Materials Literature
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A water-quenching technique was employed to investigate the effect of porosity on the thermal shock behavior of Si3N4 ceramics. It is shown that the critical temperature difference for crack initiation decreases with increasing porosity. However, the presence of more pores increases the resistance to crack propagation…
In this paper we report the effect of thermal cycling, between 20 °C and 800 °C in a gas mixture of 4% H2 and 96%Ar, on the physical and mechanical properties of Ni-YSZ/YSZ bilayers. It was found that the porosity and Young's modulus of the bi-layers did not change significantly after thermal cycling. However, the cha…
A model was formulated to determine the effect of oxidation of the fibers and the fibers coating on the stress-rupture behavior of Nicalon™/C/SiC at intermediate temperatures. The model, that was reduced in part to the analysis of a fiber bundle subjected to constant loading, predicts time-dependent changes in complia…
The standard strategy developed by Van der Giessen and Needleman ( 1995 Modelling Simul. Mater. Sci. Eng. 3 689 ) to simulate dislocation dynamics in two-dimensional finite domains was modified to account for the effect of dislocations leaving the crystal through a free surface in the case of arbitrary non-convex doma…
Ceramic heat exchangers are now being used industrially in low-pressure applications such as recuperators and air preheaters. Serious consideration is being given also to ceramic materials for high-pressure heat exchangers. The basic advantage of using ceramic heat exchangers in the candidate applications is the poten…
Corrosion-resistant oxide coatings are being developed in order to increase the durability of silicon-based structural ceramics in the presence of molten alkali salts. Crystalline mullite (3Al2O32SiO2) coatings were deposited onto Si3N4 by chemical vapor deposition (CVD) at 1050°C. The resultant CVD mullite microstruc…
Ceramic matrix composites, manufactured via the Liquid Silicon Infiltration (LSI) process, show a wide variability of microstructures, thermal and mechanical properties. The high amounts of carbon fibres limit their use under oxidative atmospheres to some few hours with unprotected surfaces. External coatings based on…
The tensile-tensile fatigue behavior of a polymer-derived ceramic matrix composite was studied in air at room temperature, 982°C and 1204°C. The fatigue life was found to decrease with increasing stress according to the relationship Opeak = Guts N™, where Opeak is the peak cyclic stress, auts the monotonic ultimate te…
Abstract Lead–free ceramics (1– x )(K 0.5 Na 0.5 )NbO 3 – x BiFeO 3 doped with 1 mol% Fe 2 O 3 (KNNBF/ x ) have been synthesized by pressureless sintering. With the Fe 2 O 3 doping, the KNNBF/ x ceramics can be well sintered at 1085–1100 °C and exhibit a pure perovskite structure with x < 0.013. It was found that t…
Abstract The ternary 70P2O5-10Li2MoO4-20Li2O and 70P2O5-10Na2MoO4-20Na2O glasses, prepared by the press-melt quenching technique, were studied at temperatures between 298 and 418 K for their high dc electric field properties. For the above purpose, the effect of a strong electric field on the dc conduction of these am…
Abstract The quantitative evaluation of ATR FT‐IR spectra of chemically derivatized plasma‐modified polymer surfaces is proposed in order to derive area densities ρ (numbers or mole numbers per unit area) of chemical functional groups. Because of the very small thickness d mod of the modified surface region, a simple…
We show that analytical ultracentrifugation can be applied to derive full equations of state of colloids in a single sedimentation equilibrium experiment, by determination of single-phase boundaries as well as of osmotic pressure versus concentration at fixed temperatures. A continuous dependence of the osmotic pressu…
Using neutron and resonant X-ray scattering, we studied crystal structure and charge-ordering pattern in La 1.5 Ca 0.5 CoO 4 . Taking A 2 m m with a – b type twin structure into account, Co 2+ /Co 3+ checkerboard charge ordering pattern was suggested in La 1.5 Ca 0.5 CoO 4 by neutron scattering structure analysis. In…
Various organosilicon polymers have been converted into small diameter, finegrained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to >1600ď. The high pyrolysis temperature densifies the fiber and causes CO evolution which removes nearly all oxygen. An additive prevents the loss of strength norm…
The tensile creep behavior of a Lu-containing silicon nitride (SN 281) was characterized in the temperature range of 1350 °C to 1550 °C for test periods up to 10000 h. For the same test conditions, the minimum strain rates were several orders of magnitude less than that of other commercial grades of silicon nitride. T…
We present a rigorous description of the effects of partial coherence and detector resolution on intensity autocorrelation functions as they can be measured by x-ray photon correlation spectroscopy (XPCS). Based on the Huygens-Fresnel propagation law and on the first Born approximation, we derive a general expression…
In these decades, silicon nitride has been recognized as the most promising material for ceramic gas-turbine components. In this paper, creep and creep rupture behavior of silicon nitride, which has been developed for such applications by controlling the grain boundary phase and microstructure, are investigated at 135…
Magnetization and 7 Li-NMR measurements have been carried out for an a -axis-aligned sample of Li 2 ZrCuO 4 , which has quasi one-dimensional Cu 2+ spins ( s = 1/2) in chains of edge-sharing CuO 4 square planes and exhibits the magnetic transition at temperature T N ∼7 K. The NMR results at ∼2 K indicate that the syst…
Near-stoichiometric silicon carbide fiber “Hi-Nicalon Type S” was derived from polycarbosilane fibers with electron beam curing and pyrolysis. Hi-Nicalon Type S, on production scale, has high environmental stability and sufficient mechanical properties even at high temperature.
Abstract— Coatings of indium tin oxide (ITO) nanoparticles on different flexible polymer substrates were investigated with respect to the achievable sheet resistance and their electrical behavior under oscillatory bending. As substrate materials, polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polyethe…