Papers by Author: Krzysztof Haberko

Abstract: Several hydroxyapatite (HAp) synthesis routes, such as solid state reactions, hydrothermal methods, wet procedures have been widely investigated. At the same time, in the last years many alternative methods to produce HAp, exploiting fish, bovine or pig bones, have been developed; among them the most used are thermal processes as well as subcritical water or alkaline hydrothermal routes. This paper deals with a natural HAp nanopowder extracted from pig bones by a treatment with hot NaOH solution. It was demonstrated that the decomposition phenomena were avoided when the extracted HAp powder was calcined in CO₂ atmosphere or by inducing the formation of CaO at 700 °C and then eliminating it through a washing procedure. The washed HAp was then exploited for producing macroporous components having controlled porosity features in terms of pore shape, size and volume percentage. For this aim, a combination of gelcasting and sacrificial template methods was applied as forming procedure, using agar as natural gelling agent and polyethylene (PE) spheres as pore former.

Abstract: Preparation technique of the particulate composite materials in the alumina/YAG system were studied. Within alumina particle suspension yttria precursor was precipitated with ammonium carbonate. Drying and calcinationa at 600oC resulted in the mixture of alumina and yttria particles. The latter being much finer than alumina particles. This mixture was additionally homogenized by short attrition milling in an aqueous suspension of pH which level was selected on the basis of zeta () potential measurements. It was found that acidic conditions (realized with HNO3) result in hard agglomerates. Such powders showed poor sintering ability and not homogenous second phase particles distribution. Much better properties were observed in case of powders homogenized under basic condition. They give dense materials composed of YAG inclusions of sizes several times smaller than shown by alumina grains and evenly distributed within the matrix. YAG particles result from the reaction of Y2O3 with Al2O3 during heat treatment. Some compositions show fracture toughness essentially higher than observed in pure alumina polycrystals.