Biomedical Engineering Reference
In-Depth Information
Wetting at High Temperature
A. Passerone , F. Valenza and M. L. Muolo
Inst. for Energetics and Interphases—IENI CNR, Via de marini, 6, 16149 Genoa, Italy
Abstract
Processes and equipments that must operate at high temperatures require materials able to face high thermal
fluxes, severe stresses, high chemical reactivity. Ultra High Temperature Ceramics (UHTC's) represent a
class of materials most promising for such applications. In particular it is often necessary, to obtain the
best performances, to join these ceramic parts one to the other or to special metallic alloys by means of
brazing processes, where liquid alloys realize the bonding between the two phases. Thus, also in relation to
metallurgical, crystal growth and composite production processes, the knowledge of wettability, interfacial
tensions and interfacial reactions is mandatory to understand what happens when a liquid metal comes into
contact with a ceramic surface. In this paper, recent systematic studies, addressing both basic (wettability,
interfacial tension, phase equilibria determination) and application (joining) aspects, are critically reviewed
with a particular reference to transition metal diborides and silicon carbide. A special attention is paid to
studies aimed at elucidating the role that dissolution, chemical reactions, additions of active metal elements
to the molten matrix have in the wetting process and on the solid-liquid adhesion, and, eventually, on
the mechanical characteristics of the brazed joints, as the main final 'sensitive' parameter for application
purposes.
Contents
A. Introduction ...............................................
300
1. Characteristics of high temperature wetting]High Temperature Wetting
...........
300
2. Exchange Phenomena at Solid-Liquid-Vapour Interfaces . . .................
300
B. Wetting Typologies . ..........................................
303
1. Non-reactive (or Adsorptive) Wetting
..............................
303
2. dissolutive wetting]Dissolutive Wetting .............................
304
3. reactive wetting]Reactive Wetting
. . ..............................
305
C. Role of the Solid Surface in Modifying the Wetting Behaviour . . .................
306
1. roughness]Roughness . . . ....................................
306
2.anisotropy]Anisotropy ......................................
307
3.Stoichiometry ...........................................
308
D.ExamplesofInteractingSystemsatHighTemperature .......................
310
1. transition metals diborides]Transition Metals Diborides . . . .................
310
2. Silicon Carbide
..........................................
318
3.Remarks ..............................................
322
Search WWH ::




Custom Search