Krzysztof Haberko

Zirconia matrix–tungsten carbide particulate composites manufactured by hot-pressing technique

Zirconia matrix composites with tungsten carbide inclusions were obtained by hot pressing at 1400°C for 40 min. The carbide particle content was changed from 10 to 50 vol.%. All the samples achieved densities higher than 98% of the theoretical value. Elastic properties were measured by ultrasonic methods. Hardness and fracture toughness were estimated by Vickers indentation technique. The microstructure of the composites was determined by TEM observations.

Barium zirconate ceramic powder synthesis by the coprecipitation–calcination technique

The coprecipitation technique was used to prepare an intimate mixture of barium carbonate and hydrous zirconia gel. A part of barium ions became incorporated in the zirconia gel structure. Heat treatment of the system results in the crystallisation of the BaO in ZrO2 solid solution of tetragonal symmetry. The solid solution, when heated without contact with BaCO3, decomposes at elevated temperatures. It results in the formation of BaZrO3 and monoclinic zirconia solid solution. No solid solution of monoclinic symmetry appears when barium carbonate is present in the system. In this case, the reaction of the tetragonal solid solution with BaCO3 leads to the synthesis of BaZrO3. The highest sintering ability is observed in the powder, a small part of which remains unreacted.

Implantation of natural hydroxyapatite from porcine bone into soft tissues in mice.

The natural origin of hydroxyapatite (HA) derived from pig bones (Polish patent No.P-359 960 pending from 5th May 2003) was histologically examined for its biocompatibility following implantation into mouse muscles. The implanted ceramic was encapsulated by well vascularized connective tissue and very slowly resorbed by multinucleated cells. This material did not elicit an immune reaction and adjacent bones were unaffected. This ceramic could be safely used as a filling material alone, or as a composite graft.

The TZP–Chromium Oxide and Chromium Carbide Composites

Microstructure and mechanical properties of the 2.9(Y) TZP matrix composites with chromium carbide and chromium oxide inclusions were investigated. Two chromium carbides were used, Cr 3 C 2 and Cr 7 C 3 . The TZP matrix powder was prepared by the coprecipitation-calcination technique. Attrition mixing allowed to homogenise the matrix and the additive powders. Coprecipitation was additionally applied in the case of the TZP-Cr 2 O 3 system. Hot pressing at 1400°C for 40min resulted in the higher densification than the pressureless sintering at 1500°C for 120 min. The TZP--carbide systems showed better properties and higher densification in the case of the Cr 7 C 3 additive. It was related to the reaction between the matrix and Cr 3 C 2 . Microscopic observations revealed quite different crack propagation path in the system with the oxide and carbide additives. It allowed to suggest mechanisms of the toughness increase over the value of the pure matrix.

Zirconia stabilized with a mixture of the rare earth oxides

Abstract A hydrothermal technique was used to prepare micropowders of ZrO 2 solid solutions stabilized by the mixture of rare earth oxides and yttria (Ln 2 O 3 ) recovered from phosphogypsum. Phase compositions and particle sizes of the powders were measured. Zirconia solid solutions of cubic and tetragonal symmetry are the major phases. A larger Ln 2 O 3 concentration promotes a greater cubic phase content. Powders having low Ln 2 O 3 concentrations have small amounts of monoclinic phase present. The phase composition, fracture toughness (K Ic ) and Vickers hardness of samples sintered at temperatures ranging from 1250 to 1350°C were measured. Tetragonal and, in some cases, monoclinic zirconia solid solutions are found in the microstructure of the sintered bodies. Two ordered phases with the formulae Ln 2 Zr 2 O 7 and Ce 2 Zr 3 O 10 were also detected in the system. Tetragonal zirconia polycrystals (TZP) with high (10 MPaM 0·5 ) fracture toughness were found.

