Flemish Institute for Technology Research VITO Nv

Mol, Belgium

Flemish Institute for Technology Research VITO Nv

Mol, Belgium
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Akbulut Ozen S.,Bursa Technical University | Ozen M.,University of Antwerp | Sahin M.,Recep Tayyip Erdoğan University | Mertens M.,Flemish Institute for Technology Research VITO NV
Materials Characterization | Year: 2017

In this work, the X-ray mass attenuation coefficients of hydrothermally synthesized barium titanate (BaTiO3) samples were calculated with the purpose of determining the crystallization sequence of BaTiO3. Hydrothermally synthesized samples prepared at 100 °C and 200 °C, and reacted for varying reaction times between 15 min up to 120 h were studied. Attenuation coefficient measurements were done with a coaxial HPGe gamma detector (Ortec, GEM55P4-95) with a working range in the X-ray energy region. The samples were made into pellets and were exposed to 241Am radioisotopes at an energy of 59.54 keV for 300 s. Additionally, FT-Raman and XRD measurements were done to support the X-ray mass attenuation measurements. It was found that secondary barium titanate (BT) phases (BaTi2O5 and Ba2TiO4) were formed from the precursor material at the early stages of the hydrothermal reaction and that phase pure BaTiO3 was formed at longer reaction times. The sequence of barium titanate crystallization was determined as follows: BaTi2O5; BaTi2O5 and BaTiO3; BaTi2O5, Ba2TiO4 and BaTiO3: and phase pure BaTiO3. © 2017 Elsevier Inc.


Ozen M.,University of Antwerp | Mertens M.,Flemish Institute for Technology Research VITO Nv | Snijkers F.,Flemish Institute for Technology Research VITO Nv | Tendeloo G.V.,University of Antwerp | Cool P.,University of Antwerp
Ceramics International | Year: 2016

Barium titanate powder was processed by slip casting in a rotating strong magnetic field of 9.4 T. The orientation factor of the sintered compact was analyzed by the X-ray diffraction technique and the microstructure (grain-size) was analyzed by scanning electron microscope. The hydrothermally prepared barium titanate was used as matrix material and the molten-salt synthesized barium titanate, with a larger particle-size, was used as template for the templated grain-growth process. Addition of large template particles was observed to increase the orientation factor of the sintered cast (5 vol% loading). Template particles acted as starting grains for the abnormal grain-growth process and the average grain-size was increased after sintering. Increasing the solid loading (15 vol%) resulted in a similar orientation factor with a decrease of the average grain-size by more than half. However, addition of templates to the 15 vol% cast had a negative effect on the orientation factor. The impingement of growing particles was stated as the primary cause of particle misorientation resulting in a low orientation factor after sintering. Different heating conditions were tested and it was determined that a slow heating rate gave the highest orientation factor, the smallest average grain-size and the highest relative density. © 2015 Elsevier Ltd and Techna Group S.r.l.


Ozen M.,University of Antwerp | Mertens M.,Flemish Institute for Technology Research VITO Nv | Snijkers F.,Flemish Institute for Technology Research VITO Nv | Cool P.,University of Antwerp
Ceramics International | Year: 2016

Tetragonal cube-shaped barium titanate (BaTiO3) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2-0.5 μm range were formed at temperatures above 80 °C. Also, the cube-shaped morphology of the BaTiO3 product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO3 proceeded alongside secondary BaTi2O5 and Ba2TiO4 phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO3 as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO3 crystallization by the Johnson-Mehl-Avrami method showed that BaTiO3 crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process. © 2016 Elsevier Ltd and Techna Group S.r.l.


Ozen M.,University of Antwerp | Mertens M.,Flemish Institute for Technology Research VITO NV | Schroeven M.,Flemish Institute for Technology Research VITO NV | Snijkers F.,Flemish Institute for Technology Research VITO NV | Cool P.,University of Antwerp
Materials Letters | Year: 2012

Hydrothermally prepared BaTiO 3 powders were tested inside a 9.4 T magnet. 5 vol.% and 15 vol.% BaTiO 3 suspensions were slip casted inside a 9.4 T magnet and the sintered (1400 °C) compacts were XRD analysed. Texture degrees of 0.25 and 0.43 were calculated according to the lotgering method. 15 vol.% suspensions did not yield texture. High powder loadings may give colloidally stable suspensions with low viscosities. However, agglomerates inhibit the rotational freedom of individual particles in the strong magnetic field which resulted in not or weakly textured BaTiO 3 at 15 vol.%. © 2011 Elsevier B.V. All rights reserved.

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