Cr2O3 Content Research Articles

Corrosion behaviors and mechanism of AlxCrFeMnCu high-entropy alloys in a 3.5 wt% NaCl solution

This study investigated the corrosion behavior of as-cast AlxCrFeMnCu (x = 0, 0.5, 1.0, 1.5, 2.0) high-entropy alloys (HEAs) in a 3.5 wt% NaCl solution at room temperature. The results indicated that the corrosion resistance of the AlxCrFeMnCu HEAs decreased with increasing Al content. Intergranular corrosion was the primary corrosion type for CrFeMnCu and Al0.5CrFeMnCu HEAs, while Al1.0CrFeMnCu, Al1.5CrFeMnCu, and Al2.0CrFeMnCu HEAs exhibited selective corrosion with enrichment of Al and Cu in the BCC2 phase. The XPS fitting calculations indicated that an increase in the molar ratio of Al led to a decrease in Cr2O3 content and an increase in Al2O3 content, which weakened the stability and protective properties of the passive film.

Mineral chemistry and alteration patterns of Cr-spinel in serpentinized peridotites from NW Iran

The Late Cretaceous ophiolite mélange in the Salmas area of NW Iran is a part of the Neotethys ophiolites. The mélange includes serpentinized harzburgite, serpentinites, mafic rocks, radiolarite, layered red pelagic limestones and grey and white marbles. Harzburgite main primary mineral phases are olivine, orthopyroxene, clinopyroxene and Cr-spinel. Cr-spinel has Cr2O3 contents of 21.13 to 30.18 wt% and high Al2O3 (38.67–48.52 wt%), FeO (15.18–18.13 wt%) and MgO (15.18–17.51 wt%) contents. The 100 × Cr/(Cr + Al) ratios of 23 to 34 indicate 9 to 13 % partial melting in the Mid Ocean Ridge (MOR) environment for the origin of the peridotites. An alteration zone is developed around the altered Cr-spinel. Fine-grained minerals assemblage at the spinel crystals’ margin includes Cr-rich chlorite, Cr-rich garnet and spinel-silicate mixture. A 2–5 μm wide transitional zone is developed between the chromite-silicate assemblage and the Cr-rich garnet zone. The chemical variations of major oxides across the alteration zone are mainly diffusion controlled. Al, Cr and Mg have diffused out from the primary spinel and Fe and Mn have diffused into the spinel. Cr-spinel is altered in two stages due to serpentinization. During the first stage and following hydration, spinel reacted with olivine and orthopyroxene to form Cr-rich chlorite and ferrian chromite. Silica formed at this stage. At the second stage, the reaction between the chromite-silicate assemblage and Cr-rich chlorite plus silica form the first stage and Ca2+ in the fluid (released from clinopyroxene alteration) produced Cr-rich garnet and H2O-rich fluid, at temperature between 400 and 600 °C.

Crystallization, microstructural evolution, heavy metals migration, and solidification mechanism of blast furnace slag glass-ceramics

In recent years, researchers have prepared glass-ceramics using a mixture of multiple solid waste materials, which is an effective and resourceful way to use and store solid waste. However, solid waste usually contains multiple heavy metals, which presents challenges during the mixing and co-solidification processes. In this study, high-performance glass-ceramics with low leaching were prepared from blast furnace slag (BFS). The synergistic curing mechanism of BFS glass-ceramics for heavy metals Cr, Mn, Cu, Zn, Ni, and Co was investigated in detail, as well as the migration pattern and storage state of heavy metals under different heat treatment stages and different Cr contents. The results show that the increases in temperature and Cr2O3 content contribute to the incorporation of heavy metals into the crystal lattice and promote crystal growth. Excessive crystallization of spinel causes aggregation, which further curtails the leaching of heavy metals. The leaching concentration of heavy metals mainly depends on the heavy metal content in the glass network and the degree of network polymerization. Thus, spinel acts as a crystal core for the solidification of heavy metals, while augite and glass phases act as a double barrier to physically encapsulate them, which is effective for the storage of a wide range of heavy metals. Furthermore, the physical and chemical properties of BFS glass-ceramics are consistent with the Chinese industry standard “Glass-ceramics plate for industrial application” (JC/T 2097-2011). This study provides important theoretical support for the synergistic solidification of multiple heavy metals in glass-ceramics, as well as insights into the preparation of glass-ceramics by mixing BFS with other solid wastes.

