Partial Substitution Of Cr Research Articles

The origin of coercivity enhancement in the Co77Zr18Cr3B2 magnet

The effects of a partial substitution of Cr for Co on the magnetic properties of Co80Zr18B2 alloy are investigated in this paper. An appropriate addition of Cr can improve the coercivity (iHc) significantly. The maximum iHc of 7.0 kOe is obtained in the melt-spun Co77Zr18Cr3B2 after annealed at 550°C. X-ray diffraction (XRD) and thermomagnetic analysis (TMA) are employed to determine the phase composition. It is found that the sample is comprised of the single Co11Zr2 which is responsible for the magnetic hardness. The Cr atoms enter into the lattice of Co11Zr2 and increase the magnetocrystalline anisotropy field (Ha). SEM investigations show a microstructure consisting of equiaxed grains whose average size is about 300–350nm. The origin of coercivity enhancement in Co77Zr18Cr3B2 is ascribed to the increase in Ha.

Characterization of low-temperature synthesized FeCr0.05Se superconductors

Polycrystalline samples of FeCr0.05Se were synthesized by solid-state reaction using the two-step sintering method to study the effects of various low temperatures on the microstructure and superconductivity in this system. These synthesis temperatures have been established by optimization. Electrical resistivity measurements confirmed that superconducting transition temperature Tconset reached a maximum of 10.2K at 450°C as β-FeSe phase content reached the maximum under this condition. As the sintering temperature increased, the partial substitution of Cr by Fe caused an enhancement of lattice parameters, and consequently Tconset was much higher at 550°C than at 400°C, though the amounts of β-FeSe were appropriately the same in these two samples.

Carbon dioxide reforming of methane to synthesis gas over LaNi1−x Cr x O3 perovskite catalysts

Carbon dioxide reforming of methane was investigated over LaNi1−xCrxO3 perovskite catalysts which were prepared by the malic acid method. The respective perovskite catalysts were a single phase of perovskite oxide without impurity phases. Their reduction behavior was characterized by temperature programmed reduction. In the LaNi1−xCrxO3 perovskite catalysts, the catalytic activities were closely related to the reduction behavior of the catalysts, and the partial substitution of Cr to the B-site of perovskite catalysts promoted stability against reduction. When the x values were lower than 0.4, the LaNi1−xCrxO3 perovskite catalysts were decomposed to La2O3 and Ni and the decomposition of perovskite structure led to large coke deposition. When the x values were higher than 0.4, the LaNi1−xCrxO3 perovskite catalysts showed reduced catalytic activity but became stable to reduction and coke formation in the reforming reaction.

Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets

Four cermets of composition TiC–10TiN–16Mo–6.5WC–0.8C–0.6Cr 3C 2–(32 − x)Ni– xCr ( x = 0, 3.2, 6.4 and 9.6 wt%) were prepared, to investigate the effect of the partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets. The partial substitution of Cr for Ni decreased full densification temperature, and the higher the content of Cr additive was, the lower full densification temperature was. The partial substitution of Cr for Ni had no significant effect of the formation of Mo 2C and Ti(C,N) and the dissolution of WC, and however, it had a significant effect on the dissolution of Mo 2C. Cr in Ni-based binder phase diffused into undissolved Mo 2C to form (Mo,Cr) 2C above 1000 °C at 6.4–9.6 wt% Cr additive, and a small amount of (Mo,Cr) 2C did not dissolve after sintering at 1410 °C for 1 h at 9.6 wt% Cr additive. In the final microstructure, Cr content in Ni-based binder phase increased with increasing the content of Cr additive, and however, regardless of the content of Cr additive, coarse Ti(C,N) grains generally consisted of black core, white inner rim and grey outer rim, and fine Ti(C,N) grains generally consisted of white core and grey rim. The partial substitution of Cr for Ni increased hardness and decreased transverse rupture strength (TRS). Ni-based binder phase became hard with increasing the content of Cr additive, therefore resulting in the increase of hardness and the decrease of TRS. TRS was fairly low at 9.6 wt% Cr additive, which was mainly attributed hardening of Ni-based binder phase and undissolved (Mo,Cr) 2C.

