Nebojsa Labus

Application of the Master Sintering Curve Theory to Non-Isothermal Sintering of BaTiO3 Ceramics

In this paper a practical approach to the analysis of sintering of BaTiO3 using the Master Sintering Curve concept has been presented. Non-isothermal sintering of high-purity non-doped BaTiO3 ceramics was monitored using a sensitive dilatometer at three different heating rates (10, 20 and 30 oC/min) up to 1380oC. Densification of BaTiO3 during sintering was analyzed using the Master Curve Sintering Theory. A MSC was defined characterizing the sintering behavior of barium-titanate regardless of the heating rate. Construction of the MSC enabled estimation of the process activation energy. Using defined MSC, densification behavior of BaTiO3 ceramics during sintering can be predicted for arbitrary temperature-time excursions and these predictions can be used in controlling and planning the sintering process of this material.

Influence of Mechanical Activation on Synthesis of Zinc Metatitanate

Investigations of a ZnO-TiO2 binary oxide mixture during mechanical treatment were mainly focused on obtaining orthotitanate Zn2TiO4 with a spinel structure. Due to the specific way of energy transfer during mechanical treatment using a high-energy ball mill, the system passes through low temperature ZnTiO3 metatitanate phase formation. Mechanical activation was performed on an equimolar ratio mixture of ZnO and TiO2. The anatase phase was previously submitted to heat treatment for achieving а starting mixture rich in a rutile phase. Milling conditions were preset for observing the formation of a low temperature ZnTiO3 phase with a perovskite structure. The powder microstructure was characterized using scanning electron microscopy. A nitrogen gas sorption analyzer with the BET method was used to determine the specific surface area and porosity, indicating changes of powder sample properties during mechanical activation. Also, X ray powder diffractometry was applied to obtain the phase composition. Powders were then pressed into pellets and their compressibility was observed through density changes. According to microstructures obtained by scanning electron microscopy analysis, the system underwent a primary and secondary agglomeration process. Specific surface area measurements supported that conclusion. Compressibility investigations established the difference between compressibility of the non-activated mixture and activated powders. X-ray diffraction analysis revealed that a perovskite structure forms simultaneously with a spinel phase during the process of

The Influence of Tribophysical Activation on Zn2TiO4 Synthesis

The influence of tribophysical activation on Zn2TiO4 synthesis along with the changes in powders during tribophysical treatment was observed. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill at different time intervals from 0 to 300 minutes. XRD was performed in order to obtain information about phase composition variations. Microstructure parameters were revealed from an approximation method. Particle size distribution along with scanning electron microscopy gave very useful information about powder morphology.

Enhancing Synthesis and Sintering of Zinc Titanate Using Mechanical Activation

Mechanical activation and sintering are used for obtaining zinc titanate, Zn2TiO4. Starting powder mixtures of ZnO and TiO2, in the molar ratio that is in accordance with the stoichiometry of zinc titanate Zn2TiO4, were mechanically activated using a planetary mill during different time intervals from 0 to180 minutes. Scanning electron microscopy was employed to probe the powders microstructure. Progress of the solid-state reaction from the starting powders and evolution of the phases were followed using X-ray powder diffraction. Sintering kinetics was investigated during isothermal heating at 1100 o C from 0 to 120 minutes. The main conclusion based on the analysis made is that Zn2TiO4 ceramics could be obtained by mechanical activation after a certain time without additional thermal treatment. Also, shorter activation times together with calcination at 900 o C show that the required sintering temperature and sintering time could be lower than those reported in literature.

Dilatometer Investigations of Reactive Sintering of Zinc Titanate Ceramics

Starting powder mixtures of ZnO and TiO2, at the molar ratio that is in accordance with the stoichiometry of zinc titanate Zn2TiO4, were mechanically activated using a planetary ball mill in different time intervals from 0 to 90 minutes. X-ray diffraction analysis, scanning electron microscopy and non-isothermal dilatometric measurements were performed in order to investigate zinc titanate formation. Processes occurring during mechanical activation led to the formation of a specific structure of obtained powders that promoted and accelerated solid-state reactions and densification during sintering. The main conclusion based on analysis is that mechanical activation enables better compaction of activated powders, i.e. possibility of achieving higher densities of green bodies without binders, but first of all that Zn2TiO4 ceramics can be obtained by mechanical activation after a certain time with appropriate thermal treatment, i.e. heating rate and sintering time, at temperatures lower than those when non-activated mixtures were used.

High TC superconducting powders synthesis from aerosol

Abstract Spray pyrolysis, as one of the novel powder processing methods, has been applied for the synthesis of 2223 phase of the Bi-based high T c superconducting oxide ceramic materials. The process is performed through heterogeneous chemical reactions in dispersed system (aerosol) formed from common nitrates solution ultrasonically with the resonant frequency of 1.7 MHz. Synthesis through aerosol enables generation of ultrafine multicomponent particles with improved compositional homogeneity provided by higher surface reaction and the absence of compositional segregation. Consequently, spherical, solid, slightly agglomerated submicronic particles (below 400 nm) with the uniform particle size and the particle size distribution are produced. The obtained particle morphology is discussed in terms of precursor chemistry and processing parameters.

Reaction Sintering of the 2ZnO-TiO2 System

Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal phenomenological analyses were performed in order to describe the specimen’s behavior during isothermal sintering at 1100 o C. Non-isothermal sintering was investigated by dilatometer measurements up to 1100 o C with a constant heating rate. The Dorn method was applied in order to give

Investigation of Sintering Kinetics of ZnO by Observing Reduction of the Specific Surface Area

Reduction of the specific surface area of porous Z nO during the sintering process was studied. ZnO powder was sintered at temperature s from 673 K to 1173 K. The decrease in the specific surface area was observed as a func tion of temperature and sintering time. Two different models were involved in order to defi ne the appropriate parameters. The Arrhenius equation was used to give information on the activation energy of sintering. The LSE method was applied for determining optimum para meter values.

Two step sintering of ZnTiO3 nanopowder

Metastable nanopowder ZnTiO3 was pressed into cylindrical compacts at 200 MPa. Compacts were treated by conventional heating with isothermal holding at 931 oC for 10 minutes, 25 minutes and 40 minutes. ZnTiO3 compacts were also heated with a two-step sintering schedule with maximal 913 oC and isothermal holding at 896 oC, for approximately the same holding times as the isothermal schedule. Shrinkage during heating was monitored with a dilatometric device, while microstructure was determined with atomic force microscopy. XRD patterns were collected for the most interesting samples. Microstructures of sintered specimens showed differences introduced during the last sintering stage by the two different heating schedules. Goal of the presented work was to discuss the possible sintering mechanisms for the two step sintering schedulle according to the presented results.

A Phenomenological Analysis of Sintering Kinetics of Alumina

In this paper a phenomenological analysis of the sintering kinetics of alumina powder compacts with different proportions of small and large particles has been made. A phenomenological approach enables definition of functional connections between parameters characteristic of a certain material and the sintering time. A phenomenological equation is defined, which can be used to describe the densification process of alumina during isothermal sintering. Its parameters enable identification of the dominant diffusion mechanism.