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Journal of Ceramic Science and Technology 3/2014
Vol. 5, No. 3 · September 2014
Solid Solution in LnTiO2N and MTaO2N Oxynitrides, Ln = La,Nd; M = Ca, Sr, Ba
J. Ahchawarattaworn, D.P. Thompson
Pages 173-183 · DOI: 10.4416/JCST2014-00003
The last fifty years have witnessed a considerable level of interest in the field of oxynitrides. This has mainly been because of their thermal and mechanical properties, but certain members of this group have the perovskite atomic arrangement, and as such might be expected to have interesting electrical and electronic properties. Foremost among these are the rare earth titanium oxynitrides, LnTiO2N, with Ln = La and Nd the two rare earths most commonly investigated, and also the Group II tantalum oxynitrides of the type MTaO2N where M = Ca, Sr and Ba. The present paper explores the changes in …
The Effect of the SiO2/Na2O Ratio in the Structural Modification of Metakaolin-Based Geopolymers Studied by XRD, FTIR and MAS-NMR
G.M. Nasab, F. Golestanifard, F. Golestanifard, K.J.D. MacKenzie
Pages 185-192 · DOI: 10.4416/JCST2014-00007
A series of metakaolin-based geopolymers with different SiO2/Na2O compositions were synthesized to investigate the influence of the activator on the molecular nature and microstructure of the geopolymers. The structures and microstructures of the resulting products were systematically studied by means of XRD, FTIR, MASNMR, and SEM. The results show that the chemical composition of the activator and hence the ratios SiO2/Na2O and SiO2/Al2O3 exert a significant effect on the structure of the geopolymers. The XRD diffractograms indicated that the higher the concentration of silicate species in th …
Effect of Alkali Concentration and Reaction Time on the Morphology of ZnO Nano-Microparticles Prepared by Hydrothermal Method
A. M. EL-Rafei, M. F. Zawrah
Pages 193-198 · DOI: 10.4416/JCST2014-00002
A low-temperature hydrothermal method was used to prepare ZnO nano-microparticles using surfactant-free solutions. The effect of the alkali concentration (Zn2+/OH- = 1:1, 1:2, 1:4 and 1:8) and reaction time (1, 2 and 3 hours) on the morphology of the ZnO was studied. The structure and the morphology of the ZnO obtained were investigated by means of XRD and SEM techniques, respectively. The results revealed that the solution basicity and reaction time were important factors affecting the morphology. With an increase in the reaction time, the crystallinity of the phases formed was enhanced. At a …
Inorganic water-glass-based thermal pastes exhibit a higher thermal conductivity coefficient than silicon-based pastes. They can also be used at elevated temperatures. The optimum filler content, silicate modulus, application of a modifier and pressure were studied. As the result, a significant increase in the thermal conductivity at 508 °C could be explained. The MgO-Na2O-SiO2 system with high magnesium oxide content has not been studied adequately, so special attention is paid to this system composition.
Yttrium Disilicate Micro-Cellular Architecture from Biotemplating of Luffa Cylindrica
S.C. Santos, C. Yamagata, A.C. Silva, L.F.G. Setz, S.R.H. Mello-Castanho
Pages 203-208 · DOI: 10.4416/JCST2014-00008
The aim of this study consists in producing porous yttrium disilicate components by using Luffa Cylindrica vegetable sponge as a template for the replica method. With consideration of the effectiveness of additives, solids content and pH, the rheological behavior of yttrium disilicate aqueous suspensions was evaluated. Stabilization of the suspensions was achieved with an electrostatic mechanism using tetraethylammonium hydroxide and with an electrosteric mechanism by adding polyacrylic ammonium salt. Shear thinning suspensions were prepared by adding 2 wt% polyelectrolyte, pH 10, and 0.4 wt% …
Chemical Degradation of Screen-Printed Thick Films on LTCC
Nils Junker, Thomas J. Rabbow, Michael Schneider, Jochen Schilm, Alexander Michaelis
Pages 209-216 · DOI: 10.4416/JCST2014-00009
The degradation behavior of screen-printed thick films on LTCC was investigated in sulfuric and nitric acid. The samples were examined with regard to their mass loss as well as by means of scanning electron microscopy. Additionally, the eluates were analyzed with voltammetric and spectroscopic methods. In any case, the degradation is dominated by the dissolution of an alumosilicate phase. The degradation in sulfuric acid is generally lower than in nitric acid, caused by kinetic inhibition owing to the formation of sulfates. Delamination of the thick film, resulting from the low chemical resist …
Synthesis and Characterization of Nano-/Micro-Crystalline SnO using Microwave and Hydrothermal Techniques
A.M. EL-Rafei, H. Youssef, N. M. Ahmed
Pages 217-222 · DOI: 10.4416/JCST2014-00010
Microwave (M-H) and conventional hydrothermal (C-H) synthesis of nano-/micro-sized SnO are compared. The phase composition and morphology of the products were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD results of microwave-heated samples indicated early crystallization of tetragonal romarchite phase after only 1 h at 120 °C compared to 4 h at 120 °C for the conventional method. The crystallization path under microwave heating showed the presence of abhurite phase with an intermediate composition between tin oxide and the start …
Thermoplastic Forming as an Alternative Shaping Process for Near-Net-Shape Production of C-SiSiC Ceramics via Liquid Silicon Infiltration (LSI) Process
S. Weber, F. Sommer, F. Kern, R. Gadow, H. Voggenreiter, D. Koch
Pages 223-236 · DOI: 10.4416/JCST2014-00011
The present study demonstrated the feasibility of producing carbon-based green bodies by means of extrusion, pyrolysis and subsequent conversion to C-SiSiC ceramics according to the LSI process. A thermoplastic binder system was used for the development of feedstocks that differ from conventional duroplastic binder systems as these would have created difficulties during processing owing to their curing behavior. Activated carbon, carbon fibers and semi-coke were used as fillers and a source of a sufficiently stable carbon backbone in the carbonized intermediate. Special attention was paid to t …
Solid Solutions and Thermal Transformations in Nanosized LaPO4-YPO4-H2O and LaPO4-LuPO4-H2O Systems
V. Popova, L. Mezentseva, A. Osipov, V. Ugolkov, I. Kruchinina, A. Yakovlev, T. Maslennikova
Pages 237-244 · DOI: 10.4416/JCST2014-00013
Nanosized powders of orthophosphates in the LaPO4-YPO4(-H2O) and LaPO4-LuPO4-H2O systems are synthesized to increase the mutual solubility of LaPO4·nH2O, YPO4·nH2O and LuPO4·nH2O initial components and to investigate physicochemical properties of nanosized solid solutions and their mixtures. The temperature dependence of nanoparticle size is investigated in the 200 – 1100 °C temperature range. Formation of limited hexagonal, monoclinic or tetragonal solid solutions is revealed, and the limits of their concentration and thermal stability are determined. In the LaPO4-YPO4(-H2O) system a series o …
