Indium Tin Oxide

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Indium tin oxide (ITO) or tin-doped indium oxide is a mixture of indium oxide and tin oxide in which the tin component can contribute up to one-fifth of the material composition. Indium tin oxide is a transparent (see-through) material with electrical conductivity. Indium tin oxide is applied mainly as a film to create transparent conductive coatings in the opto-electronic industry, for example to protect image sensors of digital cameras, or displays based on LED technology (LED = light emitting diode). It is used in heated defrosting coatings for the cockpit windows of the Airbus. Another interesting new application is the usage of indium tin oxide in a new generation of solar cells.

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How can I come into contact with this material?

The most likely route for indium tin oxide nanoparticles to enter the human body is through inhalation (breathing in) of the raw material during processing. Other uptake routes like accidental swallowing of ITO nanoparticles are extremely unlikely. Eye contact should be avoided.

Is there any risk from this material to humans and the environment?

Irritation of the nose, throat and eyes are symptoms that can occur in humans upon exposure to high concentrations of ITO nanoparticles. Thus, air-borne exposure to indium tin oxide dust, e.g. during the production of displays, should be avoided. Indium tin oxide particles of 950 nm in size have been shown to cause lung damage in hamsters and this was linked to its accumulation in lung tissues. There is some evidence that indium tin oxide appears to dissolve in the body and forms soluble indium. Another study has shown a negative effect of indium tin oxide (ITO) on the reproductive capacity in animals.

Conclusion

For the consumer the chances of being exposed to indium tin oxide (ITO) are very small. However at the workplace (e.g. in in the solar cell industry) it is important to take the necessary safety precautions to avoid inhalation when handling this material.

Properties and Applications

Indium tin oxide (short: ITO) is a mixture of indium oxide (In2O3) and tin oxide (SnO2) with the total formula In2-xSnxO3. Its share of tin may amount to up to 20 percent. Being semiconductive, it has a high electrical conductivity. Moreover, thin layers of about 200 nm are transparent in the area of visible light while infrared light is reflected. Indium tin oxide has a density of approximately 7 g/cm³ and a white to yellowish color. According to composition, it can take on other colors (blue, green, yellow, etc.). ITO is almost insoluble in water.

 

Indium tin oxide is one of the most important transparent, electrically conductive materials. In the optoelectronic industry, it is mainly used to coat semiconductor sensor wirings and manufacture diverse electro-optical components and devices such as liquid-crystal screens, organic light-emitting diodes (OLEDs), and touchscreens. In addition, it is used as transparent heating glass in de-icing systems, heatable object slides or hot states. Indium tin oxide is found in invisible antennae and thin-film solar cells. Indium tin oxide layers protect image sensors of high-quality digital cameras. Due to its transparency and electrical conductivity, ITO is used for coating non-conductive materials such as plastics to prevent electrostatic charging.

 

To increase the conductivity and IR reflectivity of the materials, indium tin oxide is added to transparent varnishes, adhesives, plastic films, and fibers in the form of fine to nanoscale particles (powders) of different compositions. Besides, one finds ITO powder coatings, and transparent ITO-based conductors that have been manufactured by means of special printing techniques.

It is due to the limited availability and high prices of indium that intensive efforts are made worldwide to replace indium tin oxide by other transparent and conductive materials.

 

ITO is not self-inflammable as nanometer-sized powder. Also as a mixture with air (dust) under the influence of an ignition source, ITO is not inflammable, so there is no possibility of a dust explosion.

 

Occurrence and Production

Indium tin oxide is a technical product. It can be applied to substrates, mainly to glass and plastic films, by means of different coating methods. High-vacuum sputtering is the most commonly used method. Although it reduces the coating area, it can ensure a high homogeneity of the coating layers. Larger surfaces can be coated through reactive thermal evaporation in air at temperatures above 300 °C or by means of the sol-gel technique.

 

Fine-grained to nanocrystalline powders are preferably obtained by co-precipitation from aqueous solutions: Soluble indium or tin components are precipitated through an increase in pH values. To obtain the desired properties, a thermal aftertreatment is carried out at temperatures above 300 °C.


Literature

  1. Wikipedia (EN): Indium Tin Oxide (ITO) (last access date: Jul 2011).
  2. Kaune, Gunar (2005). Röntgenografische Charakterisierung von Indium-Zinn-Oxid-Dünnschichten, Diploma Thesis, Faculty of  Natural Sciences, TU Chemnitz, 2005.
  3. Patents on the use and manufacturing of ITO powders: DE69818404T2 vom 01.07.2004; Degussa DE102004041747A1 vom 02.03.2006; Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. DE10261541A1 vom 01.07.2004

Since indium tin oxide (ITO) is firmly embedded in displays and liquid crystal screens, humans do not come into contact with the particles. So far, only few data on exposure to indium tin oxide particles are available.

Studies on Living Organisms - in vivo

Both studies report lung injury after treatment, culminating in neoplastic transformations. Furthermore increased indium levels in the serum of the animals could be detected. A third study, again performed with hamsters, investigated the influence of ITO particles on the testis. Only minor effects on seminiferous tubules could be detected while the reproductive capacity of the hamsters was not affected. In general the observed effects of ITO were less severe than those reported for other indium compounds such as Indium Arsenic (InAs) or Indium Phosphide (InP).


Literature

  1. Tanaka, A et al. (2002), J Occup Health, 44(2): 99-102.
  2. Omura, M et al. (2002), J Occup Health, 44(2): 105-107.
  3. Tanaka, A et al. (2010), J Occup Health, 52(1): 14-22.

Currently, there are no data regarding the environmental exposure of nanoscale indium tin oxide (ITO).

In all animal studies conducted with hamsters, indium tin oxide particles (and other indium particles) were administered via the lungs.

All reported animal studies apply to indium tin oxide (ITO) particles as well as other indium containing particles of different composition which were administered by intratracheal instillation into the lung. The reported effects are described in the article on exposure.

There are indications of harmful effects of indium tin oxide (ITO) nanoparticles towards various aquatic organisms, especially to invertebrates and algae.

However, these indications need a critical review, since they are based on only one available study dealing with the environmental risk of ITO nanoparticles [1]. Due to lack of data for particle characterisation, this study does notz meet the literature quality criteria of the DaNa Consortium. In particular, data on particle size and size distribution in the appropriate dispersing media, as well as surface characteristics and chemistry, and morphology are missing.

 

  1. Blaise, C et al. (2008), Environ Toxicol, 23(5): 591-598.

The distribution of indium tin oxide (ITO) particles in the body is poorly studied.

Behaviour inside the Body

A considerable amount of ITO particles could still be observed in the lung of hamsters even 78 weeks after the last application. This result indicates that the residual particles might be the cause of the detected lung damage. Moreover an increasing amount of dissolved indium could be detected in the serum of the animals. This suggests that at least a fraction of the particles is soluble. Different particles, e.g. ITO in comparison to indium phosphide (InP), show different dissolution behavior.

No distribution data could be found for ITO particles in particular. However soluble indium distributes relatively even among the major organs of rats (liver, kidney, lung, spleen and testes) after intratracheal instillation of indium phosphide (InP).


Literature

  1. Tanaka, A et al. (2010), J Occup Health, 52(1): 14-22.
  2. Homma, T et al. (2003), J Occup Health, 45(3): 137-139.
  3. Zheng, W et al. (1994), J Toxicol Environ Health, 43(4): 483-494.
  4. Uemura, T et al. (1997), J Occup Health, 39(3): 205-210.

Currently, there are no data available regarding the environmental behaviour of nanoscale indium tin oxide (ITO) particles.

Further Materials


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Diamond
Zirconium Dioxide
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