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.

Process Study on Green Treatment of Waste Anolyte

2014 ◽  
Vol 1015 ◽  
pp. 350-354
Author(s):  
Li Na Chen ◽  
Wan Yi Liu ◽  
Qi Lin Hu
Keyword(s):  
Ph Value ◽  
Removal Rate ◽  
Chemical Precipitation ◽  
Environmental Benefits ◽  
Precipitation Method ◽  
Molar Ratio ◽  
Dihydrogen Phosphate ◽  
Waste Solution ◽  
Hydrogen Carbonate ◽  
Ammonium Hydrogen

Contraposing the waste anolyte of industry, the paper proposed a new chemical precipitation method to recover Mn (II) ions and Mg (II) ions from the waste solution using ammonium hydrogen carbonate and ammonium dihydrogen phosphate as precipitants, respectively. The technological conditions of dealing procedure such as the molar ratio of reactants, pH value, reaction temperature and time, aging time were investigated. The results shown that the removal rate of Mn (II) ions and Mg (II) ions reached to 96 % and 98 %, and the yields of MnCO3 and NH4MgPO4·6H2O reached to 91 % and 94 %, respectively. The residual solution was recycled to realize the treatment greenly, which could meet the needs of production and increase environmental benefits.

Crystal Structure Stabilization of Gadolinium Aluminum Garnet (Gd3Al5O12) and Photoluminescence Properties

2013 ◽  
Vol 544 ◽  
pp. 245-251 ◽  
Author(s):  
Jin Kai Li ◽  
Ji Guang Li ◽  
Xiao Li Wu ◽  
Shao Hong Liu ◽  
Xiao Dong Li ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Thermal Decomposition ◽  
Solid Solutions ◽  
Elevated Temperatures ◽  
Particle Morphology ◽  
Mixed Solution ◽  
Photoluminescence Properties ◽  
Hydrogen Carbonate ◽  
Ammonium Hydrogen ◽  
Structure Stabilization

To suppress the thermal decomposition and to stabilize the crystal structure of Gd3Al5O12 (GdAG) garnet, doping GdAG with smaller Ln3+ (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, respectively) to form (Gd,Ln)AG solid solutions was proposed in work. Carbonate precursors of (Gd,Ln)AG with an approximate composition of (NH4)x(Gd,Ln)3Al5(OH)y(CO3)z•nH2O were synthesized via coprecipitation from a mixed solution of ammonium aluminum sulfate and rare earth nitrate, using ammonium hydrogen carbonate as the precipitant. The precursors and the calcination derived oxides were characterized using FT-IR spectroscopy, DTA/TG, XRD, BET and FE-SEM. The results showed that smaller Ln3+ doping can indeed stabilize GdAG against its thermal decomposition to a mixture of GdAlO3 (GdAP) and Al2O3 phases at elevated temperatures and at the same time effectively lowers the temperature for garnet crystallization. The carbonate precursors are loosely agglomerated and the resultant (Gd,Ln)AG powders show good dispersion and a fairly uniform particle morphology. The (Gd,Ln)AG solid solutions exhibit decreasing lattice parameters along with decreasing radius of the dopant ions at the same dopant content of 50 at%. Photoluminescence properties of some of the garnet solid solutions are also studied. The materials developed herein may potentially be used for photoluminescent and scintillation applications.

Nanocrystalline Particle Coatings on α-Alumina Powders by a Carbonate Precipitation and Thermal-Assisted Combustion Route

2007 ◽  
Vol 7 (11) ◽  
pp. 3906-3909
Author(s):  
Sang Woo Kim ◽  
Young Mi Jung
Keyword(s):  
Aluminum Sulfate ◽  
Ultrafine Particle ◽  
Precipitation Reaction ◽  
Carbonate Precipitation ◽  
Surface Complexes ◽  
Ammonium Hydrogen Carbonate ◽  
Nanocrystalline Particle ◽  
Hydrogen Carbonate ◽  
Ammonium Hydrogen ◽  
Combustion Route

We have suggested ultrafine particle coating processes for preparing nanocrystalline particle coated α-alumina powders by a carbonate precipitation and thermal-assisted combustion route, which is environmentally friendly. The nanometric ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of alumina was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The synthetic crystalline size and morphology were greatly dependent on pH and temperature. By adding ammonium aluminum sulfate solution dispersed the α-alumina core particle in the ammonium hydrogen carbonate aqueous solution, nanometric AACHwith a size of 5 nm was tightly bonded and uniformly coated on the core powder due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of aluminum oxide. The synthetic precursor rapidly converted to amorphous- and γ-alumina phase without significant change in the morphological features through decomposition of surface complexes and thermal-assisted phase transformation. As a result, the nanocrystalline polymorphic particle coated α-alumina core powders with highly uniform distribution were prepared from the route of carbonate precipitation and thermal-assisted combustion.

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.

Ammonothermal Preparation of Barium Zirconate Fine Powders

2008 ◽  
Vol 55-57 ◽  
pp. 85-88
Author(s):  
S. Wannapaiboon ◽  
A. Rujiwatra
Keyword(s):  
Low Temperature ◽  
Phase Formation ◽  
Particle Morphology ◽  
Cubic Phase ◽  
Barium Zirconate ◽  
Fine Powders ◽  
Primary Particles ◽  
Aggregation Formation ◽  
Very Low Temperature ◽  
Phase Formation Mechanism

Barium zirconate fine powders of pure cubic phase were readily prepared from the reactions between BaCl22H2O and ZrOCl28H2O under ammonothermal conditions at a very low temperature of 130oC as the lowest. KOH concentration was important in determining phase formation and particle morphology. Reaction temperature and time showed influences on the evolution of particle morphology and aggregation formation, respectively. Sizes of the primary particles critically depended on the BaII:ZrIV mole ratio. Phase formation mechanism is suggested.

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