Materials – Which is better: Man made or Natural?
Students like myself need to know what materials are available, how they behave in use and how they can be worked or processed during manufacture and construction. Having a good understanding of these will help me to select suitable materials for my products.
In choosing materials for a particular project, I will need to consider their physical and working properties, so that I am able to decide which material is best and which method of processing is required in order to turn raw materials into finished products.
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I have to use a procedure called product analysis. This involves analysing and existing product in order to identify the materials that have been used, the properties that make them suitable for the task for which they have been designed as well as an awareness of the processes used in their manufacture, construction and assembly. All man-made materials are derived from one or several naturally found materials.
History of materials
Early human history is divided into eras named after the materials that were predominantly used at the time. The Stone Age, Copper age, Bronze Age and Iron Age suggest how important these materials were in the development of early technology.
Early humans could only utilize the materials that they found to hand. Stone, reeds, clay, wood, animal hides, hair and bone enabled them to survive in otherwise inhospitable conditions. During these earliest periods organic materials were by far the most important and useful. Human resources were greatly enhanced by the discovery that mixing and heating materials, often change their characteristics. Ceramics (the earliest inorganic material to be used and worked) are good examples. A pliable clay can be moulded into the required shape and heated to create a much harder and tougher material, because the micro-structure of the clay changes during the firing process.
From about 8000BC humans in the middle-east, crafted locally found gold and copper to make decorative items. By about 4000BC they had learned how to smelt copper from ore. Around 2000BC it was found that another soft metal, tin, could be added to copper to produce an alloy which possessed some of the features of both parent metals. This alloy was an attractive gold coloured metal, which was much harder than either copper or tin. This led to the beginning of the Bronze Age.
The extraction of iron from haematite (iron ore) began about 1200BC. In its pure form iron is inferior to bronze in almost every way, but people found that by heating iron and charcoal and hammering it into shape produced a much tougher metal, steel. They also found that by plunging heated metal into cold water (quenching) they were able to produce a very hard, but brittle steel (hardening). They soon learned that these properties could be modified by reheating and cooling more slowly (tempering) so that most of the initial hardness was retained whilst at the same time making it much tougher and less brittle. This of course would not have been possible without natural materials like wood and plants, to set on fire to melt the metals.
Although naturally occurring polymers such as bitumen shellac and rosin have been used since 2000BC it was not until 1862 that the first manufactured plastic called parkesine was developed. In 1906 a chemist called Baekeland produced the first synthetic polymer Bakelite. Since then many new plastics with different colours and properties have been developed.
In the last 100 years our knowledge and understanding of materials has grown considerably. Today our use of traditional materials are constantly being improved and new materials are being synthesised from natural and man-made materials. We now have glass that is stronger than steel, ceramics that remain tough and rigid even when white hot, and optical fibres that can transmit information at the speed of light. There are a large number of materials available to product designers today, and they can be supplied in many different forms.
Metals and Alloys
Metals either in pure form or combined to make alloys, are crystallising structures which have their atoms arranged in a regular or symmetrical pattern. The crystals grow around a central nucleus as molten metal cools and expands to form grains. The crystal structure gives rise to the typical properties and characteristics of metals: high strength, stiffness, ductility and ease of working and toughness.
A pure, natural metal consists of a single element (a substance with only one type of atom present). Some common pure metals are aluminium, copper, zinc, lead, tin and gold.
An alloy is a combination of one or more pure metals mixed with other elements. Alloys are made to give metals which have properties not available in the naturally occurring metals. If two alloying elements are used it is called a binary alloy. Three alloying elements produce a ternary alloy. Alloying alters the properties of the base (parent) metals.
Alloying can lower the melting point, increase strength, hardness and ductility, change the colour, change the electrical or thermal properties, or change a materials resistance to corrosion.
Metals are either ferrous or non-ferrous. Ferrous metals consist mainly of the natural material iron with small amounts of other metals or elements added, to give the required properties. Almost all ferrous metals can be picked up with a magnet. Most of these metals have a high strength. They are very versatile, and they conduct heat and electricity. They are joined by a variety of methods, however they are likely to rust unless treated.
Examples are, Mild steel, High carbon steel, Stainless steel.
Non-ferrous metals do not contain iron. They usually have very good working properties, and are usually very easily joined by heat. They can be softened by annealing or hardened by cold working. They have a lower melting point than ferrous metals. Examples are, aluminium, copper, lead, tin, brass, nickel alloys, silver, gold, zinc.
Ceramics and be crystalline or amorphous (glassy). They are very complicated combinations of metallic, non metallic including natural elements. All clays are plastic until they are fired when they become hard and durable. They are good electrical insulators. When glazed they are hygienic. There are three main types:
China/Porcelain – An elegant fine material. White and smooth, it is a very hard, strong material.
Earthenware – A good general-purpose material, you can glaze it or finish it with oxides. It is coarser than china but is finer than stoneware. It is porous unless it is glazed.
Stoneware – This has a coarse texture unless glazed. It is a hard material which is a favourite with studio potters, as it is no porous and only needs glazing for hygienic purposes.
