Roughness factor, determination

The uncertainty in the product, 200 calories, is not simply the sum of the uncertainties in the factors, 0.4°C and 2 grams. Instead, the sum of the percentage uncertainties in the factors determines the uncertainty in a product or a quotient. Fortunately, there is an easy method for estimating it roughly without calculating percentages. This method, based upon the number of figures written, is described in Section 1-2.5. 

It is important to distinguish clearly between the surface area of a decomposing solid [i.e. aggregate external boundaries of both reactant and product(s)] measured by adsorption methods and the effective area of the active reaction interface which, in most systems, is an internal structure. The area of the contact zone is of fundamental significance in kinetic studies since its determination would allow the Arrhenius pre-exponential term to be expressed in dimensions of area"1 (as in catalysis). This parameter is, however, inaccessible to direct measurement. Estimates from microscopy cannot identify all those regions which participate in reaction or ascertain the effective roughness factor of observed interfaces. Preferential dissolution of either reactant or product in a suitable solvent prior to area measurement may result in sintering [286]. The problems of identify-... 

Such an approach revealed objective limitations as it became evident that the equality in the capacitance values for different metals was only a first approximation. The case of Ga is representative. Ga is a liquid metal and the value of capacitance cannot depend on the exact determination of the surface area as for solid metals (i.e., the roughness factor is unambiguously =1). 

Such information can be obtained from cyclic voltammetric measme-ments. It is possible to determine the quantity of electricity involved in the adsorption of hydrogen, or for the electrooxidation of previously adsorbed CO, and then to estimate the real surface area and the roughness factor (y) of a R-C electrode. From the real surface area and the R loading, it is possible to estimate the specific surface area, S (in m g ), as follows ... 

The lack of knowledge of precise values of the roughness factor makes it difficult to compare data reported from different studies. This applies in particular to the double-layer capacity data, the values of surface concentration of the adsorbates, and the rates of electrochemical reactions. Therefore, the question of how to determine the real surface of the electrode is of cmcial importance. A survey of various methods for determining roughness was given by Trasatti and Petrii. For noble metal electrodes, the charges of hydrogen deposition and surface oxide formation can be utilized in real-surface determination." ... 

The electrode roughness factor can be determined by using the capacitance measurements and one of the models of the double layer. In the absence of specific adsorption of ions, the inner layer capacitance is independent of the electrolyte concentration, in contrast to the capacitance of the diffuse layer Q, which is concentration dependent. The real surface area can be obtained by measuring the total capacitance C and plotting C against Cj, calculated at pzc from the Gouy-Chapman theory for different electrolyte concentrations. Such plots, called Parsons-Zobel plots, were found to be linear at several charges of the mercury electrode. ... 

The Wheeler model thus provides an average pore radius, r and pore length, L, in terms of the experimentally determinable parameters v, and fj. The only adjustable parameter is the roughness factor, r. The usefulness of this model was demonstrated by Wheeler, who successfully predicted the reaction rates of several catalytic reactions of industrial importance. 

Because so many factors determine the response obtained for a chemical substance in a sample, it is usually not possible to derive directly the concentration from the measured response. The relationship between signal, or response and concentration has to be determined experimentally, a step which is called calibration. The complexity of the calibration depends upon the type of expected problems. These are roughly divided into three categories interferences, matrix effects or interactions and a combination of both, a so-called interacting interference. 

The results of studies of copper surfaces by low-temperature adsorption isotherms may be summarized as follows. True surface areas of metallic specimens as small as 10 sq. cm. can be derived with a precision of 6% from low-temperature adsorption isotherms using vacuum microbalance techniques. This method is of special value in determining the average thickness of corrosion films formed by the reaction of gases or liquids with solids. The effect of progressive oxidation of a rough polycrystalline metal surface is to decrease the surface area to a point where the roughness factor approaches unity. 

The observed roughness factors (ratio of true to geometric surface) of the surfaces employed in this study varied from 1.2 to 1.4 (Table IV). This checked with electron microscope pictures of alumina and silica replicas from electropolished single crystal copper surfaces. It is unlikely that the surface areas determined by the Brunauer-Emmett-Teller analysis are too high by 50% or even by 25%, because in several cases this would lead to a roughness factor of less than unity. 

Interfacial processes take place on the surface of solid (rock or soil), so the specific surface area (area per mass) is one of the most important parameters. The specific surface area depends on the particle size or the particle size distribution, and the roughness of the surface. These factors determine the external specific surface area. In addition, rocks and soils contain a network of pores with different sizes and shapes. Some of them are in a direct connection with the external surface (open pores). Therefore, depending on the relative sizes of the pores and the particles of the substance, the different substances of the surroundings can enter the pores. Two especially important types of pores are... 

Roughness factor is standard deviation of the fiim thickness. The doping level was determined by eiementai anaiysis. 

In turbulent flow, wall roughness increases the heat transfer coefficient h by a factor of 2 or more [Dipprey and Saber.sky (1963)]. The convection heat transfer coefficient for rough tubes can be calculated approximately from the Nusselt number relations such as Eq. 8-71 by using the friction factor determined from the Moody chart or the Colebrook equation. However, this approach is not very accurate since there is no further increase in h with/for /> 4/sn,ooih [Norris (1970)1 and correlations developed specifically for rough tubes should be used when more accuracy is desired. 

What would the heating curve of ethanol look like Make a rough sketch of ethanol s curve from 120°C to 90°C. Ethanol melts at 114°C and boils at 78°C. What factors determine the... 

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