Synthesis methods for nanosized hydroxyapatite with diverse structures.

Functional radiation absorbent materials (RAMs) can transform incident microwave energy into heat energy, hence being essential to impede reflections of microwaves generated by modern radars in military, aerospace, and commercial applications. For such applications, use of composites is imperative to maintain an optimum bandwidth, enhance the magnetoelectric functional activity, ensure a flexible design, and reduce weight, which can be achieved by tuning the volume fractions of such materials. Use of ferrites is widely recommended for microwave (MW) suppression due to their appropriate magnetodielectric characteristics. This review first describes the requirements for an ideal MW absorber and accurate measurements for quantification of MW absorption. Then, the significance, applications, approaches, and experimental developments of magnetodielectric polymer composite RAMs are presented. Moreover, such composites facilitate exploration of nanoscale functional properties to achieve efficient RAMs. The permeability and permittivity at microwave frequencies, magnetic properties induced by unique elemental doping mechanisms, as well as physical and chemical properties of these composites are also presented. The resonance-dependent absorption condition for different families of magnetic ferrites, as well as the dependence of their magnetic properties on the resonant frequency and their absorption bandwidth (spinels up to 30 GHz, hexaferrites 1 GHz to 100 GHz), are presented for applications. Furthermore, magnetodielectric composites decorated with carbon fillers (carbon nanotubes/multiwall carbon nanotubes, graphene, reduced graphene oxide, etc.) with enhanced microwave absorption properties are discussed. Additionally, core–shell magnetodielectric materials are also discussed in detail. Finally, this review highlights the importance of magnetodielectric polymer composites decorated with conducting materials and core–shell magnetodielectric materials as effective broadband RAMs achieving the primary application requirement of broadband absorption of at least −10 dB with reduced thickness.

Magnetodielectric Microwave Radiation Absorbent Materials and Their Polymer Composites

Hydroxyapatite (HA) was synthesized in situ by the precipitation method, with and without the presence of collagen (COLL), to study its influence on HA’s structural and morphological characteristics. The material was characterized by energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). The Ca/P molar ratio was influenced by collagen addition—1.89 and 2.38 for samples without and with collagen, respectively. The WAXD pattern revealed better resolution and intensity besides higher crystallinity degree of the HA in the presence of collagen. The photomicrographs showed a strong influence of collagen on the HA morphology.

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In Situ Hydroxyapatite Synthesis: Influence of Collagen on Its Structural and Morphological Characteristic

Hydroxyapatite (HAP) is the main mineral component in the bones and teeth of mammals. It is the hardest and toughest mineral material in the phosphate family. HAP nanomaterials with various shapes (i.e., granular, rod-shaped, fibrous, flake-shaped, and tubular) can be easily synthesized by various methods, such as hydrothermal, mechanochemical, and sol-gel methods. HAP is similar to clay minerals in that it also has excellent stability, reinforcing properties, carrier properties, and biocompatibility. The cations and anions in the crystal structure can be changed by ion exchange, which causes it to exhibit diverse performance. In recent years, the synthesis and application of HAP have received extensive attention and made great progress. This chapter introduces in detail the basic structure, properties, synthesis, modification of hydroxyapatite, and its potential applications in the fields of adsorption, catalysis, polymer materials, biomedical materials, and nanopapers. Although HAP is not strictly a clay mineral, its unique nanomaterial properties give it many advantages in biomedical materials that other materials cannot match. In this book, we also aim to appeal topeople to pay attention to not only clay mineral, but also note that HAP has a similar performance and usage as that of clay minerals. It was expected that the synergy of clay minerals and HAP would provide a new idea to develop better nanofunctional materials, especially in the biomedical industry.

