Process optimization and material properties for nanofluid manufacturing

Using an innovative nanofluid preparation method, ultrasonic-aidedsubmerged arc nanoparticle synthesis system, this paper employs the robustness design method to examine the optimal parameters, such as peak current, pulse duration, open voltage and amplitude of ultrasonic vibration, for obtaining the optimal process for TiO₂ nanofluid preparation. Experimental results show that the proposed manufacturing system can successfully prepare uniformly distributed TiO₂ nanoparticle using the optimal parameters. The pH of the as prepared TiO₂ nanofluid is 7.5, which is much higher than that of isoelectric point, about 4.4. Hence, the suspended TiO₂ nanoparticles already possess electrostatic stability properties. Regarding ultraviolet/visible absorbency, the produced TiO₂ nanofluid would absorb UV energy when the wavelength is 280 nm to 400 nm. According to the UV-Vis absorption spectrum analysis, the energy band gap of the prepared TiO₂ nanoparticle is 3.4 eV.     

Process development of a novel arc spray nanoparticle synthesis system (ASNSS) for preparation of a TiO 2 nanoparticle suspension

This article presents the development of an innovative technology to manufacture TiO₂ nanoparticles. Manufacturing nanoparticles is considered as a crucial step towards product and process innovation. In our proposed process, a titanium rod, as the electrode, is melted and vaporised in deionised water, which is used as an insulating liquid. The vaporised metal particles are then rapidly quenched by the designed cooling system, and thus nanocrystalline powders are nucleated and formed. By implementing the system, we have successfully developed the processing equipment of the arc spray nanoparticle synthesis system (ASNSS). The experimental results indicate that uniformly distributed and well-controlled TiO₂ nanoparticle size can be manufactured by ASNSS.     

Analysis of suspension stability for nanofluid applied in minimum quantity lubricant grinding

The nanofluid is usually applied in minimum quantity lubricant (MQL) grinding to decrease grinding temperature and to improve surface integrity of workpiece. However, a large challenge in the application process of nanofluid is the sedimentation of the nanoparticles due to their poor suspension stability in the base fluid. Then, the lubrication and heat conduction characteristics of nanofluid will be deteriorated, and the nanofluid cannot be atomized as expected during grinding. Therefore, the heat transfer performance of nanofluid during MQL grinding severely decreased. In this study, the force state of nanoparticle in base fluid was analyzed and the effect of dispersant on the force state of nanoparticle was researched. The suspension stability of Al₂O₃ (0.5 wt.%) nanofluid was investigated under different ultrasonic vibration times, pH values, and dispersant concentrations (sodium dodecyl benzene sulfonate, SDBS). It is found that the suspension stability of nanofluid is quite poor under short-time ultrasonic vibration condition, and the nanofluid with good suspension stability can be obtained when the ultrasonic vibration time exceeds 0.5 h. A higher concentration of SDBS will lead to a better suspension stability of nanofluid when the concentration of SDBS is quite low. However, if the concentration of SDBS exceeds 0.5 wt.%, there is oversaturated adsorption on the nanoparticles surface which results in the deterioration of suspension stability of nanofluid with the increase of the SDBS concentration. As pH value is below 7, the suspension stability of nanofluid is significantly improved with the increase of pH value. The sedimentation clearly appeared in the disperse system when pH value is higher than 7. The dispersion morphology of the Al₂O₃ nanoparticles in disperse system is analyzed by using a scanning electron microscope. It is found that some large aggregates appeared when no dispersant was applied in the disperse system, and the Al₂O₃ nanoparticles are uniformly dispersed in disperse system with the application of the dispersant.     

What atomic resolution annular dark field imaging can tell us about gold nanoparticles on (1 1 0)

Annular dark field scanning transmission electron microscopy imaging was recently applied to a catalyst consisting of gold nanoparticles on TiO₂ (1 1 0), showing directly that the gold atoms in small nanoparticles preferentially attach to specific sites on the TiO₂ (1 1 0) surface. Here, through simulation, a parameter exploration of the imaging conditions which maximise the visibility of such nanoparticles is presented. Aberration correction, finite source size and profile imaging are all considered while trying to extracting the maximum amount of information from a given sample. Comment is made on the role of the thermal vibration of the atoms in the nanoparticle, the magnitude of which is generally not known a priori but which affects the visibility of the nanoparticles in this imaging mode.     

