Process and property characterization of La-Al-B-O/Al2O3 glass ceramic composites

Wen-Cheng J. Wei,Chih-Lung Chen,S.F. Wang 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.1

A LAB glass with a composition of 10 mol% La2O3 + 10 mol% Al2O3 + 80% B2O3 made into a composite with 30-50% Al2O3 filler was prepared and investigated. Processing optimization and several engineering properties used for microwave substrates are reported, including densification, interaction with Ag electrodes, dielectric properties as a function of frequency, acid dissolution and microstructure. The glass ceramic composite, i.e. L30A, without lead and alkali, can be densified by two-step sintering to a density better than 99% with minimal glass residue. The densified composite does not react with Ag up to 950 oC in 1 h, and does not dissolve in an acid solution (pH=3.5) in 2 h. The dielectric constant and loss are in the range of 5.6-5.9 and 1.4 × 10−3-5.5 × 10−3, respectively. The coefficient of thermal expansion (CTE) and thermal conductivity of the composite are reported.

Dispersive and rheological properties of Mg-PSZ feedstocks for precision powder injection molding

Wen-Cheng J. Wei,Rong-Yuan Wu 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.3

The effects of various surfactants on the dispersive and rheological properties of ZrO2 and MgO mixtures in heptane, melt wax and feedstocks were investigated. Several properties of the mixtures were tested to reveal the stabilization in various non-polar binder systems. The feedstocks which contained the surfactant (FP1) with an ester function group produced the highest critical solid loading (56.6 vol%) and least dimensional variation (<0.07%) among five formulations, either choosing from SA, FP1 or NZ38 surfactant. The sintered PSZ (partially stabilized zirconia) samples could reach 99% theoretical density (T.D.) and an average fracture strength of 345 MPa. Dual surfactants, containing FP1 and SA, were also tested, resulting in feedstocks better in rheological properties and homogeneity. The surfactant FP1 apparently improved the homogeneity of the powders in the feedstocks, and consequently refined the properties of parts in the stages of injection molding and sintering.

Calcium aluminate composites with controlled duplex structures:II. Microstructural development and mechanical properties

Wen-Cheng J. Wei,H.J. Liaw 한양대학교 세라믹연구소 2005 Journal of Ceramic Processing Research Vol.6 No.3

This study used monocalcium aluminate (CaAl2O4, CA) to produce ceramic composites with duplex microstructures by hydration and gelation reactions of the aluminate, and compared the properties with those made by a die-pressing process with mixed powders. The microstructure of sintered bodies, the fracture strengths and toughness of the composites with and without thermal shock was characterized by different techniques. Experimental results show that the composites with the addition of CA resulted in the formation of CA6 (CaO*6Al2O3) platelets, so as to reveal two types of microstructures, either in a cluster of agglomerated platelets or with a uniform distribution of platelet CA6 grains. The former, which appeared as a duplex microstructure consisted of a dense matrix and distributed clusters of CA6 platelets, gave an improvement in toughness and thermal shock resistance. The toughness mechanisms of the samples with duplex microstructures are discussed.

Colloidal processing of Pb(Zr,Ti)O3, Part I-Pb dissolution

Wen-Cheng J. Wei,Wen-Ting Hsu,Bang-Ying Yu 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.3

The dissolution behavior of aqueous Pb(Zr,Ti) O3(PZT) suspensions were studied by Atomic Adsorption (AA) and Inductively Coupling Plasma (ICP) spectroscopies, specially emphasizing the change of solution acidity within pH 2 to 12, the effects of polymeric dispersant, and comparing with the dissolution behavior of PbO. The iso-electric-point (IEP) of a 2.0 wt % PZT solution was measured and compared to the minimal dissolution case (less than 10 ppm) to be in the range of pH 7 to 10. The effects of one dispersants, poly (α-N,N-dimethyl-N-acryloxyethyl) ammonium ethnate acrylamide (PMAA/DAAE) was investigated in comparison with a commercial anionic dispersant, an ammonium salt of polymethylacrylic acid (PMAAN). A possible dissolution model and the thickness of the Pb depletion zone on PZT particles are proposed based on the experimental observation. The dissolution behavior of aqueous Pb(Zr,Ti) O3(PZT) suspensions were studied by Atomic Adsorption (AA) and Inductively Coupling Plasma (ICP) spectroscopies, specially emphasizing the change of solution acidity within pH 2 to 12, the effects of polymeric dispersant, and comparing with the dissolution behavior of PbO. The iso-electric-point (IEP) of a 2.0 wt % PZT solution was measured and compared to the minimal dissolution case (less than 10 ppm) to be in the range of pH 7 to 10. The effects of one dispersants, poly (α-N,N-dimethyl-N-acryloxyethyl) ammonium ethnate acrylamide (PMAA/DAAE) was investigated in comparison with a commercial anionic dispersant, an ammonium salt of polymethylacrylic acid (PMAAN). A possible dissolution model and the thickness of the Pb depletion zone on PZT particles are proposed based on the experimental observation.

