SOFC Powder Synthesis by the Organic Steric Entrapment Method

Journal of the American Ceramic Society

2008

Three‐phase (triplex) ceramic composites with improved thermal stabilities resulting from minimized grain growth due to extended grain separations are introduced. Al2O3, yttrium aluminum garnet (YAG, Y3Al5O12), and ZrO2 were chemically compatible to make a stable triplex composite. Another stable composite could be made due to chemical compatibility among Al2O3, NiAl2O4, and 3 mol% yttria‐tetragonal zirconia polycrystals (3Y‐TZP). The composites of 33 vol% Al2O3–33 vol% YAG–33 vol% ZrO2, 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP, and 50 vol% Al2O3–25 vol% NiAl2O4–25 vol% 3Y‐TZP were fabricated using either sintering or hot pressing procedures. The sintered 33 vol% Al2O3–33 vol% YAG–33 vol% ZrO2 and 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP composites demonstrated a “self accommodating sintering effect” having a wide sintering range without any extensive change in properties. Annealing of the 33 vol% Al2O3–33 vol% NiAl2O4–33 vol% 3Y‐TZP composite at 1600°C for 50 h resulted in higher strength retention after heat treatment compared with that expected from the sum of the strengths of constituent phases. This was attributed to a mutual, grain growth retardation effect. Chemical compatibilities, mechanical properties, microstructures, and thermal stabilities of the composites were studied.

Section: Methodsmentioning

confidence: 99%

Processing and Characterization of Multiphase Ceramic Composites Part II: Triplex Composites with a Wide Sintering Temperature Range

Kim

Journal of the American Ceramic Society

2008

“…The material fabrication technique includes powder synthesis by using the organic steric entrapment (PVA) method invented in our laboratory and used for preparation of many kinds of oxide powders, 36–44 followed by a powder attrition milling treatment, cold isostatic pressing, and pressureless sintering. The processing flowchart for synthesizing the porous gehlenite ceramic is shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

Sintering Behavior of Gehlenite. Part I: Self‐Forming, Macro‐/Mesoporous Gehlenite—Pore‐Forming Mechanism, Microstructure, Mechanical, and Physical Properties

Jia

Kim

Journal of the American Ceramic Society

2007

A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaO . Al 2 O 3 . SiO 2 ) ceramic (abbreviated C 2 AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore selfforming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore selfforming ability over a very wide range of temperature from 9001 to 14501C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C 2 AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C 2 AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 lm, corresponding to a porosity of 75%-80%, respectively. The porous ceramic can preserve nanometer-sized (26-50 nm) crystallites up to 10001C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 10001C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied.

“…However, the process is often expensive and complicated. The organic steric entrapment method using polyvinyl alcohol (PVA), polyethylene glycol (PEG), or ethylene glycol (EG) as a polymer carrier has been developed to facilitate and make the soft solution processing more efficient 2–35 . The PVA, partially substituted with 17 mol% acetate groups, ensures a homogeneous distribution of the metal ions in its polymeric network structure and inhibits their segregation and/or precipitation from the solution.…”

Section: Introductionmentioning

confidence: 99%

Comparative study of titanate syntheses by the organic steric entrapment method

Rosczyk

Lee

Int J Applied Ceramic Tech

2021

Homogeneous and stable, one‐, two‐, and three‐component titanate powders can be synthesized by an ethylene glycol or polyvinyl alcohol steric entrapment method. The powders synthesized were titania (TiO2), and titanates of barium (BaTiO3), strontium (SrTiO3), aluminum (Al2TiO5), dysprosium (Dy2O5), calcium (CaTiO3) as well as lead zirconate titanate of stoichiometry Pb(Zr0.44Ti0.56)O3 or “PZT.” Titanium isopropoxide and other metal ionic salts were dissolved in ethylene glycol without any precipitation, where the organic carrier, ethylene glycol, sterically entrapped and immobilized the metal ions. At the optimum amount of polymer, the metal ions were dispersed in solution and a homogeneous polymeric network was formed. The ternary PZT compound was prepared by an aqueous route, where water soluble Pb and Zr cations were dissolved in a polyvinyl alcohol solution containing titania nanoparticles around which the aqueous phase precipitated upon water removal. This method is a relatively simple process for making any titanate oxides of complex chemistry.