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Nanocrystalline alumina (Al2O3) powders were sintered by Spark Plasma Sintering (SPS) method in a vacuum atmosphere to obtain highly dense and fine grained final ceramic products. In the first section of experiments, 0.4 % wt MgO doped and 0.4 wt % Y2O3 doped Al2O3 were sintered at high temperatures and under high pressure with a SPS system. Later sintering procedures were carried out with codoping Y2O3 with the cathodic ratio of 0.4 wt % in order to investigate dopant effects on spark plasma sintered alumina. The microstructures of all samples were observed using scanning electron microscope and the properties such as density, hardness and fracture toughness were examined.
The aim of this study was to produce dense and mechanically strong boron carbide ceramics with the help of different oxide additives. Physical properties of two different grades of pure boron carbide powders were analysed and sintered by Spark Plasma Sintering method. Starting powders were prepared by ball milling with the addition of 5 wt. % Y2O3, Al2O3, SiO2 and Y2O3 + Al2O3. In the sintering step, powder mixtures were sintered by SPS method in round-shaped graphite dies under 50 MPa for 5 minutes in the range of 1700-1800oC. In the characterization step, sintered sample compositions and microstructures were characterized by XRD and SEM analysis respectively. The hardness values were measured under 1000 g load and the density values were measured with Archimedes' principle. The fracture toughness analysis were also carried out.
Stabilized zirconia shows rather high microwave absorbency at room temperature, and the absorbency become higher with increasing temperature. In this study, stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber were subjected for microwave absorption measurements at elevated temperature. Microwave absorption measurements were done by using a system consists of a microwave vector network analyzer, a circular wave-guide fixture and a vacuum furnace. Microwave absorbency was evaluated by the reflection power change from the sample in the circular wave-guide fixture under vacuum heating. Microwave absorbency of stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber gradually increased with the increase of temperature. We supposed that the increase of microwave absorbency is related to the ionic (oxygen) conduction behavior of stabilized zirconia. Stoichiometric composition ZrO2 powder was also subjected for a measurement to consider the relation between microwave absorbency and ion conduction of zirconia. As the result, stoichiometric composition ZrO2 powder was not absorbed microwave power even when the powder was heated up to 900oC because it isn’t an oxygen ion conductor.
Mullite- zirconia composites have better mechanical properties than monolithic mullite ceramics and can be produced by reaction sintering of ZrSiO4 and α -Al2O3. The samples were prepared from high-purity (99.9%) α-alumina and fine zircon (ZrO2>65 wt.%) powders using PVA as binder. The powder mixtures were compacted under 80 MPa as coin shaped samples by uniaxial dry pressing and then sintered in a multimode microwave field of 2.45 GHz. The microwave effect on ZrSiO4 dissociation and mullite formation was evaluated by comparing the microwave sintered samples with those sintered conventionally. The as-reacted compacts were characterized by X-ray diffraction and scanning electron microscopy (SEM). The effects of sintering parameters on mullitization and mullite grain growth were investigated.
Today chemistry of materials and as such the ceramic field of research are addressed through more and more complex synthetic methodologies in order to optimize final material performances. The notion of complexity in chemical science is illustrated inhere through the concept of integrative chemistry. Particularly the integration between bi-liquid foams, sol-gel process, organo-silane functionnalization, lanthanides complexation and Pd heterogeneous nucleation is proposed as a non-exhaustive synthetic tool box to reach specific advanced ceramics. The first section is dealing with the synthesis of the first series of Si(HIPE) macrocellular foams where the oil volume fraction of the starting emulsion allows a nice tuning of the foams macroporosity. The second section is dealing with Europium complexation of β−diketone and malonamide hybrid Organo-Si(HIPE) leading to the Eu3+@Organo-Si(HIPE) luminescent foams, while the third part is dedicated to Pd heterogeneous nucleation within host hybrid foams. This last series of macrocellular ceramics are labeled Pd@Organo-Si(HIPE) which demonstrates good turn over number (TON) and turn over frequencies (TOF) when acting as supported catalysts for the Mizoroki-Heck coupling reactions. In the above mentioned foams the HIPE acronym is for High Internal Phase Emulsion.