Heat transfer enhancement of pool boiling for a horizontal U-tube using TiO2-R141b nanofluid

An experimental investigation is performed into the pool boiling heat transfer performance of TiO₂-R141b nanofluid containing 0 vol%, 0.0001 vol%, 0.001 vol%, and 0.01 vol% TiO₂ nanoparticles. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) observations reveal that some of the TiO₂ nanoparticles adhere to the heated surface during the boiling process. As a result, the heat transfer performance is poorer than that obtained using pure R141b as the working fluid. Accordingly, a further investigation is performed in which the heated surface is vibrated ultrasonically. It is shown that the ultrasonic vibration creates an acoustic cavitation effect, which inhibits the formation of the nano-sorption layer and improves the heat transfer performance as a result.

     

Effect of the Normal Load on the Release of Aerosol Wear Particles During Abrasion

A study highlighting the aspect of the generation of aerosol wear particles during abrasion is presented. The substrate chosen is a masonry brick which is reinforced with TiO₂ nanoparticles. This is done using a pin on plate arrangement. The material removal mechanism via fracturing is first understood. The parameter chosen for the study is the normal load. The formed aerosols are then characterized by their number concentration, particle size distribution, individual particle shape, size and chemical composition. Having irregular shapes, the aerosol wear particles have unimodal size distributions with 5–7 % (in mass) of Ti content. The size mode increases with the increase in normal load. However, at higher normal loads, while there is an unexpected increase in the wear mass, the maximum concentration of the aerosol particles saturates. During the whole study, no free nanoparticles of TiO₂ were found.     

Modelling and experimental investigations of thin filmsof Mg phosphorus‐doped tungsten bronzes obtainedby ultrasonic spray pyrolysis

In this study, the synthesis of thin films of Mg phosphorus doped tungsten bronzes (MgPTB; MgHPW₁₂O₄₀·29H₂O) by the self‐assembly of nano‐structured particles of MgPTB obtained using the ultrasonic spray pyrolysis method was investigated. As the precursor, MgPTB, prepared by the ionic exchange method, was used. Nano‐structured particles of MgPTB were obtained using the ultrasonic spray pyrolysis method. The nano‐structure of the particles used as the building blocks in the MgPTB thin film were investigated experimentally and theoretically, applying the model given in this article. The obtained data for the mean particle size and their size distribution show a high degree of agreement. These previously tailored particles used for the preparation of thin films during the next synthesis step, by their self‐assembly over slow deposition on a silica glass substrate, show how it is possible to create thin MgPTB films under advance projected conditions of the applied physical fields with a fully determined nanostructure of their building block particles, with a relatively small roughness and unique physical properties.     

Slurry Erosion Behaviour of Detonation Gun Spray Al2O3 and Al2O3–13TiO2-Coated CF8M Steel Under Hydro Accelerated Conditions

Slurry erosion performance of detonation gun (D-gun) spray ceramic coatings (Al₂O₃ and Al₂O₃–13TiO₂) on CF8M steel has been investigated. Slurry collected from an actual hydro power plant was used as the abrasive media in a high speed erosion test rig. Attempt has been made to study the effect of concentration (ppm), average particle size and rotational speed on the slurry erosion behaviour of these ceramic-coated steels under different experimental conditions. The analysis of eroded samples was done using SEM, XRD and stylus profilometry. The slurry erosion performance of the D-gun spray Al₂O₃–13TiO₂-coated steel has been found to be superior to that of Al₂O₃-coated steel. Both the coatings showed brittle fracture mechanism of material removal during the slurry erosion exposure.     

