Near-Stoichiometric Barium Titanate Synthesis by Low Temperature Hydrothermal Reaction

1999 ◽  
Vol 606 ◽  
Author(s):  
Kyoungja Woo ◽  
Guang J. Choi ◽  
Young S. Cho
Keyword(s):  
Particle Size ◽  
Barium Titanate ◽  
Low Temperature ◽  
Hydrothermal Reaction ◽  
Ultrafine Particle ◽  
Molar Ratio ◽  
Barium Ions ◽  
Strong Force ◽  
Cubic Form ◽  
Tetragonal Form

AbstractBarium-deficiency of barium titanate particles prepared by low temperature hydrothermal reaction has been notorious. It has been believed that barium-deficiency is caused by the high solubility of barium source compared with titanium. Here is reported the synthesis of nearstoichiometric barium titanate powders with ultrafine particle size and high crystallinity by low temperature hydrothermal reaction from barium acetate and titanium tetra(methoxyethoxide). Barium titanate particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60 ∼ 90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor. Increasing barium to titanium molar ratio in reactant could not overcome the notorious barium-deficiency but, improved stoichiometry and produced finer and less agglomerated particles. Interestingly, adding a slight pressure to autogeneous one to make total 4 ∼ 10 atm has yielded near-stoichiometric, highly crystalline, and less agglomerated barium titanate particles. It seems like that the total pressure around 4 ∼ 10 atm provides strong force enough to push barium ions into the interstitial points of perovskite structure and stabilize it. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at 400 °C.

Effect of the Synthesis Method on the Properties of Ultrafine YAG Powder

2018 ◽  
Vol 281 ◽  
pp. 40-45
Author(s):  
Jie Guang Song ◽  
Lin Chen ◽  
Cai Liang Pang ◽  
Jia Zhang ◽  
Xian Zhong Wang ◽  
...  
Keyword(s):  
Particle Size ◽  
Calcination Temperature ◽  
Hydrothermal Reaction ◽  
Synthesis Method ◽  
Particle Morphology ◽  
Precipitation Method ◽  
Molar Ratio ◽  
Synthesis Process ◽  
Powder Materials ◽  
Co Precipitation

YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by co-precipitation method and hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that the precursor powder prepared via the co-precipitation method is mainly from amorphous to crystalline transition with the increasing calcination temperature, the precursor agglomeration is more serious, In the process of increasing the calcination temperature, the dispersibility of the roasted powder is greatly improved, which is favorable for the growth of the crystal grains, so that the particle size of the powder is gradually increased, the YAG precursor prepared by the co-precipitation method is transformed into YAG crystals, the phase transition occurs mainly between 900 and 1100°C. When the molar ratio of salt to alkali is Y3+: OH-=1: 8 via the hydrothermal reaction, the YAG particles with homogeneous morphology can be obtained. When the molar ratio of salt and alkali is increased continuously, the morphology of YAG particles is not obviously changed. The co-precipitation method is easy to control the particle size, the hydrothermal method is easy to control the particle morphology.

Low Temperature Hydrothermal Synthesis of Nanophase BaTiO3 and BaFe12O19 Powders

1996 ◽  
Vol 457 ◽  
Author(s):  
Fatih Dogan ◽  
Shawn O'rourke ◽  
Mao-Xu Qian ◽  
Mehmet Sarikaya
Keyword(s):  
Particle Size ◽  
Hydrothermal Reaction ◽  
Average Particle Size ◽  
Reaction Times ◽  
Nanocrystalline Powders ◽  
Molar Ratio ◽  
Average Particle ◽  
Hydrothermal Conditions ◽  
Processing Variables ◽  
Xrd And Tem

ABSTRACTNanocrystalline powders with an average particle size of 50 nm has been synthesized in two materials systems under hydrothermal conditions below 100°C. Processing variables, such as temperature, concentration and molar ratio of reactants and reaction time were optimized to obtain particles of reduced size and stoichiometric compositions. Hydrothermal reaction takes place between Ba(OH)2 solution and titanium/iron precursors in sealed polyethylene bottles in the BaTiO3 and BaFe12O19 systems, respectively. While crystalline BaTiO3 forms relatively fast within a few hours, formation of fully crystalline and stoichiometric BaFei20i9 require considerably longer reaction times up to several weeks and strongly dependent on the Ba:Fe ratio of the precursors. The structural and compositional evaluation of the nanophase powders were studied by XRD and TEM techniques.

