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This study presents the comparison of microstructure, mechanical, tribological, and optical properties of the ternary chromium-aluminum oxide films ((Cr 1-x Al x) 2 O 3) with binary Cr 2 O 3 and Al 2 O 3 films, deposited by atomic layer deposition at 275 °C. The atomic growth per cycle of the Al atoms increased from 3.1 to 8.5 atoms/nm2 on chromium oxide film. The Al 2 O 3 films were X-ray amorphous. The Cr 2 O 3 films contained crystallites of the eskolaite phase. Nano-size (diameter from 3 to 5 nm) crystallites with cubic symmetry and matching with that of cubic γ-Al 2 O 3 or η-Al 2 O 3 phases were observed in (Cr 1-x Al x) 2 O 3 films. The ternary film with Al/(Al + Cr) of 0.40 showed the highest hardness (18.4 GPa) and elastic modulus (169.4 GPa), whereas the wear rate of this film decreased by ∼80 % compared with Cr 2 O 3 films. Optical band gap energy values corresponding to the indirect transition model decreased from 2.93 eV for the Cr 2 O 3 film to 2.58 eV for the Cr-Al-O films. [Display omitted] • The process of atomic layer deposition of (Cr 1-x Al x) 2 O 3 films was studied. • Nanocrystallites with size of 3–5 were observed in (Cr 1-x Al x) 2 O 3 films. • The increase in hardness and elastic modulus for (Cr 1-x Al x) 2 O 3 films was observed. • The wear resistance of the ternary films improved by about 80 % compared with Cr 2 O 3. • Changes in optical properties of the Cr 2 O 3 films were detected by doping with Al. [ABSTRACT FROM AUTHOR]

In this work, Cr3+ ion introduced germanate transparent glass-ceramics with one-step heat treatment around the glass transition temperature were prepared. By using TEM and other structural characterizations, it was demonstrated that the microstructure of glass-ceramics had uniform distribution and excellent grain development. Through XPS, FTIR, Raman and JMA model calculation, it was found that the substitution of Cr 2 O 3 for Ga 2 O 3 led to the decrease of [TO 4 ] ratio in the glass network, and the crystallization behavior changed to the whole crystallization. The results of optical performance tests indicated that the transmittance of the transparent glass-ceramics with one-step heat treatment was 46 % higher than that of glass-ceramics prepared by the two-step heat treatment, and the broadband emission intensity at 980 nm was 1.69 times higher than that of the basic glass. There is some guiding relevance to the innovative preparation approach suggested in this work for the creation of transparent glass-ceramics. [ABSTRACT FROM AUTHOR]

A series of Cr 2− x Fe x O 3 (0.0 ≤ x ≤ 0.3) nanoparticles were successfully synthesized using a sol-gel-based method. Analysis through XRD and SAED of both pure and Fe-doped Cr 2 O 3 nanoparticles revealed a rhombohedral structure belonging to the R 3 ‾ c D 3 d 6 space group, without the formation of secondary phases or Fe clusters. Fe ions were well integrated, as indicated by fluctuations in lattice parameters, and lattice strain. The crystallite size decreased from 38.42 to 27.54 nm with increasing doping concentration. HRTEM images depicted evenly distributed nanoparticles. At lower dopant concentrations (x = 0.1), smaller and more heterogeneous nanorod-like structures emerged, with average sizes and lengths of 36.56 and 39 nm, respectively. Increasing the doping content to x = 0.2 resulted in a morphological shift towards semi-spherical and ellipsoidal shapes, with average dimensions of 22.84 and 31 nm, respectively. At higher doping levels (x = 0.3), nanoparticles grew to 66.5 nm in size and exhibited a spherical morphology. Raman and Fourier transform infrared spectra showed red-shifting of absorption bands with increasing Fe content, attributed to variations in bond length and Cr/Fe–O–Cr/Fe structural perturbation. XPS and Mössbauer spectroscopy analyses confirmed the oxidation states of Fe3+ and ionized oxygen vacancies in the crystal lattice of Cr 2 O 3 nanoparticles. Higher values of quadrupolar splitting Δ indicated greater structural disorder induced by Fe3+ in octahedral positions and in an oxygen-deficient environment. Atomistic simulations confirmed that Fe3+ dopants can induce the presence of vacancy-complexes, forming a stable double-defect configuration with vacant Cr sites along the c-axis, proximal to oxygen vacancies with a single positive charge. These findings offer both experimental and theoretical insights into the dynamics of structural defects in trivalent transition metal doping of Cr 2 O 3 nanoparticles, which holds significant implications for spintronics research. [ABSTRACT FROM AUTHOR]

The superior anti-oxidation layer induced by the PVA-boehmite sol-gel film on the AISI304 steel during the cyclic oxidation is investigated in this work. The moderate PVA addition in the boehmite sol conduces to increase the film thickness and is beneficial to the adhesion between the film and the substrate. The presence of the PVA-boehmite film leads to a significant reduction in mass gain during the high-temperature cyclic oxidation at 800 °C, demonstrating the enhanced oxidation resistance. The generated oxide layer induced by the PVA-boehmite film presents as a thin, compact, and continuous layer without spalling, offering sustainable protection against oxidation etching. The PVA-boehmite film promotes the preferential formation of the corundum (Al, Cr) 2 O 3 phase rather than the detrimental hematite Fe 2 O 3 phase during the oxidation procedure, which facilitates the development of the above compact oxide layer. Finally, the superior anti-oxidation oxide layer is characterized as a novel dual-layer structure: the outer spinel MnCr 2 O 4 layer and the inner corundum (Al, Cr) 2 O 3 layer, effectively delaying the oxidation process. [ABSTRACT FROM AUTHOR]

Magnetic graphene hybrid has encouraging application in environmental remediation. Herein, adsorption-reduction behavior of Cr (Ⅵ) on Fe 3 O 4 -graphene oxide (Fe 3 O 4 -GO) surface was inspected via both theoretical and experimental methods. In the theoretical level, acidity impact on Cr (Ⅵ) species evolution and Cr (Ⅵ)→Cr (Ⅲ) reduction was investigated with the methodology of equilibrium thermodynamics. In the experimental level, adsorption fittings and spectroscopic tests (FTIR, UV–Vis, XPS) were performed to clarify the adsorbent-adsorbate interaction. Results indicate: (1) Under acidic condition, Cr (Ⅵ) is adsorbed by Fe 3 O 4 -GO in the form of H 2 CrO 4. Afterwards, over three-fifths of H 2 CrO 4 is reduced to Cr (Ⅲ), reaching adsorption percent and quantity 95.53 % and 382.10 mg g−1 in 10 min (2) Under basic condition, Cr (Ⅵ) is adsorbed in the form of CrO 4 2− without reduction. In the context of environmental remediation, two special implications are thereby procured. (1) Under acidic condition, Cr (Ⅵ) removal efficiency at the first cycle is maximized, while magnetic recovery is deteriorated, resulting in unsatisfactory cyclic performance. (2) Under basic condition, Cr (Ⅵ) removal efficiency is inferior to that under acidic condition, while magnetic recovery is guaranteed, leading to satisfactory cyclic performance. Exploration of this work provides reference especially for developing Fe 3 O 4 -GO architecture towards efficient sequestering of hexavalent chromium. Adsorption-reduction behavior of Cr (Ⅵ) on Fe 3 O 4 -GO surface(a) Illumination of redox reaction between Cr (Ⅵ) and Fe 3 O 4 given by thermodynamic calculation. Under acidic condition: spontaneous reaction H2CrO4+3Fe 2+ +6H + ⇌Cr 3+ +3Fe 3+ +4H2O owing to highly negative standard molar Gibbs free energy change. Under basic condition, non spontaneous reaction CrO4 2− +3Fe 2+ +4H2O⇌Cr(OH)4 - +3Fe 3+ +4OH − owing to highly positive standard molar Gibbs free energy change. (b) Adsorption-reduction behavior of Cr (Ⅵ) on Fe 3 O 4 -GO surface deciphered by Cr (Ⅵ) species distribution and XPS test. Under acidic condition: five small orange balls symbolizing H 2 CrO 4 adsorbed onto the surface of the big green ball representing Fe 3 O 4 -GO. Subsequently, three out of five small orange balls were transformed into small violet balls representing Cr3+, approaching the molar ratio Cr (Ⅲ)/Cr (Ⅵ) = 1.52 of the sample Fe 3 O 4 -GO-Cr as determined by XPS test (Fig. 8). The big blue ball represents Fe 3 O 4 -GO oxidized by H 2 CrO 4. Under basic condition: five small pink balls symbolizing CrO 4 2− adsorbed onto the surface of the big green ball representing Fe 3 O 4 -GO ensued by no reduction, as confirmed by thermodynamic analysis. [Display omitted] • Adsorption-reduction behavior of Cr (Ⅵ) on Fe 3 O 4 -graphene oxide surface is inspected. • In acidic media, H 2 CrO 4 is adsorbed, three-fifths of which is reduced to Cr (Ⅲ). • In basic media, CrO 4 2− is adsorbed without reduction. • Superior Cr (Ⅵ) removal efficiency but unsatisfactory cyclic performance in acidic media. [ABSTRACT FROM AUTHOR]

This article uses a high-temperature sintering imaging instrument to test the flowability of borosilicate glass melt doped with Cr 2 O 3 , and establishes a mathematical model for high-temperature glass melt spreading. Discuss the glass melt from a thermodynamic perspective by combining model interpretation with experimental characterization. The results indicate that the thermodynamic judgment formula for high-temperature flow spreading of borosilicate glass is: Q ≥ ρ [ A 0 exp (− T / k 0) + S 0 ] − M · δ [ A 0 exp (− T / k 0) + S 0 ] 1 / 2 . To improve the high-temperature flow ability of borosilicate glass, it is necessary to increase the spreading activation energy Q. On the other hand, it is necessary to reduce the spreading coefficients A 0 、 k 0 and S 0. As a refractory metal oxide and active oxide, Cr 2 O 3 plays a role in reducing the spreading coefficient of glass systems. [ABSTRACT FROM AUTHOR]

Zirconia-toughened alumina (ZTA) ceramics have attracted much attention in the medical field as joint replacement materials due to their good mechanical properties and biocompatibility. However, the flexural strength of conventional ZTA is still slightly insufficient in traditional preparation techniques. In this study, by improving the slurry system, the effects of the solid content of the slurry, additives, and the pH of the slurry on the slurry system were investigated. ZTA powders with a uniform particle size distribution, high degree of sphericity and high flowability were prepared by spray granulation. The mechanical properties, microstructure and biocompatibility of the ZTA pressing were investigated after degreasing and sintering processes. The results showed that the hardness of the prepared ZTA ceramics was 1658.24 ± 28.04 H V, the fracture toughness was 4.016 ± 0.027 MPa m1/2, and the biaxial bending strength was 501.43 ± 21.44 MPa, and the three-point bending strength reached 635 MPa. The ZTA ceramics also possessed good biocompatibility and a low haemolysis rate, which aligns with the requirements of clinical biomedical implant materials. [ABSTRACT FROM AUTHOR]

CrN/TiSiN multilayer coatings deposited at 316 L substrate were selected to explore the effects of irradiation on LBE (Liquid Pb–Bi eutectic alloy) corrosion. The as-deposited and irradiated coatings were exposed in LBE. After exposure, all CrN/TiSiN coatings presented oxidation accompanied with PbBi penetration. Irradiated coatings revealed better corrosion resistance with thinner oxide layer and smaller penetration thickness. The largest decrement of 39 % in oxidation thickness was observed in CrN/TiSiN deposited with Ti 80 Si 20 under 150 V. The irradiation-decelerated LBE corrosion could be attributed to the rapidly formed protective oxide layer resulting from the irradiation defects which accelerated nucleation and diffusion process during oxides formation. The decelerated effect was relatively weak in coatings deposited with a bias voltage under 100 V, in which the decrement is under 10 %. The enhanced corrosion resistance was attributed to the quickly formed dense and continuous chromium oxide which rapidly formed due to the irradiation induced defects and acted as diffusion barrier to slow down LBE penetration. [ABSTRACT FROM AUTHOR]

α-Al 2 O 3 as a preferred material for hydrogen isotopes permeation barrier (HIPB) can effectively prevent hydrogen embrittlement in structural steel and has higher thermal stability. However, its application is limited by the issue that it is hard to prepare α-Al 2 O 3 at relatively low temperature and its formation temperature is too high (>1000 °C) to damage the mechanical properties of structural steel. To overcome this issue, this paper presents a novel method (combining Al electrodeposition, aluminizing, Cr deposition and air oxidation) for the preparation of α-Al 2 O 3 (Cr 2 O 3)/Fe–Al composite coating on 316 L stainless steel for the first time. The formation temperature of α-Al 2 O 3 was successfully reduced to 800 °C. The post-oxidation samples were characterized by SEM, XPS, XRD, EDS and TEM. The results showed that the oxide film was composed of highly crystalline α-Al 2 O 3 and Cr 2 O 3 nanoparticles, where the later were diffusely distributed in the internal α-Al 2 O 3 film. And there was an epitaxial growth relationship between α-Al 2 O 3 and Cr 2 O 3. The low-temperature formation of the α-Al 2 O 3 film was due to the fact that the Cr 2 O 3 nanoparticles formed during the oxidation process acted as templates and nucleation sites, which reduced the nucleation barrier of α-Al 2 O 3. Deuterium permeation tests showed that its deuterium permeation reduction factor (DPRF) was 8892 at 500 °C, which met the standard for practical application. [ABSTRACT FROM AUTHOR]

Within the present work, a series of spinel-structured (MnFeCoNiX) 3 O 4 (X = Zn, Cu, Cr) high entropy oxides (HEOs) were fabricated by co-precipitation method and the subsequent heat treatment. The phase composition, microstructure, thermal stability, magnetic property and electromagnetic (EM) wave loss ability were comprehensively studied. It is found that spinel-structural (MnFeCoNiX) 3 O 4 HEOs are well-crystallized at above 800 °C with a space group Fd-3m. Morphological analysis reveals that grains of different HEOs contain nano-domains with particle sizes between 100 nm and 500 nm. In addition, Mn, Ni, Co, Fe, Zn, Cr and Cu elements are homogeneously distributed and the chemical states of Mn, Ni, Co and Fe are all +2 and + 3, while Cu only exists in +2 state. Thermal stability analysis shows that (MnFeCoNiCu) 3 O 4 HEO is able to keep stable at 1000 °C. Moreover, the (MnFeCoNiCu) 3 O 4 sample exhibits the best magnetic properties and EM microwave loss ability in comparison with (MnFeCoNiZn) 3 O 4 and (MnFeCoNiCr) 3 O 4. For (MnFeCoNiCu) 3 O 4 , the values of saturation magnetization (M s) and coercivity (H c) are 38.6 emu/g and 52.6 Oe, respectively. Meanwhile, (MnFeCoNiCu) 3 O 4 displays a minimum reflection loss (RL) of −15.5 dB at 8.48 GHz with a thickness of 4.5 mm and a wide effective absorption bandwidth (EAB) of 8.84 GHz with the sample thickness of 5 mm. It is expected that the excellent high-temperature stability and good EM wave absorbing performance of high entropy (MnFeCoNiCu) 3 O 4 could make it potentially useful in EM wave absorption under elevated temperatures. [ABSTRACT FROM AUTHOR]

The sintered glass-ceramic always has an uneven microstructure due to the surface crystallization, which limits the enhancement of its mechanical properties. In the present work, Cr 2 O 3 was added into CaO–MgO–Al 2 O 3 –SiO 2 –CaCl 2 glass as the nucleating agent, and the low-pressure (14 kPa) sintering technology was utilized to promote the densification process of the glass frits (0.42–2 mm). It was found that by adding 1 wt% of Cr 2 O 3 , the bulk crystallization can be achieved inside the glass particle and the microstructure of the glass-ceramic became more homogeneous. Correspondingly, the bending strength was improved from 127 to 147 MPa, and the Vickers hardness was enhanced from 6.5 to 6.7 GPa, comparing with the Cr 2 O 3 -free glass-ceramic. The current study confirmed the positive impact of nucleating agent in the performance of sintered glass-ceramic, which also provided a route for the utilizations of CaCl 2 -and Cr 2 O 3 -bearing wastes. [ABSTRACT FROM AUTHOR]

