Tin Dioxide Essay

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1.1 Introduction
Tin dioxide, also known by the systematic name tin(IV) oxide and stannic oxide in the older notation, is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin. With many other names, this oxide of tin is the most important raw material in tin chemistry. This colorless, diamagnetic solid is amphoteric.
1.2 Structure
It crystallises with the rutile structure, wherein the tin atoms are six coordinate and the oxygen atoms three coordinate. SnO2 is usually regarded as an oxygen-deficient n-type semiconductor.[4] Hydrous forms of SnO2 have been described in the past as stannic acids, although such materials appear to be hydrated particles
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The scientific investigation of colloid sand their properties was reported by Faraday (1857) in his experiments with gold. He used the term “divided metals” to describe the material which he produced. Zsigmondy (1905)describes the formation of a red gold sol which is now understood to comprise particles in the 10 nm size range. Throughout the last century the field of colloid science has developed enormously and has been used to produce many materials including metals, oxides, organic sand pharmaceutical products.
Many other well known industrial processes produce materials which have dimensions in the nanometre size range. One example is the synthesis of carbon black by flame pyrolysis which produces a powdered form of carbon with a very high surface to mass ratio. This is usually highly agglomerated but has a primary particle size which can be of the order of 100 nm.
Worldwide production of carbon black was approximately 6 million tonnes in 1993 (IARC,1996). Other common materials produced by flame pyrolysis or similar thermal processes include fumed silica (silicon dioxide), ultrafine titanium dioxide (TiO2) and ultrafine metalssuch as
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DG SANCO 2004). This report also stated that the “biological activity of nanoparticles – including potential adverse as well as beneficial effects - tends to increase as their size decreases”. Evidence for other particle types (e.g. “low toxicity dusts”) clearly shows that the toxicity of these materials is strongly dependant on their surface area (Tran etal; 2000). Such ideas are consistent with current views on the links between environmental pollution and health. Epidemiological evidence from industrial processes, such as the manufacture of carbon black, where in principle workers may potentially be exposed to nanoparticles, also indicates potential (respiratory) health issues. The large surface area, crystalline structure, reactivity and exotic properties of some nanoparticles, coupled with what appears to be an imminent shift away from laboratory based development to industrial manufacture, strongly indicates a need for a clearer understanding of the

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