Polymers such as rubbers and plastics are organic structures. They can be natural, modified, or synthetic. Synthetic polymers are produced from coal, gas and oil. Most plastics have good electrical and chemical resistance, they are light in weight, durable, and have good strength to weight ratios. Some types are:
Thermosets – Once cured they cannot be softened. They have a harder surface than thermoplastics, only few are used for construction purposes in school. Examples are, Polyester Resin, Epoxy Resin, Melamine Formaldehyde, Phenolic Resin.
Thermoplastics – Can be softened by heating and hardened by cooling. Each time a thermoplastic is re-heated, it will return to its original flat state, unless it has been damaged by overheating or overstretching. This property is called plastic memory. Examples are, ABS, Nylon, PVC, Polypropylene, Polystyrene, Expanded Polystyrene, Acrylic (PMMA), Polythene.
Elastomers – The most common elastomer is natural or synthetic rubber. It can deform elastically to astonishing amount, without permanent distortion.
Plastics are available in a wide variety of forms. Not all types of plastic are available in every form. Some of them are, Powders, Granules, Liquid, Foams, Rods, Tubes, Slabs, Sheets and Films.
Sometimes two or more materials are combined to obtain different properties than those available in the original materials or substances. Common examples are concrete, plywood, and glass reinforced plastic. These are known as composite materials.
Composite materials are usually formed to increase the strength to weight ratio, toughness, or resistance to shock and temperature. Composites can be any combination of natural or man made metal, ceramic, and polymer. They can be in liquid, powder, particle, fibre or sheet form.
Paper and card
Paper can be described as a web-like material consisting of vegetable fibres, which contain cellulose. The vegetable fibres are usually blended or coated with various chemicals to produce the texture and finish required. The cellulose is usually extracted from wood. Both coniferous and deciduous trees are used, but other plant fibres such as cotton, flaz, hemp, bamboo, sugar cane and cereal straw can be used.
Paper is an everyday natural product taken for granted and there is an enormous variety of different types of paper and cardboard in use today. Just some of the examples are newsprint, writing paper and toilet paper.
Each type of paper or board has been designed for a specific purpose. Paper used for books and magazines has to be treated so that its surface is smooth and glossy, it has to be capable of being printed on and carry clear and accurate reproductions of text and colour photographs. Paper tissues on the other hand have to be made from paper that is soft, thin and absorbent.
Paper can be made to burn (e.g. cigarette paper) or made fire resistant (e.g. Christmas decorations). It can be tough enough to be used as a gasket in a car engine or soft enough for a baby’s napkin. It can be made opaque, translucent or transparent. It can be made waterproof or absorbent. It can be recycled many times to save both energy and raw materials. Some types of paper are made in very small quantities and are very expensive.
We depend on paper throughout our lives and its range of uses is almost limitless. It is a very versatile material that we sometimes take for granted.
There are two main types of natural wood, hardwood and softwood. This doesn’t describe the properties of the wood but refer to the types of tree from which the wood is obtained. Wood products like waste from timber preparation, are often re-constituted to form manufactured materials such as chipboard, plywood, MDF etc. Some examples of natural products are solid woods like mahogany, spruce, birch etc. Man made boards are available in very large sizes, 2440x1220mm. They are very stable, flat, and equally strong in both directions. They are less expensive than using solid natural timber. Some examples are, blockboard, hardboard.
Most hardwoods are more stable than softwoods, they often have a strong aesthetic appeal. They possess many desirable properties that a designer can exploit; they have a high strength to weight ratio using tension and compression. They are also elastic and can be laminated. The heavy/dense woods are definitely stronger. Most hardwoods are expensive, but they are ideal for small-scale projects. Softwoods are usually less expensive than hardwoods, they are usually lighter in weight than most hardwoods and can be used for many purposes.
Wood is available in many forms, which are:
Planks – They are the largest form, over 40mm thick.
Boards – They are thinner than 40mm and wider than 75mm.
Strips – They are narrower than 75mm
Squares – They are square sections of various sizes.
Veneers – They are thin slices of wood often used to decorate other wood.
Various words are used to describe materials; some refer to the physical characteristics such as its appearance, whilst others refer to its physical properties i.e. the way it behaves under certain conditions. Although many of these words have precise meanings, they are often used in a very general way. These words are; appearance, weight, durability, rigid, flexible, toughness, brittleness, hardness, softness, malleable, ductility, elasticity, strength, conductivity, cost, and availability.
I have to look at things like colour and texture, as they can influence the way things look. I have to see if it will be fixed or if it will be carried, as these factors could be very important. Weight in the right place might be needed for balance and stability. I have to look at how long a material will last before it is affected by its environment, and how much energy the material can absorb.
After looking at all the information, and thinking about what materials I use and how I use them, I have decided that the most useful materials are natural. These were around at the beginning of time when man didn’t even exist. Apart from using these for products, we eat them and use them in everyday life. If there wasn’t wood to burn for fire, there would not have been various man made materials. Man-made materials are necessary in everyday life, but not as necessary as natural materials.