Study of Ceramic Slurries for Investment Casting with Ice Patterns

Ice patterns generated by rapid freeze prototyping or a molding process can be used to make ceramic investment molds for metal castings. Due to the use of ice, the ceramic slurries must be poured around the pattern and cured at sub-freezing temperatures. Success of this process depends greatly on the mold strength after the gelation of the slurries. This paper describes the experimental results of the mold strength after the gelation of the slurries under different compositions. The parameters considered include mixing time, alumino-silicate vs. fused silica ratio, volume of binder, and volume of catalyst. The strength of the gelled slurries is examined by breaking test bars on a four-point bending apparatus. Weibull modulus for each trial is calculated based on the breaking strength from four-point bend tests. Analysis of variance for breaking strength and Weibull analysis is performed to evaluate the significance of the effect of each parameter. The casting of a bolt is used to demonstrate that metal castings of complex geometry can be fabricated using investment casting with ice patterns.Mechanical Engineerin

Dichloropalladium complexes ligated by 4,5-bis(arylimino)pyrenylidenes: Synthesis, characterization, and catalytic behavior towards Heck-reaction

A series of 4,5-bis(arylimino)pyrenylidenylpalladium(II) chloride complexes (C1–C4) were synthesized and characterized by FT-IR and NMR spectroscopy, elemental analysis as well as by single crystal X-ray diffraction for the representative complexes C1 and C3, which revealed a square planar geometry at the palladium center. All palladium complexes exhibited high activity for the Heck cross-coupling reaction, which were effective when conducted in various solvents. Furthermore, the in-situ mixture of palladium dichloride and the ligand (L1) provided an effective catalytic system for the Heck-reaction

Synthesis, characterization and ethylene polymerization behaviour of binuclear nickel halides bearing 4,5,9,10-tetra(arylimino)pyrenylidenes

Pyrene-4,5,9,10-tetraone was prepared via the oxidation of pyrene, and reacted with various anilines to afford a series of 4,5,9,10-tetra(arylimino)pyrenylidene derivatives (L1–L4). The tetraimino-pyrene compounds L1 and L2 were reacted with two equivalents of (DME)NiBr₂ in CH₂Cl₂ to afford the corresponding dinickel bromide complexes (Ni1 and Ni2). The organic compounds were fully characterized, whilst the bi-metallic complexes were characterized by FT-IR spectra and elemental analysis. The molecular structures of representative organic and nickel compounds were confirmed by single-crystal X-ray diffraction studies. These nickel complexes exhibited high activities towards ethylene polymerization in the presence of either MAO or Me₂AlCl, maintaining a high activity over a prolonged period (longer than previously reported dinickel complex pre-catalysts). The polyethylene obtained was characterized by GPC, DSC and FT-IR spectroscopy and was found to possess branched features

Manufacturing optimizations for micro-tubular fuel cells by extrusion and dip coating techniques

The optimisation of micro-tubular Solid Oxide Fuel Cells (mSOFCs) was studied, including anode extrusion, electrolyte dip coating and heat treatment of the resultant half-cells. The study of NiO-YSZ anode extrusion started with an analysis of powder packing, followed by the determination of the optimum liquid content required to produce reliable roll milled viscous paste mixtures. Rheological tests were carried out using a simple die configuration to predict the extrusion pressure during the anode processing. The mechanisms, which lead to differences between the predicted and experimental extrusion pressures were explored. The pore former (corn starch) in the paste formulation was used as a microscopic indicator of phase maldistribution distribution. This redistribution gave a dense ceramic layer at the interface between the bulk paste and the die pin or mandrel. It was suggested that this redistribution was the major contributor to the varied extrusion pressure recordings as extrusion progressed. The phenomenon was thought to be a significant contributor to the experimentally measured pressure being three times of the predicted value. Extrusions with a solid load of ~70 vol% were shown to exhibit stable pressures and produce homogeneous defect-free anode tubes. A YSZ electrolyte coating method was developed, involving the determination of binder and dispersant fractions within the slurry to optimise performance, plus the control of coating thickness by adjusting processing parameters (solid weight fraction and withdrawal speed). Two-step heat treatments were employed to generate a dense electrolyte layer. Dip coated electrolyte layers with a dense sintered thickness between 20 and 30 µm were obtained at a solid mass fraction of 50 wt% in the slurry and a withdrawal rate of 80 mm/min. The heat treatment to develop a dense electrolyte structure was determined as a pre-heating of the anode tube at 1100 °C followed by a re-heating of the electrolyte coated dual structure at 1350 °C. After the addition of cathode (La$_0$$_.$$_8$Sr$_0$$_.$$_2$MnO$_3$, LSM) and current collection (silver) components by brush coating, the fabricated full cells are electrically characterised in terms of current-voltage polarization and electrochemical impedance spectroscopy (EIS). The open circuit voltage (OCV) and peak power density were 0.82 V and 0.11 W/cm$^2$ respectively