Hydrothermal preparation of TiO₂-Ag nanoparticles and its antimicrobial performance against human pathogenic microbial cells in water

Water contaminated with pathogenic microbes is considered as one of the most common routes for transmitting diseases in human beings. Different methods have been applied for the decontamination of microbes in contaminated water. In the current study, an easy to do hydrothermal method has been used for the preparation of TiO₂-Ag nanoparticles. The obtained material was characterised using a scanning electron microscope (SEM) and fourier transform infra-red spectroscopy (FTIR). The morphological appearance of the obtained nanoparticles was in the shape of a sphere with a size range of 60-90 nm. The antimicrobial activity of the prepared nanoparticles was tested against several pathogenic bacteria and fungi. The obtained results proved that the nanoparticles succeeded to affect all the tested microbes in the following order: Bacillus cereus ATCC6633>Pseudomonas aeruginosa ATCC9027= Klebsiella pneumoniae ATCC13883>Vibrio cholera ATCC700=Candida albicans ATCC 700=Escherichia coli NCTC10418>Staphylococcus aureus ATCC6538. The minimum inhibitory concentration (MIC) of the prepared nanoparticles varied among the tested microbes at range of 12 mg/ml and 25 mg/ml. These results encourage the application of prepared TiO₂-Ag nanoparticles for treatment of microbe-contaminated waters.     

Nanoparticle shape and configuration analysis by transmission electron tomography

Tomographic reconstruction by transmission electron microscopy is used to reveal three‐dimensional nanoparticle shapes and the stacking configurations of nanoparticle ensembles. Reconstructions are generated from bright‐field image tilt series, with a sample tilt range up to ± 70°, using single or dual tilt axes. We demonstrate the feasibility of this technique for the analysis of nanomaterials, using appropriate acquisition conditions. Tomography reveals both cubic and hexagonal close‐packing configurations in multi‐layered arrays of size‐selected In nanospheres. By tomography and phase‐contrast lattice imaging, we relate the three‐dimensional shape of PbSe octahedral nanoparticles to the underlying crystal structure. We also confirm simple‐cubic packing in multi‐layers of PbSe nanocubes and see evidence that the particle shapes have cubic symmetry. The shapes of TiO₂ nanorod bundles are shown by tomographic reconstruction to resemble flattened ellipsoids.     

Effect of nanoparticles additives on the performance of an externally adjustable fluid film bearing

This paper presents the effect of CuO, TiO₂ and Nano-Diamond nanoparticles additives in API-SF engine oil, on static characteristics of an externally adjustable fluid-film bearing. Modified form of Reynolds equation is solved numerically for various simulated operating conditions. Static characteristics evaluated are in terms of load carrying capacity, end leakage and friction. This study predicts that, a bearing having negative radial and negative tilt adjustments, and operating with API-SF engine oil blended particularly with TiO₂ nanoparticles, results in better load capacity with reduced end leakage and increased friction, as compared to API-SF engine oil and Base oil without nanoparticle additives.     

Effect of nano additives (titanium and zirconium oxides) and diethyl ether on biodiesel-ethanol fuelled CI engine

The present work is dedicated to the comparative experimental study of biodiesel-ethanol blends in a compression ignition engine using TiO₂ (Titanium oxide) nanoparticle, ZrO₂ (Zirconium oxide) nanoparticle and DEE (Diethyl ether) additives. The test fuels used are a blend of biodiesel (80%) -ethanol (20%) (denoted as BE), a blend of BE with 25 ppm Titanium oxide nanoparticle (denoted as BE-Ti), a blend of BE with 25 ppm Zirconium oxide nanoparticle (denoted as BE-Zr) and a blend of BE with 50 ml Diethyl ether (denoted as BE-DEE). Addition of nanoparticles increases the oxidation rate, reduces the light-off temperature and creates large contact surface area with the base fuel thereby enhancing the combustion with minimal emissions. Experimental results shown that addition of Titanium nanoparticles increased NOx, HC and smoke with lowered BSFC and CO. Whereas addition of Zirconium nanoparticles increases BSFC and HC emissions with lowered CO, CO₂ and smoke emissions in comparison with BE blends. DEE addition to BE blends improved the heat release rate and increased HC, CO emissions were observed with lowered BSFC, NOx and smoke. Simultaneous reduction of NOx and smoke indicates the effect of DEE on Low temperature combustion (LTC).

