between Co 2 Mo 3 N and chromium concentrations. The magnetization in ZFC and FC modes at different temperatures (2–300 K) and in applied magnetic fields (up to 70 kOe) have been investigated. It has been detected that many magnetic characteristics of the studied four nanocomposites correlate not with the chromium concentration but with nanocrystallite sizes. The obtained results were interpreted in terms of magnetic core-shell model of a nanoparticle involving paramagnetic core with two magnetic sublattices and a ferromagnetic shell related to chromium doping.

This paper presents a detailed study of the formation of chromium-based alloys, Cr–Ta–W + plasticizing additives (Nb and Zr) and Cr–Ta–Si, during milling of powder mixtures in a Fritsch (P-7) planetary mill under an Ar atmosphere. It is shown that, after milling for 18 h, all the components of the starting mixtures convert into a Cr-based BCC solid solution. The powders of chromium alloys obtained in this study are readily compacted by hot isostatic pressing (HIP) under conditions typical of the processing of powders of high-temperature nickel alloys. Heating of the powders and compacts leads to the decomposition of the supersaturated solid solution and the formation of two forms of the Cr2M Laves phase with cubic crystal lattices. The formation of a mixed-phase fine microstructure in the chromium alloys after HIP suggests that the materials studied here are potentially attractive as a base of next-generation chromium-based high-temperature alloys.

Purpose. This article a nalyzes the formation conditions, transformation and systematization of carbide phases formed in the system Fe – C – Cr. Methodology. Conversion of the elements’ content from mass % into atomic % and vice versa was carried out using standard methods. In order to identify the structural components and etching of carbides the Marble etchant was applied. Cast iron 300Х28Н2 in cast state without heat treatment and after isothermal holding at 1050 °С during 4.5 hours with further normalization was studied. Findings. Isothermal state diagrams of the Fe–C–Cr system don’t take into account the existence of Fe 7 C 3 carbide alloyed with chromium. But there is evidence of the existence of chromic carbides containing 24…37.6 % of chromium, which exceeds its maximum solubility in cementite, but is not enough to form Cr 7 C 3 . Analysis of chromium and carbon content in carbide phases which are formed in high-chromium cast irons allowed to substantiate the formation of Fe 7 С 3 carbide, stabilized with chromium. Assessment of the carbide phase by chemical composition in mass percent doesn’t allow determining the main carbide-forming element with sufficient accuracy. It is shown that with the increase of chromium concentration in carbides, mass content of carbon increases. Areas of existence of carbides of different types depending on carbon and chromium content in them were determined. Maximum content of chromium in the carbide (Fe, Cr) 7 C 3 is 44.0 %. Allocation of alloyed cementite occurs on the present carbides Ме 7 C 3 or grain boundaries, and with the increase of cooling rate – in the grain volume. This process is thermodynamically inevitable due to the decrease of carbon solubility in ferrite or austenite at temperatures when chromium diffusion is impeded, and only carbon diffusion is possible. At high chromium concentrations carbide Fe 7 C 3 is formed, which transforms into Cr 7 C 3 carbide as chromium diffusion takes place. Originality. The model of laminated structure of carbides, formed out of the liquid phase in the system Fe–C–Cr was built. The identification of the carbide phase based on the elements’ concentration in atomic percent was suggested. The model of the change of carbon content in carbides of different types depending on chromium concentration was built. Practical value. The suggested system of carbide classification and their structural model allows optimizing the cast irons’ composition and heat treatment modes for different exploitation conditions.

