Sol-Gel Preparation of Selective Emitters for Thermophotovoltaic Conversion

Selective emitters are materials characterized by a high temperature emissivity significantly changing in different spectral regions. One of the crucial steps for the development of Thermophotovoltaic (TPV) generators is given by an optimal matching of the spectral emissivity of an IR radiation source with the spectral region where is maximum the efficiency of photovoltaic cells. The emitters should retain good structural properties at the working temperature above 1300°C and they can be either an external coating for the a burner or, as a structural material, a burner and emitter at once.In this work, oxide glass and ceramics containing rare earths have been prepared and characterized as selective emitters candidates. Different approaches and materials have been attempted all based on a colloidal route. Rare earths oxides (erbium and holmium) have been incorporated in transparent silica glass and in polycrystalline alumina and zirconia using their hydrated salts as oxide precursors. Rare earth modified silica glass were obtained by sintering silica xerogel containing fumed silica and hydrolysed ortholisicate. Rare earth modified alumina and mixed alumina-zirconia ceramics were obtained from slurries containing alumina colloidal particles and milled ceramic fibres. Functional properties i.e. the high temperature spectral emissivities have been measured by means of a specially designed apparatus where the working conditions of the selective emitters can be reproduced and monitored.     

Spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics

In this paper, the spectroscopic properties of Nd(3+) doped transparent oxyfluoride glass ceramics containing LaF(3) nano-crystals were systematically studied. The formation and distribution of LaF(3) nano-crystals in the glass matrix were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on Judd-Ofelt theory, the intensity parameters Omega(t) (t=2, 4, 6), spontaneous emission probability, radiative lifetime, radiative quantum efficiency, width of the emission line and stimulated emission cross-section of Nd(3+) were evaluated. Particularly, the effect of Nd(3+) doping level on them was discussed. With the increase of Nd(3+) concentration in the glass ceramic, the experimental luminescence lifetime, radiative quantum efficiency and stimulated emission cross-section vary from 353.4 micros, 78.3% and 1.86 x 10(-20)cm(2) to 214.7 micros, 39.9% and 1.52 x 10(-20)cm(2), respectively. The comparative study of Nd(3+) spectroscopic parameters in different hosts suggests that the investigated glass ceramic system is potentially applicable as laser materials for 1.06 microm emission.     

Exploring the Porosity in Ceramics at the nm Scale: From Understanding Historical Ceramics to Innovative Materials Design

Ceramics are complex objects and a rich source of information: they constitute a large part of the staple memory of past and present human activities. A deep understanding of traditional ceramics is an essential key to designing new ceramic materials. The demanding synthesis of ceramics with fine-tuned properties, such as enhanced mechanical, electrical, optical or magnetic characteristics, must be associated with cutting-edge analysis procedures in order to improve the engineering process. In this context, we describe a neutron-based non-destructive approach to investigating the nanoporosity of an historical pottery matrix as an effective investigation technique for exploring both traditional and advanced ceramic materials.     

Thermo-optic characteristics in transparent glass fabric reinforced composite using inorganic–organic hybrid materials

The thermo-optic characteristics of the transparent glass fabric composite and matrix resin have been investigated. The inorganic–organic hybrid materials modified with sulfur are synthesized as transparent matrix resin with the same refractive index and Abbe number as glass. The optical characteristics of the transparent composite relate to temperature due to the fact that the thermo-optic coefficient (dn/dT) for glass fiber (1.00 × 10⁻⁵K⁻¹) is different to that of inorganic–organic hybrid materials (−1.99 × 10⁻⁴K⁻¹). As the temperature increases, the transparent composite gradually becomes opaque and hazy due to the increased difference in the refractive index between the glass fiber and the matrix. The change in optical characteristics is reversible, meaning that the transparent composites can be used in for various applications in optical devices.     

Trends in development of calcium phosphate-based ceramic and composite materials for medical applications: Transition to nanoscale

Current status and lines of research were considered for calcium phosphate-based ceramic materials intended for application in new technologies for damaged bone tissue regeneration. The main trend is toward mimicking the composition, structure, and properties of biological bone tissues by ceramic materials. This necessitated developmental efforts on synthesizing polysubstituted, in particular nanocrystalline, biphasic calcium phosphates and on preparing ceramics and composite materials thereof. The progress achieved in this area was reviewed, and certain benefits associated with medical application of these materials were discussed.     