A study on preparation of Tetragonal Zirconia Polycrystals (TZP) in the TiO2Y2O3ZrO2 system

Abstract Hydrothermal techniques were used to prepare micropowders within the TiO 2 Y 2 O 3 ZrO 2 system. Phase compositions and particle sizes of the powders were determined. Monoclinic and tetragonal zirconia were the major phases. In compositions with high TiO 2 concentrations, ZrTiO 4 was found. Both TiO 2 and Y 2 O 3 affect crystallite sizes of the powders. The fracture toughness of the samples sintered at 1300°C was measured. The TZP bodies show good mechanical properties.

A TZP matrix composite with in situ grown TiC inclusions

Abstract A TiO 2 –Y 2 O 3 –ZrO 2 solid solution was prepared by the coprecipitation–calcination technique. The resulting powder of +100 m 2 /g specific surface area was mixed with a phenol-formaldehyde resin whose in situ thermal decomposition resulted in carbon formation. The reaction of the carbon and Ti coming from the solid solution gave TiC evenly distributed within the system. Hot-pressed samples showed hardness higher than conventional TZP bodies.

Hydroxyapatite: An Environmentally Friendly Filler for Elastomers

Natural hydroxyapatite HAP, extracted from the animal bones was used as filler for carboxylated acrylonitrile-butadiene rubber XNBR. Physicochemical properties of the HAP were investigated. It demonstrated the tendency to create the structure in paraffin oil. When added to rubber, HAP formed a molecular filler network, which was observed from the dynamical mechanical analysis. Hydroxyapatite appeared to be active filler, since mechanical properties of the vulcanizates were improved upon filling. However, the dispersive component of the hydroxyapatite surface energy was slightly higher in comparison to the value which corresponds to the rubber.

Zirconia Nanopowder - Its Shaping and Sintering

Nanopowders are composed of elementary particles (crystallites) of sizes smaller than 20 nm. Their heat treatment at lower temperatures than is the cas e with classic powders results in polycrystals of very small grain sizes which possess enhanced me chanical properties. Although numerous methods of producing nanopowders were elaborated, serious processing problems ar e still encountered, mainly due to the friction between powder particles. It fol lows that dry pressing of such powders does not lead to satisfactory results. In the present wor k his is investigated using nanopowders in the yttria-zirconia system. A method for their synthes is under hydrothermal conditions is described. The effect of the two forming methods on the powde r behavior during sintering, dry pressing and pressure filtration, is shown. Introduction. Nearly all properties possessed by ceramic polycrystals are essentially dependent on the grain size. This is exceptionally clear in the case of nano-crystalline materials. It is customary to use this name, in case of polycrystals, when grain sizes are not larger than 100 – 150 nm. The mechanical strength of brittle materials is governed by sizes of the microstructural defects. The defect sizes are the smaller the smaller the polycrystall ine grain sizel, unless the method of preparation introduces other microstructural discontinuities. If this c ondition is met, the distribution of defect sizes becomes smaller with decreasing grain sizes and automatically the Weibull modulus increases, which improves the reliability of the material. Another eff ct of nanometric grain sizes is the easy deformation of a material at elevated temperatures. T his so called superplastic behaviour leads to surface defect healing which has a beneficial effect on the mechanical strength of the material. Sintering is the most frequently used method of manufacturing bulk cera mic polycrystals. This is also the case in nanometric materials, but it is often difficult to control grain growth at the same time as one is attempting to stimulate densification. This proces s is usually accompanied with tenfold or even higher grain growth. So, assuming the grain sizes of t he nanometric polycrystals given above, particle sizes of the starting powder should not exceed 15 – 30 nm. They are usually smaller and such fine powders tend to form mechanically strong aggl omerates. It is known that the mechanical strength of agglomerates is proportional to the square of the particle sizes [1]: Pc = K K 2 p F L d V 1

Shaping and Sintering of Ceramic Nano-Powders

The yttria (3 mol %) – zirconia powder of particle size about 8 nm was applied in the present work. It was synthesized by crystallization under hydrothermal condition. Shaping by pressure filtration technique resulted in very uniform packing of nanometric particles. It allowed us to reach nearly fully densified polycrystal of maximum grain sizes of 150 nm at sintering temperature of 1150 o C.