Comparison of different synthesis methods for nasicon ceramics

Various methods for the synthesis of Na₂Zr₂P₂SiO₁₂ ceramics have been investigated. The methods differ by the order of mixing and the use of acetylacetone to decrease the reactivity of zirconium. The homogeneity of the powders prior to calcination has been checked by ³¹P NMR. Their reactivity towards crystallization is not drastically different. The sintering behaviour is much better in powders in which the zirconium reactivity has been decreased. The effect of the processing on the resulting ionic conductivity of the ceramics has been studied.     

Characterization of lead and lead leaching properties of lead glazed ceramics from the Solis Valley, Mexico, using inductively coupled plasma-mass spectrometry (ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

Ingestion of relatively small amounts of lead is now recognized to cause significant neurological and cognitive effects in humans. Large quantities may be fatal, yet lead poisoning, especially of children, is still a major public health concern in many parts of the world. In rural Mexican communities lead oxide (PbO) is added to ceramic glaze as a fluxing agent, lowering starting firing temperatures to 500 °C. The purpose of this study is to characterize the lead chemical forms in ceramic glazes from the Solis Valley, Mexico, to investigate lead leaching properties of these ceramics, and to demonstrate the applicability of lead isotope signatures as a means of tracing lead source origins. Ceramics were collected from the rural village of Santa Maria de Canchesda, State of Mexico, Mexico. Dried liquid glazes, post-fired glaze material, and pure PbO were analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Results from DRIFT analysis indicate that PbO (1429 cm⁻¹ band) is the active form of lead found in liquid glazes and ceramics. Some shifting of 1429 cm⁻¹ PbO peak to lower wavenumbers occurs in post-fired ceramics, and this may be due to the formation of lead bisilicate during firing. Ceramics samples were leached in 0.02 M citric acid solution for 1 min, and leached lead concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Lead concentrations in these leachates varied from 0.4-80.4 μg ml⁻¹, while the control pottery from the US leached only 0.1 μg ml⁻¹ lead. Elemental distributions on glaze surfaces were identified by laser ablation (LA)-ICP-MS. Nitric acid extracts of soils, teeth, and ceramic glazes were analyzed for lead isotope ratios (²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb) using ICP-MS. Similarities of tooth and ceramic lead isotope ratios indicate that ceramics may be a substantial source of body lead burden in the Solis Valley. This study demonstrates the applicability of lead isotope ratios for lead source identification, and it identifies potential health risks from ceramic use induced lead toxicity within the Solis Valley.     

Fluoride optical nanoceramics

The methods for preparation of highly transparent optical ceramics based on simple and complex fluoride compounds of elements of the first, second, and third Group in the Periodical system are considered. The use of precursors as nanopowders and processes of their self-assembling on heating results in maximally homogeneous, transparent, and mechanically strong ceramics. The resulting calcium fluoride ceramics possess optical losses of 10⁻²–10⁻³ cm⁻¹ at 1.06 μm and shock resistance characterized by the fracture toughness K _1C = 4.7±0.3 MPa m^1/2 (for comparison, for a calcium fluoride single crystal K _1C = 1.5±0.15 MPa m^1/2). Regularities of the chemistry of fluoride nanopowders were considered in comparison with the oxide nanopowders: the fluorides are prone to hydrolysis, and powder nanoparticles precipitated from aqueous solutions have complex and heterogeneous (over the volume) chemical composition. The spectral luminescence properties of the ceramics activated by rare-earth metals (Ce³⁺, Nd³⁺, Er³⁺, Yb³⁺) or containing active color centers are presented. The generation properties of the lithium fluoride ceramics with the color centers and the ternary Ca-Sr-Yb fluoride during diode laser pumping are describe Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 863–872, May, 2008.     

Colossal dielectric constant in PrFeO3 semiconductor ceramics

The perovskite PrFeO₃ ceramics were synthesized via sol–gel method. The dielectric properties and impedance spectroscopy (IS) of these ceramics were studied in the frequency range from 100 Hz to 1000 kHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ∼10⁴ at room temperature. The response is similar to that observed for relaxorferroelectrics. IS data analysis indicates the ceramics to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 30 and more resistive grain boundaries with effective dielectric constant ∼10⁴. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrFeO₃ ceramics.     

Mussel-inspired fabrication of encoded polymer films for electrochemical identification

Encoded polymer films for electrochemical identification have been achieved by embedding different semiconductor nanocrystals into self-polymerized dopamine films. Such encoded polydopamine films based on mussel-inspired surface chemistry show high adhesive ability and can be created on a wide range of inorganic and organic materials, including noble metals, oxides, ceramics, and synthetic polymers. By incorporating different predetermined levels of various redox nanomarkers, the use of multi-film system composed of multiple, sequenced polydopamine identification films could theoretically generate nearly unlimited (>10¹²) distinct voltammetric signatures (electric codes).     

Processible Cyclopentadithiophene Copolymers for Photovoltaic Applications

We designed and synthesized a series of conjugated polymers containing alternating 4H-cyclopenta[2,1-b:3,4-b′]dithiophene units and comonomers consisting of 2,2′-bithiophene, 3^″, 4^″ -dihexyl-α -pentathiophene, 3,4-ethylenedioxythiophene and 5,5′ -bis(2-thienyl)-4,4′ -dihexyl-2,2′ -bithiazole. These polymers possess optical bandgaps in the range of 1.75 to 2.0 eV. The desirable absorption attributes of these materials make then excellent candidates for use in photovoltaic cells. Electrochemical studies indicate desirable HOMO-LUMO levels for use with fullerene derivatives as electron transporters. Field effect transistors made of these materials show hole mobilities in the range of 7.5 × 10^?4 cm²/Vs to 2.0 × 10^?3 cm²/Vs. Due to the combination of these characteristics, power conversion efficiencies up to 3.1% were achieved on devices made of bulk heterojunction composites of these materials with soluble fullerene derivatives.     

Structure and electrical properties of single-phase cobalt manganese oxide spinels Mn3−xCoxO4 sintered classically and by spark plasma sintering (SPS)

Cobalt manganese oxide spinels Mn_3−xCo_xO₄ (with 0.98?x?3) were prepared by the thermal decomposition in air of oxalate precursors. The influence of the thermal treatments on the structure of these materials is emphasized. Single-phase ceramics were obtained after optimization of the sintering parameters. A precise phase diagram for the Co-Mn-O system is proposed according to thermal stability and structure of oxide powders. The electrical measurements on single-phase ceramics show that low values of resistivity can be achieved. The conduction could take place through jumps of polarons between Mn³⁺ and Mn⁴⁺ on octahedral sites. These compounds present interesting electrical characteristics for negative temperature coefficient (NTC) thermistor applications.     

99mTc radiolabeling of crotoxin as a tool for biodistribution studies

Summary Crotoxin (Crtx) is the main toxin of South American rattlesnake (Crotalus durissus terrificus) venom. Research on antitumoral drugs has demonstrated the potential use of Crtx as tumour reducing agent. Tissue distribution studies are very important for clinical use and ^99mTc-labeling is a very convenient method for studies related to biodistribution. The aim of the present study was to label Crtx with ^99mTc keeping its biological activity for use in biodistribution and binding studies. High labeling yield was obtained using stannous chloride and sodium borohydride. Results demonstrated that biological activity of ^99mTc-Crtx was preserved and confirmed kidneys as the target organ. Biological activities of unlabeled and ^99mTc-labeled Crtx were evaluated after labeling. ^99mTc-Crtx can be a useful tool for imaging and binding studies.     

