Electrochemical Processing of Reaction-bonded Ceramic Composite Coatings

Ceramic matrix composite coatings are currently of much interest for application in high-temperature and highly corrosive environments. Formation of ceramic coatings by electrochemical processing is a relatively new mean^[1-2]. It presents several advantages over alternative coating techniques, the thickness and morphology of the deposit can be controlled by the electrochemical parameters, relatively uniform deposits are obtainable on complex shapes, the deposition rate is higher than that using most other methods and the equipment required is of low cost Recently we developed a novel fabrication technique for the production of ceramic/ceramic and ceramic/metal composite coatings by electrochemical processing^[3]. The technique combined two electrochemical deposition methods, electrophoretic deposition (EPD) and electrolytic deposition (ELD), which can produce uniform composite layers of closely controlled thickness on both metallic and ceramic substrates at ambient temperature with inexpensive equipment. However, the main problem associated with electrochemical processing is the difficulty in sintering of the coatings. First, high temperature is required for sintering of the coatings. Secondly, the volume shrinkage of the coatings during sintering leads to the formation of cracks in coatings bonded to metal substrates. So a reaction forming technique, reaction bonding process, also has been developed to produce near net-shape ceramic coatings, which overcome problems caused by the shrinkage of ceramics during sintering.     

Kinetic Exponents of Grain Growth in Practical and Simulated ABO3 Ceramics

It is now established that there is a strong correlation between the physical properties of ceramics and their microstructures, which result mainly from the grain growth process^[1-3]. Therefore, the study of grain growth during the ceramic evolution is one of fundamental importance^[4-6].     

Enhancement of luminescence efficiency of f–f transitions from Tb due to energy transfer from Ce in Al2O3 crystalline ceramic powders prepared by low temperature direct combustion synthesis

In this Letter, we report the structural and luminescent properties of Tb:Ce:Al₂O₃ crystalline ceramic powders prepared through combustion synthesis at low temperature (280 °C). The presence of Ce³⁺ (1.0 mol%) in the sample resulted in an enhancement of Tb³⁺ (1.0 mol%) overall emission intensity by a factor of 50. The analysis of the luminescence dynamics for the ⁵D₄ → ⁷F₆ transition (545 nm) of Tb³⁺ demonstrated that the mechanism responsible for the large enhancement of luminescence observed is efficient energy transfer from Ce³⁺ to Tb³⁺.     

Ce1-xGdxO2-x/2的溶胶-凝胶法合成及其性质

利用溶胶-凝胶法合成了Ce₁-xGdxO_2-x/2(x=0.1～0.6)系列固体电解质,系统地研究了其结构、热膨胀系数和导电性.XRD结果表明,160℃即完全形成立方萤石结构.由于溶胶-凝胶法合成的物质粒度均匀,颗粒小,故在较低温度(1300℃)时即可形成高致密样品,此温度明显低于传统的高温固相法烧结温度(1600～1650℃).高温X射线衍射测得Ce_0.8Gd_0.2O_1.9的热膨胀系数为8.125×10^-6K₁.阻抗谱表明,溶胶-凝胶法合成可减少或消除固体电解质的晶界电阻,600℃时Ce_0.8Gd_0.2O_1.9的电导率为5.26×10^-3S/cm,活化能E_a=0.82eV.     

Realization of Low Temperature Densification of Nickelate Ceramics for MLCC Application

We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates the formation of nickelate phase through solid state reaction. Moreover, although high-purity nickelate powders can only be obtained by calcining the mixture of starting materials at temperature higher than 1100 oC. The adoption of powders calcined at 1000 oC, rather than those calcined at higher temperature, is conductive to the low-temperature densification of nickelate ceramics, which is attributed to the small and dispersive particles, and the solid state reaction of the residual starting materials during sintering. Compared with the conventional process, the improved method can reduce the sintering temperature of nickelate ceramics by about 100 oC and decrease the grain size of the obtained ceramics, and therefore makes nickelate meet the fabrication requirements of multi-layer ceramic capacitors(MLCC).     

酸性溶液中SO2选择性还原分解钨过氧配合物——钨中微量钼的除去

用SO₂还原4:2钨过氧配合物[H₄W₄O₁₂(O₂)₂]已被作为在室温和低酸度条件下生产钨酸的一种新方法--络合均相沉淀法^[1,2].有意义的是,这一方法还能用SO₂对钨、钼过氧配合物的选择性分解,同时除去钨中的微量钼.本文研究了不同游离酸度和不同反应温度条件下选择性分解时的除钼效果,并初步给予理论上的解释.     