Effect of Mn addition on microstructure and corrosion behavior of AlCoCrFeNi high-entropy alloy

In this study, the effects of Mn content on the microstructure and corrosion resistance of AlCoCrFeNiMnx (x = 0, 0.25, 0.5, 0.75, and 1) high-entropy alloys were investigated. The results indicate that with increasing Mn content, the HEAs consistently comprise nanophase BCC geometry with different shapes embedded in the ordered B2-phase matrix, and the morphology of the microstructure changes from a coarse dendritic structure to a fine dendritic structure, then to a completely columnar dendrite structure. The microhardness of the HEAs increases gradually to 620 HV0.2 when x = 1, owing to the solid-solution and fine-grain strengthening. The corrosion resistance of the HEAs in 3.5 wt% NaCl solution first increases and then decreases, reaching a maximum with the lowest self-corrosion current density of 2.869 × 10−8 A∙cm−2 when x = 0.5. Improvement in corrosion resistance is related to a reduction in degree of composition segregation in the microstructure of HEAs, which leads to the formation of a dense and complete passivation film on the surface of the alloys. However, when the Mn content is in the range of 0–0.5, the pitting potential of the HEAs gradually decreases, although the passivation current density also gradually decreases. Higher Mn content (x > 0.5) leads to a transition of the HEAs from passivation to active dissolution. This indicates that the stability of the passivation film on the HEAs decreases with higher Mn content. XPS analysis revealed a gradual decline in the relative content of Cr2O3 and a gradual increase in the presence of unstable oxides such as MnO and Mn2O3 in the passivation film, leading to this phenomenon. The present work reveals that the addition of Mn in the AlCoCrFeNi HEA affects not only the microstructure and composition segregation but also the composition and stability of the passivation film, leading to a non-monotonic variation in the corrosion performance of the present HEAs with respect to the Mn content.

Effect of annealing on corrosion resistance and mechanical properties of Cr–Fe–Ni–Co–Mo–Si–B amorphous coating

Cr–Fe–Ni–Co–Mo–Si–B amorphous coating was successfully prepared on 316 L steel using atmospheric plasma spraying (APS). The effects of different annealing temperatures on the crystallization process of amorphous coatings, thus on the corrosion resistance and mechanical properties of coatings were studied. The results indicated that heat treatment can increase the hardness of the amorphous coating by 12.5% and reduce the wear rate by 30%. In addition, compared to heat-treated coatings, the amorphous coating had the highest corrosion voltage (−0.506V) and lower corrosion current (5.609 × 10−6 A). The passivation film on the amorphous coating provided the best protection due to the relatively high content of Cr2O3. The molecular dynamics (MD) calculation results also indicated that the adsorption energy of hydrogen chloride molecules on Cr–Fe–Ni–Co–Mo–Si–B amorphous coating (−90.94 kcal/mol) was greater than that of 316 L (−293.03 kcal/mol).

Synergistic effects of Cr addition on surface characteristics and its implications on wear and in vitro biocompatibility of TiMoNbTaW alloys

