Serpentine Powders Research Articles

Facet-dependent adsorption of heavy metal ions on Janus clay nanosheets

Understanding the facet-dependent adsorption behavior and mechanism of heavy metal ions (HMs) on two-dimensional (2D) Janus nanoclays has important implications for the environment and ecosystem but still remains elusive. Herein, ultrathin Janus serpentene (2D serpentine) nanosheets were fabricated via a facile, nontoxic, and residue-free exfoliation strategy. Fabricated serpentene nanosheets exhibited promising Cd(II) and Pb(II) adsorption capacities due to their high surface areas and abundant active sites, approximately four times higher than those of bulk serpentine powders. Interestingly, Cd(II) and Pb(II) adsorption on serpentene nanosheets exhibited a facet-dependent feature, with the adsorption amount on the Mg–OH plane considerably higher than that on the Si–O plane. This facet-dependent adsorption behavior was mainly attributed to the difference in the interaction mechanisms of HMs with the Mg–OH (monodentate inner-sphere complexation) and Si–O (outer-sphere complexation) planes, which was further confirmed via density functional theory calculations. The Cd(II) adsorption on serpentene nanosheets was limited by strong kinetic restrictions (e.g., stronger electrostatic repulsion and higher dehydration energy barrier than that for Pb(II) adsorption). This study provides insights into the facet-dependent adsorption mechanisms of HMs on Janus serpentene nanosheets, which can be extended to other nanoclays used in wastewater treatment and many environmental processes.

Soil microbial community structure and environmental effects of serpentine weathering under different vegetative covers in the serpentine mining area of Donghai County, China

The use of serpentine biological weathering to capture atmospheric CO2 has attracted much attention. In the long-term mining activities in a serpentine mining area, a large amount of serpentine powder diffused into the surrounding forest and farmland soil. The study of the serpentine weathering in soils of different vegetative covers and the composition characteristics of soil carbonate has important implications for understanding the serpentine weathering and carbon sequestration under natural conditions. The microbial diversity on exposed rock serpentine surfaces and soil under different vegetative covers in the serpentine mining area in Donghai County, China was investigated by high-throughput sequencing technology, and the characteristics of serpentine weathering and soil carbonate in related area were also explored by XRF, XRD, SEM-EDS, and chemical analysis methods. The results showed that the richness and uniformity of the bacteria species community increased significantly with the increasing complexity of plant groups covering the rock surface, but the species richness and uniformity of fungi showed an overall declining trend. Furthermore, high‑magnesium calcite (HMC) is ubiquitous on the exposed rock surface and the soil under different vegetative covers in this area. Based on these results, combined with the verification test results of HMC fixed heavy metal ions, the model of serpentine weathering in serpentine mining soil to synthesize carbonate and fix heavy metal ions was developed. That is, with the increase in the degree of rock weathering and the colonization of plants, the soil and plants seem to shape jointly a relatively stable microbial community structure adapted to the environment of the serpentine mining area, which promotes the serpentine weathering coupled with the formation of HMC and immobilization of metal ions in the serpentine soil. This study provides a theoretical basis for the serpentine bio-weathering in the mine area to capture atmospheric CO2.

Influence of Natural Serpentine on Tribological Performance of Phosphate Bonded Solid Coatings

Natural serpentine powders as functional fillers were incorporated to promote the anti-wear performance of phosphate-bonded solid coatings. Optimal mass percent of natural serpentine in phosphate coatings was first explored. Thereafter, to further stimulate strengthening effect of natural serpentine on tribological performance of phosphate composite coatings, harsher friction condition on the phosphate composite coatings was conducted. The experimental result indicated that the optimal incorporation of natural serpentine in phosphate coatings was 10 wt.%, through which anti-wear performance of phosphate coatings was significantly elevated. Additionally, accompanied by the increase of applied load and sliding speed, natural serpentine was gradually activated, and interfacial interactions between naturals serpentine and counterface were intensified. As a result, a continuous protective tribo-film was in situ formed on the counterface, through which serious furrows generated on the counterface were effectively self-repaired during the friction process. What’s more, further abrasion on both phosphate composite coatings and counterface was also greatly restrained. Natural serpentine as the enhanced phase was incorporated into phosphate bonded solid coatings. The experimental results indicated that when applied load and sliding speed were increased, transfer and adhesion of phosphate composite coatings on the counterface were apparently intensified, and simultaneously, serious furrows generated on the wear spot were obviously reduced. What’s more, a continuous tribo-film was in-situ formed on the counterface, through which the direct abrasion between phosphate composite coatings and counterpart steel ball was restrained, and therefore, the anti-wear performance of phosphate composite coatings was significantly promoted.

