Search

The impact of the addition of TiO2 nanoparticles and nanowires on the morphology, phase characteristics, contact angle, and electrochemical performance of chemically bonded phosphate ceramic coatings (CBPCs) was investigated. The chemical composition and surface morphology of the TiO2 nanoparticle and nanowire modified with and without (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane were characterized. Results indicated that the hydrophobic –CF2– and –CF3 groups were successfully introduced into the TiO2 nanoparticles and nanowires after modification. Corrosion resistance of CBPCs with TiO2 was evidently improved compared with that without TiO2. Such improvement was mainly due to the combined effects of low surface energy materials and micro/nano structures. In addition, CBPCs with TiO2 nanowires exhibited higher hydrophobicity and corrosion resistance than those with TiO2 nanoparticles because of the special columnar structure of the nanowires.

Zinc oxide (ZnO) decorated multi-walled carbon nanotubes (MWCNTs) hybrid material was prepared to improve the tribological performance of chemically bonded ceramic coatings. TEM results reveal that ZnO has been successfully fabricated on the surface of MWCNTs. The tribological performance of the ceramic coatings with MWCNTs–ZnO hybrid material was investigated using a ball-on-disc method. The results show that the friction coefficient and wear rate of the ceramic coatings decrease with the increase of MWCNTs–ZnO hybrid material. The ceramic coatings with MWCNTs-ZnO hybrid material shows a smooth worn surface with less cracks and delamination. In addition, the worn surface of the counterpart ball shows a smaller worn area and a smooth surface. The excellent wear resistance of the ceramic coatings is attributed to the good bonding strength between MWCNTs–ZnO hybrid material and ceramic matrix.

The chemical mechanical planarization (CMP) performance of the Si-face and C-face 6H-SiC substrates were compared using potassium permanganate (KMnO4) as an oxidizer and the alumina (Al2O3) nanoparticles as the abrasive particles over a pH range from 2 to 10. The results indicate that there was a significant difference in the CMP performance between Si-face and C-face 6H-SiC substrates, indicating that the CMP process was sensitive to the surface polarity of the 6H-SiC substrates. A higher material removal rate (MRR) was obtained during the CMP of C-face 6H-SiC substrates, as compared to that of Si-face 6H-SiC substrates. The maximum MRR of the C-face 6H-SiC substrates was reached to 6412 nm/h with an average surface roughness Ra of 0.54 nm when using the slurries containing 2 wt% alumina nanoparticles, 0.05 M KMnO4 at pH 2. While the Si-face 6H-SiC substrates was 1554 nm/h with an average surface roughness Ra of 0.53 nm. Furthermore, the polishing mechanism was also discussed based on the MRR, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analysis of the dipped and polished 6H-SiC surfaces.

In this study, microstructure and corrosion property of CoCrMo coatings reinforced with different content of multi-walled carbon nanotubes (MWCNTs) nanoparticles fabricated by laser cladding (LC) on titanium alloy (TC4) substrates are investigated. Microhardness, metallographic, X-ray diffraction (XRD), and the electrochemical analysis are carried out to clarify the role of CNTs on the improvement of corrosion resistance. The results indicate that the addition of CNTs can significantly refine the structure of the CoCrMo alloy coating. Besides, the hardness of CoCrMo coating reinforced with 1.5 percentage of CNTs is about 9.8 times of the non-addition one. Additionally, CNTs have a positive influence on the corrosion performance of the CoCrMo coating in acid simulation saliva environment, which may be mainly attributed to the superior property of CNTs themselves and the formation of carbide and martensite hard phases in the cladding layers.

