This critical review presents an overview of the various classes of oxide materials exhibiting fast oxide-ion or proton conductivity for use as solid electrolytes in clean energy applications such as solid oxide fuel cells. Emphasis is placed on the relationship between structural and mechanistic features of the crystalline materials and their ion conduction properties. After describing well-established classes such as fluorite- and perovskite-based oxides, new materials and structure-types are presented. These include a variety of molybdate, gallate, apatite silicate/germanate and niobate systems, many of which contain flexible structural networks, and exhibit different defect properties and transport mechanisms to the conventional materials. It is concluded that the rich chemistry of these important systems provides diverse possibilities for developing superior ionic conductors for use as solid electrolytes in fuel cells and related applications. In most cases, a greater atomic-level understanding of the structures, defects and conduction mechanisms is achieved through a combination of experimental and computational techniques (217 references).

Oxide-ion and proton conducting electrolyte materials for clean energy applications: structural and mechanistic features

Thermoelectric energy conversion can be used to capture electric power from waste heat in a variety of applications. The materials that have been shown to have the best thermoelectric properties are compounds containing elements such as tellurium and antimony. These compounds can be oxidized if exposed to the high temperature air that may be present in heat recovery applications. Oxide materials have better stability in oxidizing environments, so their use enables the fabrication of more durable devices. Thus, although the thermoelectric properties of oxides are inferior to those of the compounds mentioned above, their superior stability may expand potential the high temperature application of thermoelectric energy conversion. In this paper, the thermoelectric properties of promising oxide materials are reviewed. The different types of oxides used for thermoelectric applications are compared and approaches for improving performance through doping are discussed.

Oxide materials for high temperature thermoelectric energy conversion

Metal oxides (Ca3Co4O9, CaMnO3, SrTiO3, In2O3), Ti sulfides, and Mn silicides are promising thermoelectric (TE) material candidates for cascade-type modules that are usable in a temperature range of 300–1200 K in air. In this paper, we review previous studies in the field of TE materials development and make recommendations for each material regarding future research. Furthermore, the R&D of TE modules composed of metal oxide materials and the prospect of their commercialization for energy harvesting is demonstrated.

Thermoelectric Ceramics for Energy Harvesting

Functionally graded materials (FGMs) are a broad research area and attract considerable tremendous attention today in the materials science and engineering society. In recent years, FGMs have experienced remarkable developments in manufacturing methods. FGMs can be produced using several well-known processing techniques from conventional to advanced. This research provides an overview of manufacturing methods for FGMs, thus describing the fundamental difficulties and strengths of these methods based on the available literature over 30 years. Besides, this critical review gives a comprehensive summary of the various applications and the future trends for research required for the design and production of these materials properly with a smooth graded. The anticipated findings of the current paper can be considered as a milestone for future production and analysis investigations for FGMs and are beneficial for researchers, designers, and manufacturers in this scope.

30 Years of functionally graded materials: An overview of manufacturing methods, Applications and Future Challenges

Dynamic compressive behaviour of cellular materials: A review of phenomenon, mechanism and modelling

High strain rate compression of cenosphere-pure aluminum syntactic foams

In this research, the researchers applied the squeeze casting technology to integrally produced the B4C/AA2024 functionally graded materials (FGMs). The volume fraction of B4C were 70 vol%, 47 vol% and 25 vol% in the top, middle and bottom layer respectively. The ballistic tests of different samples with areal density of 80 kg/m2 and 38 kg/m2 were carried out using 7.62 mm armor-piercing incendiary (API). For comparison, homogeneous 70 vol% and 47 vol% B4C/AA2024 targets were tested under the same conditions. The results demonstrate that the three layers 70-47-25 vol% B4C/AA2024 FGMs has a better ability to maintain integrity than homogeneous 70 vol% B4C/AA2024 target and the areal density of penetration is reduced by 14% compared to homogeneous 47% B4C/AA2024 composites. The microstructure of targets and projectiles were investigated. Large amounts of fragmentation of B4C particles and plastic deformation of composites are observed near the bullet hole at the top and bottom layer respectively. Crack deflection appears in the interface of the top and middle layer. By stress wave analysis, it is found that the existence of gradient structure reduces the magnitude of reflected tensile wave by 12%, which improves the ability of the target to resist fracture. The results indicate the FGMs with high ceramic content at the top layer were of good application prospects in lightweight armor.

The microstructure and ballistic performance of B4C/AA2024 functionally graded composites with wide range B4C volume fraction

Industrial pure aluminum (0.5 wt% impurity elements) was utilized in many investigations of aluminum matrix composites at home and abroad. However, impurity elements in industrial pure aluminum may influence the interface during fabrication of composite at high temperature. Thereby, it is necessary to use high-purity aluminum (impurity elements less than 0.01%) as matrix to enable study the interface reaction between reinforcement and matrix. In this study, stretches of brittle Al4C3 at the fiber/matrix interfaces in Grf/Al composite were observed. The fracture surface of the composite after tensile and bending tests was flat with no fiber pull-out, which revealed characteristic of brittle fracture. This was related to Al4C3, as this brittle phase may break before the fiber during loading and become a crack initiation point, while the corresponding crack may propagate in the fiber and the surrounding aluminum matrix, finally resulting in low stress fracture of composites.

Microstructure and mechanical properties of graphite fiber-reinforced high-purity aluminum matrix composite

Molten salt synthesis and thermoelectric properties of Ca2Co2O5

This study is concerned with investigation of forming Ti fiber reinforced TiAl3 composite by infiltration-in situ reaction. The as-cast material was obtained by pressing molten pure Al into a preform which was composed of Ti particles and Ti fibers. Based on the differential scanning calorimetry (DSC) result, in situ reaction samples were obtained by heating as-cast materials to 660, 950, and 1300 °C, and held for 1 h, respectively. The microstructure evolution of in situ reaction samples was analyzed by scanning electron microscope and Energy dispersive X-ray (EDX). In addition, the phase composition of products was inspected by X-ray diffraction (XRD). Experiment results show that TiAl3 was formed initially, which was the unique product between Ti and Al. While at high temperature, products of Ti fibers and Al were complex, and TixAl1−x (0.25 < x < 0.75) compounds were formed around Ti fibers. Finally, TiAl3 decomposed, and oxidation occurred. The mechanism of in situ reaction between Ti and Al in this system was discussed.

Chen Guoqin

Papers

High strain rate compression of cenosphere-pure aluminum syntactic foams

The microstructure and ballistic performance of B4C/AA2024 functionally graded composites with wide range B4C volume fraction

Microstructure and mechanical properties of graphite fiber-reinforced high-purity aluminum matrix composite

Molten salt synthesis and thermoelectric properties of Ca2Co2O5

Study on Ti fiber reinforced TiAl3 composite by infiltration-in situ reaction