Product deposition rate measurements

Experiments of propane pyrolysis were carried out using a thin tubular CVD reactor as shown in Fig. 1 [4]. The inner diameter and heating length of the tube were 4.8 mm and 30 cm, respectively. Temperature was around 1000°C. Propane pressure was 0.1-6.7 kPa. Total pressure was 6.7 kPa. Helium was used as carrier gas. The product gas was analyzed by gas chromatography and the carbon deposition rate was calculated from the film thickness measured by electron microscopy. The effects of the residence time and the temperature... 

Consequently the photoresponse tTph/deposition rate as about lO exp(Frf). Activation energies amounted typically to 0.7-1.0 eV. From thermally stimulated conductivity (TSC) measurements [489-492] a midgap density of states (DOS) of 1.5 x lO cm eV is determined. The product/zr at 300 K is 9 X 10 cm V . Both DOS and /rr are independent of frequency. 

FIG. 66. Effects of modulating the RF excitation frequency (a) deposition rate and average light intensity as a function of the modulation frequency, with the deposition rate at cw conditions indicated by the dotted line, (b) measured spectrally integrated emission and calculated production of SiH3 radicals as a function of time, at a modulation frequency of 50 kHz and a 509f duty cycle. [From A. C. W. Biebericher. J, Bezemer. W. F. van der Weg, and W. J. Goedheer, Appl. Phys. Lett. 76, 2002 (2000), 2000, American Institute of Physics, w ith permission.]... 

The photoablation behaviour of a number of polymers has been described with the aid of the moving interface model. The kinetics of ablation is characterized by the rate constant k and a laser beam attenuation by the desorbing products is quantified by the screening coefficient 6. The polymer structure strongly influences the ablation parameters and some general trends are inferred. The deposition rates and yields of the ablation products can also be precisely measured with the quartz crystal microbalance. The yields usually depend on fluence, wavelength, polymer structure and background pressure. 

Although direct measurements are extremely limited, the dry component of deposition can be estimated qualitatively from data noting that the deposition rate is the product of a deposition velocity and ambient concentration observations at ground level. 

The product of deposition rate and deposition time determines the film thickness. Hence, W FM)t is an important practical parameter to control the thickness of the deposition. In many practical applications in which the actual thickness of deposition is extremely difficult to measure, the overall functional character of LCVD process itself can be controlled by this parameter. 

Carbon deposition rates were measured in a microreactor connected to a Sartorius 4436 high pressure microbalance [11]. The catalyst (17-70 mg) was placed on quartz wool in a perforated quartz basket in a stainless steel reactor lined with an alumina tube (i.d. = 15 mm) and hung from one arm of the microbalance by a quartz fiber. Water was fed using a Lewa M3 pump. A flow of inert gas was always maintained through the microbalance. The composition of the product gas could be determined by on-line gas chromatography. 

Upon contact of gas-phase I2 with stainless steel surfaces, a deposited amount of iodine on the order of 0.1 mg /cm was measured, whereas comparable experiments with liquid I2 solution did not result in a measurable deposition of iodine, apparently due to the rapid dissolution of the metal iodides formed (Deane and Marsh, 1990). From the earlier desorption experiments performed by Rosenberg et al. (1969) it was assumed that FeU is the main primary product of this reaction, but that parallel formation of NiU and/or Cris cannot be ruled out all these compounds are readily soluble in water. Experiments using tubes made of steel 1.4541 (Funke et al., 1994) showed an I2 deposition rate constant in dry air at 120 °C of about 6 10" m/s. Under condensing steam conditions at the same temperature a considerably higher value of 1.4- 10 m/s was measured, indicating that under such conditions the U-U conversion on steel surfaces is a fast process. Analysis of the surfaces after completion of the test yielded only a small iodine retention in the condensed steam no iodate could be detected, indicating that no unreacted I2 had passed through the reaction tube and that only metal iodides had been... 

Daily intakes of lead through inhalation by human or experimental populations are the product of ventilation rate and air Pb concentration, further adjusted for lead deposition rates of the inhaled volumes in the respiratory tract. The ventilation rate, i.e., total volumes of inhaled air per unit time, typically 24 hours, can be determined by either direct measurement or via food-energy intakes. The latter may also be employed to arrive at the ratios of total energy expendimre to basal metabolic rate (BMR). 

---