Rajendra K. Bordia

Planar, Polysilazane-Derived Porous Ceramic Supports for Membrane and Catalysis Applications.

Porous, silicon carbonitride‐based ceramic support structures for potential membrane and catalysis applications were generated from a preceramic polysilazane precursor in combination with spherical, ultrahigh‐molecular weight polyethylene microparticles through a sacrificial filler approach. A screening evaluation was used for the determination of the impact of both porogen content and porogen size on pore structure, strength, and permeability characteristics of planar specimens. By optimizing both the composition as well as cross‐linking parameters, maximum characteristic biaxial flexural strengths of 65 MPa and porosities of 42% were achieved. The evolution of an interconnected, open‐pore network during thermal porogen removal and conversion of the preceramic polymer led to air permeabilities in the order of 10−14 m². The materials were further exposed to long‐term heat treatments to demonstrate the stability of properties after 100 h at 800°C in oxidizing, inert, and reducing environments. The determined performance, in combination with the versatile preparation method, illustrates the feasibility of this processing approach for the generation of porous ceramic support structures for applications at elevated temperatures in a variety of fields, including membrane and catalysis science.

Processing and characterization of large diameter ceramic SiCN monofilaments from commercial oligosilazanes

This work reports the processing of large diameter ceramic SiCN monofilaments via the precursor route using two chemically different polysilazanes ML33S and HTTS self-synthesized from respective commercially available oligosilazanes. The melt-spinning of continuous polymer fibers with controllable diameters from 35 to 150 μm and their pyrolysis to ceramic SiCN fibers is not influenced by differences in the chemical structure of the polysilazanes. In contrast, the necessary e-beam curing dose is reduced by Si-vinyl groups from 600 kGy for ML33S (vinyl free) to 200 kGy for HTTS derived polymer fibers. The curing step leads to an enhanced handleability important for further pyrolysis at 1100 °C in nitrogen and to an increase in ceramic yield. The resulting ceramic SiCN fibers from both systems have similar mechanical and thermal behavior, indicating quite a low influence of the polysilazane type on these properties. For the first time a comprehensive investigation of the effect of fiber diameter on the tensile strength is reported for SiCN fibers. The average strength increases from ∼800 MPa for 90 μm diameter fibers to ∼1600 MPa for the 30 μm diameter fibers. Bend Stress Relaxation (BSR) tests demonstrated that no stress relaxation occurs up to 1000 °C for SiCN monofilaments and the creep resistance is equal to or better than commercially available SiC monofilaments produced by chemical vapour deposition (CVD). The oxidation resistance is also comparable to commercially available oxygen free CVD SiC fibers (SCS-6). The ceramic fibers in this study were pyrolyzed at low temperature (1100 °C) and have high oxygen content (13 to 29 wt%). The high temperature creep resistance and oxidation resistance is expected to improve if the oxygen content is reduced and the pyrolysis temperature increased.

Rat Aortic Smooth Muscle Cells Cultured on Hydroxyapatite Differentiate into Osteoblast-Like Cells via BMP-2–SMAD-5 Pathway

Vascular calcification is an important pathological condition associated with increased risk of cardiovascular mortality. Hydroxyapatite (HA) found in such deposits is the same polymorph of calcium (Ca) found in bone, indicating calcification may involve mechanisms akin to bone formation. Vascular smooth muscle cells (Vsmcs) have been shown to undergo phenotypic change to osteoblast-like cells. However, the mechanisms underlying this phenotypic change are unclear, and whether the stimulus to become osteogenic is a result of loss of mineralization inhibitors or early mineral deposits is not known. Our aim in this study is to identify mechanisms and signal transduction pathways that cause differentiation of Vsmcs into osteoblast-like cells in the presence of HA. We first characterized vascular origin of Vsmcs by studying the expression of smooth muscle cell markers: myosin heavy chain and smooth muscle actin along with SM22α at both mRNA and protein levels. Vsmcs grown on HA exhibited progressive change in cellular morphology at 3-, 7-, and 14-day time points. Culturing of Vsmcs on HA disc resulted in decrease in media Ca levels and increased expression of Ca-sensing receptor (CaSR) on Vsmcs resulting inxa0upregulation of intracellular CaSR signaling leading to increased BMP-2 secretion. BMP-2 pathway mediated differentiation of Vsmcs to osteoblast-like cells shown by expression of osteogenic markers like runt-related transcription factor 2, osteocalcin, and alkaline phosphatase at mRNA and protein levels. Blocking CaSR by NPS-2143 reduced BMP-2 secretion and blocking the BMP-2 pathway by LDN-193189, a BMP inhibitor, modulated expression of osteogenic markers confirming their role in osteogenesis of Vsmcs.

