Interfaces In Glass-Containing Ceramics

1999 ◽  
Vol 5 (S2) ◽  
pp. 98-99
Author(s):  
C. Barry Carter ◽  
N. Ravishankar ◽  
Carsten Korte ◽  
M.P. Mallamaci
Keyword(s):  
Grain Boundaries ◽  
Strong Dependence ◽  
Solid Substrate ◽  
Special Boundaries ◽  
Intergranular Films ◽  
The Subject ◽  
Microscopy Techniques ◽  
Sintered Oxide ◽  
Microstructural Examination

The interaction of a liquid with a solid substrate has been the subject of intense research since the early 1800s. The subject is relevant and very important even today from a basic science as well as technological standpoint. Liquid-phase-sintered oxide ceramics often contain a siliceous glassy layer in the grain boundaries which affect the properties of the ceramic. The wetting of the grain boundaries by the liquid has a strong dependence on the crystallography. While some boundaries are preferably wet, other special boundaries appear to be completely ‘dry’. The presence of the liquid film also affects the faceting behavior of the boundary plane. While several studies have been carried out on these intergranular glass films, many of the basic issues still remain unclear. The development of modern microscopy techniques facilitate the characterization of structure and chemistry at a high spatial resolution. This paper deals with the microstructural examination of two of the important issues involved with these intergranular films, i.e., faceting of grain boundaries in the presence of a glassy phase and the behavior of interfaces between two glassy phases of different compositions.

Migration of Silicate Liquid Out of Grain Boundaries in Ceramics

1999 ◽  
Vol 5 (S2) ◽  
pp. 800-801
Author(s):  
N. Ravishankar ◽  
C. Barry Carter
Keyword(s):  
Grain Boundaries ◽  
Strong Dependence ◽  
Liquid Phase Sintering ◽  
Laser Deposition ◽  
Intergranular Phase ◽  
Commercial Alumina ◽  
Special Boundaries ◽  
Polycrystalline Ceramics ◽  
Film Assembly ◽  
Twist Boundaries

Liquid-Phase Sintering (LPS) is a conventional fabrication route for the densification of alumina and other ceramics. The polycrystalline ceramics processed by LPS contain siliceous phases along the grain boundaries. This wetting of the grain boundaries has a strong dependence on the crystallography of the boundary. The liquid preferentially wets certain orientations while some special boundaries are ‘dry’. The mechanism of dewetting of these boundaries is not well understood. Several approaches have been adopted to study the nature of the liquid-solid interaction at the grain boundaries. In commercial alumina, anorthite is the most commonly found intergranular phase.Basal twist boundaries in alumina which contain a thin layer of anorthite glass have been investigated in the present study. Pulsed laser deposition has been used to deposit thin films of anorthite glass on optically flat basal sapphire. The substrate-film assembly is then bonded to an optically polished basal sapphire by sintering the assembly at 1650°C for 2h.

Characterization of Grain Boundaries in Electronic Ceramics by Transmission Electron Microscopy

1981 ◽  
Vol 5 ◽  
Author(s):  
David R. Clarke
Keyword(s):  
Electron Microscopy ◽  
Boundary Layer ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Electronic Ceramics ◽  
Transmission Electron ◽  
Zno Varistors ◽  
Microscopy Techniques

ABSTRACTThe principal high resolution transmission electron microscopy techniques used in characterizing grain boundaries in electronic ceramics are described, including those recently developed for detecting the presence of extremely thin (∼10Å) intergranular phases. The capabilities of the techniques are illustrated with examples drawn from studies of ZnO varistors, PTC BaTiO3 devices and boundary layer capacitors.

Critical issues in ceramic microstructures

1996 ◽  
Vol 54 ◽  
pp. 640-641
Author(s):  
D. R. Clarke
Keyword(s):  
Ceramic Materials ◽  
Intergranular Films ◽  
Oxide Substrates ◽  
Critical Issues ◽  
Technical Issues ◽  
Compositional Variations ◽  
Microscopy Techniques ◽  
Ferroelectric Oxides

As the number and variety of ceramic materials have grown so rapidly in the last few decades, ranging from silicon nitride structural ceramics to the perovskite superconductors to the ferroelectric oxides to semiconducting sensors, the number of scientific and technical issues has also grown rapidly. Many of the basic questions relate to the role the microstructures play in determining the observed physical behavior but increasingly it is not the geometric properties of the microstructure that are of central concern but rather compositional variations and associated electrical characteristics. These require the continued development of microscopy techniques to complement the tremendous advances in microstructural understanding that have already been made possible by microscopy in the past.Since the role of microscopy is such a broad one, only a few of the most generic problems in microstructure characterization will be described in this talk. The topics selected include the characterization of intergranular films in liquid-phase sintered ceramics, the charge distribution at interfaces and the associated space charge, the epitaxial growth of oxides on oxide substrates, and the use of fluorescence imaging to identify phases and non-destructively measure local strains.

High-resolution electron microscopy of nanostructured materials

1995 ◽  
Vol 53 ◽  
pp. 172-173
Author(s):  
M. José-Yacamán
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Nanostructured Materials ◽  
High Resolution Electron Microscopy ◽  
Hrem Image ◽  
Small Particles ◽  
Resolution Electron ◽  
Nanophase Materials

Electron microscopy is a fundamental tool in materials characterization. In the case of nanostructured materials we are looking for features with a size in the nanometer range. Therefore often the conventional TEM techniques are not enough for characterization of nanophases. High Resolution Electron Microscopy (HREM), is a key technique in order to characterize those materials with a resolution of ~ 1.7A. High resolution studies of metallic nanostructured materials has been also reported in the literature. It is concluded that boundaries in nanophase materials are similar in structure to the regular grain boundaries. That work therefore did not confirm the early hipothesis on the field that grain boundaries in nanostructured materials have a special behavior. We will show in this paper that by a combination of HREM image processing, and image calculations, it is possible to prove that small particles and coalesced grains have a significant surface roughness, as well as large internal strain.

CBED analysis of impurity distributions in AlN

1990 ◽  
Vol 48 (4) ◽  
pp. 214-215
Author(s):  
Daniel Callahan ◽  
G. Thomas
Keyword(s):  
Aluminum Nitride ◽  
Bulk Material ◽  
Strong Dependence ◽  
Lattice Parameter ◽  
Promising Technique ◽  
Nitride Ceramics ◽  
Surface Phases ◽  
Convergent Beam ◽  
Oxygen Impurities

Oxygen impurities may significantly influence the properties of nitride ceramics with a strong dependence on the microstructural distribution of the impurity. For example, amorphous oxygen-rich grain boundary phases are well-known to cause high-temperature mechanical strength degradation in silicon nitride whereas solutionized oxygen is known to decrease the thermal conductivity of aluminum nitride. Microanalytical characterization of these impurities by spectral methods in the AEM is complicated by reactions which form oxygen-rich surface phases not representative of the bulk material. Furthermore, the impurity concentrations found in higher quality ceramics may be too low to measure by EDS or PEELS. Consequently an alternate method for the characterization of impurities in these ceramics has been investigated.Convergent beam electron diffraction (CBED) is a promising technique for the study of impurity distributions in aluminum nitride ceramics. Oxygen is known to enter into stoichiometric solutions with AIN with a consequent decrease in lattice parameter.

Characterization of Serrated Grain Boundaries in Ni-Based Alloy 690

2014 ◽  
Vol 52 (9) ◽  
pp. 695-704
Author(s):  
Yun Soo Lim ◽  
Dong Jim Kim ◽  
Seong Sik Hwang
Keyword(s):  
Grain Boundaries ◽  
Alloy 690

MISORIENTATION DISTRIBUTION FUNCTION FOR CUBIC CRYSTALS

2019 ◽  
Vol 85 (5) ◽  
pp. 28-32
Author(s):  
A. S. Kolyanova ◽  
Y. N. Yaltsev
Keyword(s):  
Distribution Function ◽  
Grain Boundaries ◽  
Orientation Distribution ◽  
Recrystallization Annealing ◽  
Misorientation Distribution ◽  
Cubic Crystals ◽  
Special Boundaries ◽  
Pole Figures ◽  
Two Samples ◽  
Euler Space