掺钕氟氧化物玻璃陶瓷的制备及表征

采用熔融和晶化技术合成出含CaF2微晶的Nd3+离子掺杂透明氟氧化物玻璃陶瓷材料, 并通过DTA, XRD, FEG-ESEM和UV-Vis-Nir分光光度计和傅里叶变换荧光光谱仪等对样品进行了表征. 结果表明, 玻璃陶瓷主晶相为CaF2, 晶相粒径为15 nm; 可见光透过率为78%~87%, 近红外透过率为84%~93%; 由于Nd3+在热处理后优先富集在具有低声子能量的CaF2晶相中, 从而改变了配体场, 使荧光谱线在1060 nm处的峰值比原始玻璃强度大.     

Tunable red-green upconversion luminescence in novel transparent glass ceramics containing Er: NaYF4 nanocrystals

To develop NaYF(4) as bulk luminescence material, transparent glass ceramics containing Er(3+): NaYF(4) nanocrystals were fabricated for the first time, and the influences of heat-treatment temperature and Er(3+) doping level on their upconversion luminescence were investigated. With increasing heating temperature, the upconversion intensity enhanced accordingly, attributing to the incorporation of more Er(3+) into the grown NaYF(4). Notably, when the heating temperature reached 650 degrees C, the upconversion intensity augmented drastically due to the occurrence of phase transition from the cubic NaYF(4) to the hexagonal one. Interestingly, for the samples heat-treated at 620 degrees C, when the Er(3+) doping level was increased from 0.05 to 2.0 mol %, the upconversion emission was whole-range tunable from monochromatic green to approximately monochromatic red, which could be mainly attributed to the cross-relaxation between Er(3+) ions. The excellent optical properties and its convenient, low-cost synthesis of the present glass ceramic imply that it is an excellent substitution material for the unobtainable bulk NaYF(4) crystal, potentially applicable in many fields.     

Luminescence and long-lasting afterglow in Mn<Superscript>2+</Superscript> and Eu<Superscript>3+</Superscript> co-doped ZnO–GeO<Subscript>2</Subscript> glasses and glass ceramics prepared by sol–gel method

To develop new fluorescent and afterglow materials, Mn²⁺ and Eu³⁺ co-doped ZnO–GeO₂ glasses and glass ceramics were prepared by a sol–gel method and their optical properties were investigated by measuring luminescence, excitation and afterglow spectra, and luminescence quantum yield (QY). Under UV irradiation at 254 nm, some glasses and all of the glass ceramics showed green luminescence peaking at 534 nm due to the ⁴T₁ → ⁶A₁ transition of tetrahedrally coordinated Mn²⁺ ions. The strongest luminescence was observed in a glass ceramic of 0.1MnO–0.3Eu₂O₃–25ZnO–75GeO₂ heat treated at 900 °C, with QY of 49.8%. All of the green-luminescent glasses and glass ceramics showed green afterglow, and the afterglow lasting for more than 60 min was obtained in a glass ceramic heat treated at 900 °C. It is considered that the Eu³⁺ ions may behave as electron trapping centers to be associated with the occurrence of the green afterglow due to the Mn²⁺ ions in the co-doped system.     

Use of Sol-Gel or Coacervate Process to Formulate Glassy or Ceramic Phosphates for Coating

Abstract

One of the objectives of present research on glassy and ceramic phosphates for coating materials is the synthesis of new precursors and the formulation of their mixtures. The properties of these materials depend mainly on the relative proportions of their constituents. Being able to varie at will the formulation of the materials the importance of the sol gel to glass or ceramics is dearly shown. This soft process is in a number of cases, preferable to the conventional high-temperature process.     

生物模板法制备木材陶瓷

生物模板法是一种制备具有生物形貌特点的结构和功能材料的新方法。由于木材组织结构方面的独特性,制备其多级孔结构的木材生态陶瓷在探索特殊微观结构和性能之间的关系方面有着重大的意义。本文总结了生物模板法制备陶瓷材料技术的发展现状,并且指出了各种工艺的优缺点,着重介绍了木材陶瓷的发展历史、制备方法、机理和性能,概述了木材陶瓷在骨移植材料和催化材料方面的应用和发展前景。     

Nucleation and Crystal Formation in Lithium Disilicate‐Apatite Glass‐Ceramic from a Combined Use of X‐Ray Diffraction,Solid‐State NMR,and Microscopy

Glass‐ceramics are multi‐phase materials that are comprised of one amorphous phase and at least one crystalline phase. Their versatile performance and properties can be engineered by alterations of the three fundamental steps – formulation and production of the amorphous base glass, nucleation, and crystallization. Efforts have been made on syntheses of glass‐ceramics with different components, yet little is known about the details of nucleation and crystallization processes that are essential for tailoring glass‐ceramic properties. Herein, we investigate the nucleation and crystallization mechanisms of a multi‐component, that is SiO₂‐Al₂O₃‐CaO‐Li₂O‐K₂O‐P₂O₅‐F, glass‐ceramic system by a combined use of powder X‐ray diffraction (pXRD), solid‐state nuclear magnetic resonance (NMR), and electron microscopic (EM) techniques. The role of P₂O₅ in the nucleation and crystallization processes is particularly studied. We show that the formation of lithium silicate crystals being independent of the P₂O₅‐associated crystals, and the separation of P₂O₅ phases into individual growth domains of lithium orthophosphate and fluorapatite. We also observe the non‐uniform distribution of fluorapatite particles that explains the opalescence effect of this glass‐ceramic.     

