Cases can be made of either plastic or metal; watches with metal cases often include a stainless steel backing. Microchips are typically made of silicon, while LEDs are usually made of gallium arsenide, gallium phosphide, or gallium arsenide phosphide. LCDs consist of liquid crystals sandwiched between glass pieces.
Selected 3 Materials:
a.Processing of Plastic by way of the injection molding process
melts resin pellets inside the injection machine with a heated barrel. An auger moves the plastic forward and ensures an even mix of melted plastic. The machine then drives the melted plastic into a metal mold. The plastic fills the mold and results in a solid plastic part or product.
The harmful chemicals associated with plastics can be divided into three categories: ingredients of the plastic material, byproducts of manufacturing and chemicals adsorbed from the environment. The possible toxicological responses caused by plastic can thus be a combination of all of these chemicals. Some of these chemicals are defined as priority pollutants, which are regulated by governmental agencies because of their toxicity or persistence in organisms and food webs. These chemicals include heavy metals, pesticides, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which can disrupt important physiological processes of animals causing for example diseases and problems in reproduction. It has been found that at least 78 % of priority pollutants listed by EPA (US Environmental Protection Agency) and 61 % listed by EU are associated with plastic litter either deriving from the manufacturing or from the environment.
a.Extraction and Processing of Stainless Steel
The steelmaking process starts with the processing of iron ore. The rock containing iron ore is ground and the ore is extracted using magnetic rollers. … A mixture of iron ore and coal is then heated in a blast furnace to produce molten iron, or pig iron, from which steel is made.
Common food/medical-grade stainless steel (18-8 or 18-10, 304 grade) can release trace amounts of certain elements – but the higher the quality of the stainless steel, the less the leaching. There are four key possibilities for release from 300 grade stainless steel: iron (Fe), chromium (Cr), manganese (Mn) and nickel (Ni).
Iron is the base material from which steel is made. The nickel and chromium are what make stainless steel stainless, corrosion-resistant and durable. The ’18’ refers to the percentage of chromium in the stainless steel, and the ‘8’ or ’10’ the percentage of nickel.
Our bodies need iron to produce red blood cells. While large amounts can be poisonous, in North America the chances are much greater that we lack iron. In general, use of stainless steel or cast iron cookware and dishes would provide less than 20% of the total daily iron intake, which is well within safe levels.
Chromium, like iron, can also be positive for human health in small doses. The safe intake range is around 50 to 200 micrograms per day and one meal prepared with stainless steel products might release around 45 micrograms of chromium, which is well within safe levels. Even eating with stainless steel dishes several times a day is fine, as less chromium is released from just eating off the dishes compared with cooking in them using heat. Keep in mind that if the stainless steel is of high quality it will be stable and very little if any will be released. And any releases through normal wear and tear of high quality stainless steel should be miniscule at most.
Please note that stainless steel does not contain hexavalent chromium (VI), which is a highly toxic carcinogen.
Manganese is an essential trace nutrient in all forms of life. The form of manganese used in industrial applications is considered toxic at levels above 500 micrograms. The US Environmental Protection Agency has determined that exposure to manganese in drinking water at concentrations of the equivalent of 1 milligram/litre for up to 10 days is not expected to cause any adverse effects in a child. The uptake of manganese by humans mainly takes place through food, such as spinach, tea and herbs. Other foods containing high concentrations of manganese are grains and rice, soya beans, eggs, nuts, olive oil, green beans and oysters. For more information on manganese, take a look at this US Department of Health and Human Services Manganese Fact Sheet.
Nickel is not toxic in small amounts, but it can provoke a reaction in people allergic to nickel. An allergic reaction may consist of a metallic taste in the mouth or a skin rash on the hands (eczema) or elsewhere on the body. Small amounts of nickel can be transferred from stainless steel containers or cookware to foods – especially when the food in question is acidic (e.g., tomatoes, rhubarb).
Stainless steel is one of the most environmentally efficient raw materials available because of its durability and ability to be recycled.
That said, the making of stainless steel is a polluting and energy-intensive process that uses mined metals, such as iron, chromium and nickel. Over the past two decades, improved process technology has enabled manufacturers to decrease significantly the amount of embodied energy required to produce stainless steel. The mined materials used to make the stainless steel may have travelled significant distances to arrive at the manufacturing facility, and then the final product often travels great distances through various supply chains to reach the final consumer. So there is a significant carbon footprint attached to stainless steel.
