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Questions and Answers
What is the line separating the β phase from the α + β phase called below the eutectic temperature?
What happens to the solid solution when it reaches the solvus?
What is the composition of the solid solution in the alloy of 10% tin and 90% lead?
What happens to the tin in the solid solution as it cools further below the solvus?
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In the alloy of 30% tin and 70% lead, what happens as it cools below the liquidus?
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What is the result of the continued cooling of the alloy of 30% tin and 70% lead?
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What is the composition of the eutectic alloy?
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What happens to the solid solution as it cools below the eutectic temperature?
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What is the morphology of the eutectic crystals formed?
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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.
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Description
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.
