Low Chromium Research Articles

Understanding of leaching, immobilization and oxidation behaviors of chromium in Cr2O3-doped aluminosilicate glasses

Vitrification is an efficient and green approach to prepare cement supplementary material using hazardous solid waste. However, research on the safety and toxicity of chromium-containing glass remains limited. In this study, chromium leaching, immobilization and oxidation behaviors in calcium aluminosilicate glass with various SiO2:Al2O3 and Cr2O3 are studied. The glass system with the lowest Cr leaching amount was obtained at the SiO2:Al2O3 ratios of 3:4, with 50.87 % chromium distribute in glass and 49.13% in Al2O3 phases, enhancing the chromium immobilization capacity. Double immobilization mechanism was proposed, which involves the solid solution of Cr in the glass network structure and chemical consolidation in the Al2O3 phase. The dissolution and erosion of minerals is the main reason of chromium leaching. A higher degree of polymerization glass exhibits stronger corrosion resistance and lower chromium leaching amounts, contributing to the stable connection of [SiO4] tetrahedra in the glass network structure. The initial pH value of the extractant had little effect on the chromium leaching amount. The chemical composition of glass mainly affects the pH of final leaching solution. The glass with SiO2:Al2O3 ratios of 3:4 shows the safest chemical composition, the final leaching solution exhibits acidity, which inhibits the oxidation chromium.

Experimental Study on Enhancement in the Tribological Behaviour of Military Grade Lubricant Using Titanium Dioxide Nanoadditives for Aerospace Applications

ABSTRACTThe coefficient of friction of low carbon chromium alloy steel with military grade lubricant was high, resulting in increased heat generation and temperature rise of the lubricant in the aircraft power transmission units such as engine gearbox, accessory gearbox and so on. To address this, the current research proposes the addition of TiO2 nanoparticles to MIL grade lubricant as an additive to enhance the tribological performance. In this experimental study, TiO2 nanolubricant was prepared using various surfactants for better suspension of TiO2 nanoparticles, and properties were evaluated for both base lubricant and nanolubricant. The tribological experiments were conducted using a four ball tester, a shear stability tester and a reichert tester. In a four ball test, TiO2 nanolubricant resulted in a 27.3% reduction in wear scar diameter by the addition of TiO2 nanoparticles to the base lubricant. In a shear stability test, TiO2 nanolubricant showed 80% better shear stability than the base lubricant. In the reichert test, the coefficient of friction was reduced by 13% with the TiO2 nanolubricant. The experimental findings demonstrated that the TiO2 nanoparticles, as an additive to a military grade lubricant, have superior tribological properties for aerospace applications.

Crystal structure evolution and solid solution mechanism of Al2O3-Cr2O3 system under different reaction conditions

The (Al1-xCrx)2O3 solid solution (ACS) is expected to be an low pollution chromium source for high-performance alumina-chromium oxide refractory materials. In this work, the effects of Cr2O3 content and reaction conditions on the solid solution behavior in the Al2O3-Cr2O3 system were explored and the mechanism was revealed. The relationship between the lattice parameters of the formed ACS phase and the content of Cr2O3 was closer to a linear one as the temperature rose, serving as an indicator for a higher degree of reaction. The solid solution reaction between Al2O3 and Cr2O3 was governed by the diffusion processes of Al3+ and Cr3+ at 1300–1500 °C and 1200 °C, respectively, and thus the increase of Cr2O3 content slowed the solid solution reaction at a low temperature whereas promoted it at elevated temperatures. The diffusion process of solid solution reaction within the Al2O3-Cr2O3 system was consistent with the Cater model; The diffusion activation energy (Ea) decreased as the content of Cr2O3 increased at 1300–1500 °C. When the content of Cr2O3 increased from 25 to 60 mol%, the diffusion activation energy decreased from 92.48 to 86.49 kJ/mol−1, which was attributed to the augmentation in the diffusion rate of Cr3+ caused by the increase of Cr2O3 content and its vapor-phase transport mechanism at high temperatures.