In order to obtain a high material removal rate and good surface quality, the effect of Cu2+ ions and glycine complex as a catalyst on the chemical mechanical polishing (CMP) performance of Si-face 6H-SiC substrates was investigated. The results indicated that the slurry with Cu2+-glycine complex had a higher material removal rate (MRR) and better surface quality than that without Cu2+-glycine complex. The maximum MRR of the Si-face 6H-SiC substrate was 83 nm/h with an average roughness (Ra) of 0.336 nm using the slurry containing 6wt% silica (SiO2) and 4wt% hydrogen peroxide (H2O2) at pH 10. In contrast, when Cu2+-glycine complex were added as a catalyst, the maximum MRR was increased to 118 nm/h with Ra of 0.155 nm. The ultraviolet–visible (UV–vis) spectroscopy analysis indicated that the Cu2+-glycine complex was an effective catalyst for the decomposition of H2O2 to generate more hydroxyl (·OH) radicals. Meanwhile, due to the fact that more softened layer was formed and the SiO2 abrasive nanoparticles were deeply pressed into the softened layer to produce a plowing action under the polishing pressure, coefficient of friction (COF) was increased by adding the Cu2+-glycine complex. Finally, the polishing mechanism of the Si-face 6H-SiC substrates using the Cu2+-glycine complex was discussed.

Introduction Randomized trials of new agents for HIV pre‐exposure prophylaxis (PrEP) compare against emtricitabine and tenofovir disoproxil fumarate (F/TDF), without a placebo group. We used the well‐characterized adherence‐efficacy relationship for F/TDF to back‐calculate the (non‐PrEP) counterfactual background HIV incidence (bHIV) in a randomized trial of a novel PrEP agent and estimate comparative efficacy (to counterfactual bHIV). Methods The DISCOVER trial (ClinicalTrials.gov: NCT02842086) randomized 5387 men who have sex with men (MSM) and transgender women who have sex with men and demonstrated non‐inferiority of emtricitabine and tenofovir alafenamide (F/TAF) to F/TDF (HIV incidence rate ratio [IRR] 0·47, 95% CI: 0·19 to 1.15). Tenofovir diphosphate (TFV‐DP) levels in dried blood spots (DBS) were assessed for all diagnosed with HIV and in a random 10% of the cohort. We used a Bayesian model with a diffuse prior distribution, derived from established data relating tenofovir diphosphate levels to HIV prevention efficacy. This prior, combined with the F/TDF seroconversion rate and tenofovir diphosphate levels in DISCOVER, yielded Bayesian inferences on the counterfactual bHIV. Results There were six versus 11 postbaseline HIV infections (0.14 vs. 0.25/100 person‐years [PY]) on F/TAF and F/TDF respectively. Of the 11 on F/TDF, 10 had low, none had medium and one had high tenofovir diphosphate levels; among HIV‐negative controls, 5% of the person‐time years had low, 9% had medium and 86% had high TFV‐DP levels. A non‐informative prior distribution for counterfactual bHIV, combined with the prior for TFV‐DP level‐efficacy relationship, yielded a posterior counterfactual bHIV of 3·4 infections/100 PY (0.80 Bayesian credible interval [CrI] 1·9 to 5·9), which suggests a median HIV efficacy of 96% (0.95 CrI [88% to 99%]) for F/TAF and 93% (0.95 CrI [87% to 96%]) for F/TDF compared to bHIV. Conclusions Based on the established connection of drug concentrations to PrEP prevention efficacy, a Bayesian framework can be used to estimate a synthetic non‐PrEP control group in randomized, active‐controlled PrEP trials that include a F/TDF‐comparator group.

To enhance the compactness of the chemically bonded phosphate ceramic coatings (CBPCs), different inorganic curing agents (MgO, CaO, and ZnO) are selected as the reinforcement. Tribological experiment and the analysis of microstructure, phase characterization and mechanical performance are carried out to clarify the mechanism of different curing agents on the effect of wear performance. It is found that the curing agents place a significant role on the wear performance of the coating. Compared with coating without curing agents, more bonded phase (AlPO4) can be detected when curing agents (MgO, CaO) are used, which is mainly resulted by the high heat release from MgO and CaO related reactions, and this released heat energy enhances the formation of AlPO4. The results indicate that the morphology and tribological performance of CBPCs using different kinds of curing agents are dependent on the weight ratio of AlPO4 to α-Al2O3 (defined as RPA). The suitable value of RPA will not only improve the bonding strength among the ceramic particles, but also decreases the quantity of defects (such as pores). Upon the above results, CBPCs with MgO process superior wear resistance due to their dense and uniform microstructure.