In the present study, the evolution of hexavalent chromium evolution in a trivalent chromium conversion coating has been investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. In terms of Raman spectroscopy, the presence of CrF3 in the coating (538-540 cm(-1)) generates an overlapped shift with the trivalent chromium hydroxide and oxide (536-550 cm(-1)). For the hexavalent chromium (845-866 cm(-1)) reactivity, post-treatment in sodium sulfite solution was revealed to be an effective process to eliminate Cr(VI) species on the coating surface. However, the diffusion kinetics of sulfite ions into the coating inner layer were found to become a limiting factor. The Raman peak intensity of hexavalent chromium in the air aged coating for 24 h revealed a significant decrease compared to that in the freshly-formed coating after the same conversion treatment process. This was attributed to Cr (VI) degradation at the base of coating cracks as evidenced by scanning electron and atomic force micrographs. Interestingly, 3.5 wt% NaCl droplets induced the trivalent chromium oxidation in the air-aged coating specimen, as evidenced by Raman peak at 845 cm(-1). For this reason, the oxygen in the corrosive electrolyte caused the oxidation of trivalent chromium species; the electrolyte might play a role in coating degradation, which, in turn, permits an increase of oxygen ingress. The hexavalent chromium in the freshly-formed, air-aged and corroded trivalent chromium conversion coating on aluminum is an environmental concern for its application. (C) 2016 The Electrochemical Society. All rights reserved.

The spectral-luminescent properties of potassium-aluminoborate glass activated by trivalent chromium ions and subjected to thermal treatment at various temperature and duration regimes are studied. The X-ray-phase studies have shown that by thermal treatment of such potassium-aluminoborate glass a crystalline phase of Al2O3: Cr is evolved. The embedding of chromium ions into the crystalline phase causes changes in the absorption and luminescence spectra.

Effects of chromium additions on the microstructure, ordered phase and magnetic properties of the Fe-6.5 wt.% Si alloy fabricated by hot-rolling and warm-rolling were investigated. The results showed that the additions of chromium reduced the grain size of the alloy effectively, and the dislocation density was reduced with the increasing of the chromium content. The amount of ordered phase was reduced in the alloy with the chromium content of 1.0wt%. The magnetic properties of the alloy with chromium were not deteriorated.

The paper reviews black chromium electrodeposited from a trivalent chromium bath containing ZnO as a second main component. The chemical compositions of the top layers of the black chromium coatings were studied by the X-ray photoelectron spectroscopy method. The surface of black chromium was found to be almost entirely covered with organic substances. To gain information on the state of each element in the deposit bulk, the layer-by-layer etching of the black chromium surface with argon gas was used. Analysis of XPS spectra has shown that the top layers of black chromium without zinc are composed of various Cr(III) components, organic substances and metallic Cr, whereas metallic Cr is almost absent in black chromium containing some amount of Zn(II) compounds. The ratios of metal/oxide phases were found to be 10/27 and 2/28 for black chromium without and with zinc, respectively. It has been determined that owing to the presence of ZnO in the Cr(III) bath, the percentage of metallic chromium is substantially reduced in black chromium which is quite important for good solar selective characteristics of the coating. The results confirm some of earlier observations and provide new information on the composition of the near-surface layers.

Laser short-pulse treatment of ultradispersed powdered chromium(III) oxide supported on the surface of steel 20 was used to obtain nanosize surface layers containing chromium and iron oxides dispersed in α- and γ-iron, as well as mixed oxides with a FeO · Cr2O3 spinel structure. Reduced metallic chromium is also found. Measurement of anodic potentiodynamic curves in neutral and weakly basic borate buffer solutions shows that the formed surface layers promote enhancement of corrosion stability of steel due to transition of the surface into a passive state.

The structure of deuterides based on V0.9Cr0.1 and V0.5Cr0.5 alloys has been investigated by neutron diffraction at room and low (77 K) temperatures. It is found that V0.9Cr0.1D2.0 deuteride has a CaF2 (Fm3m) crystal structure, which corresponds to vanadium dihydride. V0.5Cr0.5D0.7 deuteride has a NiAs (P6/3 mmc) structure type, similar to chromium hydride.