IMC hydrides with high hydrogen dissociation pressure

Hydrogen sorption properties of a large variety of solid solutions on the base of ZrCr 2 and TiFe 2 intermetallic compounds are studied at pressures up to 300 MPa. Partial substitution of Cr by small amounts of Me = Al, Mn, Mo, Ni and B does not significantly change the H/M ratio of hydrides of the Ti(Cr 1− x Me x ) 2− a alloys with 0 < a < 0.2, whereas the substitution by Me = Si results in a steep decrease of this ratio. An increase in the concentration of the substituting metal inhibits the transformation of the studied hydrides from the initial Laves phase to a CaF 2-type structure with increasing hydrogen pressure at a temperature of −50 °C. In the case of the ZrFe 2 compound, substituting Zr by Dy and Y, and also substituting Fe by V, Cr, Mn, Ni, Cu and Mo decrease the equilibrium absorption and desorption pressures, unlike Ti substitution for Zr and Co substitution for Fe. Substituting Zr by Dy, Y and Ti, as well as substituting Fe by V, Cr, Ni and Cu decrease the hysteresis between the formation and decomposition pressures of the hydrides. In the case of Zr 1− x Ti x (Fe 1− y Me y ) 2 multicomponent alloys with Me = V and/or Ni, the decomposition pressure varies in a wide range of 0.5–250 MPa. Some of the investigated alloys can be used for designing metal hydride compressors.

Effect of partial substitution of Cr 3+ for Fe 3+ on magnetism, magnetocaloric effect and transport properties of Ba 2FeMoO 6 double perovskites

Magnetism, magnetocaloric effect and transport properties of Cr doped double perovskites compound Ba 2Fe 1− x Cr x MoO 6 with (0 ≤ x ≤ 1) were investigated by magnetization and electrical resistivity measurements. The samples show a cubic structure of cell parameter, a, decreases with increasing Cr content. The temperature variation in magnetization reveals a ferromagnetism for all samples with T C decreases significantly as the Cr doping content increases from 340 K to 310 K for x = 0 and 1, respectively. The saturation magnetic moment, μ S, was found to decrease with increasing the Cr doped content from 3.63 μ B/f.u. for x = 0 to 2.69 μ B/f.u. for x = 1 which may relate to the increase of the anti-site disorder defects or magnetic dilution due to the substitution of Cr for Fe. The magnetocaloric effect is calculated from the measurement of initial isothermal magnetization versus magnetic field at various temperatures. The maximum magnetic entropy change, Δ S M max , of Cr doped double perovskite is found to decrease with increasing of Cr content from 2.08 J/kg K for x = 0 to 0.55 J/kg K for x = 1 upon 1 T applied field change. Interestingly, the value of Δ S M max = 2.08 J / kg K for x = 0 at 1 T was found to be about 64% that of pure Gd, which is thought to be the optimum magnetic refrigerant for use near room temperature. Thus, this perovskite is beneficial for the household application of active magnetic refrigerant materials. The zero field electrical resistivity measurements exhibit a change from metallic behavior at x = 0 to semiconducting like behavior for all doped samples ( x ≥ 0.2) over the entire measurement temperature region from 4.2 K to 300 K.

Electronic structure of Cr-dopedSrRuO3: Supercell calculations

The effects of partial Cr substitution for Ru in $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ are studied using supercell calculations. We find a strong tendency towards antiparallel alignments of Ru and Cr moments resulting from hybridization between Cr ${t}_{2g}$ orbitals and spin-polarized O states near the Fermi energy. The resulting strong local exchange interaction provides an explanation for the increase in the Curie temperature of $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ when alloying with Cr.

The effects of partial substitution of Cr for Ni on the electrochemical properties of Mg 1.75Al 0.25Ni 1− xCr x (0 ≤ x ≤ 0.3) electrode alloys

In this paper, the substitution of different amounts of Cr for Ni in the hydrogen storage electrode alloy of Mg 1.75Al 0.25Ni has been carried out to form quaternary Mg 1.75Al 0.25Ni 1− x Cr x (0 ≤ x ≤ 0.3) alloys by means of solid diffusion method (DM). The XRD profiles exhibited that the quaternary alloys still kept the same main phase of Mg 3AlNi 2 (S.G. Fd3m) as that of ternary Mg 1.75Al 0.25Ni alloy. The electrochemical studies found that Cr substituted quaternary alloy reached its maximum discharge capacity (165 mAh g −1) after 2 cycles, which was larger than that of the Mg 1.75Al 0.25Ni alloy (154 mAh g −1). Among these quaternary alloys, the Mg 1.75Al 0.25Ni 0.9Cr 0.1 electrode alloy was found possessing the highest cycling capacity retention rate. Cyclic voltammetry (CV) results and anodic polarization curves demonstrated that appropriate content ( x lower than 0.1) of Cr effectively improved the reaction activity of electrode and inhibited the cycling capacity degradation to some degree. Electrochemical impedance spectroscopy (EIS) analyses indicated that the increase of Cr content would raise the polarization resistance R p on the particle surface of these quaternary alloys.

