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61.
Jeewoong Kim 《Cement and Concrete Research》2003,33(5):621-627
The ethylenediaminetetraacetic acid (EDTA) titration method limits the measurement of calcium concentration to 50 mg/l in water. However, various acids and salt solutions are used in the investigation of the durability of concrete, and the adaptability of the EDTA titration method to determine the calcium in these solutions must be investigated. Hence, the purpose of this study was to investigate the interfering effects of hydrochloric acid, sulfuric acid, sodium chloride and sodium sulfate on measuring the calcium in the aqueous leaching solutions using the EDTA titration method. The calcium standard solutions were prepared using CaCl2 with initial pH from −0.8 to 7 and calcium concentration up to 160 mg/l. Sulfuric acid and hydrochloric acid were used to prepare calcium solutions with lower pH. Salt solutions with 3% NaCl and 3% Na2SO4 were used to evaluate the interfering effects of salt elements such as sulfate and sodium on the EDTA titration. Results indicated that the EDTA titration method was reliable in measuring the calcium up to 160 mg/l, the maximum concentration investigated in this study, in hydrochloric acid with pH higher than zero and 3% sodium chloride solution. Sulfuric acid with pH higher than zero and 3% sodium sulfate solutions showed 3% to 4% less calcium in the solutions. Acid solutions with pH less than zero showed interference with calcium measurement. 相似文献
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In membrane filtration, solution environment factors such as pH and solvent density are important in controlling the filtration
rate and the rejection of the particles and/or the macromolecules. The filtration rate and the rejection in membrane filtration
have been investigated from physicochemical aspects. It was shown that the properties of the filter cake formed on the membrane
surface play a vital role in determining the filtration rate in mem-brane filtration. It was clearly demonstrated that such
filtration behaviors as the filtration rate and the rejection are highly dependent on the electrical nature of the particles
and/or the macromolecules. Furthermore, it was shown that the solvent density ρ has a large effect on the steady filtration
rate in upward ultrafiltration. 相似文献
65.
By means of contact angle measurements on dry layers of electrostatically neutral dextran with pure water (pH 6.1), water acidified with HCl (to pH 1.94) and water made alkaline with NaOH (to pH 12.8), it could be shown that there was essentially no change as a function of pH in the ratio of γ+/γ- of water as compared with the aqueous acid and alkaline solutions. (Here γ+ is the Lewis acid parameter of the polar surface tension component of water and γ- is its Lewis base parameter). In contrast, with contact angles measured with the same liquids on negatively charged clean glass, a significant decrease in contact angle was observed with water at pH 12.8, which was caused by the fact that at this alkaline pH an increase in surface hydrophilicity took place. This is because surfaces that have a given surface electrical potential at neutral pH generally acquire an even higher surface potential under more alkaline conditions which, concomitantly, also gives rise to an increase in surface hydrophilicity, and thus to lower contact angles with water. Finally, contact angles with acid water, pure water, and alkaline water, deposited on hydrophobic Parafilm surfaces, were exactly the same. 相似文献
66.
Equilibrium exchange isotherms were determined for the exchange of Cu2+ with NaZSM-5 at varying Cu(Ac)2 concentrations in solutions of constant volume and zeolite weight. At low Cu2+ levels the solid scavenged all the copper ions. When copper could be detected in the equilibrated solutions, overexchange was observed. The extent of overexchange was higher at pH 6 than at pH 4. These results were analyzed in relation to catalytic activity.On leave from the Central Institute for Chemistry, Hungarian Academy of Sciences, H1525 Budapest, Hungary. 相似文献
67.
《Journal of Process Control》2014,24(7):1023-1037
In this research the use of a feedback PID-like fuzzy controller scheme for pH control is presented to deal with instability problems near the equivalence point in neutralization processes. State space analysis of the titration curves and a fuzzy clustering algorithm based on calculating a measure of potential derived from the square distance of the pH data are complementary applied to define the membership structure and the fuzzy sets of the controller. To test the performance of the controller, both simulated and experimental runs were used. The fuzzy controller was tested for compensating step-change perturbations of propionic acidic flow rates, propionic acid concentration, and buffering conditions. Stationary cycling behavior has been observed for large loads of acidic flow rates. It was found that though the rejection time was strongly dependent on the mean residence time of the liquid solutions, the proposed controller keep the neutralization process operating close to the specified set point of pH = 7. 相似文献
68.
为了探究影响GH5家族β-甘露聚糖酶最适pH的各种因素,利用该酶的序列信息,构建了基于氨基酸组成的β-甘露聚糖酶理化性质与其最适pH的相关性模型。结果表明:该酶N端氨基酸序列是影响其最适pH的重要因素,在243个理化性质中有17个呈极显著相关,其中7个呈正相关。优化的转移能量参数相关性最高,为0.78:7个正相关的理化性质中,与螺旋相关的理化性质占3个。优化的转移能量参数和螺旋是影响pH稳定性的最重要的因素。所建立的模型为研究该酶酸碱适应性机理提供了一种简单有效的方法。 相似文献
69.
Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha–1 yr–1 or 0, 16.9, 33.8 g N emitter–1 yr–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha–1 yr–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg–1 and 78µg g–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha–1 yr–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth. 相似文献
70.