Ferroelectric ceramics by sol–gel methods and applications: a review

New advances in the sol?Cgel processing of ferroelectric ceramic powders and thin films and recently, scientific and technological interests in ferroelectric ceramics have been focused particularly on thin films. This is mainly due to their great potential applications in integrated electronics as passive components and as non-volatile ferroelectric memories, optoelectronic devices, etc. Special attention has been paid to the effects of the microstructure and composition on the piezoelectric properties of ferroelectric ceramic powders and thin films, and various characterization techniques are reported. This paper introduces the basic principles governing ferroelectricity and lists the various materials which exhibit these properties. The processing of ferroelectric ceramics and thin films in general and sol?Cgel processing in particular, with some examples are described. Finally, important applications of ferroelectric films and microstructure examination as well as powerful techniques are briefly discussed.     

Templated ceramic microstructures by using the breath-figure method

We describe the synthesis of two cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies by using the breath-figure method. Such breath figures can be washed away with an appropriate solvent. Upon pyrolysis at 500 degrees C under either nitrogen or air, the bubble arrays persist as ceramics and are insoluble in organic solvents or water. The formed pyrolyzed bubble arrays were analyzed by optical and scanning electron microscopy, as well as energy dispersive X-ray microanalysis (EDX). The composition of the ceramic materials is discussed based on EDX and IR data.     

Spectroscopy of chromium(III) in β-quartz and petalite-like transparent glass ceramics: Ligand field strengths of chromium(III)

Absorption, emission and excitation spectra of chromium(III) were obtained for transparent glass ceramics containing β-quartz and petalite-like phases. Emission from the ²E and ⁴T₂ levels was observed simultaneously at room temperature. Ligand field strengths of Cr(III) in the crystalline phase are comparable to those obtained in materials which provide high-field Cr(III) sites, while in the glassy phase low-field sites are observed.     

硅基聚合物前驱体转化陶瓷微观结构研究进展

聚合物前驱体转化法使得陶瓷材料的制备实现了可分子设计和可聚合物工艺加工,在陶瓷基复合材料、陶瓷纤维、功能涂层、特种胶粘剂等方面具有重要应用价值.不同于传统粉末烧结工艺,该方法涉及有机聚合物至无机陶瓷的转化过程,因此,聚合物前驱体的分子结构以及陶瓷化工艺对所制备陶瓷材料的微观结构和功能特性具有直接影响.本文综述了基于聚合...     

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9–1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1–10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.     

Diverse Supports for Immobilization of Catalysts in Continuous Flow Reactors

The rapid development of continuous flow processes is driving innovations in various chemical syntheses and industrial productions. Immobilizing catalysts in flow reactors allows transformations with high-efficiency and excludes the subsequent separation procedures. This concept outlines the approaches to incorporate catalysts within flow reactors, with particular focus on the application of additional supports including inorganic materials like silica, zeolite and reduced graphene oxide, polymeric materials like polymer packings, monoliths, cross-linked gels and polymer brushes, and other materials for specific conditions like transparent glass fibers and glass beads. Furthermore, advanced methods to develop ordered micro-/nanoarrays from internal walls of flow channels for immobilization of catalysts as well as application of innovative vortex fluidic devices are discussed to inspire new designs of supports for novel fluidic reactors with broad applications.     

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9-1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1-10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.     

Crystallization, mechanical properties and in vitro bioactivity of sol–gel derived Na2O–CaO–SiO2–P2O5 glass–ceramics by partial substitution of CaF2 for CaO

The partial substitution of CaF₂ for CaO in the Na₂O–CaO–SiO₂–P₂O₅ system was conducted by the sol–gel method and a comparison of the glass–ceramic properties was reported. Based on thermogravimetric and differential thermal analysis, the gels were sintered with a suitable heat treatment procedure. The glass–ceramic properties were characterized by X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectrometer and so on, and the bioactivity of the glass–ceramic was evaluated by in vitro assays in simulated body fluid. Results indicate that with the partial substitution of CaF₂ for CaO in glass composition, the volume density, apparent porosity, bending strength and microhardness of the glass–ceramics have been significantly improved. Furthermore, CaF₂ promotes glass crystallization which does not inhibit the glass–ceramic bioactivity.