摘要:

A ceramic fuel cell in an all solid‐state energy conversion device that produces electricity by electrochemically combining fuel and oxidant gases across an ionic conducting oxide. Current ceramic fuel cells use an oxygen‐ion conductor or a proton conductor as the electrolyte and operate at high temperatures (>600°C). Ceramic fuel cells, commonly referred to as solid‐oxide fuel cells (SOFCs), are presently under development for a variety of power generation applications. This paper reviews the science and technology of ceramic fuel cells and discusses the critical issues posed by the development of this type of fuel cell. The emphasis is given to the discussion of component materials (especially, ZrO2electrolyte, nickel/ZrO2cermet anode, LaMnO3cathode, and LaCrO3interconnect), gas reactions at the electrodes, stack designs, and processing techniques used in the fabrication of required ceramic stru

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03645.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Fracture surfaces of cement and mortar specimens were characterized using a confocal microscope to create three‐dimensional computer‐based topographic maps. The texture of the fracture surfaces was quantified using image analysis techniques to compute a roughness parameter and fractal dimension. Total porosity, pore‐size distribution, compressive strength, and fracture properties of the specimens were determined and compared with the roughness parameter. Fracture properties were determined by notched‐beam tests and the results were analyzed both by using conventional linear elastic fracture mechanics as well as a compliance‐based approach that incorporatedR‐curve type of behavior. A positive correlation between fracture surface roughness and fracture toughness was d

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03646.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

To identify each glass melting reaction in a multicomponent system, one‐component and two‐component reaction processes were studied using DTA, TGA, and XRD. Two‐component mixtures were prepared by choosing pairs in the same ratio as in a commercial container glass batch composition (sand‐soda ash‐calcite‐dolomite‐feldspar). The presence of silica in the silica‐calcite system decreased the termination temperature of the decomposition of calcite, but did not alter the onset of decomposition. Similar behavior was found in the dolomite‐silica system. A double carbonate (Na2Ca(CO3)2) formed via solid‐state reaction in the calcite‐soda ash system, and metasilicate/disilicate phases were detected during the fusion process in the soda ash‐silica system. The effects of reaction accelerant additions in the soda ash‐silica system were investigated using 1 wt% additions of sodium sulfate, sodium nitrate, and sodium chloride. Sodium chloride was the most effective melting accelerant, lowering the termination temperature of CO2release by ∼80°C compared with the soda ash‐silica system with no additives. NaCl additions caused complete reaction and/or fusion of Na2CO3prior to its melting temperature. Sodium sulfate additions acted to suppress metasilicate/ disilicate formation by coating quartz grains and shifted consequent CO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03647.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The glass melting reactions in a multicomponent system (sand–soda ash–calcite–dolomite–feldspar) were studied using data from DTA, TGA, and XRD interactively. The first‐formed liquid phase occurred at 700°C from eutectic melting among CaCO3, Na2CO3, and MgO. Further liquid phase formed at the CaCO3–Na2CO3, eutectic at 785°C and a fusion reaction among SiO2, CaO, and the molten phase at 812°C. Reactions between molten soda ash and silica grains to form a sodium disilicate coating also occurred in this temperature range. The effects of reaction accelerant additions (Na2SO4, NaNO3, NaCI) on batch fusion were analyzed. Sodium chloride was found to be the most effective melting accelerant due to the formation of a NaCI–Na2CO3eutectic liquid phase at ∼636°C, which effectively attacked the silica relic. CO2gas release terminated ∼80°C earlier with 1 wt% NaCI addit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03648.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Investigations have been made on the low‐temperature sinterability of calcium‐doped lanthanum chromites which are to be used as interconnectors in solid oxide fuel cells (SOFCs). Nominally chromium deficient lanthanum calcium chromites (La0.7Ca0.3Cr1‐yO3,y= 0.02) were found to be sinterable to 94% theoretical density at 1573 K in air, whereas no densification was observed for samples with y = 0. The two‐step shrinkage process suggests a liquid phase sintering mechanism with calcium oxychromates playing an important role as the liquid phase. After sintering at 1573 K, calcium‐rich substances remained at grain b