Stoichiometric Determination of Carbon in Ceramic Materials by Low Energy Deuteron Activation Analysis

The ¹²C(d,n)¹³N reaction, at 2 MeV, was used for the stoichiometric determination of carbon in reference materials and sintered pellets of SiC ceramics. The preliminary results show higher percentage of carbon on the surface in comparison to the core of the sintered ceramics, indicating the existence of carbon contamination on the surface, possibly caused by the sintering process itself.     

Dielectric behavior and impedance analysis of lead-free CuO doped (Na0.50K0.50)0.95(Li0.05Sb0.05Nb0.95)O3 ceramics

Pure (Na_0.50K_0.50)_0.95(Li_0.05Sb_0.05Nb_0.95)O₃ (NKNLS) and CuO doped NKNLS perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. x wt% of CuO (x = 0.2–0.8 wt%) was added in the NKNLS ceramics. X-ray diffraction patterns indicate that single phase was formed for pure NKNLS while a small amount of second phase (K₆Li₄Nb₁₀O₃₀ ∼ 3%) was present in Cu²⁺ doped NKNLS ceramics. Dielectric anomalies around the temperatures of 120 °C and 350 °C have been identified as the ferroelectric–paraelectric transition (orthorhombic to tetragonal and tetragonal to cubic) temperatures for pure NKNLS compound. The electrical behavior of the ceramics was studied by impedance study in the high temperature range. Impedance analysis has shown the grain and grain boundary contribution using an equivalent circuit model. The impedance response in pure and Cu²⁺ doped NKNLS ceramics could be resolved into two contributions, associated with the bulk (∼grains) and the grain boundaries. From the conductivity studies, it is found that activation energies are strongly frequency dependent. The activation energy obtained from dielectric relaxation data may be attributed to oxygen ion vacancies.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

Structural variations and cation distributions in Mn3−xCoxO4 (0 ≤ x ≤ 3) dense ceramics using neutron diffraction data

Single phase ceramics of cobalt manganese oxide spinels Mn_3?xCo_xO₄ were structurally characterized by neutron powder diffraction over the whole solid solution range. For x < 1.75, ceramics obtained at room temperature by conventional sintering techniques are tetragonal, while for x ≥ 1.75 ceramics sintered by Spark Plasma Sintering are of cubic symmetry. The unit cells, metal–metal and metal–oxygen average bonds decrease regularly with increasing cobalt content. Rietveld refinements using neutron data show that cobalt is first preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site for increasing x values. Structural methods (bond valence sum computations and calculations based on Poix's work in oxide spinels) applied to our ceramics using element repartitions and [M–O] distances determined after neutron data refinements allowed us to specify the cation distributions in all phases. Mn²⁺ and/or Co²⁺ occupy the tetrahedral site while Mn³⁺, Co²⁺, Co^III (cobalt in low-spin state) and Mn⁴⁺ occupy the octahedral site. The electronic conduction mechanisms in our highly densified ceramics of pure cobalt and manganese oxide spinels are explained by the hopping of polarons between adjacent Mn³⁺/Mn⁴⁺ and Co²⁺/Co^III on the octahedral sites.     

Measurement of total Zn and Zn isotope ratios by quadrupole ICP-MS for evaluation of Zn uptake in gills of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss)

This study evaluates the potential use of stable zinc isotopes in toxicity studies measuring zinc uptake by the gills of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). The use of stable isotopes in such studies has several advantages over the use of radioisotopes, including cost, ease of handling, elimination of permit requirements, and waste disposal. A pilot study using brown trout was performed to evaluate sample preparation methods and the ability of a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) system to successfully measure changes in the ⁶⁷Zn/⁶⁶Zn ratios for planned exposure levels and duration. After completion of the pilot study, a full-scale zinc exposure study using rainbow trout was performed. The results of these studies indicate that there are several factors that affect the precision of the measured ⁶⁷Zn/⁶⁶Zn ratios in the sample digests, including variations in sample size, endogenous zinc levels, and zinc uptake rates by individual fish. However, since these factors were incorporated in the calculation of the total zinc accumulated by the gills during the exposures, the data obtained were adequate for their intended use in calculating zinc binding and evaluating the influences of differences in water quality parameters.     

