Effects of Magnetic Field, Temperature and Impurity on Crystal Growth of Calcite
Date Issued
2009
Date
2009
Author(s)
Liu, Chong-Cheng
Abstract
The buildup of scale deposit inside cooling water pipes and boiler walls is a common and costly problem for many industrial processes. The scale deposit leads to a reduction in heat transfer efficiency and to a partial or complete blockage of water flow. Due to the variation in pH and temperature, the scale is formed, which composes of calcium carbonate in the majority. Calcite is one of the polymorphs of calcium carbonate and the most common form of scales. The scale formation usually occurs in the equipments operated at higher temperature, such as heat exchanger and boiler. Since calcium carbonate becomes less soluble with increasing temperature, the hot water turns into supersaturated conditions with regard to CaCO3, which deposits on the hot surfaces. There are several scale prevention methods, among which the magnetic treatment is the most controversial one. However, the magnetic treatment device has been available in the market for about 80 years. Moreover, the process water contains various kinds of impurity ions, which would accelerate or inhibit the growth of calcite crystals. In this research, a constant – composition method was adopted to measure the calcite growth rate in a stirred crystallizer. The principal subject of this research is to investigate the effects of magnetic field, temperature and impurity on the calcite growth.n the series of calcite growth experiments at 25°C, the calcite growth rate increased with increasing supersaturation and pH value without magnetic treatment. In the absence of magnetic field, the enhancement of calcite growth rate was about 10 % when the concentration of strontium ion was varied by a factor of 2, i.e., from 0.5 to 1.0 ppm or from 1.0 to 2.0 ppm. On the other hand, the reducing percentage of growth rate was about 22 % when the concentration of iron(II) ion was altered by a factor of 2. As to the temperature effect, the calcite growth rate decreased with an increase in temperature, from 25 to 40°C. When the supersaturated solution at 35°C contained various concentrations of strontium or iron(II) ion, we found that an increase in Sr2+ concentration was accompanied by an increase in calcite growth rate. However, the effects of Fe2+ concentration on the calcite growth rate were opposite to that of Sr2+.n the presence of magnetic field, the calcite growth rate was also influenced by the solution variables, including supersaturation, pH value and temperature. Although the growth rate was suppressed completely in the presence of magnetic field for the supersaturation from 0.8 to 1.2, the pH value from 8.5 to 9.5, and the temperature from 25 to 40°C, the time needed to suppress the growth rate completely is shorter under high temperature, low pH and supersaturation.hen the supersaturated solution containing a small quantity of strontium or iron(II) ion at 25°C was magnetized by the Descal-A-Matic DC-1 for 20 hours, the calcite growth rate would not be suppressed completely. The growth rate increased with increasing Sr2+ concentration, from 0.5 to 2.0 ppm. On the other hand, the growth rate decreased with increasing Fe2+ concentration.he experiment was further conducted to investigate the interaction of magnetic field, temperature and impurity on the growth of calcite crystal. The supersaturated solution containing impurity was magnetized for 20 hours at 35°C before growth experiment. Under these circumstances, the growth rate of calcite would not be suppressed completely either. When the concentration of Sr2+ increased from 0.5 to 2.0 ppm, the growth rate also increased. Furthermore, the trend of Fe2+ concentration on growth rate was opposite. As to the temperature effect, the higher temperature led to a reduction in the calcite growth rate, when magnetic field and impurities were present.
Subjects
Crystal growth
Calcite
Magnetic field effect
Temperature effect
Impurity effect
Strontium ion
Iron(II) ion
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-R96524010-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):e62efb9df8b2db8fc30f5d5dff31dc13