Eutectic Systems

       A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature. On a phase diagram the intersection of the eutectic temperature and the eutectic composition gives the eutectic point. Not all binary alloys have a eutectic point; for example, in the silver-gold system the melt temperature (liquidus) and freeze temperature (solidus) both increase monotonically as the mix changes from pure silver to pure gold.

The eutectic reaction is defined as follows:

        This type of reaction is an invariant reaction, because it is in thermal equilibrium; another way to define this is the Gibbs free energy equals zero. Tangibly, this means the liquid and two solid solutions all coexist at the same time and are in chemical equilibrium. There is also a thermal arrest for the duration of the reaction.

        The resulting solid macrostructure from a eutectic reaction depends on a few factors. The most important factor is how the two solid solutions nucleate and grow. The most common structure is a lamellar structure, but other possible structures include rodlike, globular, and acicula

         The above info is taken from Wikipedia. Please do refer to them for further info.

with warm regards

allmyposts

Presentation on Binary Isomorphous System

I was surfing the web for some good presentation on Binary Isomorhous Systems. I found one here. I am embedding the same here:

with warm regards

almyposts

Eutectic reaction

Eutectic reaction:

A three-phase reaction in which, upon cooling, a liquid transforms to give two solid phases. 

e.g:                                 L ® α + b

The above information is taken from here

Tie Line

Tie Line:

An imaginary horizontal line (isotherm) spanning a two-phase region of an equilibrium phase diagram, terminating at the nearest phase boundaries on either side.

 Tie lines are important when using phase diagrams to predict the constitution of two-phase materials.

The above information is taken from here. 

Old Questions, Material Science, Chap 3

      I understand that AMIE is tough and its not enough to just read the study material. So I decided to scan through the old question papers. As of now I am studying the second chapter ( phase diagrams ). So I segregated the questions in this chapter for the benefit of all. Please do go through them and decide on what all topics to be studied for the exams.

with warm regards
Abhishek Boinapalli

Phase diagrams & Lever Rule

Hello Everyone,


     This blog is about my preparation to crack section A of AMIE in single go. As of now, I am studying Material Science & Engineering and I post notes, question papers, solved problems, tips info & such here.


    I found a very very cool ppt on Phase Diagrams, Gibbs Rule & Solubility stuff, alloy steels and lever rules. It is shown below:

Alloys steel

View more presentations from allmyonlineearnings.

The above pdf is taken from http://www.ce.berkeley.edu/~paulmont/CE60New/alloys_steel.pdf.

Triple Points & Gibbs Rule

Hello Everyone,

    I intend to write small note on triple point which I came across while studying for Phase Diagrams chapter of Material Science in section A of AMIE.

    In thermodynamics, the triple point of a substance is the temperature and pressure at which three phases (for example, gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. For example, the triple point of mercury occurs at a temperature of −38.8344 °C and a pressure of 0.2 mPa.

In addition to the triple point between solid, liquid, and gas, there can be triple points involving more than one solid phase, for substances with multiple polymorphs. Helium-4 is a special case that presents a triple point involving two different fluid phases (see lambda point). In general, for a system with p possible phases, there are triple points.

        The triple point of water is used to define the kelvin, the SI base unit of thermodynamic temperature. The number given for the temperature of the triple point of water is an exact definition rather than a measured quantity. The triple points of several substances are used to define points in the ITS-90 international temperature scale, ranging from the triple point of hydrogen (13.8033 K) to the triple point of water (273.16 K).

The above information is taken from Wikipedia. Please do refer to them for more info.

Basics of Phase diagrams

      Phase diagrams are one of the most important sources of information concerning the behavior of elements, compounds and solutions. They provide us with the knowledge of phase composition and phase stability as a function of temperature (T), pressure (P) and composition (C). Furthermore, they permit us to study and control important processes such as phase separation, solidification, sintering, purification, growth and doping of single crystals for technological and other applications. Although phase diagrams provide information about systems at equilibrium, they can also assist in predicting phase relations, compositional changes and structures in systems not at equilibrium.

     The phase rule, also known as the Gibbs phase rule, relates the number of components and the number of degrees of freedom in a system at equilibrium by the formula
                                       F = C – P + 2

where F equals the number of degrees of freedom or the number of independent variables, C equals the number of components in a system in equilibrium and P equals the number of phases. The digit 2 stands for the two variables, temperature and pressure.

    The number of degrees of freedom (F) of a system is the number of variables that may be changed independently without causing the appearance of a new phase or disappearance of an existing phase.

    Please note that the value of F cannot be less than 0. So the maximum number of phases can be found out using the Gibbs Formula with taking thermodynamics into consideration.

    The point at which F = 0 , is called invariant point. The point at which the three phases can co-exist is called triple point. 

with warm regards

AllmMyPosts

Some of the info on this post has been taken from the url: http://web.mit.edu/3.091/www/archives/Notes_10.pdf. Please do refer to the same for more info.