Podcast Beta
Questions and Answers
What type of bond can ceramics have?
The 'A' and 'X' atoms in an AX-type ceramic structure are always of the same size.
False
What is the net charge in ceramics usually required to be?
zero
In the Sodium Chloride structure, the larger ion occupies the regular FCC sites, while the __________________ occupies the interstitial positions.
Signup and view all the answers
Match the following ceramic structures with their characteristics:
Signup and view all the answers
Which structure has the chlorine ions at the corners and cesium ions in the body?
Signup and view all the answers
Crystals always maintain a charge imbalance to stabilize their structure.
Signup and view all the answers
What type of unit cell do AX-type ceramic crystals typically have?
Signup and view all the answers
The smaller atom in AX-type ceramics sits in __________ locations while the larger atom occupies regular atomic sites.
Signup and view all the answers
What is the coordination number of FeO predicted based on the ionic radii?
Signup and view all the answers
What is the coordination number typically associated with the Zinc Blende structure?
Signup and view all the answers
Both Na+ and Cl- ions form BCC unit cells.
Signup and view all the answers
What is the atomic weight of Chlorine (Cl)?
Signup and view all the answers
The units for ionic radius of an atom is in ______.
Signup and view all the answers
Match the following compounds with their crystal structures:
Signup and view all the answers
Which of the following represents the sum of atomic weights of all the 'A' atoms in NaCl?
Signup and view all the answers
Window glass is considered non-crystalline and has a high melting temperature.
Signup and view all the answers
What is the primary structure of Calcium Fluorite (CaF2)?
Signup and view all the answers
The melting temperature of quartz is approximately ______ degrees Celsius.
Signup and view all the answers
Which anion has the largest ionic radius among the following?
Signup and view all the answers
Study Notes
Crystal Structures of Metals
- Body-Centered Cubic (BCC) - has 2 atoms per unit cell, and its close-packed direction runs diagonally through the cell.
- Face-Centered Cubic (FCC) - has 4 atoms per unit cell, and its close-packed direction runs diagonally across each face of the cell.
- Hexagonal Close-Packed (HCP) - has 6 atoms per unit cell, and its close-packed direction runs diagonally across the close-packed plane.
- Examples of BCC metals include iron, chromium, tungsten.
- Examples of FCC metals include copper, nickel, aluminum, gold, zinc, titanium.
- Examples of HCP metals include magnesium.
Crystal Structures of Ceramics
- Ceramics are compounds composed of two or more elements, usually with different atomic radii.
- Bonding in ceramics can be covalent, ionic, or a combination of both.
- Ceramics have ordered atomic arrangements, forming crystal structures.
-
Oxide Structures
- Oxygen anions are larger than metal cations due to size effects.
- Oxygen anions are typically close-packed in a lattice, usually FCC.
- Metal cations occupy interstitial sites within the oxygen ion lattice.
Factors Determining Crystal Structure
-
Relative Size of Ions
- Stable structures maximize the number of oppositely charged ion neighbors.
-
Charge Neutrality
- The net charge of a ceramic must be zero, which is reflected in its chemical formula.
AX-Type Ceramic Crystal Structures
- AX-type ceramics have equal numbers of A and X atoms in their unit cells.
- A and X atoms usually have different sizes.
- The smaller atom occupies interstitial locations in the unit cell, while the larger atom occupies regular atomic sites.
Common AX-Type Crystal Structures
-
Sodium Chloride (Rock Salt Structure)
- Has an FCC unit cell.
- Cl- ions occupy regular FCC sites, while Na+ ions occupy interstitial positions.
-
Zinc Blende Structure
- Has an FCC unit cell.
- S atoms occupy regular FCC sites, while Zn atoms occupy interstitial positions.
-
Cesium Chloride Structure
- Has a BCC unit cell.
- Cl- ions are at the corners, and a Cs+ ion is at the body center.
Density Calculation for Crystalline Ceramics
-
Equation:
- Density = (n' * (∑AA + ∑AX)) / (V * N)
-
Where:
- n' = number of formula units (molecules) in the unit cell
- ∑AA = sum of atomic weights of all A atoms in the formula unit.
- ∑AX= sum of atomic weights of all X atoms in the formula unit.
- V = volume of the unit cell.
- N = Avogadro's number.
Coordination Number and Ionic Radii
- Coordination Number: The number of nearest neighboring atoms for a particular atom.
-
Ionic Radii: The relative sizes of ions affect the coordination number and crystal structure.
- ZnS (Zinc Blende): Coordination number = 4.
- NaCl (Rock Salt): Coordination number = 6.
- CsCl (Cesium Chloride): Coordination number = 8.
Predicting Crystal Structure
-
Example: Predicting the crystal structure of FeO.
- 𝑟𝑐𝑎𝑡𝑖𝑜𝑛 / 𝑟𝑎𝑛𝑖𝑜𝑛 = 0.550
- Coordination number = 6.
- Crystal structure = NaCl (Rock Salt).
AX2 Crystal Structure
-
Fluorite Structure:
- Example: Calcium Fluorite (CaF2)
- Cations occupy cubic sites.
- Other examples include ZrO2, CeO2, etc.
-
Antifluorite Structure:
- Positions of cations and anions are reversed.
ABX3 Crystal Structure
-
Perovskite Structure:
- Example: Complex oxide BaTiO3.
Glass materials
-
Quartz:
- Crystalline SiO2.
- Strong and brittle.
- High melting temperature (Tmelt ≈ 1750oC)
-
Window Glass:
- Non-crystalline SiO2.
- Weak and brittle at room temperature.
- Low melting temperature (Tmelt ≈ 780oC)
- Becomes ductile (viscous) at high temperatures.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the various crystal structures of metals and ceramics including Body-Centered Cubic (BCC), Face-Centered Cubic (FCC), and Hexagonal Close-Packed (HCP). This quiz covers atomic arrangements and examples of each type of structure found in both metals and ceramics. Test your understanding of these fundamental concepts in material science.
