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Compositionally-induced surface phas...

Cheng, Wei-Chun.

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Compositionally-induced surface phase transitions in alloys.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Compositionally-induced surface phase transitions in alloys./
Author:	Cheng, Wei-Chun.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 1995,
Description:	170 p.
Notes:	Source: Dissertations Abstracts International, Volume: 57-07, Section: B.
Contained By:	Dissertations Abstracts International57-07B.
Subject:	Materials science. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9601450

Compositionally-induced surface phase transitions in alloys.
Cheng, Wei-Chun.

Compositionally-induced surface phase transitions in alloys. - Ann Arbor : ProQuest Dissertations & Theses, 1995 - 170 p.

Source: Dissertations Abstracts International, Volume: 57-07, Section: B.

Thesis (Ph.D.)--Carnegie Mellon University, 1995.

This item must not be sold to any third party vendors.

A model of surface phase transition and a new expression for the surface excess free energy of ternary alloys are presented. An abrupt change in surface composition associated with a compositional surface phase transition have been observed in a polycrystalline Pb-Bi-Ni alloy. Equilibrium surface composition measurements on a polycrystalline alloy containing 5 at% Bi and 0.04 at% Ni, at temperatures from 190 to 290$\\sp\\circ$C, have shown that the surface composition changes from a lead-rich to a bismuth-nickel-rich surface (or vice versa) in the range 230-255$\\sp\\circ$C. A faceting phase transition has also been observed in Pb-Bi-Ni alloys. The cosegregation of Bi-Ni to the surfaces of small crystals of these alloys changes the crystalline equilibrium crystal shape (ECS) in relation to that of pure Pb and leads to the reversible formation of $\\{227\\}$ and $\\{110\\}$ facets at faceting phase transition temperatures of 240$\\sp\\circ$C and 230$\\sp\\circ$C, respectively. In addition to this stable ECS, the co-segregation of Bi and Ni also leads to the formation of $\\{112\\},\\ \\{114\\},\\ \\{331\\}$ and $\\{991\\}$ facets on the "metastable ECS 1" and the formation of $\\{112\\},\\ \\{114\\}$ and $\\{110\\}$ facets on the "metastable ECS 2". These faceting phase transitions occur at temperatures that are higher than in pure Pb, thereby increasing the kinetics of equilibration to the point that the observation of the appearance and disappearance of facets at those orientations becomes possible. Most interesting is the fact that the appearance and disappearance of these new facets is coupled with the compositional surface phase transition which manifests itself as an abrupt change in the surface concentrations of the Bi and Ni solutes. The equilibrium wetting of Pb-rich solid by Ga-rich liquid has been investigated between 290$\\sp\\circ$C and the monotectic temperature of the Ga-Pb system. At temperatures below 300$\\sp\\circ$C the Ga-rich liquid is distributed in droplets in a three-fold pattern around the $\\{111\\}$ facets on the Pb crystal. The wetted orientations are close to $\\{210\\},$ which have the highest surface free energy of the crystal.Subjects--Topical Terms:

543314
Materials science.

Compositionally-induced surface phase transitions in alloys.
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035 $a (MiAaPQ)AAI9601450
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100 1 $a Cheng, Wei-Chun. $3 3433834
245 1 0 $a Compositionally-induced surface phase transitions in alloys.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 1995
300 $a 170 p.
500 $a Source: Dissertations Abstracts International, Volume: 57-07, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Wynblatt, Paul.
502 $a Thesis (Ph.D.)--Carnegie Mellon University, 1995.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a A model of surface phase transition and a new expression for the surface excess free energy of ternary alloys are presented. An abrupt change in surface composition associated with a compositional surface phase transition have been observed in a polycrystalline Pb-Bi-Ni alloy. Equilibrium surface composition measurements on a polycrystalline alloy containing 5 at% Bi and 0.04 at% Ni, at temperatures from 190 to 290$\\sp\\circ$C, have shown that the surface composition changes from a lead-rich to a bismuth-nickel-rich surface (or vice versa) in the range 230-255$\\sp\\circ$C. A faceting phase transition has also been observed in Pb-Bi-Ni alloys. The cosegregation of Bi-Ni to the surfaces of small crystals of these alloys changes the crystalline equilibrium crystal shape (ECS) in relation to that of pure Pb and leads to the reversible formation of $\\{227\\}$ and $\\{110\\}$ facets at faceting phase transition temperatures of 240$\\sp\\circ$C and 230$\\sp\\circ$C, respectively. In addition to this stable ECS, the co-segregation of Bi and Ni also leads to the formation of $\\{112\\},\\ \\{114\\},\\ \\{331\\}$ and $\\{991\\}$ facets on the "metastable ECS 1" and the formation of $\\{112\\},\\ \\{114\\}$ and $\\{110\\}$ facets on the "metastable ECS 2". These faceting phase transitions occur at temperatures that are higher than in pure Pb, thereby increasing the kinetics of equilibration to the point that the observation of the appearance and disappearance of facets at those orientations becomes possible. Most interesting is the fact that the appearance and disappearance of these new facets is coupled with the compositional surface phase transition which manifests itself as an abrupt change in the surface concentrations of the Bi and Ni solutes. The equilibrium wetting of Pb-rich solid by Ga-rich liquid has been investigated between 290$\\sp\\circ$C and the monotectic temperature of the Ga-Pb system. At temperatures below 300$\\sp\\circ$C the Ga-rich liquid is distributed in droplets in a three-fold pattern around the $\\{111\\}$ facets on the Pb crystal. The wetted orientations are close to $\\{210\\},$ which have the highest surface free energy of the crystal.
590 $a School code: 0041.
650 4 $a Materials science. $3 543314
650 4 $a Metallurgy. $3 535414
690 $a 0794
690 $a 0743
710 2 $a Carnegie Mellon University. $3 1018096
773 0 $t Dissertations Abstracts International $g 57-07B.
790 $a 0041
791 $a Ph.D.
792 $a 1995
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9601450