Thermal analyses applied to ceramic nanopowders: from synthesis to sintering

The free sintering of ceramic powders into fully dense nanostructured materials is still a challenging process, even more complex when nanostructured transition alumina is used as starting powder. In this paper, biphasic (Alumina–YAG) and triphasic (Alumina–YAG–ZrO₂) composite powders were produced by doping the same nanocrystalline transition alumina with inorganic precursors of the second-phases, which were subsequently yielded under controlled thermal treatments. The added dopants significantly increased both the θ- to α-phase transformation and the sintering temperatures, making even more difficult the retention of the starting nanometric grain size into the final dense materials. Thermal analyses (such as TG–DTA and dilatometry) are here used to support most of the ceramic processing steps involved in a successful elaboration of the desired ultra-fine structures. In fact, the thermal pre-treatments of the doped powders were set up on the ground of the DTA–TG curves whereas the dilatometric analyses were exploited to design optimised sintering cycles, through which the green bodies were successfully consolidated into fully dense materials, characterised by highly homogeneous and tailored micro/nanostructures.     

Reactivity of tri- and tetra-nuclear ethylidyne cyclopentadienylcobalt clusters towards protonic acids

The bis(μ₃-ethylidyne) tricobalt cluster [(CpCo)₃(μ₃-CCH₃)₂] (1b) is protonated by trifluoroacetic acid to give the dicobalt edge-protonated cation [H(CpCo)₃(μ₃-CCH₃)₂]⁺ [lb + H]⁺. Protonation of the μ₃-ethylidyne tetracobalt cluster hydride [H(CpCo)₄(μ₃-CCH₃)] (3) takes place in two consecutive steps. At low temperature [H₂(CpCo)₄(μ₃-CCH₃)]⁺ [3 + H]⁺ is formed first, and is then slowly converted into [H₃(CpCo)₄(μ₃-CCH₃)]²⁺ [3 + 2H]²⁺ by an excess of acid. As judged by the ¹H NMR data and the crystal structure of [3 + X]⁺[(CF₃COO)₂X]⁻ (X = H or D) the endo hydrogens in [3 + H]⁺ and [3 + 2H]²⁺ occupy μ₃-(Co₃) face capping hydridic positions. The cations [1b + H]⁺ and [3 + H]⁺ show hydride fluxionality in solution, which in the case of [3 + H]⁺ can be frozen out on the NMR timescale at low temperature (ΔG ^≠ (203 K) = 40.8 kJ/mol). The structure of [3 + X]⁺ [(CF₃COO)₂X]⁻ (X = H or D) was determined by X-ray crystallography. One of the hydrides/deuterides is located on the crystallographic mirror plane, capping a tricobalt face of the cluster cation. The other endo hydrogen atom is believed to be disordered between the other two μ₃-(Co₃) sites, which are related by space group symmetry. Deuteronation of 3 shows a strong normal kinetic deuterium isotope effect. From the temperature independence of the ¹H NMR spectrum of [3 + 2D]²⁺ a non-fluxional solution structure can be inferred. In all the systems studied, hydridic (μ₂- or μ₃-) sites are thermodynamically preferred to possible isomeric agostic CoHC or Co₂HC sites for the endo hydrogens. Agostic interactions cannot, however, be ruled out in transient intermediates during the course of the protonations.     

Synthesis of Silica Hollow Spheres with Diameter Around 50 nm by Anionic Surfactant

Silica hollow spheres(SHSs) have attracted great attention because of their low toxicity,low density,large surface area,high chemical and thermal stability,and surface permeability.They can be widely applied in storage[1],catalysis[2],drug delivery[3,4],low-dielectric-constant materials[5],low-refractive materials[6-8],and so on.Up to now,there have been various methods to produce SHSs.Inorganic[9] or organic particles[10],such as polystyrene or calcium carbonate,were used as hard templates to create hollow cavities.However,the multistep synthetic process and the lack of structural robustness of the shells upon template removal process weaken their application.Soft templates,including oil-in-water emulsions[1],[2],vesicles[13],micelle[14,15] and gas bubbles[16],are applied widely.     

