摘要:

An aluminum (Al) target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm2and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase‐pure AlN by X‐ray diffraction (XRD). The surface area of this powder is 82 m2/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observ

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04451.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Aluminum‐doped zinc oxide films prepared using a normal‐pressure CVD (NP‐CVD) method were studied as a transparent electrode material. The films were prepared on fused quartz substrates at 500°C using bis(2,4‐pentanedionato)zinc and tris(2,4‐pentanedionato)aluminum as source material. The transparent films, ∼0.3 μm in thickness, with a transmittance above 80% at a wavelength between 400 and 820 nm, were easily obtained. The optical band gap of the films increased from 3.3 to 3.6 eV with increasing amounts of aluminum dopant. The minimum resistivity of the film was about

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04452.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Al2TiO5formation in Al2O3/TiO2multilayer composites obtained by slip casting has been studied in the temperature interval ranging from 1200° to 1450°C. It has been found that nucleation plays a fundamental role in Al2TiO5formation. Furthermore, it has been observed that initial growth of Al2TiO5is substantially enhanced when in contact with TiO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04453.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Diffusion profiles of Sr in single‐crystal MgO at 1473 to 1843 K have been determined by a depth‐profiling technique using secondary ion mass spectrometry. The diffusion experiments were performed using a focusing infrared furnace. The temperature dependences of lattice and dislocation diffusion areD1= 2.6 × 10−11exp(–268.2/RT[kJ/mol])[m2.s‐1],Dd= 1.7 × 104exp(–562.3/RT), respectively. The present lattice diffusion coefficients are three orders of magnitude smaller than those previously reported. Si diffused with Sr in MgO over 1583 K, and the diffusion coefficients of Si were also determined. The results of Si diffusion were equivalent to those of our p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04454.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Theθ‐projection parametric method is used to analyze the creep strain‐versus‐time data, obtained in four‐point flexure, for a 25 wt% silicon whisker‐reinforced polycrystalline alumina composite material. The results, used in conjunction with a suggested value of the activation energy for the creep‐rate‐controlling process for this material of about 620 kJ/mol, led to a postulate that grain‐boundary sliding is the rate‐determining mechanism. In addition, the use of the results in obtaining the values of relevant design creep parameters (namely, life or stra

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04455.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Recent reports have suggested that an exponential dependence of failure time on applied stress provides a more fundamental description of fatigue, but the power law is usually used to assess the long‐term mechanical reliability of lightguide fibers. A consequence of the exponential expression is a linear dependence of applied stress and activation energy. This study applies the exponential law to all temperature‐dependent fatigue data for lightguide fibers reported in the literature. The results show consistency with the prediction of the exponential express

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04456.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Multiple cracking due to pseudo strain–hardening of fiber‐reinforced brittle matrix composites contributes significantly to enhanced composite strain capacity as well as toughness. This unique phenomenon is true for both continuous aligned and discontinuous random fiber composites. Theoretical formulation of multiple crack spacing is reviewed in this paper. In particular, a snubbing effect of fiber pullout and a bundling effect of fiber strands on crack spacing are discussed. Taking account of these effects, expressed via the snubbing coefficient,f, and effective bond strength, τeff, a better spacing prediction has been obtained for a discontinuous random glass‐strand‐reinforced cement c

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04457.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Submicrometer powders of complex oxides were prepared via resin intermediates based on a starch type of organic precursor. A commercially available water‐soluble starch derivative was (for the first time) used as the organic base for solution synthesis of ceramic powders. Calcination of the charred, fluffy, amorphous resins at a temperature below 600°C for 4 h yielded perovskite powders of Sr‐doped LaMnO3and Sr‐doped La(Fe,Co)O3. Sr‐doped LaCrO3needed to be calcined above 750°C to ensure phase purity and to remove organic residue. Due to the low cost of starch derivatives, the process has the potential of being more economical than the commonly used Pechini's type process, which utilizes citric acid and ethyle

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04458.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The strain rate dependence of the stress‐inducedt–mtransformation behavior of a Ce‐TZP ceramic with a grain size of 1.1 μm has been investigated both in four‐point bend and Charpy impact tests. The crosshead speed was varied from 8.3 × 10−8m/s to 8.3 × 10−3m/s in the four‐point bend tests. In the impact tests, the striking velocity was 2.5 m/s. Double notches (a/w= 0.5) were made on one side of the specimen to measure the stress‐inducedt–mtransformation zone size at the nonpropagated notch tip. It was found that a transition of the transformation zone size with crosshead speed occurred at about 10−6to 10−5m/s. Above this critical speed, the transformation zone was at least an order of magnitude larger in size. This new strain‐rate‐dependent transformation behavior has

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04459.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Mercury porosimetry was used to study the pore‐size distribution of both green and partially sintered alumina compacts. Experiments showed that using the mercury‐penetration volume data to study the pore structure changes during sintering for a compact with a bimodal pore‐size distribution could lead to wrong conclusions because the mercury‐penetration volume was not linearly proportional to the porosity. Instead, the porosity distribution should be used. When the porosity of large pores was<10%, some large pores within the compact were observed to become isolated or channeled to the compact surface; this caused errors in the porosity distribution measured by mercury p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04460.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY