Ferromagnetism in B2-Ordered Alloys Induced via Lattice Defects

The most well known application of the scanning microscope to the crystals is known as Coates pattern. The contrast of this image depends on the variation of the incident angle of the beam to the crystal surface. The defect in the crystal surface causes to make contrast in normal scanning image with constant incident angle. The intensity variation of the backscattered electrons in the scanning microscopy was calculated for the defect in the crystals by Clarke and Howie. Clarke also observed the defect using a scanning microscope.This paper reports the observation of lattice defects appears in thin crystals through backscattered, secondary and transmitted electron image. As a backscattered electron detector, a p-n junction detector of 0.9 π solid angle has been prepared for JSM-50A. The gain of the detector itself is 1.2 x 104 at 50 kV and the gain of additional AC amplifier using band width 100 Hz ∼ 10 kHz is 106.

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TEM study of boron additions to cobalt aluminide

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104790 ◽

1988 ◽

Vol 46 ◽

pp. 546-547

Author(s):

Gerald B. Feldewerth

Keyword(s):

High Temperature ◽

Turbine Engines ◽

Major Drawback ◽

University Of Missouri ◽

Specific Strength ◽

Aerospace Applications ◽

Wide Range ◽

Ordered Alloys ◽

The University ◽

Very High

In recent years an increasing emphasis has been placed on the study of high temperature intermetallic compounds for possible aerospace applications. One group of interest is the B2 aiuminides. This group of intermetaliics has a very high melting temperature, good high temperature, and excellent specific strength. These qualities make it a candidate for applications such as turbine engines. The B2 aiuminides exist over a wide range of compositions and also have a large solubility for third element substitutional additions, which may allow alloying additions to overcome their major drawback, their brittle nature.One B2 aluminide currently being studied is cobalt aluminide. Optical microscopy of CoAl alloys produced at the University of Missouri-Rolla showed a dramatic decrease in the grain size which affects the yield strength and flow stress of long range ordered alloys, and a change in the grain shape with the addition of 0.5 % boron.

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Crystal structure-size relationship in ultrafine metallic particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153300 ◽

1989 ◽

Vol 47 ◽

pp. 266-267

Author(s):

Jun Liu ◽

Mehmet Sarikaya ◽

Ilhan A. Aksay

Keyword(s):

Ultrafine Particles ◽

Carbon Film ◽

Lattice Defects ◽

Careful Examination ◽

Seeded Growth ◽

Gold Particles ◽

Metallic Particles ◽

Interfacial Structures ◽

Typical Particle ◽

Many Particles

Ultrafine particles usually have unique physical properties. This study illustrates how the lattice defects and interfacial structures between particles are related to the size of ultrafine crystalline gold particles.Colloidal gold particles were produced by reducing gold chloride with sodium citrate at 100°C. In this process, particle size can be controlled by changing the concentration of the reactant. TEM samples are prepared by transferring a small amount of solution onto a thin (5 nm) carbon film which is suspended on a copper grid. In this work, all experiments were performed with Philips 430T at 300 kV.With controlled seeded growth, particles of different sizes are produced, as shown in Figure 1. By a careful examination, it can be resolved that very small particles have lattice defects with complex interfaces. Some typical particle structures include multiple twins, resulting in a five-fold symmetry bicrystals, and highly disordered regions. Many particles are too complex to be described by simple models.

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