Two lanthanide（Ⅲ）-copper（Ⅱ） chains based on [Cu2Ln2] clusters exhibiting high stability,magnetocaloric effect and slow magnetic relaxation

Two 3d-4f heterometallic one-dimensional chains with neutral 4,4＇-bipyridine ligands as linkers and[Cu2Ln2] clusters （Ln = Gd for 1, Dy for 2） as nodes have been hydrothermally synthesized and structurally characterized. Magnetic studies indicate that complex 1 exhibits a relatively large magnetocaloric effect, with an entropy change -△Smax m= 24.8 J kg 1 K^-1, whilst, complex 2 features slow magnetic relaxation at low temperature.     

Electrophoretic Deposition of Hydroxyapatite from Non-aqueous Media

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA) is an important material for bone and tooth implants, as its chemical composition is similar to that of bone tissue. Owing to the inferior mechanical properties of HA, significant research activity has been associated with the development of HA coatings and composites. The interest in electrophoresis for biomedical applications steins from a variety of reasons such as the possibility of deposition of stoichiometric, high purity material to a degree not easily achievable by other processing techniques and the possibility of forming coatings and bodies of complex shape^[1]. In this work, the experimental results of a study of electrophoretic deposition of HA powders, performed in isopropyl alcohol or ethanol as a suspension medium, are reported.     

A New Chemiluminescence Method for the Determination of Pyrogallol

Pyrogallol(Py) is a chemiluminescence(CL) reagent with a low emission efficiency. The pyrogallol structural group is also found in molecules of many important natural and synthetic confounds, such as gallic acid humic acid and pyrogallol red. Studies of the metablism of phenolic compounds requires the development of specific and sensitive methods for the determination of pyrogallol. HPLC^[1], spectrophotometry^[2] and CL^[3-7] have been used to determined polyphenols, but these methods are complicated or low sensitivity.In this paper, a new Chemiluminense(CL) analytical method for determination of Py was established.This method is more sensitive than those methods reported in the literature^[3-7].     

Vanadium-based Mixed Oxides Prepared from Thermal Decomposition of Citratorvanadium(IV) Precursor

Citrate method is broadly used for the preparation of mixed oxides and their highly dispersive pure phases^[1]. Up to now, most of the mixed oxides are prepared from putting the related chemical compounds together and sintering the mixture at high temperature, while the complexes formed during this process are uncertain. This will limit the design of high dispersibility and the purities of the resulted mixed oxides. Vanadium-based oxides are catalysts used in the partial oxidation of propane and butane. It has been demonstrated previously that the vanadium citrate complex with well-defined composition and structure is the better precursors for the preparation of V-based mixed oxide^[2], Using the precursor of barium dimeric(citrato) oxovanadium(IV) tetrahydrates Ba₂[VO(cit)]₂·4H₂O, barium pyrovanadate may be prepared with pre-determinated compositions and higher purities from thermal decomposition of the well-defined complexes at lower temperature.     

The High-spin↔Low-spin Equilibrium of Iron(Ⅱ) Complexes with Schiff Base Ligand:Optical,Magnetic and Spectroscopic Properties

Spin transition compounds are of great interest because of their potential application in molecular based electronic devices such as optical memoty and switch, display and data record^[1]. The occurrence of iron(Ⅱ) spin crossover systems depends on the ligand field strength. Iron(Ⅱ) spin crossover compounds mainly have sixfold nitrogen coordination and the range of lODq is very narrow:10Dq^HS≈11500-12500 cm^-1 and 10Dq^LS≈19000-21000 cm^-1[2]. The sensitivity of the spin state to small perturbations suggests that new coordination complexes exhibiting spin transition phenomena could be designed through a fine tuning of the ligands surrounding the metal. The derivatives of 1,2,4-triazole have been found to generate an intermediate ligand field force and the iron(Ⅱ) compounds containing such ligands which yielded spin-crossover materials exhibiting cooperative behavior have been reported recently^[3]. In this paper we present two new iron(Ⅱ) compounds FeL₃(ClO₄)₂·2H₂O (1) and FeL₃(BF₄)₂·3H₂O (2),where L is the Schiff base ligand derived from 4-amino-l,2,4-triazole and benzaldehyde. The compounds appear as white (HS) powders at room temperature and the color changes to pink (LS) upon decreasing the temperature to liquid nitrogen. 1 and 2 are investigated by the optical setup (520 nm, 293-77 K), ⁵⁷Fe Mössbauer Spectroscopy (293-77 K) and magnetic susceptibility (293-4 K). The HS→LS and LS→HS transitions were observed at Tc↓=135 K (1) and 169 K (2), and Tc↑=150 K (1) and 180 K (2), respectively. The thermal hysteresis is found to be 15 K and 11 K for 1 and 2. The area fractions are calculated to be 57% for 1 and 43% for 2. Variable temperature magnetic susceptibility data were fitted to magnetic susceptibility equations derived from domain model, two level Ising-type model and regular solution model. The calculated variations of enthalpy and entropy of the compounds fall within the limits ΔH≈8.1-10.9 kJ·mol^-1 and ΔS≈47-61 J·K^-1·mol^-1 found for mononuclear iron(Ⅱ) spin transition compounds from calorimetric measurements. The cooperativity parameter y determines the occurrence of hysteresis.     