Sodium/lithium 3d transition metalates for chemisorption of gaseous pollutants: a review

Sodium/lithium transition metalates have found tremendous potential as cathode materials for Na/Li batteries. These metalates have acid-base and redox characteristics, which could be utilized for the chemisorption of gaseous pollutants. Their use was focused mainly on CO₂ gas chemisorption at elevated temperatures. In recent years, these materials have found interesting applications in the chemisorption of CO, NO, SO₂, and H₂S gases. Some of these alkali ceramics have shown tremendous potential for the wet-oxidative removal of acidic gases, even in ambient conditions. The review presents an up-to-date account of alkali ceramics of 3d transition metals for the chemisorption of toxic gases, including CO₂, CO, NO, SO₂, and H₂S. To the best of our knowledge, Na/Li 3d transition metalates have never been reviewed in the context of air decontamination, which needs to be presented to the readers for air purification applications.     

Microstructural Evolution and High-Performance Giant Dielectric Properties of Lu3+/Nb5+ Co-Doped TiO2 Ceramics

Giant dielectric (GD) oxides exhibiting extremely large dielectric permittivities (ε’ > 10⁴) have been extensively studied because of their potential for use in passive electronic devices. However, the unacceptable loss tangents (tanδ) and temperature instability with respect to ε’ continue to be a significant hindrance to their development. In this study, a novel GD oxide, exhibiting an extremely large ε’ value of approximately 7.55 × 10⁴ and an extremely low tanδ value of approximately 0.007 at 10³ Hz, has been reported. These remarkable properties were attributed to the synthesis of a Lu³⁺/Nb⁵⁺ co-doped TiO₂ (LuNTO) ceramic containing an appropriate co-dopant concentration. Furthermore, the variation in the ε’ values between the temperatures of −60 °C and 210 °C did not exceed ±15% of the reference value obtained at 25 °C. The effects of the grains, grain boundaries, and second phase particles on the dielectric properties were evaluated to determine the dielectric properties exhibited by LuNTO ceramics. A highly dense microstructure was obtained in the as-sintered ceramics. The existence of a LuNbTiO₆ microwave-dielectric phase was confirmed when the co-dopant concentration was increased to 1%, thereby affecting the dielectric behavior of the LuNTO ceramics. The excellent dielectric properties exhibited by the LuNTO ceramics were attributed to their inhomogeneous microstructure. The microstructure was composed of semiconducting grains, consisting of Ti³⁺ ions formed by Nb⁵⁺ dopant ions, alongside ultra-high-resistance grain boundaries. The effects of the semiconducting grains, insulating grain boundaries (GBs), and secondary microwave phase particles on the dielectric relaxations are explained based on their interfacial polarizations. The results suggest that a significant enhancement of the GB properties is the key toward improvement of the GD properties, while the presence of second phase particles may not always be effective.     

Preparation and Electrical Properties of Hydroxyapatite Containing Yttrium

Abstract

Hydroxyapatite (HAP) containing yttrium ion was synthesized and sintered for obtaining apatite ceramics with new functional properties. The preparation of the ceramics was carried out by synthesis using the wet process and by sintering under water vapor atmosphere. The product was recognized to be a solid solution. By substituting Y for Ca, O^2- and lattice defect (□) will form as follows: OH^? → O^2- + H₂O + □. Then, a following formula can be described for this solid solution produced:

Ca₁0-x^yx^(PO₄)2-x-2y^Ox+2y□y. The ionic conductivity of the product was measured by the ac two probe method. The plot.of conductivity-Y content relation gave a characteristic curve with a sharp peak at a fixed composition, Y=0.65. It was considered that this tendency was due to a change in the charge carrier in HAp crystal from OH- to H⁺ and O^2? with varying Y content. Electromotive force was observed in a water vapor cell assembled using the phosphate ceramics, and hydrogen gas generation was recognized. These phenomena led a fact that proton conduction exists in the ceramics. It was concluded that this ceramics will be used as a fuel cell.     

