Flashcards
Ceramics structure
Flashcards do conjunto (12)
- 1What are some ceramics?Rocks and minerals, clays, glass, cements, engineering ceramics (focus).
- 2What are some characteristics?Compared with metals:
- Very high elastic modulus
- Weaker in tension, stronger in compression
- Lower fracture toughness
No ductility
- Less dense - 3What kind of atomic bonding is present?Ionic and covalent bonding. Percent differs between material.
- 4What is ionic and covalent bonding?Ionic bonding is about ions attracting.
- Electrical neutrality
Covalent bonding is sharing of electrons.
- Directionality - 5What ions are present?Cations (positive ions) and anions (negative ions)
- 6When is a ceramic crystal structure stable?When the anions are touching a cation, if not, the structure is unstable.
- 7What are a couple rules of thumb that guide ceramic structures about?1. Cations must be surrounded by the max no. of anions.
2. Bond strength of cation = bond strength of anion.
*Note that sometimes the rules aren't followed. Ex. antifluorite structure. - 8Define coordination number.Defined as no. of nearest (touching) neighbouring ions.
- 9What does the ratio r_c/r_a say?Ratio of between radius of cation and radius of anion.
Also determines preferred coordinate number. - 10Why are cations smaller than anions?Cations(usually metallic element) release electrons whilst anions receive those electrons, increasing its size.
- 11What are interstices?Interstitial sites between ions.
2 main kinds:
1. Tetrahedral
2. Octohedral - 12What are tetrahedral and octohedral sites?Tetrahedral: Space between one corner ion and three closest face-centred ions.
Octohedral: Space between 6 face-centred ions.
Informações
- Descrição
- Postgraduate Materials (Topics) FlashCards sobre Ceramics structure, criado por John Wang em 01-06-2024.
- Criado por
- John Wang
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