Phosphorous silicon glass

Sacrificial oxide. The sacrificial oxide layer is deposited by low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The layer is made of either undoped glass or phosphorous-silicon glass (PSG)-doped resulting in a final thickness of 1.5-2.5 pm. Low defect density, good etch rate control, uniformity and stress control have been accomplished for updoped oxide with a Novellus Concept One tool. 

It is well established that the degree of selectivity can vary extremely going from one dielectric to the other [Chow et al.67, Broadbent et al.131, Chow et al.133, Bradbury et al.134, Wilson et al.135]. Silicon nitride, for instance, is notorious for its low selectivity whereas phosphorous doped glasses show an improved selectivity compared with undoped glasses (see also section 3.5). 

These cements are formed by a similar process to the silicate minerals described in Chapter 1, the difference being the rate. Silicate minerals are formed at a rate lower by orders of magnitude compared with dental cements. In the case of dental cements, the phosphoric acid releases protons in the solution and lowers its pH. This decomposes the glass and releases silicon in the solution, and silicic acid forms as an intermediate product [26,27]. Simultaneously, cations such as Ap, Ca " ", and Na" " and the anion F are also released [28]. The cations and anions are attracted to each other, and neutral bonding phases form. Such a bonding network, especially that of aluminum, results in gelation and subsequent polymerization of a hard product. 

In the second procedure, calcium nitrate was replaced by calcium alkoxide (60). Calcium and silicon alkoxides have very different rates of hydrolysis. To avoid the production of inhomogeneities, a slow and controlled hydrolysis of a mixture of silicon, calcium, and phosphorous alkoxide was performed. The resulting materials were highly homogenous, and monolithic pieces could be produced. The bioactivity of the gel-derived materials is equivalent or greater than melt-derived glasses. 

A Aced, E Anklam, K-D Asmus, K Pohl, RS Glass, LK Steffen, GS Wilson. Phosphor Sulfur Silicon 48 53, 1990. 

Baumann has also made heat flux measurements using thermographic phosphors.Wind tunnel models made of three different materials (steel, Macor glass ceramic, and Norcoat 4000 silicone elastomer), all of which had thin coatings of Y202S Eu (0.15%) applied, were monitored during blow-down tests in a hypersonic flow facility. The response time of the measurement system was typically less than 200 msec, and the values of the heat flux measurements obtained with... 

Transparent, tasteless crystals, or amorphous powder, d (amorphous) 2.2. d° (quartz) 2.65. Melts to a glass. Silica has the lowest coefficient of expansion by heat of any known substance. It is practically insol in water Or acids, except hydrofluoric add in which it readily dissolves forming the gas silicon tetrafluoride it is also slowly attacked by heating with coned phosphoric acid. The crystallized forms of silica are scarcely attacked by alkalies, while the amorphous is sol. especially when finely divided. See also Infusorial Earth. 

In common silicate glasses silicon dioxide is used. If instead of silicon dioxide, phosphorous pentoxide is used, a kind of phosphate glass is obtained. Some phosphate glasses are water soluble, as well as biocompatible and can be used in biodegradable tissue formulations. 

Glass is produced by fusing the oxides of silicon, boron, or phosphorous with a basic oxide or sodium, calcium, magnesium, or potassium, and cooling the product rapidly to prevent crystallization. It is a transparent, hard, brittle and amorphous material resistant to all acids except hydrofluoric acid. 

Special adhesives are required for high temperature use. Silicone rubber is an excellent flexible adhesive with a temperature limit of 250 °C. For higher operating temperatures, one must resort to inorganic adhesives and cements. These are usually based on silicates (water glass), phosphates (phosphoric acid), and Portland cement. 

Several variations of Bioglass and Ceravital glass ceramics have been used by various workers within the last decade. Glass ceramics used for implantation are silicon oxide based systems with or without phosphorous pentoxide. 

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