Deciphering the alleviation potential of nitric oxide, for low temperature and chromium stress via maintaining photosynthetic capacity, antioxidant defence, and redox homeostasis in rice (Oryza sativa)

Sodium nitroprusside (SNP) is a potent nitric oxide (NO) donor that enhances plant tolerance to various abiotic stresses. This research aims to assess the effect of SNP application on rice seedlings subjected to individual and combined exposure to two abiotic stresses viz., low-temperature (LT) and chromium (Cr). Exposure to LT, Cr, and LT+Cr caused severe oxidative damage by stimulating greater production and accumulation of reactive oxygen species (ROS) leading to lipid peroxidation and cell membrane instability. The combined LT+CR stress more intensly increased the cellular oxidative stress and excessive Cr uptake that in turn deteriorated the chlorophyll pigments and photosynthesis, as well as effected the level of tetrapyrrole biosynthesis in rice plants. The reduction in rice seedling growth was more obvious under LT+Cr treatment than their individual effects. The exogenous application of SNP diminished the toxic impact of LT and Cr stress. This was attributed to the positive role of SNP in regulating the endogenous NO levels, free amino acids (FAAs) contents, tetrapyrrole biosynthesis and antioxidants. Consequently, SNP-induced NO decreased photorespiration, ROS generation, lipid peroxidation, and electrolyte leakage. Moreover, exogenous SNP diminished the Cr uptake and accumulation by modulating the ionic homeostasis and strengthening the heavy metals detoxification mechanism, thus improving plant height, biomass and photosynthetic indexes. Essentially, SNP boosts plant tolerance to LT and Cr stress by regulating antioxidants, detoxification mechanism, and the plant's physio-biochemical. Hence, applying SNP is an effective method for boosting rice plant resilience and productivity in the face of escalating environmental stresses and pollutants.

Effect of tempering temperature on microstructure and properties of low silicon hypereutectic high chromium cast iron

Effect of tempering temperature on microstructure and properties of low silicon hypereutectic high chromium cast iron

Effects of Mn addition on oxidation behaviour of heat-resistant steel in a high-temperature steam environment

A comparative study of high chromium (Super304H) and high manganese low chromium heat-resistant steel (HT630) was carried out at 650 °C in steam. Results indicate that the high manganese content in HT630 significantly improved its oxidation resistance. It is ascribed to the formation of a dense protective MnCr2O4 oxide layer during oxidation. MnCr2O4 layer effectively inhibits the diffusion of iron, suppresses the growth of iron-rich oxides, promotes the formation of an iron-rich protective interface with the matrix, and improves the overall oxidation resistance.

Associations among neighborhood walkability, metal exposure, and sex steroid hormone levels: Results from Hangzhou Birth Cohort Study Ⅱ

BackgroundNeighborhood walkability may influence maternal-fetal exposure to environmental hazards and maternal-fetal health (e.g., fetal growth restriction, reproductive toxicity). However, few studies have explored the association between neighborhood walkability and hormones in pregnant women. MethodsWe included 533 pregnant women from the Hangzhou Birth Cohort Study II (HBCS-II) with testosterone (TTE) and estradiol (E2) measured for analysis. Neighborhood walkability was evaluated by calculating a walkability index based on geo-coded addresses. Placental metals were measured using inductively coupled plasma mass spectrometry (ICP-MS). TTE and E2 levels in umbilical cord blood were measured using chemiluminescence microparticle immunoassay (CMIA). Linear regression model was used to estimate the relationship between the walkability index, placental metals, and sex steroid hormones. Effect modification was also assessed to estimate the effect of placental metals on the associations of neighborhood walkability with TTE and E2. ResultsNeighborhood walkability was significantly linked to increased E2 levels (P trend=0.023). Compared with participants at the first quintile (Q1) of walkability index, those at the third quintiles (Q3) had lower chromium (Cr) levels (β = −0.212, 95% CI = −0.421 to −0.003). Arsenic (As), cobalt (Co), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), antimony (Sb), selenium (Se), tin (Sn), and vanadium (V) were linked to decreased TTE levels, and cadmium (Cd) was linked to increased TTE levels. No metal was significantly associated with E2 levels in trend analysis. In the analysis of effect modification, the associations of neighborhood walkability with TTE and E2 were significantly modified by Mn (P = 0.005) and Cu (P = 0.049) respectively. ConclusionNeighborhood walkability could be a favorable factor for E2 production during pregnancy, which may be inhibited by maternal exposure to heavy metals.

Four millennia of garnet trade in Northeast Africa—chemical analysis of ancient and Late Antiquity beads from Lower Nubian sites

AbstractRaman spectroscopy and laser ablation‐inductively coupled plasma‐mass spectrometry were used to characterize the chemical composition of 34 red garnet beads from Lower Nubian sites, dated between about 3200 BCE and 600 CE. All beads from the A‐Group to the Meroitic period feature a similar calcium‐poor almandine composition (69%–78% almandine, 15%–22% pyrope, 2%–6% grossular, 3%–9% spessartine), which differs from other calcium‐poor almandine garnet types, sourced mostly from Indian deposits in Antiquity. The Nubian beads constitute a new garnet type, named “cluster I”, featuring high yttrium (180 to 1205 ppm), moderately low chromium (13–70 ppm), and high scandium (119–213 ppm) concentrations. Their compositions match with previous and two new analyses from two alluvial garnet deposits, Wadi El‐Haraz and Wadi Abu Dom, near the Fourth Cataract of the Nile in Upper Nubia, about 670 km as the crow flies from the Lower Nubian graves. Garnet trade between the Bayuda desert and Lower Nubia sites, and possibly even Egypt, flourished for almost four millennia. Northeastern Africa is the cradle for the oldest use of a gemstone that is harder than quartz—the red almandine garnet.A Post‐Meroitic bead, the youngest in the assembly, displays an unusual faceting, a diamond tipped drill hole, excellent polish, distinct short‐ and long‐prismatic colorless mineral inclusions, and a calcium‐ and manganese‐poor pyrope composition. This suggests that it was not of a local, Nubian, production, but imported, most probably from a South Asian site.

Challenges in power scaling of Cr:LiCAF lasers: effect of passive losses.

In this work, we have investigated the continuous-wave (cw) lasing potential of thin slab-shaped Cr:LiCAF crystals with a low chromium doping level of around 1% and various lengths of 1 to 2cm. These relatively long crystals with low Cr-doping facilitate the distribution of heat load in a larger volume and could enable power scaling of Cr:LiCAF lasers. However, long crystals tend to have larger passive losses, and it is also more challenging to achieve efficient mode-matching to the low-brightness pump mode in a longer gain element, which could hinder laser performance. To explore the issue, we have performed detailed cw lasing experiments in single- and multimode diode-pumped Cr:LiCAF laser systems employing crystals with different doping and length. Our results showed that current state-of-the-art crystal growth methods provide Cr:LiCAF crystals with low enough passive losses to enable cw laser efficiencies of up to 50%, even in these long samples. The pump powers available in this study (5.35W) limited the cw powers we could achieve experimentally to 2.25W level; however, our simulations indicate that thin slab-type Cr:LiCAF crystals with low Cr-doping have the potential to achieve cw powers above 10W level.

Investigation of Long-Term Corrosion of CoCrMoW Alloys under Simulated Physiological Conditions

The corrosion resistance of two cast CoCr-based alloys with different amounts of chromium and with different alloying elements in the bulk composition of the alloy was assessed. In this study, we investigated the corrosion behavior of Co21Cr8Mo7W and Co29Cr7W by open-circuit potential (OCP), potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) in 0.1 M phosphate buffer solution (PBS) at 37 °C with long immersion times. After 1000 h of immersion, the corrosion current density (icor), estimated from anodic polarization tests, was lower for the Co21Cr8Mo7W (i.e., 49 nA cm−2) alloy compared to the Co29Cr7W alloy (180 nA cm−2). As regards the corrosion potential (Ecor), a greater value was observed for Co21Cr8Mo7W (i.e., −59 mV vs. Ag/AgCl) compared to Co29Cr7W (i.e., −114 mV vs. Ag/AgCl). Microstructure analysis before and after immersion revealed the formation of a more compact passive film on the Co21Cr8Mo7W alloy, suggesting superior corrosion resistance compared to Co29Cr7W. These findings suggest better corrosion resistance for the film formed on the alloy containing lower amounts of Cr and two alloying elements, Mo and W. These results are promising in terms of medical applications because they open the door to new strategies for obtaining alloys with lower chromium content and with more protective anti-corrosion properties.

