Jaroslav Cihlar

Thermal removal of multicomponent binder from ceramic injection mouldings

Thermal removal of polymer binder containing low-molecular-weight components from ceramic injection mouldings was studied. The effect of the shape and size of bodies on the process of binder removal was examined. Evaporation of low-molecular-weight components represented the most important process at the beginning of binder removal. It was found that a bed of activated carbon speed up removal of low-molecular-weight components. The mechanism of binder removal in a bed of activated carbon was described. Binder redistribution and evolution of porosity in the body during binder removal was investigated. A high rate of binder removal resulted in non-uniform binder distribution in the body. The formation of defects due to non-uniform binder removal was described and requirements for their elimination were proposed.

Injection moulded hydroxyapatite ceramics

The injection moulding of hydroxyapatite (HA) and properties (relative density, shrinkage, microstructure, thermal strength and phase composition) of HA ceramics sintered at temperatures of 1373-1773 K were studied. Particles of oval shape and size of 0.5 microns were most suitable for injection moulding. Polymer/HA mixture contained 63 vol% of the HA powder. Maximum relative density (98.7%) and shrinkage (16%) of HA ceramics were obtained at a sintering temperature of 1523 K. Maximum flexural strength (60 MPa) of HA ceramics occurred at a sintering temperature of 1473 K. The strength of these ceramics decreased at sintering temperatures higher than 1473 K. Loss in strength was owing to the grain growth and decomposition of HA ceramics. The relationship between grain size and strength is described by the equation: sigma = 53.3d1/2. The calculated activation energy of grain growth obtained was 215kJ mol-1 K-1. The decomposition of HA to alpha-tricalcium phosphate was important at temperatures greater than 1573 K.

Direct synthesis of nanocrystalline hydroxyapatite by hydrothermal hydrolysis of alkylphosphates

The influence of reaction conditions (temperature, type of catalyst, time) on the base-catalyzed reaction of mono-, di-, and trialkylphosphates (alkyl = methyl, ethyl, i-propyl, n-butyl) with Ca2+ ions and on the structure and composition of the reaction products was studied. The composition of the calcium phosphates depends mainly on the reaction temperature. At temperatures below 100°C, a nanocrystalline solid product transforming into dicalcium phosphate by heating (calcination) was found. Pure nanocrystalline hydroxyapatite was prepared by hydrothermal synthesis at 160°C from mono- and dialkylphosphates. The size of hydroxyapatite crystallites was about 1 nm, the particle size about 150 nm. Agglomerated particles of hydroxyapatite larger than 2 μm were prepared at 200°C. Hydrothermal reaction of trialkylphosphates with Ca2+ ions at 200°C produced CaHPO4. The experimental results were used to propose a reaction mechanism for base-catalyzed hydrothermal reactions of alkylphosphates with Ca2+ ions.

SYNTHESIS AND PROCESSING OF InVO4 CERAMICS

Indium vanadates for severe applications as photocatalysts, anodes for Li rechargeable batteries or electrochromic devices were prepared via conventional and non-conventional preparation methods. The conventional high temperature solid state reaction was performed at 800°C for 25 hours and the non-conventional microwave-assisted synthesis was performed at 220°C for different reaction times under hydrothermal conditions. The as-prepared powders were characterized in terms of phase composition by X-Ray diffraction analysis (XRD) and infrared spectroscopy (IR) and of powder morphology by scanning electron microscopy (SEM) and BET method. Nanosized indium vanadate powders were successfully synthesized by non-conventional microwave-assisted hydrothermal method. The dense ceramic bodies suitable for electrical conductivity measurements with 96% t.d. were obtained by sintering of powders prepared by high-temperature solid state reaction at 1100°C for 4 h with admission of oleic acid as a binder additive.

Influence of synthesis conditions on physical properties of lanthanide-doped titania for photocatalytic decomposition of metazachlor

Abstract Heterogeneous photocatalysis is a very effective method for the decomposition of a whole range of water pollutants. In this work, the influence of synthesis conditions on the physical properties and photocatalytic activity of lanthanide-doped titanium dioxide photocatalysts was evaluated. Titanium dioxide was prepared via sol-gel synthesis followed by a solid state reaction under different conditions, including different temperatures (450, 550, and 650 °C) and reaction times (4, 8, and 12 h). The crystalline phase of the products was determined to be solely anatase using X-ray diffraction, and this result was confirmed by Raman spectroscopy. The structure, as well as particle size, of the samples was examined using scanning electron microscopy, and their specific surface area was calculated using Brunauer-Emmett-Teller analysis. The band gap energy of the samples was examined using ultraviolet-visible spectroscopy from diffuse reflectance measurements. Doping with lanthanide species, dysprosium and praseodymium, caused the absorption edge to shift towards higher wavelengths and enhanced photocatalytic activity in comparison with pure titania. The photocatalytic activity of the samples was studied in terms of the degradation of the commonly used herbicide metazachlor. The decomposition was carried under UV light and the decrease in metazachlor concentration was measured using high performance liquid chromatography. The best performance was obtained for samples treated at 550 °C for 8 h during the solid state reaction step.

Biphasic calcium phosphate scaffolds with controlled pore size distribution prepared by in-situ foaming

In this study, a reproducible method of fabricating hierarchically 3D porous scaffolds with high porosity and pore interconnectivity is reported. The method is based on in-situ foaming of a dispersion of diisocyanate, polyol, water and hydroxyapatite (HA) to form a hard foamed HA/polyurethane composite which after heat treatment provided a bi-phase calcium phosphate scaffold. This technique, combining the advantages of polymer sponge and direct foaming methods, provides a better control over the macrostructure of the scaffold. A modification of the multi-scaled porous macrostructure of scaffolds produced by changing the ratio of input reactants and by sintering temperature was studied. The pore morphology, size, and distribution were characterized using a scanning electron microscope and mercury porosimetry. The pores were open and interconnected with multi-scale (from several nanometres to millimetres) sizes convenient for using in tissue engineering applications. The bioactivity was confirmed by growing an apatite layer on the surfaces after immersion in simulated body fluid. The material was biocompatible, as shown by using normal human adipose tissue-derived stem cells (ASC). When seeded onto the scaffolds, the ASC adhered and remained healthy while maintaining their typical morphology.