Control of Working Temperature of Large Isothermal Magnetic Entropy Change in La(Fe&lt;I&gt;&lt;SUB&gt;x&lt;/SUB&gt;&lt;/I&gt;TM&lt;I&gt;&lt;SUB&gt;y&lt;/SUB&gt;&lt;/I&gt;Si&lt;SUB&gt;1&amp;minus;&lt;I&gt;x&lt;/I&gt;&amp;minus;&lt;I&gt;y&lt;/I&gt;&lt;/SUB&gt;)&lt;SUB&gt;13&lt;/SUB&gt; (TM=Cr, Mn, Ni) and La&lt;SUB&gt;1&amp;minus;&lt;I&gt;z&lt;/I&gt;&lt;/SUB&gt;Ce&lt;I&gt;&lt;SUB&gt;z&lt;/SUB&gt;&lt;/I&gt;(Fe&lt;I&gt;&lt;SUB&gt;x&lt;/SUB&gt;&lt;/I&gt;Mn&lt;I&gt;&lt;SUB&gt;y&lt;/SUB&gt;&lt;/I&gt;Si&lt;SUB&gt;1&amp;minus;&lt;I&gt;x&lt;/I&gt;&amp;minus;&lt;I&gt;y&lt;/I&gt;&lt;/SUB&gt;)&lt;SUB&gt;13&lt;/SUB&gt;

The Curie temperature TC of La(FexSi1−x)13 is increased by a partial substitution of Ni for Fe. On the contrary, TC is decreased by a partial substitution of Cr or Mn. In addition, a partial substitution of Ce for La in La(FexMnySi1−x−y)13 causes the further decrease of TC. As a result, La0.65Ce0.35(Fe0.85Mn0.03Si0.12)13 exhibits a thermal-induced first-order transition at TC=60 K. This result means that TC of the La1−zCez(FexMnySi1−x−y)13 is tunable in the temperature range between 60 and 180 K by adjusting composition with keeping the itinerant-electron metamagnetic transition. In the magnetic field change from 0 to 4 T in the vicinity of TC=60 K, the La0.65Ce0.35(Fe0.85Mn0.03Si0.12)13 shows the isothermal magnetic entropy change ΔSm=−13 J kg−1 K−1 and the relative cooling power RCP=458 J kg−1. Consequently, the La1−zCez(FexMnySi1−x−y)13 compounds are useful for magnetic refrigerants working in a temperature range between 60 and 180 K.

Doping Ru/Cr on B-site of La(BaCa)MnO thin films: driving insulator-to-metal transition temperature far apart from Curie temperature

Magnetic and transport properties of Ru/Cr doped La(Ba,Ca)MnO thin films fabricated by the pulsed laser deposition technique on (1 0 0) LaAlO 3 substrates have been investigated. Ru-doping reduces both Curie temperature ( T C) and insulator-to-metal temperature ( T IM) in LaBaCaMnO thin films: under zero field, La 0.7Ba 0.1Ca 0.2Mn 0.9Ru 0.1O 3 thin films which have T C about 190 K show an insulator-to-metal transition at 75 K. It is likely that Ru-doping creates some antiferromagnetic insulating matrix which separates a basically ferromagnetic background into isolated ferromagnetic domains. In the case of partial substitution of Cr for Mn in La 0.9Ba 0.1MnO 3 thin films, while T C remains almost the same as non-doped films, the magnitude of the magnetization is increased very much due to doping. However, this enhancement does not go along with the enhancement of metallicity: upon doping, T IM shifts to lower temperatures, and the resistivity becomes several orders higher as well. The nature of T IM being far apart from T C in Cr-doped samples are thought to be different from that of Ru-doped ones: it is supposed that the Cr substitution created inhomogeneities resulting in various bonds such as Cr 3+OCr 3+, Mn 3+OCr 3+ and MnOMn. The observation of T IM far below T C in B-site doping manganite thin films is very anomalous and cannot be explained by double-exchange theory.

Enhanced the flux pinning in Bi-2223/Ag by induced Cr-ion defects

(Bi,Pb) 2.2Sr 2Ca 2.2Cu 3− x Cr x O y silver sheathed tapes with x=0.0 (un-doped), 0.0005, 0.001, 0.002 and 0.004 (Cr-doped) have been investigated. X-ray diffraction analyses and transmission electron microscopy observation manifest that partial Cr substitution for Cu may introduce a lot of fine Cr-ion defects into the samples. The different performances of critical current densities (at 77 K) under applied magnetic fields, the irreversibility lines and activation energies of flux motion indicate that their flux pinning has been enhanced by induced Cr-ion defects obviously. Their pinning forces have also been analyzed, and the results imply that the flux pinning in Cr-doped tapes enhanced mainly originate from the fine normal-like Cr-ion defects.

Effect of Nitrogen Addition on Shape Memory Characteristics of Fe-Mn-Si-Cr Alloy

Nitrogen-microalloying and partial substitution of Cr for Mn have been employed to enhance the shape memory effect and corrosion resistance of Fe–Mn–Si based alloys. Typically, the tested alloys with nominal composition Fe–25Mn–6Si–5Cr–(0.12–0.14)N in mass% exhibit perfect shape recovery for a 3% pre-strain after only one cycle of thermomechanical training. The related mechanism has been discussed, taking account of the effect of nitrogen on the stacking fault energy (SFE) or the stacking fault probability ( Psf) of the alloy and the strengthening of the austenite matrix. Thermodynamic calculation and Psf measurement showed that the SFE increases with increasing N-content in the concentration range investigated, e.g. less than 0.3 mass%. Thus, the critical stress for the formation of stress-induced martensite increases with N-content. It is believed that the interstitial strengthening of the matrix by nitrogen predominantly contributes to the improvement of shape memory effect. Besides, nitrogen-microalloying remarkably improves the corrosion resistance of the alloys in aqueous solutions containing NaOH and NaCl, but not in HCl solution as indicated by the long-term immersion tests.

Chromium oxide supported on zirconium- and lanthanum-doped mesoporous silica for oxidative dehydrogenation of propane

Two series of supported chromium oxide catalysts (1–5 wt.% Cr) have been prepared by using two different mesoporous MCM-41-type solids, zirconium- and lanthanum-doped silica, as supports. These catalysts have been fully characterised in order to correlate their superficial properties, mainly the nature of the chromium species and the acidity, with the catalytic behaviour in the oxidative dehydrogenation of propane, between 350 and 550°C. The partial substitution of Cr(III) ions by aluminium or gallium in the supported chromium oxide reveals that the enhancement of the concentration of Brønsted acid centres due to aluminium ions favours the selectivity to propene, whereas gallium increased the number of Lewis acid sites and the oxidising power of this catalyst. The lower catalytic activity of chromium oxide supported on lanthanum-doped silica has been attributed to the formation of polymerised chromate species, which are less active in the ODH of propane.

Magnetoresistance in electron doped Cr1−xMnxO2 double exchange ferromagnet

Electron doping in the half-metallic ferromagnet CrO2 oxide has been reached via partial Cr substitution by Mn. Synthesis of ceramic samples is accomplished under high temperature and high oxygen pressure. It is found that electron doping reduces the magnetization and the Curie temperature of the samples. Simultaneously, the low temperature and low field magnetoresistance of the samples increase. The results are discussed on the light of the current models for the electronic structure of this oxide and the possible role of segregated insulating impurity phases.

Magnetic behavior in the incommensurate phase ∼LaCrS 3: : effect of the partial substitution of Cr by Ti on the magnetic properties

Dilution of the magnetic interactions between Cr 3+ ions by Ti 3+ ions was observed in the CrS 2 layer of the misfit-layer compound ∼LaCrS 3. Pure ∼LaCrS 3 has complex magnetic properties which are reminiscent of spin glass behavior. This magnetic behavior comes from both the modulated character of the structure and the magnetic frustration of the planar-antiferromagnetic-triangular network of Cr 3+ ions. Thus, there is a large hysteresis between the zero field cooled and the field cooled magnetic susceptibility curves below the transition temperature (≈75 K). Formation of a solid solution ∼LaCr 1− x Ti x S 3 by the addition of Ti 3+ ions results in the decrease of transition temperature up to a doping level of x≈0.5, where the transition is no longer observed. The magnetic behavior of the phase with x≈0.5 is similar to that of several random exchange antiferromagnetic compounds.

Study of the performance of Ti–Zr based hydrogen storage alloys

Abstract The P–C–I and charging–discharging properties of three Ti–Zr based alloys have been studied. Ni substitution for Mn and Cr in the alloy was found to increase the plateau pressure of the P–C–I curve. In addition, the partial substitution of Cr by V greatly improved the discharge capacity. However, the six-element alloy, Ti 0.5 Zr 0.5 V 0.2 Mn 0.7 Cr 0.5 Ni 0.6 , degraded rapidly in the gas–solid reaction. Hydrogen contents in the alloy under low pressure were increased during hydrogen absorption–desorption cycling. Annealing at 1050°C for 4 h before the P–C–I experiment helped in releasing the retained hydrogen under low pressure. Only a slightly flattened P–C–I slope was obtained for the annealed alloy. Microstructures of the as-cast and annealed alloys were examined and related to the above results. Alloy powder was poisoned after 2-month storage in air, which resulted in the deterioration of discharge capacity. Surface pretreatment on alloy powders by HCl–HF solution decreased the activation time of charge–discharge reaction.

