摘要:

Infrared spectroscopy was used to monitor and characterize solutions used in the preparation of PZT 53/47 powders, dried gels, and thin layers deposited on platinized silicon substrates. It was found that careful control of the chemistry of the precursor solutions, in particular the control of the formation of esters and their elimination, resulted in reproducible solutions which could be used to prepare thin layers with superior properties. In addition, it was found that phase development and microstructure were related to the precursor chemistry. Single‐phase perovskite layers with uniform microstructures resulted from ester‐free solutions and were suitable for ferroelectric applications (Pr∼ 22 μC/cm2,Ec∼ 80 kV/cm,K∼ 800, ta

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04392.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

To further our understanding of the mechanism of environmentally enhanced crack growth, molecular oribital calculations (MO) using the ab initio self‐consistent‐field (SCF) technique have been employed to investigate the effect of applied strain on the atomic charge distribution and the bond overlap population of the Si–O bond at the crack tip of silica. Pyrosilicic acid (H6Si2O7) with eclipsed conformation has been employed as the model molecule. Strain effects up to 20% were simulated in terms of bond stretching and angle distortion. The results indicate that, regardless of how the external strain is applied on the model molecule, the gross electron population on the bridged oxygen increases as strain increases and that on the silicon decr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04393.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The viscosity of some borosilicate glasses increases with heat‐treatment time for phase separation. The viscosity increase in the initial stage of phase separation is attributed to the composition change of the separated phases. The origin of the viscosity increase in the later stage of phase separation is the subject of controversy. Namely, the viscosity increase has been attributed to two different mechanisms: (1) environmental relaxation and (2) the increase of silica content in the high‐viscosity silica‐rich continuous phase. Analyses are presented to show that the latter model is consistent with the experimental

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04394.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Crack bridging by inclined fibers has been studied in a brittle fiber–brittle matrix model ceramic composite. Results of the fiber bridging force vs the crack opening displacement have been obtained for different fiber inclination angles using a fracture mechanics approach. Localized matrix cracking has been observed for inclined fibers and related to fiber inclination angle. The experimental results showing the influence of fiber inclination angle are discussed and compared with theoretical analyses to provide insight into crack bridging by inclined fibers/whiskers. Implications for toughening by whisker bridging are also discusse

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04395.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The adhesion and interfacial bonding between nonreactive liquid metals and solid inocovalent oxides are studied on the basis of the experimental work of adhesionWdata. An analysis of the experimentalWvalues of different liquid metals on various solid oxides is first performed to put into evidence the dependences of the work of adhesion of a metal/oxide system on the electron density of the metal and on the thermodynamic stability of the oxide. An electronic model is then proposed to describe the microscopic mechanism of metal–oxide interactions. Based on the model, the work of adhesion and the contact angle of different liquid metals on various solid oxides can be interpreted and estimated, and their correlations to the various physical properties of the oxides can be easily deduced. The basic consideration of the model is that the adhesion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valence band which is not completely filled with electrons at high temperatures, and is enhanced when this electron transfer at the metal/oxide interface is increased. The extension and application of the model to solid metal/solid oxide systems is also presente

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04396.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Planar faults on the basal planes of zinc oxide are formed during sintering with 0.1 mol% antimony oxide at 1200°C. Spatially resolved energy‐dispersive X‐ray analysis and electron energy loss spectroscopy microanalysis reveal the presence of significant quantities of Sb. Quantification of the data suggests that up to a monolayer of Sb is distributed uniformly on the faulted

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04397.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

In order to evaluate the crystallization tendency of glasses, the ratio of the crystallization temperature to the liquidus temperature (Tc/TL) was obtained by DTA measurement for the Na2O–B2O3and Na2O–B2O3–Al2O3systems. The critical cooling rate for glass formation (Q*) was also measured. The measurements were performed in the composition range of (100 −x)Na2O–(x)B2O3, (x= 25–35 and 60–100 mol%), and (100 −y)0.5Na2O·0.5B2O3−(y)Al2O3, (y= 6–34 mol%). The relationship betweenTc/TLandQ* was discussed. A linear relationship betweenTc/TLand logQ* for these systems was found. Furthermore, the relationship betweenTc/TLandQ* was verified by computer simulation based on the crystallization kinetics of glass o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04398.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

As a consequence ofR‐curve behavior, ceramic materials may exhibit increased fracture toughness (KIc) following slow crack extention. In this investigation, the effect of crack propagation on fracture toughness is studied in static bending tests. For the calculation of stress intensity factors (KI) the stress distribution must be known at the moment of fracture. As a consequence of creep, this stress distribution must deviate from the linear distribution. The corresponding stress intensity factors are computed using the fracture mechanical weight function. Experimental results for fracture toughness are communicated for a 2.5%‐MgO‐doped hot‐pressed Si3N4a

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04399.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The thermal conductivity of a 40 vol% silicon carbide‐particulate‐reinforced aluminum matrix composite was determined as a function of silicon carbide mean particle size ranging from 0.7 to 28 μm. A size dependence was found consisting of a decrease in thermal conductivity with decreasing SiC particle size. This effect is in accordance with theoretical expectations for composites with an interfacial thermal barrier at the dispersion–matrix interface. At the finest particle size of the silicon carbide, the composite thermal conductivity approached the value for the matrix with pores, as expected from theory. Only at the largest SiC particle size did the composite thermal conductivity exceed the value for the matrix. These results suggest that in maximizing the thermal conductivity of composites with an interfacial thermal barrier, the reinforcement particle size should be as large as practically po

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04400.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Electrical behavior of a few compositions withx0.50 in the system La1−xNaxCo1−xNbxO3has been studied by complex‐plane‐impedance analysis in the temperature range 300–525 K. Three depressed semicircular arcs have been observed in the complex impedance plot of the composition withx= 0.50. These arcs represent the contributions of bulk, grain boundaries, and electrode polarization to the total observed resistance. Two semicircular arcs have been observed in the complex‐impedance plot of the compositions withx= 0.70 and 0.80. They represent the bulk and the grain boundaries contribution to the total observed resistance. The values of the resistance for the bulk and grain boundaries in each sample indicate the formation of barrier layers in thes

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04401.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY