摘要:

In the present paper we examine the influence of the secondorder term of the asympotic stress solution for mode‐I, steady‐state, plane‐strain, quasi‐static crack growth in a supercritically trasforming material. It was found that the second‐order term can affect the toughness, not always in a positive way. The second‐order term includes the effects of the loading, of the overall geometry, and of the crack length. The findings can be used for the evaluation of the purely material resistance curves of small‐scale transforming ceramics, as well as for the toughness predictions of these materials. The results may be useful for unifying different test results, and for a better understanding of the strength‐tou

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05501.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

An experimental investigation of the packing of some ternary mixtures of nonspherical particles has been conducted. The double extrapolation method is used to determine the packing density of a particle mixture in infinite space. The application of experimental design to particulate mixture problems is demonstrated. The results indicate that the similarity between the packing systems of spherical and nonspherical particles can be readily depicted in terms of specific volume variation.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05502.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

This paper discribes the adaptation of the layer removal method for the measurement of residual stresses in the plane of a plate for a ceramic injection molding suspension. The latter contained 56 vol% alumina in a polypropylenebased organic vehicle. A strain gauge method was used to measure curvatures. The experimental precautions are discussed and the errors evaluated. The method is applied to conventional moldings made at high and low pressures, to annealed moldings, and to moldings made with a heated sprue.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05503.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The ball‐milling hydration of highly reactive β‐Ca2SiO4synthesized from hillebrandite, Ca2(SiO3)(OH)2, was investigated and compared with its static hydration under a water/solid ratio of 10. In static hydration, the hydration is completed in 8 d to yield C‐S‐H with a Ca/Si ratio of 1.81 and Ca(OH)2. There is no major change after this period. In the case of ball milling, the hydration is completed in 2 d to yield C‐S‐H with Ca/Si = 1.81 and Ca(OH)2. After this, the two products react to form a C‐S‐H(II)‐like monophase hydrate having a Ca/Si ratio of 1.98. The morphology and structure of this hydrate are different from those of the earlier hydrate, and afwillite is not formed.29Si MAS NMR measurements indicated the C‐S‐H to be a mixture of dimers and single‐chain structures. Dimeric species are the main species up to completion of the reaction, but polymerization progresses very rapi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05504.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Crack‐free Pb(Zr,Ti)O3(PZT) thin films with preferred orientation were prepared successfully on MgO (100), SrTiO3(100), and Pt/Ti/SiO2/Si substrates from metal alkoxide solutions. Calcination of precursor films in a H2O─‐O2gas mixture was found to be effective not only for low‐temperature crystallization of perovskite PZT, but also for obtaining the preferred orientation of PZT films. Single‐phase PZT films with high preferred orientation were synthesized on MgO (100) and Pt/Ti/SiO2/Si substrates at 550° and 600°C for 2 h, respectively. The PZT film on the Pt/Ti/SiO2/Si substrate showed a permittivity of 520, tan δ of 0.03, a remanent polarization of 24 μC/cm2, and a coercive fiel

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05505.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The electrical conductivity of high‐purity, single‐crystal alumina is determined parallel to and perpendicular to thec‐axis. The mean conductivity of four samples of each orientation is a factor 3.3 higher parallel to thec‐axis than perpendicular to it. The conductivity as a function of temperature is attributed to extrinsic electron conduction at temperatures from 400° to 900°C and intrinsic semiconduction at temperatures from 900° to 1300°C. In the high‐temperature regime, the slope on all eight specimens is 4.7 ± 0.1 eV. Hence, the thermal bandgap at 0 K i

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05506.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

An experimental setup and novel measurement technique are described which allow reliable conductivity measurements to be made at conductivities as low as 10−17Ω−1.cm−1and temperatures up to at least 1300°C. This capability is of particular interest for conductivity measurements on high‐resistivity insulators over a large range of temperatures. This technique has been used to measure the conductivity of single‐crystal alumina from 400° to 1300°C in a 10−7torr (∼1.3 × 10−5Pa) vacuum, equivalent to an oxygen partial pressure of about 10−8torr (∼1.3 × 10−11atm or ∼ 1.3 × 10−6Pa). Surface and gas‐phase conductance are determined as a function of temperature, and the requirements for their minimization are described. A key requirement is a very low voltage between the volume guard and the guarded electrode. The effect of leakage currents due to the sample fixture, electrical feedthroughs, and electronic instrumentation are also evaluated, and proper design features to make the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05507.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The crystal structure and surface morphology of Si3N4prepared by LPCVD were characterized as a function of processing conditions. Temperature was the most dominant variable which affected the coating microstructure. Strongly faceted crystalline Si3N4was deposited at temperatures above ∼ 1410°C. In the temperature range of 1300° to 1410°C, crystalline and amorphous phases were codeposited. The content of the crystalline phase rapidly decreased with decreased temperature. In this temperature range, the coating crystallinity was also influenced by kinetic factors such as deposition rate and reagent depletion. For example, Si3N4became more crystalline as the deposition rate was decreased by either decreasing the flow rate or increasing the NH3/SiF4molar ratio. At ∼ 1300°C, the coating surface appeared fully botryoidal, and the coatings were mostly amorphous. Changes in the orientation and size of Si3N4crystallites were parametrically documented. As the temperature was increased, the Si3N4grains generally became more preferentially oriented to the (102) and/or (l0l) wherel= 1,2,3,., directions. The average facet size increased with coating th

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05508.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Most theories on abrasive machining of brittle materials are based on indentation experiments. Little attention has been paid to the consequences of indentation interaction. In this study it is shown that the residual stress field of an adjacent indentation strongly influences the radial crack length. This effect is analyzed on the basis of the concept of the expanding cavity. The presence of an adjacent indentation leads to the formation of a large new lateral crack system. Crack–crack interaction is found to be of minor importance. Implications for the description of machining processes are discusse

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05509.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Microstructural characterization of a high‐Al2O3substrate containing cofired thick‐film tungsten metallization, with particular emphasis on the metal/ceramic interface, was conducted. The substrate contained tabular Al2O3grains surrounded by a continuous calcium magnesium aluminum silicate glass containing particles of monoclinic ZrO2and reduced rutile (TiO2‐x). The metal/ceramic adhesion was caused by mechanical interlocking between the W and Al2O3grains by the glass phase which penetrated the porous W layers during sintering; there was no interfacial reaction or diffusion zone. The mechanical properties of the W metallization did not limit interfacial strength. Heat treatments of the substrate at 1400 K in air and under vacuum resulted in the devitrification of the intergranular glass. The most abundant devitrification product was anorthite (CaAl2Si2O8), accompanied by magnesium aluminate titanate, magnesium aluminate spinel, α‐cristobalite (SiO2), and α‐cordierite (Mg2Al4Si5O18). In addition, small rutile particles precipitated within the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05510.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY