peroxo-oxalate preparation of doped barium titanate

The peroxo-oxalate complexation method is a method that can be used for the preparation of doped barium titanate. In this paper we focus on BaTi0.91Zr0.09O3, which can be used for discharge capacitors in lamp starters. The preparation method described here is based on the complexation and subsequent precipitation in basic environment of Ba, Ti, and Zr ions with hydrogen peroxide and oxalate. The influence of several process parameters, like precipitation temperature and pH, on powder properties is described. A single-phase perovskite crystal structure is obtained after calcination starting from a chloride precursor solution using a precipitation temperature of 40°C and a pH of 9. Because the peroxo-oxalate process starts with inexpensive chlorides and is performed in air, the peroxo-oxalate process is suitable for the commercial production of doped barium titanate

Preparation of BaTiO3 by homogeneous precipitation

Three different methods are studied for the preparation of fine-grained BaTiO3 by homogeneous precipitation: (1)Hydrolysis of barium and titanium alkoxide precursors, in which the required water is generated by an esterification reaction; (2)Precipitation of a barium¿titanium complex as a result of thermal decomposition of Ba-EDTA; (3)Precipitation of a barium and titanium complex by the increase of pH caused by the hydrolysis of urea. The properties of powders, prepared via these methods, and their sintering behaviour are as follows: (1)The esterification method results in a powder with medium average aggregate size of about 3 ¿m and a sintered density of 90% which is higher than the value obtained with the other precipitation methods. The considerable differences, in hydrolysis rate between the barium and titanium precursors used, lead to second phase formation; (2)The complexation method gives the most promising results; 1 ¿m sized spherical aggregates were obtained which consist of smaller particles. Sintered densities obtained were up to 88% and the method can be optimised further to obtain values in excess of 95%; (3)The urea method results in large irregular aggregates and is found to be unsuitable for the preparation of BaTiO3 ceramics

preparation of BaTiO3 by homogeneous precipitation

Three different methods are studied for the preparation of fine-grained BaTiO3 by homogeneous precipitation: (1)Hydrolysis of barium and titanium alkoxide precursors, in which the required water is generated by an esterification reaction; (2)Precipitation of a barium¿titanium complex as a result of thermal decomposition of Ba-EDTA; (3)Precipitation of a barium and titanium complex by the increase of pH caused by the hydrolysis of urea. The properties of powders, prepared via these methods, and their sintering behaviour are as follows: (1)The esterification method results in a powder with medium average aggregate size of about 3 ¿m and a sintered density of 90% which is higher than the value obtained with the other precipitation methods. The considerable differences, in hydrolysis rate between the barium and titanium precursors used, lead to second phase formation; (2)The complexation method gives the most promising results; 1 ¿m sized spherical aggregates were obtained which consist of smaller particles. Sintered densities obtained were up to 88% and the method can be optimised further to obtain values in excess of 95%; (3)The urea method results in large irregular aggregates and is found to be unsuitable for the preparation of BaTiO3 ceramics

Fourteen years of progress testing in radiology residency training: experiences from The Netherlands

Objectives: To describe the development of the Dutch Radiology Progress Test (DRPT) for knowledge testing in radiology residency training in The Netherlands from its start in 2003 up to 2016. Methods: We reviewed all DRPTs conducted since 2003. We assessed key changes and events in the test throughout the years, as well as resident participation and dispensation for the DRPT, test reliability and discriminative power of test items. Results: The DRPT has been conducted semi-annually since 2003, except for 2015 when one digital DRPT failed. Key changes in these years were improvements in test analysis and feedback, test digitalization (2013) and inclusion of test items on nuclear medicine (2016). From 2003 to 2016, resident dispensation rates increased (Pearson\xe2\x80\x99s correlation coefficient 0.74, P-value <0.01) to maximally 16 %. Cronbach\xc2\xb4s alpha for test reliability varied between 0.83 and 0.93. The percentage of DRPT test items with negative item-rest-correlations, indicating relatively poor discriminative power, varied between 4 % and 11 %. Conclusions: Progress testing has proven feasible and sustainable in Dutch radiology residency training, keeping up with innovations in the radiological profession. Test reliability and discriminative power of test items have remained fair over the years, while resident dispensation rates have increased. Key Points: \xe2\x80\xa2 Progress testing allows for monitoring knowledge development from novice to senior trainee.\xe2\x80\xa2 In postgraduate medical training, progress testing is used infrequently.\xe2\x80\xa2 Progress testing is feasible and sustainable in radiology residency training