Tribological behaviors of hybrid PTFE/nomex fabric/phenolic composite reinforced with multiwalled carbon nanotubes

Modification of composites was a general method to improve their tribological behaviors. On the way to explore composites with enhanced tribological behaviors, we have successfully prepared hybrid PTFE/Nomex fabric/phenolic composite filled with multiwalled carbon nanotubes (MWCNTs) or MWCNTs modified by polystyrene (PS) with a grafting to method. The results of pin‐on‐disc type wear tests indicated tribological behaviors were improved both for hybrid PTFE/Nomex fabric/phenolic composite filled with MWCNTs and MWCNTs‐PS, especially for that of filled with MWCNTs‐PS. And the probable reason was also discussed based on the characterization results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dependence of rheological behaviors of polymeric composites on the morphological structure of carbonaceous nanoparticles

Carbonaceous nanoparticles (CNPs), including carbon black, carbon nanotubes, and graphene nanopiece, were selected as nanoadditives for investigating the rheological behavior dependence of their polymer‐based composites on morphological and interfacial structure. Polypropylene (PP) was adopted as matrix and a series of contents of CNPs were used for sample compounding. With identical concentration, the morphological structure of CNPs was emphasized as the dominant effect affecting the shear viscosity and the compressibility of PP/CNPs melts. The viscosity dependence on the CNPs contents and physical structure, such as particle size, aspect ratio, and specific area, was fully discussed in this work. The newly‐introduced inner voids, induced around the interface region between matrix and CNPs during physical mixing, were contributive to the rheological deviation, which was further reflected from the melt compressibility. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46416.     

Biolubricants: Raw materials,chemical modifications and environmental benefits

The depletion of the world's crude oil reserve, increasing crude oil prices, and issues related to conservation have brought about renewed interest in the use of bio‐based materials. Emphasis on the development of renewable, biodegradable, and environmentally friendly industrial fluids, such as lubricants, has resulted in the widespread use of natural oils and fats for non‐edible purposes. In this study, we have reviewed the available literature and recently published data related to bio‐based raw materials and the chemical modifications of raw materials. Additionally, we have analyzed the impacts and benefits of the use of bio‐based raw materials as functional fluids or biolubricants. The term biolubricants applies to all lubricants, which are both rapidly biodegradable and non‐toxic to humans and other living organisms, especially in aquatic environments. Biodegradability provides an indication of the persistence of the substance in the environment and is the yardstick for assessing the eco‐friendliness of substances. Scientists are discovering economical and safe ways to improve the properties of biolubricants, such as increasing their poor oxidative stability and decreasing high pour points. “Green” biolubricants must be used for all applications where there is an environmental risk.     

Functionalization of multi‐walled carbon nanotubes and their effect on the tribological properties of poly(ether ether ketone) composites

A series of copolymers containing conjugated fluorene groups as a compatibilizer to improve the dispersion of multi‐walled carbon nanotubes (MWCNTs) were prepared and used to improve the wear resistance of poly(ether ether ketone)/graphite (PEEK/GP) composites. The solubility of MWCNTs had a maximum at a concentration ratio of 2:1 polymer:MWCNTs. Transmission electron microscopy indicated that polymer ? MWCNT interactions were capable of partially debundling the nanotubes in chloroform, with individual nanotubes or small bundles clearly observed. The tribological properties of PEEK composites incorporating the modified MWCNTs were investigated using a pin‐on‐disc apparatus and a block‐on‐ring apparatus. The PEEK composites had a lower frictional coefficient under the block‐on‐ring testing condition, but a lower wear rate was achieved in the pin‐on‐disc test. © 2017 Society of Chemical Industry     

Direct electrochemical regeneration of enzymatic cofactor 1,4‐NADH on a cathode composed of multi‐walled carbon nanotubes decorated with nickel nanoparticles