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03649.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Crystallization of BaTiO3from an X‐ray amorphous, metal organic precursor was investigated by comparing samples heated in O2, air, argon, and CO2. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500° and 620°C and that BaTiO3forms directly by the endothermic decomposition of this phase between 635° and 700°C. From thermodynamic calculations, thermal analysis, X‐ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba2T

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03650.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Reaction mechanisms in the formation of PZT solid solution were studied under hydrothermal conditions (Pb/(Zr+Ti) = 1.0 to 1.9, Zr/Ti = 0/10 to 10/0, 1Mto 5MKOH, 100° to 220°C, 2 h). A yellow tabular crystallite with tetragonal symmetry and Pb/Ti ∼ 2 was formed at 100° to 130°C. A PZT crystallite was formed just above 150°C. The crystallite was a mixture of Ti‐rich PZT and Zr‐rich PZT phases. When the temperature and KOH concentration were increased, the composition of the PZT product tended to be homogeneous. The PZT in the morphotropic phase boundary zone was formed at Zr/Ti = 5/5,5MKOH, 220°C, 2 h. Neither PbTiO3nor PbZrO3was detected as a separate phase under the above hydrothermal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03651.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The local structure of a Na2O─SiO2oxide glass and a Na2O─iO2─Si3N4oxynitride glass has been investigated by the pulsed neutron diffraction method. In the oxide glass, the first peak of radial distribution function (RDF) curves appeared at 0.1627 nm corresponding to Si─O boxh length. In the oxynitride glass, the first peak of the RDF curve was shifted to longer distances at 0.1650 nm due to the coexistence of Si─O and Si─N boxhs. The first peak in the RDF curve of the oxynitride glass was deconvoluted into two peaks whose positions are located at 0.1626 and 0.1709 nm. The one at 0.1626 nm is ascribed to Si─O boxhs and the other at 0.1709 nm to Si─N boxhs. The number of silicon atoms around a nitrogen was found to be 2.42, suggesting that not all of the nitrogen atoms are boxhed to three silicon atoms, but 58% twofold (─N─) and 42% threefold (>N─) nitrogens coexist in the present Na‐Si‐O‐N oxynitride glass. The formation of twofold nitrogens may arise from the reaction between ≡Si─O−and ≡Si3N groups. This model is compatible with the experimental observation that the density and Vickers hardness of oxynitride glasses

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03652.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

By a combination of conventional physical property measurements and high‐temperature electrical property studies, the solid solution limit, transport parameters, and potential defect regimes of the Bi2.1Sr1.9(Ca1 ‐xYx)Cu2Oysolid solution were established. A continuous solid solution extends tox= 0.7 or 0.8. The electrical properties indicate that the product of the hole density‐of‐states and mobility for semiconducting compositions is approximately an order of magnitude smaller than for the otherp‐type superconducting cuprates. A pronounced drop in hole concentration accompanies the tetragonal‐to‐orthorhombic transition atx= 0.5, whereafter superconductivity disappears. The electrical properties also indicate that a compositionxchange occurred reversibly

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03653.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The cubic‐tetragonal phase transition of 14 mol% ErO1.5‐ZrO2was investigated through high‐temperature powder X‐ray diffraction. A new tetragonal form without tetragonality,t″‐ZrO2, was taken into consideration, although only two forms oft‐andt′‐ZrO2have previously been distinguished. The metastablet″‐ZrO2, which could be obtained by rapid quenching of 14 mol% ErO1.5‐ZrO2melts, partially changed intot′‐ZrO2through a thermal activation process above 500°C. Thet′‐ZrO2continuously changed intot″‐ZrO2or transformed into cubic phase at about 1200°C. Thet′‐

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03654.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY