Alloys eutectic temperatures

Fig. 7. Dsc scan for glassy Alg Ni Fe2Gdg alloy where is the crystallisation temperature and T the eutectic temperature.

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

C. Consider the cooling of an Al-6% Si casting alloy. The liquidus is reached at about 635°C, when solid (Al) starts to separate out (top of Fig. A1.32). As the temperature falls further the liquid composition moves along the liquidus line, and the amount of solid (Al) increases. When the eutectic temperature (577°C) is reached, about half the liquid has solidified (middle of Fig. A1.32). The solid that appears in this way is called primary solid, primary (Al) in this case. 

The phase-diagram (temperature vs concentration) for a eutectic two-component alloy shows at low temperatures a central two-phase region and two solid one-phase regions at low and high relative concentrations. At the eutectic temperature the liquid phase at an intermediate concentration can all of a sudden coexist with the two solid phases. Upon further increase of temperature, the liquidus lines open up a V-shaped liquid... 

Eutectic temperature Melting temperature of an alloy with a eutectic mixture it is at the interaction of two or more liquid solubility curves. 

Europium(III) reduction, 14 640 Eutectic alloys, solidification of, 16 173 Eutectic temperature, of sodium... 

For the alloy marked 1 , on cooling, the liquidus curve was intercepted at a relatively high temperature and there was a fair temperature interval during which for the Mg crystals it was possible to grow within the remaining part of liquid. The solidification finally ended at the eutectic temperature. At this temperature the eutectic crystallization occurs (L (Mg) + Cu2Mg) in isothermal conditions, where the simultaneous separation of the two solid phases results in a fine mixture... 

In the inter-alkali alloys, eutectic equilibria have been observed in a number of systems very low melting points have been determined for instance in the Rb-Na system (L (Rb) + (Na), at 82.5 at.% Rb and —4.5°C) and even lower melting temperatures have been observed in ternary systems. Binary sodium-potassium alloys, liquid at room temperature (at 25°C in a composition range of about 15-70 at.% Na, about 7-57 mass% Na), have a good thermal conductivity and a wide temperature range where they are liquid they may be used in heat-exchange systems. Their extremely high chemical reactivity must of course be taken into account. 

At one period, dimes and quarters were made from lamination of two alloys. The composition of the interior sheet was 90% Cu— 10% Ag and the composition of the outer sheet was 10% Cu—90% Ag. Plot how the composition would vary with distance from the center after a long time just below the eutectic temperature. The copper-silver diagram is given in Figure 9.18. 

In the eutectic alloy system AB, the compositions of the three conjugate phases of the eutectic are pure A, pure B and liquid of 80% B. Assuming equilibrium solidification of an alloy composed of 40% A and 60% B at a temperature just below the eutectic temperature, calculate the percentage of the primary A. Calculate the percentage of the total A. 

Hydrogen-Absorption Isotherms. The isotherms for the 25 weight % uranium alloy constitute a family of curves closely resembling each other. Seven of the 13 isotherms which were measured are plotted in Figure 3. Isotherms intermediate between each adjacent pair were omitted to reduce the complexity of the plot. The isotherms at 572° C. (not shown) and at 601° C. cross only two phase boundaries, because they are below the eutectic temperature. 

This method is used for bonding two silicon surfaces. A thin layer of gold is coated onto the surface of one of the wafers, or a thin sheet of gold-siiicon or gold-tin mixture is placed between the two surfaces (a preform). The assembled device is then clamped together and heated in a vacuum chamber above the eutectic temperature for the particular materials (e.g., eutectic temperature for Si/Au is 36 °C). The preform melts and a diffusion process (gold into the silicon surface) leads to the formation of a silicon alloy between the contacted surfaces. As this cools, a bond is formed between the two surfaces. ... 

Table 4. Tensile properties and temperature parameters of alloyed eutectic a-Al + Mg2Si alloys ...

Al-Pb. Both lead [7439-92-1], Pb, and bismuth [7440-69-9], Bi, which form similar systems (Fig. 17), are added to aluminum alloys to promote machinabiHty by providing particles to act as chip breakers. The Al—Pb system has a monotectic reaction in which Al-rich Hquid freezes partially to soHd aluminum plus a Pb-rich Hquid. This Pb-rich Hquid does not freeze until the temperature has fallen to the eutectic temperature of 327°C. SoHd solubiHty of lead in aluminum is negligible the products contain small spherical particles of lead which melt if they are heated above 327°C. 

Mazyr V.J., Kapustnikova S.V., Blochina O.A. Researching High temperature gas corrosion in new titanium alloys eutectic type //3rd Int. Symp. Corros. Resist Alloys Cracow , 20-22, June, 1996 Conf Pap.- Cracow, [1996].- P. 141-148. 

A major potential problem for coal gasification materials due to high-sulfur coals is indicated by Table I. The table compares the melting points of sulfides and eutectic temperatures of the metal-metal sulfide systems for iron, nickel, cobalt, and chromium ( ). It may be seen that the metal-metal sulfide eutectic temperatures vary from 1193 F for nickel to 2462for chromium. All three elemental bases of high-temperature alloys, iron, nickel, and cobalt, exhibit eutectic temperatures of 1810 F or less. The nickel-nickel sulfide eutectic is 1193 F. 

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