**4. Required apparatus and materials**

In this paragraph we cite the main required apparatus and materials:

Simple vacuum post is presented in Fig.10.


Trap with liquid nitrogen (Fig.11) serves to catch aggressive substances vapors and it can be used as the sorption pump. In the second case it is recommended to use the zeolytes annealed at 300°C.

Sorption column serves to purificate the argon against the traces of oxigen and moisture. Sorbtion is performed by the activated copper deposited on silicagel at 170°C (Brauer, 1954).

<sup>1</sup> *Me<sup>n</sup>* , <sup>0</sup>

E1 = all. - Me1 ; E2 = Me2 - all. One compare E1 + E2 with E3 (E1 + E2 = E3) to verify the accuracy of the electromotive forces

Electric furnaces with precise control of temperature. To speed up the work it is

 Microfurnaces. Microfurnace presents a porcelain tube with an inner diameter of 65-70 mm and a length of 100-120 mm. This microfurnace can be easily made in the laboratory.

 Pyrex cells. In perspective, using the intermediate glass between Pyrex and quartz is possible for applying the electrochemical cells up to 1200-1300K. The coefficient of

Trap with liquid nitrogen (Fig.11) serves to catch aggressive substances vapors and it can be used as the sorption pump. In the second case it is recommended to use the zeolytes

Sorption column serves to purificate the argon against the traces of oxigen and moisture. Sorbtion is performed by the activated copper deposited on silicagel at 170°C (Brauer, 1954).

<sup>2</sup> *Me<sup>z</sup>* , <sup>0</sup>

2 *<sup>p</sup> Me*

M1 is more electronegative than Me2 in a series of electrode potentials.

0 <sup>1</sup> *Me<sup>m</sup>* , <sup>0</sup>

In this paragraph we cite the main required apparatus and materials:

Primary and secondary vacuum pumps or turbomolecular one.

Thermostat for cold ends of the thermocouples or Dewor bottle.

expansion of this type of glass must be as closer to the tungsten.

Tungsten wire 0.5 mm. Simple vacuum post is presented in Fig.10.


**4. Required apparatus and materials** 

Simple vacuum post is presented in Fig.10.

desirable to use several furnaces.

Digital millivoltmeter at high impedance.

Computer in case of automatic measurement system.

Hand or automatic commutation.

 Vacuum post with multiple outputs. Vacuum comb for making of alloys. Hard steel mold of the four sections.

Manuel or automatic press.

Laboratory transformers.

Gauge (Vacuummeter)

Vacuum baker.

Analytic balance.

Electrode leak detector

Portable gas torch.

annealed at 300°C.

 Pt/Pt–10% Rh thermocouples. Oxygen and propane cylinders.

of the chain.

Fig. 10. Simple vacuum post: 1- three-way valve (T=valve), 2- two way valve, 3- gauge, 4 cell sleeve 5- ampule sleeve, 6- to air, 7- to pump.

Vacuum comb permits to accelerate the preparation of alloys (Fig.12). The block-scheme of the EMF measuring is presented in the Fig.13. The configuration of the vacuum post and related details may be changed by the experimenter (Fig.10).

Fig. 11. Liquid-nitrogen trap.

Electrochemical Cells with the Liquid Electrolyte

influence on the potentiometric measurements:

4. Liquation (or phase separation) of liquid alloys.

5. Evaporation of element and the temperature of the experiment.

**5.1 Choice of different types of halides as the electrolyte** 

to the exchange reaction, it can be replaced by another.

electrodes and reference.

EMF of the cell.

two reference electrodes

thermodynamics of the Cu-Ni system.

in the Study of Semiconductor, Metallic and Oxide Systems 85

On the difficult path of the experimental study we overcame the various methodological problems that had significantly and successfully improved the method of the EMF. Let us consider these main methodological problems of the EMF method, having a significant

1. Exchange reaction between electrodes caused by a small difference of electrode

2. Spontaneous reactions due to a large chemical potential difference between measured

3. Presence of multiple oxidation states of ions involved in redox reaction generating the

It is possible to use different types of halides as the electrolyte: chlorides, bromides and iodides. All these salts are hygroscopic and their treatment by the corresponding hydrogen halide (HCl, HBr, HI) is necessary to avoid water marks. If one type of halide unsuitable due

For the study of the Ni-Cu (Geyderih et al. 1969), measurements of EMF were made from

(-) Ni(sol) KCI + LiCl + NiCl2 NixCu(1-x) (sol) (+)

(-) Cu(sol) KCl + LiCl + CuCl CuxNi(1-x) (sol) (+) In both cases there is a reduction of the second metal; the electrodes of pure metals are covered with crystals of the second metal. So, there are two oxidoreduction reactions:

NiCl2 + 2 Cu (from alloy) Ni + 2CuCl2

2 CuCl + Ni (from alloy) 2 Cu + NiCl2

The replacement of the chloride on iodide electrolyte permits to determine the

(1/nB) B (in AxB(1-x)) + (1/nA) An+ (1/nA) A + (1/nB)Bn+ (II)

potentials components of the alloy in the given electrolyte (Hladik, 1972).

**5. Methodological problems most frequently encountered in EMF method** 

Fig. 12. Vacuum comb for alloy preparation.

Fig. 13. Block-scheme of the measuring assembly: 1- cell, 2- stainless steel protector nozzle, 3- furnace, 4- ground, 5 – clamp of current leafs, 6-thermocouple, 7- thermostat for cold ends of the thermocouples, 8- hand or automatic commutation, 9- digital millivoltmeter at high impedance, 10- computer.

Fig. 13. Block-scheme of the measuring assembly: 1- cell, 2- stainless steel protector nozzle, 3- furnace, 4- ground, 5 – clamp of current leafs, 6-thermocouple, 7- thermostat for cold ends of the thermocouples, 8- hand or automatic commutation, 9- digital millivoltmeter at

Fig. 12. Vacuum comb for alloy preparation.

high impedance, 10- computer.