Joining of barium titanate (BaTiO 3 , BT) ceramics to metals plays an important role in their wide applications. However, conventional joining methods, including solid state diffusion joining and liquid state joining, have several drawbacks. In this paper, BT ceramic was flash joined to NiCrFe medium-entropy alloy (MEA) in seconds with an electric field (E-field) using current density of 10–80 mA/mm2 at 700–1000 °C. Shear strength of the joint first increased with applied current density and dwell time of the E-field and then decreased. It exceeded 40 MPa when the temperature was above 900 °C with current density of 60 mA/mm2 for 60 s. Both the real part (ε') and imaginary part (ε ") of complex permittivity of the joined sample were larger than those of the as-sintered BT ceramic at high frequency range. Microstructure of the joint suggests that a layer of chromium oxide was formed at faying surfaces, achieving effective bonding of BT and MEA. This research provides an efficient method for the manufacturing of BT based devices. [ABSTRACT FROM AUTHOR]

CaO solubility in the FeO t -SiO 2 -CaO-Al 2 O 3 -(ZnO, Cr 2 O 3) system has been experimentally investigated at 1200 and 1250 °C under pO 2 of 10−10 atm. Synthetic slags rich in CaO were equilibrated at desired temperatures, followed by water quenching, and analyzed using electron probe X-ray microanalysis (EPMA). In the quaternary FeO t -SiO 2 -CaO-(6 to 10 wt%) Al 2 O 3 system, CaO solubility exhibits a linear increase from 27.5 to 36.9 wt% with decreasing the FeO/SiO 2 (F/S) ratio from 1.66 to 0.62 at 1250 °C. Similarly, at 1200 °C, the CaO solubility increases from 24.9 to 30.8 wt% as the F/S ratio drops from 1.25 to 0.56. Excessive CaO addition to the slags results in the precipitation of melilite phase. Wustite is observed in the F/S ratio range of 1.66 to 1.0, and the size of wustite particles decreases as the F/S ratio decreases. At both 1200 and 1250 °C, the liquid phase with an F/S ratio below 0.42 is in equilibrium with wollastonite (CaSiO 3) in the FeO t -SiO 2 -CaO-Al 2 O 3 system. The addition of a small amount of ZnO (0.4–1.1 wt%) in the slags leads to a slight decrease in CaO solubility by 1–3 wt%, while the presence of 3.3–8.1 wt% of ZnO in the slags results in a decrease of 5–11 wt% in CaO solubility. Similar to the FeO t -SiO 2 -CaO-Al 2 O 3 system, the equilibrated CaO-containing solid phase is also melilite in the FeO t -SiO 2 -CaO-Al 2 O 3 -ZnO system. With the addition of a small amount of Cr 2 O 3 (1.0 wt%) to the FeO t -SiO 2 -CaO-Al 2 O 3 -ZnO system, spinel and dicalcium silicate (Ca 2 SiO 4) precipitate from the liquid slag, and the dissolved CaO concentration in liquid slag increases by 1–3.6 wt% in the F/S ratio range of 1.58 to 0.84, compared to the Cr 2 O 3 -free system. [ABSTRACT FROM AUTHOR]

In the present contribution, p-n type heterojunction α-Fe 2 O 3 /Cr 2 O 3 S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H 2 evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe 2 O 3 /Cr 2 O 3 nanocomposites verified the construction of Fe 2 O 3 and Cr 2 O 3 with rhombohedral phases. TEM images of Cr 2 O 3 NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe 2 O 3 NPs (3-5 nm) were distributed on the mesoporous Cr 2 O 3 networks. The obtained α-Fe 2 O 3 /Cr 2 O 3 photocatalyst exhibited noteworthy photocatalytic H 2 evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H 2 evolution rate gradually boosted with the extent of Fe 2 O 3 percentage up to 15% and its rate of 2215.4 μmol g-1h-1, which was fostered 7.25 folds larger than that of Cr 2 O 3 NPs (305.7 μmol g-1h-1). The enhancement H 2 evolution rate of Fe 2 O 3 /Cr 2 O 3 photocatalyst in comparison with bare Cr 2 O 3 NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe 2 O 3 and p-type Cr 2 O 3 with close contact is essential in improving the H 2 evolution rate. The possible photocatalytic mechanism over Fe 2 O 3 /Cr 2 O 3 nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe 2 O 3 /Cr 2 O 3 nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H 2 evolution through visible exposure. [ABSTRACT FROM AUTHOR]

The weak interface is a key issue that needs to be addressed for the carbon nanotubes (CNTs) reinforced metal matrix composites. Herein, uniform and continuous Cr(OH) 3 coating was firstly decorated on the surface of CNTs, and Cr(OH) 3 coating was subsequently thermally decomposed into the Cr 2 O 3 transition layer during the fabrication processes for the Cu matrix composite. It is found that the precoating Cr(OH) 3 on CNTs can promote the dispersion of CNTs in the Cu matrix because the coating can reduce the density difference between CNTs and Cu powders. Meanwhile, the Cr 2 O 3 transition layer has obvious constituent interaction with the Cu matrix, and in-situ nanosized Cr carbides (Cr 2 C 3 and Cr 23 C 6) form between the CNTs and Cr 2 O 3 layer, forming a composite interface structure. Benefiting from the homogeneous dispersion of the decorated CNTs and enhanced interfacial bonding, the compression yield strength of the bulk composite reaches 383.5±21.0 MPa, showing a 217% and 147% increase over the pure Cu and the composite reinforced by uncoated CNTs, respectively. The substantially enhanced strength mainly derives from the strengthening mechanisms of Orowan looping and load transfer. The developed novel strategy paves a new route for interface regulation and strength improvement of other CNTs reinforced metal matrix composites. [ABSTRACT FROM AUTHOR]

This study aims to synthesise novel biocomposites by combining fungal hyphae (Aspergillus oryzae or Penicillium roqueforti) and reduced graphene oxide to evaluate their adsorption potential for hexavalent chromium (Cr(VI)) from synthetic solutions and real wastewater. Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analyses were used to characterize the effects of the carbon-based materials on microbial structure. In addition, independent variables including with a contact time (1–11 h), reduced graphene oxide concentration (0.1–1 g.L−1), and initial Cr(VI) concentration (10–50 mg L−1) were tested in batch-scale laboratory experiments by response surface methodology. Accordingly, maximum adsorption was achieved at 11 h contact time, 1.0 g L−1 rGO, and 50 mg L−1 Cr(VI) with a removal rate of 98.9%. The pseudo-first-order and Freundlich isotherm models were well fitted. The results show that these biocomposites can serve as novel adsorbent for the removal of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

The dual effects of Cr 2 O 3 in the fabrication of glass-ceramics from ferronickel slag (FNS) with the addition of coal fly ash (CFA) were investigated by varying the content of Cr 2 O 3 from 0 wt % to 2.0 wt %. The crystallization kinetics results showed that as the Cr 2 O 3 content increased from 0 wt % to 1.6 wt %, the crystallization activation energy of the parent glass decreased from 448.23 kJ/mol to 232.65 kJ/mol with the change of crystallization mode from surface crystallization to bulk crystallization. When the content of Cr 2 O 3 reached 1.6 wt %, there existed the highest degree of depolymerization of the glass network and the strongest crystallization tendency. The prepared glass-ceramic was composed of enstatite as the main crystalline phase and spinel as the secondary crystalline phase. The microstructure changed from a loose tabular structure to a dense spherical structure. As the Cr 2 O 3 content further increased to 2.0 wt %, the crystallization activation energy increased to 304.21 kJ/mol and the spherical structure became inhomogeneous due to the coexistence of enstatite particles with different sizes. By controlling the Cr 2 O 3 content of 1.6 wt %, an optimal glass-ceramic with density of 3.17 g/cm3, bending strength of 175 MPa, Vickers microhardness of 9.51 GPa, acid resistance of 99.99% and alkali resistance of 99.97% was obtained. This study provided a novel method for promoting conversion of FNS to glass-ceramics. [ABSTRACT FROM AUTHOR]

Better anti-corrosion protection is essential for the service life of thermal barrier materials. This study investigates the corrosion behaviors of RE 2 CrTaO 7 and CMAS at high temperatures. Results revealed that RE 2 CrTaO 7 exhibits good corrosion resistance as a new thermal barrier material. Meanwhile, the chemical stability and compactness of the crystal structure of Sm 2 CrTaO 7 , exhibiting pyrochlore structure, are better than those of Yb 2 CrTaO 7 , exhibiting defective fluorite structure. Therefore, the anti-corrosion effect of Sm 2 CrTaO 7 is also better than that of Yb 2 CrTaO 7. After being corroded by CMAS for 10 h, the thickness of the dissolution and reaction layer of Yb 2 CrTaO 7 is 67.49 μm. However, the Sm 2 CrTaO 7 is only 33.69 μm under the same conditions. [ABSTRACT FROM AUTHOR]

In this work, two Cr-free high entropy oxides (HEOs), an equimolar (MnFeCoNiCu) 3 O 4 and a non-equimolar (Mn 0.272 Fe 0.272 Co 0.272 Ni 0.092 Cu 0.092) 3 O 4 have been synthesized by a solid-state reaction method. The reaction sequence and electrical conductivity were also studied for these two HEOs. It is demonstrated that a rock-salt phase containing a solid solution of NiO and CuO appears in the synthesizing process of (MnFeCoNiCu) 3 O 4 , which is ascribed to the incomplete solubilization of rock-salt phase in the spinel phase. For (Mn 0.272 Fe 0.272 Co 0.272 Ni 0.092 Cu 0.092) 3 O 4 , a single spinel phase (Fd-3m) is obtained at 750 °C, which is much lower than that of the (MnFeCoNiCu) 3 O 4 sample. Furthermore, Mn, Fe, Co, Ni elements exist in the chemical states of +2 and + 3, and Cu exists in Cu2+ state. The electrical conductivity of (Mn 0.272 Fe 0.272 Co 0.272 Ni 0.092 Cu 0.092) 3 O 4 is approximately 15.77 S cm-1 at 800 °C, which is nearly three times higher than that of the (MnFeCoNiCu) 3 O 4 sample. [ABSTRACT FROM AUTHOR]

The current paper investigates the impact of silver iodide (AgI) on the structure, optical, and radiation shielding parameters of borate glasses embedded with low amounts of CrO 3 , high levels of Na 2 O, and various quantities of AgI (from 1 to 5 mol%). These glasses (named BNaCrAg-glasses) were synthesized and their properties were investigated. Fourier transform infrared (FTIR) analyses of BNaCrAg-glasses demonstrated that the ratio of BO 4 /BO 3 units increased with increasing AgI. The existence of Cr cations, with their Cr6+ state, was recognized from the absorption bands at 384–392 nm and 334–338 nm. Furthermore, the absorption bands at 580–589 nm at 409–440 nm through the visible region confirmed the existence of Cr-ions as Cr3+ in the octahedral symmetry. The crystal field splitting (10Dq) was calculated from the 580–589 nm bands. The values of 10Dq decreased with AgI doping due to replacing oxygen with iodide anions. The transmittance at 700 nm increased from 24 to 80%, while AgI addition increased from 0 to 5 mol%. The glass sample with the highest AgI content had the lowest half-value layer and maximum linear attenuation coefficient. Thus, the new BNaCrAg-glasses combine good transparency with good attenuation of low energy radiation and can be used to protect the radiation workers. Furthermore, these glasses offer high-energy optical transitions suitable for UV optics, such as ultraviolet digital photography and insect light traps. [ABSTRACT FROM AUTHOR]

This study aims to investigate the impact of the rare earth element yttrium on the optical properties of chromium (Cr)-doped borate glasses. A series of borate glasses (labeled as BNaCrY glasses) were prepared and studied, each with a constant amount of chromium trioxide (CrO 3) but doped with varying amounts of yttrium oxide (Y 2 O 3). Infrared analysis revealed four distinct spectral areas in the internal structure of all BNaCrY glasses. Optical absorption spectra were used to investigate the impact of Y 2 O 3 doping on the optical transitions of BNaCrY glasses. The presence of Cr cations caused the appearance of an absorption band at 379–383 nm, which overlapped with the Urbach edge that is commonly given an edge-like at 430 nm. The Urbach edge has been manifested through a full deconvolution attempt. Cr cations in the Cr3+ state were confirmed by visible absorption bands and are nestled in the octahedral positions. The band at 574–593 nm was used to determine the crystal field splitting (10Dq) for all BNaCrY glasses. Due to the increased number of O anions around the Cr cation, the values of 10Dq increased with Y 2 O 3 doping. The remarkable increase in 10Dq was attributed to increased interaction between Cr cations and their surroundings. In contrast, the shielding parameters were taken into account when evaluating the ability of these transparent glasses to protect against nuclear radiation. We found that the sample with the highest Y 2 O 3 concentration had the highest linear attenuation coefficient and the lowest half-value layer. Thus, BNaCrY glasses are more efficient as attenuators than commercial glasses (such as the Rider and Osmania glasses), especially at low photon energies. [ABSTRACT FROM AUTHOR]

Existing refractory-life-extending technologies had concentrated on the preparation of homogeneous high-performance refractory materials in advance. In this paper, an in situ anti-erosion approach of conventional corundum-mullite refractory material was proposed for the incineration of hazardous spent high-salt organic liquor, in which the powdery additives were directly added into the spent liquor. The phase transformation, interfacial morphology evolution, and pore distribution of the corundum-mullite refractory with and without Cr 2 O 3 /ZrO 2 addition were compared, and the in situ anti-erosion mechanism was determined via the XRD, SEM, XPS, mercury intrusion porosimetry, and thermodynamic analyses. In conventional corrosion, molten Na 2 SO 4 , the primary phase of incinerating slag, directly entered the interior of the corundum-mullite refractory through pores on the interface. The Na 2 SO 4 strongly reacted with alumina and silica at 1000–1300 °C to produce liquid albite and nepheline. Upon the addition of Cr 2 O 3 into the spent liquor, the Cr 2 O 3 powder was suspended in the spent liquor and deposited at the refractory interface to form a protective (Al,Cr) 2 O 3 solid solution layer with Al 2 O 3. The dense corrosion-resistant layer of (Al,Cr) 2 O 3 with a depth of 0–3 mm on the surface of the firebricks seldom reacted with molten Na 2 SO 4. This protective layer can effectively slow down the penetration and erosion of incinerating slag. The environmental risks of Cr(VI) contamination associated with the Cr 2 O 3 addition in the incineration process were also evaluated in this work. Eventually, preliminary trial operation results showed that the service life of the corundum-mullite firebrick was prolonged after 5% Cr 2 O 3 addition into the spent liquor. [ABSTRACT FROM AUTHOR]

Carbide coatings are very important in molding industries due to their good anti-wear properties increasing the life of molds of hot and cold forging, extrusion and powder metallurgy exposing to abrasive forces. Diverse processes are applied to produce carbide coatings. One of them is the thermo-reactive diffusion method (TRD) using a molten salt bath. This process has many advantages including cost-effectiveness over other similar surface coating methods. The aim of this study is the formation of carbide-composite coatings using molten salt baths containing oxides of carbide forming elements individually and in a mixed form on SKD-11 cold work tool steel at 1000 °C. For this purpose, two sets of experiments were considered in this study. In experiment A, a chromium oxide bath and then a mixed chromium oxide and vanadium oxide bath with a molar ratio of Cr to V equal to 0.66 were used. In experiment B, at first a mixed chromium oxide and vanadium oxide bath (Cr/V ratio = 0.66) and next a single bath of vanadium oxide were utilized. To evaluate and compare the produced coatings, FE-SEM, EPMA (point, line and map), XRD analysis, nano-indentation and wear tests were performed. The results showed that the coatings include chromium carbides (Cr 3 C 2 , Cr 7 C 3 and Cr 23 C 6) and vanadium carbides (V 2 C, V 6 C 5 and V 8 C 7) as well as a carbon-chromium-vanadium triple phase with the composition of Cr 2 C 2 V. Moreover, the best hardness and abrasion resistance were gained for the coating produced in the molten bath containing chromium oxide and vanadium oxide after experiencing a chromium oxide bath. For the sample, the hardness was between 17.2 and 19.6 GPa and the lowest amount of COF was 0.32. [ABSTRACT FROM AUTHOR]

The influence of micro-sized Cr 2 O 3 particles on the corrosion, mechanical and thermal control performance of plasma electrolytic oxidation coated Mg was studied. More contents of Cr 2 O 3 particles were embedded into phosphate containing PEO coatings compared with coatings produced from silicate based electrolytes, resulting in green coatings with enhanced thermal control and mechanical property. The existence of particles has slightly improved the corrosion resistance and hardness of the coating. It was found that the absorptance of the coating was increased if higher concentration of Cr 2 O 3 particles is incorporated into the layer, which is probably ascribed to low band gap of Cr 2 O 3. [ABSTRACT FROM AUTHOR]

In this study, individual Al 2 O 3 and Cr 2 O 3 coatings and Cr 2 O 3 -25, 50, 75 wt% Al 2 O 3 composite coatings were applied on carbon steel by atmospheric plasma spraying method. Corrosion experiments were performed on as-sprayed and epoxy resin sealed coatings including potentiodynamic polarization, electrochemical impedance spectroscopy and long-term immersion in 3.5 wt% NaCl solution. Phase composition and microstructure of the coatings were investigated by x-ray diffraction, optical microscopy and scanning electron microscopy, before and after the corrosion experiment. The results showed that the Cr 2 O 3 coating exhibited the best corrosion resistance, due to the densest microstructure and highest adhesion strength. The Cr 2 O 3 -25 wt% Al 2 O 3 coating had the highest interconnected porosities and thus had the least corrosion resistance compared to other coatings. In general, the as-sprayed coatings induced a maximum increase of 3.93 times the polarization resistance (R p) in the polarization experiment and a 3.5 times increase in the charge transfer resistance (R ct) in the EIS experiment, which was not significant. Stresses caused by increased volume of corrosion products in the coating-substrate interface resulted in the spallation of Cr 2 O 3 -25, 50 wt% Al 2 O 3 coatings from the substrate over long-term of immersion. The adhesion strength of the coatings was a determining criterion for the long-term durability of the coatings. The sealing treatment resulted in a significant increase in R p and R ct. [ABSTRACT FROM AUTHOR]

A Pd/Cr 2 O 3 hybrid catalyst for cyanation reaction of some aryl halides was synthesized and characterized by XRD, SEM/EDS and TEM. The porous structure of the catalyst was also investigated by BET analysis. All XRD characteristic lines were obtained for Cr 2 O 3 and Pd/Cr 2 O 3 hybrid in good agreement with the reference XRD data. It was found that average particle size of Pd/Cr 2 O 3 composite was about 22 nm. The catalytic efficiency of the Pd/Cr 2 O 3 –catalyzed cyanation reaction was evaluated for some m- and p-substituted aryl halides. The influence of solvent, reaction time, and base on the activity of the Pd/Cr 2 O 3 catalyst was investigated, and the optimal reaction conditions were systematically obtained. Catalytic investigations showed that Pd/Cr 2 O 3 hybrid can exhibit very good catalytic performance for cyanation reaction of aryl halides with a high yield of around 90%, and retained its catalytic activity throughout successive 5 cycles. Comparative TEM images of Pd/Cr 2 O 3 hybrid catalyst, as-synthesized and after 5th cycle, showed that nano-sized structure of Pd/Cr 2 O 3 catalyst was protected without significant change. [Display omitted] [ABSTRACT FROM AUTHOR]

Surface modification of ceramic materials by laser irradiation is widely used as a non-contact, fast and thermally activated process to generate micro and nanostructures. The effects of liquids while surface modification by laser irradiation of ceramic materials under liquid environment are least explored so far. This study reports the effects of pulsed laser irradiation in air and liquids on the microstructure and morphologies of ceramic materials. Chromium oxide (Cr 2 O 3) was mixed in different concentrations (3, 5 and 7% in weight) into magnesium oxide (MgO) matrix and was sintered at 1650 °C. The structure and morphology of the sintered ceramic pellets were characterized using X-ray diffraction and scanning electron microscopy. Presence of the spinel magnesium chromium oxide (MgCr 2 O 4) was identified in these samples. For surface modification of these samples, laser irradiation is carried out in air and liquids (methanol, isopropyl alcohol and acetone) using 2 ns pulsed lasers (532 nm) of different pulse repetition rates and energies. The microstructure and morphologies of the samples after irradiation was analyzed and their crystalline structure and composition were maintained after laser irradiation. It was observed that the surface morphologies of the ceramic pellets were modified by laser irradiation as a combined effect of the medium (air/liquids), energy fluence and the concentration of the Cr 2 O 3 in MgO. Our results show that pulsed laser irradiation especially in liquids is an effective technique for modifying surface morphology of ceramic materials. [ABSTRACT FROM AUTHOR]

Silica-titania core-shell nanocomposite (SiO 2 –TiO 2) was successfully synthesized via nanoparticle encapsulation route. The morphology and the chemical properties of the prepared nanocomposite were evaluated by different instrumental techniques before and after adsorption of Cr(VI) as required to check the existence of Cr and its oxides on the surface of the adsorbent. Subsequently, the efficiency of the nanocomposite to adsorb Cr(VI) from synthetic solution was studied in different experimental conditions like solution temperature (30–80 °C), pH (2–10), initial Cr(VI) concentration (10–100 mg L−1), reaction time (10–120 min), and, amount of the adsorbent (0.1–1 g). The maximum adsorption reached 98% by utilizing 0.5 g L−1 of the nanocomposite at pH 5, with 30 mg L−1 initial Cr(VI) concentration, while the temperature was maintained 50 °C and the equilibrium time was 70 min. Besides, the process of Cr(VI) adsorption is well fitted with the Langmuir adsorption isotherm model and pseudo-second-order kinetic model. On the other hand, endothermic and spontaneous nature of the adsorption process was revealed by the negative ΔG and the positive ΔH values. The cytotoxicity of the nanocomposite was examined by using Drosophila as a model organism. The effects of oral ingestion of the nanocomposite (10, 40, 60, 80, and 100 μg mL−1) were observed on the growth, development, and behavior of Drosophila and the result showed there are no major phenotypic defect on Drosophila. The above outcomes suggested that the SiO 2 –TiO 2 core-shell nanocomposite could be a promising nontoxic material for Cr(VI) removal from contaminated water. [ABSTRACT FROM AUTHOR]

In this study, the properties of machinable glass-ceramic materials produced from basalt and chromite ore were investigated. Three different compositions by adding chromite ore in different ratios to the main composition produced from basalt and MgF 2 were prepared. In this way, the effects on the machinable glass-ceramic of chromium and iron oxides in the chromite ore were investigated. Thermal degradation of chromite ore and the effect of its compounds on the crystallization of machinable glass-ceramics were investigated. The samples were subjected to machinability testing. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used for characterization. The results show that chromite addition has positive effects on crystallization and machinability. Also, crystallization kinetic studies were realized. It was seen that the effect of iron oxide in chromite ore on crystallization is higher than that of chromium oxide for the crystallization conditions that used chromite ore as a nucleating agent. [ABSTRACT FROM AUTHOR]

