High-fidelity 3D microstructural characterization of ZrB2 during hot-pressing (Invited)

Standard ultra-high temperature ceramic (UHTC) manufacturing results in components with large differences in properties due to variability in microstructural “critical flaw” distributions. Critical flaws can be any irregularity in a component, such as a secondary phase, cracks, pores, etc. This is problematic when designing reproducible UHTC components. The goal of this project is to understand how these critical flaws evolve during hot pressing of ZrB2 (a UHTC) by examining them in 3D. This study incorporates 3D imaging such as (i) preliminary in-situ high-temperature pressureless sintering X-ray µ-CT, (ii) ex-situ X-ray µ-CT, and (iii) 3D electron imaging and backscattered diffraction data collected at different stages of densification. 3D microstructure statistics along with unique observations of individual pore and secondary phase evolution will be presented. This data is brought together to give a holistic view of the densification of ZrB2 during hot pressing at multiple length scales. This data will be incorporated into a process-structure-property (PSP) database for statistical modeling to reduce uncertainty during ZrB2 processing

Morphological and structural characterization of spinel MgAl2O4

Magnesium aluminate has spinel structure and very good mechanical, chemical, and thermal properties. Owing to these properties, it has a wide range of applications including refractory ceramics, optically transparent ceramic windows and armors. Its low dielectric permeability and low loss tangent enable its using for integrated electronic devices, as well. Furthermore, as a porous ceramic, magnesium aluminate has important application as humidity sensor, catalyst and filter for waste water purification. In this paper, synthesis and characterization of MgAl2O4 was performed. Stochiometric ratio of MgO and Al2O3powders was mixed and calcined within the temperatures range 1500-1800 oC to produce pure spinel phase. Thereafter pellets were crushed and treated in planetary ball mill for 60 minutes to obtained fine grain. All powders, calcined and milled, were examined for phase composition, crystal structure, and morphology. The obtained results showed that by increasing the temperature denser samples but more fragile have been synthesized. Milling for 1 hour leads to crumble of bigger particles and getting finer, single phase powders. XRPD and Raman spectroscopy showed disorder in crystal structure after milling

Vav3/Rac1 Signaling Promotes Castration-Resistant Prostate Cancer

Objectives. To define more clearly the role of Vav3 in the progression to castration resistant prostate cancer( CRPC). Background. Increased androgen receptor (AR) transcriptional activity drives growth of castration-resistant prostate cancer (CRPC). This enhanced AR activity is due to different mechanisms, including increased levels of AR coactivator proteins and ligand-independent activation of AR by growth factor-initiated signaling. We and others have shown that Vav3, a growth factor-activated Rho GTPase guanine nucleotide exchange factor (GEF), is up-regulated in cell and mouse models of CRPC and in a large proportion of primary prostate cancer clinical specimens. Methods. These studies used cell imaging of human prostate cancer cell lines, tumor xenograft models , three-dimensional protein modeling, and biochemical and molecular approaches. Results. We found that Vav3 activates the Rho GTPase, Rac1, in prostate cancer cells. Further, expression of wild type Vav3 or a constitutively active Rac1 mutant was sufficient for robust castration-resistant xenograft tumor growth. Further, Vav3 potentiates AR activity in the presence of very low androgen concentrations, in a PH dependent, yet GEF independent manner. We found that Vav3 nuclear localization is important to its coactivator function, and sequential chromatin immunoprecipitation experiments revealed that Vav3 and AR were simultaneously recruited to the same transcriptional complexes. Conclusions. Vav3 and Rac1 signaling pathways can act in concert to drive AR transcriptional activity and prostate cancer progression. These studies suggest a Key role for Vav3/Rac1 in CRPC progression and support therapeutic disruption of this signaling pathway

Silicon Carbide-titanium Diboride Ceramic Composites

The effect of TiB2 content on mechanical properties of silicon carbide-titanium diboride ceramic composites was studied. The hardness of the ceramics decreased from 27.8 GPa for nominally pure SiC to 24.4 GPa for nominally pure TiB2. In contrast, fracture toughness of the ceramics increased from 2.1 MPa m1/2 for SiC to ~6 MPa m1/2 for SiC with TiB2 contents of 40 vol.% or higher. Flexure strengths were measured for three composites containing 15, 20, and 40 vol.% TiB2 and analyzed using a two parameter Weibull analysis. The Weibull modulus increased from 12 for 15 vol.% TiB2 to 17 for 20 and 40 vol.% TiB2. Microstructural analysis revealed microcracking in the ceramics containing 20 and 40 vol.% TiB2. The ceramic containing 40 vol.% TiB2 had the best combination of properties with a fracture toughness of 6.2 MPa m1/2, hardness of 25.3 GPa, Weibull modulus of 17, and a strength of 423 MPa

