Zifeng Ni

Mechanical and thermal properties of graphene oxide/ultrahigh molecular weight polyethylene nanocomposites

Graphene oxide (GO) was prepared according to a modified Hummers method, and a range of GO/ultrahigh molecular weight polyethylene (UHMWPE) composites were fabricated using liquid-phase ultrasonication mixing followed by hot-pressing. The thermal performances of the GO/UHMWPE composites were characterized by TGA and DSC. The dispersion of GO in GO/UHMWPE composites was investigated by FTIR and XRD. Moreover, the mechanical properties, including micro-hardness, tensile properties, and impact strength of GO/UHMWPE composites were also studied and the fractured surfaces were observed under SEM. The results show that the melting temperature of these composites was about 135 °C and the crystallinity was improved with the addition of GO. Moreover, the initial decomposition temperature was about 472 °C and the addition of GO improved the thermal performance of GO/UHMWPE. Furthermore, not only was the impact strength increased substantially with the addition of GO, but the micro-hardness was also improved gradually and the tensile properties were improved with the addition of GO. The thermal and mechanical performances of the GO/UHMWPE composites are influenced by the free-space effect and interaction-force effect.

Effects of gamma irradiation and accelerated aging on GO/UHMWPE nanocomposites

ABSTRACT This article investigates irradiated and accelerated aged graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites. The prepared GO/UHMWPE nanocomposites are gamma-irradiated at a high irradiation dose in a vacuum and then accelerated aging procedure is performed at 80°C in an air oven for 21 days. Irradiated and aged samples are characterized by Raman spectrum, Fourier transform infrared (FT-IR) spectrum, differential scanning calorimetry, contact angle, and gel content. Filling GO reduces the intensity of Raman spectrum of UHMWPE and irradiation or aging cannot affect vibrational modes of UHMWPE and GO/UHMWPE. The result of the FT-IR spectrum shows that UHMWPE and GO/UHMWPE basically have the same oxidation index values, whether with irradiation or accelerated aging. Irradiation or aging can slightly increase the melting temperature. GO, irradiation, or aging can significantly increase the crystallinity and improve wetting properties. In irradiated GO/UHMWPE, GO is able to maintain the efficiency of the cross-linking. However, after aging, the cross-linking density of GO/UHMWPE is reduced significantly. According to the above results, it is proposed that GO shows a very weak scavenging free radicals capacity in GO/UHMWPE composites and cannot display antioxidant capacity.

The role of interactions between abrasive particles and the substrate surface in chemical-mechanical planarization of Si-face 6H-SiC

The interactions between abrasive particles and the wafer surface play a significant role in the chemical-mechanical planarization (CMP) process. The influence of interactions between silica or ceria nanoparticles and the substrate surface on the CMP of Si-face (0001) 6H-SiC in different slurries with varied pH values was investigated using zeta potential measurements, SEM observations, friction tests, polishing experiments and XPS analysis. Meanwhile, the interaction forces between the substrate surfaces and the abrasive nanoparticles were also estimated using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Silica particles are prone to adhere to the Si-face 6H-SiC surface below pH 5 and are repelled above pH 5, while ceria particles tend to adhere to the similarly charged and oppositely charged 6H-SiC surfaces. This can be attributed to the fact that the ceria particle possesses a chemical tooth and Si–O–Ce bonds are formed between ceria particles and the 6H-SiC surface. The friction coefficient and material removal rate during the CMP of 6H-SiC could be reduced significantly by the adhesion of silica particles on the 6H-SiC surface resulting from the electrostatic interaction at pH 2 and 4, while this phenomenon was not observed when ceria particles were adsorbed. The XPS analysis indicated that more oxidized species (e.g. Si–C–O, Si–Ox–Cy, Si–O2, Si4–C4−x–O2, Si4–C4–O4 and C–O) were formed during immersion in aq. KMnO4 solution. Finally, an ideal electrostatic interaction between the abrasive particles and the 6H-SiC substrate surface during the CMP process was proposed.

Experimental investigation on the rheological properties of castor oil at different temperatures

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 Influence of Irradiation on Thermal and Mechanical Properties of UHMWPE/GO Nanocomposites

A method of adding graphene oxide (GO) and further reinforcing by the treatment of gamma-irradiation was used to enhance the properties of ultrahigh molecular weight polyethylene (UHMWPE). The effects of GO and irradiation on UHMWPE, particularly the influence of irradiation on UHMWPE/GO nanocomposites, were investigated from the aspects of thermal and mechanical properties. The results show that the thermal stability of UHMWPE/GO nanocomposites was slightly decreased by irradiation. But both GO doping and irradiation increased the crystallinity of UHMWPE. A similar variation tendency was appeared between compressive properties and crystallinity. A postulated mechanism was established to explain how GO doping and irradiation actually improved the properties of UHMWPE.