Low-temperature preparation of dense 10 mol%-Y2O3-doped CeO2 ceramics using powders synthesized via carbonate coprecipitation

2003 ◽  
Vol 18 (5) ◽  
pp. 1239-1246 ◽  
Author(s):  
Yarong Wang ◽  
Toshiyuki Mori ◽  
Ji-Guang Li ◽  
Takayasu Ikegami ◽  
Yoshiyuki Yajima
Keyword(s):  
Low Temperature ◽  
Ultrafine Particle ◽  
Particle Morphology ◽  
Molar Ratio ◽  
Low Temperature Preparation ◽  
Hydrogen Carbonate ◽  
Ammonium Hydrogen ◽  
Final Yield ◽  
Carbonate Coprecipitation Method ◽  
Very Low Temperature

A carbonate coprecipitation method was used for the facile synthesis of highly reactive 10 mol%-Y2O3-doped CeO2 (20YDC) nanopowders, employing nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. The AHC/RE3+ (RE = Ce + Y) molar ratio (R) and the reaction temperature (T) significantly affect the final yield and precursor properties, including chemical composition and particle morphology. Suitable processing conditions are T = 60 °C and R = 2.5 to 10, under which precipitation is complete, and the resultant precursors show ultrafine particle size, spherical particle shape, and good dispersion. The thus-processed precursors are basic carbonates with an approximate formula of Ce0.8Y0.2(OH)CO3 · 2H2O, which directly yield oxide solid solutions upon thermal decomposition at a very low temperature of approximately 400 °C. The 20YDC solid-solution powders calcined at 700 °C show excellent reactivity and were densified to >99% of theoretical via pressureless sintering at a very low temperature of 950 °C for 6 h.

Preparation of Potassium Niobate/Barium Titanate Nanocomposite Ceramics with a Wide Barium Titanate Particle Size Distribution and their Dielectric Properties

2013 ◽  
Vol 582 ◽  
pp. 76-79
Author(s):  
Ichiro Fujii ◽  
Kenta Yamashita ◽  
Kouichi Nakashima ◽  
Yoshinori Fujikawa ◽  
Daisuke Tanaka ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Particle Size ◽  
Barium Titanate ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Molar Ratio ◽  
Narrow Particle Size Distribution ◽  
Potassium Niobate ◽  
Barium Titanate Powder ◽  
Wide Particle Size Distribution

Denser, solvothermally synthesized KNbO3 (KN) / BaTiO3 (BT) composites with heteroepitaxial interfaces were prepared using the barium titanate powder with a wide particle size distribution. The relative density was 68 - 80 %, which was larger than that of the composites prepared using the barium titanate powder with a narrow particle size distribution. The dielectric constant was 300 450 and it was maximized at the KN/BT molar ratio of 0.5. The origin was discussed with the microstructure and crystal structure.

scholarly journals Barium Titanate Nanoparticles Formed by Chlorine-Free Ambient Condition Sol Process Using Tetrabutylammonium Hydroxide

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Wooje Han ◽  
Byungwook Yoo ◽  
Hyung-Ho Park
Keyword(s):  
Particle Size ◽  
Dielectric Constant ◽  
Barium Titanate ◽  
Ambient Condition ◽  
Molar Ratio ◽  
Diffraction Measurement ◽  
Capping Agent ◽  
Synthetic Control ◽  
Tetrabutylammonium Hydroxide ◽  
Particle Size Range

Barium titanate (BaTiO3: BTO) nanoparticles (NPs) were synthesized by chlorine-free ambient condition sol (ACS) process using heat reflux at low temperature of 90°C. The size distribution and morphology of BTO NPs were investigated by varying the concentration of tetrabutylammonium hydroxide (TBAH). The crystalline size of BTO NPs was decreased with increasing the amount of TBAH capping agent (average size changes from 54.3 to 38.7 nm for 0 to 0.5 M TBAH in X-ray diffraction measurement). The particle size of BTO NPs was principally controlled by a synthetic control of butyl chain of TBAH and also a steric effect of excess amount of TBAH. The dielectric constant of BTO NPs was decreased from 152 to 144 at 1 MHz after an adoption of TBAH capping agent with almost uniform dielectric loss (<0.027). But the dielectric constant of BTO NPs synthesized with various molar ratio of TBAH (0.1, 0.3, and 0.5) did not show a distinguished decrease. At the particle size range in this experiment, the dielectric behavior of BTO NPs was found to be mainly dependent on the TBAH ligands at BTO NPs formed during capping process, not on the size of BTO NPs.

Optimization Sol Gel Process Parameter of CaCu3Mn4O12

2014 ◽  
Vol 548-549 ◽  
pp. 326-330
Author(s):  
A. Nurulhuda ◽  
Y. Hafizzal ◽  
A.R.M. Warikh ◽  
A. Rafidah ◽  
Y. Suhaila ◽  
...  
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Low Temperature ◽  
Room Temperature ◽  
Single Phase ◽  
Sol Gel ◽  
Molar Ratio ◽  
Three Dimension ◽  
Sol Gel Process ◽  
Sintering Condition

The influence in optimization of processing, calcinations and sintering parameter on the physical properties and characteristic of CaCu3Mn4O12 were investigated. The stoichiometric CaCu3Mn4O12 powders were successfully prepared by the citric gel method. Dried gel with three dimension network consisted of molar ratio of [citrates/metallic ion]; 1:2 was formed. The precursor gel formed was calcined and sintered at range 400 °C to 800 °C. A single-phase CaCu3Mn4O12 fairly well densified at relative low temperature under atmospheric sintering condition. FESEM results turned out that CaCu3Mn4O12 powder particle is submicron in size and highly agglomerates due to high calcinations temperature. The smaller particle size with higher grain boundary and less of porosity were found for the sample sintered at 700 °C to 800 °C. The samples show the ‘superparamagnetism’ behavior where the M-H curves are linear with the field and have a smaller value of coercivity at room temperature. Sintering at 800 °C produced the sample with lowest Hc value due to the phenomenon of over grown magnetocrystallites, grain size and grain boundaries.

Kinetics of low-temperature aluminothermic reduction of iron tantalate

2021 ◽  
Vol 6 ◽  
pp. 60-72
Author(s):  
R. I. Gulyaeva ◽  
◽  
A. M. Klyushnikov ◽  
S. A. Petrova ◽  
L. Yu. Udoeva ◽  
...  
Keyword(s):  
Particle Size ◽  
Low Temperature ◽  
Raw Materials ◽  
Aluminum Particle ◽  
Preexponential Factor ◽  
Molar Ratio ◽  
Scanning Calorimetry ◽  
Isothermal Exposure ◽  
Reduction Of Iron ◽  
Kinetics Of

The kinetics of low-temperature (900 – 1180 °C) reduction of iron tantalate (98.2 wt % FeTa2O6, 1.8 wt % Ta2O5, particle size < 0.1 mm) by excess aluminum (particle size < 0.14 mm) at the molar ratio Al:FeTa2O6 = 6 was studied. According to differential scanning calorimetry and X-ray powder diffraction, reduction is almost completed at 1180 °C, the metal products are TaFeAl, TaAl3, and Ta17Al12. Based on the results of thermokinetic calculations (Ozawa – Flynn – Wall and nonlinear regression methods), the formal mechanism of the process is represented by the Bna → CnC model, which includes two consecutive steps controlled by autocatalytically activated reactions. Kinetic parameters of the steps are: 1) Е1 = 429 kJ·mol–1, A1 = 1015.3 s–1; 2) Е2 = 176 kJ·mol–1, A2 = 103.9 s–1 (Ej is the activation energy, Aj is the preexponential factor). Prediction in the Bna → CnC model frames indicates the possibility of obtaining a reaction mixture containing ≥ 98 mol. % the final formal reduction product, with isothermal exposure in the temperature range of 1040 – 1120 °C during 1.5 – 5 minutes. The proposed model can be used to develop scientific foundations and substantiate technological modes for obtaining tantalum alloys from mineral and technogenic raw materials.

Structures of chemically stabilized ceramics

1993 ◽  
Vol 51 ◽  
pp. 924-925
Author(s):  
Pratibha L. Gai ◽  
M. A. Saltzberg ◽  
L.G. Hanna ◽  
S.C. Winchester
Keyword(s):  
High Temperature ◽  
Calcium Nitrate ◽  
Nitrate Hexahydrate ◽  
Chemical Route ◽  
Cubic Form ◽  
Tetragonal Form ◽  
Wet Chemical ◽  
Wet Chemical Route ◽  
Final Composition ◽  
Aluminium Nitrate Nonahydrate

Silica based ceramics are some of the most fundamental in crystal chemistry. The cristobalite form of silica has two modifications, α (low temperature, tetragonal form) and β (high temperature, cubic form). This paper describes our structural studies of unusual chemically stabilized cristobalite (CSC) material, a room temperature silica-based ceramic containing small amounts of dopants, prepared by a wet chemical route. It displays many of the structural charatcteristics of the high temperature β-cristobalite (∼270°C), but does not undergo phase inversion to α-cristobalite upon cooling. The Structure of α-cristobalite is well established, but that of β is not yet fully understood.Compositions with varying Ca/Al ratio and substitutions in cristobalite were prepared in the series, CaO:Al2O3:SiO2 : 3-x: x : 40, with x= 0-3. For CSC, a clear sol was prepared from Du Pont colloidal silica, Ludox AS-40®, aluminium nitrate nonahydrate, and calcium nitrate hexahydrate in proportions to form a final composition 1:2:40 composition.

Phase transformation and Raman spectra in BaTiO3 nanocrystals

2002 ◽  
Vol 718 ◽  
Author(s):  
Jian Yu ◽  
X. J. Meng ◽  
J.L. Sun ◽  
G.S. Wang ◽  
J.H. Chu
Keyword(s):  
Particle Size ◽  
Phase Transformation ◽  
Low Temperature ◽  
Long Range ◽  
Lattice Expansion ◽  
Inversion Symmetry ◽  
Range Interaction ◽  
Cooperative Phenomena ◽  
Long Range Interaction ◽  
Hydrothermal Methods

AbstractIn this paper, size-induced ferroelectricit yweakening, phase transformation, and anomalous lattice expansion are observed in nanocrystalline BaTiO3 (nc-BaTiO3) deriv ed b y low temperature hydrothermal methods, and they are w ellunderstood using the terms of the long-range interaction and its cooperative phenomena altered by particle size in covalen t ionic nanocrystals. In cubic nc-BaTiO3, five modes centerd at 186, 254, 308, 512 and 716 cm-1 are observed Raman active in cubic nanophase, and they are attributed to local rhombohedral distortion breaking inversion-symmetry in cubic nanophase. The254 and 308 cm-1 modes are significantly affected not only by the concentration of hydroxyl defects, but also their particular configuration. And the 806 cm-1 modes found to be closely associated with OH - absorbed on grain boundaries.

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