Refractory metal based high entropy alloys (RHEAs) presents promising anti-wear and cytocompatibility to meet the articulating demands in artificial hip/knee prosthesis. In this study, TiMoNbTaW RHEAs were fabricated through arc melting, and modified with Cr to enhance their bulk, and surface characteristics. The Cr addition resulted in a gradual increase in bulk hardness from ⁓4.9 GPa to ⁓7.1 GPa, and yield strength from ⁓1.3 GPa to ⁓1.9 GPa, attributed to lattice distortion induced misfit strain. X-ray photoelectron spectroscopy (XPS) confirmed the formation of a native passive film on alloys surface, consisting of oxides TiO2, MoO2, MoO3, WO3, Nb2O5, Cr2O3 and Ta2O5. The wear resistance improved in accordance with Archard's law, while friction responses were influenced by Cr2O3 content. Higher Cr2O3 content imparted lubricating effect, reducing friction coefficient ⁓0.18–0.23, and wear rate in the order 10−5 mm3/Nm. Moreover, higher Cr2O3 in the native film contributed to the excellent cytocompatibility against MC3T3-E1 cells. Cell proliferation increased with increase in Cr content in the RHEA and showed higher alkaline phosphatase activity (ALP) activity when Cr content was 10% or more. This study evaluates the effect of Cr increment on the microstructural and mechanical properties in TiMoNbTaW RHEAs, and highlights the synergistic effects of the passivation-mediated native film, influencing tribological, and in-vitro cellular response.

Ramifications of chromium-to-bismuth ions substitution on the structural and optical characteristics of bismuth borate glasses for optoelectronic applications

The exploration of optoelectronic materials with distinctive properties is still ongoing. To this end, a series of quaternary glassy materials of the composition 15Na2O–65B2O3–(20–x)Bi2O3–xCr2O3, denoted as NBBC, is synthesized using the melt quenching method, where x = 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mol%. X-ray diffraction (XRD) confirms that the glasses under investigation are amorphous, except for the sample with a molar ratio of 10% Cr2O3, which showed a polycrystalline structure. FTIR analysis of the NBBC glasses reveals structural changes affecting Bi-O and B-O vibrations, suggesting a correlation between composition and optical properties. Interestingly, the bandgap energy of the NBBC glasses, determined optically, demonstrates a reduction from 2.881 eV to 1.941 eV with increasing Cr2O3 content. Conversely, the tail energy exhibits an opposite trend. The observed reduction in the bandgap with increasing Cr-ions is attributed to the introduction of chromium in the glassy matrix, which changes the electronic structure and enhances the light absorption efficiency. Furthermore, various optical parameters are calculated, such as the optical constants, dielectric constants, loss energy, the density of coverage, sheet resistance, the figure of merit factor, and dispersion parameters. Notably, all of these parameters demonstrate a remarkable sensitivity to the gradual increment of chromium ions. These findings imply that the NBBC glasses could be appropriate for optoelectronic purposes.

Inclusions and Spectral Characterization of Demantoid from Baluchistan, Pakistan

Demantoid is the green variety of andradite [Ca3Fe2(SiO4)3], an exceptionally rare and precious gemstone worldwide. In recent years, a small amount of gem-quality demantoid has been found in Pakistan. This research focuses on nine demantoids sourced from Muslim Bagh, Baluchistan, Pakistan, presenting a comprehensive analysis of the spectral characteristics and inclusions of Pakistani demantoid using classical gemological methods, energy dispersive X-ray fluorescence (EDXRF) chemical analyses, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and ultraviolet and visible (UV-vis) spectroscopy. The results show that the content of Cr and V in most samples is lower than the detection line of EDXRF, with only one sample containing a Cr2O3 content of 0.032%. The extremely low Cr content sets Pakistani demantoid apart from demantoid of the serpentinite type found in other regions. Notably, the UV-vis spectrum reveals characteristic absorption at 443 nm due to Fe3+, while a further contribution from Cr3+ would be highly likely, and weak absorption at 550 nm caused by Fe3+. This suggests that iron (Fe) is the primary chromogenic element of Pakistani demantoid, but the role of Cr3+ cannot be ignored. The FTIR spectrum of Pakistani demantoid displays the absorption peaks associated with [SiO4]4− groups at 937 cm−1, 848 cm−1, and 817 cm−1, while the absorption peaks resulting from trivalent cations appear at 481 cm−1 and 442 cm−1, which are the characteristic FTIR spectra of demantoid. Raman spectroscopy further reveals absorption peaks are displayed near 994 cm−1, 843 cm−1, 818 cm−1, associated with (Si–O)Str vibrations (Si–O stretching vibration), and absorption peaks are displayed near 350 cm−1 and 310 cm−1, related to the rotation of SiO4–R(SiO4)4−, and the peaks near 514 cm−1 and 494 cm−1 are related to (Si–O)bend vibrations (Si–O bending vibration). Additionally, related absorption peaks near 168 cm−1 are attributed to the translation of SiO4–T(SiO4)4−, and absorption peaks near 234 cm−1 are associated with the translation of X2+–T(X2+) (X2+ represents divalent ions). The common dark opaque inclusions found in Pakistani demantoid consist of a combination of magnetite and hematite. Additionally, some samples of Pakistani demantoid display inclusions of calcite. This unique combination of inclusions differentiates Pakistani demantoid from demantoids sourced from other regions. It signifies that Pakistani demantoid has a distinctive geological origin resulting from the interplay of serpentinization and skarnization processes. This geological formation distinguishes it from demantoids solely hosted in serpentinite or skarn environments in other origins. The identification of these characteristics holds significant importance for accurately determining the origin of Pakistani demantoid.