Multi-physics modeling and simulations of reactive melt infiltration process used in fabrication of ceramic-matrix composites (CMCs)

Purpose – A multi-physics process model is developed to analyze reactive melt infiltration (RMI) fabrication of ceramic-matrix composite (CMC) materials and components. The paper aims to discuss this issue. Design/methodology/approach – Within this model, the following key physical phenomena governing this process are accounted for: capillary and gravity-driven unsaturated flow of the molten silicon into the SiC/SiC CMC preform; chemical reactions between the silicon melt and carbon (either the one produced by the polymer-binder pyrolysis or the one residing within the dried matrix slurry); thermal-energy transfer and source/sink phenomena accompanying reactive-flow infiltration; volumetric changes accompanying chemical reactions of the molten silicon with the SiC preform and cooling of the as-fabricated CMC component to room temperature; development of residual stresses within, and thermal distortions of, the as-fabricated CMC component; and grain-microstructure development within the SiC matrix during R...

Polaronic conduction and Anderson localization in reduced strontium barium niobate

Electron transport mechanisms in reduced Sr0.5Ba0.5Nb2O6 (SBN50) are investigated from ∼100 to 955u2009K through an analysis of the electrical conductivity (σ) and the Seebeck coefficient (S) with respect to temperature (T). Notably, experimental evidence is presented that supports a scenario of Anderson localization below 600u2009K and carrier excitation across a mobility edge at higher temperature. As a relaxor ferroelectric, stoichiometric SBN has intrinsic disorder associated with both the distribution of Sr/Ba vacancies and the formation of polarized nanoregions. The removal of oxygen through reduction generates conduction electrons in SBN. At the lowest temperatures measured (100–155u2009K), the electrical conductivity exhibits a temperature dependence characteristic of variable range hopping, followed by a transition to small polaron hopping at intermediate temperatures (250–545u2009K). In both the variable range and small polaron hopping regimes, a semiconductor-like temperature dependence of the electrical condu...

Preparation of Polymer-Derived Ceramic Coatings by Dip-Coating

Polysilazane-based coatings were prepared on dense and porous substrates by dip-coating. Both the pure, liquid polymer and polymer solutions in cyclohexane were investigated. Relevant properties of the coating solutions, including rheological properties and surface tension, were determined and used to predict the resulting layer thickness as a function of dip-coating parameters on dense borosilicate glass substrates. A good correlation between existing model (Landau and Levich) and experiment was found for the pure polymer. In the presence of a solvent, evaporation phenomena led to a predicted coating thickness that is much less than the experimental value for all dip coating withdrawal spends. The introduction of a correction factor was found to adequately describe the deviation. In case of porous substrates, the coating thickness could not be predicted using the model due to infiltration of the base structure, resulting in an interpenetrating ceramic composite layer after pyrolytic conversion of the preceramic polymer compound. When preparing polymer-derived ceramic films on porous base materials, e.g. for membrane applications, this phenomenon has to be taken into account.

Ceramics for Sustainable Energy Technologies with a Focus on Polymer-Derived Ceramics

Due to their high hardness, high temperature stability, and high chemical stability, ceramic materials have significant uses and potential in existing and emerging sustainable technologies . In this paper, we provide a thorough overview of ceramics in a variety of sustainable applications. This is followed by a detailed discussion of an emerging process to make ceramics called polymer (or precursor)-derived ceramics . It is shown that due to the versatility of this process in making a wide range of shapes—fibers, coatings , and porous ceramics, this is an attractive route to make ceramics that will be a critical element in the next generation of sustainable technologies.