Information regarding the influence of alloying elements and impurities on the properties of chromium and its alloys and methods of producing such alloys is reviewed. The physical and physicochemical principles for the production of dispersely strengthened alloys are considered in detail. The strengthening of disperse particles on heating and holding the metal (Ostwald ripening) is discussed. These processes are associated with decrease in the excess Gibbs free energy. The need for thermodynamic assessment of those processes is established.

Three different synthetic routes to chromium nitrides were investigated using in situ neutron diffraction (SPODI, FRM-II) and thermal analysis in ammonia: (i) The direct conversion of chromium powder in ammonia, (ii) the ammonolysis of chromium(III) chloride CrCl3, and (iii) the ammonolysis of chromium(III) sulfide Cr2S3. During the direct conversion of chromium first γ-CrN was formed above 385 °C, above 567 °C additionally β-Cr2N was detected. Finally, a complete conversion of γ-CrN to β-Cr2N was observed at 1080 °C. The ammonolysis of chromium(III) compounds (CrCl3 and Cr2S3) revealed a so far in 3d metal nitride synthesis unprecedented redox sequence: The compounds are reduced to chromium(II) chloride CrCl2 and chromium(II, III) sulfide Cr3S4, respectively, prior to the reoxidation of those intermediates to γ-CrN. In contrast to the ammonolysis of 3d metal(II) halides, for chromium(III) chloride no temporary formation of ammoniates was observed. Since formation of γ-CrN was detected only after annealing chromium(III) sulfide in flowing ammonia for 4 h to 5 h at maximum temperature, the formation of sufficient amounts of chromium(II, III) sulfide as the rate-determining step for the nitride formation appears likely.

Almost all of the currently achievable chromium coatings using Cr(III) electrolytes are amorphous. In this work, a crystalline chromium coating with an attractive appearance was produced on Cu substrates. This was achieved using direct current (DC) electrodepositing of a wholly environmentally acceptable sulfate Cr(III) electrolyte without a subsequent heat treatment. Structural characterization revealed that the crystalline chromium coating deposited at 5 A/dm 2 from the electrolyte solution is composed of body-centered cubic (bcc) Cr crystals, which demonstrated significant preferred orientation and a size range of 50–60 nm. The results also show that, in general, the color and luster of the chromium coating are greatly affected by the current density employed, and the larger the current density is, the dimmer the coating.

The paper examines the influence of sintering temperature in the range 1150–1300°C on interaction of chromium carbide Cr3C2 and a Kh13M2 steel matrix. It is shown that molybdenum actively participates in the interaction process, which leads to the formation of M7C3, M23C6, and M3C carbides even at 1150°C.

Chromium(II) chloride reacts with lithium pentamethylcyclopentadienide (LiCp*, Cp* = C5Me5) and LiE(SiMe3)2 (E = P or As) to give the heterocubane chromium phosphide [(η5-Cp*Cr)(μ3-P)]4 (1) or the chromium arsenide cage [(η5-Cp*Cr)3(μ3-As)2] (2), respectively. The crystal and molecular structures of both compounds have been determined by X-ray crystallography. The reactions represent unusual oxidative additions of pnictogen atoms to chromium(II), which in the case of 1 results in the formation of the unusual chromium(IV) formal oxidation state, and in the case of 2 provides access to chromium(III). Compound 1 is also a rare example of a transition metal μ3-phosphide-ligated cubane. Magnetic susceptibility and magnetization measurements, with support from DFT calculations, indicate S = 2 and S = 9/2 ground states for 1 and 2, respectively, which can be rationalized by considering the electronic structure in terms of chromium–chromium bonding.

The transformations in nanosized chromium layers at different layer thicknesses (d = 14–154 nm) and thermal treatment temperatures (T = 673–873 K) were studied by optical spectroscopy, microscopy, and gravimetry. The kinetic curves of conversion at different chromium film thicknesses and treatment temperatures are well approximated by the linear, inverse logarithmic, cubic, and logarithmic functions. The contact potential difference for Cr and Cr2O3 films and photo-emf for Cr-Cr2O3 systems were measured. An energy band diagram of Cr-Cr2O3 systems was constructed. A model of thermal transformation was constructed for Cr films that included the stages of oxygen adsorption, charge carrier redistribution in the contact field of Cr-Cr2O3, and chromium(III) oxide formation.

Changes of microstructure, chemical and phase compositions in thin surface layers of low carbon steel saturated by chromium oxide have been studied by TEM, XPS and XRD methods. Ultrafine chromium oxide powder was spread on a steel surface and subjected to laser processing with nanosecond pulses. It was found that such conditions of processing as overheating of small volume of metal, high temperature gradient, rapid solidification and laser-induced plasma formation lead to dissolution of chromium oxide in the metal matrix. As a result of laser processing the surface layers contain chromium oxide, chrome-spinel FeO $$\cdot $$ Cr $$_{2}$$ O $$_{3}$$ and chromium in metal state dispersed in alpha and gamma iron. The processing technique allows to obtain surface layers whose chemical composition might be equivalent to the composition of stainless steels.

The regularities of the formation of a solid solution in a Ni-Cr(20 at %) system are studied using X-ray diffraction, optical microscopy, and particle-size distribution analysis within the framework of an energetical approach to the analysis of the kinetics of mechanochemical synthesis. It is established that the curves of the consumption of chromium atoms and the formation of the reaction product (a solid solution of chromium in nickel) coincide with each other. The rate-limiting step of the reaction is the formation of a contact surface between chromium and nickel, while the “stirring” of chromium atoms in nickel matrix has a very high rate. The rate of the formation of the contact surface in the mixture of brittle chromium and plastic nickel is determined by the rate of chromium particle disintegration. To a conversion of about 60%, the reaction kinetics is described by a quadratic dependence on the dose (D) of the mechanical treatment (N ∼ D 2).

Mossbauer spectroscopy and X-ray diffraction analysis have been used to study mechanical solidstate alloying with nitrogen and chromium of iron and an Fe-3Al alloy in the process of the mechanical activation with chromium nitrides in a ball mill. It is shown that the deformation-induced dissolution of chromium nitrides in iron and Fe-3Al matrices results in the formation of substitutional chromium and interstitial nitrogen solid solutions. The alloying of iron with aluminum accelerates the process of the deformation-induced dissolution of chromium nitrides, but reduces the nitrogen content in the interstitial solid solution. Post-deformation annealing generally leads to the escape of aluminum from the matrix, the substitution of chromium for aluminum, and the formation of fine nitrides AlN.

Inner crack behavior of electro-deposited trivalent chromium was analyzed in-situ by small angle neutron scattering to study the abrasive heating effect on neutral salt fog spray life. The trivalent chromium was prepared by different current wave forms, namely, direct and pulse current-plating with a modified chromium chloride bath. The trivalent chromium layer has columnar grains in which small chromium clusters and inner cracks are present. Pulse current plated trivalent chromium has a longer neutral salt fog spray life than direct current plated trivalent chromium. As surface temperature increases to 80 °C, inner cracks of the trivalent chromium layer formed by direct current plating tend to have a fractal shape by opening crack tips, whereas those of the chromium layer formed by pulse current plating are relatively stable. The inner crack with a fractal shape is related to an abrupt reduction of the neutral salt fog spray life of the trivalent chromium.

In this study, pressureless sintering of silicon nitride via the addition of chromium oxide was investigated. Silicon nitride samples containing additives from the Cr–Cr2O3–SiO2 system were sintered under different conditions. The phase transformation, the degree of densification and the in situ reactions between Si3N4 and chromium compounds were investigated and the reactions were validated thermodynamically. It was found that Si3N4 reacts with Cr2O3 and Cr and these in situ reactions lead to Si3N4 decomposition and consequently formation of a series of chromium silicides including Cr3Si, Cr5Si, and CrSi2. Due to the presence of chromium silicides as liquid phases during sintering, the α-Si3N4 to β-Si3N4 phase transformation started around 1400°C and was completed around 1800°C. On the other hand, densification of Si3N4 samples with chromium oxide addition was not observed. The participation of Cr2O3 in these in situ reactions prevents sufficient formation of chromium silicate and leads to insufficient liquid phase with poor wettability during sintering, resulting in poor densification.

