Thermoelectric gas sensors (TGSs) were developed using a series of materials combined with gas-selective combustion catalysts. The TGSs have a micro-device structure formed on a membrane-type micro-hotplate to enhance their sensitivity. The working principle of the TGSs involves a synergetic combination of thermoelectric detection and the catalytic combustion of detection gas, which can eliminate the effects of humidity and other inflammable gases, allowing highly sensitive gas detection. This paper introduces the thin-film processing and the methodology of integrating the ceramic catalyst on the micro-device for the TGSs, and the mass production of gas sensors was demonstrated in this study. The TGSs can detect a wide H concentration range of several parts per million (ppm) to percent in air, exhibiting robust sensing performance with long-term stability. We developed new applications such as breath H₂ measurement with a H₂ concentration of 0–200 ppm.

In this paper, the damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) subjected to thermal cyclic fatigue loading at elevated temperatures in oxidizing atmosphere are investigated. The temperature/cyclic dependent fiber/matrix interface shear stress is determined as a function of testing temperature, applied cycle number and material properties, which affects multiple thermal fatigue damage mechanisms. The microstress field of the thermal fatigue damaged composite is analyzed using the Budiansky-Hutchinson-Evans shear-lag model, considering matrix stochastic cracking, fiber/matrix interface debonding/sliding and fibers fracture. The matrix stochastic cracking, fiber/matrix interface debonding and sliding, fibers fracture in the interface damage zones are determined using the micromechanical approach. The relationships between the thermal fatigue cycling, multiple thermal fatigue damage mechanisms, fatigue hysteresis-based damage parameters and thermal fatigue lifetime are established. The effects of fiber/matrix interface properties, fiber radius, fiber volume fraction, matrix crack spacing and fatigue peak stress on thermal fatigue damage evolution in fiber-reinforced CMCs are analyzed. The thermal fatigue damage evolution and lifetime prediction of two different fiber-reinforced CMCs, i.e., cross-ply SiC/MAS and 2D SiC/SiC composites, subjected to thermal cycling fatigue in oxidizing atmosphere are predicted.

Normally, it is very difficult to process thin ceramic films (<10 µm) except by vapor deposition methods. This is because in traditional ceramics processing, initial powder particle sizes (typical average particle sizes, APSs >200 nm) make it difficult to realize mechanically robust thin films after sintering to full density due to excessive grain growth. One solution to this problem is to start with nanopowders (APSs <100 nm). Here we present efforts to use simple, easily available nano δ-Al₂O₃ (transition or t-Al₂O₃) nanopowders (NPs) to process the subject films. Thus t-Al₂O₃ NPs when properly dispersed, doped with 0.5–5 wt.% MgO and ball milled with a polymeric binder provide castable systems. Wire wound roller drawing/tape casting provides access to thin green films (10–30 µm) with ≈75 wt.% ceramic loadings. Following binder burnout and careful sintering to temperatures of up to 1500°C/7 h/air but preferably slightly lesser conditions leads to dense ≤10 µm films with average α-Al₂O₃ grain sizes of 500–800 nm. At higher MgO concentrations, spinel phase separates during sintering likely inhibiting grain growth. These relatively dense films are flexible and translucent. Such films, because of their flexibility, may offer utility as catalyst supports, electronic substrates or as hard facings for other materials.

The mullite was directly extracted from coal fly ash through removing iron and silica without sintering process by-product sodium silicate. The effect of processing parameters on the leaching rate of iron and silica was investigated. The physical properties, phase composition and microstructure of the mullite extracted from the original fly ash were characterized by using X-ray fluorescence spectrometer, X-ray diffractometer, fourier transform infrared spectroscopy, scanning electronic microscope and energy dispersive spectroscope. The technical indicators of sodium silicate were also tested. The results show that the maximum iron extraction reaches 85.9 mass % when firstly with a magnetic separation process then leaching with 20 mass % of hydrochloric acid solution at 85°C for 3 h. The 40.4 mass % leaching rate of silica was presented after leaching with 25 mass % of sodium hydroxide at 95°C for 4.5 h. As a result, the beneficiated extracted sample exhibited a mullite content of 82 mass %, the corundum content of 18 mass %. This method provides a potential way on the utilization of coal fly ash to prepare mullite.

