Yanchun Zhou

Electrochemical Deposition and Microstructure of Copper (I) Oxide Films

Chinese Acad Sci, Inst Met Res, Shenyang 110015, Peoples R China. Univ Missouri, Dept Chem, Rolla, MO 65401 USA. Univ Missouri, Grad Ctr Mat Res, Rolla, MO 65401 USA.;Zhou, YC (reprint author), Chinese Acad Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110015, Peoples R China

POTENTIAL OSCILLATIONS DURING THE ELECTROCHEMICAL SELF-ASSEMBLY OF COPPER/CUPROUS OXIDE LAYERED NANOSTRUCTURES

Layered nanostructures of copper metal and cuprous oxide are electrodeposited from alkaline solutions of Cu(II) lactate at room temperature. No subsequent heat treatment is necessary to effect crystallization. The electrode potential spontaneously oscillates during constant-current deposition. At a fixed current density the oscillation period decreases as either the pH or temperature is increased. The oscillations are periodic in stirred solution, but show period doubling and evidence of quasi-periodic or chaotic behavior in unstirred solution. The phase composition and resistivity of the films can be controlled by varying the applied current density. The resistivity of the films can be varied over ten orders of magnitude. Scanning electron microscopy shows that the films are layered.

Crystallographic relations between Ti3SiC2 and TiC

Ti3SiC2 is a so-called not-so-brittle ceramic that combines the merits of both metals and ceramics. However, many previous works demonstrated that its bonding nature and properties were strongly related to TiC. In this paper the crystallographic relations between Ti3SiC2 and TiC were established and described based on the transmission electron microscopy investigation on the Ti3SiC2/TiC interface in Ti3SiC2 based material. At Ti3SiC2/TiC interface, the following crystallographic relationships were identified: (111)TiC//(001)Ti3SiC2, (002) TiC//(104)Ti3SiC2, and [11¯0]TiC//[110]Ti3SiC2. Based on the above interfacial relations an interfacial structure model was established. The structure of Ti3SiC2 could be considered as two-dimensional closed packed layers of Si periodically intercalated into the (111) twin boundary of TiC0.67 (Ti3C2). The intercalation resulted in the transformation from cubic TiC0.67 to hexagonal Ti3SiC2. In the opposite case, de-intercalation of Si from Ti3SiC2 caused the transformation from hexagonal Ti3SiC2 to cubic TiC0.67. Understanding the crystallographic relations between Ti3SiC2 and TiC is of vital importance in both understanding the properties and optimizing the processing route for preparing pure Ti3SiC2.

Preparation and mechanical properties of dense polycrystalline hydroxyapatite through freeze-drying

High purity hydroxyapatite (HAp) powders were synthesized through the wet-chemical method and subsequent freeze-drying or heat-drying, respectively. Dense polycrystalline HAp ceramics were obtained by sintering the powder compacts in air in the temperature range 1100–1350°C. Results show that the freeze-drying method can produce highly homogeneous, fine-grained HAp powders. The relative density, Vickers hardness and flexural strength of the sintered freeze-dried HAp ceramics increased with the sintering temperature, reaching a maximum at around 1350°C, and the highest values obtained were 99.0%, 820 and 110 MPa, respectively. All these mechanical properties of the freeze-dried HAp ceramics are much higher than those of the conventionally heat-dried HAp ceramics. The drying method can significantly influence the properties of the HAp powders as well as the HAp ceramics.

The anomalous flow behaviour in the layered Ti3SiC2 ceramic

The temperature dependence of flow stress for polycrystalline titanium silicon carbide (Ti3SiC2) has been investigated from room temperature to 1423K. An anomalous positive temperature dependence of flow stress was observed in this ceramic. This anomalous phenomenon is attributed to the change in the mechanism controlling the flow stress. However, it is not in good agreement with the widely accepted Kear-Wilsdorf mechanism.

Explanation of the melting behaviour of embedded particles; equilibrium melting point elevation and superheating

The observed melting temperature of embedded particles can be either lower or higher than the bulk equilibrium melting point. Explanations for the observed melting-temperature elevation are still controversial and have been attributed either to an elevation caused by a strain energy effect and/or an interfacial energy effect, or to metastable superheating. Furthermore, there seems to be some confusion regarding the relationship between equilibrium melting-point elevation and the superheating effect. We suggest that the observed increase in melting temperature for embedded particles is caused by both an equilibrium melting-point elevation and a metastable superheating effect, and the two effects tend to be concurrent. An attempt has been made to clarify the two effects in the melting process of indium particles embedded in an aluminium matrix.

Low-temperature chemical synthesis of lanthanum copper oxide

Lanthanum copper oxide (La2CuO4) precursors for superconductors were synthesized by acetate/nitrate self-propagating combustion synthesis (SPCS) in the presence of urea at different ratio of O/F. Phase-pure La2CuO4 powder could be obtained by calcining the as-prepared precursors at temperature as low as 600 °C. It was demonstrated that the ratio of O/F strongly influenced the composition and morphology of the precursors as well as the samples calcined at various temperatures. We have studied the synthesis conditions, demonstrating the existence of a relationship between the calcination temperature and the calcination time needed to obtain the pure phase. An interesting stereoscopic network structure was observed on the samples synthesized at the ratio of O/F = 0.20, morphology evolution of the samples was also investigated. The emission of H2O as well as CO2 was responsible for the formation of the structure during the calcination process.

Superheating of bulk polycrystalline selenium

A superheating of 5 degrees C has been observed in bulk polycrystalline selenium with a mean grain size of about 10 mu m. The superheating is interpreted on the basis of the unique grain boundary structure inside the Se samples, which gives rise to a free energy barrier to liquid nuclei formation in the grain boundaries.

Branching phenomena in SiC whiskers

The branching phenomena in SiC whiskers was investigated by TEM in order to understand the growth mechanism and behaviour of the whiskers