The Influence of Irradiation and Accelerated Aging on the Mechanical and Tribological Properties of the Graphene Oxide/Ultra-High-Molecular-Weight Polyethylene Nanocomposites

Graphene oxide/ultra-high-molecular-weight polyethylene (GO/UHMWPE) nanocomposite is a potential and promising candidate for artificial joint applications. However, after irradiation and accelerated aging, the mechanical and tribological behaviors of the nanocomposites are still unclear and require further investigation. GO/UHMWPE nanocomposites were successfully fabricated using ultrasonication dispersion, ball-milling, and hot-pressing process. Then, the nanocomposites were irradiated by gamma ray at doses of 100 kGy. Finally, GO/UHMWPE nanocomposites underwent accelerated aging at 80°C for 21 days in air. The mechanical and tribological properties of GO/UHMWPE nanocomposites have been evaluated after irradiation and accelerated aging. The results indicated that the incorporation of GO could enhance the mechanical, wear, and antiscratch properties of UHMWPE. After irradiation, these properties could be further enhanced, compared to unirradiated ones. After accelerated aging, however, these properties have been significantly reduced when compared to unirradiated ones. Moreover, GO and irradiation can synergistically enhance these properties.

Biotribological behaviour of Vitamin E-blended highly cross-linked UHMWPE in a hip joint simulator

Purpose The purposes of this paper are to investigate the biotribological behaviour of Vitamin E-blended highly cross-linked ultra-high molecular weight polyethylene (HXL-UHMWPE) under multi-directional motion by using a CUMT II artificial joint hip simulator and compare it with HXL-UHMWPE and conventional UHMWPE. Design/methodology/approach The biotribological behaviour of conventional, highly cross-linked and Vitamin E-blended highly cross-linked UHMWPE acetabular cups counterfaced with CoCrMo alloy femoral head under multi-directional motion were investigated by using CUMT-II artificial hip joint simulator for one-million walking cycles. The test environment was at 36.5 ± 0.5°C and 25 per cent bovine serum was used as lubricant. A Paul cycle load with a peak of 784 N was applied; the motion and loading were synchronized at 1 Hz. Findings The wear resistance of Vitamin E-blended highly cross-linked UHMWPE was significantly higher than that of highly cross-linked and conventional UHMWPE. The wear marks observed from the worn surface of UHMWPE were multi-directional, with no dominant wear direction. Only abrasion occurred on the surface of Vitamin E-blended highly cross-linked UHMWPE, while yielding and accumulated plastic flow processes occurred on the surface of conventional UHMWPE and flaking-like facture and abrasion occurred on the surface of highly cross-linked UHMWPE. Originality/value Besides the prevention of oxidative degradation, blending with Vitamin E can also reduce the incidence of fatigue crack occurred in the surface layer of HXL-UHMWPE samples. Therefore, the wear resistance of HXL-UHMWPE under multi-directional motion can be further enhanced by blending with Vitamin E.

Investigation of irradiated graphene oxide/ultra-high-molecular-weight polyethylene nanocomposites by ESR and FTIR spectroscopy

ABSTRACT Graphene oxide/ultra-high-molecular-weight polyethylene (GO/UHMWPE) nanocomposite has a potential application for artificial joints. However, free radicals and antioxidative properties of irradiated GO/UHMWPE were not clearly clarified. In this paper, GO/UHMWPE nanocomposites were prepared and irradiated by gamma-irradiation with a dose of 100 kGy. Afterward, test samples were aged in air. Free radicals and molecular structures of test samples were investigated by electron spin resonance (ESR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy, respectively. These studies indicated that irradiation enhanced GO radical concentrations. And GO radicals were stable in air and even could not be quenched after accelerated aging. GO radicals were superimposed on free radicals of irradiated UHMWPE. Although GO showed free radical-scavenging capacity, the influence of GO on free radicals of irradiated UHMWPE was too weak to be observed in ESR spectroscopy. Free radicals concentrations of irradiated GO/UHMWPE nanocomposites were gradually decayed with aging time evolving in air. Observing the oxidation index values of test samples, it was proposed that irradiated GO/UHMWPE might show very weak antioxidative properties.