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This study aims to achieve the fabrication of three-dimensional core-shell filament-based lattice structures by means of robocasting combined with co-extrusion. For core and shell materials, colloidal gels composed of submicron carbon and alumina powders were developed, respectively. Simultaneously, the co-extrusion process was also studied by numerical simulation to investigate the feed pressure-dependent wall thickness.

Significant differences in the rheological behavior of the carbon and alumina gels were observed because of differences of the particle morphology and surface chemistry of the carbon and alumina powders. Precise control over the cross-sectional diameter of the core and shell green state elements was achieved by alteration of the feed pressures used during co-extrusion.

After subsequent thermal treatment in an oxidizing atmosphere (e.g. air), in which the carbon core was oxidized and burned out, lattice structures formed of hollow filaments of predetermined wall thickness were manufactured; additionally, C-Al₂O₃ core-shell filament lattice structures could be derived after firing in an argon atmosphere.

Green lattice truss structures with carbon core and alumina shell filaments were successfully manufactured by robotically controlled co-extrusion. As feedstocks carbon and alumina gels with significantly different rheological properties were prepared. During co-extrusion, the core paste exhibited a much higher viscosity than the shell paste, which benefited the co-extrusion process. Simultaneously, the core and shell diameters were exactly controlled by core and shell feed pressures and studied by numerical simulation. The experimentally and numerically derived filament wall thickness showed qualitative agreement with each other; with decreasing core pressure during co-extrusion, the wall thickness increased.

Strain gauges can be realised by printing and firing thick‐film resistors on ceramic substrates that are usually based on alumina. However, sensing elements made on some other substrates – tetragonal zirconia or stainless steel – would exhibit some improved characteristics, either due to a lower modulus of elasticity or a higher mechanical strength. As thick‐film resistors are developed for firing on alumina substrates their compatibility and possible interactions with other kinds of substrates have to be evaluated. The sheet resistivities and noise indices of the resistors were comparable, whereas the gauge factors were lower for the dielectric‐on‐steel substrates. The temperature coefficients of resistivity (TCR) of the resistors on the ZrO₂ and dielectric‐on‐steel substrates were higher than the TCRs on the alumina substrates, which was attributed to the higher thermal expansion coefficient of the tetragonal zirconia and the stainless steel.

The purpose this paper is to develop an additive manufacturing (AM) technique for high‐strength oxide ceramics. The process development aims at directly manufacturing fully dense ceramic freeform‐components with good mechanical properties.

The selective laser melting of the ceramic materials zirconia and alumina has been investigated experimentally. The approach followed up is to completely melt ZrO₂/Al₂O₃ powder mixtures by a focused laser beam. In order to reduce thermally induced stresses, the ceramic is preheated to a temperature of at least 1,600°C during the build up process.

It is possible to manufacture ceramic objects with almost 100 percent density, without any sintering processes or any post‐processing. Crack‐free specimens have been manufactured that have a flexural strength of more than 500 MPa. Manufactured objects have a fine‐grained two‐phase microstructure consisting of tetragonal zirconia and alpha‐alumina.

Future research may focus on improving the surface quality of manufactured components, solving issues related to the cold powder deposition on the preheated ceramic, further increasing the mechanical strength and transferring the technology from laboratory scale to industrial application.

Potential applications of this technique include manufacturing individual all‐ceramic dental restorations, ceramic prototypes and complex‐shaped ceramic components that cannot be made by any other manufacturing technique.

This new manufacturing technique based on melting and solidification of high‐performance ceramic material has some significant advantages compared to laser sintering techniques or other manufacturing techniques relying on solid‐state sintering processes.

The deterioration of surface mounted solder and adhesive joints on different substrate materials under thermal cycling was investigated metallographically. Ceramic chip resistors and leadless chip carriers were soft‐soldered or glued onto alumina, FR‐4, aluminium or steel boards and the various cracking modes were observed. Fatigue cracking in the solder under the component (mode A) took place in the case of resistors on an Al substrate and carriers on all boards except alumina. Cracking on the outward surface near the upper and lower corners (mode B) occurred on all boards, but most notably on alumina. Adhesive joints seemed to offer the highest fatigue strength, but their electrical properties suffered continuously in the course of cycling even though cracking was not observed at all in many cases.

Aims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.

LTCC materials are sintered at the low temperatures typically used for thick‐film processing, i.e. around 850°C, The thick‐film resistor materials for use as strain and temperature sensors on LTCC tapes are studied. Thick‐film piezo‐resistors in the form of strain‐gauges are realised with 10 kΩ/sq. 2041 (Du Pont)and 3414‐B (ESL), resistor materials; thick‐film temperature‐dependent resistors were made from PTC 5093 (Du Pont), and NTC‐4993 (EMCA Remex) resistor materials.

