Application of poly(methylsilane) and Nicalon® polycarbosilane precursors as binders for metal/ceramic powders in preparation of functionally graded materials

For the first time, ceramic precursors were applied in the powder metallurgy (P/M) preparation of Functionally Graded Materials (FGM). Two types of FGMs were prepared: Al/SiC for possible aerospace applications and Cu/SiC for dynamic seal applications. There are two main advantages of using ceramic precursors for P/M preparation of FGMs (1) avoidance of the commercially used debinding step and (2) shrinkage control of the individual layers of the composite. This revised version was published online in November 2006 with corrections to the Cover Date.     

(1 − x)PNZ-xBT ceramics derived from mechanochemically synthesized powders

Nanosized (1−x)Pb(Zn_1/3Nb_2/3)O₃-xBaTiO₃ (PZN-BT, x=0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) powders were synthesized directly from their corresponding oxide mixture via a high-energy ball milling process. Almost single phase was achieved in the composition range of PZN-BT. The grain size estimated from SEM observation was about 50 nm, being in good agreement with that (20 nm) calculated from XRD patterns. PZN-BT ceramics were also obtained by sintering the synthesized powders at 1050°C for 1 h. The grain size of the final ceramics decreases from 4.5 to 1.2 μm as BT content increases from 0.05 to 0.30. The properties, such as microstructure, lattice constant, phase composition, dielectric constant as a function of composition of the PZN-BT ceramics, were investigated and discussed.     

A systematic study on solid-state synthesis of monticellite (CaMgSiO4) based ceramic powders obtained from boron derivative waste

Solid-state synthesis of monticellite based ceramic powders from boron derivative waste in an eco-friendly route and the investigation of phase transformation mechanisms were studied. The heat-treatment of boron derivative waste, mainly composed of dolomite, calcite and quartz, was systematically carried out at 650?°C and 800?°C for various dwell times between 1?min and 4?h. The heat-treatment temperatures were selected considering TG-DTA curves of waste and ΔG – T diagrams obtained using FactSage Thermochemical Software. XRF, XRD, FTIR, TG-DTA and SEM analysis, particle size measurement and crystallite size determination carried out extensively. The obtained results showed that monticellite based ceramic powder synthesized at 800?°C for 4?h was composed of monticellite, akermanite, diopside, calcium magnesium borate and zeolite. The calcination of dolomite was completed both at 650?°C for 1?h and up to 800?°C, and calcite was decomposed at 800?°C for 30?min. Both diopside and monticellite were firstly detected at 650?°C for 30?min and at 800?°C for 1?min. Also, akermanite was presented at 800?°C for 1?min. The presented method offers the lowest temperature (800?°C) in literature for synthesis of monticellite and akermanite which reduces the energy consumption during heat-treatment.     

Preparation of ultra-fine cobalt-nickel manganite powders and ceramics derived from mixed oxalate

Co_0.30Ni_0.66Mn_2.04O₄ negative temperature coefficient ceramics were derived from mixed oxalate Co_0.30Ni_0.66Mn_2.04(C₂O₄)₃·nH₂O. The mixed oxalate was synthesized by milling a mixture of cobalt acetate, nickel acetate, manganese acetate, and oxalic acid at room temperature. An ultra-fine Co_0.30Ni_0.66Mn_2.04O₄ powder was obtained by calcining the mixed oxalate in air at 800 °C for 3 h. The oxide powder compact was sintered at a relatively low temperature of 1100 °C for 5 h, achieving a relative density of ∼98%. The specific resistivity ρ_25 °C and the thermal constant B_25/85 °C were 765.2 Ω cm and 3604 K, respectively. The resistance drift after aging at 150 °C for 500 h was 1.5%.     

Isopropanol-assisted hydrothermal synthesis of (K, Na)NbO3 piezoelectric ceramic powders

(K, Na)NbO₃ particles were synthesized using the isopropanol-assisted hydrothermal method. The addition of isopropanol made it possible to prepare (K, Na)NbO₃ solid solutions under a mild hydrothermal condition of 2 mol/L alkali solution. The effects of the K/(K + Na) molar ratio, (K + Na)/Nb molar ratio in the starting suspensions, and annealing process on the phase evolutions of the (K, Na)NbO₃ solid solutions were investigated. The phases of the as-prepared particles were investigated by X-ray diffraction technique. The microstructure and composition were analyzed by scanning electron microscope and energy dispersive X-ray analysis. (K, Na)NbO₃ solid solutions were successfully synthesized by hydrothermal method with the addition of isopropanol through adjusting the K/(K + Na) molar ratio and (K + Na)/Nb molar ratio in the starting suspensions. The change of morphology is also in agreement with the phase evolution. The phase evolutions were discussed and the formation mechanism of the (K, Na)NbO₃ solid solutions was proposed.     

Synthesis and characterization of CaO-stabilized ZrO2 fine powders for oxygen ionic conductors

13 mol% calcia-stabilized zirconia (CSZ) powders were synthesized by the coprecipitation method. The characterization of powders has been investigated using thermogravimetry and differential thermal analysis for thermal analysis, X-ray diffraction and infrared spectroscopy for crystalline phases identification, Brunauer-Emmett Teller, X-ray diffraction-line broadening and transmission electron microscopy (TEM) for particle size and morphology determination. The characteristics of powders prepared by the coprecipitation method are discussed.     

陶瓷微滤膜洗涤碱法制备Al(OH)3中杂质Na+的研究

采用无机陶瓷微滤膜,以错流过滤方式对工业上碱法生产的Al(OH)3粉体浆料进行Na^ 离子的清洗过滤研究．实验考察了操作压力、错流速率、浆料浓度等工艺参数的影响,确立了适合于超细粉体膜清洗过滤的工艺条件．经过陶瓷膜洗涤过滤过程,Al(OH)3粉体粒子仍保持其原始形貌,但粉体的分散性和纯度获得大幅度提高,膜清洗后的Al(OH)3粉体中Na2O含量降为57mg／kg;粒径尺寸约为50nm．研究结果表明,膜清洗过滤效率、操作方式以及产品质量等方面均明显优于目前工业生产上普遍应用的板框压滤机,为无机陶瓷微滤膜技术应用于碱法制备Al(OH)3工艺中的洗涤过滤提供了科学与工程化依据．     

A refined,self-consistent Poisson-Nernst-Planck (PNP) model for electrically induced transport of multiple ionic species through concrete

A fundamental re-look of the use of Poisson-Nernst-Planck (PNP) model for predicting electrically accelerated ionic transport through concrete is carried out. The PNP model is augmented with concentration-based diffusion coefficients and explicit considerations of transport path in the formulations since the electric field is distributed only along the connected pore path. The geometric tortuosity obtained from electrical property measurements is modified with a multiplicative correction factor that is a function of the ratio of dominant pore sizes in the specimen. Idealized models of the pore structure are used to arrive at this correction factor, which ranges between 1.5-to-3.0 for typically used concretes. Time-dependent changes in boundary conditions induced by the electrode reactions are also accounted for. The effect of chloride binding as a time-dependent process during the test, is also ascertained. The model is verified on a series of concretes of different water-to-cement ratios and containing different cement replacement materials (fillers and/or reactive materials) subjected to the non-steady state migration test.     

Synthesis and Characterization of Fe_(50)Cr_(14)Mo_(14)C_(14)B_6Gd_2 Bulk Amorphous Steel

Bulk amorphous steel having 7 mm thickness was synthesized to evaluate its thermal stability and mechanical properties.The steel was synthesized by Cu mold casting technique using 1-2N pure metals.Characterization of the material was done by X-ray diffraction,differential scanning calorimetry and scanning electron microscopy.The activation energies were calculated by Kissinger equation and it was found that the steel had better stability against crystallization.Mechanical properties like Vicker s hardness,n...     

Effect of the structure of bidentate neutral organophosphorus compounds on the extraction of Sr(II) from aqueous solutions in the presence of ionic liquids

The extraction of microamounts of Sr(II) from aqueous solutions with solutions of bidentate neutral organophosphorus compounds is considerably enhanced in the presence of ionic liquids. The efficiency of the Sr(II) extraction varies in a wide range depending on the nature of the coordinating groups in the extractant molecule, substituents at the P and N atoms, and structure of the fragment linking the coordinating groups.     

