Many types of sensors have been developed to detect chemical species in the gas phase. These include optical based on color change or fluoresence, surface acoustic wave (SAW) devices, electrochemical, chemoresistive/semiconductive, field effect transistors (FET), metal-insulator-semiconductor (MIS) diode devices, and many other. Among these, resistive type sensors based on ceramic oxides are particularly attractive because of their low cost, wide range of applications and potential for use in electronic nose. This article focuses mainly on the resistive/semiconductive, especially the surface conductive ceramic oxide type gas sensors. The main emphasis is on the basic principles involving gas-solid reactions. Also discussed are selected applications with an emphasis on sensor design issues. Since SnO2 can be used as a model system for oxide-based sensors, most of the discussions focuses on this system, though other systems are occasionally highlighted illustrating recent developments.

Ceramics for chemical sensing

Additive manufacturing (AM) has gained significant attention due to its ability to drive technological development as a sustainable, flexible, and customizable manufacturing scheme. Among the various AM techniques, direct ink writing (DIW) has emerged as the most versatile 3D printing technique for the broadest range of materials. DIW allows printing of practically any material, as long as the precursor ink can be engineered to demonstrate appropriate rheological behavior. This technique acts as a unique pathway to introduce design freedom, multifunctionality, and stability simultaneously into its printed structures. Here, a comprehensive review of DIW of complex 3D structures from various materials, including polymers, ceramics, glass, cement, graphene, metals, and their combinations through multimaterial printing is presented. The review begins with an overview of the fundamentals of ink rheology, followed by an in‐depth discussion of the various methods to tailor the ink for DIW of different classes of materials. Then, the diverse applications of DIW ranging from electronics to food to biomedical industries are discussed. Finally, the current challenges and limitations of this technique are highlighted, followed by its prospects as a guideline toward possible futuristic innovations.

Direct Ink Writing: A 3D Printing Technology for Diverse Materials

Metal cutting fluids (MCFs) under flood conditions do not meet the urgent needs of reducing carbon emission. Biolubricant-based minimum quantity lubrication (MQL) is an effective alternative to flood lubrication. However, pneumatic atomization MQL has poor atomization properties, which is detrimental to occupational health. Therefore, electrostatic atomization MQL requires preliminary exploratory studies. However, systematic reviews are lacking in terms of capturing the current research status and development direction of this technology. This study aims to provide a comprehensive review and critical assessment of the existing understanding of electrostatic atomization MQL. This research can be used by scientists to gain insights into the action mechanism, theoretical basis, machining performance, and development direction of this technology. First, the critical equipment, eco-friendly atomization media (biolubricants), and empowering mechanisms of electrostatic atomization MQL are presented. Second, the advanced lubrication and heat transfer mechanisms of biolubricants are revealed by quantitatively comparing MQL with MCF-based wet machining. Third, the distinctive wetting and infiltration mechanisms of electrostatic atomization MQL, combined with its unique empowering mechanism and atomization method, are compared with those of pneumatic atomization MQL. Previous experiments have shown that electrostatic atomization MQL can reduce tool wear by 42.4% in metal cutting and improve the machined surface R a by 47% compared with pneumatic atomization MQL. Finally, future development directions, including the improvement of the coordination parameters and equipment integration aspects, are proposed.

https://iopscience.iop.org/article/10.1088/2631-7990/ac9652/pdf

Electrostatic atomization minimum quantity lubrication machining: from mechanism to application

This is an accepted manuscript of an article published by Elsevier in Additive Manufacturing on 02/10/2021, available online: https://doi.org/10.1016/j.addma.2021.102378 
The accepted version of the publication may differ from the final published version.

Fused Deposition Modelling: Current Status, Methodology, Applications and Future Prospects

Technology development has led to the need of micro and miniaturized products in the field of automobile, aerospace, electronics, medical implants, biomedicine, robotics, and so on. Micromachining is the key technology to satisfy the need of the industry in terms of functionality and miniaturization in size. In this article, state-of-the-art review on tool-based micromachining processes such as microturning, microdrilling, micromilling, electric discharge micromachining (Micro-EDM), and electrochemical micromachining (Micro-ECM) has been carried out. The review begins with an overview of micromachining, classifications, and discussions about different aspects of tool-based micromachining processes. The research works carried out for the past 10 years are analyzed in terms of materials perspective, process parameters, size effects, performance characteristics, condition monitoring, product development, micro features generation, and fabrication of micro tools. A statistical analysis has been performed with...

A Review on Current Research Aspects in Tool-Based Micromachining Processes

Micro machining processes are becoming popular in this modern era of miniaturization. Microelectric discharge machining (MEDM) is one of the micromachining processes capable of machining all electrically conductive materials. The overall machining performance of electricdischarge machining (EDM) process depends on the electrical, thermal properties of both tool and workpiece materials. Cryogenic treatment has a history of improving mechanical, electrical, and thermal properties of materials. Recently, very few researchers applied cryogenic cooling in conventional EDM and found notable improvement in machining performance. In the present work, a comparative study on machining performance of both cryogenically treated and untreated micro electrodes in MEDM were analyzed alongwith electrical resistivity, crystallite size, microhardness and microscopic analysis. From the study, it is evident that there is significant reduction of 58% in tool wear rate (TWR) for Tungsten electrode followed by brass and copper ...

Machining Performance of Cryogenically Treated Electrodes in Microelectric Discharge Machining: A Comparative Experimental Study

Micro-electric discharge milling (μ-EDM milling) is one of the micromachining processes which draw the attention of researchers in fabricating microcavities and microchannels. Improving the efficiency of this process remains challenging. There are publications that report the benefits of applying ultrasonic vibration to tool or workpiece and using magnetic fields to enhance debris removal. In almost all the literature, magnetic field and/or ultrasonic vibration were applied separately in micro-/macro-EDM. The aim of this study is to apply ultrasonic vibration and magnetic field simultaneously/separately, and compare the machining performance by analyzing material removal rate and tool wear rate (TWR) while fabricating microchannels on nonmagnetic materials using μ-EDM milling. From the results, it is recommended to use magnetic field or ultrasonic vibrations separately for achieving high MRR, but the combination of both gave poor results.

Effects of Ultrasonic Vibration and Magnetic Field in Micro-EDM Milling of Nonmagnetic Material

Natural fibers reinforced FDM 3D printing filaments

A review on polymeric materials in additive manufacturing

Micromachining processes have become more imperative in this modern era of miniaturization. Micro-EDM (µEDM) is an excellent micromachining process capable of producing microholes and microfeatures in all electrically conductive materials, irrespective of their mechanical properties. µEDM is a proven process for producing microholes. The quality of microholes is imperative in many applications. The aim of the present study is to investigate the role of capacitance and voltage in determining the perfection of microholes edges that machined using die sinking µEDM by applying image processing techniques. The experimental results reveal that the capacitance significantly influences circularity more than open circuit voltage. The quality of the microholes is also affected by flushing force of dielectric fluid and tool adhesion. Best circularity was achieved with capacitance values between 0.001–0.00001 µF and voltage between 80–100. Discharge energies greater than 50 µJ gradually reduce the quality of microhol...

J.M. Jafferson

Papers

Machining Performance of Cryogenically Treated Electrodes in Microelectric Discharge Machining: A Comparative Experimental Study

Effects of Ultrasonic Vibration and Magnetic Field in Micro-EDM Milling of Nonmagnetic Material

Natural fibers reinforced FDM 3D printing filaments

A review on polymeric materials in additive manufacturing

Investigation of the Quality of Microholes Machined by µEDM Using Image Processing