M. Zhu

Mechanical alloying of immiscible Pb-Al binary system by high energy ball milling

In the present work, mechanical alloying has been applied to the Pb-Al immiscible binary system by using the method of high energy ball milling. The microstructural features of the milled powder, such as grain size, lattice constant and morphology of phases have been studied by X-ray diffraction, analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, energy dispersive spectroscopy was used to analysis chemical composition of phases presented after milling. Differential Scanning Calorimetry measurement was also made on the milled Pb-Al powder. The results show that homogenous blending of Pb and Al can be easily achieved by high energy ball milling in spite of their mutual immiscibility and large difference in density. The obtained alloy exhibits nanocrystalline microstructure. Further more, the experiment result implies the formation of supersaturated solid solution in immiscible Pb-Al system by high energy ball milling.

Microstructure characterization and effect of thermal cycling and ageing on vanadium-doped Cu-Al-Ni-Mn high-temperature shape memory alloy

The effect of vanadium addition on the microstructure of Cu–Al–Ni–Mn high-temperature shape memory alloy (SMA) and its thermal cycling and ageing behaviour has been investigated. Using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis, the morphology, distribution and structure of secondary phase, induced by vanadium addition, have been identified. The effect of secondary phase on grain refining of Cu–Al–Ni–Mn has also been revealed. Differential scanning calorimetry measurement was used to investigate the effect of thermal cycling and ageing on the transformation temperature. It has been found that thermal cycling has a strong influence on the transformation temperature of the present Cu–Al–Ni–Mn–V high-temperature SMA. Ageing also caused an apparent change of the transformation temperature. It has been suggested that this was mainly due to the precipitation of secondary phase, because the sample was heated to a rather high temperature in both thermal cycling and the ageing process. The experiment showed that the transformation temperature could be maintained stable in the thermal cycling process by pre-ageing the sample at a suitable temperature.

Microstructure and hydrogen absorption properties of nano-phase composite prepared by mechanical alloying of MmNi5−x(CoAlMn)x and Mg

Abstract In this work high energy ball milling was used to prepare composite hydrogen storage alloy in the MmNi 5− x M x –Mg system. X-ray diffraction and TEM analysis were used to characterise the microstructure of the composite alloy obtained by ball milling. It has been shown that the grain size of MmNi 5− x M x and Mg components were reduced to nanometre range after about 20 h of milling. Besides, a Mm 2 Mg 17 phase of nanometre size was also formed in the milling process. Thus, a composite alloy, referred to as nano-phase composite here, composed of MmNi 5− x M x , Mg and Mm 2 Mg 17 phase of nanometre size was obtained. Hydrogen storage behaviour of the nano-phase composite was compared with that of conventional MmNi 5− x M x alloy by measuring PCT and kinetics. It showed that the hydrogen absorption properties were improved.

Growth of HT-LiCoO2 thin films on Pt-metalized silicon substrates

Abstract Layered LiCoO2 (HT-LiCoO2) films were grown on Pt-metalized silicon (PMS) substrates and polished bulk nickel (PBN) substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [00l] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [00l] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45 μA·h·cm−2·μm−1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.

Hydrogen storage properties of preferentially orientated Mg-Ni multilayer film prepared by magnetron sputtering

Mg-Ni multi-layer thin film was deposited on (001) Si wafer by magnetron sputtering with dual-target. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis reveal that the microstructure of the Mg-Ni multilayer thin film is composed of fine-crystalline Ni layer and crystalline [001] Mg layer. Hydrogenation process of the films were carried out by using the automatic gas reaction controller. The films undergone hydrogenation for different time were analyzed by XRD. The results show that hydrogenation properties of Mg with different preferential orientations are different. (002) diffraction peak of Mg disappears in compensating the appearing of the peaks of Mg2NiH4 and MgH2 in hydrogenation at 533 K, while the (101) peak still remains. The result reveals that the Mg film with (001) preferential orientation absorbs hydrogen at certain temperature easier than that of the Mg film with (101) orientation. This phenomenon can be explained in the view point of the energy change for the nucleation and growth of hydride in different crystal plane.

Kinetics of Li+ transport and capacity retention capability of HT- LiCoO2 films

In this work, HT-LiCoO2 films with preferential c-axis orientation were prepared using pulsed laser deposition. The kinetics of lithium ion transport through the HT-LiCoO2 film was investigated by applying potentiostatic intermittent titration technique (PITT). The capacity retention capability of the HT-LiCoO2 film was studied using constant-current (CC) cycling. PITT measurement showed that the lithium chemical diffusion coefficient () of the HT-LiCoO2 films reached as high as 10−8–10−10u2009cm2u2009s−1 and the value of in the two-phase coexistence region was lower than that in other single-phase regions. CC cycling revealed that the HT-LiCoO2 film delivered an initial discharge capacity of 40u2009μAhu2009μm−1u2009cm−2 and the discharge capacity decreased to 22.4u2009μAhu2009μm−1u2009cm−2 after 100 CC cycles. The observation was found to be caused by the continuous formation of the spinel phase (LiCo2O4 or Co3O4).

A microstructural and neutron-diffraction study on the interactions between microwave-irradiated multiwalled carbon nanotubes and hydrogen

Microwave irradiation is a simple yet effective way of altering the properties of multiwalled carbon nanotubes (MWNTs). This work studies the interactions between microwave-irradiated MWNTs and hydrogen. Effects of MWNT diameter and irradiation duration on the hydrogen-storage capacity have been investigated. We find that microwave irradiation induces damage to the MWNTs that can enhance hydrogen-storage capacity, with excessive damage being detrimental. Smaller-diameter tubes suffer less damage than larger tubes do. MWNTs with a diameter of 20–40xa0nm irradiated for 10xa0min had the highest hydrogen uptake of the samples measured, of 0.87 wt% at room temperature and under a hydrogen pressure of 3xa0MPa. Neutron powder-diffraction data revealed structural changes that were consistent with the insertion of hydrogen in the interstitial cavities of the microwave-irradiated MWNTs, as well as an expansion between the graphene layers of samples that were microwave irradiated. Hence, this simple treatment could be a promising solution to improve the hydrogen-storage capacities of MWNTs.

Effect of Ni on Mg based hydrogen storage alloy Mg3Nd

Abstract Magnesium-neodymium based alloys were prepared by induction melting in an alumina crucible under protection of pure argon atmosphere. XRD patterns show that the as-melted Mg-Nd and Mg 3 NdNi 0.1 diffraction peaks can be excellently indexed with DO 3 structure (BiF 3 type, space group Fm 3 m ). The lattice constant of Mg 3 Nd phase is 0.7390 nm, which is determined by XRD analysis using Cohens extrapolation method. The reversible hydrogen storage capacity reaches 1.95wt.% for Mg 3 Nd and 2.68wt.% for Mg 3 NdNi 0.1 . The desorption of hydrogen takes place at 291 °C for Mg 3 Nd and at 250 °C for Mg 3 NdNi 0.1 . The alloys could absorb hydrogen at room temperature with rapid hydriding and dehydriding kinetics after only one cycle. The enthalpy (Δ H ) and entropy (Δ S ) of Mg 3 Nd-H dehydriding reaction were −68.2 kJ.mol −1 H 2 and −0.121 kJ.(K.mol) −1 H 2 determined by using vant Hoff plot according to the pressurecomposition-isotherms (P-C-I) curve measured at different temperatures. Hydrogen absorption kinetic property of Mg 3 NdNi 0.1 alloy was also measured at room temperature.