A calculation method for obtaining the misorientation distribution function (MDF) for cubic crystals which can be used to estimate the presence or absence of special boundaries in the materials is presented. The calculation was carried out for two samples of Al-Mg-Si alloy subjected to various mechanical and thermal treatments: the first sample is subjected to rolling; the second sample is subjected to recrystallization annealing. MDF is calculated for each sample; the results are presented in the Euler space and in the angle-axis space. The novelty of the method consists in the possibility of gaining data on the grain boundaries from X-ray texture analysis without using electron microscopy. A calculation involving only mathematical operations on matrices was performed on the basis of the orientation distribution function restored from incomplete pole figures. It is shown that no special boundaries are observed in the deformed sample, whereas in the recrystallized alloy, special boundaries are detected at Ʃ = 23, 13, and 17. The shortcoming of the proposed method can be attributed to the lack of accurate data on grain boundaries, since all possible orientation in the polycrystal should be taken into account in MDF calculation.

The Image of the Accountant in a German Context

2004 ◽  
Vol 4 (1) ◽  
pp. 62-89 ◽  
Author(s):  
Andreas Hoffjan
Keyword(s):  
Content Analysis ◽  
Empirical Study ◽  
Cost Reduction ◽  
Maximum Degree ◽  
Work Ethic ◽  
Personal Characteristics ◽  
Management Accountant ◽  
The Subject ◽  
Professional Context

This study introduces content analysis as a method of examining the accountant's role. The empirical study is based on 73 advertisements, which are directed primarily at employees who are affected by the management accountant's work. The findings of the study indicate that the subject of accountancy is used particularly in connection with promises of “cost reduction.” Consequently, the majority of advertisements use the accountant stereotype of “savings personified.” In a professional context, the work ethic of the management accountant is given particular emphasis in the advertisements. He/she identifies him/herself with his/her task to the maximum degree, is regarded as loyal to his/her company and, for the most part, is well organized in his/her work. However, the characterization of the management accountant as a well disciplined company-person conflicts with the negative portrayal of his/her professional qualities. In advertisements, the management accountant is portrayed as a rather inflexible, passive, and uncreative specialist who, as a result of these qualities, often demotivates others. The personal characteristics of the management accountant are shown in a negative light. This gives him/her the unappealing image of a humorless, envious, dissociated, and ascetic corporate-person.

scholarly journals Biofilm Formation in Xanthomonas arboricola pv. pruni: Structure and Development

Agronomy ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 546
Author(s):  
Pilar Sabuquillo ◽  
Jaime Cubero
Keyword(s):  
Biofilm Formation ◽  
Extracellular Polymeric Substances ◽  
Environmental Changes ◽  
Nutrient Content ◽  
Infection Process ◽  
Bacterial Attachment ◽  
Key Factors ◽  
Cell Structures ◽  
Microscopy Techniques

Xanthomonasarboricola pv. pruni (Xap) causes bacterial spot of stone fruit and almond, an important plant disease with a high economic impact. Biofilm formation is one of the mechanisms that microbial communities use to adapt to environmental changes and to survive and colonize plants. Herein, biofilm formation by Xap was analyzed on abiotic and biotic surfaces using different microscopy techniques which allowed characterization of the different biofilm stages compared to the planktonic condition. All Xap strains assayed were able to form real biofilms creating organized structures comprised by viable cells. Xap in biofilms differentiated from free-living bacteria forming complex matrix-encased multicellular structures which become surrounded by a network of extracellular polymeric substances (EPS). Moreover, nutrient content of the environment and bacterial growth have been shown as key factors for biofilm formation and its development. Besides, this is the first work where different cell structures involved in bacterial attachment and aggregation have been identified during Xap biofilm progression. Our findings provide insights regarding different aspects of the biofilm formation of Xap which improve our understanding of the bacterial infection process occurred in Prunus spp and that may help in future disease control approaches.

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