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.

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

Precise and effective control of droplet generation is critical for applications of droplet microfluidics ranging from materials synthesis to lab-on-a-chip systems. Methods for droplet generation can be either passive or active, where the former generates droplets without external actuation, and the latter makes use of additional energy input in promoting interfacial instabilities for droplet generation. A unified physical understanding of both passive and active droplet generation is beneficial for effectively developing new techniques meeting various demands arising from applications. Our review of passive approaches focuses on the characteristics and mechanisms of breakup modes of droplet generation occurring in microfluidic cross-flow, co-flow, flow-focusing, and step emulsification configurations. The review of active approaches covers the state-of-the-art techniques employing either external forces from electrical, magnetic and centrifugal fields or methods of modifying intrinsic properties of flows or fluids such as velocity, viscosity, interfacial tension, channel wettability, and fluid density, with a focus on their implementations and actuation mechanisms. Also included in this review is the contrast among different approaches of either passive or active nature.

Passive and active droplet generation with microfluidics: a review

http://doras.dcu.ie/17607/1/Review_of_residual_stresses-Final.pdf

Methods of measuring residual stresses in components

https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Droplet microfluidics offers exquisite control over the flows of multiple fluids in microscale, enabling fabrication of advanced microparticles with precisely tunable structures and compositions in a high throughput manner The combination of these remarkable features with proper materials and fabrication methods has enabled high efficiency, direct encapsulation of actives in microparticles whose features and functionalities can be well controlled These microparticles have great potential in a wide range of bio-related applications including drug delivery, cell-laden matrices, biosensors and even as artificial cells In this review, we briefly summarize the materials, fabrication methods, and microparticle structures produced with droplet microfluidics We also provide a comprehensive overview of their recent uses in biomedical applications Finally, we discuss the existing challenges and perspectives to promote the future development of these engineered microparticles

/pdf/microfluidic-fabrication-of-microparticles-for-biomedical-2tsrw0ufu5.pdf

Microfluidic fabrication of microparticles for biomedical applications

http://www.dem.uminho.pt/People/fsamuel/project2010/refbib_FSamuel/[13].pdf

Spark plasma sintering of hydroxyapatite powders.

The reliable generation of micron-sized droplets is an important process for various applications in droplet-based microfluidics. The generated droplets work as a self-contained reaction platform in droplet-based lab-on-a-chip systems. With the maturity of this platform technology, sophisticated and delicate control of the droplet generation process is needed to address increasingly complex applications. This review presents the state of the art of active droplet generation concepts, which are categorized according to the nature of the induced energy. At the liquid/liquid interface, an energy imbalance leads to instability and droplet breakup.

/pdf/active-droplet-generation-in-microfluidics-4t8x6prman.pdf

Active droplet generation in microfluidics

Mixing and characterization of feedstock for powder injection molding

Sintering is a key step in the metal injection molding process, which affects the final density as well as the mechanical properties of the sintered part. To achieve a high final density, the effects of various sintering factors pertaining to the temperature–time profile and sintering atmosphere have to be characterized and optimized as well. This paper reports the use of Taguchi method in characterizing and optimizing the process factors for sintering water-atomized 316L stainless steel (of average size 6 μm). The effects of four sintering factors: sintering temperature, heating rate, sintering time and sintering atmosphere on the final density were studied. The various factors were assigned to an L9 orthogonal array. It was found that all the chosen sintering factors have significant effects on the final density. Optimum fractional final density of 96.14% of wrought material was achieved with a sintering temperature of 1250°C, a heating rate of 20°C min−1 and isothermal heating at 1250°C for 90 min in a vacuum atmosphere. Confirmatory experiments have produced results that lay within the 90% confidence interval.

Ngiap Hiang Loh

Papers

Spark plasma sintering of hydroxyapatite powders.

Active droplet generation in microfluidics

Mixing and characterization of feedstock for powder injection molding

Sintering study of 316L stainless steel metal injection molding parts using Taguchi method: final density

Micro-powder injection molding