Effect of Mg treatment on inclusion behaviors in 430 ferritic stainless steel during solidification

To understand the effect of Mg treatment on the precipitation, growth, and transformation of inclusions in 430 ferritic stainless steel during solidification, slag refining and Mg treatment experiments with different cooling methods were conducted at 1873 K (1600 °C). Experimental results showed that the oxide inclusions in 430 stainless steel without Mg treatment were mainly Al2O3–SiO2–MnO (slag phase), Al2O3–Cr2O3–MnO (spinel phase), high-Al2O3 (corundum phase) and CaO–SiO2–Al2O3–MnO (slag phase), while all of the oxides except CaO–SiO2–Al2O3–MnO inclusions transformed to MgO–Al2O3–Cr2O3–MnO (spinel phase) after Mg treatment. With water quenching, the average inclusion diameters were about 1.4 μm in both of the Mg-free and Mg-bearing steels, while they increased to approximate 3.1 and 1.9 μm after furnace cooling, separately. With the decrease of cooling rate from 26.2 to 1.24 K s−1, in the Mg-free steel, the average Al2O3 and Cr2O3 contents in the inclusion increased from 19.6 to 42.6 mass% and from 12.22 to 19.44 mass%, respectively, and the average SiO2 content decreased from 43.5 to 17.1 mass%. However, the average composition of inclusions in Mg-bearing steel was relatively stable and independent of cooling rate. A kinetic model was established with the solute micro-segregation model to predict oxide inclusion growth during cooling and solidification. Without and with Mg treatment, under a cooling rate of 1 K s−1, the calculated final sizes of the most stable oxide inclusions were 3.27 and 1.88 μm, respectively. The predicted average compositions and diameters of oxide inclusions were generally consistent with the experimental results.

Phlogopite phenocrystals with inclusions of chrome spinelides from non-diamond-bearing kimberlites: the case of An-195 body of the West Ukukit field

