Design and Processing of Alumina Plate Composites for Ballistic Nacre Alumina Structures

ABSTRACTNacre is a hierarchical multi-composite matrix consisting of mineral plate-like structures stacked up similar to brick and mortar. When impacted with a projectile this type of structure is expected to reduce the overall shock loading into the system as well as projectile velocity as a consequence of variations in structural stiffness between the composite plates and the organic interlayers. Bio-mimicked nacre derived from alumina as the base ceramic is also shown to have increased fracture toughness over an alumina monolith. One challenge to building the nacre alumina structure is the design and processing of the composite mineral plates which should be comprised of roughly 90-95% nano-filler and 5-10% organic binder. In order for these plates to accurately mimic the nacre mineral plates they must also emulate aspect ratios on the order of 1:10 to 1:20. This paper will discuss the design and processing of nacre-alumina plates for studies into the impact behavior of nacre composites.

Preparation and investigation on properties of BST-base ceramic with high-energy storage density

The Ba0.3Sr0.6Ca0.1TiO3 (BSCT) powder was prepared through the solid-state reaction. And then preparing ceramic samples with quantitative doped- Bi2O3⋅3TiO2 and different doped- MgO . X-ray diffractometer (XRD) and scanning electron microscopy (SEM) were used to investigate the phase compositions, distribution and morphology of the ceramic samples. SM–11J49 capacitance measurement instrument and CS2674A pressure tester were used to measure the dielectric properties of the samples. The results show that the compactness and the dielectric constant of the ceramics increases first and then decreases when the doped MgO content was changed from 1.5 to 4.5 wt.%. The trend of breakdown strength is characterized by M-shaped pattern with the increase of doped- MgO content. Calculation results demonstrate that when the doped- MgO content is 2.0%, the samples have the highest energy storage density.

Silicon Carbide Base Ceramic Fiber Synthesis from Polycarbosilane-Modified Polymethylsilane Blend Polymers by Melt Spinning

A melt-spinnable precursor for SiC based fibers was prepared from blend polymers of polycarbosilane (PCS) and modified polymethylsilane (M-PMS). The blend polymers cured at 320°C are different from M-PMS and PCS. The ceramic yield of these blend polymers is about 83%. The C/Si ratio of M-PMS/PCS derived ceramics (pyrolyzed at 1250°C) is linear to the content of MPMS in M-PMS/PCS. After melt spinning, thermal oxidation curing, and pyrolysis, Si-C-O fibers were obtained. The diameter and the tensile strength of the resulted fibers are 16.5μm and 1.62GPa, respectively.

Thin Film Multichip Packaging for High Temperature Digital Electronics

Digital silicon carbide integrated circuits provide enhanced functionality for electronics in geothermal, aircraft and other high temperature applications. A multilayer thin film substrate technology has been developed to interconnect multiple SiC devices along with passive components. The conductor is vacuum deposited Ti/Ti:W/Au followed by an electroplated Au. A PECVD silicon nitride is used for the interlayer dielectric. Adhesion testing of the conductor and the dielectric was performed as deposited and after aging at 320°C. The electrical characteristics of the dielectric as a function of temperature were measured. Thermocompression flip chip bonding of Au stud bumped SiC die was used for electrical connection of the digital die to the thin film substrate metallization. Since polymer underfills are not compatible with 300°C operation, AlN was used as the base ceramic substrate to minimize the coefficient of thermal expansion mismatch between the SiC die and the substrate. Initial die shear results are presented.

A Novel Design of a Planar SOFC with the Anode Supported on the Base Ceramic Structure

The paper presents the innovative design of a ceramic high temperature solid oxide fuel cell (SOFC) in which the anode consists of two parts: the bottom supportive part with microchannels for fuel distribution and the upper operating part which takes part in the electrochemical reaction in the cell. Both parts of the anode are made of co-fired yttrium-stabilized zirconia (Ni/YSZ) foils. Microchannels as well as the manifold for combustion products are engraved mechanically in the isostatic pressed stack of Ni/YSZ foils before their firing. The electrolyte and the cathode are performed on the upper functional part of the anode by successive screen printing and firing of the electrolyte paste and the cathode paste. The paper reveals details of the fuel cell processing, test fixture and measurement set-up for testing the cells as well as the results of open circuit voltage and short-circuit current measurements.

Impedance Changes and Carbon Stability during the Heat Treatment of Si3N4–Carbon Composites

Electrical properties of the insulator silicon nitride ceramics may be improved by addition of electrical conductive parts. The conductive carbon parts were mixed with the base ceramic matrix to form a percolation network. Electrical current can flow through the ceramic by using the connected carbon channels. In air atmosphere however, the carbon can oxidize and burn out. Heat treatments were performed to observe the carbon degradation in composites in atmosphere. As resulted, the carbon exhaust started at 400°C from surface and finished above 750°C. Electrical measurements showed the conductor-insulator transformation. Thermo-gravimetric measurements suggested that some carbon inclusion still remained in isolated closed porosities.