取代基对咪唑[4,5-f]-1,10-邻菲罗啉Ru(Ⅱ)配合物的温敏性能影响

合成了3种具有不同取代基的咪唑[4, 5-f]-1,10-邻菲罗啉配体L¹~L³及其Ru(Ⅱ)配合物[Ru(L¹)₃]、[Ru(L²)₃]和[Ru(L³)₃],并进行了表征。这些Ru(Ⅱ)配合物在溶液中具有π→π^*跃迁吸收峰和金属到配体的电荷转移跃迁(MLCT)吸收峰,其发光峰位约为590 nm左右。将Ru(Ⅱ)配合物掺杂到聚甲基丙烯酸甲酯(PMMA)中得到相应的温敏漆。Ru(Ⅱ)配合物在PMMA膜中的吸收峰精细结构消失,且在长波方向663 nm附近有新的发射峰,表明Ru(Ⅱ)配合物在PMMA膜中有聚集。温度升高后,Ru(Ⅱ)配合物在PMMA膜中的发射峰强度逐渐减弱。分别计算了在30~60 ℃和60~90 ℃区间内非辐射活化能E_nr和温度灵敏度S_T。结果表明,具有苯基取代的咪唑[4, 5-f]-1,10-邻菲罗啉配体的[Ru(L¹)₃]配合物,比咪唑[4, 5-f]-1,10-邻菲罗啉Ru(Ⅱ)配合物[Ru(L²)₃]及烷基取代基的咪唑[4, 5-f]-1,10-邻菲罗啉Ru(Ⅱ)配合物[Ru(L³)₃]具有更高的温度灵敏度。     

Palladium-Catalyzed Carbonylative Reaction of Iodine Heterocyclic Compound with Alcohol

In the past few decades, much attention has been focused on palladium-catalyzed carbonylative reactions^[1,2], which is a simple method to synthesize some complicated compounds^[3,4]. This kind of reactions, however, can be carried out only when the substrates are arylhalide, heteroaryl halide, alkene halide,aryltrifluoromethyl-sulfonate and hypervalent iodonium salt^[5] etc. Herein, we report a palladium-catalyzed carbonylative reaction between 3,7-bis(N,N-dimethylamino)-10H-dibenz[b,e] iodinium iodide(1)^[6] with alcohols (2) at ambient temperature as shown in scheme.     

Quantitative analysis of fluorimated ethylchloroformate derivatives of non-protein amino acids using positive and negative chemical ionization gas chromatography-mass spectometry

The GC-MS characterization of the ethylchloroformate derivatives of amino acids in an aqueous medium has been applied to non-protein amino acids. Derivatization of non-protein amino acids using ethylchloroformate, trifluoroethanol, and pyridine produced strong [M + 1]⁺ and [M - 1]⁻ ions in positive and negative chemical ionization (CI) modes, respectively. Twenty-one out of the twenty-three non-protein amino acids studied produced detectable ion chromatograms in both ionization modes when methane was used as the CI reagent gas. Mass spectra of these non-protein amino acid derivatives showed characteristic [M - 19]⁺, [M + 1]⁺, [M + 29]⁺, and [M + 41]⁺ peaks in the positive chemical ionization mode, and [M - 1]⁻, and [M + 35]⁻ peaks in the negative chemical ionization mode. The detection limits and the linear dynamic range of trifluorethanol ethylchloroformate derivatives of non-protein amino acids were studied using positive chemical ionization. The detection limits are mostly in the femtomole range.     

Synthesis of Carbon Nanotubes:A New Solid-state Approach

In recent years, investigation on layered double hydroxide materials (LDHs, anionic clays) becomes an active field in layered materials research owing to their many important applications^[1-7]. Among the LDHs, hydrotalcite-like compounds (HTlcs) have attracted great attention due to their synthetic flexibility in preparing catalyst and ceramic precursors, and in tailor-making adsorbents, medicine stabilizers, and ion exchangers^[1,2]. In the structure of HTlcs, divalent and trivalent cations are located in the center of oxygen octahedron formed by six hydroxyl groups of the two-dimensional brucite-like sheets^[1,2]. To balance the extra charges carried by trivalent cations, anions have to be intercalated into the inter-brucite-like-sheet space (interlayer space) during the synthesis, which leads to the formation of a sandwich-like structure alternatively stacked in vertical direction of the sheets (c-axis), forming a 3D structure.     