The article presents the results of a microprobe study of the composition of phlogopite macrocrystals with inclusions of chrome spinelides from An-195 kimberlite body of the West Ukukit field; Yakut kimberlite province. The purpose of this study was to establish the genesis of such phlogopites: whether they are representatives of deep mantle matter or their formation is directly related to the formation of kimberlites composing An-195. It was found that the inclusions of chrome spinelides are confined only to chromic non–zonal phlogopites or to chromic sites of zonal macrocrystals (Cr2O3 0.75–1.55 wt.%; TiO2 2.67-3.84 wt.%; Mg# 83-88). Based on a comparative analysis of the studied phlogopites and chromespinelides with the composition of analogues from the parageneses of these minerals in various mantle xenoliths of ultrabasic rocks; eclogites and rocks of the MARID series; it was concluded that these phlogopites most likely represent a phenocrystal association of kimberlite minerals. They clearly differ from phlogopites of the MARID series rocks with equal Mg# and TiO2 in higher Al2O3 contents; from phlogopites of ultrabasic mantle rocks xenoliths – generally with lower magnesia content. Phlogopites from eclogites have a generally higher Cr2O3 content. Inclusions of high–chromium spinelides in phlogopite (Cr2O3 44-50 wt.%; TiO2 3-5.5 wt.%; Fe3+ < 0.35 f.e.) correspond in composition to spinelides from cataclysmic dunites and are products of their recrystallization under the influence of high-temperature mantle fluid. Inclusions of less chromic spinelides (Cr2O3 30-44 wt.%; TiO2 4-7.5 wt.%; Fe3+ > 0.35 fe) probably crystallized simultaneously with phlogopite macrocrystals and were captured by them during long-term co-growth.

Effect of ultraviolet illumination on corrosion resistance of 304 austenitic stainless steel in molybdate-containing solution

This study investigates the effect of ultraviolet (UV) illumination on the corrosion resistance of 304 stainless steel in molybdate-containing solution. The UV illumination was found to reduce the passivation and pitting resistance of the passive films. In addition, the passive film exhibited n-type semiconductor characteristics. Under UV illumination, the content of Cr2O3 within the passive film decreased. Moreover, the formation of a built-in electric field inhibited the absorption of MoO42− on the substrate surface, thereby weakening the corrosion inhibition of Na2MoO4. This leads to a reduction in the corrosion resistance of the passive film.

Mineralogical anatomy of the Cr-rich quenched angrite Northwest Africa 12774: Implication to mantle heterogeneity

Angrites are a small group of basaltic meteorites and their origin is currently disputed. Among these, Northwest Africa (NWA) 12774 is a quenched angrite that was reported having an anomalously high bulk Cr2O3 content (∼0.45 wt%). However, the reason behind this anomaly, which is critical for understanding the evolution of the angrite parent body, remains unknown. Here, we performed a detailed petrographic, mineralogical, and bulk oxygen and chromium isotopic composition study on this meteorite. NWA 12774 consists of porous olivine macrocrysts, phenocrysts of olivine and Al-Ti-rich augite, and spinel micro-phenocrysts with fine-grained groundmass. The olivine macrocrysts and the magnesian cores of olivine phenocrysts show compositional correlations distinctly different from typical olivine phenocrysts. The olivine macrocrysts contain small chromite/chrome-spinel inclusions which have the highest Cr2O3 content (53.2 wt%) for chromite/spinel in angrites to date. Based on these textural and chemical features, the olivine macrocrysts and the magnesian cores of olivine phenocrysts are identified as xenocrysts. Some pyroxene phenocrysts contain regions with complexly zoned microtextures, which have much larger chemical variations compared with those with simply zoned microtextures. The regions with complexly zoned microtextures are likely to be of xenocrystic origin. The bulk Cr2O3 content in NWA 12774 was estimated through two approaches, both of which show the bulk Cr2O3 content to be around 0.3 wt% or possibly up to ∼ 0.45 wt%, which is consistent with previously measured values. The high Cr2O3 content in NWA 12774 could be attributed to both the high abundance of spinel micro-phenocrysts and their high Cr2O3 contents, rather than the presence of Cr-rich xenocrysts. The calculated melt rare earth element concentration in NWA 12774 equilibrated with the most Mg-rich augite is essentially identical to those in LEW 87051 and Asuka 881371, which however have Cr2O3 contents much lower than NWA 12774. We suggest that the mantle source of NWA 12774 may not be as depleted in Cr and probably other volatile elements as other angrite sources. The various Cr2O3 contents in different quenched angrites probably reflect that their mantle sources have not been homogenized.

