Tin Oxide Systems

Tin oxide is the only TCO material, which is prepared on an industrial scale by CVD. The literature on this material is enormous and, therefore, we have chosen to focus on work since 1987 to keep the length of this section reasonable. 

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Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

Tin ll) oxides. Lower tin oxides SnO (white, NH4OH to SnCli solution black, heat on white SnO red), form a complex system. 

Alloys suitable for castings that ate to be bonded to porcelain must have expansion coefficients matching those of porcelain as well as soHdus temperatures above that at which the ceramic is fired. These ate composed of gold and palladium and small quantities of other constituents silver, calcium, iron, indium, tin, iridium, rhenium, and rhodium. The readily oxidi2able components increase the bond strength with the porcelain by chemical interaction of the oxidi2ed species with the oxide system of the enamel (see Dental materials). 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

The inorganic tin compound that has received the most study from a toxicological viewpoint is stannic oxide. Autopsies performed on workers in the tin mining and refining industry, who inhaled tin oxide dust for as long as 20 yr, disclosed no pulmonary fibrosis (57). Inhalation for long periods produces a benign, symptomless pneumoconiosis with no toxic systemic effects (58). 

The chrome—tin system is the only family to produce purple and maroon shades, as well as pinks. The system can be defined as pigments that are produced by the calcination of mixtures of small amounts of chromium oxide with substantial amounts of tin oxide. In addition, most formulations contain substantial amounts of siHca and calcium oxide. 

Dyes for Color Filters. Colorhquid crystal display systems consist of LSI drivers, glass plates, polarizers, electrodes (indium—tin oxide), and microcolor filters. The iadependent microcolor filter containing dyes is placed on each Hquid crystal pixel addressed electrically and acts as an iadividual light switch. All colors can be expressed by the light transmitted through each filter layer of the three primary colors, ie, red, green, and blue (Fig. 12). 

Fig. 12. General stmcture of LCD. A, polarizer plate B, glass plate C, electrodes (indium—tin oxide) D, Hquid crystal E, common electrode (ITO) F, overcoated layer G, colored pixel H, back light. In an improved color LCD system today, retardation films are placed between A and B.

The deliberate growth of tin oxide or mixed oxide films in both acid and alkaline solutions has been reviewed recently . The effect of additions to alkaline solutions on their attack on tin has been considered as has the tendency for pitting corrosion to occur in solutions containing chloride ions" . In connection with this, potential pH diagrams for Sn-H O-Cl systems have been published . 

To appreciate the potential changes in food cans, it is necessary to describe briefly the steel-based materials used in modern can manufacturing operations. The tin can is made from a special grade of thin gage, low carbon, cold-rolled steel, which is generally referred to as a tin mill product. The base steel is coated with either tin, a chromium-chromium oxide system, or it is just cleaned and oiled. It may also be coated with organic coatings. 

NB. Mixed solvent systems are shown as e.g. acn-aq (0.01 M) where the number in parentheses indicates the concentration of the lesser constituent ITO-Indium/tin oxide-coated glass, Ar- Solutions purged with argon, Ar atm - Experiment performed under an argon atmosphere, N2 atm - Experiment performed under a nitrogen atmosphere b All potentials are measured vs. SCE unless otherwise stated ... 

Tin oxide Resistance Neodym Systems 0-20,000 ppm Yes Uses Figaro sensors, but selectively ... 

Of the tin additives studied, the anhydrous and hydrated zinc stannates, ZnSnO and ZnSn(OH), respectively, are considerably more effective flame-retardant synergists with the bromine present in the plastic than 8-stannic acid (Figure 1). In line with this observation, oxidic tin-zinc systems have previously been found to exhibit superior flame-retardant properties to tin oxides alone (19-22). In addition, ZnSnO, gives higher values of 01 than Sb20, incorporation levels studied, and, in fact, the 1% ZnSnO - containing plastics outperform samples containing 2% Sb O,. 

I.G. Hill and A. Kahn, Combined photoemission in vacuotransport study of the indium tin oxide/copper phthalocyanine/A, iV8-diphenyl- N, NR-bis. l-naphthyl.-l,18biphenyM,49diamine molecular organic semiconductor system, J. Appl. Phys., 86 2116-2122 (1991). 

Most microhotplate-based chemical sensors have been realized as multi-chip solutions with separate transducer and electronics chips. One example includes a gas sensor based on a thin metal film [16]. Another example is a hybrid sensor system comprising a tin-oxide-coated microhotplate, an alcohol sensor, a humidity sensor and a corresponding ASIC chip (Application Specific Integrated Circuit) [17]. More recent developments include an interface-circuit chip for metal oxide gas sensors and the conccept for an on-chip driving circuitry architecture of a gas sensor array [18,19]. 

The first device is a circular microhotplate (Sect. 4.1). One important guideline was to implement the microhotplate in CMOS technology with a minimum of post-CMOS micromachining steps. Additionally the hotplate had to be optimized for drop-coating with nano crystalline tin-oxide layers. This microhotplate was cointegrated with circuitry, and the respective monolithic sensor system will be discussed in Sect. 5.1. 

The features of the monoHthic integrated sensor systems have not yet been fully exploited. The almost linear relationship between input reference voltage and microhotplate temperature renders the systems suitable for applying any temperature modulation protocol. Due their compatibility with other CMOS-based chemical sensors the microhotplates can be also combined with, e.g., polymer-based mass sensitive, calorimetric or capacitive sensors. The co-integration with such sensors can help to alleviate problems resulting from cross-sensitivities of tin-oxide based sensors to, e.g., volatile compounds such as hydrocarbons. A well-known problem is the crosssensitivity of tin oxide to humidity or ethanol. The co-integration of a capacitive sensor, which does not show any sensitivity to CO, could help to independently assess humidity changes. 

Bu2Sn=0 Selective oxidation of 1,2-diols to a-hydroxy ketones was electro-chemically achieved in a double mediatory system consisting of dialkyl tin oxide and the bromide ion (Fig. 3) [34]. 

The set of results from TPR is consistent with the interpretations made so far, based on other characterization techniques used. In aU cases, the reduction in tin oxides occurs at temperatures much lower than those in the literature, where values above 900 K are reported for Sn02 [59]. The selectivity of the preparation reaction leads to a close relationship between M and Sn atoms transition metal atoms generate atomic hydrogen by dissociative adsorption, these hydrogen atoms being able to reduce tin oxides closely related to transition metals. Thus, the reduction temperature of the transition metal is the one that controls the global reduction process. As Pt is the metal that can be reduced most easily, the PtSn-BM catalyst exhibits the highest reducibiUty (lower reduction temperature) of aU the bimetalUc systems studied. 

The oxidation of ethanol to acetic acid was among the first heterogeneous catalyzed reactions to be reported, but it has not attracted continued interest. During the 1990ies, however, 100% conversion of ethanol coupled with 100% selectivity to acetic acid was reported in a gas-phase reaction using molybdenum oxide catalytic systems on various supports, at temperatures below 250 Similarly, a tin oxide and molybdenum oxide catalyst was... 

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