9 Questions
What is the line separating the β phase from the α + β phase called below the eutectic temperature?
Solvus
What happens to the solid solution when it reaches the solvus?
It becomes saturated with tin
What is the composition of the solid solution in the alloy of 10% tin and 90% lead?
19.2% tin, 80.8% lead
What happens to the tin in the solid solution as it cools further below the solvus?
It precipitates out to form the β phase
In the alloy of 30% tin and 70% lead, what happens as it cools below the liquidus?
Crystals of α phase start to grow
What is the result of the continued cooling of the alloy of 30% tin and 70% lead?
Formation of lamellar eutectic crystals
What is the composition of the eutectic alloy?
None of the above
What happens to the solid solution as it cools below the eutectic temperature?
It precipitates out to form both α and β phases
What is the morphology of the eutectic crystals formed?
Lamellar
Study Notes
Atomic Structure
- The nucleus is the basic core of an atom, consisting of protons and neutrons.
- Protons are positively charged particles with a much greater mass than electrons.
- Neutrons have the same mass as protons but carry no electrical charge.
- Electrons are negatively charged particles that orbit the nucleus, with a mass of 1/1836 that of a proton or neutron.
- Atoms are electrically neutral, with an equal number of electrons and protons.
- The chemical properties of an atom are determined by the number of electrons it has.
Ions
- Ions are atoms that have gained or lost one or more electrons.
- Loss of an electron makes an atom electropositive, resulting in a positive ion.
- Gaining an electron makes an atom electronegative, resulting in a negative ion.
Crystal Structure
- Once a nucleus of a crystal forms, it provides a solid/liquid interface where crystallization can proceed.
- The nuclei which form will be crystal unit cells, typically face-centred cubic, body-centred cubic, or close-packed hexagonal.
- As the crystal grows, it tends to develop spikes and changes into a tree-like shape called a dendrite.
- The dendritic crystal grows until the spaces between the branches fill up, and eventually, the entire liquid solidifies.
Solubility
- A substance can be dissolved in a solvent to form a solution.
- The solubility of a substance can increase or decrease with temperature changes.
- Solubility curves can be used to determine the maximum amount of a substance that can be dissolved in a solvent at a given temperature.
- Substances that will not dissolve in a solvent are said to be insoluble.
Solid Solutions
- Most metals are completely and mutually soluble in the liquid state, but some remain in solution upon cooling and become solid solutions.
- There are two types of solid solutions: substitutional and interstitial solid solutions.
- Substitutional solid solutions occur when the atoms of the solvent and solute are approximately the same size and have similar electrochemical properties.
- The formation of a substitutional solid solution is also influenced by the valency of the metals involved.
Examples of Solid Solutions
- The copper-nickel alloy is a substitutional solid solution, where atoms of nickel replace atoms of copper in the lattice.
- The composition of a solid solution can change as the temperature changes, leading to the precipitation of one phase out of another.
- The final composition of an alloy can consist of crystals of different phases dispersed through a matrix.
This quiz is about understanding the electron configuration of atoms, including the number of electrons in different shells and the total number of electrons. It's a concept in chemistry that helps explain the structure of atoms.
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