Identify key serpentines antigorite, lizardite and chrysotile with various compositions and crystallographic orientations using micro-Raman spectroscopy

Serpentines are geologically important minerals, and antigorite (Atg), lizardite (Lz) and chrysotile (Ctl) are the three key varieties. Their quick and accurate identification with micro-Raman spectroscopy requires to consider the effects of different crystallographic orientations and different chemical compositions. By collecting from existing literatures all Raman spectroscopic data and compositional data acquired from the same or identical Atg, Lz and Ctl samples, we critically examined the compositional effects for the first time, and found that some compositional parameters like the Al2O3 and Cr2O3 contents have significant impacts on the Raman features. Taking into account the effects of both compositional difference and crystallographic orientation difference, we propose two identification schemes for Atg, Lz and Ctl: the first one uses those weak but characteristic Raman peaks at 1200–1000 cm−1, and the second one uses those intense and unanimously-observed Raman peaks at ∼688, 378 and 229 cm−1. As for the first identification scheme, no peak at 1200–1000 cm−1 suggests the presence of Lz; a single peak at ∼1045, at ∼1070, or at ∼1106 cm−1 indicates the presence of Atg, Lz, or Ctl, respectively; two Raman peaks at ∼1040 and 1070 cm−1 implies the presence of Lz; the occasionally observed one single peak at ∼1040 cm−1 may imply the presence of either Atg or Lz, which can be sought out by resorting to the peak position ratio R∼1045/688 (Atg having R∼1045/688 > ∼1.521 whereas Lz attaining R∼1045/688 < ∼1.521). As for the second identification scheme, Atg can be readily separated from Lz and Ctl by using the exact wavenumbers of the Raman peaks at ∼688 and ∼378 cm−1, and Lz and Ctl can be further discriminated by using the exact wavenumbers of the Raman peaks at ∼378 and ∼229 cm−1. Under most circumstances, both identification schemes do not require the information of crystallographic orientation or composition, and can be conveniently applied to identify the serpentines of Atg, Lz and Ctl.

Improved corrosion resistance of laser melting deposited CoCrFeNi-series high-entropy alloys by Al addition

The microstructural evolution, pitting performance, and passive-film properties of AlxCoCrFeNi high-entropy alloys (HEAs) fabricated via laser melting deposition (LMD) were investigated using material characterization techniques and electrochemical measurements. The substrates of the LMD HEAs transform from a face-centred cubic (FCC) to a body-centred cubic (BCC) structure with increasing Al addition. The BCC-structured B2 and A2 phases precipitate in the HEA substrate when the Al content reaches 10 mol.%. Ternary-phase HEA with Al addition of 10 mol.% exhibits the best corrosion resistance, which is attributed to favourable modifications in the Cr2O3 content and passive-film thickness.

Ceramic-inorganic polymer composites for protection against electromagnetic radiation mechanical properties designing

The possibility of designing mechanical properties of ceramic-inorganic polymer composites for protection against electromagnetic radiation is considered. As a result, the mechanical properties of polymer composite based on polyamide, modified with ceramic-inorganic graphite-ferromagnetic fillers (silicon carbide, chromium oxide Cr2O3 and graphite) was received and optimized. The strength characteristics complex of ceramic-inorganic polymer composites with silicon carbide SiC, chromium oxide Cr2O3 and graphite content in diapason 5-15 % wt. were studied. It was established that the optimal strength characteristics can be received using binary modification of polyamide with ceramic-inorganic graphite-ferromagnetic fillers: polyamide 6 – SiC 10% wt. – Cr2O3 10% wt. and polyamide 6 – SiC 10% wt. – graphite 10% wt. Using mathematical modeling, it was established that the polyamide 6 – SiC 10% wt system is the most optimal for three-component complex modification with ceramic-inorganic graphite-ferromagnetic fillers – Cr2O3 10% wt. – graphite 10% wt. By design experimental-statistical mathematical models in equal regressions, mathematical optimization of mechanical properties of polymeric ceramic-inorganic composites contains for protection against electromagnetic radiation was carried out. Designed polymer ceramic-inorganic composites for protection against electromagnetic radiation according to their strength characteristics can be used for modern radio absorbing materials production.