Multi‐walled carbon nanotubes (MWCNTs) were grown on a stainless steel mesh and decorated with nickel nanoparticles (Ni NPs). The developed Ni NP‐MWCNT material was then used as a cathode in an electrochemical batch reactor to electrocatalytically convert NAD⁺ to enzymatically‐active 1,4‐NADH. The regeneration of 1,4‐NADH was studied at various electrode potentials. At electrode potential of ?1.6 V, a very high recovery (relative amount of 1,4‐NADH in the product mixture) was obtained, 98 ± 1 %. In comparison, to achieve the same recovery on a non‐decorated MWCNT cathode, a much higher cathodic potential was needed (?2.3 V), establishing the importance of Ni NPs on the electrocatalytic activity in reducing NAD⁺ to 1,4‐NADH. It was postulated that hydrogen adsorbs on Ni NPs immobilized on MWCNTs to form Ni‐H_ads, and this activated hydrogen rapidly reacts with neighbouring NAD‐radicals, preventing the dimerization of the latter species, ultimately yielding 1,4‐NADH.     

Frictional dependence of graphene and carbon nanotube in diamond-like carbon/ionic liquids hybrid films in vacuum

The use of graphene and multi-walled carbon nanotubes (MWCNTs) additives as lubricants has received considerable interest because of their excellent mechanical and frictional properties. Given their structural differences, both carbon nano-additives are expected to have different synergistic effects at various conditions (from boundary to mixed lubrication). For applications in space, the tribological properties of graphene and MWCNTs additives in diamond-like carbon/ionic liquids hybrid films in different lubricating states at high vacuum were compared. The wear surfaces, transfer films, wear debris, and microstructures of the hybrid films were analyzed via Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results showed that MWCNTs and graphene present the different nano-scale tribological mechanisms and produce different lubricating effect on the hybrid films at different lubricating states.     

纳米粒子作为润滑添加剂的摩擦学特性

作为润滑添加剂,纳米粒子具有独特的物理化学特性和优良的摩擦学性能。纳米添加剂可以提高基础油的润滑性能,减摩抗磨性能。综述了纳米粒子润滑添加剂的摩擦学特性和润滑机理。目前关于纳米粒子减摩抗磨机理比较一致的观点是纳米粒子在摩擦表面较易吸附且形成润滑保护膜。     

Synthesis and characterization of size controlled nano copper oxide structures for antioxidant study and as eco-friendly lubricant additive for bio-oils

This research work aims at the synthesis of Copper oxide (CuO) nanostructures with the application as additives for biolubricant oils, particularly Pongamia oil. The CuO particles were synthesized by a simple co-precipitation methodology. The nanostructures were characterized via analytical and microscopic techniques. The p-XRD analysis reveals the formation of size-controlled CuO formation, and the particle size was affirmed using both scherrer and William son Hall methods with particle size less than 14 nm. The surface morphology studies were substantiated by microscopic techniques. Elemental analysis reveal the purity of the prepared nanostructures. The monodispersed nanostructures are obtained with polydispersity index (PDI) of a value of 0.0550. The antioxidant property of CuO NPs was analyzed and is found in dose dependent manner, with efficiency of 71.9% at 50 μg/mL The influence of CuO nanoparticles on the viscosity of the lubricant is studied using the rheometer. The effect of these nanostructures on the friction characteristic is studied using a Ring-On-Block lubricity tester. The particles varied from 0.5 to 1 % wt. The CuO nanoparticles reduces the viscosity of the pongamia oil bio lubricants by 5.52% in comparision with the pongamia oil blended neem oil. The coefficient of Friction (COF) was found to be superlative for 0.75 % wt CuO added to Pongamia oil. The experimental result shows that CuO nanostructures is more effective than the blending of Neem oil with Pongamia oil and cane be used as an additives in the bio lubricants as the viscosity and friction modifier.     