Abundances of Iron-peak Elements in the B8 Mn Star HD 110073

The synthesis of spectral intervals in the optical range allows the determination of LTE abundances of several iron-peak elements for the chemically peculiar B8 Mn star HD 110073. Titanium, chromium and manganese are found to be overabundant by factors of 19, 4 and 250 times their respective solar abundances. Iron and nickel are deficient by factors of 0.25 and 0.10. Weak lines of Cr ii formed deep in the atmosphere yield lower chromium abundances than strong lines do by a factor of 2. This supports that chromium is probably stratified vertically in the atmosphere of HD 110073. Several weak flat-bottomed lines which could be caused by vertical stratification of the abundances are present throughout the spectra. The new abundance determinations differ from previous determinations partly because the atomic data have changed. A non-uniform distribution of the elements over the surface of HD 110073 could also account for variation of the lines with time.

Integrative analysis of microbiota and metabolomics in chromium-exposed silkworm (Bombyx mori) midguts based on 16S rDNA sequencing and LC/MS metabolomics.

The gut microbiota, a complex ecosystem integral to host wellbeing, is modulated by environmental triggers, including exposure to heavy metals such as chromium. This study aims to comprehensively explore chromium-induced gut microbiota and metabolomic shifts in the quintessential lepidopteran model organism, the silkworm (Bombyx mori). The research deployed 16S rDNA sequence analysis and LC/MS metabolomics in its experimental design, encompassing a control group alongside low (12 g/kg) and high (24 g/kg) feeding chromium dosing regimens. Considerable heterogeneity in microbial diversity resulted between groups. Weissella emerged as potentially resilient to chromium stress, while elevated Propionibacterium was noted in the high chromium treatment group. Differential analysis tools LEfSe and random forest estimation identified key species like like Cupriavidus and unspecified Myxococcales, offering potential avenues for bioremediation. An examination of gut functionality revealed alterations in the KEGG pathways correlated with biosynthesis and degradation, suggesting an adaptive metabolic response to chromium-mediated stress. Further results indicated consequential fallout in the context of metabolomic alterations. These included an uptick in histidine and dihydropyrimidine levels under moderate-dose exposure and a surge of gentisic acid with high-dose chromium exposure. These are critical players in diverse biological processes ranging from energy metabolism and stress response to immune regulation and antioxidative mechanisms. Correlative analyses between bacterial abundance and metabolites mapped noteworthy relationships between marker bacterial species, such as Weissella and Pelomonas, and specific metabolites, emphasizing their roles in enzyme regulation, synaptic processes, and lipid metabolism. Probiotic bacteria showed robust correlations with metabolites implicated in stress response, lipid metabolism, and antioxidant processes. Our study reaffirms the intricate ties between gut microbiota and metabolite profiles and decodes some systemic adaptations under heavy-metal stress. It provides valuable insights into ecological and toxicological aspects of chromium exposure that can potentially influence silkworm resilience.

Effects of acute and chronic chromium stress on the expression of heat shock protein genes and activities of antioxidant enzymes in larvae of Orthetrum albistylum

The dragonfly species Orthetrum albistylum, can accumulate heavy metals from its aquatic environment and thus serves as a biological indicator for monitoring and evaluating water quality. Heat shock proteins (HSPs) play important biological roles in resistance to various types of environmental stress. The full-length cDNA sequences of the heat shock cognate (hsc) 70 and heat shock protein (hsp) 70 genes were cloned from O. albistylum larvae. Relative levels of expression of hsc70 and hsp70 in the head, epidermis, midgut, and adipose tissue were measured by qRT-PCR after chronic and acute contamination of 5–8 instar larvae with chromium (Cr) solution, and under control conditions. Activities of superoxide dismutase (SOD) and catalase (CAT) in chronically contaminated larvae were also measured. Phylogenetic analysis revealed that the cloned hsc70 and hsp70 genes were highly homologous to known HSP70 family members reported in other insects. The mRNA levels of hsc70 and hsp70 did not differ significantly in various larval tissues. Under chronic chromium stress, hsc70 and hsp70 expression were upregulated to a maximum and then downregulated; hsp70 mRNA levels were higher than those of hsc70 at all concentrations of chromium. Under acute chromium stress, hsc70 expression was inhibited at low chromium concentrations and upregulated at chromium concentrations higher than 125 mg/L. However, hsp70 expression was higher than that in the control group and markedly higher than that of hsc70. Changes in SOD and CAT activities displayed consistent trends for different chronic chromium concentrations, first increasing and then decreasing over time. Collectively, these findings demonstrated the response of the HSP family of genes and antioxidant enzymes following exposure to heavy metal stress, as well as their potential applicability as biomarkers for monitoring environmental pollutants.