The X‐ray spectra of the 2041 and 3414‐Bb low TCR resistors after drying at 150°C and after firing display more or less the same peaks. The electrical characteristics of 2041 resistors fired on alumina and LTCC substrates are similar indicating that the resistors are compatible with the LTCC material. After firing on LTCC substrates the sheet resistivities and TCRs of the 3414‐B resistors increased. Also, there is a significant increase in the GFs from 13 to over 25.

Investigates the compatibility of thick‐film materials and the characteristics of the force and temperature sensors.

Present‐day electronics are shifting increasingly towards surface mounting technology (SMT) and hybrid technology (thick and thin film), which offer greater advantages due to their fabrication processes. Capacitors, like other components used in these processes, must occupy the smallest volume possible. Because of miniaturisation of the capacitors, the reliability of the surface mounting process is affected not only by the reliability of the components themselves but also by that of the assembly. In this study, a thermo‐mechanical simulation has been performed by means of ANSYS software based on the finite element method. This paper deals with the evaluation of a ceramic capacitor module (capacitors soldered on copper lands) on FR‐4 or alumina substrates during cooling to room temperature (25°C). The parameters of the assembly — temperature, length and thickness of the capacitor, thickness of the solder joint and nature of the substrate — were chosen by using the Design Of Experiments (DOE) method, which permits optimisation of these parameters and reduces the investigation time. The results showed a correlation between the length of the capacitor and the nature of the substrate used. Greater capacitor length is required for alumina substrate while a shorter length is preferred for FR‐4. It appears that a solder joint more than 100 urn thick may induce significant constraints on the copper lands and on the capacitor leads. It was noted that shear stress and voids in the solder joint can occur at temperatures higher than 250°C. This investigation makes it possible to prevent thermo‐mechanical stress damage during the mounting process and gives some recommendations for the choice of assembly variables.

The use of ceramic instead of metallic parts in devices that operate in aggressive conditions increases the service life of machines and equipment for chemical, metallurgical and other industries. The wear resistant zirconia/alumina composites were sintered from nanopowders obtained by co-precipitation technique. In the case of addition of 1wt% of alumina in zirconia ceramics the wear resistance increased by approximately 30%.

The formation of complex multilevel composite structures, such as Al³⁺ ion segregation on zirconia grain boundaries and intracrystalline alumina inclusions in zirconia grains, increased the fracture toughness values of composites obtained from co-precipitated nanopowders and consequently decreased the volume loss of ceramic material.

In this study, we investigated the effect of nanopowders synthesis methods and alumina concentration on composite structure, fracture toughness and tribological behavior of 3Y-TZP/alumina ceramic composites and searched correlation between structures and mechanical properties.

This paper reviews the role of alloying elements in aluminium and alloy fabrication on performance during surface treatment and surface finishing. Such elements may be present in solid solution as fine segregates, strengthening phase and equilibrium phases. For surface treatment and finishes, which generally proceed in the presence of alumina film, knowledge of the processes proceeding at the alloy/film and film/electrolyte interfaces, and those within anodic alumina films, gives rise to the possibility of controlling features of nanoscale dimensions, for improved performance, arises. Its influence on nanotextures at treated surfaces and compositionally and morphologically modified films is explained briefly.

This work aims to analyze the effect of mechanical activation on structural disordering (amorphization) in an alumina-silica ceramics system and formation of mullite most notably at a lower temperature using X-ray diffraction (XRD). Also, an objective of this work is to focus on a low-temperature fabrication route for the production of mullite powders.

A batch composition of kaolin, alumina and silica was manually pre-milled and then mechanically activated in a ball mill for 30 and 60 min. The activated samples were sintered at 1,150°C for a soaking period of 2 h. Mullite formation was characterized by XRD and scanning electron microscopy (SEM).

It was determined that the mechanical activation increased the quantity of the mullite phase. SEM results revealed that short milling times only helped in mixing of the precursor powders and caused partial agglomeration, while longer milling times, however, resulted in greater agglomeration.

It is noted that, a manual pre-milling of approximately 20 min and a ball milling approach of 60 min milling time can be suggested as the optimum milling time for the temperature decrease succeeded for the production of mullite from the specific stoichiometric batch formed.

Three‐dimensional photonic bandgap (PBG) structures using alumina (Al₂O₃) as the high permittivity material were modeled and then the structures were fabricated by Fused Deposition of Multi‐materials (FDMM) technology. A finite element method and a real‐time electromagnetic wave propagation software were used to simulate and design the layered PBG structures for applications in the microwave frequency range. The modeling predicted a 3‐D photonic bandgap in the 16.5–23.5 GHz range. FDMM provides a computer‐controlled process to generate 3‐D structures, allowing high fabrication flexibility and efficiency. Electromagnetic measurements displayed the presence of a bandgap between 17.1–23.3 GHz, showing a good agreement with the predicted values. These PBG structures are potential candidates for applications in advanced communication systems.