The effect of silica nanoparticles and carbon nanotubes on the toughness of a thermosetting epoxy polymer

Silica nanoparticles and multiwalled carbon nanotubes (MWCNTs) have been incorporated into an anhydride‐cured epoxy resin to form “hybrid” nanocomposites. A good dispersion of the silica nanoparticles was found to occur, even at relatively high concentrations of the nanoparticles. However, in contrast, the MWCNTs were not so well dispersed but relatively agglomerated. The glass transition temperature of the epoxy polymer was 145°C and was not significantly affected by the addition of the silica nanoparticles or the MWCNTs. The Young's modulus was increased by the addition of the silica nanoparticles, but the addition of up to 0.18 wt % MWCNTs had no further significant effect. The addition of both MWCNTs and silica nanoparticles led to a significant improvement in the fracture toughness of these polymeric nanocomposites. For example, the fracture toughness was increased from 0.69 MPam^1/2 for the unmodified epoxy polymer to 1.03 MPam^1/2 for the hybrid nanocomposite containing both 0.18 wt % MWCNTs and 6.0 wt % silica nanoparticles; the fracture energy was also increased from 133 to 204 J/m². The mechanisms responsible for the enhancements in the measured toughness were identified by observing the fracture surfaces using field‐emission gun scanning electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Simultaneous synthesis of carbon nanobelts and carbon/Fe-Cu hybrids for microwave absorption

By acetylene decomposition at 450 °C over the Fe-Cu nanoparticles (Fe:Cu molar ratio = 29:1, 5:1) derived from a combined sol-gel/reduction method, carbon nanobelts (CNBs) and carbon/Fe-Cu hybrid nanoparticles (CNPs) were synthesized simultaneously with high yield. The two carbon species could be easily separated according to color and were collected at different locations of the ceramic plates where the catalysts were placed. Over Fe-Cu nanoparticles of high Cu content (Fe:Cu = 2:1), the product was carbon nanofibers. A series of comparison experiments was designed to study the optimal conditions for the formation of CNBs, and the results indicate that CNBs and CNPs can be selectively synthesized at 450 °C by adjusting the Cu content of the catalyst. Moreover, the complex permittivity and permeability of the mixture that contains CNPs or CNBs (30 wt.%) (paraffin wax as binder matrix) were measured in the 2-18 GHz frequency range. Despite the low mass percentage of CNBs, microwave absorption is good. Below −10 dB, there are two, three, and four distinct reflection loss peaks when the thicknesses of CNB composites are within the 5.5-7.5 mm, 9.5-11.5 mm, and 11.5-13.5 mm ranges, respectively.     

Development of Fully Bio‐Based Lubricants from Agro‐Industrial Residues under Environmentally Friendly Processes

Biolubricants are becoming interesting alternatives to mineral lubricants. Despite their advantages, development of lubricants from vegetable oils may compete with food production, turning their use impractical due to socio‐economic aspects. Here, cardanol is used as raw material in the synthesis of novel biolubricants under environmentally friendly conditions. These compounds are characterized by NMR and Fourier transform infrared spectroscopy. Thermal‐oxidative studies show the elevated stability and higher onset oxidative temperatures. Tribological analyses performed under high‐frequency linear‐oscillation motion indicate lower coefficients of friction and wear rates compared to a synthetic oil. Therefore, cardanol, under simple, fast, and sustainable processes can be transformed into valuable alternatives for petroleum‐based lubricants. Practical Applications: The novel cardanol‐based biolubricants presented in this work show interesting chemical and lubricity properties superior to standard synthetic oils, which make them potential substitutes for the current oil‐based products used as lubricants. Additionally, the ecofriendly methodologies employed reduce significantly the reaction time as well as eliminating the need for catalysts or solvents, making these processes viable alternatives for the traditional methods reported in literature for the synthesis of this class of compounds.     

