Titanium Dioxide - Characteristics, Major Uses and Minor Applications - Essay Example

1. Characteristics of Titanuim dioxide (TiO2) Titanuim dioxide a natural oxide of titanium, also know as titania or titanium IV. Its most common composition is TiO2. Molecular weight is 79.90 g/mol. Its color is white. X-ray density is 4.35 g/cm³. Its most common crystal structure is tetragonal. It decomposes above 1500°C and its melting point is 1850°C. Thermal Conductivity and Thermal expansion is (W/m•°C): 8 and (10‾6/ °C ): 9.0 respectively. Its refrective index is 2.6 to 2.9 and electrical resistivty is insulator. Test temperature is usually 20°C unless otherwise stated Pierson (1999, p. 310 in table 11.7) It is also called titanium white or pigment white 6 when used as pigment. Titanium dioxide white is mostly used in plastic industry. Its refrective index is higher than other whitepigments and chemically it is more stable. It is non toxic and have good dispersability and thermal stability. 2. Major uses and minor applications of Titanuim dioxide (TiO2) It is well known for its wide range of applications e.g. used in tooth pastes to make it white and sunscreens – to protect skin from ultra violet rays. It is being used to develop wide range of environmental friendly products like ceramic tiles, self cleaning fabrics and bodies of car becasue of its potent photocatalyst character. Its catalytic properties are helping to remove nitrogen oxide from the air. Other experimental uses involve removal of ethelyne (a ripening hormone) from storage facilities of perishible products. It strips organic polluntants like trichloroethelyne and methyl-tert-butyl ether from water and toxins from green algea. It act as photocatalyst for water and air treatment. Titanium dioxide is not toxic so used in cosmatic products like sunscreens, lipsticks, bodypowders etc. It is also used in some special pharmaceutical items like tooth pastes. It is also used in food stuff like wraping material and cigar tobacoo. Its photocatalyst reaction is like photosynthesis – continues through out the day. This characterstic of Titanium dioxide is enhanced due to start of nanotechnology. Its other application includes; deodorization, water purification, environmental improvements and antibacterial. Its thin film on glass prevents it from clouding. Pierson (1999, p.310) states ‘the application of Titanium dioxide are mostly optical and include the following; High - index films in multilayer interface filters Anti-reflection coatings, optical wave guides and photoelectrochemical cells Dieelectric layers in thin-film capacitors.’ Titanium and its alloys are widely used in areo industry, architectural, auto condensors, desilation plants, roads, food stuffs, jewellary maufactureres, nuclear and environmental safety, refineries, sports equipments, springs, turbines, malitary hardware, pulp and paper and heat exchangers etc. It is mostly used as white pigment as having brightness and high refrective index. It is also used as white food coloring – E number 171. It is used for surface coatings, paper coatings and fillers, plastics and miscellaneous stuff like ceramics, glass, catalysts, coated fabrics, printing inks, roofing granules and welding fluxes. 3. Demand of Titanuim dioxide (TiO2) Titanium is mostly found in minerals like anatase, brookite, ilmenite, leucoxene, pervoskite, rutile and sphene. From these Ilmenite, leucoxene and rutile have economic importance. It is the fourth structural metal found in earth crust and ninth industrial metal. Titanium as a metal has high resistence for correcion. It also has high strength weight ratio. Titanium dioxide is the most common consumed form of titanium- almost 95%. Becaue of its clarity it is used as white pigment in paints, pastes, papers and plastics. Titanium dioxide is known because of its properties of purity, refrective index, particle size and surface. Its particle size should be within range of 0.2 to 0.4 micrometer to develop its pigment properties maximum. Its white pigmentation is due to its high refrective index results into light scattering. Tiatium and its alloys are available in all forms. Its cost can be comparable to other high performance materials. It is in demand because of high weldability and machinability. It is as strong as steal but half of the weight of steal. It shows resistance against fire and shock. It has cyrogenic properties. It is non toxic and bio compatable. It is cost effective so have lot of commercial, industrial and marine applications. In engineering application titanium has replaced heavier, less servicable and costly materials. Titanium if part of machinery convert it into reliable, economical and durable piece. (Table 10.1) shows how major rasin categories are pigmented by Charvat, 2003, p.151) Common Routes to Pigmentation with Tiatanium dioxide Most common Route Manufacturing Process Polyolefins: LDPE, LLDPE, HDPE,PP Solid concentrates Internal mixers, continuous mixers multiple-screw extruders Polyvinyl Chloride Rigid PVC Plastcized PVC “Dry blends” Liquid or paste dispersions Intesive high speed mixers Roll mills or disk impeller mixers Polystyrene family: GPS, HIPS, SAN, ABS Solud concentrates Some intensive blends Internal mixers, continuous mixers, multiple-screw extruders High speed dry blenders Other: acetols PC, PA, PET Melt compounding Predominately multiple-screw extruders LDPE, Low density polyethelene; LLDPE, Linear low density polyethelene; HDPE, High density polyethelene; PP, Polyproplyne, PVC, Polyvinyl chloride; GPS, General purpose polystyrene; HIPS, High impact polystyrene; SAN, Styrene acrylonitrile; ABS, Acrylonitrile butadiene styrene; PC, Poly -corbonate; PE, Polyamid, PET, Polyethelene terephthalate. 93% of titanium is used in dioxide form world wide. In powder form it is one of the whitest substance available on earth. Titaiun dioxide is mostly used to produce pigment. From last 25 years demand for titanium dioxide is growing @ 3% per annum. It is expected to continu because of its divesre applications in architectural paints, areospace and bottleing. 4. Potential hazards associated with the Titanuim dioxide (TiO2) Nanotechnology is considered one of the important work of 21st century. Products in nano meter size range offer “uniqueness” because of their altered properties as compared to their macro counterparts. Improvd soluability, permeability, ot targetability of nano particles seems to be beneficial in the drug delivery area. Dubey (2006 as cited In Shah & Khan work on nanopharmaceuticals (2008) p.621) ‘As an example “nano” paclitaxel molucles may reach a tumor cell line sooner than the bulk paclitaxel. Similarly, if a nano drug is unable to reach a particular receptor, specialized nano particles have been proven to have the ability to reach that receptor’. Nano technology proved good to deliver drugs. All major countries like USA, Japan, Canada, Australia, Russia, Korea, Ukrine and other European countries are putting lot of money to research nanotechnology. Technology always offers good and bad. Maynard (2006a as cited In Shah & Khan work on nanopharmaceuticals (2008, p.622) states that ‘there are increasing concerns that new nanotechnologies might bring risks to human health and environment’. In the same page Shah & Khan refer Donaldsons et al., Granum, Oberdoster, Saxton, Davis stating ‘Due to their small size, there is fear that they might unintentionally penetrate the normal biological barriers that protect human health. Research has demonstrated that exposure to nanoparticulaes might be associated with inhalation toxicity including pulmonory edema (Donaldsons et al., 2000), immune adjuvant effects (Granum & Lovik, 2002), and systematic effects including blood coagulation and cardiovascular effects (Oberdoster, 2001; Borm and Kreyling, 2004). Also there is growing public fear due to possible “nanotoxocity” and its impact on socio-economic growth ( Saxton, 2007). Some researches have called for increasing the government’s power to regulate nanoproducts (Davies, 2006; Kimbrell, 2006)’. Shah & Khan , 2008 also refer UK CSTand MHRA state ‘Howevers other including the UK’s Council for Science and Technology (CST) have a different position on this. “ Existing preclinical trials for medicines and medical devices are very expensive, requiring manufacturers of medical devices to carry out extensive risk analysis. (UK, 2007). MHRA (Medicines and Health Care Products Regulatory Agency of UK) has concluded that “the existing trial procedures are sufficiently rigorous to safely include medicines and medical devices that incorporate nanotechnologies. CST would thus agree that no additional legislation for nano medicines or new medical devices is required at the current time (UK, 2007). Use of nanotechnology in drug delivey needs expediation instead of minimizing its use on potential hazards. FDA (Food and Drug Administration) usued to approve products having nanoparticles like nano crystals, nano suspensions, dissocubes, liposums, self emulsfying drug delivery system (SEDDS), nanoemulsion, dendrimers, fullerenes, nanotube, quantum dots and nano shells etc. Question is whether FDA has