Chapter 8: Processing of Materials - Study
Notes
Summary:
Key Concepts:
1. Processing of materials enhances product durability.
2. Metals can be preserved through processes like painting, galvanizing, and electroplating.
3. Indigenous food preservation methods are still in use.
4. Food preservation methods include storing, pickling, drying, and salting.
5. Plastics come in two main types: thermoplastics and thermosets.
6. Thermoplastics can be heated and shaped repeatedly; thermosets can be heated and shaped only once.
7. Plastics are suitable for packaging due to their lightweight, hygienic, durable, versatile, and transparent
properties.
8. Plastics have identifying codes for recycling.
9. Recycling reduces waste and landfill usage.
10. Plastics can be reduced, reused, recycled, remanufactured, and remolded into new products.
Unit 1: Preserving Metals
Processing to Preserve Metals:
● - Processing improves product longevity.
● - Corrosion is the reaction of metal with oxygen, causing decay.
● - To prevent corrosion, metals can be coated with protective layers, including painting,
galvanizing, and electroplating.
Preventing Corrosion of Metals:
1. Painting:
● - Clean the surface thoroughly, removing rust and dirt.
● - Apply an oil-based primer, allowing it to dry for 24 hours.
● - Use a suitable paint for metals.
2. Galvanizing:
Steps:
1. Cleaning: Remove dirt and grease.
2. Pickling: Eliminate surface rust and other impurities.
,3. Fluxing: Dip the metal in zinc ammonium chloride to prevent oxidation.
4. Galvanizing: Coat the object with a layer of zinc.
5. Finishing: Remove excess zinc and cool the object.
6. Inspection: Ensure the galvanizing process was successful.
3. Electroplating:
● - Electroplating is used to protect metal objects from corrosion and wear.
● - Steps involve transferring a metal coating to the object using an electric current and an
electrolyte solution.
● - Positively charged metal ions move from the plating metal to the object being plated.
● - The longer the object stays in the bath, the thicker the electroplated coating becomes.
Self-Test Questions:
1. What is corrosion, and how does it affect metals?
2. Name three methods of preserving metals from corrosion.
3. Describe the steps involved in galvanizing a metal object.
4. Explain the process of electroplating and its purpose.
5. How does the composition of an electrolyte affect electroplating?
Answers:
1. Corrosion is the reaction of metal with oxygen, causing decay. It results in the formation of substances
like rust on the metal's surface, leading to deterioration.
2. Three methods of preserving metals from corrosion are painting, galvanizing, and electroplating.
3. The steps in galvanizing are cleaning, pickling, fluxing, galvanizing, finishing, and inspection. These
steps protect metals by applying a layer of zinc.
4. Electroplating is a process of adding a metal coating to an object using an electric current and an
electrolyte solution. It's used to protect metal objects from corrosion and wear.
5. The composition of an electrolyte affects electroplating by determining the flow of metal ions from the
plating metal to the object. It impacts the thickness and quality of the electroplated coating.
Unit 2: Using Indigenous Technology to Preserve Food
Summary:
, Key Concepts:
● - Many South African cultures contributed knowledge about preserving food.
● - Food preservation is crucial for ensuring food security.
● - Warm, damp, and alkaline conditions lead to rapid food decay due to bacterial growth.
● - Indigenous methods were developed to slow or stop bacterial growth in the absence of modern
preservation techniques.
● - This unit explores ancient methods still used today for food preservation:
- Storing grain
- Pickling
- Drying and salting
1. Storing Grain:
● - Grain is a staple in African diets and was stored in underground pits to protect it from pests and
decay.
● - Underground pits were lined with stones and clay, and grain was covered with a lid made of
roots and sticks.
● - Carbon dioxide produced during fermentation suffocates pests in the pit.
● - Similar technology is still in use, and modern silos rely on carbon dioxide for preservation.
2. Pickling:
● - Pickling preserves food with high moisture content using liquids like brine or vinegar.
● - It prevents the growth of microscopic organisms causing food spoilage.
● - Follow pickle recipes precisely to avoid bacterial spread.
● - Use crisp, fresh food and pickling salt.
● - Avoid powdered spices and use stainless steel or glass containers for pickling.
3. Preserving Food by Drying and Salting:
● - Indigenous people used drying to remove moisture from food, preventing bacterial growth.
● - Sun or wind drying is a traditional method.
● - Salt was rubbed into meat to prevent decay.
● - Mopani worms were preserved by salting and drying for later consumption.
● - Factors like climate and food type affect drying times.
● - Dried foods can be rehydrated for various uses.
Self-Test Questions:
1. Why is food preservation important in South Africa?
2. What conditions lead to rapid food decay?
3. Describe the traditional method of storing grain in underground pits.
4. What is the purpose of pickling food, and what precautions should be taken when pickling?
5. How do indigenous people use drying and salting to preserve food, and what factors influence the
preservation process?