Micro-/Mesoporous Polymer-Derived Ceramic Structures Using Molecular Porogens

Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO2/TiO2 supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

Analysis and simulation guided processing of hierarchical porous and multi-layered ceramics for energy applications

Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. Accepted Manuscript NanoscaleG has outstanding mechanical properties and unique electrical and thermal properties which makes it an attractive filler and a good reinforcement for producing multifunctional ceramics for a wide range of applications. Here, alumina (Al2O3) based nanocomposites have been developed using exfoliated graphite nanoplatelets (xGnP) as reinforcement. The xGnP were synthesized by subjecting a graphite intercalation compound (GIC) to a thermal shock. The Al2O3 and xGnP powders were mixed by milling them for a short period of time in order to ensure homogeneous distribution of xGnP in the Al2O3 matrix. Al2O3-0.2, 0.5, 0.8, 3 and 5 vol. %xGnP nanocomposites were developed by powder metallurgy route. Sintering was done by conventional sintering process. The hardness, fracture toughness and tribological properties of the composites having different vol. %xGnP loading were investigated. Results show a significant improvement in the wear resistance of the Al2O3-xGnP composites having more than 0.8 vol. %xGnP loading. The improvement in mechanical properties is attributed to the uniform dispersion of xGnPs and toughening mechanism such as xGnP bridging, crack deflection and strong interaction between xGnP and Al2O3 at the interfaces. Results of the dry sliding wear tests of the composites with different vol. %xGnP loading suggest a significant improvement in the wear resistance of the composites upto the addition of 3 vol. %xGnP. The hardness of the composites also show a gradual increase upto the addition of 3 vol. %xGnP beyond which there is a deterioration in both the hardness and the wear properties.C hollow spheres have many unique properties, such as high surface-to-volume ratio, thermal insulation, high chemical stability and structural stability, and are applied in fields of catalyst supports, fuel cells, gas storage and separation, batteries and supercapacitors. Here, hydrothermal carbonization and emulsion template method were combined to facilely prepare carbon hollow spheres. About the formation mechanism in our synthesis, trioctylamine droplet in water played the role of soft template, and the hydrothermal carbonization took place on the surface of the droplet. The shapes of carbon hollow spheres were different with varying the amount of surfactant and reaction time. And bow-like hollow spheres, nut-like hollow spheres and smooth carbon hollow spheres could be obtained. The metal catalyst of hydrothermal carbonization could also result in the change of morphology of the product.Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou, Fujian 350002, China Terahertz Laser Sources Based on Defference Frequency Generation of Infrared Nonlinear Optical Materials SnGa4Q7 (Q = S (SGS), Se (SGSe) ) Acknowledgments Chen-Sheng Lin (Dr. , Associate Prof.) Zhong-Zhen Luo (Dr.) Hao Zhang (Assistant Prof.) Wen-Long Zhang (Dr. Associate Prof.) Yi-Zhi Huang (Drs. Associate Prof.) Yi Yang (Dr.)

High Temperature Thermoelectric Oxides Engineered At Multiple Length Scales For Energy Harvesting

Thermoelectric aspects of the processing parameters the n-type relaxors, including SrxBa1-xNb2O6 (SBN100x), Sr2Nb2O7 (SN) and SrBi2Nb2O9 (SBiN), were investigated. A solution combustion synthesis (SCS) route was devised to fabricate SBN, SN and SBiN nanoparticles with excellent phase purity. X-ray photoelectron spectroscopy (XPS) was used to deduce the local cation site occupancy, and detailed thermoelectric transport processes were investigated. Based on the identified behavior, effectiveness of pore formers on the thermoelectric performance was investigated with the goal of decreasing κ through enhanced phonon scattering while preserving the electron transport characteristics.