Multi-material additive manufacturing of low sintering temperature Bi2Mo2O9 ceramics with Ag floating electrodes by selective laser burnout

Additive manufacturing (AM) of co-fired low temperature ceramics offers a unique route for fabrication of novel 3D radio frequency (RF) and microwave communication components, embedded electronics and sensors. This paper describes the first-ever direct 3D printing of low temperature co-fired ceramics/floating electrode 3D structures. Slurry-based AM and selective laser burnout (SLB) were used to fabricate bulk dielectric, Bi2Mo2O9 (BMO, sintering temperature = 620–650°C, εr = 38) with silver (Ag) internal floating electrodes. A printable BMO slurry was developed and the SLB optimised to improve edge definition and burn out the binder without damaging the ceramic. The SLB increased the green strength needed for shape retention, produced crack-free parts and prevented Ag leaching into the ceramic during co-firing. The green parts were sintered after SLB in a conventional furnace at 645°C for 4 h and achieved 94.5% density, compressive strength of 4097 MPa, a relative permittivity (εr) of 33.8 and a loss tangent (tan δ) of 0.0004 (8 GHz) for BMO. The feasibility of using SLB followed by a post-printing sintering step to create BMO/Ag 3D structures was thus demonstrated

Microwave assisted processing of X8R nanocrystalline BaTiO3 based ceramic capacitors and multilayer devices

BaTiO3 based multilayer ceramic capacitor (MLCC) is an important component in electronic devices. Achieving high dielectric performance, miniaturisation and cost effectiveness are still challenging. Co-sintering ceramic layers with metal electrodes and use of expensive Pt and high-Pd content compositions as electrodes are other key issues. Thus, the major factors that could lead to cost effectiveness of MLCCs are reduction in sintering temperature and using less expensive metal electrodes without compromising dielectric performance and these traits could auger well for the next generation low-cost high performance electroceramic devices – this is the subject matter of the present study. In this work, initially we have fabricated and analysed the dielectric performance of BaTiO3 (BT) ceramics with different BT particle sizes (50 nm, 100 nm and 200 nm). Based on results, 200 nm BaTiO3 was used for further studies due to its superior dielectric performance. Then, to reduce the sintering temperature and improve the dielectric performance of 200 nm BaTiO3 ceramics, Bi2O3 was used as a dopant which acts both as a sintering aid and helps to improve the dielectric performance. A combination of rare earth dopant system (proprietary from the industrial partner Knowles, UK) with Bi2O3 was also added to tune the defect chemistry of BaTiO3 for enhancement in dielectric performance further. A homogeneously mixed BT-based ceramic slurry system (containing the above dopants) with optimum rheology was developed using a non-aqueous medium, dispersant and a binder system. Addition of glass frits for lowering the sintering temperature and its effect on dielectric performance was also investigated on both discs (made using dry pressing of the powders obtained via drying of the slurry) as well as multilayer ceramic capacitors (MLCCs) fabricated through screen printing. Conventional, microwave and hybrid sintering procedures were employed for the densification of the electroceramic devices and these were characterized for density, microstructure, composition and dielectric performance systematically. Conventional sintering resulted in undesired large micron sized surface features which are detrimental to device durability, whereas formation and growth of these features have been demonstrated to be significantly minimised using the rapid microwave assisted sintering procedures for the first time. Further efficient co-sintering of ceramic layers with less expensive (Ag/Pd) alloy has also been accomplished using the microwave methodology. The resultant BaTiO3 based capacitive devices exhibited high dielectric permittivity, superior X8R performance and low dissipation factor, asserting their massive potential for widespread high temperature applications in automotive, sensing and space sectors

Additively manufactured ultra-low sintering temperature, low loss Ag2Mo2O7 ceramic substrates