The detonation modification of nanodiamonds with chromium (III) oxide (Cr 2 O 3) was studied in this paper. The thermostability, surface properties, crystal structure, specific surface area, pore diameters, and particle diameters of the detonation-modified nanodiamonds were analyzed using thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffractometer, transmission electron microscopy, automatic physical adsorption, and laser particle size analysis. Cr 2 O 3 and the surface functional groups of nanodiamonds were combined with C–Cr. We obtained a dispersed distribution of 0.1–0.5 μm. The thermal stability characteristics and the particle diameter of nanodiamonds increased because of Cr 2 O 3. The technology involved in the detonation modification of nanodiamonds with Cr 2 O 3 is simple and low-cost. [ABSTRACT FROM AUTHOR]

The main objective of this work is the design, preparation, and characterization of YSZ coatings by electrophoretic deposition (EPD) technique. The suspensions used for the preparation of zirconia-derived coatings by EPD have been thoroughly characterized. YSZ suspensions containing particles of different morphology and size have been used to optimize the electrophoretic characteristics of the suspensions. The correlation between the experimental results and the theoretical values predicted by the Hamaker's equation has been analyzed. Coatings have been thoroughly characterized. Surface morphology has been studied by Scanning Electron Microscopy. X-Ray Diffraction and Time of Flight-Secondary Ions Mass Spectrometry have been used to analyze the structure and composition of the samples. Finally, nanoindentation tests have provided information regarding the mechanical properties of the coatings. Optimal coating results were achieved using stainless steel substrates previously treated thermally so that a thin anchoring layer of chromium oxide was generated. [Display omitted] [ABSTRACT FROM AUTHOR]

The chromium-promoted preparation of forsterite refractory materials from ferronickel slag was investigated by microwave sintering of the slag with the additions of sintered magnesia and 0–10 wt% chromium oxide (Cr 2 O 3). The thermodynamic calculations revealed that the addition of Cr 2 O 3 can promote the formations of spinel and liquid phase and maintain high content of forsterite below 1500 °C. The experimental results showed that there existed a stronger promoting effect of Cr 2 O 3 additive on the properties of refractory materials in the microwave field than that in conventional sintering. It was attributed to the preferential formation and growth of spinel with stronger microwave absorption than other phases (e.g., enstatite), the existence of more forsterite, and the enhanced densification in association with the presence of more liquid phase at the same temperature. By microwave sintering of the mixture of ferronickel slag, 25 wt% sintered magnesia, and 4 wt% Cr 2 O 3 at 1350 °C for 20 min, a superior refractory material with refractoriness of 1801 °C, thermal shock resistance of 6 times, bulk density of 2.97 g/cm3, apparent porosity of 1.4%, and compressive strength of 197 MPa was obtained. Compared with that prepared by conventional sintering at 1350 °C for 2 h, the refractoriness and thermal shock resistance were increased by 175 °C and 100%, respectively. The present study provided a novel method for preparing high-quality refractory materials from ferronickel slag and relevant industrial wastes. [ABSTRACT FROM AUTHOR]

Pristine chromium oxide (Cr 2 O 3) and nickel ions (Ni2+) substituted Cr 2 O 3 nanoparticles were synthesized using a simple co-precipitation technique. The main objective of this work is to investigate Ni2+ substituent's role at different concentrations on the structural, morphological, optical, and magnetic properties of Cr 2 O 3 nanoparticles. Structural analyses based on X-ray diffraction (XRD), Raman and Fourier transform infra-red (FTIR) data confirmed the successful incorporation of Ni2+ into Cr 2 O 3 nanoparticles up to x = 0.05 of Ni2+ content, without affecting the rhombohedral crystal structure of Cr 2 O 3 nanoparticles. Rietveld refinement results showed the variation in lattice parameters and cell volumes alongwith the substitution of Ni2+ into Cr 2 O 3 nanoparticles. Raman and FTIR spectra also depicted a considerable shift in the characteristic vibration modes of Cr 2 O 3 nanoparticles due to strain-induced by Ni2+ substitution. Beyond x = 0.05, the structural transformation took place from rhombohedral to cubic crystal structure. Subsequently, new peaks (apart from Cr 2 O 3 phase modes) have been observed at x = 0.1 of Ni2+ content due to the formation of secondary phase i.e., nickel chromate (NiCr 2 O 4). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) illustrated the changes in the morphology of Cr 2 O 3 nanoparticles with Ni2+ substitution. UV–Vis analysis revealed a narrowing of optical band energy (E g) of Ni2+ substituted Cr 2 O 3 nanoparticles from 3 to 1.85 eV as Ni2+ content varies from x = 0 to 0.2, respectively. Afterward, there is an increase in optical band gap energy (E g) when Ni2+ content increased from x = 0.3 to 0.5, as NiCr 2 O 4 started dominating the Cr 2 O 3 phase. Single-phase Ni2+ substituted Cr 2 O 3 nanoparticles exhibited a superparamagnetic behavior, whereas the multi-phase compound ascribed to both superparamagnetic and paramagnetic. These changes in optical and magnetic properties can lead to novel strategies to render applications in the field of optoelectronics and optomagnetic devices. [ABSTRACT FROM AUTHOR]

Magnesia carbon (MgO–C) refractory, one of the most commonly used refractories in the steelmaking system, relies on graphite to improve the thermal shock resistance and slag corrosion resistance. The oxidation of graphite carbon in a MgO–C brick usually leads to the destruction of the carbon network in the brick, which causes the structure of the brick to become loose and easily eroded. At present, metal powders, carbides, and borides are used as antioxidants to prevent the oxidation of carbon in MgO–C bricks. The metal carbide Cr 7 C 3 can be prepared from aluminum chromium slag through a simple synthetic process and at a low cost. In this work, we investigated the oxidation resistance of low carbon MgO–C refractories with different amounts of Cr 7 C 3 powder (1, 2, 3, and 4 wt%). The refractories with 3 wt% Cr 7 C 3 powder showed optimal resistance to oxidation. The microstructure indicated that oxygen reacts with Cr 7 C 3 preferentially over carbon to form chromium oxide and magnesium chromium spinel, blocking the pores and hindering oxygen diffusion. Carbon arising from the reduction of carbon monoxide by Cr 7 C 3 can act as a supplementary carbon source. The bette r oxidation resistance also contributed to the improvements in slag corrosion and thermal shock resistance of the refractories. [ABSTRACT FROM AUTHOR]

In this work, we investigated FeCrMo coatings with 35 wt% ceramic, which were produced on a cylinder surface by an internal rotating plasma spraying and oxidized in air. The ceramic particles consisted of 80 wt% alumina and 20 wt% zirconia, which can improve the mechanical properties of the coating. For microstructural characterization, scanning electron microscopy was combined with energy dispersive X-ray analysis and electron probe micro analysis, and the nanomechanical properties were measured by a nanoindentation tester. The structure of Fe-base coating matrix consists of Al 2 O 3 , ZrO 2 and a small amount of mixed Fe–Cr oxides, and the ceramic particles exhibit a uniform distribution. During oxidation, a mixed oxide layer containing Fe 2 O 3 and Fe 3 O 4 forms on the surface of the Fe-base coating, and the thickness of the oxide layer increases with increasing oxidation temperature. Due to the in-situ oxidation, the nanohardness and Young's modulus of the Fe-base coating decreased with increasing oxidation temperature. The nanohardness evolution of Fe-base coatings oxidized at different temperatures is discussed. [ABSTRACT FROM AUTHOR]

The (S, N) co-doped Ba 2 In 2- x Cr x O 5+ y (0 ≤ x ≤ 0.5) oxides are successfully obtained by mixing the Ba 2 In 2- x Cr x O 5+ y oxides and thiourea through a simple ball milling method followed by sintering at 400 °C for 3 h. The colors of the compounds change from orange-brown to yellow-green after reacting with thiourea. When Cr amount is small (x = 0.1), the crystal structure of (S, N) co-doped Ba 2 In 2- x Cr x O 5+ y is orthorhombic Ba 2 In 2 O 5 phase. When x ≥ 0.3, the crystal structure of the sample is cubic BaInO 2.5 phase. And this phase transition is the same as Ba 2 In 2- x Cr x O 5+ y. XPS results reveal that Cr6+ in Ba 2 In 2- x Cr x O 5+ y (0 ≤ x ≤ 0.5) oxides are reduced to Cr3+ after sintering. S exists in both cation and anion forms, and N exists in substitutional forms. UV–Vis analysis indicates that the yellow-green hue comes from the d-d transition of Cr3+, and the doping of S, N ions leads to a red shift of the absorption edge of the samples. [ABSTRACT FROM AUTHOR]

