Erosion constant

In Equation (9.1), X is the instantaneous scale thickness, t is time, k is the scaling constant (cm s ) and eo is the erosion constant for the oxide (cm s ). This relationship is valid, so long as the erosive impacts affect only the outer surface of the scale. The scale will continue to grow, so long as the term > fceo- However, as the scale grows it reaches a critical thickness, X, given by Equation (9.2),... 

The value of the erosion constant will vary with the erosion conditions, thus under strong erosion the actual rate of scale formation will increase as the scale thickness is held to low values. The rate of scale formation is also the rate at which the metal degrades by conversion to oxide. 

Erosion is the deterioration of a surface by the abrasive action of solid particles in a liquid or gas, gas bubbles in a liquid, liquid droplets in a gas or due to (local) high-flow velocities. This type of attack is often accompanied by corrosion (erosion-corrosion). The most significant effect of a joint action of erosion and corrosion is the constant removal of protective films from a metal s surface. This can also be caused by liquid movement at high velocities, and will be particularly prone to occur if the solution contains solid particles that have an abrasive action. 

The advantages claimed for organotin polymer-based antifouling paints include constant toxicant deHvery vs time, erosion rate and toxicant deHvery are controUable, no depleted paint residue to remove and dispose, 100% utilization of toxicant, polishing at high erosion rates, surface is self-cleaning, and function is continuously reactivated. 

Superheaters and Reheaters A superheater raises the temperature of the steam generated above the saturation level. An important function is to minimize moisture in the last stages of a turbine to avoid blade erosion. With continued increase of evaporation temperatures and pressures, however, a point is reached at which the available superheat temperature is insufficient to prevent excessive moisture from forming in the low-pressure turbine stages. This condition is resolved by removing the vapor for reheat at constant pressure in the... 

How these factors affect erosion can be determined from the empirical equation shown in Table 4-14. The equation shows erosion rate proportional to a constant, the mass of the particle, its velocity, and angle of attack. 

The most significant effect of erosion-corrosion is the constant removal... 

Green (G3) has proposed an alternate approach based on the concept of a critical mass-velocity required to produce a Mach number of 1 in a constant-area channel. Green showed this approach was able to correlate the erosive-burning data he obtained for both a double-base propellant and a composite propellant. 

The dominant processes controlling the movements of P through terrestrial ecosystems are schematically presented in Fig. 14-4. In a general way, the overall movement of P on the continents may be envisioned as the constant erosion of P from continental rocks and transport in both dissolved and particulate form by rivers to the ocean, stopping occasionally along this pathway to interact with biological and mineralogical systems. 

In disc form, when prepared by compression molding, the more hydrophobic polymers, PCPP and PCPP-SA, 85 15, displayed constant erosion kinetics over 8 months. By extrapolation, 1-mm-thick discs of PCPP will completely degrade in over 3 years. The degradation rates were increased by copolymerization with sebacic acid. An increase of 800 times was observed when the sebacic acid concentration reached 80%. By altering the CPP-SA ratio, nearly any degradation rate between 1 day and 3 years can be achieved (4). 

Surface erosion not only leads to zero-order drug release from devices that maintain a constant surface area, but has other important consequences. Among these are the following (1) the rate of drug release is directly proportional to drug loading, (2) the lifetime... 

Although it was possible to achieve constant in vitro release of levonorgestrel for up to 410 days at which point the experiment was discontinued, release of the drug was not controlled by surface erosion of the polymer but instead the device underwent bulk erosion and release of levonorgestrel was completely controlled by its rate of dissolution. Bulk erosion of the rod-shaped device was evident by scanning electron microscopy as shown in Fig. 17. 

Wilson, Kent Lewis (1970) in a long-term study found that most of the soluble phosphate was eluted from the cement in the first 24 hours. By contrast the rate of elution of zinc remained constant for 160 days, the length of the study. They concluded that long-term erosion took place at the surface of the oxide particles rather than in the matrix. 

Fig. 33. Variation of dimensionless radius with dimensionless time for compact carbon black particles suspended in silicone oil undergoing a simple shear flow. Top Data for initial radius Ho 1.7 mm for different viscosities and different shear rates, but with Fa = 0.28. Bottom Data for initial radius R0 = 2.0 mm for different densities and different shear rates, but with Fa 0.28. For all cases the erosion rate constant kc = 0.37. (See Eq. 53).

As a first approximation, a simple linear relation may be assumed to convert the time of sputtering to depth. Thus for a constant sputtering rate, the depth of erosion z will be given by ... 

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