Physical, Optical, and Photoluminescence Properties of Cr2O3 in Borosilicate Glasses

The glass samples (35-x)B2O3:35SiO2:12Na2O:7.9CaO:0.1Sb2O3:10BaO:xCr2O3 with a variation of Cr2O3 content were successfully fabricated and characterized for solid-state lighting material applications. The results showed the most suitable composition within the range of study at 0.02 mol% of Cr2O3. This composition gave higher reflection loss (RL), lower oxide polarizability, and lower molar refractivity. The Commission International de I'Eclairage (CIE) chromaticity coordinates confirmed a strong orange color emission. Hence, this suggests that the 0.02 mol% Cr2O3 glass is a good candidate and cost-effective for orange-emitting solid-state lighting material applications. This study will be a useful literature source for further development in this field.

Improved tribological and electrochemical behavior of concentrated chromite coatings developed by HVOF and plasma spray techniques

Mineral coatings have the ability to tackle the most common degradation processes (wear and corrosion) in industries at amazing ‘quality to cost’ ratio, as compared to synthetic ceramics. In the current study, concentrated natural chromite with 55 wt.% Chromium oxide (Cr2O3) is deposited on steel substrate through High Velocity Oxygen Fuel (HVOF) and Atmospheric plasma spray (APS) techniques. Effect of deposition processes and Cr2O3 enrichment on microstructure, hardness, tribological and electrochemical behavior of coatings is studied. Tribological tests were performed using pin-on-disc setup, coatings deposited with APS have shown excellent wear resistance behavior as compared to HVOF coating. Owing to the brittle nature of chromite coatings, they were worn by abrasive wear irrespective of the deposition process. Electrochemical behavior of coatings is evaluated by potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. APS and HVOF coatings have exhibited very high protective efficiency of 93 and 88% respectively, against steel substrate. Equivalent electrical circuit (EEC) based on EIS results has also been conceptualized and verified with ZSimpWin analysis software. Established EEC has illustrated capacitive behavior due to the protective oxide nature of coatings. Despite having relatively higher porosities in APS coatings, they display an excellent potential for wear and corrosion resistant applications. Results revealed that hardness, compactness, tribological and corrosion performance of chromite coatings have been substantially improved due to higher Cr2O3 content.

Novel strategies for the enhancement of the NIR emission in the Ca doped ZnO system: Doping with Cr or adding Sb2S3

We report two novel strategies to enhance the NIR emission in the ZnO:Ca system. In the first strategy, we synthesized ZnO:Ca nanoparticles using a wet chemical method and doped them with various concentration of Cr. SEM images showed that the ZnO:Ca,Cr nanoparticles had a grain-like morphology and their sizes increased from 33 to 110 nm after incrementing the Cr concentration from 4 to 17 mol%. The analysis by X-ray diffraction (XRD) revealed that he ZnO:Ca,Cr sample made with 4 mol% of Cr had a pure hexagonal phase but the other samples synthesized with Cr concentration above 11 mol% presented the hexagonal phase and a small content of Cr2O3 (<3%). Moreover, the photoluminescence (PL) spectra of these samples showed two main emission peaks in the blue and NIR regions (λexc = 265 and 365 nm). In particular, the ZnO:Ca,Cr sample made with 17 mol% of Cr had the strongest NIR emission in the 700–850 nm region and only this sample showed a prominent NIR emission peak at 805 nm. Moreover, the CIE maps showed that the emissions of the ZnO:Ca,Cr samples are located in the blue region under excitation at 265 nm, but it was tuned to the orange region under excitation at 365 nm. In the second strategy, different amounts of Sb2S3 was added during the synthesis of ZnO:Ca to form ZnO:Ca/Sb2S3 composites. In this case, we obtained different morphologies of grains, rod-like and sheet-like for Sb2S3 contents of 10, 28 and 34 wt%, respectively. In addition, the composites presented a mixture of hexagonal and orthorhombic phases, which corresponded to the ZnO and Sb2S3, respectively. The ZnO:Ca/Sb2S3 composites had NIR emissions peaks in the 650–800 nm region and their intensity increased with the content of Sb2S3. Furthermore, their visible emission was tuned from blue to orange-red or to cold white light according to the CIE maps. Overall, the best ZnO:Ca,Cr sample had 312% and 37% higher emission than the ZnO:Ca reference sample and the best ZnO:Ca/Sb2S3 composite (under 265 nm excitation), respectively. In general, XPS studies showed the existence of oxygen vacancy defects, which produced the visible-NIR emissions in all the samples. The strategies presented here for NIR emission enhancement are feasible at low cost and the NIR emissions produced here occur within the first biological window (700–1000 nm), which is of interest for biomedical applications.