Abstract In this study, the microstructure and mechanical properties of the atmospheric plasma-sprayed Cr 2 O 3 (C), Cr 2 O 3 -20YSZ (CZ), and Cr 2 O 3 -20YSZ-10SiC (CZS) coatings were evaluated and also compared with each other, so as to explain the coatings wear behavior. Microstructural evaluations included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and porosity measurements. Mechanical tests including bonding strength, fracture toughness, and micro-hardness tests were used to advance our understanding of the correlation between the coatings properties and their wear behavior. The sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of multimodal YSZ and subsequent SiC reinforcements to the Cr 2 O 3 matrix resulted in an increase in the fracture toughness and Vickers micro-hardness, respectively. It was found that the composite coatings had comparable coefficients of friction with pure Cr 2 O 3 coatings. When compared with the C coating, the CZ and CZS composite coatings with higher fracture toughness exhibited superior wear resistance. Observation of the wear tracks of the coatings indicated that the lower wear rates of the CZ and CZS coatings were due to the higher plastic deformation of the detached materials. In fact, improvement in the wear resistance of the composite coatings was attributed to a phase transformation toughening mechanism associated with tetragonal zirconia which created more ductile tribofilms during the wear test participated in filling the pores of coatings. [ABSTRACT FROM AUTHOR]

Abstract In this study, we report the preparation of CuCrO 2 -TiO 2 composite by a self-combustion glycine nitrate process. The effects of glycine-nitrate ratios on the phase evolution and surface area of CuCrO 2 -TiO 2 composite nanopowders were investigated. The precursor solution was prepared by adding glycine-nitrate in different ratios to an aqueous solution of Cu-Cr metal nitrates and titanium (IV) isopropoxide. The structures of the prepared powders were confirmed by X-ray diffraction, SEM and TEM studies. Moreover, the diffraction studies of the cotton-like CuCrO 2 -TiO 2 (GN = 1.7) showed the tetragonal anatase phase of TiO 2 and the rhombohedral phase of CuCrO 2. These studies confirmed the nanosized nature and porous structure of the CuCrO 2 -TiO 2 composite. The specific surface area of the nanopowder was measured using BET analysis. Increasing the GN ratio (1.5–2) decreased the specific surface area (51.2 m2/g to 21.7) due to particle grain growth. [ABSTRACT FROM AUTHOR]

The effect of chromium admixture on the processes in the HfB 2 -SiC ceramic powder system during its pressureless sintering at 1600 °C was studied. It was shown that an increase in chromium content from 0% to 15.5% in the HfB 2 -SiC ceramic powder mixture leads to a continuous increase in its relative density up to 90%. A transient liquid phase Cr-Si-C-B is formed at 1600 °C, and it promotes intense sintering of HfB 2 and SiC powders. The oxidation resistance of HfB 2 -SiC-Cr ceramics was studied in static air at 1000–1500 °C. It was shown that the oxidation resistance is greatly improved due to a decrease in the porosity of the sintered ceramic system because of chromium additive. The presence of chromium oxide in the formed surface glassy layer can also lead to the increase in the oxidation resistance. These results suggest that chromium can be considered as a promising sintering additive for HfB 2 -SiC and similar systems. [ABSTRACT FROM AUTHOR]

Ni doped Cr 2 O 3 (NCO) films have attracted much attention due to their applications in the field of photovoltaics. This study reports the tailoring of structural, electrical and optical properties as a function of Ni doping in Chromium oxide (Cr 2 O 3 ). NCO thin films were grown by Pulsed laser deposition (PLD) using 2nd harmonic Nd:YAG Laser on n-Si (100) with in-situ annealing of 450 °C. Structural analyses based on X-ray diffractometry (XRD) and Raman Spectroscopy showed the inconsistent variation in crystallinity and shift in A 1 g band in turn revealing the successful incorporation of Ni into Chromium oxide host lattice. In addition, electrical measurements also showed an inconsistent variation in resistivity ranging from 10 2 to 10 4 Ω − cm . The properties showed widening of band gap energy (E g ) from 3.41 to 3.60 eV as a function of Ni doping concentration with significantly decreased reflectance in the range of 500–600 nm thereby increasing the absorption, a pre-requisite for solar absorbers. [ABSTRACT FROM AUTHOR]

The wear resistance of chromium oxide (Cr 2 O 3 ) coatings could be improved by doping modification and changing the structural scale, etc. In this study, micrometric Cr 2 O 3 coatings were doped with different additives, CeO 2 and Nb 2 O 5 . Moreover, Cr 2 O 3 coatings were deposited from nanostructured feedstock by the combination process of plasma spraying and dry-ice blasting. The correlation between the microstructure, chemical components and tribological properties of plasma-sprayed Cr 2 O 3 -based coatings was discussed based on the investigation of their porosity, hardness and friction behaviors. The results showed that the composite coatings doped with additives exhibited a higher microhardness, corresponding to a lower porosity than pure Cr 2 O 3 coating under the identical plasma-spray condition. CeO 2 constituent was found to improve the wear resistance of Cr 2 O 3 coating while Nb 2 O 5 incorporation corresponds to a steep rise in the friction coefficient. The mismatch of coefficient of thermal expansion (CTE) between Cr 2 O 3 and Nb 2 O 5 lamellae facilitated the origin of fatigue cracks and the formation of microfracture pits. Although the combination process promotes a porosity reduction, the nanostructured Cr 2 O 3 (n-Cr 2 O 3 ) coatings present a lower microhardness than micrometric coatings, due to their loosen microstructure from insufficient plasma power compared to microscaled coatings. The wear mechanisms of both the micro- and nanometric Cr 2 O 3 coatings are fatigue cracks and material transfer. [ABSTRACT FROM AUTHOR]

Geopolymer (GP) consists of polymeric Al and Si tetrahedral network, with alkali metal cation (Na + or K + ) balancing the negative charge of Al tetrahedra. Although immobilization of heavy metal cations, that could balance the negatively charged Al tetrahedra in GP, was extensively studied, this is the first study that deals with immobilization of metal anions (dichromate, permanganate and hexacyanoferrate). GP samples were prepared from metakaolin (MK) as an aluminosilicate material and sodium silicate activator (Si/Al molar ratio 2) in the presence of the three anions. The efficiency of immobilization was studied in terms of % leaching of metal anions using atomic absorption spectrophotometry and in terms of leaching of total metal anions by conductivity measurements. The % leaching was less than 10% when 0.2% (w/w) of metal anion salts were incorporated in the GP. However, the % leaching increased from 10% to 20% with increasing loading of dichromate salt from 0.2% to 1.5% (w/w) which indicates that GP has limited capacity (limited number of pores) for immobilization of metal anions. When silica gel and alumina were employed as additives to MK (changing Si/Al ratio), the leaching of dichromate and total ions increased substantially and the surface of GP becomes more crystalline as indicated by SEM and EDS studies. The present work suggests that the mechanism of heavy metals immobilization by balancing the negatively charged Al tetrahedra of GP is not true. [ABSTRACT FROM AUTHOR]

