The Wettability of Solids by Liquid Metals

The surface tension and the density of some gold alloys have been measured and their wetting behaviour investigated in relation to different ceramic supports. Relationships between surface tension and density as a function of temperature are proposed.The primary objective of jewellery production is the optimization of melting processes (1) and the choice of suitable ceramic materials for the crucibles is required, and this choice can be critical. Accordingly, there is a need for a range of materials with excellent thermal and mechanical properties to withstand high temperatures and, at the same time, resist attack by the molten metal, so that there is no metal-ceramic interaction (2, 3). To date, the materials used have been graphite, silicon carbide or the more common 'refractory materials', but there are still complaints about problems, principally related to the rapid consumption of the crucible, or pollution of the melt due to the detachment of particles from the crucible. A knowledge of the interaction between the ceramic and the liquid gold alloys can help in the definition of more suitable ceramic material for the melting processes used by goldsmiths. It is necessary to use materials that are highly resistant to wetting by metallic melts, thus a knowledge of the interface properties of liquid gold alloys in relation to ceramic materials is needed.The interactions between the liquid metallic material and the ceramic are usually studied using: 1 Surface tension measurements of the liquid metal in contact with the ceramic material 2 Measurements of both surface tension and contact angle as a function of temperature 3 Surface tension measurements in the presence of liquid metal vapour. Ott (4) has stated that there is insufficient data on the thermal properties of jewellery alloys in the liquid state and at solidification, including that on surface /interface tension. Surface tension is a thermophysical property that must be considered because it influences the surface structure of castings, and determines the interfacial interactions between melts and solid containers (ie interfacial tensions); and it is influenced by the presence of alloying elements such as zinc or silicon. Consequently, the study of its variation can provide useful information on the outcome of casting processes. We have therefore measured the surface tension and the density of some precious gold alloys as a function of temperature, and investigated their wetting behaviour on a number of relevant ceramic supports. THEORETICAL BACKGROUNDFor the sake of clarity, we provide some details on the nature of adhesion and wettability of liquid metals on solid substrates and the behaviour of surface tension. WettabilityOne of the basic equations which describes the behaviour of a liquid phase in contact with a solid surface is Young's equation (5):where σ SV , σ SL , σ LV are respectively the interface energies between the solid and the vapour phase, the solid and the liquid phase, and the liquid and the

show abstract

“…In wettability studies the work of adhesion W A is defined by Dupré's equation (6), which can be written in both of the following two forms:…”

Section: Wettabilitymentioning

confidence: 99%

Wetting and surface tension measurements on gold alloys

Ricci

Novaković

2001

Gold Bull

View full text Add to dashboard Cite

show abstract

“…If rapid spreading precludes this, several nonequilibrium situations have been hypothesized [2,29,33,43]. One likely situation arises when the primary source of adsorbate for the solid surface is the liquid itself (solvent or solute), but spreading is too rapid for equilibrium levels to actually develop on the surface ahead of the liquid [33,43].…”

Section: Adsorption Controlmentioning

confidence: 99%

“…Most pure, noble metals (e.g., Pt, Au, Ag, Cu, Ni) exhibit obtuse contact angles on higher melting-point ceramics (such as SiC, Si 3 N 4 or Al 2 O 3 ) or graphite [1][2][3][4][5][6], and this hampers their use in applications like brazing, bonding, liquid-phase sintering, or infiltration. The angles range typically between 100° and 150° and increase roughly with the free energy of formation or band gap of the ceramic.…”

Section: Introductionmentioning

confidence: 99%

“…This problem can be alleviated by alloying a small amount of a reactive metal (such as Ti, V, Cr, Zr, Nb, Hf, or even Al) into the liquid. These additions can enhance wetting angles [2][3][4][7][8][9][10][11][12][13], often strongly ( Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…Because of their technological importance, a large body of empirical knowledge about the effects of reactive elements on spreading has been accumulated, but the results are complex, ambiguous and even inconsistent. Contact angles usually evolve unaccountably slowly over 10 2 −10 4 seconds [2,10,11,21] (Fig. 2), 1 and reaction products such as nitrides, silicides or oxides have frequently been found at or near the interface after solidification [7][8][9][10][11]22].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reactive spreading: adsorption, ridging and compound formation

2000

View full text Add to dashboard Cite

Reactive spreading, in which a chemically active element is added to promote wetting of noble metals on nonmetallic materials, is evaluated. Theories for the energetics and kinetics of the necessary steps involved in spreading are outlined and compared to the steps in compound formation that typically accompany reactive wetting. These include: fluid flow, active metal adsorption, including nonequilibrium effects, and triple line ridging. All of these can be faster than compound nucleation under certain conditions. Analysis and assessment of recently reported experiments on metal/ceramic systems lead to a focus on those conditions under which spreading proceeds ahead of the actual formation of a new phase at the interface. This scenario may be more typical than believed, and perhaps the most effective situation leading to enhanced spreading. A rationale for the pervasive variability and hysteresis observed during high temperature wetting also emerges.

show abstract