SPS sintering of B4C-SiC composites

Boron carbide (B4C) - silicon carbide (SiC) ceramic composites were obtained through the densification of B4C and -SiC powders with different ratios using the spark plasma sintering (SPS) technique. The thermal treatment was carried out for 5 min in Ar atmosphere in a temperature range from 1850 to 2000 C under a pressure of 70 MPa. The effect of starting powders ratio on the sintering behavior, relative density, microstructural development, and mechanical properties of the obtained composites was investigated. The obtained results showed that only starting compounds, i.e. B4C and SiC phase, are observed in the sintered ceramic materials. SEM micrographs revealed that the sintered composites are composed of densely compacted B4C and SiC grains with a uniform distribution of both phases. The maximal relative density value (100 %) was achieved for the sample densified at 2000 C with 25 % of B4C and 75 % of SiC. The microhardness of obtained composites ranges from 33 GPa to 43 GPa, depending on the constituents' content and the densification temperature. The maximal microhardness value was achieved for the composite densified at 2000 C which contains a maximal amount of B4C (75 %). In order to examine the behavior of composites in extreme conditions, the surface changes induced through the interaction of obtained composite materials and CO2 pulse laser were also studied. During the irradiation, the laser pulse duration was ~2 µs with average pulse energy of 120 mJ. The results of this study show that the SPS technique can be a very effective densification method for the obtainment of additive-free B4C - -SiC ceramic composites with promising properties for application in radiation at extremes

Preface

This JIMEC issue is dedicated to our esteemed colleague Dr. Snežana Bošković for her 80th birthday

Processing and Properties of Silicon Nitride Ceramics: A Review

The progress in monolithic Si3N4 as well as Si3N4/Si3N4 composites (seeded materials) for structural applications is reviewed. The conventional processing involving the powder synthesis, densification, phase transformation and microstructure design is discussed. Special attention is paid to basic theory of liquid phase sintering due to the complexity and difficulty in understanding consolidation of Si3N4 powders. The mechanical properties of the resulting Si3N4 based ceramics and their industrial applications are summarized. A key factor for the future development in the field of conventionally processed Si3N4 ceramics is given

Controllable Synthesis of Doped Ceria Nanopowders by Cations With Different Valence State

Great attention has been devoted to the development of new technologies for the synthesis of nanoparticles and nanostructured materials, which are profitable for industrial production and are environmentally safe. Such materials have new and specific physical properties and find application in almost all spheres of human life. When it comes to nanoparticle materials, there are significant changes in physical characteristics, compared to microcrystalline ones, which in some cases can differ to several orders of magnitude. These specific changes in properties of the nanomaterial are observed in the change of magnetic, mechanical and optical characteristics, phase relations, the conductivity, etc. In this presentation, self-propagating room temperature synthesis has been applied for controllable synthesis of nanostructured CeO2 powders with fluorite-type structure, as well as single Me-ceria solid solutions (Me: cations with different valence state; monovalent (Ag+), divalent (Sr2+, Fe2+, Mg2+ and Pb2+), trivalent (Bi3+) and tetravalent (Pr4+). The solid solubility of Me into ceria lattice was the topmost reported so far. Due to rapid change of its oxidation state and its ability to store and realize oxygen, different dopants enable the same compound to be used for different purposes: biomedicine, catalysis, nuclear waste immobilization, environmental protection, energy related application, pigments. All these applications will be practically shown and discussed individually. Powder properties such as, crystallite and particle size, its thermal stability, as well as lattice parameters have been studied. Crystal structure of fluorites, point defects, specific features and properties connected to it, this innovative method of nanopowders synthesis, and properties of ceria based materials will be discussed through: crystal structure and defect chemistry, synthesis of nanostructured solid solutions, hot consolidation of ceria nanopowders, some key properties of nanostructured ceria.15th International symposium „Novel technologies and sustainable development", October 20-21 2023, Leskovac

XRD Analysis of Boron Doped Glassy Carbon

Glassy carbon samples containing boron are produced via two different procedures. Boron was introduced into the glassy carbon precursor to avoid the commonly used high temperature doping process and also to obtain the samples of glassy carbon with boron uniformly distributed throughout the bulk of a material. Structural analysis of specimens treated under different temperature-pressure conditions shows that boron enhances the structural ordering of all samples but not to the same extent, clearly indicating that boron in different samples occupies different structural positions

Impact of the geographic factors on the transport of lead and cadmium in the air

The aim of this study is to describe the effect of geographical varieties on the transport of lead and cadmium in the air. During period between 1997- 2006, the concentrations of lead in suspended in the air at 5 measuring sites in Serbia were measured. The minimal measured daily concentrations of lead ranged from 0,42 μg/m3 (2002.) in Kraljevo. The maximal measured daily concentrations of lead to 251,8 μg/m3 (2004.) in Belgrade. During the period between 1997-2006., the concentrations of cadmium in suspended in the air at 5 measuring sites in Serbia were measured. The minimal measured daily concentrations of cadmium ranged from 0,1 μg/m3 (1999) in Kraljevo. The maximal measured daily concentrations of lead to 42,0 μg/m3 (2000) in Belgrade. Results from our experiments demonstrated that when rapid infiltration conditions or a rainstorm exist, particle-facilitated transport of contaminants is likely to the dominant metal transport pathway influenced by acid rain.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Reactions responsible for mass loss during pressure less sintering of Si3N4 ceramics with LiYO2 additive

The reactions were investigated with emphasis on the mass loss during pressureless sintering of Si3N4 ceramics without powder bad. A Si3N4 powder compacts with LiYO2 additive were heat-treated at different temperatures under the pressure of N2 of 0.1 MPa.. The mass loss increased with increasing temperature as well as with increasing additive content. It is expected that the major mass loss should be caused by volatilisation of lithia due to its high vapour pressure. However, the results of the chemical analysis of the samples are in contradiction with this assumption.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200