Agnieszka Gubernat

Ceramic Pigments with Perovskite Structure

The results of preliminary investigation on preparation of perovskite pigments by solid state reaction are presented. The effects of different raw materials used as component carriers on formation of colored pigments were examined. Pigment composition, optimum chromophore addition, type of mineralizer and the conditions of synthesis were determined experimentally as well as the resulting color, phase composition and morphology of powders. The wet method of preparation of starting mixtures was also analyzed.

Dihedral angles in silicon carbide

The commonly accepted hypothesis says that the role of sintering activators such as carbon and boron consists in modifying the relation between the energy of surface and that of grain boundaries in SiC. This means that dihedral angles in samples containing one of the activators, both of them or none should be different. To verify this hypothesis we measured dihedral angles in all the mentioned cases. The observed values of dihedral angles were always much bigger than the limiting one of 60°. Moreover, they did not differ significantly and, according to the statistical analysis could be treated as constant. As a consequence our results contradict the opinion saying that the activators modify the energy of surface and grain boundaries.

Mechanical and thermal properties of tungsten carbide – graphite nanoparticles nanocomposites

Abstract Previous studies concerning pure tungsten carbide polycrystalline materials revealed that nanolayers of graphite located between WC grains improve its thermal properties. What is more, pressure-induced orientation of graphene nano platelets (GNP) in hot pressed silicon nitride-graphene composites results in anisotropy of thermal conductivity. Aim of this study was to investigate if addition of GNP to WC will improve its thermal properties. For this purpose, tungsten carbide with 0.5–6 wt.% of GNP(12)-additive underwent hot pressing. The microstructure observations performed by SEM microscopy. The anisotropy was determined via ultrasonic measurements. The following mechanical properties were evaluated: Vickers hardness, bending strength, fracture toughness KIc. The influence of GNP(12) addition on oxidation resistance and thermal conductivity was examined. It was possible to manufacture hot-pressed WC-graphene composites with oriented GNP(12) particles, however, the addition of graphene decreased both thermal and mechanical properties of the material.

Fractography of Dense Metal-Like Carbides Sintered with Carbon

Metals belonging to groups 4-6 of periodic table of elements form with carbon compounds named metal-like carbides (WC, TiC1-x, NbC, TaC, CryCz). It was established that is possible to achieve dense sintered bodies of this carbides at temperatures near 2000oC using only carbon powder as an additive. Its role consists in reduction of oxide impurities. Presented paper summarized investigations on sintering of metal-like carbides with carbon. Dense WC, TiC1-x, NbC, TaC and CryCz bodies were characterized by KIc factor value. A special care was taken on microstructure and the way of fracture description in relation to the critical stress intensity factor (KIc). It was established that the way of fracture and the finally fracture toughness depend on type of microstructure and degree of nonstoichiometry.

SiC Powder for Casting from Aqueous Suspension

The activation of silicon carbide by boron and carbon is required to obtain dense monophase sintered body from SiC powder. The presence of carbon renders casting from aqueous suspension impossible. The SiC powders with boron and extra carbon were prepared by combustion method (SHS), where carbon was bound to SiC particles in a stable way. The experiments showed that this powder could be used for processing by casting of aqueous suspension. Finally nearly dense polycrystals were obtained by pressureless sintering.

Description of Carbides Sintering Process Using Kuczynski and Frenkel Sintering Models

This work presents measurements concerning sintering description according to two the: Kuczynski and Frenkel models. Investigation covered selected metal–like carbides: TiC0,8, NbC and WC. Kinetic equations were also developed, according to Kuczynski model to describe sintering of each carbide and it was attempted to determine mechanisms of mass transport mechanism dominating at each sintering stage. Parameters describing sintering process of each of investigated carbides: α and β constants, the initial shrinkage rate α-1, the limit of shrinkage at infinite time β-1 and initial apparent viscosity of system were in turn determined using Frenkel model. Such data allowed to achieve full characterization of carbide sintering.