Hydroxyapatite Nanomaterials: Synthesis, Properties, and Functional Applications

Chemical aspects of the formation of microcomposites based on superconducting cuprates are considered. The materials are composed of a superconducting ceramic matrix and micro- or nanoinclusions of the non-superconducting phase, which are uniformly distributed in the matrix. Requirements on the operating characteristics of the superconducting ceramics are described and routes to high critical current densites are outlined. Phase equilibria in the generic systems are considered. Physical and chemical criteria for the choice of phases that can form non-superconducting inclusions are proposed. Methods of preparation and the microstructures and superconducting properties of the composites based on cuprates RBa2Cu3O7–δ (R is the rare-earth element) and on Bi2Sr2CaCu2O8+δ and (Bi,Pb)2Sr2Ca2Cu3O10+δ are considered. The bibliography includes 247 references.

Microcomposites based on superconducting cuprates

(Bi,Pb)-2223 superconducting ceramics prepared by heat treatment at 840°C and containing 0.1 to 0.5 wt % fine-particle NbC additions were characterized by microstructural analysis, x-ray diffraction, and magnetic susceptibility measurements. The introduction of 0.1 wt % NbC was found to raise the 77-K zero-field critical current density by a factor of 2 to 3, reduce the superconducting transition width, and slightly increase T
c .

Effect of fine-particle NbC additions on the structure and superconducting properties of (Bi, Pb)2Sr2Ca2Cu3O10+x ceramics

The microstructure, phase composition, and superconducting properties of Bi-2223 ceramics doped with 0.05–0.5 wt % TaC were investigated. The materials were heat-treated at 840°C in three steps (10 + 24 + 24 h). By optimizing the TaC content and heat-treatment conditions, the 77-K critical current density of the Bi-2223 ceramics in zero field was raised by a factor of 2.

Microstructure and Superconducting Properties of TaC-Doped Bi-2223 Ceramics

The possibility of using high pressures in uniaxial pressing and rolling of nanopowders is investigated. Obtainment of a nanocrystalline hydroxyapatite ceramic intended for use in medicine is studied. The sintering temperature is reduced by approximately 600°C, and a ceramic with a grain size of less than 50 nm and high values of microhardness (up to 5.7 GPa) after annealing at 750°C is obtained. A substantial collective recrystallization of crystallite powder is overcome.

Nanocrystalline Hydroxyapatite Ceramics

In the present paper the structure, phase composition, superconducting properties and transport current for (BiPb)2Sr2Ca2Cu3Oy doped by TiC and NbC are investigated and their characteristics are presented. Concentration of impurities-was varied from 0.5 to 4.0 wt %. It was found that TiC impurity doesn 't affect on superconducting properties of specimens when its concentration less than 2 wt %. It was observed that superconducting properties of Bicontaining compounds are significantly suppressed with introducing of the same quantity of NbC impurity.

Influence of doping of TiC and NbC on structure and superconducting properties of Bi-containing compounds

The effect of ultrafine hafnium nitride additions (0.05–0.2 wt %) on the microstructure, phase composition, density, and superconducting properties (Tc and jc) of (Bi,Pb)2Sr2Ca2Cu3O10 + x ceramics is studied. The elemental composition of individual phases is determined, and the magnetic-field distribution in the ceramics is examined. The introduction of hafnium nitride increases the density of the ceramics and improves their microstructural stability at sintering temperatures between 840 and 850°С. The low hafnium solubility in the superconductor offers the possibility of attaining higher magnetizations and 77-K critical current densities.

B. P. Mikhailov

Papers

Effect of fine-particle NbC additions on the structure and superconducting properties of (Bi, Pb)2Sr2Ca2Cu3O10+x ceramics

Microstructure and Superconducting Properties of TaC-Doped Bi-2223 Ceramics

Nanocrystalline Hydroxyapatite Ceramics

Influence of doping of TiC and NbC on structure and superconducting properties of Bi-containing compounds

Effect of HfN Microadditions on the Microstructure and Superconducting Properties of (Bi,Pb)2Sr2Ca2Cu3O10 + x Ceramics