Tribological behaviors of surfactant-functionalized carbon nanotubes as lubricant additive in water

The multi-walled carbon nanotubes (MWCNTs) are functionalized by self-assembled surfactant layers after sonication in anionic surfactant sodium dodecyl sulfate (SDS) aqueous solution. The tribological properties of the SDS-functionalized MWCNTs as additive in water-based lubricants were evaluated with a four-ball tester. The results show that the SDS-functionalized MWCNTs exhibit good anti-wear and friction reduction properties as well as enhanced load-carrying capacity. The maximum non-seizure load (PB value) can be raised about 3–7 times when SDS-functionalized MWCNTs were added into water. The mechanism of SDS-functionalized MWCNT additive was investigated with scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and Raman spectroscopy. These preliminary results show a promise in applications of surfactant functional carbon nanotubes as an additive in water.     

EVALUATION AND COMPARISON OF LUBRICANT PROPERTIES IN MINIMUM QUANTITY LUBRICATION MACHINING

Minimum Quantity Lubrication (MQL) machining involves the application of a minute amount of an oil-based lubricant to the machining process in an attempt to replace the conventional flood coolant system. Understanding the correlations between fluid properties and MQL performance can help in selecting lubricants from a variety of choices without going through extensive machining tests. This study compared nine different MQL fluids in terms of their physical properties, wettability, tribological properties (lubricity and extreme pressure (EP) properties), mist characteristics and machinability to determine the correlation of measured properties and MQL drilling and reaming performance. Results show that low fluid viscosity, high mist concentration, large mist droplet diameter and high wettability were best correlated with good machinability. Although it is difficult to draw strong relationships, the optimal machining in a mild cutting condition was found with the low viscosity fluids, which may also have the highest mist concentration, largest drops and best wettability.     

On machining of Ti-6Al-4V using multi-walled carbon nanotubes-based nano-fluid under minimum quantity lubrication

Titanium alloys are the primary candidates in several applications due to its promising characteristics, such as high strength to weight ratio, high yield strength, and high wear resistance. Despite its superior performance, some inherent properties, such as low thermal conductivity and high chemical reactivity lead to poor machinability and result in premature tool failure. In order to overcome the heat dissipation challenge during machining of titanium alloys, nano-cutting fluids are utilized as they offer higher observed thermal conductivity values compared to the base oil. The objective of this work is to investigate the effects of multi-walled-carbon nanotubes (MWCNTs) cutting fluid during cutting of Ti-6Al-4V. The investigations are carried out to study the induced surface quality under different cutting design variables including cutting speed, feed rate, and added nano-additive percentage (wt%). The novelty here lies on enhancing the MQL heat capacity using nanotubes-based fluid in order to improve Ti-6Al-4V machinability. Analysis of variance (ANOVA) has been implemented to study the effects of the studied design variables on the machining performance. It was found that 4 wt% MWCNTs nano-fluid decreases the surface roughness by 38% compared to the tests performed without nano-additives, while 2 wt% MWCNTs nano-fluids improve the surface quality by 50%.     

多壁碳纳米管改性UHMWPE的热膨胀和摩擦学性能研究

为了降低摩擦副用聚合物的热膨胀系数,用多壁碳纳米管(MWCNTs)改性超高分子量聚乙烯(UHM-WPE),通过热压成型法制备MWCNTs/UHMWPE复合材料.通过测量电导率计算渗流阈值来表征分散性;用热膨胀仪(DIL)测试复合材料的热膨胀率,并在干摩擦环境下,测试不同MWCNTs含量复合材料的摩擦学性能.结果表明:通...     

Influence of surfactants on tribological behaviors of MWCNTs (multi-walled carbon nano-tubes)

Multi-Walled Carbon Nano-Tubes (MWCNTs) are employed as anti-wear and anti-friction additives in mineral oil. The MWCNTs are known for their superior thermal conductivity, mechanical and optical properties. It is expected that hollow-core carbon nano-tubes provide easy sliding as well as rotating action with respect to one another; therefore, there is a need to explore the use of MWCNT as lubricant additive. In the present research work, experimental investigations have been conducted to explore the importance of the MWCNTs as additives in the lubricating oils. Tests were performed on three oil samples: Sample 1 (Base oil), Sample 2 (MWCNT with base oil) and Sample 3 (MWCNT and surfactant with base oil), by employing block on disc set-up. To understand the role of surfactant on MWCNT towards reducing the friction and wear, sensitivity analysis performed using fractional factorial table has been detailed. The results of cumulative wear and friction have been reported in this study.     