Ultra-low sintering temperature silver molybdenum oxide (Ag2Mo2O7) ceramics have been printed using direct ink writing (a material extrusion additive manufacturing process) for the first time. An optimum densification conditions of 460 °C / 2 h was determined, resulting in relative permittivity, εr = 13.45, dielectric loss, tanδ = 0.0005, microwave quality factor, Q × f = 17,056 GHz and the temperature coefficient of resonant frequency τf = −121 ppm/°C. The results were comparable to the dielectric properties of conventionally fabricated ceramics. A series of metal/ceramic antenna designs were produced via dual-printing and co-firing, to demonstrate the potential of Ag2Mo2O7, to be used as a co-firable dielectric material for functional integrated circuits and/or microwave RF devices through multi-material direct ink writing

Direct ink writing of bismuth molybdate microwave dielectric ceramics

Additive manufacturing via direct ink writing and microwave dielectric characterisation of commercially produced low sintering temperature bismuth molybdenum oxide ceramics, have been both performed for the first time, following a powder-to-product holistic approach. We demonstrated that direct ink writing is an excellent candidate for producing dielectric substrates to be used for wireless telecommunication applications operating at microwave (MW) frequencies, with great repeatability and properties comparable to ceramics fabricated via conventional processing routes. The optimum density (relative density of ρr ≈ 93%) of the 3D printed test samples was obtained by sintering at 660 °C for 2 h, resulting in a relative permittivity εr = 35.7, dielectric loss tanδ = 0.0004 and microwave quality factor Q × f = 14,928 GHz. Sintering at higher temperatures promoted a porosity increase due to mismatching grain growth mechanisms and phase decomposition, that collectively hindered the test samples’ microwave dielectric performance in terms of achievable relative permittivity (εr) and dielectric loss (tanδ)

Psychological distress and burnout among healthcare worker during COVID-19 pandemic in India-A cross-sectional study.

BackgroundCOVID-19 has inundated the entire world disrupting the lives of millions of people. The pandemic has stressed the healthcare system of India impacting the psychological status and functioning of health care workers. The aim of this study is to determine the burnout levels and factors associated with the risk of psychological distress among healthcare workers (HCW) engaged in the management of COVID 19 in India.MethodsA cross-sectional study was conducted from 1 September 2020 to 30 November 2020 by telephonic interviews using a web-based Google form. Health facilities and community centres from 12 cities located in 10 states were selected for data collection. Data on socio-demographic and occupation-related variables like age, sex, type of family, income, type of occupation, hours of work and income were obtained was obtained from 967 participants, including doctors, nurses, ambulance drivers, emergency response teams, lab personnel, and others directly involved in COVID 19 patient care. Levels of psychological distress was assessed by the General health Questionnaire -GHQ-5 and levels of burnout was assessed using the ICMR-NIOH Burnout questionnaire. Multivariable logistic regression analysis was performed to identify factors associated with the risk of psychological distress. The third quartile values of the three subscales of burnout viz EE, DP and PA were used to identify burnout profiles of the healthcare workers.ResultsOverall, 52.9% of the participants had the risk of psychological distress that needed further evaluation. Risk of psychological distress was significantly associated with longer hours of work (≥ 8 hours a day) (AOR = 2.38, 95% CI(1.66-3.41), income≥20000(AOR = 1.74, 95% CI, (1.16-2.6); screening of COVID-19 patients (AOR = 1.63 95% CI (1.09-2.46), contact tracing (AOR = 2.05, 95% CI (1.1-3.81), High Emotional exhaustion score (EE ≥16) (AOR = 4.41 95% CI (3.14-6.28) and High Depersonalisation score (DP≥7) (AOR = 1.79, 95% CI (1.28-2.51)). About 4.7% of the HCWs were overextended (EE>18); 6.5% were disengaged (DP>8) and 9.7% HCWs were showing signs of burnout (high on all three dimensions).ConclusionThe study has identified key factors that could have been likely triggers for psychological distress among healthcare workers who were engaged in management of COVID cases in India. The study also demonstrates the use of GHQ-5 and ICMR-NIOH Burnout questionnaire as important tools to identify persons at risk of psychological distress and occurrence of burnout symptoms respectively. The findings provide useful guide to planning interventions to mitigate mental health problems among HCW in future epidemic/pandemic scenarios in the country