International Baccalaureate: Design & Technology
Topic 7/Option A: Raw Material to Final Product
This option considers the conversion of some important raw materials (timber, ceramic (glass), metal, textile fibre, plastic and new materials such as mycroprotein and superconductor) to final products. It explores the different ways materials are treated to ensure their suitability for particular applications.
7.1.1
Outline that timber can be classified according to the conditions needed for tree growth, namely temperate and tropical conditions. A general knowledge of the geographical distribution of world timber resources is required.
7.1.2
Outline that conifer trees are referred to as softwoods and that these grow only in temperate regions and have features in common. Recognize the characteristics of softwood trees.
7.1.3
Outline that deciduous trees are referred to as hardwoods and that these grow in both temperate and tropical regions and have features in common. Recognize the characteristics of hardwood trees.
7.1.4
Discuss the issues involved in reforestation including time to reach maturity, soil erosion, greenhouse effect and extinction of species. The issues should be placed in local, national and international contexts.
7.1.5
State that particle board and plywood are examples of composite timbers. Particle board is sometimes referred to as chipboard.
7.1.6
Compare the characteristics of particle board, a pine wood and plywood with reference to their composition, hardness, tensile strength, resistance to damp environments, and the aesthetic properties of grain, colour and texture. The ability to produce sketches depicting cross-sectional views of the structure of the materials is expected.
7.1.7
7.1.8
Explain the need to season natural timber. Refer to the moisture content of workable timber and the consequences of manufacturing products using seasoned and non-seasoned timber.
7.1.9
Describe the reasons for treating or finishing wood including reducing attack by organisms and chemicals, enhancing aesthetic properties and modifying other properties. Knowledge of all the finishes and treatments available is not required; understanding the general principles is sufficient.
7.1.10
Explain three differences in the treatment or finishes of a desk if it were to be made of particle board or pine, with reference to durability, ease of maintenance and aesthetics. It is assumed that the particle board is veneered.
7.1.11
Identify a different (type of) wood (not particle board or pine) and explain how it is processed and finished to make it appropriate for manufacturing a child's toy. Justify the selection of the timber for this application in relation to the qualities set out in 7.1.6. This refers to the three types of wood. Any toy can be chosen but health and safety considerations must be taken into account.
7.2.1
State that glass is composed primarily of silicon dioxide (SiO2), together with some sodium oxide (Na2O) and calcium oxide (CaO) and small quantities of a few other chemicals. The raw materials come from sand (SiO2), limestone (CaCO3 for making CaO) and sodium carbonate (Na2CO3 for making Na2O). Knowledge of the mineral ore names or their geographical locations is
not required.
7.2.2
Explain the requirement of large quantities of energy to manufacture glass, and that scrap glass is added to new raw materials to make the process economic. Refer to the very high melting points of the raw materials and the strength of chemical bonds involved (they are ionic). SiO2 has a melting point of 2000 K. Between 15% and 30% powdered scrap glass is added to the raw materials and this lowers the temperatures needed, the electrical energy used and the time required.
7.2.3
Explain the characteristics of glass with reference to its brittleness, transparency, hardness, unreactivity and aesthetic properties.
7.2.4
Explain, with reference to soda glass and pyrex, that the desired characteristics of glass can be accurately determined by altering its composition. Most glasses consist of silica (SiO2) mixed with metal oxides. High volume products (bottles, windows) are made from soda-lime silica glass. This glass has poor “thermal shock” resistance and, to overcome this, borosilicate (pyrex) glasses are available (with 60–80% SiO2, 10–25% B2O3, 2–10% Na2O and 1–4% Al2O3).
7.2.5
Outline the differences between toughened and laminated glass with reference to their responses to being deflected and to impact. Toughened glass is made by heating glass almost to the melting point. The surfaces are then cooled while the centre remains hot and plastic. It will shatter into tiny fragments when broken (eg windscreens). Laminated glass has a thin layer of material, usually plastic, between the layers. This prevents cracks from growing and it can even be made bullet proof.
7.2.6
Explain how a selected glass’s composition and finish is modified to make it appropriate for the manufacture of some decorative article. Students should select an appropriate type of glass.