Effect of Cr2O3 Content on the Viscosity and Crystallization Properties of Continuous Casting Mold Slag

Herein, the effect of Cr2O3 on the crystallization and flow behavior of CaO–SiO2–Al2O3–Na2O–CaF2 continuous casting mold slags is investigated. The viscosity in the slag at 1200–1500 °C is measured by the rotating cylinder method and a quantitative relationship between the viscosity and the Raman structure Q3/Q2 is constructed. The time–temperature–transformation and continuous cooling transformation diagrams for various slags are obtained using a single hot‐thermocouple technique. The results show that with the crystallization temperature decreases, it can be observed that the crystal growth mode gradually changes from 3D spherical and 2D massive to 1D needle‐like. The study finds the transition from network modifier to network forming agent in the slag for Cr2O3 content from 0 to 3 wt%. The Cr2O3 added to 1–2 wt% decreases the viscosity and promotes crystallization. The viscosity increases and the crystallization is inhibited when the content of Cr2O3 increases to 3 wt%. Meanwhile, when Cr2O3 is added to 3 wt%, the Cr2O3 crystalline phase precipitates except for the main crystalline phase 2CaO·SiO2.

Effects of TiO2 addition on phase, mechanical properties, and microstructure of Cr2O3–Al2O3 ceramic composite

TiO2 is a sintering additive that can significantly improve the sintering and mechanical properties of Cr2O3–Al2O3 refractory materials with high Cr2O3 contents. In this study, TiO2-reinforced Cr2O3–Al2O3 composite refractories were prepared using a reaction-sintering process. The microstructure, phase composition, mechanical properties, and strengthening mechanism of the TiO2-reinforced Cr2O3–Al2O3 composite refractories were investigated. The results indicated that the Al2O3–Cr2O3–TiO2 composite refractory with a TiO2 content of 3.0–4.5 wt% had good compactness (porosity of 5.89%), hardness (17.21 GPa), wear resistance (wear rate of 0.4 mm3/Nm), flexural strength (101.10 MPa), and compressive strength (420.90 MPa). This is mainly because when the added amount of TiO2 was <3.0 wt%, TiO2 was solidly soluble in the matrix, forming a Ti3+-doped (Cr, Al)2O3 solid solution, inhibiting abnormal grain growth, rapidly increasing the sintering shrinkage of the sample, rapidly increasing the bulk density, rapidly decreasing the apparent porosity, and improving the sintering and mechanical properties of the composite resistant material. When the TiO2 addition exceeded 4.5 wt%, a large amount of (Cr, Al)2TiO5 phase was distributed between the grain boundaries of the solid solution, and its bulk density started to decrease. The sintering shrinkage and apparent porosity did not change significantly, and the bonding between the solid solution was not improved. Thus, the sintering and mechanical properties of the composite resistant material deteriorated. Taking into account the slag resistance and mechanical properties of the material, Al2O3–Cr2O3–TiO2 with a TiO2 content of 3.0–4.5 wt% can meet the service requirements for mechanical properties of the lining of smelting reduction ironmaking furnaces.