[C3mim][NTf2]/DEC/[Li][NTf2]体系的基础性质

The hydrophobic ionic liquid (IL) 1-propyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₃mim][NTf₂]) was synthesized according to traditional methods. By adding different amounts of diethyl carbonate (DEC) solvent and lithium bis[(trifluoromethyl)sulfonyl]imide ([Li][NTf₂]) salt to [C₃mim][NTf₂] IL, eight solution systems were prepared. First, the thermodynamic properties of the eight solution systems were characterized by differential scanning calorimetry (DSC). The semi-stable temperature of the system gradually disappeared with increasing lithium salt content, but the melting point temperature was not apparent in the experiment. These results indicate that DEC and lithium salts can dissolve in ILs within the tested temperature range. The basic properties of the eight systems, including thermodynamic and dynamic properties, were systematically studied at different temperatures. The variation in the self-diffusion coefficient of lithium ion ([Li]⁺) as a function of DEC concentration, density changes, viscosity, conductivity, and the viscosity/conductivity activation energy of the eight systems was calculated by the Vogel Fulcher Taman (VFT), Final Vogel Fulcher Taman (FVFT), and Arrhenius equations. The effect of temperature on the properties of the system was studied in detail. Within the temperature range measured herein, the deviation between the fitting equation and experimental value was small. Consequently, these equations were successfully used to calculate the properties of the system at various temperatures. All fitting parameters of the corresponding equations are provided herein. The viscosity for all systems decreased rapidly with increasing temperature, which increased the conductivity. Based on these experiments, the influence of DEC on the system microstructure was discussed in the context of the molecular dynamics simulation results. In particular, the interaction between [Li]⁺ and [NTf₂]^-/DEC was examined. In all solution systems, [NTf₂]^- coordinates to [Li]⁺ through only the O atom and not the N atom. Radial distribution function (RDF) analysis showed that the interaction between [Li]⁺ and [NTf₂]^- weakened with increasing DEC concentration. DEC molecules were observed in the first solvation layer of [Li]⁺ coordinating to [Li]⁺ through the carbonyl O atom. Although the interaction between [Li]⁺ and DEC was weakened, competition between [NTf₂]^- and DEC in the first solvation layer of [Li]⁺ was observed by the coordination number analysis of the O atom around [Li]⁺. Therefore, the introduction of DEC is beneficial for Li⁺ diffusion, which is consistent with the experimental results.     

还原氧化石墨烯/TiO2复合材料在钠离子电池中的电化学性能

二氧化钛(TiO₂)作为有前景的钠离子电池负极材料, 具有良好的循环稳定性, 但由于其导电率较低, 而导致容量和倍率性能不佳限制了其实际应用. 本文采用喷雾干燥技术制备了氧化石墨烯/纳米TiO₂复合材料(GO/TiO₂), 通过热处理获得还原氧化石墨烯/TiO₂复合材料(RGO/TiO₂). 电化学测试结果表明, 还原氧化石墨烯改性的RGO/TiO₂复合材料的电化学性能得到显著提升, RGO含量为4.0%(w)的RGO/TiO₂复合材料在各种电流密度下的可逆容量分别为183.7 mAh·g^-1 (20 mA·g^-1), 153.7 mAh·g^-1 (100 mA·g^-1)和114.4 mAh·g^-1 (600mA·g^-1), 而纯TiO₂的比容量仅为93.6 mAh·g^-1 (20 mA·g^-1), 69.6 mAh·g^-1 (100 mA·g^-1)和26.5 mAh·g^-1 (600mA·g^-1). 4.0%(w) RGO/TiO₂复合材料体现了良好的循环稳定性, 在100 mA·g^-1电流密度下充放电循环350个周期后, 比容量仍然保持146.7 mAh·g^-1. 同等条件下, 纯TiO₂电极比容量只有68.8 mAh·g^-1. RGO包覆改性极大提高了TiO₂在钠离子电池中的电化学嵌钠/脱钠性能. RGO包覆改性技术在改进钠离子电池材料性能中将有很好的应用前景.