The hybrid materials consisting of plate-like potassium lithium titanate (K0.81Li0.27Ti1.73O4) micro particles coated with calcia-doped ceria (Ce0.8Ca0.2O1.8) nano particles were prepared by the co-precipitation method and sol-gel method. Broad-spectrum UV-shielding composite materials with good comfort and low oxidation catalytic activity were successfully synthesized. The comfort when applied on skin and UV-shielding ability of the composites prepared by the sol-gel method were superior to those by the co-precipitation method.
Availability of advanced materials has opened up opportunities in meeting several functional requirements through hybridization. Hybrids consisting of ceramics, metals and high performance polymers could benefit many aircraft and space satellite applications. They could meet requirements of low weight, high environmental stability, and high thermal or dimensional stability. In this study, hybrid materials consisting of high performance polymer, porous ceramics (glass microballoons) and other constituents such as Zircornium Tungstate (with negative coefficient of thermal expansion (CTE)) and nanoclay were studied. Specimens were successfully produced with a range of density from 0.4 to 1.1 g/cm3 depending on the degree of fill in the syntactic foams. CTE tailoring was achieved to greatly reduce the residual stress arising from processing and CTE mismatch of dissimilar materials. The evaluations of dimensional stability were examined from thermomechanical analysis. The synergistic effects of resin, ceramic constituents and pores on the hybrid properties will be presented.
The mismatch of the coefficient of the thermal expansion (CTE) is one of the main causes of crack initiation and delamination for carbon fiber-reinforced polymer hybrids and metal/polymer hybrid materials. In this research, a negative CTE ceramic material (zirconium tungstate) was incorporated with a thermoset polymer (bismaleimide) resulting in a ~40% reduction in CTE and a significant improvement in thermal stability. The morphology showed good dispersion of the zirconium tungstate particles within the bismaleimide. Comparisons of the experimental CTE values with the rule-of-mixture and the analytical micromechanical models will be discussed.
Gold nanorods (GNRs) were deposited in ordered mesoporous silica SBA-15 by a liquid-phase synthesis. The X-ray diffraction pattern of GNRs-deposited SBA-15 (GNRs/SBA-15) confirmed that the mesoporous structure of the SBA-15 was maintained even after depositing GNRs in the SBA-15 pores. Laser irradiation and heat treatment for GNRs/SBA-15 were carried out to check the effect on the GNRs morphology alteration. These treatments were found to shorten the length of the GNRs in SBA-15, leading to a blue shift of the surface plasmon resonance wavelength of the GNRs. Especially, heat treatment at high temperatures, e.g. at 500 °C, showed unique result that the inner wall of SBA-15 was collapsed by the overgrowth of gold nanoparticles.
Heterogeneous sol-gel systems (suspensions), synthesized by mixing sols and fillers of various dispersity (oxides, minerals, etc.), are successfully used to prepare glass-ceramic coatings. Sol composition (precursor, catalyst, solvent, dopants), filler dispersity and a homogenization mode for obtained suspensions essentially influence the properties of coatings formed. Here ways of the control of properties of heterogeneous sol-gel systems (by using various dopants, additives of organic low- and high-molecular compounds, as well as ultrasound) to reach set electro-physical and mechanical characteristics of coatings are considered in details. A number of examples of applications of glass-ceramic and hybrid coatings as well as ‘skin’ - layers are resulted.
Smart processing for ceramics structure tectonics is new strategy of science and engineering to create novel functional materials with special patterns and morphologies. In this lecture, various investigations to develop the functionally structured materials by using smart processes of stereo- lithography will be introduced. For example, photonic crystals with periodic arrangements in dielectric constants are strong candidates of artificial functional materials to control electromagnetic wave energies effectively. Special modifications of dielectric micro patterns to harmonize electromagnetic waves in terahertz frequency ranges with molecule vibrations of various biochemical solutions will be introduced as investigative results of artificial photosynthesis.
A simple, inexpensive, and environmentally-friendly process for converting mixtures of clays and polymers has been developed. Polymer and clay are combined in water, and the mixtures are freeze dried to produce materials which have bulk densities typically in the range of 0.03 – 0.15 g/cm3. These low density polymer/clay aerogel materials possess good mechanical properties similar to those of traditional polymer foams, can be reinforced with fibers, modified with nanoparticles, biomineralized, or converted into porous ceramics.
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