The formation of fungus-serpentine aggregation and its immobilization of lead(II) under acidic conditions.

Serpentine has weak immobilization capacity for Pb(II), especially under acidic conditions. In order to improve its application potential, a new biological modification method was adopted, i.e., the serpentine powder was weathered by Aspergillus niger and the fungus-serpentine aggregation (FSA) formed was investigated for its Pb(II) immobilization potential and underlying mechanism. Batch adsorption of Pb(II) by FSA closely followed the Langmuir model, while the maximum adsorption capacity of FSA (370.37 mg/g) was significantly higher than fungal mycelium (31.85 mg/g) and serpentine (8.92 mg/g). The adsorption process can be accurately simulated by pseudo-second-order kinetic model. Our data revealed the loading of organic matter is closely related to the adsorption of FSA, and the stronger immobilization capacity was mainly related to its modified porous organic-inorganic composite structure with extensive exchangeable ions. Moreover, FSA is an economical bio-material with excellent Pb(II) adsorption (pH = 1-8) along with significantly lower desorption efficiency (pH = 3-8), especially under acidic conditions. These findings provide a new perspective to explore the usage of fungus-minerals aggregation on heavy metals immobilization in acidic environments. Key Points • Co-culture of Aspergillus niger and serpentine produced a porous composite material like fungus-serpentine aggregation. • Fungus-serpentine aggregation has a surprisingly higher adsorption capacity of Pb(II) and significantly lower desorption efficiency under acidic conditions. • The loading of organic matter is closely related to the adsorption of FSA.

Friction and wear behaviors of steel/ bronze tribopairs lubricated by oil with serpentine natural mineral additive

The effect of serpentine natural mineral powder as additive on the friction and wear of tin bronze against steel under oil lubrication was investigated by four-factor and three-level orthogonal experiments using SRV4 sliding wear tester. Results show that the tribological properties of tin bronze were remarkably improved by the addition of serpentine powder into the oil. The importance order that affects the friction reducing performance was load, serpentine content, reciprocating frequency, and sliding time. The order of the antiwear property was frequency, content, load, and time. During the friction process, a non-conductive tribofilm consisting of metal oxides, oxide ceramic particles, graphite, and organics was formed on the tin bronze worn surface by serpentine mineral. The nanohardness and elastic modulus of the film demonstrated the gradient variation that low in the surface and high in the sub-surface, which is favorable for the improvement of the tribological behaviors.

Nano Serpentine Powders as Lubricant Additive: Tribological Behaviors and Self-Repairing Performance on Worn Surface

Natural serpentine powders are applicable as additives for various lubricating oils. However, no uniform theories explain their tribological performance, lubrication, and wear mechanism, especially their self-repairing mechanism. Herein, the influence of different nano serpentine powders (NSPs) contents in liquid paraffin on the friction and wear characteristics of steel balls and the self-repairing process of NSPs on the worn surface were studied. Results show that the optimal amount of NSPs was 0.5 wt %. Relative to those of the base oil, the friction coefficients and wear spot diameters were reduced by 22.8% and 34.2%, respectively. Moreover, the long-term tribological test shows that the wear scar diameter decreased slightly after 3 h, reaching the state of dynamic balance between wear and repair. The outstanding tribological performance should be attributed to the formed bilayer tribofilm, the first layer of which contains nanoparticles surrounded by lubricants and the second layer of which contains nanoparticles compacted onto the surface of the steel ball.