Graphene oxide (GO) decorated by titanium dioxide (TiO2) was fabricated and introduced into the chemically bonded ceramic coatings as a nanofiller. The analysis of the results of thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electronic microscopy (SEM), and transmission electron microscopy (TEM) show that TiO2 has decorated on the surface of GO by chemical bonds. Furthermore, the effect of incorporating GO-TiO2 on properties of ceramic coatings was investigated. The results show that GO-TiO2 achieved a homogeneous dispersion and compatibility in ceramic matrix without obvious cracks. The potentiodynamic polarization test was conducted to investigate the influence of GO-TiO2 on the corrosion behavior. The results demonstrated that corrosion resistance of ceramic coatings remarkably enhanced by adding GO-TiO2. Furthermore, the anticorrosive mechanisms of ceramic coatings with GO-TiO2 were tentatively discussed.

In this study, the chemically bonded phosphate ceramic coating reinforced with nano-titanium dioxide is prepared on the AISI 304L stainless steel by different curing temperatures. The structure evolution, surface roughness, wettability and corrosion resistance of the coating are investigated. The results indicate that with the increase of the curing temperature, the main curing reactions become different, resulting in different reactants as the bonded phase. When the curing temperature increases, the bonded phase translates from aluminum hydrogen phosphate hydrate (AlH3(PO4)2·3H2O) phase to berlinite (AlPO4) phase, leading to the increase of the corrosion protection property of the coating. That is because berlinite phase can provide a strong bond between ceramic particles and enhance the strength of the coating. Moreover, berlinite phase possesses the low density and more likely distributes on the surface of the coating, which can more effectively protect the stainless steel free from chloride ions destruction. In addition, berlinite phase also increases with the introduction of nano-titanium dioxide. However, compared with nano-titanium dioxide, the curing temperature can better promote the formation of berlinite phase. Therefore, the curing temperature more contributes to the wettability and corrosion protection property of the coating.

The curing agents play an important role on the properties of the chemically bonded phosphate ceramic coatings (CBPCs). To investigate the influence of curing agents on the thermal property and corrosion resistance of CBPCs, the coatings with different curing agents were prepared on the mild steel (Q235). The analysis of thermal property and phase characterization shows that the high peak temperature of curing decreases with the introduction of curing agents, and the weight ratio of AlPO4 to α-Al2O3 (RAA) of the coatings is also influenced by curing agents resulted by the high heat release from MgO, CaO, and ZnO-related reactions. In addition, the results of scanning electron microscopy (SEM) and electrochemical experiments reveal that the bonding strength among the ceramic particles and the defects content of the coatings, which affects the inhibition properties of CBPCs have a relationship with the value of RAA. Typically, the impedance value of CBPC with the best curing agent (MgO) are around 40,000 ohm cm2, which is 4624 times larger than that of the bare mild steel (8.65 ohm cm2).

To promote anti-corrosion property of chemically bonded phosphate ceramic coatings (CBPCs), the nano-TiO2 is selected as the reinforcement. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy Dispersive Spectrometer (EDS) and the electrochemical analysis are carried out to clarify the role of nano-TiO2 on the improvement of anti-corrosion performance. The experiments show that with the addition of nano-TiO2, the curing temperature and the activation energy of the curing process increase, which allows longest reaction and positively drives curing reactions at elevated conversions. The enhancement of anti-corrosion performance of CBPCs reinforced by nano-TiO2 particles is based on three main mechanisms. Firstly, more bonded phase (AlPO4) can be formed with the addition of nano-TiO2, which can help CBPCs to get more compact microstructure. Additionally, AlPO4 particles possess the low density and good corrosion resistance, which leads to the increase in the corrosion resistance of CBPCs. Secondly, increasing content of nano-TiO2 can also strengthen the compactness of CBPCs to protect the substrates from the penetration of aggressive electrolyte and prolong electrolyte diffusion path. Thirdly, through the analysis of microstructure of CBPCs, it is found that most of the hydrophobic nano-TiO2 particles homogeneously distribute on the surface of CBPCs. Therefore, CBPCs show well hydrophobic performance, which can further improve the anti-corrosion property of themselves.

