Silicon content

The Type N thermocouple (Table 11.60) is similar to Type K but it has been designed to minimize some of the instabilities in the conventional Chromel-Alumel combination. Changes in the alloy content have improved the order/disorder h ansformations occurring at 500°C and a higher silicon content of the positive element improves the oxidation resistance at elevated temperatures. 

Gray iron is resistant to concentrated acids (nitric, sulfuric, phosphoric) as well as to some alkahne and caustic solutions. Caustic fusion pots are usually made from gray cast iron with low silicon content cast-iron valves, pumps, and piping are common in sulfuric acid plants. 

To meet this requirement, the use of steel with a still better silicon content and lower losses is imperative. A cold-rolled non-grain oriented (CRNGO) type of sheet steel is generally used for such applications, in the thickness range of 0.35-0.5 mm, with a higher silicon content of the order of 2.0-1.8% and losses as low as 1.0-1.5 W/kg. 

Clearly the best protection from oxidation by a silicide as a coating on a reactive substrate would be the disilicide, which has the highest silicon content, and could be expected to provide a relatively protective silica coating. 

For special applications special silicon-bearing austenitic steels are produced by a few manufacturers. Silicon contents are 4-5-3% and there is a corresponding increase in nickel and very low (<0-015%) carbon. In the welded state these are giving good service in nitric acid of over 90% strength up to 75°C. 

In de-aerated 10sulphuric acid (Fig. 3.45) the active dissolution of the austenitic irons occurs at more noble potentials than that of the ferritic irons due to the ennobling effect of nickel in the matrix. This indicates that the austenitic irons should show lower rates of attack when corroding in the active state such as in dilute mineral acids. The current density maximum in the active region, i.e. the critical current density (/ ii) for the austenitic irons tends to decrease with increasing chromium and silicon content. Also the current densities in the passive region are lower for the austenitic irons... 

The high-chromium irons undoubtedly owe their corrosion-resistant properties to the development on the surface of the alloys of an impervious and highly tenacious film, probably consisting of a complex mixture of chromium and iron oxides. Since the chromium oxide will be derived from the chromium present in the matrix and not from that combined with the carbide, it follows that a stainless iron will be produced only when an adequate excess (probably not less than 12% of chromium over the amount required to form carbides is present. It is commonly held, and with some theoretical backing, that carbon combines with ten times its own weight of chromium to produce carbides. It has been said that an increase in the silicon content increases the corrosion resistance of the iron this result is probably achieved because the silicon refines the carbides and so aids the development of a more continuous oxide film over the metal surface. It seems likely that the addition of molybdenum has a similar effect, although it is possible that the molybdenum displaces some chromium from combination with the carbon and therefore increases the chromium content of the ferrite. 

Fig. 3.61 Dependence of corrosion resistance of high-silicon iron on silicon content. A 70% HNOj, B20% HjSOj at b.p., C 10% HNO, at b.p., D 10% HCI at 80 C...

Fig. 7.29 Temperature to give a scaling index of 100 versus silicon content (10-89-13-14% Cr)...

It is widely recognised that improved resistance to sulphur attack can be obtained in commercial alloys by small additions of certain elements, notably manganese, silicon and aluminium. Figure 7.43 shows how the depth of metal converted to scale, and more particularly the total penetration by sulphur, is reduced by increasing silicon content in nickel-chromium-iron... 

Fig. 7.43 Effect of silicon content on corrosion of Ni-Cr-Fe alloys in a reducing flue-gas atmosphere containing 6-9 g m S (100-h tests at 982°C) a. Ni-28Fe-12Cr b. Ni-50Fe-15Cr...

Fig. 7.53 Carbon concentration profiles of various centrifugally cast steels of differing silicon content, after 100 h at 1 093°C in a gas mixture with the following composition at the furnace inlet H2/34% CH4/30% HjO (after Kane" )...

The low temperature ALD process for hafnium silicate films using HfCl2[N(SiMe3)2]2 and H2O was modified to improve the film properties by two different methods. With hydrogen peroxide, the silicon content in the film increased to Si/(Hf+Si)=0.2 at 2001 and the impurity levels decreased due to its strong oxidation effect. By introducing TBOS as an additional Si precursor, the silicon content in the film increased to Si/(Hf+Si)=0.5 at 200 °C and the hafiiium silicate films became fully oxidized with O/(Hf+Si)=2.0. 

In Figure 3b and c the absolute atomic concentrations of carbon and silicon, respectively, are shown as a function of the carbon fraction. As expected, the carbon concentration increases upon alloying. In contrast, the silicon content decreases rapidly, which implies that the material becomes less dense. As it was reported that the Si—Si bond length does not change upon carbon alloying [116], it thus... 

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

The ash contents of the total trace elements and nitrogen are similar in Tundra ecosystem biomass. The highest concentrations, >0.1% by dry ash weight, are typical for Ca, K, Mg, P, and Si. We can note the increase of iron, aluminum and silicon contents in the underground parts of any plants. 

The silicon content of 1 was determined by inductive-coupled plasma-optical emission spectroscopy (ICP-OES) of sodium tetraborate melt samples. It approximated lmmol/g resin. Results shown in Tables 13.1 and 13.2 were obtained using a resin containing 1.3 mmol Si per gram of 1, and results shown in Table 13.3 were obtained using a resin containg 0.9 mmol Si per gram of 1. 

A series of o-cresol novolac-PDMSX materials with a range of silicon contents (3.2-16.1 wt %) were prepared to examine the O2 REE response and to determine whether a solubility limit existed as a function of wt % silicon. All copolymer preparations exhibited good solubility in dilute TMAH and an asymptotic relationship (12) between wt % silicon and film thickness loss (3,12) during an 02 plasma RIE process was found. 

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