Separation of fluoride from aqueous solution by electrodialysis: effect of process parameters and other ionic species

Removal of fluoride from aqueous solution by electrodialysis was studied. Applied voltage, feed flow rate, fluoride concentration in the solution and effect of the other anions as sulfate, chloride were investigated as experimental parameters on fluoride removal from aqueous solution. The separation performance was evaluated in terms of mass transfer and energy consumption. It was obtained that the separation performance increased when the initial concentration of fluoride in the feed solution increased. Percent removal of fluoride increased as the applied potential increased. However, the effect of feed flow rate was not apparent in the range of applied feed flow rate. Separation of fluoride was influenced by chloride but not by sulfate ions.     

Synthesis and characterization of novel poly(aryleneethynylene)s derived from squaraines for photovoltaic applications

Two novel π-conjugated polymers composed of alkyl carbazole/dialkoxyphenylene and squaraine units were synthesized by Sonogashira cross-coupling reactions. The structures and properties of these copolymers were characterized using FT-IR, NMR, UV–Vis, gel permeation chromatography and cyclic voltammetry (CV). Both polymers possess adequate thermal stability and exhibit good solubility in common organic solvents such as chloroform, THF, and toluene. The polymer films show intense and broad visible and near IR absorption with the long wavelength absorption maximum peaks of 796 and 851 nm for P ₁ and P ₂ , respectively, which are apparently red-shifted compared with poly(phenyleneethynylene). CV studies reveal that the band gaps of these copolymers are about 1.45 eV, implying that the resulted polymers may be promising candidates for solar cells.     

Luminescence properties of YAG:Nd 3+ nano-sized ceramic powders via co-microemulsion and microwave heating

Nano-sized ceramic powders with weaker aggregation of Nd ^{3 +}-doped yttrium aluminum garnet (YAG:Nd ^{3 +}) were synthesized via co-microemulsion and microwave heating. This method provides a limited small space in a micelle for the formation of nano-sized precursors. It also requires a very short heating time, thus reducing energy consumption in comparison with conventional solid-state sintering processes. As a result, small-sized particles with narrow size distribution, weaker aggregation and high purity were obtained. Powder X-ray diffraction results revealed that the structure of pure YAG:Nd ^{3 +}nanoparticles was cubic garnet. Transmission electron microscopy results indicated that the synthesized particles were almost spherical with average diameters of 40 and 80 nm. The luminescent properties of YAG:Nd ^{3 +}were investigated through PL. Under excitation at 488 nm, YAG:Nd ^{3 +}nano-sized ceramic powders showed main emission bands of 1045–1080 nm because of ⁴ F _3/2 → 4 I _11/2 transitions that are identical to those observed for a single YAG:Nd ^{3 +}crystal.     

Strengthening of poly-crystalline (ceramic) Nd:YAG elements for high-power laser applications

In the last decade, poly-crystalline (ceramic) Nd:YAG components emerged as very promising candidates for high-power lasers, exhibiting some advantages over single-crystal Nd:YAG ones. Such devices are required to endure high thermal stress during operation. In our present work we present experimental results on the strengthening of poly-crystalline YAG and Nd:YAG fine-ground components by chemical etching in hot ortho-phosphoric acid. The strength of poly-crystalline Nd:YAG laser rods was measured inside a laser head by applying the pump power till rod fracture. A factor of ∼3 increase in the fracture longitudinal heat power density for etched poly-crystalline Nd:YAG rods as compared to standard commercial poly-crystalline rods was obtained. This effect is similar to our previous results on single-crystal Nd:YAG laser rods which showed a factor of 3.6-5.0 increase in tensile strength by the same treatment. A modified Weibull analysis was used to assess the fracture probability parameters.     

Co-delivery of drug and DNA from cationic dual-responsive micelles derived from poly(DMAEMA-co-PPGMA)

The synthesis and gene transfection efficiency of a series of amphiphilic copolymers with poly(dimethylaminoethyl methacrylate) (PDMAEMA), and poly(propylene glycol methacrylate) (PPGMA) segments is reported. The hydrophobic PPGMA interior allows a cell-sensitizing drug such as paclitaxel to be incorporated while the cationic and hydrophilic PDMAEMA corona allows the complexation of anionic DNA to form a nano-sized polyplex. These drug-encapsulated copolymers display excellent gene transfection efficiency as compared to PEI or PDMAEMA homopolymers.     

Optimization of sintering temperature for realizing enhanced magnetic properties of YFeO3 ceramic derived from the sol-gel technique

Journal of Materials Science: Materials in Electronics - In the present communication, we are reporting the optimization of sintering temperature to realize the highest magnetization value from...