Showing papers by "Patrick S. Nicholson published in 1990"
TL;DR: Etude des composites constitues par un verre bioactif de composition (% molaire): 46,2 SiO 2 •26,9 CaO•24,3 Na 2 O•2,6P 2 O 5 renforces par 20% en volume de particules d'argent ou 20% in volume of trichite SiC as discussed by the authors.
Abstract: Etude des composites constitues par un verre bioactif de composition (% molaire): 46,2 SiO 2 •26,9 CaO•24,3 Na 2 O•2,6P 2 O 5 renforces par 20% en volume de particules d'argent ou 20% en volume de trichite SiC
9 citations
TL;DR: In this article, polycrystalline samples of Na, K-β″ β -aluminas with a c0-textured microstructure have been successfully produced and a significant difference of electric conductivity between directions perpendicular and parallel to the pressing direction was determined by ac impedance spectroscopy.
7 citations
TL;DR: In this article, the fracture of a part-through elliptical crack was modeled for a spherical inclusion using a weight function method to compute the residual stress intensity factor for a part through elliptical fracture.
Abstract: The fracture of ceramics initiating from a typical inclusion is analyzed. The inclusion is considered to have a thermal expansion coefficient and fracture toughness lower than those of the matrix and a Young's modulus higher than that of the matrix. Inclusion-initiated fracture is modeled for a spherical inclusion using a weight function method to compute the residual stress intensity factor for a part-through elliptical crack. The results are applied to an {alpha}-Al{sub 2}O{sub 3} inclusion embedded in a tetragonal ZrO{sub 2} ceramic. The strength predictions agree well with experimental data.
7 citations
TL;DR: The ac impedance conductivity of H 3 O + -β''/β-Al 2 O 3 ceramic electrolytes has been determined from 20 to 240°C in saturated steam and air.
6 citations
TL;DR: In this paper, a proton conductor based on H 3 O + -β β/ββ-Al 2 O 3 was fabricated for steam electrolysis cells and the cell performances were discussed.
4 citations
TL;DR: In this article, the ionic conduction mechanism in the mixed-alkali/mixed-phase β″/β-alumina electrolytes is discussed and the total conductivity of the ceramics can be described in terms of conductivities of the β″- and β-Al 2 O 3 grains and their boundaries.
4 citations
TL;DR: In this paper, it is suggested that the difference of relative defect severity is related to local residual stresses which develop during sintering and cooling and to elastic modulus differences in the case of solid inclusions on external loading.
Abstract: Equivalent-sized fracture-origin defect in partially stabilized zirconia ceramics show dissimilar behavior in initiating fracture It is suggested that the difference of relative defect severity is related to local residual stresses which develop during sintering and cooling and to elastic modulus differences in the case of solid inclusions on external loading The existence of residual stresses associated with various defect types is demonstrated, and their variation with temperature is explored The relative severity of {alpha}-alumina defects in tetragonal zirconia varies with temperature, and it is suggested that this is associated with matrix compressive stress relaxation The residual stress associated with agglomerate defects is temperature independent, and no residual stress is associated with pores
4 citations
TL;DR: In this paper, a constant-K I, double-cantilever-beam (DCB) test is described wherein a computer is used to adjust the load continuously as crack growth occurs.
Abstract: A constant-K I , double-cantilever-beam (DCB) test is described wherein a computer is used to adjust the load continuously as crack growth occurs. DCB samples of float glass were used to experimentally verify the procedure.
3 citations
TL;DR: In this paper, the influence of increased temperature at the notch tips of magnesia stabilized sodium β/β′'-alumina bars during sodium-ion electrolysis was investigated using a galvanostatic/galvanostatic-interrupter technique.
2 citations
TL;DR: In this article, a dc-field-assisted, H3O+ ion exchange process for K+/Na+s''-Al2O3 in HAC has been accelerated by cyclic switching of the dc field (cycle = 3secs) or injecting ultrasonic energy.
Abstract: H3O+- and NH4 + -Al2O3 polycrystals have been conductivity-optimised by eliminating metastable grain-boundary phases (NaAlO2 and MgAl2O4) and texturing the microstructure. The grain-boundary conductivity is considerably improved (up to 5x10-5(Ω-cm)-i) from 10-6 (Ω-cm)-l). The dc-field-assisted, H3O+ ion exchange process for K+/Na+-s''-Al2O3 in HAC has been accelerated by cyclic switching of the dc field (cycle = 3secs) or injecting ultrasonic energy. The former doubles the steady-state ion-exchange current to 12 μA by dispersing the HAC/electrolyte, interfacial, H3O+ polarisation layer. The ion-exchange current-efficiency is not improved from 0.15. The ultrasound (23 MHz) markedly shortens the time to complete ion-exchange (400 hrs.vs. > 700 hrs), more than doubles the final ion-exchange current (360 μA.vs. 150 μA) and improves the ion-exchange current efficiency to 0.24. These results are interpreted in terms of ionic “activation” in the electrolyte. Evidence is presented of a mixed-cation-effect in H3O+-K=-s''-Al2O3.
1 citations
TL;DR: In this article, a series of NYS discs were ion-exchanged using KCl/NaCl mixtures to form precursor KNYS, which were then used to electrolyse steam at 100°C.
TL;DR: In this paper, the authors calculated the equilibria and equilibrium species distribution for the systems NH 3 -H 2, NH 3-H 2 and NH 3 H 2 O, and showed that if NH 3 gas mixtures were used for NH + 4 -H 3 O + -β″ /β-Al 2 O 3 solid electrolyte fuel cells operated > 100°C, the EMF would be comparable with that of H 2 -O 2 fuel cells.
TL;DR: The ionic transference number and electronic conductivity of H3O+-β″/β-Al2O3 ceramic electrolytes were measured at 293-429 K using the electrochemical cells.
TL;DR: In this article, NaNa cells were constructed using Na-β″-Al 2 O 3 electrolyte and the resistance changes measured as a function of time and current passage.
TL;DR: In this paper, the H 3 O + rare earth silicates (HNRS) hydronium-ion conductors were prepared by ion exchanging alkali-ion precursors.
01 Jan 1990
TL;DR: In this paper, an elliptical crack model was used to characterize the correlation between fracture stress and fracture origin size, which enabled definition of a "fracture origin severity parameter" for the different origin types.
Abstract: 4.5 wt% Y203-partially-stabilized ZrO2 (YPSZ) four-point bend bars densified by dry-pressing/isostatic pressing/pressureless sintering were fractured and. several fracture origin types were identified. These defects were then classified via their response to various elimination techniques. An elliptical crack model was used to characterize the correlation between fracture stress and fracture origin size. Consistent results showed that an order-of-defect-severity existed, which enabled definition of a “fracture origin severity parameter” for the different origin types. The existence of a relative fracture-origin severity is related to the residual stress fields at the defect-matrix interfaces. The improved strength obtained by secondary processing to eliminate the fracture origin defects did not extend to high temperatures. Efforts were made to improve the strength and toughness of Y-PSZ by incorporation of Na-β-Al2O3 dispersed phase. The mechanical properties of these composites are reported.