Unit 5: Ceramics, Glass and Cement
Course Code: CHM-DSC-353
Paper Name: Industrial Chemistry
Table of Contents
1. Ceramics
Ceramics are inorganic, non-metallic solids prepared by the action of heat and subsequent cooling. They are characterized by their hardness, high melting points, and low electrical conductivity.
Classification
- Structural Ceramics: Bricks, pipes, and tiles.
- Whitewares: Cookware, sanitaryware, and pottery (Porcelain/China clay).
- Technical Ceramics: Oxides (Alumina, Zirconia) used in electronics and aerospace.
2. Refractory Materials
Refractories are materials that can withstand very high temperatures without melting or deforming. They are used to line furnaces, kilns, and reactors.
- Acidic Refractories: Silica (SiO2), Fireclay.
- Basic Refractories: Magnesite (MgO), Dolomite.
- Neutral Refractories: Chromite (Cr2O3), Graphite.
3. Glass
Glass is a transparent or translucent amorphous solid, technically a supercooled liquid of silicates.
Manufacturing Process
The manufacture involves four main steps: Melting of raw materials → Shaping/Forming → Annealing (slow cooling) → Finishing.
Types of Glass
| Type | Composition | Uses |
|---|---|---|
| Soda-lime Glass | Na2O, CaO, SiO2 | Window panes, bottles (common glass). |
| Borosilicate Glass | B2O3, SiO2 | Laboratory glassware (Pyrex), high thermal resistance. |
| Lead Glass | PbO, SiO2 | High refractive index; used for lenses and decorative crystal. |
4. Cement
The most common form is Portland Cement, a complex mixture of silicates and aluminates of calcium.
Raw Materials
- Calcareous materials: Limestone, chalk (source of CaO).
- Argillaceous materials: Clay, shale (source of SiO2 and Al2O3).
- Gypsum (CaSO4·2H2O): Added during the final grinding stage.
Manufacturing: The Rotary Kiln
The raw materials are crushed, mixed (Wet or Dry process), and heated in a rotary kiln to form Clinkers.
5. Setting and Hardening of Cement
The chemical process that occurs when water is added to cement is called hydration.
- Setting: The stiffening of the original plastic mass into a solid. This is an exothermic process.
- Hardening: The subsequent development of strength over time.
- Role of Gypsum: Gypsum is added to retard the setting time of cement, allowing it to be handled and applied properly before it hardens.
6. Exam Focus: Tips and FAQs
Exam Tips
- Annealing: Be prepared to explain why glass must be cooled slowly (to remove internal stresses and prevent brittleness).
- Portland Cement: Memorize the approximate composition (CaO 60-67%, SiO2 17-25%).
- Refractories: Note that acidic refractories cannot be used in furnaces where basic slag is produced.
Frequently Asked Questions
Q: Why is glass called a supercooled liquid?
A: Because it possesses the structural characteristics of a liquid (disordered arrangement) but is rigid at room temperature due to its high viscosity.
Q: What are cement clinkers?
A: These are small, dark gray, stone-like pellets formed by heating the raw materials in the kiln. They are ground with gypsum to make the final cement powder.
Q: What gives color to glass?
A: The addition of transition metal oxides (e.g., FeO for green, CoO for blue, MnO2 for violet).