Jie Fei

Carbon-Fiber Reinforced Paper-Based Friction Material: Study on Friction Stability as a Function of Operating Variables

Carbon-fiber-reinforced paper-based friction material (CFRPF), as a new type of wet friction material for automatic transmission, was prepared by a paper-making process. The frictional response of CFRPF is highly complex under a set of dynamically variable operating conditions. To better understand the effect of operating factors (braking pressure, rotating speed, oil temperature, and oil flow rate) on friction stability of the material, tests were carried out using a single ingredient experiment and the Taguchi method. Experimental results show that the braking stability and the dynamic friction coefficient (μ d ) decrease as braking pressure, rotating speed, oil temperature, and oil flow rate increase. The influence of braking pressure on μ d is largest among the four operating factors. μ d declines gradually during the first 3000 repeated braking cycles and changes very little subsequently due to the surface topography change in friction material.

Topotactic synthesis and photocatalytic performance of one-dimensional ZnNb2O6 nanostructures and one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures

This paper introduces one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and one-dimensional ZnNb2O6 nanostructures. These nanostructures are synthesized via in situ topotactic structural transformation reaction using the tunnel structure K2Nb2O6 filiform crystal as precursor. Firstly, Zn2+ ions intercalate into K2Nb2O6 crystal by exchanging K+ ions from the K2Nb2O6 crystal with Zn2+ from Zn(NO3)2 or Zn(CH3COO)2 aqueous solution, to form two different Zn2+-exchanged samples, and then these Zn2+-exchanged samples topotacticly transform into one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and ZnNb2O6 nanostructures during heat-treatment. The formation reaction and structure of these samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and energy-dispersive spectroscopy (EDS). Photocatalytic experiments showed that one-dimensional ZnNb2O6/KNbO3 hetero-nanostructures and ZnNb2O6 nanostructures have excellent photocatalytic performance for the degradation of methylene blue (MB), rhodamine B (RhB), and methyl orange (MO).

Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide.

The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

In situ synthesis and photocatalytic performance of WO3/ZnWO4 composite powders

The WO3/ZnWO4 composite powders were synthesized through an in situ reaction process with tunnel structure K10W12O41·11H2O filiform crystallites used as a precursor. At first, Zn2+ ions was intercalated into the K10W12O41·11H2O crystal by exchanging K+ ions, then these Zn2+-exchanged samples were transformed into WO3/ZnWO4 composite powders during heat-treatment. The formation reaction and structure of these samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometer (EDS). The results showed that the WO3/ZnWO4 composite powders consisted of WO3 nanoparticles and ZnWO4 nanorods. Photocatalytic experiments exhibited an excellent photocatalytic performance for the degradation of methylene blue (MB) and the degradation efficiency was about 95% after 70 min under simulated sunlight.

Influence of compound mineral fiber on the properties of paper-based composite friction material

Paper-based composite friction material is a kind of key functional material for automatic transmission. In this study, five types of paper-based composite friction materials with different compound mineral fiber contents were prepared using the paper-making process. The effect of compound mineral fiber content on the properties such as shear strength, thermal property, friction torque curves, dynamic friction coefficient and wear resistance was studied. Meanwhile, the sensitivity of the friction coefficients was also investigated. Worn surfaces of samples were analyzed using scanning electron microscope. Experimental results revealed that the thermal properties of the samples were improved as the compound mineral fiber content increased and the shear strength increased initially and then decreased. The friction torque curve of the sample with 20% compound mineral fiber contents was the highest among all the samples and the sample with higher compound mineral fiber contents possessed the more flat friction torque curve during the mixed asperity contact phase of the engagement process. The dynamic friction coefficient increased with the increase of compound mineral fiber content and decreased as contact pressure and rotating speed increased. The wear resistance of the sample was highest when the compound mineral fiber content was about 15%.

Effects of NBR Particle Size on Performance of Carbon Fiber–Reinforced Paper-Based Friction Material

In the present work, three different sized nitrile–butadiene rubber (NBR) particles were used to modify carbon fiber–reinforced paper-based friction material (CFRPF). The effects of NBR particle size on performance of CFRPF were studied. The microstructure and properties of the samples were investigated by scanning electron microscopy, thermal analysis, and wet friction performance testing. Experimental results indicated that there were four stages in the thermal degradation of NBR-modified CFRPF. NBR particle size had a great effect on the first degradation stage (100–300°C). The highest friction coefficient was obtained with the sample containing the finest NBR particles. The wear rate of the friction materials decreased with an increase in NBR particle size. However, NBR particle size had little influence on the wear rate of the couple plate. The sample containing coarse NBR particles showed excellent friction stability under oil-lubricated conditions.