Microstructure consisting of twins domains of recovered Cr-doped CaCl 2 type TiO 2 grains synthesised at high pressure.► Chromium solubility in TiO 2 increases at high pressure. ► Chromium occupies substitutional and interstitial positions in the rutile structure. ► Interstitial chromium causes a decrease of the rutile symmetry. ► An orthorhombic CaCl 2 type structure is observed in the quenched samples.

The color of the decorative chromium coatings electrodeposited from trivalent chromium electrolytes containing formic acid or formate is usually darker than that from conventional hexavalent chromium electrolytes. For the purpose of clarifying the reason for this situation, X-ray diffraction (XRD), selected area electron diffraction (SAED), electron probe microanalyzer (EPMA) and high-resolution transmission electron microscopy (HRTEM) were employed to investigate the phases and fine microstructure of the typical decorative chromium coating produced from a typical trivalent chromium electrolyte containing formic acid. The results show that the coating is amorphous embedded with the nanocrystals of graphite, Cr 23 C 6 and body-centered cubic structure chromium (bcc Cr). The presence of the nanocrystal graphite with strong infrared emission performance is the main reason for the darker color of the coating.

The influence of chromium cast iron Cr8 treatment by Fe-45Si-6Mg-0,5REM modifier on the structure, phase transformation and heat resistance was studied experimentally.It is demonstrated that during modifying of chromium cast iron Cr8 the alloying effect takes place. The initial cast iron structure which consists of alloyed ferrite, carbide (Cr,Fe)7C3 and cementite (Fe,Cr)3C is transformed as in the process of chromium alloying according to modifier consumption increase. At the modifier consumption of 0,15 % the mass quota of cementite (Fe,Cr)3C decreases from 3,2 % to zero, and the mass quota of carbide (Cr,Fe)7C3 increases from 20 % up to 30 %.

The possibility was studied for synthesizing chromium oxide structures on the surface of K3–6 granular silicon carbide [GOST(State Standard 26327-84)] by its multiple successive treatment with chromium(VI) oxochloride, ethyl alcohol, and water vapors. The change in the chromium concentration in the modified samples was studied as a function of the number of successive treatment cycles. The samples were characterized by the X-ray phase analysis, X-ray photoelectron, IR, and electronic diffuse reflectance spectroscopies before and after the modification.

Porous chromium carbide structures have been synthesized through reactive sintering of chromium oxides in carbonaceous reducing environments. The process is simple and can be used to fabricate large size porous structures. It has been characterized that the pores in the porous structure are open in nature and the size of pores in the same porous structure can be controlled within a narrow range. Depending on the processing condition, the porosity in the porous structure was measured to be from 50% to 78%, and pore size varied from 0.5 μm to 3 μm. It has been determined that the porosity in the process was formed primarily due to volume reduction caused by phase transformation from chromium oxides to chromium carbides. It is believed that similar process can be used to form porous structures of other materials as long as a reactive sintering can occur and is accompanied with volume reduction.

The feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature. A binary Co-10Cr alloy, two ternary Co-10Cr-0.5C and Co-10Cr-1.0C alloys and two TaC-containing Co-10Cr-based alloys were elaborated by foundry for the study. 7.5h-long and 15h-long cementations at 1050°C, followed or not by a 75h-long heat treatment at 1200°C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis-Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Cr-enriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co-10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30wt.%Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation.

Thermodynamic interaction of chromium on aluminum in liquid Fe–Cr–Al alloys was studied by measuring the effect of chromium on the solubility product of AlN in liquid Fe–Cr–Al–N alloys containing chromium up to 26 mass% by the metal–nitride–gas equilibration technique in the temperature range from 1873 to 1973 K. Aluminum nitride formed in the melt was identified as a pure solid stoichiometric AlN. As the chromium content increases in the melt saturated with AlN, the critical nitrogen solubility increases significantly, while the aluminum solubility decreases. Using Wagner's formalism, the present results were thermodynamically analyzed to determine the first- and the second-order interaction parameters between chromium and aluminum given as follows:eAlCr = 0.0122±0.00028 rAlCr = 0 (1873−1973 K, Cr≤26 mass%)

Numerous chromia-forming austenitic steels and nickel-base alloys contain chromium-rich strengthening precipitates, e.g. chromium-base carbides. During high temperature exposure the formation of the chromia base oxide scale results in chromium depletion in the alloy matrix and consequently in dissolution of the strengthening phase in the sub-surface zone. The present study describes the oxidation induced phase changes in the chromium depletion layer in case of alloy 625, a nickel base alloy in which the strengthening precipitates contain hardly any or only minor amounts of chromium. Specimens of alloy 625 were subjected to oxidation up to 1000 h at 900 and 1000 °C and analyzed in respect to oxide formation and microstructural changes using light optical microscopy, scanning electron microscopy, energy and wavelength dispersive analysis, glow discharge optical emission spectroscopy, and X-ray diffraction. In spite of the fact that the alloy precipitates δ-Ni3Nb and/or (Ni, Mo)6C contain only minor amounts of chromium, the oxidation induced chromium depletion results in formation of a wide sub-surface zone in which the precipitate phases are depleted. However, in parallel, substantial niobium diffusion occurs towards the alloy surface resulting in formation of a thin layer of δ-Ni3Nb phase adjacent to the alloy/oxide interface. By modeling phase equilibria and diffusion processes using Thermo-Calc and DICTRA it could be shown that the phase changes in the sub-scale zone are governed by the influence of alloy matrix chromium concentration on the thermodynamic activities of the other alloying elements, mainly niobium and carbon. The δ-phase depletion/enrichment process is caused by a decreasing niobium activity with decreasing chromium concentration whereas the (Ni,Mo)6C dissolution finds its cause in the increasing carbon activity with decreasing chromium content.

Amorphous chromium coatings were electrodeposited from Cr(III)-based solutions containing organic (HCOONa) or phosphorus-containing (NaH 2 PO 2 ) additives. Their structure was studied by a combination of X-ray diffraction (XRD), valence-to-core X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) at the Cr K-edge. Metalloid atoms (C or P) incorporated in electroplates structure are chemically bonded to chromium (i.e. are located in the first coordination shell). Upon annealing at elevated temperatures in vacuum, these amorphous coatings crystallize into a mixture of phases containing metallic chromium and chromium carbides or chromium phosphides. Quantitative analysis of valence-to-core XES data demonstrates that the average local structure of chromium in the amorphous coatings does not change significantly during crystallization.

The influence of chromium (0.5-8 at.%) on the oxidation resistance of binary Ti and Zr alloys at 500–700°C and 50 h holding is investigated. It is shown that the oxidation of these alloys is described by a parabolic-law function at 500–600°C and a linear function at 700°C. It is established that 8 at.% Cr decreases the high-temperature oxidation resistance of titanium by 50–67%, but the chromium content up to 4 at.% hardly influences that of zirconium. Higher chromium concentrations also decrease the oxidation resistance. The results for titanium are attributed to specific chemical interaction of titanium and zirconium oxides and for zirconium to the structural factor associated with the formation of brittle ZrCr2 intermetallide.