Chemical toughening of soda-lime glass by in-diffusion of potassium from a molten salt to replace sodium is currently restricted to applications where thermal tempering is not suitable, such as toughening of thin glass and complex shaped objects. Chemical toughening would be more attractive as a commercial process if it could be made more rapid by elevating the temperature, accelerating the diffusion process. However, when the temperature is increased, stress generation processes are accompanied by stress relief through structural relaxation, limiting the stress achieved. Here we use cross sectional microscopy with energy dispersive X-ray spectroscopy analysis and a study of the vibrational spectrum using fourier transform infrared to show that there is another effect that also plays a role in determining the in-diffusion rate of potassium. Temperatures that initiate stress relaxation also accelerate the formation of excessive amounts of non-bridging oxygen which is accompanied by an increase in the surface concentration of calcium. We hypothesize that this calcium layer creates a barrier to the migration of potassium into the glass.

To manage steel-making slag (SS) produced as industrial waste and conserve ceramic raw material resources, it is significant and sustainable to develop new ways of using SS. In this study, a novel ceramic brick was prepared using SS and red clay. The influence of SS particle size and sintering temperature on the sintering process and final properties of the red clay ceramic bricks was investigated. The water absorption capacity and compressive strength of these samples were analyzed. The results showed that the water absorption rate of the samples decreased with decreasing slag particle size and that the compressive strength of the sample reached its peak value at a moderate SS particle size (<0.075 mm) and sintering temperature (1150°C). The effect of SS particle size on the properties of the red clay ceramic bricks was investigated by analyzing the liquid phase and crystal structure. In addition, the relationship between SS particle size and activation energy of the sintering reaction was established, which is expected to provide useful information for the design of a sintering schedule for red clay–SS ceramic tiles with a certain SS particle size. We demonstrated a process for preparing a new type of ceramic brick that exceeds the specifications for pedestrian paving applications, while minimizing problems related to waste SS disposal.

It is important to efficiently remove radioactive substances contained in polluted waters before they are discharged from nuclear power plants. In particular, there is an urgent need for the development of technology that can adsorb radioactive Sr²⁺, but there are currently no inexpensive Sr²⁺ adsorbents with low environmental burden. We found that scallop shell powder adsorbs Sr²⁺ in aqueous solutions at various initial concentrations. In this study, to obtain fundamental knowledge of the mechanism of Sr²⁺ removal using waste scallop shell, we analyzed the removability of Sr²⁺. Scallop shell showed the same capacity to remove Sr²⁺ at a high initial concentration (≥0.50 g/dm³) as the reagent CaCO₃, but a clear difference in removability appeared at a low initial concentration (0.010 g/dm³), where scallop shell proved to be superior. In addition, scallop shell powder had slit-shaped pores and a specific surface area of 4.3 m²/g. Measurement of the adsorption isotherm in the low concentration aqueous solution showed that Sr²⁺ removal occurred by chemisorption; the adsorbed Sr is present on the surface of the scallop shell powder particles.

In this work, we study the impact of pyrolysis temperature and time on the crystalline structure of lab made silicon carbide (SiC) fibers and their mechanical properties. The polycrystalline structure and the characteristic length scales of β-SiC in fibers were characterized with X-ray diffraction, transmission electron microscope and synchrotron small angle X-ray scattering. The sizes of crystallites, particles and interparticle distance all increase as pyrolysis temperature or time increases while the crystallinity nearly remains constant, indicating SiC crystals in the fiber grow by absorbing the surrounding small crystals. The crystal growth follows the Ostwald ripening when pyrolysis temperature reaches 1500°C. At this temperature, longer pyrolysis time seems to reduce the tensile strength, but still keep increasing the modulus. The stiffness is possibly associated with the growth of particle size, interparticle distance and the size of voids in fibers.

Microscopic structure change induced by microfabrication of Pb(Zr,Ti)O₃ (PZT) islands was investigated. The 3 µm-thick epitaxial (100)/(001)-oriented PZT film with Zr/(Zr + Ti) ratio of 0.56 consisted of both tetragonal and the rhombohedral phases. Tetragonal phase mainly existed near the film-substrate interface, while the rhombohedral one near the surface of the film. The profile of this structural non-uniformity along the film thickness was changed by the lateral size of PZT. These phenomena can be explained by the stress distribution in PZT and the understanding of this non-uniformity is the key to control the performance of the devices using PZT.

A 5 mm thick alumina ceramic plate and a 1 mm thick aluminum alloy plate were welded together by a friction stir spot welding technique. The welding was performed at tool rotation rate of 2000 rpm, plunge time of 0.4 mm, dwell time of 60 s, and plunge rate of approximately 0.1 mm/min. The interface microstructure of the welds was investigated by a scanning transmission electron microscope and energy dispersive X-ray spectrometry analysis to study the welding mechanism. A magnesium element was detected along the interface. It was expected that the alumina ceramic plate and the aluminum alloy plate were welded via magnesium oxide or a magnesium–aluminum–oxygen compound.