7.3.1
State that iron is a relatively reactive element and so is never found “free”. State also that iron ore (mainly hematite: Fe2O3 with SiO2 impurities) is relatively abundant in the earth and that iron has been extracted in blast furnaces since the Industrial Revolution using the raw materials: iron ore (Fe2O3), limestone (CaCO3) and coke (C).
Rich deposits of iron ore occur in Russia, Brazil, Australia and China. Extraction of iron from its ore requires some chemistry and energy to extract it from its oxide (ore), and needs treatment to prevent the iron reacting with air (oxygen and water) and reverting back to its oxide. Coke is required to produce the temperature and chemical conditions to reduce iron from its ore. Large scale manufacture of coke commenced during the Industrial Revolution.
Details of blast furnace structure and specific temperatures are not required.
More information on Blast Furnace
7.3.2
Outline the chemical changes that take place in a blast furnace. Carbon monoxide (CO) from the carbon (C) is used to reduce the iron oxide to iron metal via the reaction:
3CO (g) + Fe2O3 (s) • 2Fe (1) + 3CO2 (g)
Calcium oxide (CaO) from the limestone (CaCO3) is needed to remove the impurity silicon dioxide (SiO2) by combining with it to form slag (CaSiO3) via the reactions:
CaCO3 (s) • CaO (s) + CO2 (g)
CaO (s) + SiO2 (s) • CaSiO3 (l)
The iron produced in a blast furnace is an alloy called pig iron which, due to its high carbon (C) content (up to 4%), is very hard and brittle. Pig iron is not much use as an engineering material.
7.3.3
State that because wrought iron had a lower carbon content, was less brittle but had a higher tensile strength than pig iron, it led to an engineering expansion.
Wrought iron has a lower carbon content (<0.03%) and is formed by heating, rolling and laminating hot slabs together. This toughened alloy is a better engineering material than pig iron.
7.3.4
Outline how iron is converted to steel, referring to the use of oxygen to reduce the carbon content by its reaction to form carbon dioxide. Iron is converted into steel in a furnace where the carbon level in the molten iron is reduced by blowing oxygen through the liquid metal. The carbon forms carbon dioxide which bubbles off. The resulting steel has a higher tensile strength and is tough compared with high-carbon alloys.
7.3.5
Describe iron as an extremely versatile metal since the desired properties can be accurately determined by altering its composition. Refer to mild steel and stainless steel.
7.3.6
Explain two uses for mild steel (including car bodies) and stainless steel (including cutlery).
The demands are mainly mechanical: rigidity, strength, weather protection and corrosion, ease of manufacture and cost. All these contribute to its choice as the main material used for making car bodies. Any other use for mild steel can be chosen.
Stainless steel (with 18% Cr and 8% Ni) has good corrosion resistance and is used for situations where the metal must operate in a wet environment but cannot easily be protected with finishes. Any other use for stainless steel can be chosen.
7.3.7
Explain why steel must be treated or finished. Chemical details of rusting are not required. Iron alloys corrode in the presence of oxygen and water and form soft porous oxides which allow the chemical process to continue until the iron is completely converted to an oxide. Protection is provided by a non-porous material adhering to the surface to keep out oxygen, water or both.
7.3.8
Explain how mild steel is treated in the two examples chosen in 7.3.6. 3
Possibilities include galvanizing, painting, plastic coatings, vitreous enamel and electroplating.
7.3.9
Identify another different type of steel (not mild steel) and describe how it is processed and finished to make it appropriate for a stated application. Possibilities include high tensile steel (painted, enamelled or zinc coated), chromium added to steel to make it stainless, and hammer finishes with aluminium suspended in a solvent (used on cast objects).
7.4.1
Describe cotton and nylon. Cotton is a natural fibre, a cellulose polymer, obtained from the bud of
cotton plants that grow in several sub-tropical regions. A general understanding of the eographical distribution of cotton is required.
Nylon is a synthetic polyamide fibre, obtained by the polymerization of adipic acid and a diamine. Students should be able to draw a simple zig-zag form to show their understanding of how the molecular form effects the characteristics. Detailed monomer or polymer structure diagrams or chemical details of linkages are not required.