Microstructural analysis of martensitic hard surfacing on low chromium alloy steel

AbstractThis study focuses on the metallurgical characterization of single and multi‐layer martensitic hard surfacing onto non‐standardized low‐chromium alloy steel with a single buttering layer using an automatic submerged arc welding process as a standard reference. The metallurgical properties of hard surfaced samples are examined using an optical microscope, energy dispersive x‐ray spectroscopy, and x‐ray diffractometer. Micro‐Vickers hardness testing is also conducted to analyze and confirm the metallographic results of hard surfacing. The current study finds that the microstructure of each region is influenced by three key factors: chemical composition, heat input, and dilution. The structural type is determined by the chemical composition of materials, heat input influences the structural characteristics in the heat‐affected zone (needle‐shape martensite and tempered martensite), and dilution affects the structural characteristics of the hard surfacing layers (martensite with retained austenite). Comparing multi‐layer hard surfacing to single‐hard surfacing, the hardness values of the heat‐affected zone of the multi‐layer hard surfacing are greatly reduced, while the hardness values of the hard surfacing layers are raised.

The Coating Effect on Interconnect Materials After >10 Years of Furnace Exposures

One of the key components in the SOFC stack is the interconnect which requires versatile material properties for a proper functioning, e.g., high temperature corrosion stability, low ASR degradation and low chromium evaporation. At the same time, a high production capacity needs to be reached in order to fulfil the supply demand required for GW levels. The high production capacity is realized through Alleima AB’s production line with coil-coil physical vapor deposition of coated interconnects for SOFC and SOEC applications [1].More specifically, Sanergy HT 441 is the standard material intended to be used as an SOC interconnect. The substrate is a ferritic stainless steel (ASTM 441) which is coated with thin layers of Ce and Co (<1 µm). The material can be coated on both sides using the same coating or with a different coating. At elevated temperatures the Co coating forms a protective (CoMn)3O4 spinel layer which drastically reduces Cr evaporation while the Ce layer improves the corrosion resistance by reducing the chromia scale growth at the coating/substrate interface and thereby maintaining a low and stable ASR over time.Since long-term stability is a critical property for interconnects, Alleima has over the years gathered data from furnace samples and can thus present results where some samples have been exposed at elevated temperatures during >10 years. The main results include the effect of Ce thickness or choice of substrate on mass gain and subsequent chromia growth. Selected samples with coating elements different than Co have also been investigated. Samples have been further investigated using scanning electron microscopy for cross-sections, x-ray diffraction for characterization of phases and residual stresses as well as glow discharge optical emission spectroscopy for elemental analysis.

Enhancement in the Friction and Wear Resistance of Low Carbon Chromium Steel and Load Carrying Capability of MIL-PRF-23699 Grade Lubricant Using h-BN Nanoadditives for Aerospace Applications

The frictional coefficient of LCCS with MIL-PRF-23699 grade lubricant was high, which led to an increase in heat generation and temperature rise of the lubricant in aircraft parts such as the accessory gearbox and engine gearbox. To overcome this, the present study proposed the use of h-BN nanoparticles as an additive with MIL-PRF-23699 grade lubricant. To improve the stability and suspension of the h-BN nanoparticles in the NL, the NL was prepared with h-BN nanoparticles and various surfactants. The properties were evaluated for both BL and NL. The tribological experiments were carried out using a four-ball tester, a shear stability tester, and a Reichert tester. The h-BN NL resulted in a 16% reduction in WSD when compared with the BL. The LWI of h-BN NL was increased by 7.44% compared with BL. In the shear stability test, h-BN NL showed 93% better shear stability than the BL. The CoF was reduced by 13% with the h-BN NL in the Reichert test. The experimental results indicated that the h-BN nanoparticles with MIL-PRF-23699 grade lubricant had better tribological properties for aerospace applications.