     

An Investigation on the Reduced Ability of IF-MoS2 Nanoparticles to Reduce Friction and Wear in the Presence of Dispersants

Inorganic fullerene-like molybdenum disulfide (IF-MoS₂) nanoparticles are known to exhibit great friction and wear-reducing abilities in severe boundary lubrication regimes, when added to a base oil alone. Their use in fully formulated lubricants was investigated in this study, and the tribological benefits attributed to the IF-MoS₂ nanoparticles were found to be lost in the presence of dispersants. Various experimental techniques were used on three reference oils (base oil containing only IF-MoS_2, only dispersants and both IF-MoS₂ and dispersants) in order to understand the effect of succinimide-based dispersants on the three phases needed for effective nanoparticle-based lubrication, namely (1) the passing of the nanoparticles through the contact (2) the exfoliation of the IF-MoS₂ inside the contact and (3) the adhesion of the released MoS₂ platelets on the friction surfaces. The dispersants were shown to improve the dispersion of the nanoparticles in the oil by reducing their agglomeration, but prevented the adhesion of a low-friction MoS₂ tribofilm on the steel surfaces. In-situ contact visualization revealed that the well-dispersed nanoparticles passed through the contact and exfoliated nanoparticles were observed after tribological testing. These results imply that nanoparticle dispersion itself does not seem to be an issue concerning nanoparticle effectiveness, even though the reduced agglomerate size and inertia may have affected nanoparticle flow near the contact, as well as entrapment and exfoliation conditions inside the contact. The use of succinimide-based dispersants may, however, have affected the tribochemistry of the contact, by an excessive adsorption on the steel surfaces and/or by encapsulating the released MoS₂ platelets, preventing tribofilm adhesion. A balance was finally found between nanoparticle dispersion and friction reduction, but for very low dispersant concentrations and after a running-in period. The role of succinimide-based dispersants and their effect on nanoparticle lubrication were discussed in the light of these results.     

Study on tribological properties of oleic acid-modified TiO2 nanoparticle in water

A cis-9-octadecenoic acid (OA) surface-modified TiO₂ nanoparticle with average diameter of 30 nm was chemically synthesized. The tribological properties of the prepared OA–TiO₂ nanoparticle as an additive in water were evaluated with a four-ball tester. The results show that the OA–TiO₂ nanoparticle exhibits good antiwear and friction reduction properties as well as load-carrying capacity. The maximum non-seizure load (P_B value) can be raised about 6–10 times when 0.1–1.0% OA–TiO₂ nanoparticle was added into water. The rubbed surface after friction tests was investigated with X-ray photoelectron spectroscopy (XPS). The results of XPS analysis indicate that a boundary film mainly composed of TiO₂ and oleic acid complex, was formed on the rubbed surface.     

Various MoS2-, WS2- and C-Based Micro- and Nanoparticles in Boundary Lubrication

Various solid lubricant particles have been experimentally evaluated as possible additives to oils. However, information in terms of a direct comparison of their tribological properties is still missing. In this study, we have compared the tribological properties of seven different solid lubricant micro- and nanoparticles as additives in polyalphaolefin (PAO) oil: MoS₂ nanotubes, MoS₂ platelets (2 and 10 μm), WS₂ nanotubes, WS₂ fullerene-like nanoparticles, graphite platelets (20 μm) and multi-walled carbon nanotubes. The experiments were performed in the boundary lubrication regime under a contact pressure of 1 GPa (Hertz, max) using a ball-on-disc tribotester. In general, the particles significantly decreased the friction and wear compared to the base PAO oil. We found that it was the material of the particles that largely determined their tribological performance. The effect of the size of the particles was much less important, and the morphology (shape) of the particles had little or no influence. We have also investigated the effect of ultrasonication during suspension preparation on particle damage and found that the solid lubricant particles were not notably affected, except the MoS₂ and WS₂ nanotubes, which became somewhat shorter.     

Revealing local variations in nanoparticle size distributions in supported catalysts: a generic TEM specimen preparation method

The specimen preparation method is crucial for how much information can be gained from transmission electron microscopy (TEM) studies of supported nanoparticle catalysts. The aim of this work is to develop a method that allows for observation of size and location of nanoparticles deposited on a porous oxide support material. A bimetallic Pt‐Pd/Al₂O₃ catalyst in powder form was embedded in acrylic resin and lift‐out specimens were extracted using combined focused ion beam/scanning electron microscopy (FIB/SEM). These specimens allow for a cross‐section view across individual oxide support particles, including the unaltered near surface region of these particles. A site‐dependent size distribution of Pt‐Pd nanoparticles was revealed along the radial direction of the support particles by scanning transmission electron microscopy (STEM) imaging. The developed specimen preparation method enables obtaining information about the spatial distribution of nanoparticles in complex support structures which commonly is a challenge in heterogeneous catalysis.     