甲烷催化裂解制备氢气和碳纳米管

采用浸渍法制备出3种MgO负载型过渡金属催化剂Fe/MgO、Co/MgO和N i/MgO,系统研究了甲烷在3种催化剂上于650,700和750℃下的裂解产物。结果表明,该3种催化剂均对甲烷裂解产氢并协同生长碳纳米管表现出较高活性。     

Increased thermal conductivity of liquid paraffin-based suspensions in the presence of carbon nano-additives of various sizes and shapes

The effect of adding carbon nanomaterials on the thermal conductivity of liquid paraffin-based suspensions was investigated. These included pristine and carboxyl-functionalized short multi-walled carbon nanotubes (MWCNTs), long MWCNTs, carbon nanofibers, and graphene nanoplatelets (GNPs). The thermal conductivity of the suspensions was measured using the transient hot-wire method at a constant temperature. The size, shape, and dispersion of the carbon additives were observed by microscopy, and the stability and viscosity of the suspensions were also characterized. It was shown that thermal conductivity of the suspensions increases with increasing the loading of the carbon additives and the extent of relative increase depends strongly on their size and shape. Of the various carbon nanomaterials examined, GNPs caused greatest increase due to reduced thermal interface resistance associated with their two-dimensional planar structure. The viscosity of GNP-based suspensions decreases at relatively high loadings, whereas a monotonic increase was observed for suspensions with all the other carbon additives.     

Morphologies and electrical properties of electrospun poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyvalerate]/ multiwalled carbon nanotubes fibers

Electrospinning process was used to fabricate fine fibers from poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyvalerate] embedded with multiwalled carbon nanotubes (MWCNTs). Rotating disc collector was used to provide additional drawing force to stretch and align both the embedded MWCNTs and electrospun fibers themselves. Morphological observation revealed MWCNTs aligned to the fiber axis and protruding from the surface. To understand the electrical properties of the fiber, a single‐composite fiber has been deposited on a substrate, across multiple electrodes. Electrical conductivity of the single‐electrospun fiber with low MWCNT content of 0.2 wt % was calculated to be in a remarkable magnitude of about 2.07 Sm^?1. Electrical current flow spanning the fiber length of 1400 μm indicates that the presence of an interconnected network of MWCNTs exists within the fiber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The synthesis of carbon coated Fe, Co and Ni nanoparticles and an examination of their magnetic properties

Carbon coated Fe, Co and Ni nanoparticles (Fe@C, Co@C, and Ni@C, respectively) have been produced by high pressure chemical vapour deposition. Scanning electron microscopy images prove that carbon coated particles with a Fe, Co, and Ni core are formed. High-resolution transmission electron microscopy images show that the nanoparticles have a size distribution from 2 to 100 nanometers and display the core/shell structure with one or more particles forming the core in a particular shell. From X-ray diffraction peaks the phase of the core material is confirmed and the average particle size is determined from the width of the peaks to be 16, 21, and 19 nm for Fe@C, Co@C, and Ni@C, respectively. The coated nanoparticles are ferromagnetic at least up to 400 K. AC magnetic heating studies have been performed which imply their potential for applications in hyperthermia therapy.     

双金属催化剂对煤焦油模型化合物催化裂解行为的影响

以Al₂O₃为载体,Ce、Co和Fe为助剂,采用机械化学法制备了4种镍基催化剂,对其进行了XRD、H₂-TPR、BET、NH₃-TPD等表征。当载气流量为50 ml·min^-1,裂解温度为750℃时,在固定床反应器中考察了各催化剂对煤焦油模型化合物甲苯+芘裂解行为的影响。结果表明：4种催化剂均为介孔催化剂,且双金属催化剂的介孔有序度更高;催化剂中活性组分Ni主要以尖晶石NiAl₂O₄的形式存在;添加Fe助剂后,催化剂的酸强度较Ni/Al₂O₃增加,添加Ce和Co时则相反。评价实验表明,助剂对重质组分芘的裂解率影响较小,约为67%,然而Ce和Co对催化剂的抗积炭性能有利,其析碳分别较无助剂时降低28.8%和18.0%。     

Esters from castor oil functionalized with aromatic amines as a potential lubricant