Preparation, mechanical and anti-friction properties of Al/Si/serpentine composites

PurposeSerpentine is usually added into the lubricant oil to form a self-repairing protective layer on worn ferrous surface. But few works have paid close attention to the preparation of composites with the addition of serpentine. In this work, serpentine reinforced Al matrix composites were successfully prepared to be industrial lubrication components. And its fabricating parameters, compressive strength and tribological properties were analyzed.Design/methodology/approachAn MM-W1 three-pin-on-disk apparatus was used to investigate the tribological properties. The worn surface, microstructure and cross-sectional morphologies were characterized by scanning electron microscopy equipped with energy dispersive spectroscopy. The compression test was carried out on a universal testing machine. An X-ray diffractometer was used to investigate the phase constitutions. The decomposition temperature of serpentine powders was investigated by a thermal analyzer, which allows simultaneous differential scanning calorimetry and thermogravimetry. With the help of finite element method model, a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.FindingsThrough evaluating density and Brinell hardness, sintering at 560°C for 3 h are the appropriate parameters for fabricating the composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.Originality/valueSerpentine was added in fabricating the Al matrix composites for the first time. Sintering parameters were optimized to make better Al/Si/serpentine composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient under the dry sliding condition. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. It is hoped to be helpful in further confirming the factors for the formation of the self-repairing surface layer, and in designing a new industrial anti-friction composite used for dry sliding conditions.

Tribological Properties of NiAl Matrix Composites Filled with Serpentine Powders

The unexplored tribological properties of NiAl matrix composites filled with serpentine powders are investigated using a reciprocating ball-on-disk configuration. Tribological test results reveal that increasing the serpentine concentration to some extent reduces the friction coefficients and wear rates of the composites. The best anti-friction and anti-wear performance is displayed by the NiAl matrix composite filled with 8 wt.% serpentine and 2 wt.% TiC (NAST). Microstructural analyses demonstrate that after adding serpentine, the self-lubricating films with different percentages of coverage form on the worn surfaces of the composites. A self-lubricating film with the highest percentage of coverage smears on the worn surface of NAST. This clearly suggests that serpentine can act as a new type of filler for NiAl matrix composites, whereas a combination of serpentine and TiC can enable serpentine to provide a full play to its excellent lubricating performance.

Tribological analysis of the surface layer coated by sintered serpentine-reinforced composites

In this work, the serpentine powders were sintered to make the serpentine-reinforced Al-matrix composites, and the microstructures of which were characterized by differential scanning calorimetry, thermal gravimetric analyzer, and X-ray diffractometer. Scanning electron microscopy equipped with energy dispersive spectroscopy. Results show that the sintered serpentine powders were deeply absorbed on the worn surface and embedded in the furrows and scratches of the matrix, forming a self-repairing surface layer which reduces the friction coefficient. The surface layer coated by serpentine was compact, dense, and uniform with the friction time prolonged, compensating the worn loss and increasing the matrix mass.

The effect of serpentine additive on energy-saving and auto-reconditioning surface layer formation

PurposeThis paper aims to investigate the energy-saving effect and mechanism of serpentine as lubricant additive in the simulated condition.Design/methodology/approachAn ABLT-1 bearing test machine was used for 1,350 hours and an MM-W1 three-pin-on-disk apparatus was used to investigate its anti-friction effect. The worn surface was characterized by scanning electron microscopy equipped with energy dispersive spectroscopy.FindingsThe results show that the energy-saving effect was improved after adding serpentine powder in oil and that both the friction coefficient and mass loss were dramatically decreased. The analysis on worn surface layer demonstrates that an auto-reconditioning surface layer was formed on the worn surface, which was responsible for the decrease in friction and wear.Originality/valueThe simulation test for the metal bearing was conducted over 1,350 hours using lubricant with and without serpentine powder. The addition of serpentine powder enhanced the energy-saving rate over time, stabilizing at about 13 per cent after 1,000 hours. An auto-reconditioning surface layer was formed on the surfaces of disassembled bearing lubricated with serpentine doped oil, resulting in dramatic decrease of both the friction coefficient and the mass loss. In addition to normal load and the accumulation of serpentine powder in the furrows and scratches of the deformed layer, the formation of the surface layer was possibly related to the substrate deformation induced by friction force.

