Wenlan Li

Bio: Wenlan Li is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Combustion & Tungsten carbide. The author has an hindex of 18, co-authored 49 publications receiving 909 citations. Previous affiliations of Wenlan Li include Guangxi University & University of Science and Technology of China.

Electroless silver coating on fine copper powder and its effects on oxidation resistance

Abstract: Electroless silver coating on fine copper powder (3.4 μm) and its effects on oxidation resistance were investigated by varying the silver contents. As-coated copper powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the uniformity of silver coating was improved with silver content. When the silver content reached 20 wt.%, silver was homogeneously distributed around the copper particles and few free silver particles were detected. As a result, the sheet resistances of metal films reduced with the silver content (presenting the improvement of oxidation resistance), and at the level of 20 wt.% silver content, it had a minimum value and hardly increased with the increasing oxidation time.

Preparation and hot corrosion behaviour of an Al-gradient NiCoCrAlYSiB coating on a Ni-base superalloy

Abstract: A gradient NiCoCrAlYSiB coating was prepared on a Ni-base superalloy using arc ion plating (AIP) and subsequent gaseous phase aluminisation techniques. Hot corrosion of normal NiCoCrAlYSiB and the gradient coating in pure Na(2)SO(4) and Na(2)SO(4)/NaCl (75:25, wt./wt.) salts was performed at 900 degrees C in static air. The corrosion results indicated an enhanced corrosion resistance to both salts for the gradient NiCoCrAlYSiB coating, which the improved performance of it should be attributed to the beta aluminide "pool" at the surface layer. By partially sacrificing Al(2)O(3) (i.e. Al), the gradient NiCoCrAlYSiB coating specimen behaved excellently in the two kinds of salts. The grain growth during the gaseous phase aluminisation and the corrosion mechanism, including the role NaCl played in the mixture salt corrosion, are discussed. (C) 2009 Elsevier Ltd. All rights reserved.

Combustion synthesis of network silicon nitride porous ceramics

Abstract: A porous silicon nitride ceramics, composed of a network interconnected β-Si3N4 rods, was prepared by using the combustion synthesis method. Si powder with more than 20 wt.% diluent α-Si3N4 was fully nitrided under high nitrogen pressure. The interconnected open porosity of the obtained combustion products was as high as 64.40%. In the combustion products, rod-like β-Si3N4 grains were formed to build up the network silicon nitride porous ceramics.

Spark plasma sintered high hardness α/β Si3N4 composites with MgSiN2 as additives

Abstract: α/β Si3N4 composites were prepared by spark plasma sintering at 1340–1500 °C for 3–12 min with MgSiN2 as additives. The hardest α/β Si3N4 composite has a Vickers indentation hardness of 21.4 GPa, which is as hard as α-Sialon ceramics and harder than ordinary β-Si3N4 ceramics. The fracture toughness increased from 5.7 to 7.7 MPa m1/2 with the β-Si3N4 content increasing from 21 to 76 wt.%, and the Vickers indentation hardness of the latter was 19.0 GPa.

Study of Ni-Cr-Co-W-Mo-B interlayer alloy and its bonding behaviour for a Ni-base single crystal superalloy

Abstract: A new Ni-Cr-Co-W-Mo-B alloy was selected as an interlayer alloy for transient liquid phase (TLP) bonding of a Ni-base single crystal superalloy The microstructure and wettability on the substrate of the interlayer alloy were investigated The microstructure characteristics in the bond during TLP process were evaluated Single crystal could be achieved during TLP bonding if the crystallographic orientation is maintained in both mating halves (C) 2003 Acta Materialia Inc Published by Elsevier Science Ltd All rights reserved

Consolidation/synthesis of materials by electric current activated/assisted sintering

Abstract: This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Magnetoelectric coupling effects in multiferroic complex oxide composite structures.

Abstract: The study of magnetoelectric materials has recently received renewed interest, in large part stimulated by breakthroughs in the controlled growth of complex materials and by the search for novel materials with functionalities suitable for next generation electronic devices. In this Progress Report, we present an overview of recent developments in the field, with emphasis on magnetoelectric coupling effects in complex oxide multiferroic composite materials.

Homogeneous precipitation of cerium dioxide nanoparticles in alcohol/water mixed solvents

Abstract: In this work, the CeO 2 nanoparticles were synthesized by homogeneous precipitation in alcohol/water mixed solvents. Six alcohols, including methanol, ethanol, n -propanol, iso -propanol, tert -butanol, and ethylene glycol (EG), were separately mixed with water as the solvents. The effects of nature and composition of alcohol on the resultant CeO 2 nanoparticles were under investigation. From the experimental results, it is found that the CeO 2 nanoparticles obtained from alcohol/water mixed solvent were primary particles confirmed by quite good consistency in the particle sizes from TEM, XRD and BET analyses. The results also reveal that the CeO 2 nanoparticles are non-porous. Besides, no matter what kind of alcohol is used, the prepared CeO 2 nanoparticles exhibit cubic fluorite structures. In pure water environment, the size of CeO 2 particles is about 15 nm, whereas it reduces to about 7 nm in the 67% ethanol/water solution. Especially in the EG/water solvent system, the resultant samples are extremely smaller than those in other systems. As the vol.% of alcohol increases, the particle size decreases for all solvent systems, and the reverse, the specific surface area increases. This alteration in particle size can be approximately interpreted by the changes in electrostatic interactions and nucleation rate with varying the dielectric constant of mixed solvent.

Chemical formation of soft metal electrodes for flexible and wearable electronics

Abstract: Flexible and wearable electronics is one major technology after smartphones. It shows remarkable application potential in displays and informatics, robotics, sports, energy harvesting and storage, and medicine. As an indispensable part and the cornerstone of these devices, soft metal electrodes (SMEs) are of great significance. Compared with conventional physical processes such as vacuum thermal deposition and sputtering, chemical approaches for preparing SMEs show significant advantages in terms of scalability, low-cost, and compatibility with the soft materials and substrates used for the devices. This review article provides a detailed overview on how to chemically fabricate SMEs, including the material preparation, fabrication technologies, methods to characterize their key properties, and representative studies on different wearable applications.

Silicon Nitride Ceramics

Abstract: Silicon nitride ceramics is a generic term for a variety of alloys of Si3N4 with additional compounds necessary for a complete densification of the Si3N4 starting powder. They are heterogeneous, multicomponent materials characterised by the inherent properties of the crystalline modifications α and β of Si3N4 and the significant influence of the densification additives. With a view to ability of the α and β modification to form solid solutions α-Si3N4 (αss) and β-Si3N4 (βss) solid solutions can be distinguished. Each group contains engineered materials with interesting properties for special applications. Phase relations and micro-structures determine the properties decisively. Composition of the phases, the distribution of the grains, their aspect ratio and the grain boundary phase are pronounced microstructural features. The formation of the microstructure strongly depends on the one hand on the quality of the Si3N4 starting powders, which closely is related to the chemistry of the production process, and on the other on the liquid phase sintering as the most important step in the densification route. The interrelation between pure Si3N4, the densification of the powder including the role of sintering additives, microstructural engineering, physicochemical properties of the sintered Si3N4 ceramics (SSN, GPSN, HPSN, HIP-SSN, HIP-SN) are described in more detail and compared to reaction bonded Si3N4 ceramics (RBSN), which are produced by nitridation of silicon powders.