Wang Dapu

Antioxidant activity of lycopene extracted from tomato paste towards trichloromethyl peroxyl radical CCl3O2

The objectives of this paper were to evaluate the antioxidant activity of lycopene towards the trichloromethyl peroxyl radical (CCl3O2.) and to obtain a precise rate constant using a pulse radiolysis technique. Lycopene was extracted and purified from tomato paste and its purity reached 95.0% (HPLC analysis). CCl3O2. was generated from a pulsed aqueous air-saturated solution of 2-propanol (2 M), acetone (1 M) and CCl4 (10(-2) M). The observed spectrum showed an intense bleaching of the lycopene ground-state absorption in the region 350-450 nm and the bleaching rate constant was determined to be 1.17 x 10(9) M(-1)s(-1), which indicated a rapid interaction between lycopene and CCl3O2.

Chemiluminescence determination of free radical scavenging abilities of ‘tea pigments’ and comparison with ‘tea polyphenols’

Abstract The objectives of this paper were to determine the free radical scavenging abilities of ‘tea pigments’ towards superoxide radical anion (O2− ) and hydroxyl radical (OH ), and to make a comparison with ‘tea polyphenols’ using a chemiluminescence technique. O2− and OH were generated from pyrogallol autoxidation and Fenton-type reaction, respectively. ‘Tea pigments’ could scavenge O2− and OH at EC50 values of 0.08 and 0.003 mg/ml, respectively, and the kinetics of the scavenging reactions varied with the concentration, suggesting the operation of different mechanisms. In addition, the free radical scavenging abilities and kinetics of ‘tea pigments’ were similar to those of ‘tea polyphenols’.

Tribochemical investigation of tungsten carbide/titanium alloy tribo-couples under aqueous lubrication

The present paper deals with the fundamental understanding on the tribochemical mechanism of tungsten carbide (WC) coating and titanium alloy tribo-couples system. The tribological experiments were performed with a Timken-type tester. Water containing water-soluble additives was employed as the lubricating media. The rubbed surfaces of the carbide coating were characterized with scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Significant titanium transfer was observed. Results of XPS analyses show that the interfacial layers formed consist of multiple oxides which suggests that oxidative reactions predominate in frictional processes under aqueous lubrication. It is proposed that the oxide layer is responsible for the tribological behavior because it controls the diffusive and adhesive wear.

In situ triboreduction of organo-copper compound in titanium alloys tapping

Abstract In this paper, an organo-copper phosphate compound was synthesized and applied as a water-based lubricating additive in a tapping test of Ti–6Al–4V alloys. The results show that the Cu-containing compound plays an effective role in the metalworking. The machined surfaces were examined by scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. After Ar + etching, abundant metallic Cu was detected in the subsurface. This indicated that Cu(II) was reduced to Cu(0) via in situ triboreduction in the frictional process.

The tribological behaviors of various metallic cations in tapping of a titanium alloy

Abstract In this paper, various metallic cations, including Na + , K + , Ca 2+ and Ba 2+ , were introduced into water-based lubricating additives. Their tribological behaviors were investigated by the tapping test of a Ti-6Al-4V alloy. Among them, Ba-containing compound showed the best lubricating performance. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the surface morphology and chemical states of elements, respectively. It was found that the worn surface consisted of multiple oxides, which implies that tribooxidation predominated during the frictional process under aqueous lubrication. Furthermore, barium titanate (BaTiO 3 ) could be detected on the tapped surface, the existence of which was proposed to be responsible for its corresponding performance.