The viscoelastic properties of polydimethylsiloxane (PDMS) measured are demonstrated by the uniaxial indentation test. Based on the barreling deformation, the viscoelastic models are established and the factors influencing the viscoelastic properties are discussed. These results indicate that the deformation response is greatly associated with load conditions and the PDMS materials exhibited more elastic properties at large load conditions as compared to small load conditions. It was reasonable to use the stress at the middle-section zone to investigate the viscoelastic behavior of the soft materials. The number and type of these elements in viscoelastic models affected the soft materials characteristics. These results would be helpful to further understand the viscoelastic properties and characterization of soft tissues.

Pulse repetition interval (PRI) is an important parameter of signal modulation in Anti-Radiation radar systems. The accuracy directly affects the ability of target recognition and system attack. PRI transform algorithm has a high accuracy in PRI estimation and can well deinterleave some PRI jittered signals within a certain range. However, the algorithm cannot intuitively acquire and describe the PRI modulation characteristics and changing rule of complex signals. Traditional plane transform technology can show the characteristic curve on the plane. However, the width of the plane needs to be adjusted constantly for target display and cannot realize complete automatic deinterleaving, which leads to difficulties in engineering applications. To alleviate this suffering, a novel short-time PRI transform algorithm is suggested. It admits a combination of both advantages of the method of short-time windowing and PRI transform algorithm, to acquire the modulation information and changing characteristics of the target’s PRI. The simulation results showed that the proposed algorithm is successful in deinterleaving and recognizing multi-targets for complex signal types besides accurately estimating the PRI center value in high pulse density environments. Moreover, the algorithm can obtain more PRI changing characteristics from two-dimensional images and, in this sense, the current method seems to be potential method in signal deinterleaving, and also paves a way for various future intelligent recognition applications.

Purpose This paper aims to modify carbon nanotubes with oleic acid, and to study the tribological properties of castor oil with modified carbon nanotubes additives. The proper additives are sought for the future engineering application of castor oil. Design/methodology/approach Tribological properties of the castor oils mixed with the modified carbon nanotubes of four mass percentages were investigated using a four-ball testing rig. Coefficient of friction and wear scar diameter were obtained in each test, and the mechanism of modified carbon nanotubes and castor oil was discussed. Findings The results indicated that modified carbon nanotubes had better dispersion in castor oil. Coefficient of friction first increased, then decreased and finally grew stable with the time, and wear scar diameter of steel surface functioned as a first reduced then increased change with the additive mass percentage of modified carbon nanotubes. The minimum of average coefficient of friction and wear scar diameter occurred at 0.02 Wt.% modified carbon nanotubes. Originality/value A small amount of modified carbon nanotubes could improve properties of the castor oil, and the mixed castor oil with 0.02 Wt.% modified carbon nanotubes would be most possibly used in engineering applications.

A range of ultrahigh molecular weight polyethylene (UHMWPE)/graphene oxide (GO) nanocomposites were fabricated using liquid-phase ultrasonication mixing followed by hot-pressing. The wettability, water absorption and corrosion resistance of composites were studied to prove the composites were suitable for application in liquid environment. The tribological properties of composites under dry, deionized water and seawater lubricating condition were investigated. The results showed that the incorporation of GO decreased the wear rate of UHMWPE under different lubricating conditions and with the increase of GO addition, the wear rate of UHMWPE/GO composites decreased. UHMWPE/GO composites exhibited better tribological behaviors under seawater lubricating condition than other conditions, because good corrosion resistance and excellent wear resistance of UHMWPE/GO composites, and the lubricating effect of seawater is also indispensable.

To further enhance the corrosion resistance of chemically bonded phosphate ceramic coating, TiO2 was grafted on the surface of GO to enhance the interfacial adhesion between GO and the coating. SEM results show that the presence of TiO2 on GO creates a good interfacial adhesion between GO and the coating. In addition, EIS experiments were carried out to investigate the performance of the coatings on the corrosion resistance. The result indicates that the corrosion resistance is enhanced with the introduction of GO-TiO2 hybrid material. Beside of the influence of GO on the corrosion resistance, the good interfacial adhesion between GO and the coating with the presence of TiO2 hybrid material can consume more fracture energy to stop the crack propagation, which leads to the high corrosion resistance.

