Density measurement procedure

The testing procedure is based on the combined use of the density measurement along the whole length of the fuel element and computerized tomography. This procedure enables to obtain thorough information on distribution of the fuel material in the fuel element... 

Stmcture is usually measured by a void volume test such as the absorption of dibutyl phthalate (DBPA) (15), or by bulk density measurements of the carbon black under compression. In order to eliminate the effects of pelletizing conditions the DBPA test has been modified to use a sample that has been precompressed at a pressure of 165 MPa (24,000 psi) and then broken up four successive times (24M4) (16). This procedure causes some aggregate breakdown and is claimed to more closely approximate the actual breakdown that occurs duting mbber mixing. 

The sohd line in Figure 3 represents the potential vs the measured (or the appHed) current density. Measured or appHed current is the current actually measured in an external circuit ie, the amount of external current that must be appHed to the electrode in order to move the potential to each desired point. The corrosion potential and corrosion current density can also be deterrnined from the potential vs measured current behavior, which is referred to as polarization curve rather than an Evans diagram, by extrapolation of either or both the anodic or cathodic portion of the curve. This latter procedure does not require specific knowledge of the equiHbrium potentials, exchange current densities, and Tafel slope values of the specific reactions involved. Thus Evans diagrams, constmcted from information contained in the Hterature, and polarization curves, generated by experimentation, can be used to predict and analyze uniform and other forms of corrosion. Further treatment of these subjects can be found elsewhere (1—3,6,18). 

The vane anemometer is not seriously affected by small deviations in alignment in the main flow direction. However, care is necessary since over 20° misalignment causes significant errors. With regard to providing a correction for fluid density, slightly different opinions exist. T35 Based on measurements, it is recommended- that the following density correction procedure be applied ... 

Rossiter (1986) demonstrated the procedure for the production process of crystalline common salt from brine. It was found that the optimal median size is determined by the entrainment limit in the crystallizer. The crystallizer had to be operated at maximum allowable temperature and the slurry density measured for quality constraints. It was also suggested that cost discontinuities should be imposed based on temperatures of the available heat sources, possible materials of construction and other intrinsic properties of the system. 

The discussion in this section will focus on true, bulk, and tap densities. The procedure and instrumentation used for each type of density measurement will be outlined, and pharmaceutical applications involving density will be presented. 

Tap density (ptap) is an extension of bulk density measurements, and the procedure used to measure the tap density again varies from lab to lab and can affect the final results. To measure tap density, a graduated cylinder is filled with powder and the weight and volume are recorded. The difference observed between procedures is the number of taps used for the measurement. In some cases, a particular number of taps is used, such as 200 [65], 500 [66], or even 1000 taps [67]. Other procedures involve tapping the cylinder for a number of times, recording the volume, and repeating the procedure until the volume remains constant [68]. This method ensures more consistent results. 

X)Moisture in Wet LA by Density Measure ments. For rapid estimation of moisture in Nutsch blends of LA going into a drum, the following procedure was used at the Kankakee OW... 

Weighed amounts of PVC and metallic powders were mixed thoroughly for one-half hour in a rotary blender at room temperature. The mixture was compacted in a cavity mold for 10 minutes at 120°-130°C under a pressure of 10,000 psig. The mold was then allowed to cool under pressure to room temperature, and the cylindrical compact was removed. The dimensions are length 3.5 cm diameter 2 cm. Density measurements indicated that this procedure provided samples of porosity <1.5%. 

The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymerization or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of y-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the continuous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6, 7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other references by Russian authors(8,9) are known citing kinetic measurements by the density method but their procedures do not fulfill the above stated requirements. 

The method of carrying out kinetic runs depends upon the rate of nitration and the temperature. For relatively slow reactions at or near room temperature, the easiest procedure is to carry out the reaction in a volumetric flask to which are added a weighed amount of substrate (—40 mg), sulfuric acid of known composition nearly to the mark, and, finally, a measured excess (—0.5 g) of —70% nitric acid. Urea (one-tenth of the molar concentration of nitric acid) must also be added to prevent nitrosa-tion. The flask is then placed in a thermostatted bath and, at appropriate intervals, portions are removed, quenched, and the optical density measured. For kinetic runs above 50°C the procedure differs only in that aliquots are sealed in Pyrex tubes before thermostatting. 

Density. An apparatus and procedure similar to that described elsewhere (I) was used for the density measurements. A borosilicate glass... 

U-tube, 4 mm. i.d. and 10 cm. long, was used for the density measurement. The volume of the U-tube was determined as a function of the distance from a reference mark at the bottom of the tube. Calibrations were made at room temperature, initially with water and carbon tetrachloride, and again at cryogenic temperatures with liquid oxygen. A measured amount of liquid ozone was transferred to the U-tube, and the procedure was repeated with enough liquid fluorine to result in a solution of the desired concentration. 

Most surface area determinations are based on measurements of the low temperature adsorption of nitrogen or krypton on the solid and use of the BET theory. This procedure may not give reliable results because the products are chilled well below reaction temperature, possibly resulting in the sealing of internal pores. Volumes of gases adsorbed are sometimes small, as observed for dehydrated alums [37] and decomposed ammonium perchlorate [48], where the areas are consistent with product crystallites of linear dimensions between 1 and 3 pm. The results indicate, however, that little, if any, zeolitic material is formed [36]. The surface area of a solid may also be estimated from electron micrographs. Density measurements may be used to complement area measurements. 

It was possible to obtain better resolution for these compounds because there are three independent experimental methods for estimating the electron affinities that could be iterated to consistency. These were the ECD measurements, half-wave reduction potential measurements, and electronegativity values. In addition, these electron affinities had been calculated with the MINDO/3 procedure. We also calculated the values using the CURES-EC procedure and obtained estimates of the charge densities. These procedures were extended to a larger set of 80 compounds, some without gas phase Ea that will be discussed in Chapter 10. 

New density and total pressure measurements of selenium vapour are presented. A previous investigation by the same author, [67RAU], is re-evaluated and combined with the new data in an evaluation of the thermodynamic properties of the molecules Se2(g)-Seg(g). The enthalpies of formation and entropies were varied in a procedure to obtain a good fit to the observed densities. The procedure contains many parameters that can be varied and different sets may fit the experimental data almost equally well. The thermodynamic properties derived for the species Se2(g)-Seg(g) are too dependent on the choices made by the author in order to be considered by the review. However, the new measurements of the total vapour pressure in the temperature range 1073 to 1373 K were evaluated by the review for the thermodynamic properties of Sc2(g) using the third law and mole fractions of Se2(g) estimated from the selected selenium data. The enthalpy of formation derived was Af//°(Se2, g, 298.15 K) = (138.9 1.9) kJmoP. ... 

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