Stainless steel products should last an extremely long time under normal usage. Generations. Even once their service life is over or they become irreparably damaged, stainless steel items should never enter the waste stream. Stainless steel is 100% recyclable and can be reused to make new products without loss of any of the original properties, such as tensile strength, ductility and corrosion-resistance. Valuable raw materials like chromium and nickel can be easily separated from the iron and similarly recycled. The scrap material can be used to make brand new products of the highest quality.
On the average, most stainless steel items are made of approximately 60% recycled material, with 25% of that derived from end-of-life products, and the other 35% from manufacturing processes. The recycled content is limited only by the amount of scrap steel available. The global market for scrap stainless steel is active. As it is a commodity constantly in demand, its recyclability is not just economically viable, but lucrative. Anything made of stainless steel should never end up in a landfill!
-stainless steel a safe material for use in everyday life, including for items such as food containers, dishes, cookware, utensils, water bottles and dispensers. If you have a nickel allergy, you may prefer to avoid stainless steel, or try only 200 grade (nickel-free) stainless steel to see if you can use it without any allergy sysmptoms appearing.
We balance the environmental issues associated with stainless steel against those of plastics. Comparatively, plastics break down much faster and in the process may release dangerous synthetic chemicals, including endrocrine disruptors such as bishphenol A (BPA).
a.Extraction and Processing of Silicon
The Reduction Process
- 1 The raw materials are weighed and then placed into the furnace through the top using the fume hood, buckets, or cars. A typical batch contains 1000 lb (453 kg) each of gravel and chips, and 550 lb (250 kg) of coal. The lid of the furnace, which contains electrodes, is placed into position. Electric current is passed through the electrodes to form an arc. The heat generated by this arc (a temperature of 4000° F or 2350 ° C) melts the material and results in the reaction of sand with carbon to form silicon and carbon monoxide. This process takes about six to eight hours. The furnace is continuously charged with the batches of raw materials.
- 2 While the metal is in the molten state, it is treated with oxygen and air to reduce the amount of calcium and aluminum impurities. Depending on the grade, silicon metal contains 98.5-99.99% silicon with trace amounts of iron, calcium and aluminum.
- 3 Oxidized material, called slag, is poured off into pots and cooled. The silicon metal is cooled in large cast iron trays about 8 ft (2.4 m) across and 8 in (20 cm) deep. After cooling, the metal is dumped from the mold into a truck, weighed and then dumped in the storage pile. Dumping the metal from the mold to the truck breaks it up sufficiently for storage. Before shipping, the metal is sized according to customer specifications, which may require a crushing process using jaw or cone crushers.
Elemental silicon is an inert material, which appears to lack the property of causing fibrosis in lung tissue. However, slight pulmonary lesions have been reported in laboratory animals from intratracheal injections of silicon dust. Silicon dust has little adverse affect on lungs and does not appear to produce significant organic disease or toxic effects when exposures are kept beneath exposure limits. Silicon may cause chronic respiratory effects. Crystalline silica (silicon dioxide) is a potent respiratory hazard. However, the likelihood of crystalline silica generation during normal processing is very remote. LD50 (oral)- 3160 mg/kg. (LD50: Lethal dose 50. Single dose of a substance that causes the death of 50% of an animal population from exposure to the substance by any route other than inhalation. Usually expressed as milligrams or grams of material per kilogram of animal weight.)
Silicon crystalline irritates the skin and eyes on contact. Inhalation will cause irritation to the lungs and mucus membrane. Irritation to the eyes will cause watering and redness. Reddening, scaling, and itching are characteristics of skin inflammation.
Lung cancer is associated with occupational exposures to crystalline silica specifically quartz and cristobalite. An exposure-response relationship has been reported in studies of miners, diatomaceous earth workers, granite workers, pottery workers, refractory brick workers, and other workers
Several epidemiological studies have reported statistically significant numbers of excess deaths or cases of immunologic disorders and autoimmune diseases in silica-exposed workers. These diseases and disorders include scleroderma, rheumatoid arthritis, systemic lupus erythematosus, and sarcoidosis.