To improve tribological performance of chemically bonded phosphate ceramic coatings, the graphene nano-platelets (GNPs) were selected as the reinforcement. Tribological experiment and the analysis of SEM, EDS and Raman were conducted to clarify the mechanism of graphene on the improvement of tribological performance. It was found that, the worn surface of the coating with GNPs is smoother than the one without GNPs, and these GNPs were extruded out and adhered to the worn surface forming the lubricating tribofilm. Besides, the wear volume decreases with the introduction of GNPs. The reason behind this is that these GNPs can lead to the absorption of the fracture energy, which further can improve the mechanical property of the ceramic. This improvement makes the ceramic more tolerant to damage during the wear. Additionally, the decrease of the internal stress of contact surface because of the large contact surface induced by the smooth worn surface results in the lower wear. The friction coefficient shows the similar trends with the wear volume. The lubricant effect of the adhered lubricating tribofilm stemming from the weak interfacial shear strength between graphene platelets dominantly leads to the decrease in friction coefficient. Besides, the smaller internal stress induced by the smooth surface also contributes to the low friction coefficient because of the direct proportionality between the interfacial shear strength and the contact pressure.

Castor oil is one of the most enormous potential environment-friendly lubricants, and used as the base oil and additives in industrial applications. In this paper, the rheological property of castor oil was investigated using the optical interferometric test rig to analyze its flow properties under the micro gap. These results indicated that the central film thickness of castor oil in the point contact zone underwent the initial increased and then stable variation with the entrainment speed at different temperatures. The temperature and entrainment speed played an important role on the lubrication state and oil shape variation along the transverse and entrainment direction. At low temperature, the contact zone was almost in the thin lubrication regime at low entrainment speed, but was in the elastohydrodynamic lubrication regime at high entrainment speed. The side leakage went through the initial increased then decreased trend with the temperature and entrainment speed. These research results would further develop the engineering application of castor oil.

The paper investigates preparation and mechanical performances of a composite ceramic coating reinforced by graphene and multi-walled carbon nanotube. The carbon nanotube is functionalized with the carboxyl functional group (–COOH) and un-functionalized with sodium dodecyl benzene sulfonate (SDBS). The structure of the functionalized and hybrid-functionalized carbon nanotube is identified using infrared spectroscopy (FTIR analysis). The coating is brushed on the matrix and then cures under temperature lower than 250°C. The morphological and cross section features are studied by scanning electron microscopy (SEM). The distributions of hardness and fracture toughness are determined using a microhardness tester. The adhesive strength is evaluated using a universal tensile tester. The tribological properties are detected using friction wear testing machine. The experimental results show that the structure of the composite coating is compact, and both graphene and hybridtreated carbon nanotube are well dispersed. Addition of 0.2 wt % graphene and 0.2 wt % hybrid-functionalized carbon nanotube results in a prominent increase in hardness and fracture toughness. Meanwhile, the adhesive strength between the composite coating and the metallic substrate is well improved due to the high tensile strength of both graphene and carbon nanotube. Compared with pure alumina coating, the friction coefficient as well as the wear depth and width of grinding crack of the composite coating is much lower.

The anticorrosion performance of inhibitors for 7003 aluminium alloy in 2 wt.% NaCl aqueous solution at pH 6.5 by sodium gluconate (SG), sodium dodecyl sulfate (SDS), NaNO3 and their mixture was investigated using polarization tests, electrochemical impedance spectroscopy measurements, Fourier transform infrared spectroscopy, X-ray diffraction as well as scanning electronic microscopy. The results show that hybrid inhibitors reduce the polarization currents, both in cathodic reaction and in anodic reaction, by around one order of magnitude as compared with mono-inhibitor. A porous oxide layer is formed on surface of Al alloy by NaNO3, and then pores are blocked by physical adsorption of SDS, which is subsequently reinforced by the precipitation of SG complex enriched with Al O C6H11O7 bonds. The above three parts are integrated into a complex passive layer to protect Al alloy.