Silica transmittance

The spectral normal emissivity of Coming Code 7940 vitreous silica was computed from measurements of transmittance and reflectance at 25°C and is shown in Figure 8. The total normal emissivity of Code 7940 silica as a function of temperature from —200 to 1400°C is shown in Figure 9. 

Vitreous silica transmission curves are shown in Figure 7. The hydroxyl concentration for each silica type is listed in Table 9. These curves represent only the general characteristics of the different silica types and should not be used for calculations of transmittance. 

Figure 4. Raman spectra of methylated silica in the CH stretching region using 1.7 W of laser power at 488.0 nm. The scan rate and response time constant (seconds) were as follows (A) 500 cm"V min, 0.1 s (B) 50 cm 1 /min, 1 s (C) 10 cm 1 /min, 10 s. Curve D shows the IR spectrum recorded with a scan time of 83 cm 1/min and a time constant of Is. The vertical bar represents 3000 Hz for the Raman spectra and a transmittance of 0.20 for the IR spectrum (21).

Peroxy entities may indeed represent an ubiquitous type of defects in oxides and silicates, both natural and synthetic. The reason is that traces of dissolved "water" are everywhere. In optical waveguide fibers made of low-OH fused silica a dramatic increase of Si-OH and attendant loss of transmittance have been reported upon exposure to H2 probably by way of the reaction Si/°° Si + H2 2 Si-OH (15,35). ... 

Vycor will deform and melt about 100°C lower than fused silica, and it is a poor transmitter of uv light. In the early years of Vycor production, Vycor was significantly less expensive than pure quartz glass. However, as the manufacturing techniques of pure quartz glass have become more efficient, Vycor is now the more expensive material. 

Thin layers of powdered cellulose, silica gel, alumina, ion-exchange or gel-permeation material supported on glass plates, plastic sheets or aluminium foil development tanks components sometimes examined by reflectance or transmittance densitometry or removed for spectrometric analysis. 

The principal purpose of these experiments is to demonstrate that extremely sharp thresholds in optical transmittance can be obtained from laser photobleaching of a copolymerized absorber. It is not clear that these results can be applied directly to wafer processing conditions. Since the thermal characteristics of the sample are probably quite important in our experiments, the results obtained from a single polymer film on fused silica may not be the same as those found with a multilayer film on silicon. Clearly considerable additional experimentation is necessary before one can consider practical applications. 

Figure 25-2 Transmittance ranges for various optical materials. Simple glasses are fine in the visible region, while fused silica or quartz is necessary in the UV region (<380 nm). Halide salts (KBr, NaCl, AgCl) are often used in the IR region but have the disadvantages of being expensive and somewhat water soluble.

Chromatographic columns (85 X 9 cm) were packed with ca. 1500 g silica gel in benzene-MeOH-acetic acid (90 16 8,v v v) to a bed length of ca. 50 cm. 100 g portions of the biologically active dark brown gum were mixed with 200 g of silica gel in 2-propanol, and, after the 2-propanol was evaporated, the brown powder was applied to the prepared column. The column was then eluted with benzene-MeOH-acetic acid (90 16 8,v v v) and the eluate monitored via spectrophotometry. Active fractions that correlated with a maximum % transmittance at 400 nm appeared after the first 3 L of solvent eluted. Thereafter, 1 L fractions were collected and those showing activity were combined. After solvent evaporation, about 450 g of active material from 181 kg of pollen were obtained (ca. 564 g active material per 227 kg pollen, equivalent). 

Spectral transmittance of Ti02-films deposited from ethyl-dichloro-titanate solution on (a) fused silica and (b) window glass (coated on both sides)... 

As with fused silica, the ultraviolet transmission of Si02 films is dependent on purity. However, the excellent uv transmittance value of purest silica glass cannot even be attained with carefully prepared Si02 films because of incorporated traces of hydrolytic and pyrolytic residues which produce measurable absorption below 205 nm. In the infrared region there are strong absorption bands in the films between 7.8 and 11.5 pm. Those are the same frequencies at which absorption is also observed in pure fused silica. Si-0 vibrations are responsible for this absorption. However, there... 

Similar to the optical analogy, the problem is solved by acoustic quarterwave matching layers (Fig. 10). Silica aerogels with densities of around 300 kg/m have the ideal acoustic impedance to match a piezoelectric transducer to air [77]. In addition, they exhibit rather low attenuation, as opposed to many porous, polymer materials used for this purpose until now. An increase in sound transmittance by more than 30 dB was achieved in a relatively simple arrangement without optimization. More elaborate designs, eventually including multiple layers combining different materials, will probably result in transducer systems optimized with respect to output power, sensitivity, and bandwidth. 

Silicones Polymers. The outgassing products from silicone polymers initially condense on the glazing as liquid alkyl linear and/or cyclic polysiloxanes. These liquid condensates have been observed to form on solar collectors after several days of testing in the Arizona desert. The liquid polysiloxanes do not appreciably affect the relative light transmittance. However, as the thin film is exposed to the harsh environmental conditions encountered during three months of desert testing, it is slowly converted into a white colloidal silica powder through the follov/ing type of overall reaction ( ). 

A colloidal silica deposit having a density of 0.129g/square meter can reduce the relative light transmittance by as much as... 

TEM Transmittance electron microscopy (used in the determination of asbestos, silica, and other particulates, and as a tool in toxicological studies)... 

Figure 10. Linearity of Kubelka-Munk function with surface loading of [Co(neo)]. Transmittance values were obtained from diffuse reflectance UV-vis spectra taken at 654 nm. Data are shown for low loadings of [Co(neo)] on Merck silica grade 9385 and the values were converted to Kubelka-Munk units. Transmittance values < 5% were not used. The concentration of Co was determined by removal of the adsorbed complex by treatment with 1M HCl followed by colorimetric determination with ammonium thiocyanate. [Adapted from (57).]...

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