We synthesize Cr x Ti 1− x Se 2 ( x = 0–0.83) and Cr x Ti 1− x S 2 ( x = 0.3–0.4) systems and study the structure of these materials on mono- and polycrystalline samples. It appeared that an increase in chromium content leads to inversion of titanium diselenide intercalated with chromium to chromium diselenide intercalated with titanium. The XPS of core levels and valence bands of 1T-Cr x Ti 1− x Se 2 and Cr x Ti 1− x S 2 was also investigated and it was shown that in in-layer and inter-layer positions the atoms of chromium and titanium are characterized by a slightly differing oxidation state. Chromium LDOS model calculations were carried out and the results being in agreement with the experimental data show that the Cr 3d density of electronic states of chromium in Ti-positions in the host lattice displays half-metallic properties, while the Cr 3d density of electronic states of intercalated chromium is far from being half-metallic.

The electrodeposition of black chromium coatings from ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with chromium chloride, and the chemical composition of the deposits are discussed in this article. The UV–Vis spectra recorded for chromium(III) species in 1-butyl-3-methylimidazolium tetrafluoroborate suggest that along with the chromium(III) complexes containing three ligands, there are some amounts of chromium species containing four ligands in the bath employed. The cathodic process of chromium electrodeposition in the employed ionic liquid is complicated by the electrochemical reduction of water molecules, which is followed by chemical disintegration of tetrafluoroborate ions. The surface morphology of black chromium films deposited potentiostatically (–1.5 to −2.0 V) at 85 °C shows nodules and microcracks increasing in size with cathodic potential. Analysis of the X-ray photoelectron spectra recorded from surface to depth of the deposit has shown that the black oxide-rich chromium coating consists of chromium in both oxide and metallic states with small impurities of other elements (fluorine, boron, carbon and nitrogen) and the surface is covered with a thin layer of organic substances. The results of this study show that 1-butyl-3-methylimidazolium tetrafluoroborate may be considered as a promising substitute of toxic Cr(VI) baths for black chromium plating.

Two chromium-doped Raney nickel catalysts have been prepared from Al-Ni-Cr alloys where Cr was introduced in such a way as to substitute for nickel in the Ni2Al3 intermetallic phase. In comparison with the undoped catalysts, the BET and metallic surface areas remain little affected but more aluminium is retained after etching. X.P.S. shows that aluminium and nickel are in the metallic state whereas chromium is completely oxidized. Very large amounts of chromium are found on the surface, which suggests migration of chromium to the surface during leaching. Analytical electron microscopy indicates that the local chromium concentration is not perfectly uniform. Electron probe microanalysis of the precursor alloy reveals the segregation of part of chromium in a separate phase. These results are evaluated in the framework of the available literature data on the microstructure of Raney nickel catalysts.

Dense palladium membrane on oxidized porous stainless steel (oxPSS) tube was prepared. Its hydrogen permeance was observed to decline at the temperature higher than 400 °C. SEM–EDX analysis of the cross-section of the annealed tube at 500 °C indicated the occurrence of the intermetallic diffusion. The heat treatment study of the palladium membrane on oxPSS disks in hydrogen atmosphere at various temperatures was essentially carried out. Their SEM–EDX analysis results confirmed that the in situ metal oxide barrier could not inhibit the intermetallic diffusion in hydrogen atmosphere. The chromium oxide layers at different thicknesses were then developed on oxPSS disks before palladium plating by controlled chromium elctrodeposition followed by oxidation in air at 700 °C. The similar heat treatment study and SEM–EDX analysis of these disks revealed that the presence of chromium oxide layer could suppress the intermetallic diffusion. Then, the dense palladium membrane tube with chromium oxide layer was prepared and its heat treatment in hydrogen atmosphere was studied. The result showed the steady increase in hydrogen permeance with increasing temperature.