Porous TiO2 nanowire microsphere constructed by spray drying and its electrochemical lithium storage properties

Porous TiO₂ nanowire microspheres with greatly decreasing agglomeration were successfully prepared by spray drying of hydrothermal reaction suspension, followed by calcination at 350°C. The as‐obtained nanowire microspheres with TiO₂‐B structure reach an initial discharge capacity 210 mAh g^?1 with an irreversible capacity 25 mAh g^?1 at a current density of 20 mA g^?1. For the 450°C‐calcined one with anatase TiO₂ crystal structure, the initial discharge capacity is 245 mAh g^?1 but with a much higher irreversible capacity of 80 mAh g^?1. The hierarchical porous structure in the 350°C‐calcined TiO₂ nanowire microspheres collapsed at 450°C, annihilating the main benefit of nanostructuring. Microsc. Res. Tech. 77:170–175, 2014. © 2013 Wiley Periodicals, Inc.     

多模式超声振动等径角挤压超细晶纯铝成形机理研究

超细晶金属材料由于具有优异的力学性能,特别适合微小金属零件的塑性成形。大塑性变形法是制备超细晶金属材料的常用方法,等径角挤压法被认为是最具有发展前景的大塑性变形方法之一。传统等径角挤压需要通过多道次的应变量累积来获得超细晶材料,制备效率较低。将超声振动与等径角挤压过程相结合可以有效减小挤压成形载荷,提高等径角挤压制备超细晶的性能和效率。现有研究主要采用工具辅助超声振动模式,提出并研发基于工件辅助超声振动模式的等径角挤压成形工艺,并对不同超声振动模式1070纯铝等径角挤压成形机理进行对比研究,研究工具超声振动和工件超声振动两种不同振动方式对晶粒道次细化能力的影响规律。结果表明,随着超声功率的增大,工具超声振动和工件超声振动的超声软化效应逐渐增强,能更大幅度降低等径角挤压成形力,并提高晶粒道次细化能力。工件超声振动比工具超声振动更有利于吸收超声能量,从而能更有效提升超细晶金属的制备效率。     

Sintering of Sio2-Tio2 obtained by the sol-gel process from chelated Ti precursors

Two experimental procedures were used to obtain SiO₂-TiO₂. In one case, the Si precursor was prehydrolyzed before reacting with Ti to equalize the chemical reactivity of both reagents. In the other case, H₂O was produced in situ to avoid precipitation of TiO₂. Two chelating agents were also used separately to control the polymerization process. It was found that the type of chelating agent leads to differences in the particle size.     

Tribochemical Transformation of Nano TiO2 to Ilmenite on the Surface of Wearing Steel Parts: Antiwear Action of Nano TiO2 as an Additive in Engine Oil

TiO₂ nanoparticles of average size about 20–30 nm were hydrothermally synthesized from TiCl₄ under mild acidic conditions. The nanoparticles were mixed with dispersant and base oil to give a partially transparent concentrate with 1.5 wt% of Ti content. The concentrate was dispersed in hexane and base oil to characterize, respectively, by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The concentrate was diluted with base oil to a parts per million level of Ti containing dispersion blends that were evaluated for wear and friction control performance. Nano TiO₂ containing fully formulated oil blend showed excellent load-bearing capability in Swingung, Reibung, Verschleiβ (SRV; oscillation, friction, wear) tests. Four-ball test results show that the wear scar diameter was considerably reduced to 0.30 mm for TiO₂-added blend compared to neat base oil (0.60 mm). The performance of TiO₂-added blend was comparable to secondary zinc dialkyl dithiophospate (ZDDP)-added blend under identical condition. Raman spectra of the worn surface on the tested ball revealed the presence of ilmenite (FeTiO₃) and no deposits of pure TiO₂.