Zhengjun Yao

Reuse of waste cotton cloth for the extraction of cellulose nanocrystals.

Cellulose nanocrystals (CNCs) were prepared from waste cotton cloth and degreasing cotton was used as a comparison. The cellulose was first extracted by alkali and bleaching treatments, and then the CNCs were isolated by the mix acid solution hydrolysis of cellulose under the controlled conditions. The CNCs were analyzed by Attenuated total reflectance Fourier transform infrared spectroscopy, Transmission electron microscopy, X-ray diffraction analysis, thermogravimetric and differential scanning calorimetry analysis. The results confirmed that the resultant samples were the cellulose species, and the CNCs obtained from waste cotton cloth exhibited a high crystallinity index of 55.76±7.82%, which had higher thermostability than that from the degreasing cotton. The morphology analysis results showed that the ranges of length and diameter of CNC extracted from waste cotton cloth were from 28 to 470nm and 3 to 35nm. The preparation of CNCs with a high aspect ratio and good thermostability in this work paves the way for an alternative reuse of waste cotton cloth.

Interdiffusion performance and oxidation behaviours of NiCrAlY/Al coatings on γ-TiAl

Abstract The interdiffusion behaviours and oxidation resistance of the NiCrAlY/Al duplex coated specimens during the isothermal oxidation test at 950°C were investigated. It was shown that the NiCrAlY coating system with an Al bondcoat outperformed the NiCrAlY single coating system and the substrate γ-TiAl alloy during hot exposure. Analysis techniques such as X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to study the phase formation, microstructure and depth distribution of the elements in the coated specimens. The results showed that the NiCrAlY/Al duplex coating system exhibited better oxidation resistance and adhesion strength with the substrate during scratch test. The SEM-EDS profile analyses further showed that the outward Ti diffusion and the inward Ni diffusion were delayed apparently by the Al interlayer, which was also considered as Al source for forming protective α-Al2O3 scale on the NiCrAlY/Al coating surface.

High temperature oxidation behaviour of Al2O3/Al composite coating on γ-TiAl

Abstract An Al2O3/Al composite coating was introduced on the substrate γ-TiAl alloy by magnetron sputtering. The isothermal oxidation behaviour of the coated γ-TiAl alloy was investigated at 1000°C. The results suggested that the Al2O3/Al composite coating improved the oxidation resistance of γ-TiAl alloy at 1000°C air exposure. No spallation or crack was observed in the oxide scale of coated specimen, which was composed of α-Al2O3 and TiAl3 after the oxidation test. The outward Al diffusion from interlayer provided sufficient Al source for the formation of Al2O3 layer in the coating surface during the high temperature oxidation test. As an active intermetallic element with Ti, Al suppressed the outward of Ti effectively due to the formation of Ti–Al intermetallics. Owing to inward and outward diffusion, the Al interlayer was consumed after 100 h oxidation test and a Ti–Al interdiffusion zone was formed, which was beneficial for the adhesion between coating and substrate.

Oxidation behaviour of plasma surface alloying on Ti6Al4V alloy

ABSTRACT Ti–CrNi alloy coatings with 20, 40, 60 and 80 at-%Ni were prepared on Ti6Al4V alloy surface by double glow plasma surface alloying technique. The cyclic oxidation behaviour of the coatings was investigated at 750, 850 and 950°C. The results show that each coating has a complete structure of settled layer, mutual diffusion layer and sputtering affected zone. When the Ni content was 40 at-%, the Ti–CrNi alloy coating showed the best cyclic oxidation resistance. The oxide scale with ‘Cr2O3 film+NiO film’ structure showed the best resistance to peeling.

Isolation and characterization of cellulose nanocrystals from pueraria root residue

Cellulose nanocrystals (CNCs) were successfully fabricated from waste pueraria root residue after starch extraction via the phosphoric acid hydrolysis method by a series of chemical treatment processes including ultrasonic washing, pectin elimination, bleaching, alkali boiling, and phosphoric acid hydrolysis. The high aspect ratio of CNCs with a crystallinity index of 60 ± 4.10% was observed by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). The TEM results showed that CNCs were rod-like particles with 100-330 nm in length and 2 to 6 nm in width. The average aspect ratio of the CNCs was 40 ± 10. The XRD results also indicated that the crystalline structure of CNC was cellulose I, compared to that of MCC with the crystallinity index declining from 60 ± 4.10% to 48 ± 0.37%. The FTIR spectra showed the resulting samples were the cellulose species. Interestingly, stable colloidal suspensions were determined by the zeta potential measurement. The thermal properties of CNCs were investigated by thermogravimetric analysis, revealing that CNCs exhibited lower thermal stability compared to those of MCC and the raw pueraria root residue. This study provides a cost effective method and mild process conditions for preparing CNCs from waste pueraria root residue.