Oxidation resistance and tribological properties of SHS-produced chromium sulfide have been explored. The material was oxidized up to 5 to 7 μm thick from its surface upon heat treatment at 1000°C for a short time. It also exhibited a unique compositional change in sulfur and chromium at the interface between matrix and oxide layer formed during heat treatment. Meanwhile, the synthesized material showed the coefficient of kinetic friction of below 0.18, which is an acceptable value for a solid lubricant. Although the friction coefficient of CrS was initially low, it was found to grow upon high-temperature oxidation of the CrS surface. This fluctuation in the tribological property seems to depend on both the crystal structures of chromium sulfide and chromium oxide and of the interface between the oxide and matrix.

The microstructure of the chromium nitride layer formed on 316L Stainless Steel (SS) by electroplating Cr and subsequent thermal nitriding was investigated by electron microscopy. Thermal nitriding was carried out at a nitrogen partial pressure of 100 torr at 1100 °C for 2 h. The X-ray Diffraction (XRD) patterns showed that the structure of electroplated chromium was not crystalline and that the nitrided layer was composed of only hexagonal Cr2N phase nitride. The nitride layer showed uniform and columnar-shaped grains of chromium nitride and contained many micro-pores that may have formed due to the volume difference between the amorphous chromium and the crystalline chromium nitride. Chromium oxide was also observed in the nitride layer. It was discovered that the number of micro-pores and oxide particles needs to be decreased in order to improve the interfacial contact resistance.

The oxidation and nitridation of pure chromium and of chromium alloys containing 0.5 to 5at% silicon was investigated at 1300°C in several atmospheres. Global methods like thermogravimetry were associated to thickness measurements and microstructural characterisation to evaluate oxidation mechanisms. The contribution of nitridation to weight gain during high temperature exposure is discussed, examining nitride volume fraction. Experiments demonstrate that the presence of nitrogen in the substrate is always consecutive to a breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer. Silicon, when present in chromium solid solution, slows down the oxidation kinetics and limits the progression of nitrogen in the chromium lattice and at grain boundaries. The absence of the Cr2N layer beneath the metal/oxide interface does not benefit to the adherence of the oxide scale. Oxidation of silicon in chromium leads to the formation of discontinuous particles of SiO2 at the metal/oxide interface, at the grain boundaries and dispersed in the bulk in the alloy sub-surface.

Using ab initio methods, the influence of chromium on the electron structure and magnetic properties of cementite Fe3C has been investigated depending on the chromium concentration and the possibility of the formation of a chromium carbide Cr3C has been considered. It has been established that it is the general positions of iron in the lattice of cementite that are most energetically preferable for the substitution by chromium. Chromium leads to a strengthening of interatomic interactions and the change in the sign of the enthalpy of formation in the Fe3 − xCrxC system at x = 1.9. The magnetic moments at the atoms of chromium and iron are oriented antiferromagnetically and the total magnetization of the alloyed system decreases with increasing chromium concentration.

Fe Cr P amorphous alloys were electrodeposited in a trivalent chromium sulfate electrolyte containing glycine as complexing agent. The effects of bath composition and electrodeposition parameters such as current density, bath pH and plating time on the structure, morphology and composition of the amorphous Fe Cr P deposits were investigated. The optimum bath composition and electrodeposition parameters were obtained using glycine as complexing agents. It showed that glycine is a suitable complexing agent to get good quality of Fe Cr P amorphous alloys by trivalent chromium electrodeposition. The obtained Fe Cr P deposits were characterized by means of SEM, EDS, XRD as well as XPS techniques. It was observed that the chromium content in the deposits increased with increasing the cathodic current density. When current density exceeds specific value, the chromium content in the deposit would decrease. SEM results show that fine-grain, smooth and compact Fe Cr P alloy deposits were obtained. Results of EDS and XPS indicate that the deposited alloys contain chromium, iron, phosphorus, nitrogen, oxygen and carbon. The XRD pattern reveals that the Fe Cr P alloy deposit has amorphous structure. These results may be of some practical and theoretical significance for further improving chromium alloy electrodeposition process.