Vegetable oils are very promising alternatives to fossil lubricants due to their abundance, low cost, excellent performance, and environmental friendliness. Due to its multifunctional structure, castor oil is an excellent precursor in the synthesis of new biolubricants. However, it showed poor thermal-oxidative stability and a higher pour point. This study used castor oil fatty acids prepared by transesterification (EHRO), epoxidation (TEPO), and oxirane ring opening with the aromatic amines aniline (ANIL) and p-anisidine (ANIS). The chemical structure of these oils was verified by ¹H and ¹³C NMR analysis, and mass spectrometry. Measurements show that the presence of an aromatic amine increases the viscosity resulting in 172 (ANIL) and 199 (ANIS) cSt at 40°C, but reduces viscosity index to 16 and 1, respectively. In addition, the amine groups can scavenge radicals increasing their thermal and oxidative stability. These products do not oxidize copper, and tribological analysis reveals that ANIS has the lowest torque with wear equivalent to commercial mineral lubricant NH-140.     

Mechanical,rheological, and electrical properties of multiwalled carbon nanotube reinforced ASA/Na‐ionomer blend

Varying amounts of multiwalled carbon nanotubes (MWCNTs) was melt‐extruded with the acrylonitrile‐styrene‐acrylate (ASA)/Na‐ionomer blend, and mechanical, rheological, and electrical properties were studied Optical micrographs show good dispersion level at low MWCNT content and network formation at higher nanotubes percentage. DC conductivity model data shows percolation threshold reached at 1% MWCNT content and after percolation, two‐dimensional network structure was formed. The “peak and valley” type surface topology of matrix may be responsible for low percolation threshold limit. The polymer/nanotubes interactions at low MWCNT content increased the mechanical strengths, which were reduced by the network structure and agglomerates of nanotubes at higher nanotubes content. The MWCNTs interacted differently with the architecturally complex polymer chains and controlled chain dynamics accordingly. The Carreau‐Yasuda model was found fit to viscosity data and the model parameters data suggest the zero shear viscosity is function of MWCNTs content but the infinite shear viscosity is independent of nanoparticles content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42516.     

Formation and catalytic performance of supported ni nanoparticles via self‐reduction of hybrid NiAl‐LDH/C composites

In the present work, hybrid NiAl‐layered double hydroxide/carbon (LDH/C) composites with adjustable compositions were successfully assembled by crystallization of LDH in combination with carbonization of glucose under hydrothermal conditions, and further utilized as an integrated catalyst for the growth of carbon nanotubes (CNTs) in catalytic chemical vapor deposition (CCVD) of acetylene. The materials were characterized by X‐ray diffraction, Fourier transform infrared, elemental analysis, thermogravimetric and differential thermal analysis, SEM, transmission electron microscopy, X‐ray photoelectron spectra, and Raman spectroscopy. The results revealed that the supported Ni nanoparticles with the small crystallite size of about 10 nm could be obtained by in situ self‐reduction of as‐assembled hybrid LDH/C composites in the course of CCVD. The carbon in the hybrid structure as a reducing agent played a key role for the high dispersion of resulting Ni nanoparticles. Furthermore, the Ni nanoparticles obtained here exhibited excellent activity for catalytic growth of CNTs, which could be delicately tuned by varying the compositions of hybrid composites. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The Influences of H2 Plasma Pretreatment on the Growth of Vertically Aligned Carbon Nanotubes by Microwave Plasma Chemical Vapor Deposition

The effects of H₂ flow rate during plasma pretreatment on synthesizing the multiwalled carbon nanotubes (MWCNTs) by using the microwave plasma chemical vapor deposition are investigated in this study. A H₂ and CH₄ gas mixture with a 9:1 ratio was used as a precursor for the synthesis of MWCNT on Ni-coated TaN/Si(100) substrates. The structure and composition of Ni catalyst nanoparticles were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The present findings showed that denser Ni catalyst nanoparticles and more vertically aligned MWCNTs could be effectively achieved at higher flow rates. From Raman results, we found that the intensity ratio of G and D bands (I _D/I _G) decreases with an increasing flow rate. In addition, TEM results suggest that H₂ plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles. As a result, the pretreatment plays a crucial role in modifying the obtained MWCNTs structures.