Effect of hydrothermal oxidation temperatures on tribological properties of carbon fabric/resin friction materials

Carbon fabric was treated by HNO3 under hydrothermal conditions. The oxygenated functional groups were supported by Fourier transform infrared-attenuated total reflectance spectroscopy. The hydrophilicity was supported by the contact angle instrument. The treated carbon fabric was then used to prepare carbon fabric/resin friction materials. The friction and wear behaviors of the carbon fabric/resin friction material were evaluated by a friction tester. Experimental results showed that the carbon fabric treated by hydrothermal oxidation led to changes in surface morphology of fibers and appearance of carbonyl groups, which effectively improved the bonding strength of carbon fabric and resin. Moreover, hydrothermal oxidation treatment from 100 °C to 120 °C was proved beneficial to tribological properties.

Effect of hydrothermal modified carbon fiber through Diels–Alder reaction and its reinforced phenolic composites

In this work, carbon fibers were chemically modified with maleic anhydride through the Diels–Alder reaction under hydrothermal conditions, and then the modified carbon fiber reinforced phenolic resin composites were prepared by liquid impregnation processing. The structural and surface characteristics of carbon fibers were investigated by the Fourier transform infrared (FTIR) spectrum, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The tensile strength of the composites was measured by a universal material testing machine. The friction and wear behaviors of the composites were evaluated by a friction tester. Experimental results revealed that the carboxyl group was successfully grafted on the carbon fiber surface leading to the increase of surface activity without damaging the skin region and core region of the carbon fibers. The tensile strength of modified carbon fibers reinforced composites increased significantly by about 200%, while the wear volume decreased by about 50% compared with unmodified carbon fiber reinforced composites, resulting from good adhesion between the carbon fibers and resin matrix.

Rapid Chemical Bath Depositions and Properties of SnS Films

Tin sulfide films were deposited from an aqueous solution of tin dichloride, thiacetamide, and disodium citrate. X-ray diffraction, atomic force microscopy, ultraviolet–visible spectrophotometry, and electrical measurement were used to characterize the films. The films directly deposited at 70 and 80 °C for 1 and 2 h showed thicknesses of 70–400 and 120–650 nm, respectively. But the deposition at 40 °C for 1 h (nucleation step) made the films subsequently deposited at 60–80 °C denser and thicker (∼1600–7500 nm) than directly deposited films. Average transmittances of the films in UV–visible range decrease with increase in the thickness and are only in range of 0.33–2.3% for the films deposited with the nucleation step. The band gap energies of the films estimated from the transmittance spectra are in the range of ∼1.37–1.55 eV. Moreover, the films are p-type conductive. The electrical resistance and carrier mobility are in the ranges of 0.3–1.4 × 105 Ω cm and 0.77–1.56 cm2 (V s)−1, respectively. The films deposited with the nucleation step show lower resistance and higher carrier mobility than those deposited without nucleation because of their denser film microstructure and larger film thickness.

Effect of nano-SiO2 particles on the carbon fabric/resin friction materials by microwave-hydrothermal treatment

Nano-SiO2 was grafted onto the carbon fabric surface under microwave-hydrothermal condition to improve the tribological properties of carbon fabric/resin friction materials with different treatment temperature. The carbon fibers and prepared samples were characterized by the Fourier transform infrared spectrophotometer, contact angle instrument, energy dispersive spectroscopy, universal material testing machine and field emission scanning electron microscopy. The tribological behaviors of the carbon fabric/resin friction materials were evaluated by a friction tester. The results indicated that nano-SiO2 particles were successfully grafted onto carbon fabric surface under microwave-hydrothermal condition, especially at 200℃ (contact angle was almost close to 0°), which obviously improved the hydrophilicity of carbon fabric surface. The wear rate of carbon fabric/resin friction materials with microwave-hydrothermal temperature of 200℃ reduced by 81.4%, ranging from 4.3 × 10−5 mm3J−1 to 0.8 × 10−5 mm3J−1. It could effectively enhance the bonding strength of carbon fabric and resin, which improved the friction-reduction and anti-wear abilities of the friction materials.