Study of processing adsorption mechanism of amphoteric polyelectrolyte in BaTiO3 colloids suspension

Wen-Cheng J. Wei,Bang-Ying Yu,Kung-Chung Hsu 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.2

An amphoteric dispersant, copolymer (α-N,N-dimethyl-N-acryloyloxyethyl) ammonium ethanateacrylamide (PAAM/DAAE), was used for the dispersion of BaTiO3 (BT) colloids in an aqueous solution, and compared to a commercial acrylic- based polymeric dispersant, ammonium salt of polymethylacrylic acid (PMAA-NH4). Several properties, including surface potential, sedimentation height ratio, green density, and Ba2+ dissolution from the particle surface were studied. Due to the branch structure of PAAM/DAAE and more importantly the amphoteric functional groups of PAAM/DAAE, the macromolecules adsorbed on BT in much higher concentration (up to 7 mg/g) and limited the dissolution of Ba2+ ions from the BT surface. Strong steric repulsion between BT particles with PAAM/DAAE resulted in a good dispersion of fine particles and greater packing density in the green state than that of PMAA-NH4. The adsorption mechanism and interactions among BT, dispersants, and H2O are reported.

Contact wear of Low-Zirconia Toughened Alumina (ZTA) produced by a colloidal process

Ching-Wen Huang,Ming-Tsung Weng,Wen-Cheng J. Wei 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.3

This study focuses on the wear and related mechanical properties of zirconia-toughened alumina (ZTA) composites with 4.7- 30 vol% yttria doped-TZP (YTZP) particulates. A colloidal process was used to achieve a homogeneous distribution of fine TZP grains in an alumina matrix. Mechanical properties, flexural strength, hardness, fracture toughness, and contact wear were measured. Quantified microstructures by SEM are also reported. A wear-resistant ZTA with a low-zirconia content (< 5%) was obtained by improvements in microstructural homogeneity and optimization. This study focuses on the wear and related mechanical properties of zirconia-toughened alumina (ZTA) composites with 4.7- 30 vol% yttria doped-TZP (YTZP) particulates. A colloidal process was used to achieve a homogeneous distribution of fine TZP grains in an alumina matrix. Mechanical properties, flexural strength, hardness, fracture toughness, and contact wear were measured. Quantified microstructures by SEM are also reported. A wear-resistant ZTA with a low-zirconia content (< 5%) was obtained by improvements in microstructural homogeneity and optimization.

Synthesis of (Bi, Mn, Fe)-doped ceria electrolytes by low-temperature processes

Yu-Hung Cheng,Wen-Cheng J. Wei 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.2

The effects of low temperature processes and the dopants of bismuth, manganese and iron co-doping in Ce1-x,Mx)O2 materialshave been investigated. The CeO2-based powders were synthesized by EDTA-citric acid method and their sintering behaviorwas analyzed by dilatometry (DIL) and density measurement. X-ray diffraction (XRD) and various electron microscopies wereused to identify crystalline phases and microstructure. The results show that solubility limit of Mn and Fe in ceria is less than1 at% while that of Bi is at 8-9 at%. Two electrolytes, Ce0.9(Bi0.09Mn0.005Fe0.005)O2 and Ce0.9(Bi0.1)O2, are selected and sinteredto full density at 1050-1100 oC for 1 hr improved by doping trace amount of Mn and Fe The detail microstructurecharacterization of the doped samples are discussed.

Thin 8 mol% yttria stabilized zirconia interlayer for intermediate-temperature solid oxide fuel cells

Dan Wang,Wen-Cheng J. Wei 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.3

A layer of zirconia coting on anode by precision spin-coating was used to prepare thin electrolyte layer of nano-sized (ca. 60 nm) powder and modify the contact resistance of a cell. The powder was ground, dispersed and spin-coated on a(NiO+8 mol% yttrium stabilized zirconia) anode disk for flattening the electrolyte surface. Bi-layer electrolyte, consisted of thenano-zirconia and Tosho zirconia powders, for planar fuel cells were made in thickness 5.4 + 0.2 μm for comparison to the cellsonly with one layer Tosho zirconia electrolyte. The electrolyte layers are characterized on several processing factors and thepolarization resistance of half-cells by electrochemical impedance spectra (EIS) analysis. The results show that the addition ofnano-zirconia thin layer greatly decreases the surface roughness, interfacial resistance, and effectively improves short-termperformance of the cell power output.

Sublimation and high-temperature stability of SnO2-doped Bi2O3 ionic materials in controlled atmosphere

Yu-Hung Cheng,Yen-Yu Chen,Wen-Cheng J. Wei 한양대학교 세라믹연구소 2018 Journal of Ceramic Processing Research Vol.19 No.5

Sublimation of Bi2O3-based materials is an important degradation issue for the long-term applications of many electronicdevices. A series of SnO2-doped Bi2O3 materials (SBO), was synthesized, densified, and then tested in air or strong reducingatmosphere. The SnO2-doping effects and sublimation kinetics of the SBO materials were studied by X-ray diffraction (XRD),scanning electron microscope (SEM) and precise mass loss measurement. The results show that formation of Bi2Sn2O7 phasegreatly retards the mass loss of SBO. The SBO samples show a surface sublimation in an energy of 52.6 kJ.mol−1. However,the sublimation is also controlled by surface microstructure as the amount of vaporizing species (the Bi or gaseous Bi-oxides)is more than 0.1 mass%. The evaporation is retarded on the rough surface and the mechanism of surface evaporation ischanged to diffusional control.

In-situ TEM Observation of Repeating Events of Nucleation in Epitaxial Growth of Nano CoSi₂ in Nanowires of Si

Chou, Yi-Chia,Wu, Wen-Wei,Cheng, Shao-Liang,Yoo, Bong-Young,Myung, Nosang,Chen, Lih J.,Tu, K. N. American Chemical Society 2008 NANO LETTERS Vol.8 No.8