7.4.2
Explain how cotton bolls are converted into threads. Limit this to harvesting, cleaning, combing and spinning. The detail of each stage of the process is not required. Flow diagrams may be appropriate.
7.4.3
Explain how nylon threads are manufactured from petroleum. Limit this to the mixing of the two raw materials in a controlled way (each dissolved in a solvent) and the extrusion of the threads.
7.4.4
Compare the characteristics of cotton and nylon threads with reference to absorbency, strength, elasticity and effect of temperature. Cotton is very absorbent and increases in strength when wet because the degree of alignment of long polymers increases, leading to the strengthening of bonds. Cotton is relatively inelastic, so it wrinkles and creases easily. It is a good conductor of heat and so is little effected by heat and chars rather than melts when exposed to high temperatures.
7.4.5 Discuss the reasons for treating cotton. Refer to enhancing aesthetic properties, reducing flammability and the need for waterproofing. The general principles of treatments and finishes
is required, but not detailed chemical information. Cotton is also degraded by ultraviolet rays, moisture and air pollutants. This is shown as discolouration and then breakdown of fibre. Cotton is also susceptible to attack by microbes.
7.4.6
Explain that nylon needs little treatment because the desired characteristics can be designed into it.
7.4.7
Outline clothing as a major use for both cotton and nylon.
7.4.8
Explain how cotton, nylon or polyester may be incorporated into a composite fabric and how the composition of this fabric determines its characteristics. Refer to socks, shorts and waterproof garments. Knowledge is required of how the properties of fabrics change by mixing fibres in the manufacture to combine the characteristics. Also include how the type of fabric manufacture changes characteristics, eg weave.
7.4.9
Identify another different textile fibre (apart from cotton and nylon) and explain how it is processed and finished to make it appropriate for the manufacture of a blanket.
7.5.1
State that mycoprotein is a food product made from a fungus grown on grain and paper flour wastes and harvested as a mass of threads (mycelium). QuornTM is an example of such material. Mycoprotein is produced in a sealed fermenter, in the absence of air. It is grown in/on cellulose and other hydrocarbons and the pH and temperature are controlled. No other chemical or biological details are required.
7.5.2
Describe the advantages of mycoprotein, referring to the nutritional and physical characteristics.
Include its ability to be formed into chunks (that can simulate, for example, beef or chicken), its high protein and fibre content, and low salt and cholesterol levels. Mycoprotein is virtually tasteless but can be given almost any flavour before or during cooking. No details of flavourings are required.
7.5.3
Describe what is necessary for the commercially viable manufacture of mycoprotein. Include cheap substrate (ideally waste materials), safe to eat, easily processed into acceptable food product, no toxicological effects and no residues or contaminants from substrates.
7.5.4
Explain how mycoprotein can be designed in a range of novel food products. A wide range of examples is possible. For example QuornTM, the product from fermentation is a dough which can be mixed with a binding agent (eg egg white) and flavouring agents and then put through a forming machine to give any required shape (eg chicken thigh shape).
7.5.5
Discuss the importance of public acceptability in the commercial success of new foods. The look and smell of food gives an initial impression. People need to be able to compare new foods with those they are familiar with. New foods are often first introduced in ready meals and then released as a separate ingredient to incorporate in recipes.
Superconductor
7.5.6
7.5.7
Explain that superconductors are ceramic alloys made from various metal oxides, non-metal oxides and metals, and that they are sintered so there is no need for treatment or finish. No details of specific chemicals or proportions are required. The process allows whatever finish and shape is desired.
7.5.8
State that the resistivity of superconductors becomes nearly zero at temperatures below about 140 K due to pairs of electrons weakly bonded together, which can move freely at these temperatures. Please note that future technology will change this value to perhaps near room temperature. Note also that superconductors are similar to metals in terms of structure and mode of conduction.
7.5.9
Explain the advantages of being able to produce superconducting materials that operate at room temperature. Discuss the fact that while superconductors are currently of rather limited use, they are utilized in NMR brain scans and levitating trains (refer to current technological magazines). Advantages include energy savings and less raw