Copper‐Containing SiCN Precursor Ceramics (Cu@SiCN) as Selective Hydrocarbon Oxidation Catalysts Using Air as an Oxidant

A molecular approach to metal‐containing ceramics and their application as selective heterogeneous oxidation catalysts is presented. The aminopyridinato copper complex [Cu₂(Ap^TMS)₂] (Ap^TMSH=(4‐methylpyridin‐2‐yl)trimethylsilanylamine) reacts with poly(organosilazanes) via aminopyridine elimination, as shown for the commercially available ceramic precursor HTT 1800. The reaction was studied by ¹H and ¹³C NMR spectroscopy. The liberation of the free, protonated ligand Ap^TMSH is indicative of the copper polycarbosilazane binding. Crosslinking of the copper‐modified poly(organosilazane) and subsequent pyrolysis lead to the copper‐containing ceramics. The copper is reduced to copper metal during the pyrolysis step up to 1000 °C, as observed by solid‐state ⁶⁵Cu NMR spectroscopy, SEM images, and energy‐dispersive spectroscopy (EDS). Powder diffraction experiments verified the presence of crystalline copper. All Cu@SiCN ceramics show catalytic activity towards the oxidation of cycloalkanes using air as oxidant. The selectivity of the reaction increases with increasing copper content. The catalysts are recyclable. This study proves the feasibility of this molecular approach to metal‐containing SiCN precursor ceramics by using silylaminopyridinato complexes. Furthermore, the catalytic results confirm the applicability of this new class of metal‐containing ceramics as catalysts.     

Effect of heating rate on the sinterability,crystallization, and mechanical properties of sintered glass–ceramics from granite waste

Huge amounts of granite wastes have been generated in the granite-processing industry and should be properly disposed to reduce the negative impacts on the environment and health care. In this work, waste granite powder was modified and sintered to prepare high-strength and tough glass–ceramics. The heating rate was studied to clarify its effects on the sinterability, crystallization, and mechanical properties of glass–ceramics. With the increase in heating rate, the densification of sintered glass–ceramics was promoted by the liquid glassy phase from the microcline phase. The glass–ceramics were strengthened and toughened simultaneously due to the improved densification and increased crystallinity. The toughening mechanism was attributed to the crack bridging, deflection, and branching. The maximum flexural strength of 143 MPa and fracture toughness of 2.1 MPa m^1/2 were achieved with a heating rate of 50 °C min⁻¹, far superior to that of natural granite. The crystal structure of sintered glass–ceramics indicated the main crystalline phase of anorthite. These glass–ceramics with excellent mechanical properties promise the practical reutilization of granite wastes in the construction tiles.

     

透明Al2O3陶瓷中发光性能的研究

采用传统陶瓷工艺制备了不同MgO添加量的Al2O3透明多晶陶瓷;研究了Al2O3透明陶瓷的光谱性能,发现在410和294 nm处有明显的发射峰.通过对其激发和吸收光谱的研究,表明它们分别是由F+和F色心造成的.进一步的分析显示,这些色心是由于陶瓷中加入的添加剂MgO产生的氧空位所致.     

EPR,ENDOR and ESE investigations on chromium modified PbTiO3 ceramics

EPR and ENDOR studies show that chromium is incorporated in mono crystalline regions of the grains in PbTiO₃ ceramics as Cr⁵⁺ ions at Ti⁴⁺ sites. The local symmetry of the Cr⁵⁺ impurity is lower than of the host Ti⁴⁺ site in the crystallite. ESE measurements of the spin-lattice relaxation of the Cr⁵⁺ centre point to a structural transition at 10 K.