摘要:

Ultrafine and nearly spherical ferrites such as NiFe2O4, ZnFe2O4, NixZn1−xFe2O4, Mn0.5Zn0.5Fe2O4, and CoFe2O4were prepared under mild hydrothermal conditions by precipitating from metal nitrates with aqueous ammonia. These hydrothermal ferrite powders were shown to sinter to almost theoretical density at 1000°C without any sintering ai

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05773.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Hot isostatically pressed silicon nitride was produced by densifying Si3N4powder compacts and reaction‐bonded Si3N4(RBSN) parts with yttria as a sintering additive. The microstructure was analyzed using scanning electron microscopy, X‐ray diffraction, and density measurements. The influence of the microstructure on fracture strength, creep, and oxidation behavior was investigated. It is assumed that the higher amount of oxygen in the Si3N4starting powder compared with the RBSN starting material leads to an increased amount of liquid phase during densification. This results in grain growth and in a larger amount of grain boundary phase in the hot isostatically pressed material. Compared with the hot isostatically pressed RBSN samples therefore, strength decreases whereas the creep rate and the weight gain during oxidation incre

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05774.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Relatively little is known about the fundamental deformation processes in intrinsically hard, brittle materials, and even less about how these processes lead to the initiation of cracks. In this paper, transmission electron microscopy is used to study the deformation structure within Vickers indentation zones of single‐crystal sapphire with {} surface orientation. The relative misorientation of regions within these zones, as mapped by convergent‐beam kikuchi patterns, is found to be severe, indicative of shear processes operating close to the cohesive limit. Two principal types of deformation are identified, basal twinning and pyramidal slip. Incipient microcracks are observed at both the twin interfaces and the slip planes. These incipient “flaws” act as nucleation sites for the ensuing radial and lateral

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05756.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A crack which propagated naturally in 15R‐sialon was observed by high‐resolution TEM. The crack was found to be atomically sharp and there was no evidence of microplasticity near the tip. The deformation of the lattice around the crack is discussed by considering a linear fracture mechanics mo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05775.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Tetragonal‐to‐rhombohedral stress‐induced phase transformation was studied by X‐ray diffraction on the ground surfaces of tetragonal zirconia polycrystals and partially stabilized zirconia containing 2.0 to 5.0 mol% Y2O3prepared by hot isostatic pressing. The rhombohedral phase increased with Y2O3content and also with hot isostatic pressing temperature. The stability of the rhombohedral phase was studied with regard to surface finish and thermal annealing. The subsequent heat treatment of the specimens was found to cause the reverse rhombohedral‐to‐tetragonal tra

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05776.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The quench strengthening of an aluminosilicate ceramic body was studied by measuring the strengths and determining the strength distributions, estimating the residual compressive stresses at the surface by measuring the bending moments, and directly observing the surface crack patterns of quench‐strengthened specimens. When considered in combination, these related results enable the assessment of the individual contributions of the residual compressive surface stresses and the changes in the flaw populations to the quench strengthening phenomenon. The quench strengthening phenomenon is discussed as a combination of those features of the process and a general schematic diagram of the phenomenon is presente

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05757.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

K2O activity in K+‐(α+β)‐alumina was determined from emf data of the galvanic cell Pt,O2,(α+β)‐alumina/K+‐β‐alumina/K2SO4,SO2+SO3+O2,Pt. K2O activity in the K+‐(α+β)‐alumina was expressed by the equation log ak2o(±0.038)=(−18295±120)(K/T)+(0.998±0.110), where 961 K

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05777.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Partially stabilized zirconia has been rapidly sintered in a microwave apparatus to good final densities (95% to 98% of theoretical density). The grain size was not noticeably different from that of conventionally sintered material. Properties of the sintered material are given.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05778.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Computer‐modelling techniques are applied to the calculation of defect formation and migration energies in α‐Fe2O3and α‐Cr2O3: both electronic and lattice defects are considered. The results are used to predict Arrhenius energies for cation and anion migration in different composition and temperature regimes and show reasonable agreement with experimental data where these are av

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05758.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Donor‐doped, stoichiometric BaTiO3sintered at 1350°C for 1 h exhibits a maximum room‐temperature conductivity at [La3+]∼0.15 mol%. Elements of lower valence than Ba2+or Ti4+, when incorporated into semiconducting BaTiO3, are regarded as poisoning impurities, i.e., acceptors. They tend to increase the room‐temperature resistivity of the semiconducting BaTiO3. For insulating BaTiO3resulting from high Mg2+acceptor doping levels, the semiconductivity can be restored by introducing higher La3+donor‐dopant concentrations. This behavior is interpreted as a compensation effect based on the defect chemistry of the acceptor‐ and donor

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb05780.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY