Method for Measuring the Amount of Salt Deposits on Metal Foil
Abstract Generated abstract
The paper describes a method for measuring very small, nonuniform salt deposits formed on metal foil during thermochemical determination of water hardness. Because deposits corresponding to low hardness levels are estimated to be only 0.01 to 1 micrometers thick, conventional thin-film thickness methods are considered impractical for automatic continuous instrumentation. The proposed device places the scaled foil in a short-circuited mercury turn coupled to excitation and measuring transformers, so that changes in total electrical resistance caused by the salt deposit change the induced current recorded by a galvanometer. Experimental results indicate a relationship between instrument readings and water hardness, supporting the technical feasibility of continuous hardness analysis over the range 0 to 50 microgram-equivalents per liter.
Full Text
METHOD FOR MEASURING THE AMOUNT OF SALT DEPOSITS ON METAL FOIL
I. G. Minaev, Yu. V. Trukhin
The total hardness of water by the thermochemical method is determined from the amount of salt deposit formed on the surface of a metal foil immersed in a vessel with the water being analyzed, by means of guide and current-carrying electrodes. The section of foil between the electrodes is heated by an electric current. Recording
Fig. 1. Diagram of a device for measuring the thickness of scale on the surface of foil
the amount of salt deposits on the foil at a water hardness of \(0 \div 50 \ \frac{\text{µg-equiv}}{\ell}\) proved to be a difficult task, since, according to a preliminary estimate, the thickness of the deposit under study is \(0.01 \div 1\ \mu\text{m}\). The small thickness of the deposit and the nonuniform coating of the foil surface with scale make it difficult to apply known methods [1] for measuring the thickness of thin films, since the creation of automatic instruments based on these methods requires complex apparatus. With the application of the proposed method, it becomes possible to implement technically the thermochemical method for continuous analysis of water hardness \(0 \div 50 \ \frac{\text{µg-equiv}}{\ell}\).
Figure 1 shows a diagram of the measuring device, explaining the essence of the method.
Foil 3 with scale is inserted into the transverse slit of the short-circuited mercury turn 2, which serves as the common winding of the excitation transformer 4 and the measuring current transformer 1. As a result of electromagnetic interaction between the windings of the excitation transformer, a current \(I_1\) is induced in the turn, equal to
\[ I_1 = k_1 \frac{V}{R}, \tag{1} \]
where \(V\) is the transformer supply voltage;
\(k_1\) is the transformation coefficient;
\(R\) is the total resistance of the turn, equal to the sum of the resistances of the mercury, the foil, and the salt deposits.
Fig. 2. Dependence of the instrument reading on water hardness
It follows from equation (1) that the magnitude of the current \(I_1\) is inversely proportional to the resistance \(R\), which varies depending on the amount of salt deposit on the foil, which, in turn, is a function of the hardness of the water.
The magnitude of the current induced in the turn is recorded by galvanometer 5, connected into the circuit of the secondary winding of the measuring current transformer, for which the turn is the primary winding. The experimental results are shown in Fig. 2.
REFERENCES
- L. S. Palatnik, R. I. Zaichik et al. Methods for measuring the thickness of thin films. Zavod. labor. M., “Metallurgiya,” No. 2, pp. 180–190; No. 3, pp. 288–297, 1968.