High Coercive Force α-Fe/Nd2Fe14B-type Nanocomposites

α-Fe/R2Fe14B-type exchange-coupled NdFeB nanocomposites with an intrinsic coercivity, iHc, of 9.5-13.2 kOe and maximum energy product, (BH)max, of 16-19. 8 MGOe have been successfully produced from melt spun ribbons with compositions of (Nd0.95La0.05)10.5-11Febal. Cr2B10 and (Nd0.95La0.05)9.5Fe68Co10Cr2B10.5. It was found that a dilute substitution of La for Nd refines the grains, and a partial substitution of Cr for Fe suppresses the formation of the R2Fe23B3 and Fe3B phases during crystallization and promotes the formation of an α-Fe/R2Fe14B mixture. Unlike the ternary Nd-Fe-B system, La and/or Cr substitution are effective in suppressing the formation of Fe3B and R2Fe23B3 phase in the (Nd0.95La0.05)9.5Fe88.5-xCr2Bx, where x ranged from 6 to 10.5. Both Br and (BH)max decrease initially with increasing boron content, then increase slightly when the boron content was increased above 9. Some of the boron was presumed to react with Cr forming Cr-broides within R2Fe14Band near the grain boundary region. Increasing the total rare earth content in (Nd0.95La0.05)yFe88-yCr2B10 ribbons was found to enhance both the remanence, Br, and the iHc of ribbons simultaneously. A Br of 9.2 to 9.5 kG, iHc of 11.1 to 13.2 kOe and (BH)max of 16.5 to 18.0 MGOe have been obtained on (Nd0.95La0.05)10.5-11Febal.Cr2B10. Significant increases in Br and (BH)max values were obtained in (Nd0.95La0.05)9.5Fe78-zCozCr2B10.5 when z is varied from 7.5 to 10. Microstructural change may play a critical role in explaining the high Br, BHmax and iHc values obtained on (Nd0.95La0.05)9.5Fe68Co10Cr2B10.5.

Decoupling the structural and magnetic phase transformations in magneto-optic MnBi thin films by the partial substitution of Cr for Mn

The first-order nature of the magnetic phase transformation at 360 °C and the presence of a Bi-rich eutectic at 265 °C have inhibited the application of MnBi thin films for high density magneto-optical data storage. It is suggested that partial substitution of Cr for Mn should both lower the Curie temperature, Tc, and decouple the lattice and magnetic transitions so as to allow reversible Curie point writing. It is found experimentally that 10% substitution of Cr for Mn reduces the apparent Tc to ∼250 °C while retaining a Kerr rotation angle greater than 1° at 633 nm, as measured through the silica glass substrate. Observations of increasing Hc with temperature in both MnBi and (Mn,Cr)Bi thin films suggest that the low-temperature phase is ferrimagnetic.

Activity measurement and its use in predicting phase relationships in stainless steels

A combination Knudsen cell-mass spectrometer apparatus has been developed by the Bureau of Mines. This apparatus is accurate enough to permit the activity of many alloy components to be measured directly as the ratio of the ion currents of an appropriate isotope evaporated from the alloy and from the pure component. This apparatus has been used to determine the activity of each component as a function of temperature in 75Fe-10Cr-15Ni, 73Fe-6Cr-15Ni-6Al, and 75Fe-4Cr-15Ni-2Al-4Si (at%). The data indicate that additions of Ni, Cr, Al, and/or Si have practically no effect on the activity coefficient of Fe and that the partial substitution of Cr by Al and/or Si decreases the activity coefficient of Ni. In the case of Cr, temperature influences the activity coefficient more than does the content of Al and/or Si. The activity coefficient of Cr in each alloy increases with decreasing temperature, while the activity coefficients of Fe and Ni are temperature insensitive. The resistance of Fe-Ni-Cr base alloys to oxidation and sulfidation and the stability of the austenitic phase in such alloys are discussed in light of these activity changes.

Properties and stability of Nd2Fe14B particles

The stability of fine particles of Nd 2 Fe 14 B type materials visavis O 2 is investigated through Arrhenius plots. It is found that partial Cr substitution for Fe increases oxidation resistance. Conditions for obtaining relatively high coercivities (H c ) in fine particles are discussed. It is shown that for fine particles the temperature dependence of H c is positive and negative for materials based on R 2 Fe 14 B with R = Y and Nd respectively.