capability to approve all such products. FDA is a scientfic agency and has approved several complex products in the past. Its approval process based on that if a product can be produced consistently with a desired quality and its use is for public good can be approved. Shah & Khan in their work on nanapharmacuticals p. 622 also refer FDA stating ‘Some of the nano products have demonstrated safety to the point that their benefits to patients have been shown to overweigh the risks associated with them. Products such as Doxil ®, Myocet ®, Ambisome ®, and Depocyt ® have been approved which are nanometer in size range’. (“FDA”) Wakefield et al., (2004 as cited In Shah & Khan work on nanopharmaceuticals (2008) p.628) states ‘Surface reactivity, surface groups, coatings, and chargeplay a major role in nanoparticle aggregation. Introducing a small prcentage of impurities to the surface of nano-TiO2 particles may fundamentally alter their propensity to generate free radicals under UV radiation. Changes overtime such as coagulation, sintering, and chemical transformation might occur. Nanomaterials in the life sciences area are most likely to represent supermolecular aggregates of active and non-active atoms/molecules. Huang et al, 2004 in same page narrated by Shah & Khan observed reversible, surface controlled structure transformation in nanoparticles induced by an aggression state. Hollister et al., (2004 as cited by Shah & Khan, 2008) state ‘Aggregated nanoparticles might prove to be toxic in some cases. Surface changes might be responsible for their reactivity as well as aggregation potential.’ Wechsler, 2006 as cited by Shah & Khan, 2008, p 629 states ‘Nanoparticles can either increase stability or decrease due to exposure of very high surface area’. In some cases high concentartion is needed to stablize the product other wise drug will degrade easily if prone to oxidation, hydrolysis, or photolyosis. Thermodynamically nano systems are unstable so need appropriarate storage conditions on long term basis. Oberdorster et al., 1994, as cited by Shah & Khan, 2008, p 630 state ‘Comparison of micro and nano- sized TIO2 particles showed that the later was more potent and In an other study Umbreit et al., 2006 demonstrated that TIO2 nanoparticles biodistribution was different when injected intravenously versus subcutancously. In another study Shvedova et al., 2005 state that ‘For IV injected, the particles accumulated in liver, lung and spleen where as for SC injected most of the dose remained at the injection site indicating their aggregation. Nanostructure was shown to be more important in exhibiting tissue tickening due to SWCNT aggregates at a specfic site in lungs’ Maynard (2006a as cited by Shah & Khan, 2008 p. 630 states ‘ Thus determination of safety for nano pharmaceutials becomes particulary important when the material interacts with the body in a way that nano structures becomes biologically available and it elicits a biological response which is also associated with nano structure.’Shah & Khan also refere ICTA, 2006 which states ‘It is also believed that low concentration of manufactured nano particles of titanium dioxide can produce harmful free redicals in brain cells and the potential for brain cell damage.’ Dust with high concentration of titanium dioxide can genreate cough and irritation. Long inhalation of air concentrated with titanium dioxide may cause lung cancer. (being tested on animals). Studies conducted on workers exposed to titanium dioxide environment shows effets like decresed lung function, thickening of chest cavity (Pleural thickening) and fibrosis. However the findings are not confirmed as other substances like asbastos or silca (a well known cause for lung disease) were also present in same environment. However dust concentrated with titaniun dioxide may cause runny nose and irritted respiratory system. Prolonged exposuure to such environment may cause bronchities. In animal studies long term inhalation of such air has caused lung diseases. This is also noticed that effects of ultra fine particles of titanium dioxide is much less than larger particles. As per Canadian Centre for Occupational Health and Safety, ‘The International Agency for Rearch on Cancer (IARC) has determined that titanium dioxide is possibly carcinogenic to humans (Group 2B) based on inadequate evidence in humans and sufficient evidence in experimental animals. This conclusion relates to long-term inhalation exposure to high concentration of pigmentary (powdered) or ultrafine titanium dioxide.’ 5. Impact of the various uses of Titanuim dioxide (TiO2) on the environment. Plasma spraying and High Velocity Oxygen Fuel (HVOF) are used for TiO2 sub-micron powder coatings on polybutylene succinate (PBS). As PBS is a bio-degradeable plastic and Titaium dioxide (photo catalytic) will reveal purification of water and air without environmental damage. Titanium dioxide coating through HVOF has higher degradation rate because of higher anatase ratio. Fujimaki, 1998 as cited by Thermal Spray Society, 2004 states, ‘Development of bio-degradable polymeric materials has been increased in reacent years because of its impact on the environment.’ However because of high cost its production and consumption is limited. But there is no doubt in it that demand for bio-degradable polymeric material exists in near future. New bio-degradable composite material through thermal spraying can be developed without environmental disturbance. Titanium dioxide photo-catalytic powder use to clean environment is of great significance as (TiO2) is cheap, harmless and stable and can be activated through solar energy. A study conducted by Fedulov, et al. (2007) and published in American Journal of respiratory cell and molecular biology in 2008, on mouse model to analyze environmental exposure on pregnancy and its effect on offspring concludes that that maternal exposure to TiO2 and CB particles, previously considered immunologically "inert," causes enhanced immune response in pregnancy and, similarly to DEP exposure results in increased allergic susceptibility in offspring. This model may be useful for toxicology screening and for further mechanistic analysis. The International Agency for Research on Cancer (IARC) through a study concluded that high concentrations of pigment-grade (powdered) and ultrafine titanium dioxide dust caused respiratory tract cancer in rats exposed by inhalation and intratracheal instillation. The Workplace Hazardous Materials Information System (WHMIS) is Canada's hazard communication standard. The WHMIS Controlled Products Regulations require that chemicals, listed in Group 1 or Group 2 in the IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, be classified under WHMIS Class D2A (carcinogenic). The classification decision on titanium dioxide has been published on the IARC website and in a summary article published in The Lancet 6. The observations of the Titanuim dioxide (TiO2) market. There are two common forms of titanium dioxdie available commercially. Rutile and Anatase. Rutile opacity is more than Anatase however less photcatalytic than Anatase. Rutile refrectiv index is 2.70 – slightly higher from 2.55 so gives better power for light scattering. It also accepts surface treatment more quickly and creates good bonding than anatase. Anatase is mostly used in papers, thermosetting rasins system. Questions arises whether Titanium dioxide used in products is of best grade or quality, will it achive the desired opacity in products, is it availabe in right amount to be consumed in products, and how should one use it to get the brightness and opacity of desired level etc. Answers to these questions are not having a good degree of certainity. To check the opacity or hiding power, visual or instrumental methods are being used. Right answers to these question are possible by using the equation of Kubelka and Munk as cited in Dupont Titanium Technologies, ‘This equation shows the relationship among current ratio, brightness and quantity of the light scattering material in pigmented film (p.1) . The results of calculation based on input of data would suggest that a certain paint is more than adequate for the usual objective of complete hiding at 450 ft2/gal and that savings in raw materials are possible by lowering TIO2 content, total solids or some combination of these (p.3). There is a procedure to study the effect of toning on hiding power and brightness to determine what formulation changes are required to get the desired products International organization like EWG- Environmental Working Group, FDA – Food and Drug Administration and Freiends of the Earth etc. are closly monitoring the effects of products having nanoparticles of different minerals to see their effect on humans. Nano is a billionth part of meter and is found every where in nature. According to National Nanotechnologhy Initative (NNI) ‘Where is nanoscale materials found? Nanoscale materials and effects are found in nature all around us. Nature’s secrets for building from the nanoscale create processes and machinery that scientists hope to imitate. Researchers already have copied the nanostructure