Corrigendum to Plasma Arc Welding of ZrB₂-20 vol% ZrC Ceramics [J. Eur. Ceram. Soc. 34 (2014) 3549-3557]

The authors regret that an average grain size, and maximum grain size, reported in the above paper were incorrect. The average grain size for ZrB2 in weldment-2 of the manuscript was reported as 52.4 ± 53.2 μm and should be 27.7 ± 22.1 μm. The maximum ZrB2 grain size in weldment-2 was also reported to be 225.9 μm and should be 148.6 μm. The incorrect average grain size was reported in the Abstract on page 3549 and in the Results and Discussion on page 3554. The incorrect maximum grain size was reported in the Results and Discussion on page 3554. The large standard deviation of the ZrB2 grain size in weldment-2 was also discussed, on page 3554, as “… ~17% of the distribution was found to be over 100 μm in diameter.”, rather, those grains were found to be over 45 μm in diameter. The authors would like to point out that these errors do not change any of the conclusions preceding, or following, the discussion. The authors would like to apologise for any inconvenience caused

Microstructural Effects on the Mechanical Properties of SiC-15 Vol% TiB₂ Particulate-reinforced Ceramic Composites

The microstructures and mechanical properties were studied for two different SiC ceramics containing 15 vol% of TiB2 particulates. the first was prepared from commercially available spray-dried granules and the second by blending individual SiC and TiB2 powders. the average TiB2 particle sizes were 2.7 μm for the ceramic prepared from blended powders, which had a uniform distribution of TiB2, and 2.3 μm for the ceramic prepared from spray-dried granules, which had a nonuniform distribution of TiB2 agglomerates. Although the two ceramics had hardness values of 26 GPa, the other properties were different. For example, the fracture toughness was 4.3 MPa·m1/2 for the ceramic prepared from blended powders compared to 3.1 MPa·m1/2 for the ceramic prepared from spray-dried granules. in contrast, the Weibull modulus for the ceramic prepared from spray-dried granules was 21 compared to 12 for the other. Calculations predicted spontaneous microcracking in the ceramic prepared from spray-dried granules, which was confirmed by analysis of the microstructure. the presence of microcracks accounted for the higher Weibull modulus, but lower flexural strength, Young\u27s modulus and fracture toughness for the ceramic prepared from spray-dried granules

Multifunctional UV (MUV) Curable Corrosion Coatings for Aerospace Applications

The development and evaluation of an alternative corrosion coating system containing inorganic corrosion-inhibiting compounds and no VOCs, HAPs, or TRI (toxic release inventory) components is discussed. The proposed coating system would replace both the chromated primer and polyurethane topcoat with a single layer multifunctional UV (MUV) curable, corrosion inhibiting coating that acts as both the source for corrosion-inhibiting compounds and as an anti-weathering agent. Aluminum alloy 2024-T3 and 2024T0 sheets 0.032 \u27\u27thick were cut into 3\u27\u27x 6 \u27\u27panels and then alkaline cleaned, deoxidized, and coated with a commercial chromate conversion coating (CrCe) per MIL-CSS41/PS12209. After conversion coating, the substrates were coated with either a commercial, military approved, epoxy-based chromated primer and a polyurethane topcoat (chromate control) or a single layer of MUV. Evaluation of MUV coatings on non-chromate conversion coatings was also conducted and demonstrated compatibility with those surface finishes

pm Hands-free Operation of a Small Mobile Robot* (2 "23Q

Abstract The Intelligent Systems and Robotics Center of Sandia National Laboratories has an ongoing research program in advanced user interfaces. As part of thk research, promising new transduction devices, particularly handsfree devices, are being explored for the control of mobile and floor-mounted robotic systems. Brainwave control has been successfully demonstrated by other researchers in a variety of fields. In the research described here, Sandia developed and demonstrated a proof-of-concept brainwave-controlled mobile robot system. Preliminary results were encouraging. Additional work required to turn this into a reliable, fieldable system for mobile robotic control is identified. Used in conjunction with other controls, brainwave control could be an effective control method in certain circumstances