Structure–Phase Transitions in the Friction Contact Zone of High-Nitrogen Chromium–Manganese Austenitic Steel

The influence of contact stresses on the phase and concentration composition of thin surface layers and wear products in the tribological contact zone of high-nitrogen FeMn22Cr18N0.83 steel was studied using Mössbauer spectroscopy, X-ray structural analysis, and electron microscopy. It was shown that contact compressive stresses developing under the conditions of dry sliding friction in the surface layers (20–25 microns) resulted in the strain-induced dissolution of cellular precipitation products (nitrides Cr2N) and increased the average content of nitrogen in austenite. Antiferromagnetic ordering in austenite caused by the precipitation of secondary nitrides with low chromium and nitrogen content was observed in tiny external layers (~0.1 microns) of the friction surface and products of steel adhesive wear. The effect of tension stresses in the friction contact zone on the formation of strain-induced martensite and nitrides with α″-Fe16N2 structures was established in the wear products.

Effect of sodium aluminate on chromium spinels oxidation in chromite lime-free roasting process

The reaction between Na2O·Al2O3 and chromium spinels or chromite in the roasting process was systemically investigated to reveal the effects of Na2O·Al2O3 on chromium oxidation. The results of Na2O·Al2O3 roasted with MgO·Cr2O3 illustrate that only about 50% of the chromium in MgO·Cr2O3 can convert into Na2CrO4, while the remaining chromium converts into an Al-bearing spinel Mg(CrAl)O4. Mg(CrAl)O4 is found to be difficult to further react with Na2O·Al2O3. The oxidative roasting of Na2O·Al2O3 with chromite further confirms that Na2O·Al2O3 cannot fully react with some chromium spinels, which reveals the cause of the low chromium oxidation rate in the traditional chromite lime-free roasting process. Based on the experiment results, a strategy for eliminating the impacts of Na2O·Al2O3 in the lime-free roasting process was proposed, in which adding more Na2CO3 for forming Na2O·Al2O3 is considered. The chromium oxidation rate can rise close to 100% with the new strategy. This study contributes to better understanding the chromite lime-free roasting process and provides a new idea for developing the chromate salts manufacturing process more efficiently and cleanly.

The efficient removal of low concentration hexavalent chromium via combining charged microporous membrane and micellar adsorption filtration

Abstract It is challenging to effectively purge wastewater containing heavy metal ions at low concentration. In order to remove trace Cr (VI) from wastewater efficiently, a positively charged microporous membrane was prepared by firstly non-solvent induced phase separation (NIPS) of amphiphilic polymer and secondly surface quaternization modification. The morphologies, surface roughness, surface charge, hydrophilicity, and pore size of membranes were characterized. Based on the dual action of micellar adsorption and charge repulsion, when surfactant is 4 mM and Cr (VI) is 60 ppm, the surface quaternization membrane (Q-MPVD) achieves 99.8 % Cr (VI) rejection simultaneously accompanied by a permeability of 100 LMH/bar. Meanwhile, the effects of STAC concentration, Cr (VI) concentration, pH as well as inorganic salt concentration on the composite micellar size, and Cr (VI) rejection performance were investigated, respectively. Moreover, the Q-MPVD membrane shows an excellent separation stability over a wide pH range, indicating its application perspective in engineering process. In summary, this work provided a positively charged membrane with high-efficiency performance for treating practical trace Cr (VI)-containing industrial wastewater.

The Coating Effect on Interconnect Materials After >10 Years of Furnace Exposures

The present work has studied the effect of subjecting an AISI 441 ferritic stainless steel in a box furnace exposure in air at 800 °C for up to 10 years. During operation, the mass gain was repeatedly measured at selected time intervals. The results show that there are only small differences in spinel composition when a sample exposed for ~5 years is compared to a sample exposed for 10 years, with the main difference being a growth of the chromia scale from ~10 to ~14 µm. In addition, the chromium content is 12.3 wt-% after 5 years whereafter it is further reduced to 10.5 wt-% during the following exposure time. Despite a relatively low chromium content already after 5 years, there are no visible signs of material failure, e.g, neither spallation nor a a large increase in mass gain during the 10 years in the furnace.