In this paper, dynamic corrosion experiment of a high chromia refractory interaction with basic coal slag under slagging gasifier conditions was conducted by using rotary drum corrosion test with the FactSage thermodynamic analysis. The microstructures and chemical compositions of the corroded samples were analyzed by scanning electron microscopy (BEI and EDS), and the corrosion mechanism was investigated by combining thermodynamic simulation and SEM analysis. The results show that the simulation results were consistent with the results of corrosion test. Reaction layer and penetration layer are formed from the surface to the interior of the sample after corrosion. The (Mg, Fe) (Al, Cr) 2 O 4 spinel solution was formed in the reaction layer, which make the matrix structure become dense and change the overall structure of the particles’ uniformity. Corrosion of Cr 2 O 3 aggregate is relatively weak by slag. The Cr 2 O 3 dissolves into the slag through the formed spinel solution layer on the surface of aggregates. While, Cr 2 O 3 and Al 2 O 3 dissolve into molten slag through the spinel solution layer formed in the matrix. ZrO 2 in the matrix directly dissolved into molten slag and penetrates inner the matrix with the penetration of the slag to form a ZrO 2 -free region. The liquid sintering of the matrix has happened in the melt, causes the structure of the penetration layer become dense, which is different from that of the original sample. [ABSTRACT FROM AUTHOR]

Cr 2 O 3 -20 wt% Al 2 O 3 cermet composite and Cr 2 O 3 coatings were deposited by the detonation spray coating (DSC) and air plasma spray techniques on Ti-6Al-4V substrates. The microstructure and phase formation in the coatings were analysed. Micro hardness and fracture toughness of coatings were measured using Vickers diamond pyramid indenter. Owing to the well-defined layered structure with individually richer Cr 2 O 3 and Al 2 O 3 phases together with oxide-based solid solution at the splat boundaries, the DSC Cr 2 O 3 -Al 2 O 3 composite coating exhibits dense microstructure and better indentation fracture toughness than the well established plasma sprayed Cr 2 O 3 coating. Although the plasma sprayed Cr 2 O 3 coating also exhibits layered structure; the relatively poor indentation fracture toughness is attributed to the significantly higher porosity and weaker inter-splat bonding. Towards understanding the relative tribological behavior, the sliding and three-body abrasive wear tests were conducted. The material removal mechanism and associated degradation behavior of detonation sprayed Cr 2 O 3 -Al 2 O 3 coating has been correlated with coating microstructure comparatively against the plasma sprayed Cr 2 O 3 coating. Electro-chemical corrosion tests of coatings in salt solution (artificial sea water) reveals an improved corrosion protection by Cr 2 O 3 -Al 2 O 3 composite coating as compared to Cr 2 O 3 coating. Enhanced tribological performance and corrosion resistance was attributed to the dense and crack free structure of Cr 2 O 3 -Al 2 O 3 composite coating than its counterpart. [ABSTRACT FROM AUTHOR]

The crystal structures and magnetic properties of CrO 2 films of different orientations and thicknesses grown on SnO 2 were investigated and compared with those on TiO 2 . Results reveal that large anisotropic strains were found in (100) films, but only small strains existed in (110) films. The magnetic anisotropies of CrO 2 (110) films on SnO 2 and TiO 2 were found to be similar. As for CrO 2 (100) films, magnetic anisotropies were quite different-at the same thickness, the magnetic anisotropy of the film on SnO 2 substrate was higher than that on TiO 2 . However, the easy axes of the films were found to be always along c axis even at very small thickness, and no easy axis switching was observed. First-principle calculations reveal that magnetic anisotropy energy is not only concerned with anisotropic strain but also with the substrate. The competition between the anisotropic preference of interface and the effect of strains may be one important factor for determining the actual easy axis direction. The combined effects of strain and interface may also be one reason for the magnetic anisotropic difference between CrO 2 (100) films on SnO 2 and TiO 2 . [ABSTRACT FROM AUTHOR]

This work reports the preliminary synthesis of porous chromium carbide by microwave-assisted carbothermal reduction of simple reactants, Cr 2 O 3 and carbon black, in only 20 min of reaction time. XRD revealed well-crystalized chromium carbides, depending the reaction parameters as forward power and time. The particles morphology is a hollow sphere-like morphology, with porous walls, confirmed by SEM, with potential application as microfiltration and thermal barrier coating. The neck size of walls is a time-temperature dependent. [ABSTRACT FROM AUTHOR]

This work reports the preparation of morphologically well-defined chromium oxide nanoparticles with controlled sizes of 20–30 nm. The synthetic procedure encompass two stages, the first one refers to the preparation of chromium oxyhydroxide nanoparticles by a hydrothermal approach of previously precipitated xerogels, followed by a thermal transformation of CrOOH nanoparticles to Cr 2 O 3 . The series of chromium oxyhydroxide particles sized over the range 15–50 nm were prepared through the control of the pH of precipitation of the xerogels and the water/xerogel ratio of the hydrothermal aging. Results showed the formation of non-aggregated oxyhydroxide nanoparticles with two different trends: xerogels precipitated at pH 5 showed smaller particles for the higher amount of water (water/xerogel ratio in weight of 60/1); on the contrary, at pH 10 the size of oxyhydroxide nanoparticles increased with increasing the amount of water. The transformation from CrOOH to Cr 2 O 3 took place at around 450 °C; well-defined, non-aggregated crystalline nanoparticles of Cr 2 O 3 with similar sizes, regardless of the precursors, were observed after treating the different oxyhydroxides at 600 °C for one hour. Chromia nanocrystals obtained from precipitates at pH 10 displayed intense and better-defined absorption bands than those prepared at pH 5. Remarkable high reflectance intensity was shown by chromia nanocrystals prepared at pH 10 and the larger 60/1 water/xerogel ratio. The mechanisms of formation of both the CrOOH –grimaldite- and the Cr 2 O 3 –eskolaite- nanoparticles by the two subsequent steps have been proposed based on the results arisen from the different characterization techniques. [ABSTRACT FROM AUTHOR]

The Ruhrstahl-Heraeus (RH) snorkel is one of the most important parts of the RH furnace, which is the primary facility for producing high-quality steel. The magnesia-spinel refractory is the ideal replacement for the classic magnesia-chrome refractory in the RH snorkel. In this study, the effects of Cr 2 O 3 addition (0–3 wt%) on properties of magnesia-spinel refractories were investigated. It was found that the addition of Cr 2 O 3 results in the acceleration of the densification process and a decrease in the cold strength as well as a significant increase in the hot modulus of rupture. Thus, the solid solution formed with the spinel significantly improves the resistance to thermal shocks, with the greatest improvement being observed after the addition of 2 wt% Cr 2 O 3 . [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of LaCrO 3 half-doped with Al are reported in this work. Pure and half-doped samples were prepared by combustion synthesis using urea as fuel. The crystal structure was investigated by X-ray diffraction and Rietveld analysis. A structural phase transition caused by a decrease of the chemical pressure was observed. The scanning electron microscopy (SEM) images show the formation of porous samples with particles of irregular morphologies. A quantitative Energy-dispersive X-ray spectroscopy (EDS) analysis on the surface indicates the inclusion of the Al on the structure. However, a small deficiency of La and Al was observed. Magnetization measurements as a function of temperature reveal an antiferromagnetic order in both samples. A large decrease of T N (Néel temperature) and a reduction of the frustration factor is observed in the sample doped with Al. The magnetic isothermal at 5 K shows a typical antiferromagnetic behavior with a slightly spin canting for the doped sample. [ABSTRACT FROM AUTHOR]

In gasifiers, the carbon feedstock typically reacts with oxygen and water to produce synthesis gas. Chromia-free lining materials for gasifiers have to be developed with due consideration to environmental requirements. Novel Al 2 O 3 -SiC-C (ASC) refractories were considered in this work. The corrosion resistance of ASC refractories and a conventional Cr 2 O 3 -Al 2 O 3 -ZrO 2 (CAZ) refractory was evaluated in air and in coke bed. Furthermore, the corrosion behavior of ASC and CAZ refractories was simulated by FactSage. The results showed that ASC specimens exhibited better slag penetration and corrosion resistance than CAZ one in air and coke bed, which was ascribed to the fact that: 1) the presence of carbon, such as flake graphite increased the wetting angle of slag on ASC specimens; 2) the addition of flake graphite and the reduction of Fe 2 O 3 in the slag increased the viscosity of the slag; 3) in-situ formed SiC whiskers in ASC specimens could not only form the bonding system but also promote the microporous structure to hinder the slag penetration into ASC specimens. [ABSTRACT FROM AUTHOR]