Tribological behaviours of surface-modified serpentine powder as lubricant additive

Purpose – The aim of this paper is to study the tribological performance and self-repairing performance of surface-modified nanoscale serpentine powders as lubricant additives in the mineral base oil (5-CST). Design/methodology/approach – Fourier transform infrared spectroscopy spectra and thermo-gravimetric analysis of both modified and unmodified serpentine were performed to analyse their grafting ratio and suspension after modified using a long-chain naphthene aliphatic acid. The tribological properties of surface-modified serpentine as lubricant additives in 5-CST were evaluated and the worn surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Findings – The results show that the serpentine particles have high grafting ratio, improving the dispersity in 5-CST. When the serpentine concentration of 1.00 weight per cent is used as additives in 5-CST, friction coefficient reduces by 14.80 per cent under 294 N and wear scar diameter (WSD) decreases by 11.82 per cent. The results of X-ray absorption near edge structure and XANES show that the adsorption and tribochemical reactions occur to form self-repairing lubrication films. Originality/value – The paper illustrates a tribofilm form on the rubbed surface, which is responsible for the decrease in friction and wear, mainly containing iron oxides, silicon oxides, magnesium oxides and organic compounds. The results are useful for further applications in advanced environmental friendly lubricating oils and additives.

Tribological behaviours of ultrafine Sn/heat treated serpentine powder in grease

In order to improve the tribological performance of traditionally based lithium grease, ultrafine serpentine powder of 0·33 μm and Sn powder of 120 nm were prepared by ball mill and direct current arc plasma evaporation respectively. The milled serpentine powder was heat treated at 200, 500, 600 and 800°C in a muffle furnace separately with a four-ball wear test. Then, the tribological behaviours of lithium grease modified with complex powder with different ratios of ultrafine Sn/heat treated serpentine were investigated, and the effects of total concentration and load were discussed too. The optimal performance was achieved by the compound grease with 1 wt-% complex powder and 1∶1 Sn/serpentine powder (heated at 200°C). The friction coefficient and wear scar diameter decreased 25·5 and 42·5% respectively under 392 N compared with pure grease. The compound grease is much more suitable under high load rather than low load.

An amorphous Si[sbnd]O film tribo-induced by natural hydrosilicate powders on ferrous surface

The tribological properties of surface-coated serpentine powders suspended in oil were evaluated using an Optimal SRV-IV oscillating friction and wear tester. The worn surface and the tribo-induced protective film were characterized by scanning electron microscope and focused ion beam (SEM/FIB) work station, energy dispersive spectroscopy (EDS) and transmission electron microscope (TEM). Results indicate that with 0.5wt% addition of serpentine powders to oil, the friction coefficient and wear rate significantly decrease referenced to those of the base oil alone. An amorphous SiOx film with amorphous SiOx particles inserted has formed on the worn surface undergoing the interactions between serpentine particles and friction surfaces. The protective film with excellent lubricating ability and mechanical properties is responsible for the reduced friction and wear.

Lanthanum Effect on the Tribological Behaviors of Natural Serpentine as Lubricant Additive

The tribological properties of serpentine powders (Mg6Si4O10(OH)8, marked as FGM1) and the admixture of 95 wt% serpentine powders + 5 wt% La2O3 nanoparticles (FGM2) as oil additives were comparatively investigated using an optimal SRV-IV friction and wear tester. The worn surface was characterized by scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectrometry (XPS) and the friction mechanism is discussed. The results show that both FGM1 and FGM2 had excellent tribological performance and 0.5 wt% content was the most efficient in reducing friction and wear at 50 N. With the addition of La2O3 nanoparticles, the tribological properties were further improved compared to those of serpentine powders alone. A smoother and more compact tribofilm with iron oxides, silicon oxides, graphite, organic compounds, and La9.33 (SiO4)6O2 was formed on the worn surface and provided further reduced friction and wear.

Serpentine Dissolution in the Presence of Bacteria Bacillus mucilaginosus

Dissolution of serpentine in the presence of soil bacteria Bacillus mucilaginosus is examined through solution chemistry analysis, X-ray diffraction and 3D X-ray microscopy. Microbe-mineral interactions were carried out by incubating serpentine powder and the bacteria for 30 days. Measured Mg concentrations in the culture media were significantly higher than that in any of the control experiments at any time during the experiments. However, the behavior of the Mg/Si ratio was similar to what was known for inorganic dissolution of silicate minerals. XRD analysis revealed increased quantity of amorphous components in the reacted mineral samples, and tomography images showed a very porous and powdered appearance of the dissolved serpentine grains. These data suggest the dissolution probably proceeds through an incongruent route. Further, these observations imply that there is little genetic control by the microbes during the bacteria-mineral interaction; rather, the accelerated dissolution results primarily from a biologically induced process. Finally, the observed pH decrease, the presence of carboxylic acid, ketone, aldehyde, phenol, and alcohol in the metabolites suggests that organic acids and ligands secreted by the bacteria are largely responsible for the accelerated mineral dissolution.