of lotus leaves to create water repellent surfaces used today to make stain-proof clothing, other fabrics, and materials. Others are trying to imitate the strength and flexibility of spider silk, which is naturally reinforced by nanoscale crystals. Many important functions of living organisms take place at the nanoscale. Our bodies and those of all animals use natural nanoscale materials, such as proteins and other molecules, to control our bodies many systems and processes. A typical protein such as haemoglobin, which carries oxygen through the bloodstream, is 5 nanometers, or 5 billionth of a meter, in diameter. Nanoscale materials are all around us, in smoke from fire, volcanic ash, sea spray, as well as products resulting from burning or combustion processes. Some have been put to use for centuries. One material, nanoscale gold, was used in stained glass and ceramics as far as back as the 10th Century. But it took 10 more centuries before high-powered microscopes and precision equipment were developed to allow nanoscale materials to be imaged and moved around’ Zinc oxide and titanium dioxide nano particles are used in sunscreens which are regulated by FDA to be consumed as over the counter drug products. It means it is safe to use. Moreover EWG studied the effect of sunscreen on skin and concludes, ‘Skin absorption, EWG carefully studied all scientific publications and government safety assessments on the risk of nanoparticle penetration from zinc and titanium in suncreen. The current weight of evidence suggests that these nanoparticles do not penetrate the skin, dimnishing concerns for their adverse effects for sunscreen users.’ The bottom line is consumer safety and if it is there – Titanium dioxide demand will not diminish. Below is comments given by EWG about use of titanium dioxide and zinc oxide nano particles in sunscreen and their effect on consumer is enough to predict the huge demand of such substances in future. EWG, (2007) states ‘Our study shows that consumers who use sunscreen without zinc and titanium are likely exposed to more UV radiation and greater numbers of hazardous ingredients than consumers relying on zinc and titanium products for sun protection. We found that consumers using sunscreen without ZnO and Tio2 would be exposed to an average of 20% more UVA radiation- which increased risks for UVA – induced skin damage, premature aging, wrinkling, and UV-induced immune system damage – than consumers using zinc- and titanium based products. Sunscreens without zinc or titanium contain an average of 4 times as many high hazard ingredients known or strongly suspected t cause cancer or birth defects, to disrupt human reproduction or damage the growing brain of a child. They also contain more toxins on average in every major category of health harm considered: cancer (10% more), birth defects and reproductive harm (40% more), neurotoxins (20% more), endocrine system disrupts (70% more), and chemicals that can damage the immune system (70% more)’ 7. Production costs of Titanium dioxide (TiO2) manufacture Tiatinum when heated in air above 610° C or 1,130° F to produce Titanium dioxide (TiO2). There are different processes to produce Titanium dioxide. Chloride Process; a process to purify titanium dioxide from minerals contains 90% of (TiO2). In this process crude titanium mineral is reduced by carbon and oxidized by chloride which produces titanium tetrachloride (TiCl4). TiCl4 on distillation and re-oxidation with oxygen gives pure Titanium dioxide. There is another process to produce Titanium dioxide. In this process ilmenite (a mineral contain about 55% to 65% titanium dioxide) is dissolved in sulphuric acid gives ferrous sulphate, which on crystallization and filtration and further processing produce pure (TiO2) There is another method to upgrade ilmenite called Becher Process. This is an industrial process which upgrade ilmenite to synthetic rutile. 7.1 Capital costs Tiatium dioxide is either produced through chloride process or sulphate process. The sulphate process technology is simple than chloride route and can consume lower grade and cheaper ores. However this process has higher production cost and because of use of acid is more expensive than to build a chloride plant (chloroalkali unit). Thus the unit to produce Titanium dioxide has high capital costs. A plant produces 150,000 tons of titanium dioxide per year costs about $ 300 million plus infrastructure cost 0f USD 150/ton/year. So production of titanium dioxide is capital intensive at a reasonable commercial level. Although small units Read More