Multi-walled Carbon Nanotube-Imidazolium Tosylate Ionic Liquid Lubricant

Multi-walled carbon nanotubes (MWCNTs) were added in a 0.5 wt% proportion to 1-alkyl-3-methylimidazolium room temperature ionic liquids (IL) The new IL + MWCNTs dispersions obtained by mechanical grinding were used as lubricants of the polycarbonate (PC) disc/AISI 316L stainless steel pin contact, and their tribological performance compared with that of the corresponding IL. The highest friction reduction at 0.98 N and 0.10 m s^?1, of a 54 %, was obtained when MWCNT were added to 1-ethyl-3-methylimidazolium tosylate ([EMIM]Ts). The [EMIM]Ts + MWCNT dispersion was further characterised by rheological measurements, contact angle, DSC, TGA, FTIR and Raman spectroscopies, TEM microscopy and XRD. The addition of MWCNTs increases the viscosity of the IL in a 50 % at room temperature and the wettability on the PC surface, while the IL increases the purity and alignment of the nanotubes. The variation of friction coefficient was determined under variable sliding velocity conditions. The higher friction reduction for [EMIM]Ts + MWCNT with respect to [EMIM]Ts is observed for sliding velocities higher than 0.075 m s^?1. Under the experimental conditions, the surface damage on the PC and AISI 316L surfaces was negligible.     

Evaluation of performance of nanofluid using multiwalled carbon nanotubes for machining of Ti–6AL–4V

Machining of titanium alloys generate very high temperature in the cutting zone. This results in rapid tool wear and poor surface properties. Therefore, improvement in cutting performance in machining of titanium alloys is very much dependent on effectiveness of the cooling strategies applied. In the present work, performance of nanofluid using multiwalled carbon nanotubes (MWCNTs) dispersed in distilled water and sodium dodecyl sulfate (SDS) as surfactant is evaluated for turning operation on Ti–6Al–4V workpieces. Turning operations were carried out under three different conditions – dry, with conventional cutting fluid and with nanofluid. Nanofluid application was limited to 1 L/h and it was applied at the tool tip through gravity feed. Various machining responses like cutting force, surface finish and tool wear were analyzed while turning at optimum cutting parameters as 150 m/min, 0.1 mm/rev and 1 mm depth of cut. Later on, machining performance of nanofluid is confirmed at low cutting speed of 90 m/min. Nanofluid outperformed conventional cutting fluid with 34% reduction in tool wear, average 28% drop in cutting forces and 7% decrease in surface roughness at cutting speed of 150 m/min.     

多壁碳纳米管/油酸复合物纳米流体车削GCr15钢的性能研究

针对切削液不易渗入到切削区起润滑作用的问题,提出利用内部填充油酸(OA)的多壁碳纳米管(MWCNTs)复合物为添加剂制备纳米流体,该纳米流体更易渗入到切削区,且复合物可在切削时释放油酸起增强润滑的作用。首先测试了纳米流体的热物理性能,考察了它在微量润滑(MQL)条件下车削GCr15钢的性能,然后研究了切削过程中复合物的冷却润滑特性。结果表明：与普通MWCNTs相比,复合物能更好地提高纳米流体的分散稳定性、传热性和润湿性;与普通乳化液相比,复合物纳米流体车削时的切削力减小约15%,切削温度降低约25%,工件表面粗糙度值减小16%,刀具耐用度提高了22%。     

极压微乳化切削液的研制与应用

按照微乳液调配理论，研制了一种由表面活性剂、润滑剂、防锈剂、稳定剂、低粘度矿物油、杀菌剂和水等组成的透明极压微乳化切削液，详细探讨了防锈剂、油性剂、极压剂、表面活性剂等添加剂的选择；讨论了这种微乳化切削液的性能、特点及应用情况。应用结果表明：研制的极压微乳化切削液是透明稳定的，具有优良的防锈性、润滑性、冷却性和清洗性；产品不含对人体有害的氯化石蜡和亚硝酸钠等物质。     

一种新型微乳化绿色切削液研究

以低粘度润滑剂和自来水为基本原料,添加防锈剂、极压剂、消泡剂、表面活性剂,研制了一种新型微乳化绿色切削液。研制的微乳化绿色切削液稀释后适用于黑色等多种金属的切削、研磨等。具有良好的防锈、防腐、抗硬水稳定性能,且无毒无味、对皮肤无刺激,能满足工件加工的润滑性、防锈性和光洁度要求,并能延长其使用周期。     

Study on recycling of waste water from spent water-soluble coolant

We propose a recycling system that can recover the useful water from the spent water soluble coolant by using a surfactant and powdered activated carbon. The processing of about 70 liters of actual spent water soluble coolant yielded about 60 liters of clear water with 6.7 of pH and 0.0 of Brix value. About 120 liters of recycle water-soluble coolant was prepared by diluting an emulsion type cutting fluid 20 times with the recycle water. The recycle coolant has been showing the very similar Brix value and pH changes as those of virgin coolant until 100 days usage. The recycle coolant also showed the same potential to inhibit the progress of flank wear as that of virgin coolant. These facts indicate that the recycled water can be utilized as a dilutor of renewal water-soluble coolant.     

A review of the internal forced convective heat transfer characteristics of nanofluids: Experimental features,mechanisms and thermal performance criteria

In this review paper, we summarize important milestones in experimental studies that indicate the effects of volume fraction, nanoparticle size, operating temperature and pH on the internal forced convective heat transfer characteristics of nanofluids. In addition, many mechanisms for the enhancement of the convective heat transfer coefficient of nanofluids proposed by investigators are categorized into two dominant mechanisms. The first dominant mechanism is properties’ change of nanofluids such as thermal conductivity and viscosity. The other is the motion of nanoparticles in nanofluid flow due to Brownian motion, thermal dispersion and migration. Finally, the thermal performance criteria which can estimate whether nanofluids are useful in actual engineering systems, are summarized. Authors expect that the understanding of the convective heat transfer characteristics of nanofluids could help many thermal engineers to develop nanofluids which can be used in industrial applications.     

Experimental analysis on cutting fluid dispersed with silver nano particles

Cutting fluids play a significant role in machining operations, impact shop productivity, tool life and quality of work. The reduction in the consumption rate of the cutting fluid leads to the minimization of production cost and environmental hazards. This could be achieved by the enhancement of its thermal and tribological properties with the inclusion of suitable additives in the cutting fluid. In recent years various nanoparticles were used as additives in the conventional cutting fluid to enhance its properties. In the present work, silver nanoparticles was synthesized, characterized, dispersed in cutting fluid and experimented in a turning operation. Heat carrying capacities of the cutting fluid, cutting forces during machining process and surface finish of the work piece were assessed by suitable instruments for cutting fluids with and without silver nanoparticles under different machining conditions. From the experimental results, it was observed that inclusion of silver nanoparticles in cutting fluid showed a significant reduction in tool tip temperature, cutting force and surface roughness of the work piece.     

Improvement in electrical and thermal behavior of polystyrene/multiwalled carbon nanotubes nanocomposites

Polystyrene (PS)/multiwalled carbon nanotubes (MWCNTs) nanocomposite has been prepared by solvent evaporation technique  and . Tetrahydroforan (THF) has been used as a solvent. Its electrical and thermal properties have been investigated by using LCR meter, 2-probe mechanism and Thermo Gravimetric Analysis Differential Thermal Calorimeter (TGA/DTA) respectively. Increase in dielectric constant and loss is observed with the increase of MWCNTs content in the nanocomposites. Frequency dependent AC conductivity follows the universal power law. Increase in AC conductivity with temperature has been attributed to hopping of π electrons in the MWCNTs. Temperature dependent DC conductivity was found to be a typical of a semi conducting behavior following Mott’s 3-D variable range hoping model. Best fitted Mott’s parameters were determined from the observed data.     

Growth of compound single- and multi-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are complement to each other in many of their physical properties. We report the synthesis of carbon nanotube cables-a form of compound single- and multi-walled carbon nanotubes which could have the superior properties of both the SWCNTs and MWCNTs. This compound form of carbon nanotubes consists of a bundle of SWCNTs formed into a MWCNT, and the diameter of the inner most shell of the MWCNT ranges from a few to tens nanometers. The growth of these compound carbon nanotubes cannot be explained readily via existing modes of carbon nanotube growth, but promises a new way for improving and controlling the physical properties of either single- or multi-walled carbon nanotubes.     

Physical properties and cutting performance of silicon nitride ceramic

Silicon nitride, a nitrogen compound of highly covalent bond character, has low density, high hardness, low thermal expansion and high thermal conductivity and excellent oxidation and corrosion resistance. Therefore it is considered to be a promising material for high temperature engineering components.However, it has very poor sinterability compared with the conventional oxide ceramics owing to its low self-diffusivity. By investigating starting materials, sintering additives and processing, a hot-pressed silicon nitride ceramic having grains enveloped by crystalline boundary phases can be produced.The silicon-nitride-based ceramic has high strength, high Weibull modulus, fracture toughness and thermal conductivity, and low thermal expansion compared with existing cutting tool ceramics such as Al₂O₃ + TiC, and it is expected to have superior thermal shock resistance.This new ceramic cutting tool shows superior performance in cutting cast irons at high speeds (10–16.75 m s^?1 (600–1000 m min^?1)) and rates (about 1.0 mm rev^?1), where conventional tools cannot be used.     

超临界压力下CO2流体的性质研究

为了全面了解CO2在气体冷却器中的流动及传热特性以及为设计高效气体冷却器提供理论基础,对超临界CO2流体的性质进行了深入的研究,在三维图上分析了温度和压力对超临界CO2热物理性质的影响,并对超临界CO2流体进行了微观分析.结果表明,CO2的比热、密度、导热系数以及粘度在准临界点附近的变化非常剧烈.针对CO2比热的变化特点,得到了准临界温度的计算关联式,并给出了准临界区定义.CO2的密度、导热系数以及粘度变化最大时的温度与准临界温度相当接近.微观分析表明,超临界CO2流体分子间的作用力比较小,分子在临界区附近的聚集行为特别显著,这可以用来解释近临界区CO2物性独特的原因所在.     

发散形通道内的稳定电渗流动

电渗流通过外加电场来驱动液体通过微小通道,同时由于焦耳热效应的存在,也会在流体及通道表面形成热传导现象。应用计算流体力学方法,对矩形发散形微通道内电渗流流动所产生的流场、温度场进行了数值模拟和研究。由于流体的介电常数、电导率、粘性、热导率等属性依赖于温度的变化,焦耳热效应产生的温度场会改变流体的多种属性,并进而影响到流动速度、压力分布等。计算结果表明,焦耳效应在微管道芯片上产生了一个非均匀的热梯度场,并同时影响液体流动。热梯度场的存在在均匀截面通道内可以提高液体的流动速度,但在发散形通道内却不能产生相似的效果,此时的出口速度和体积流速都明显下降,分别达到约16%和60 μl/min。焦耳热效应同时通过降低流速和流动压力减弱了发散形管道的电渗流泵送性能。     

Chemical and Mechanical Characteristics of a Deep-Dewaxed Mineral Oil Hydraulic Fluid

This paper is a reasonably complete presentation of the formulation, the physical and chemical properties, and the pump loop behavior of a deep-dewaxed mineral oil, MLO 60–294. Properties given include: (a) viscosity and bulk modulus as functions of both temperature and pressure, (b) specific heat, density, thermal expansion, vapor pressure, and thermal conductivity as functions of temperature, and (c) pour, cloud, flash, and fire points. The behavior of this fluid in one pump loop to 700 F, and in a second loop to 600 F, is discussed. Excellent fluid performance was obtained in these pump loops at 400, 500, 550, and 600 F; however, the fluid degraded rapidly at 700 F.     

碳纳米管基膨润土润滑脂的制备及摩擦学性能研究

为制备摩擦学性能优良的多壁碳纳米管基膨润土润滑脂,采用油酸对多壁碳纳米管(MWCNTs)进行修饰,在实验室自主设计的超声辅助球磨试验装置上,制备在PAO6中均匀稳定分散的多壁碳纳米管悬浮液,并以悬浮液为基础油制备MWCNTs增强的膨润土润滑脂。探讨不同分散方法(球磨分散、超声分散、超声和球磨分散)对多壁碳纳米管分散稳定性的影响,研究润滑脂的摩擦因数、磨斑直径随多壁碳纳米管质量分数的变化。实验结果表明:经油酸修饰的多壁碳纳米管在超声和球磨综合作用下分散稳定性最好;随多壁碳纳米管质量分数的增加,膨润土润滑脂的摩擦因数、磨斑直径先减小后增大,其中多壁碳纳米管质量分数为0.03%时,所制备的膨润土润滑脂摩擦学性能最佳,磨斑直径最小(0.690 mm),比美孚28号航空润滑脂(符合美国军方规格MIL-G81322C,磨斑直径0.807 mm)降低了14.5%。