High pressure oxidation, silicon

At high temperature, silicon carbide exhibits either active or passive oxidation behavior depending on the ambient oxygen potential (65,66). When the partial pressure of oxygen is high, passive oxidation occurs and a protective layer of Si02 is formed on the surface. 

In this process, molten iron is refined to steel by mp-hlowing oxygen at high pressure onto the surface of the metal through a waier-eooled lance contained in a tilling furnace. The oxidation of carhon. silicon, manganese. 

Figure 9.10 Adsorbed amount of water on a silicon oxide surfaces versus relative vapor pressure at 20°C. The continuous line was calculated with the theory of Polanyi and assuming van der Waals forces only (Eq. 9.57). Experimental results as measured on Aerosil 200 were adapted from Ref. [379] (see also Fig. 9.9). The deviation at high pressure is partially due to the porosity of the adsorbent. The equilibrium vapor pressure is P0 = 3.17 kPa.

J.R. Ligenza. Effect of crystal orientation on oxidation rates of silicon in high pressure steam // J.Phys.Chem.- 1961.- V.65, No. 11.- P.2011-2014. 

Brus et al. prepared isolated silicon particles by high temperature pyrolysis of disilane with a subsequent passivation of the surface by oxidation [33]. The particles of various size are then processed by high-pressure, liquid-phase, size exclusion chromatography to separate sizes and obtain various fractions of monosize particles. Such particles represent an almost ideal model of silicon quantum dots. 

The molecular sieves are aluminosilicates of particular importance. They are crystalline materials that have open structures that contain pores and channels that have molecular dimensions. This family of materials includes the zeolites, which have numerous applications in heterogeneous catalysis, ion-exchange materials, absorption of molecular species, and gas separation. While some zeolites occur naturally, they are usually manufactured from silicon and aluminum oxides mixed with tetraaUcylammonium templates in a high-pressure autoclave (see Zeolites). 

Bulk-micromachined membranes are usually formed from dielectric materials like silicon oxide or silicon nitride combined with additional materials for example, in pressure sensors, silicon is used to increase the membrane thickness to the required values and in thermal sensors, platinum or other metals are needed for the sensing elements. The overall stress state of the membranes has to be controlled well to prevent buckhng (under high compressive stress) or fracture (under high tensile stress). With proper processing control, silicon oxide and silicon nitride thin films meet this requirement, making them ideal candidates for membrane-type devices. 

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