Microstructure, mechanical properties and tribological behavior of tribofilm generated from natural serpentine mineral powders as lubricant additive

Surface-modified serpentine powders with an average size of 1.0μm were dispersed into mineral base oil to improve the lubricating properties of oil, as well as to generate a thin tribofilm on the worn surface. SEM, TEM, nano-indentation and Stribeck testing were performed to study the morphology, microstructure, micromechanical properties and tribological behavior of the tribofilm, respectively. Results show that a nanocrystalline tribofilm, with a thickness of 500–600nm, is formed on the worn surface under the lubrication of oil with 1.5wt% serpentine. The film is mainly composed of Fe3O4, FeSi, SiO2, AlFe and Fe-C compound (Fe3C). A phenomenological model of the tribofilm generated by serpentine was developed based on the experimental results. The excellent mechanical properties, reinforced phase of embedded particles and porous structure of the tribofilm contribute to the reduction of friction and wear, especially in the case of boundary and mixed lubrication.

Comparative tribological properties of magnesium hexasilicate and serpentine powder as lubricating oil additives under High temperature

Friction and wear experiments were carried out with nanoscale serpentine (magnesium silicate mineral) and magnesium hexasilicate powder as lubricating oil additives at 400°C. The tribological test results showed that the self-repairing protective layers could be well formed on the contact surfaces, whether nanoscale serpentine or magnesium hexasilicate powder was added into lubricating oil. The SEM and EDAX analysis demonstrate that the morphology and elements of both self-repairing layers are in accordance with each other. The research results indicate that the essence of self-repairing of serpentine power is isomorphic replacement and tribochemical reaction between magnesium silicate and metal matrix.

The Antifriction Properties of Ultra-Fine Serpentine Powders as Lube Oil Additive on Iron-Based Friction Pair

X-ray diffraction (XRD) and differential thermal analysis (DTA) as well as heat treating method etc have used to study the material characteristics of ultra-fine serpentine powder and analyze its material science bases for the improvement of tribological intervention behaviors of friction pair surface. The ultra-fine serpentine powders are taken as lube oil additive in present experiment. The friction coefficient is tested on the four-ball and ring-on-block friction pairs under different working conditions, and the surface topography of friction pair are observed and measured with scanning electron microscopy (SEM) and three dimensional white light interfering profilometer. The results indicate that the ultra-fine serpentine powders as lube oil additive can significantly improve the antifriction properties of the lube oil. The content of the added ultra-fine serpentine powders can affect on the antifriction performance of the lube oil.

Effect of thermal activation on the tribological behaviours of serpentine ultrafine powders as an additive in liquid paraffin

The influence of thermal activation temperature on the tribological properties of surface-coated serpentine ultrafine powders as liquid paraffin additives was studied. It is found that the serpentine powders suspended in liquid paraffin present excellent tribological properties. Thermal activations in a temperature range from 300 to 600 °C increase the film forming ability and tribofilm completeness of the serpentine, keep the layer structure and accordingly further improve the tribological properties. However, the layer structure is destroyed and hard phases appear after thermal activated at or higher than 850 °C, as results in the aggravation of friction and wear.

CU nanoparticles effect on the tribological properties of hydrosilicate powders as lubricant additive for steel–steel contacts

The effect of Cu nanoparticles (NPs) on the tribological behaviors of serpentine powders (SPs) suspended in diesel oil was investigated. Results show that the optimum mass ratio of Cu NPs to SPs is 7.5:92.5. With the addition of the above mixture to oil, the tribological properties can be significantly improved compared with those of the oil containing SPs alone. A more smooth and compact tribofilm has formed on the worn surface, which is responsible for the further reduced friction and wear, mainly with iron oxides, silicon oxides, species enriched in Si–O structures, graphite, organic compounds, and Cu 0, Cu 1+ and Cu 2+ species.