Surface chemistry and suspension stability of oxide-nitride powder mixtures

The effect of bimetallic oxide sintering aids on the colloidal stability of homogeneous (surface-coated) and heterogeneous (mechanically mixed) silicon nitride powder mixtures in aqueous solution was studied by acoustophoretic analysis. While the surface charge generation and colloidal stability of single-phase and oxide-coated silicon nitride powder mixtures may be described according to the site dissociation model of amine and hydroxyl surface groups, the surface charge observed in heterogeneous multiphase powder mixtures is associated with the adsorption of soluble metal ion hydroxocomplexes on the nitride particles. Segregation of the mixtures by heteroflocculation, which causes the formation of agglomerates and microstructural defects upon sintering, may be avoided by generation of a threshold surface potential of equal sign on all powder constituents at a pH where the metal hydroxide dissolution is subcritical.     

Paper‐Derived Ferroelectric Ceramics: A Feasibility Study

Preceramic paper may serve as a preform to manufacture single sheet as well as multilayer porous ferroelectric ceramic products. In this article, the authors discuss the formation, microstructure, and properties of preceramic papers highly loaded with BaTiO₃ filler ranging from 70 to 80 vol% and their conversion into ceramic materials. In order to increase the density of the single sheets, post calendering is applied. These sheets are used for the fabrication of multilayer ceramics using warm lamination technique. After binder burnout and sintering up to 1300 °C for 2 h in air, porous paper‐derived multilayer BaTiO₃ is obtained. The effect of ceramic filler content and calendering on the residual porosity in sintered samples is studied. Furthermore, the influence of porosity on the microstructure, mechanical, dielectric, and piezoelectric properties of the sintered BaTiO₃ ceramics is investigated.

     

Microstructure Development of Oxycarbide Composites during Active-Filler-Controlled Polymer Pyrolysis

The microstructure development of a ceramic composite material fabricated by active-filler-controlled polymer pyrolysis (AFCOP) was investigated. During heating of a polysiloxane precursor mixed with titanium powder in argon atmosphere up to 1400°C, thermally induced decomposition of the polymer phase is combined with simultaneous carburization of the transition metal filler. Precipitation of nanocrystalline titanium carbide at the filler particle surface starts above 400°C, and larger, faceted carbide particles have growth above 800°C. A skeleton of turbostratic carbon is formed above 800°C in the polymer-derived silicon oxycarbide matrix from which b-silicon carbide and cristobalite crystallize above 1000°C. A pronounced reduction in linear shrinkage involved in polymer–ceramic conversion is observed. The shrinkage reduction ranges from more than 25% for the filler-free precursor to less than 10% in the presence of 30 vol% of the titanium filler. Thus, active-filler-controlled pyrolysis offers the possibility of controlling shrinkage and porosity formation during polymer–ceramic conversion in order to fabricate bulk components from organometallic polymer precursor systems.     

Discrete element modeling of solid formation during electrophoretic deposition

Electrophoretic deposition (EPD) of colloidal ZrO₂ ceramic powder was examined with respect to the internal colloidal forces and the external electrical field. The influence of electrolytic dissociation of water close to the deposition electrode (cathode) on the electrostatic interaction between the particles and the local electric field is discussed. The discrete element method (DEM) was used to get an insight into the kinetics determining particle packing and density gradient microstructures. The simulation indicates that high particle concentrations combined with low electric field strength result in coagulated flocs and a low packing density in the deposit layer. Tentative phase diagrams for various colloidal forces and electrical field strengths were established.     

miR-16-5p Is a Stably-Expressed Housekeeping MicroRNA in Breast Cancer Tissues from Primary Tumors and from Metastatic Sites

For quantitative microRNA analyses in formalin-fixed paraffin-embedded (FFPE) tissue, expression levels have to be normalized to endogenous controls. To investigate the most stably-expressed microRNAs in breast cancer and its surrounding tissue, we used tumor samples from primary tumors and from metastatic sites. MiRNA profiling using TaqMan^® Array Human MicroRNA Cards, enabling quantification of 754 unique human miRNAs, was performed in FFPE specimens from 58 patients with metastatic breast cancer. Forty-two (72%) samples were collected from primary tumors and 16 (28%) from metastases. In a cross-platform analysis of a validation cohort of 32 FFPE samples from patients with early breast cancer genome-wide microRNA expression analysis using SurePrintG3 miRNA (8 × 60 K)^® microarrays from Agilent^® was performed. Eleven microRNAs could be detected in all samples analyzed. Based on NormFinder and geNorm stability values and the high correlation (rho ≥ 0.8) with the median of all measured microRNAs, miR-16-5p, miR-29a-3p, miR-126-3p, and miR-222-3p are suitable single gene housekeeper candidates. In the cross-platform validation, 29 human microRNAs were strongly expressed (mean log2-intensity > 10) and 21 of these microRNAs including miR-16-5p and miR-29a-3p were also stably expressed (CV < 5%). Thus, miR-16-5p and miR-29a-3p are both strong housekeeper candidates. Their Normfinder stability values calculated across the primary tumor and metastases subgroup indicate that miR-29a-3p can be considered as the strongest housekeeper in a cohort with mainly samples from primary tumors, whereas miR-16-5p might perform better in a metastatic sample enriched cohort.     

Paper‐Derived Bioactive Glass Tape

Porous bioactive glass (BaG) structures were manufactured applying novel preceramic paper process. Preceramic papers were produced for aqueous suspensions loaded with different contents of pulp fiber and BaG filler. Pressure loading was applied in order to increase the packing density in the paper sheets. The paper sheets were sintered at 630 °C for 1 h. The porous glass–ceramic specimens were characterized for density, porosity, composition, microstructure, and mechanical properties. A pronounced volumetric shrinkage was observed, but no surface flaws or inhomogeneous areas were detected. The mechanical strength using the ball on three balls test and elastic modulus of sintered specimens vary between 21 and 33 MPa and 0.30–0.85 GPa, respectively.