An indirect method to determine the oxygen dissolved in AIN is devised for AIN(Y203) ceramics and then related to thermal conductivity. Dissolved oxygen is determined by first constructing the AIN-rich corner of the AIN-Y203-AIz03 phase diagram (isothermal section). This is achieved by (1) measuring the total oxygen content and subtracting from it the oxygen in the Y2O3, resulting in a virtual alumina content; (2) placing the sample composition on the diagram; (3) determining the phases present by XRD for each sample; and (4) drawing phase boundaries which best agree with the phases present. The intersection of these tie lines through the sample location with the AIN-A1203 axis then gives the particular AlzOj oxygen content dissolved in the AIN lattice. For the system A1N-YZO3-AI2O3, it is shown that it is indeed this fraction of the total oxygen content that has a decisive limiting influence on thermal conductivity of dense, polyphase AIN ceramics. [
The effects of concentration and temperature on the breakthrough volumes (Vb) of 23 volatile organic compounds on Carbotrap B have been determined using the frontal chromatography method. From the measured Vb, original isotherms have been produced and adsorption parameters based on the Langmuir, Freundlich, and Dubinin-Polyani adsorption models have been calculated. The calculated adsorption parameters describe the behavior of these VOC on Carbotrap B under the experimental conditions and are useful data for VOC sampling applications including adsorption modeling of pumped and diffusive sampling. Each of the adsorption models give similar results and are in good agreement with the experimental data in the ppmv concentration range. It will be shown that contrary to previous assumptions the Langmuir adsorption parameters obtained at ppmv concentrations cannot be used to predict Vb at ppbv concentrations and the calculated parameter mmax does not represent the maximum adsorbent capacity. The Freundlich and Dubinin-Polyani models are shown to be more successful in describing the adsorption behavior of the VOC at ppbv levels where Vb is independent of concentration. The isosteric heats of adsorption (-delta Hst) for some of the compounds have been determined using the Van't Hoff equation which can be used to predict the effect of temperature on Vb.
Since not all water supplies respond to a standard iron removal process, it is often necessary to carry out pilot testing in order to determine a method that is effective, as well as economical.
The authors prepared an initial report covering their work for the 90th Annual Conference (see JOURNAL, Oct. 1970). Since then, they have had the opportunity to scrutinize the use of such treatment in several communities and have arrived at several additional conclusions.Since the first presentation of the paper, "Preventing Iron Deposition with Sodium Silicate," 1 work has con tinued on the use of silicates, and some thirteen Ontario communities now add silicate to their water supply for iron control on a regular basis, with six more municipalities about to follow suit. Observations on such usage date back over 2 yr. Further investigations into the nature of the pertinent water chemistry involved have also been possible, with some ob servations being made regarding man ganese sequestering and some initial tests directed toward removal of silicastabilized iron after complex forma tion.The initial policy adopted by the commission has been generally to limit recommendation of silicate addi tion to water supplies containing up to 1.3 mg/liter of iron. Although practical limitations on the amount of iron that can be handled by the sili cate procedure have yet to be en countered, such solubilization of sig nificant quantities of ferric ion in pot able water essentially represented a new phenomenon in water technology. The process, though viewed favorably, has been approached cautiously in or der to determine possible disadvan tages of the technique prior to any much broader application. The max imum silicate addition being used mu nicipally at present is 6.2 mg/liter SiO,, Two years of experience in the town of Markham have yielded very favorable results.The possibility that domestic hot-water tanks might still tend to accumulate iron by ther mal breakup of the silicate complex has not been indicated at Markham. Iron problems with hot-water tanks dropped abruptly from about three calls a day prior to the start of silicate addition and have continued to de crease to the present low of about one every six months. Even a year after commencement of the silica feed, im provements in the water quality in outlying areas of the distribution sys tem continued to be noticed as rem nant iron-staining properties dimin ished further.The latter observation seemed to be the result of a general slow clean ing of the distribution mains of iron deposits. A recent break in the town's main was serviced to find that even an old pipeline known to have been badly tuberculated had cleared up to become almost indistinguishable from quite recently replaced valve fit tings on the same line. A thin trans lucent coating was reported to be coat ing metal surfaces, suggesting that significant corrosion protection was also taking place.Briefly, the original paper described how the addition of a small amount of N sodium silicate to a water supply at the point of chlorination (that is, iron oxidation) would fully stabilize the water's iron content. Iron thus stabil ized avoids iron deposition in water distribution mains as well as the gen eral nuisanc...
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