Flash sintering of glass containing alumina bodies

Flash sintering of glass containing alumina bodie

Flash joining of graphite with polymer derived ceramic interlayer

High-temperature ceramics for structural applications are often characterized by poor machinability and very high melting temperature. Therefore, it is difficult to manufacture them into net-shape large components with complex geometry, with manufacturing technologies such as casting, plastic forming and machining not being viable. Therefore the development of novel joining technologies for high temperature ceramics is of considerable interest. However, ceramic joining is a challenging task because of their high melting temperature; their resistance to plastic deformation; and their brittle behavior (which can cause failure when thermal stresses are developed). Please click Additional Files below to see the full abstract

Spark plasma sintering of alumina/yttria-doped silicon carbide

AbstractSilicon carbide possesses exceptional mechanical and thermal properties, but its densification by conventional sintering is often very difficult. In the present work, silicon carbide was consolidated by spark plasma sintering in the presence of alumina and yttria. The results pointed out that the use of a single oxide does not enhance the sintering kinetics significantly, while the contemporaneous addition of both oxides has a beneficial effect on densification, with a relative density increase of about 10%. Interestingly, the oxide doping allows to double the room‐temperature flexural strength

Field Assisted Material Engineering (FAME)

In order to further improve the energy saving of Spark Plasma Sintering we have developed a very rapid sintering technique called Flash SPS (FSPS) with heating rates in the order of 104-105 ˚C/minute[1]. Unlike the Flash Sintering based on high voltage (≈100V), FSPS is based on low voltage (≈10V) and it can be up-scaled to samples volumes of several tens of cubic centimetres. Flash SPS allows densification of metallic conductors like ZrB2 and HfB2, under a discharge time as short as 20-30 seconds. FSPS of semiconductors like silicon carbide and boron carbide was also demonstrated. Highly customized and versatile equipment with ultrafast responsive controls and programmable bipolar power supplies (up to 20 kHz, 1 MA, 500V) has been built. The developed methodology has been applied to produce FSPSed samples even larger than 6 cm in diameter of ultra refractory materials. Understanding the intrinsic electrical field role in the triangle properties-microstructure-processing remains one our primary scientific goal and the main open question. We tried to give some answers by approaching the problem at different length scales (see figure 1) by developing dedicated equipment/controls, simulations (FEM and ab-initio), thermo-kinetic analysis, in situ observations and accurate temperature measurements/calibrations. Please click Additional Files below to see the full abstract

Electrochemical, optical and thermal effects during flash sintering of 8YSZ

We report on the electrochemical effects occurring during the flash sintering of 8YSZ. In-situ observations for both polycrystalline and single crystal specimens confirm electrochemical blackening/darkening during the incubation period prior to flash sintering (Figure1), even though chromatic alterations are usually visible only after the samples are cooled down in a protective atmosphere rather than in air. The phenomenon is induced by cathodic partial reduction under a DC field. When using a low frequency AC (square 0.1 – 10 Hz) field, the blackening becomes reversible and it follows the imposed polarity switching. Thermal imaging combined with sample color changes (transparent single crystals) and electrical conductivity mapping give a complete picture of the multi-physical phenomena occurring during each stage of the flash sintering event. Please click Additional Files below to see the full abstract

Triggering the catalytic activity of SrTiO3-based ceramics by flash sintering

Confinement of charge carriers in nanoscopic systems has revealed to be an effective strategy to confer ceramic materials unconventional conductive properties by exploiting particle size effects and interfaces characteristics[1]. Strontium titanate (SrTiO3) is a piezoelectric oxide that requires to be doped by acceptor species (e.g. Fe substitution of Ti centers) in order to acquire fair chemical reactivity[2]. Please click Additional Files below to see the full abstract

Effect of the Precipitating Agent on the Synthesis and Sintering Behavior of 20 mol %

Nanocrystalline 20 mol% samaria-doped ceria powders (Ce0.8Sm0.2O1.9) were synthesized by coprecipitation techniques using various precipitating agents in aqueous solution: ammonia, ammonium carbonate, tetramethylammonium hydroxide, and urea. The synthesized powders after calcination at 600°C possess a fluorite structure with nanometric size although they are characterized by a very different morphology and degree of agglomeration. Remarkable differences appear in the sintering behavior, especially because of the presence of hard agglomerates. The precipitating agent has therefore a crucial role in the coprecipitation process, which influences the morphology of the powders and in turn the sintering behavior. The obtained results clearly reveal that ammonium carbonate and urea are the best precipitating agents to obtain final dense products after sintering

Viscosity, Boson Peak and Elastic Moduli in the Na2O-SiO2 System

The temperature and chemical dependence of the melt viscosity are ubiquitous in the model development of the volcanic dynamics, as well as in the glass production and design. We focussed on the yet-explored relationship between the bulk and shear moduli ratio and boson peak with the melt fragility of their parental glasses. Here, we explored the extension of the observed trend by testing the conventional binary system Na2O-SiO2, thus providing new evidence supporting the link between the flow of melts and supercooled liquids and the vibrational dynamics of their parental glasses. This was accomplished by integrating new low-frequency Raman measurements and integrating data from the literature on Brillouin light scattering and viscometry. This approach allows us to feed the MYEGA equation with reliable input parameters to quantitatively predict the viscosity of the Na2O-SiO2 system from the liquid up to the glass transition

Flash sintering of zircon: rapid consolidation of an ultrahigh bandgap ceramic

Zircon (ZrSiO4) is a refractory structural ceramic material difficult to consolidate because of its thermal dissociation into ZrO2 and SiO2. Addition of sintering aids can improve its densification, but with detrimental effects on high temperature mechanical properties and corrosion resistance. In this work, zircon was consolidated by employing the Flash Sintering (FS) technique at a furnace temperature of 1250°C under an electrical field of 1000 V cm−1. The decomposition of zircon was significantly reduced by lowering sintering time and current density. Unlike conventional sintering methods, FS approach allowed to track the degree of dissociation by measuring the electrical resistivity, providing a promising route for the consolidation of such materials. Although the obtained zircon ceramics are characterized by lower density and hardness/toughness than those sintered by alternative advanced techniques (like SPS of HEBM activated powders), the consolidation can be carried out at remarkably reduced furnace temperature.Fil: Martinez, Juan Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Biesuz, Mattia. Universita degli Studi di Trento; ItaliaFil: Dong, Jian. Southwest Jiaotong University; ChinaFil: Gauna, Matias Roberto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Suarez, Gustavo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Sglavo, Vincenzo M.. Universita degli Studi di Trento; ItaliaFil: Lin, HuaTay. Guangdong University of Technology; ChinaFil: Grasso, Salvatore. Southwest Jiaotong University; ChinaFil: Rendtorff Birrer, Nicolás Maximiliano. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentin