Field assisted processing of 3D printed ceramics

IOP Conference Series: Materials Science and Engineering, 2016

In the present study, the potential of microwave irradiation as an innovative energyefficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration.

Transactions of FAMENA

The present study examines the potential of microwave heating as an emerging and innovative energy-efficient alternative to conventional heating techniques used for different materials, with a focus on the processing of ceramic materials. Modern ceramics are studied extensively, and their use and different applications are wide due to many advantages of these materials. The most important factor in microwave sintering which differentiates it from conventional heating techniques is a unique heat transfer mechanism. Microwave energy is absorbed by the material, hence the transfer of energy takes place at the molecular level. This way, the heat is generated throughout the material, i.e. on the inside as well on the outside. This allows a very low temperature gradient throughout the material cross section. When conventional sintering is used, typically at high heating rates, high temperature gradients pose a problem. The accelerated microwave heating occurs through the whole volume, so the heating is uniform, which limits the grain growth and coarsening, and leads to a uniform and fine microstructure. The densification is accelerated as well during the unique heat transfer mechanism of microwave sintering, which enhances the mechanical properties of the sintered materials. This paper discusses the use of microwave sintering in the manufacturing of different modern technical materials, namely ceramics, composites, metals and alloys, and glasses. The improvement of different properties is described using the available literature.

Journal of Alloys and Compounds, 2010

Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. This review article first provides a summary of fundamental theoretical aspects of microwave and microwave hybrid sintering, and then advantages of microwave sintering against conventional methods are described. At the end, some applications of microwave sintering are mentioned which so far have manifested the advantages of this novel method.

International Journal of Refractory Metals & Hard Materials, 1998

Application of microwave radiation as a heat source for sintering of hardmetal is described. Sintering of hardmetal with microwaves leads to a finer microstructure because of lower sintering temperatures and shorter processing times. A further variant is the microwave reaction slntering of a powder mixture of metallic tungsten, carbon and cobalt to obtain finer mlcrostructures than by the conventional route. Moreover, this process offers a great potential for simplifying and shortening the process sequence in hardmetal production. The in-sttu formation of WC-platelets during microwave reaction sintering was observed.

Materials Today: Proceedings, 2018

In recent years microwave sintering has gained significant attention based on the improved mechanical properties as compared to the conventional material processing. Microwave sintering has found its applications for the processing of metal powder, metal matrix composites, ceramics and also in the processing of metal ores. This article reviews about basic processing aspects of microwaves, microwave sintering and some of its applications comparing it with the conventional processing.

Low-temperature sintering ceramics with high dielectric permittivity and low loss are highly valuable to the communication industry. Additive Manufacturing (AM) exhibits excellent potential to process a wide range of engineering materials and deliver complex three-dimensional structures in various scales, with several benefits over traditional manufacturing methods used in electronics manufacturing. Therefore, the advent of AM has offered a radically new way of designing and manufacturing electronic and communication components with tailored performance. In this work, a stable ink has been formulated from ultra-low loss dielectric bismuth molybdate (Bi2Mo2O9) ceramics. The formulated ink exhibited suitable rheological properties responsive to the direct ink writing technique. The 3D printed components with good structural integrity and spatial resolution were sintered at 670°C for 4 hours using the conventional heating method, achieving >94% density. A series of components with varying shapes and designed porosities were fabricated using the extrusion 3D printing method. The relative permittivity (εr) and loss tangent (tanδ) for the 3D printed and sintered Bi2Mo2O9 solid components were found to be 36.5 and 0.0005, respectively, at ~8GHz, and the values can be tailored using designed porosity. The dielectric performance was found to be excellent and stable even at very high-frequency regimes (beyond 5G) between 70-90 GHz. Further, the addition of metallic infills in the designed pores of the ceramic scaffolds resulted in an increase in permittivity values. The preliminary investigation exhibited the potential to fabricate ceramic components for high-frequency applications via the design freedom offered by AM, that can enable further miniaturization of future communication devices.

AIChE Journal, 1998

The microwave heating of ceramic materials has been analyzed by solving the equations for grain growth and porosity during the late stages of sintering, coupled with the heat conduction equation and electric field equations for 1 -D slabs. Microwave power absorption and heating profiles have been calculated for Al,O, and Sic in the absence of sintering, and calculations have been cam'ed out to study the effect of increasing dielectric loss of A1,03 as a function of temperature. A comparison of the densification and grain growth for Al,O, during microwave and conventional sintering indicates that within the ffamework of the present model, there is no difference between the two heating modes during the late stages of sintering.

International Journal of Applied Electromagnetics and Mechanics, 2020

Innovative non-conventional approaches, such microwave sintering, are being developed as method for sintering a variety of materials which shown advantages against conventional sintering procedures. This work involves an investigation of microwave sintering of ATZ composite with two different microwave applicators and frequency generators: 2.45 GHz and 5.8 GHz. Zirconia doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) is the used composite in this study. The samples were sintered by microwave in air at 1200 and 1300 ºC with 10 min of dwell time at 2.45 and 5.8 GHz in order to evaluate their effects on sintering, using optimized experimental setup. Moreover, the mechanical properties of MW-sintered samples were compared with those obtained for the same composites sintered by conventional method (1500 ºC /120 min), such as relative density, hardness and fracture toughness.

Microwave processing eliminates the need for spending energy to heat the walls of furnace or reactors, their massive components and heat carriers. Hence, the use of microwave processing methods significantly reduces energy consumption, particularly in hightemperature processes, since heat losses escalate considerably as processing temperatures increase. However, the advantages of using microwave energy in high-temperature processes are by no means limited to energy savings. In many cases, microwave processing can improve the product quality ).

2006

Microwave sintering has been applied to a wide variety of materials during the past three decades as an alternative to conventional thermal sintering. Recent experimental results showed that for semimetal or magnetic materials the magnetic field (H) can have a significantly larger contribution than the electric field (E) during sintering. We have employed the COMSOL Multiphysics TM package to simulate the sintering process by adding the magnetic field contribution into the heating source. We performed simulations with both E and H fields or with isolated E or H fields. For the systems of Fe3O4, Al2O3 and ZnO oxides, our simulated results are in good qualitative agreement with the experimental sintering findings. We also explored the sintering of nano-size ZnO/γ- Fe2O3 and macro-size ZnO/γ-Al2O3 composite particles.