CS259302B1 - A method for determining the content of peroxide and sodium hyperoxide in a system with sodium hydroxide and sodium carbonate - Google Patents

Abstract

Method enabling the determination of sodium oxide (below 0.3 wt.) in the melt system NaH-Na2O-NaOH-Na2CO3, used for steel descaling. The taken melt sample is oxidized with dried air (oxygen) to form the system Νβ2θ2 (NaO2>- -NaOH-Na2CO3· The method according to the invention enables the determination of oxidation conditions, qualitative differentiation and quantitative determination of the formed peroxides. The amount of formed peroxides is proportional to the concentration of the originally contained sodium oxide. The essence of the method lies in the fact that dried inert gas with a constant flow rate and a constant amount of oxygen is passed in a heated reaction vessel above the crucible with the sample and further through a flow-through oxygen sensor (for example, made of stable ZrO2*-), which registers the change in the oxygen concentration in the inert gas proportional to the concentration of the sample component capable of increasing the oxygen concentration in the inert gas.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method for determining the content of sodium peroxide and sodium hyperoxide in a sodium hydroxide and carbonate system, particularly useful for regulating the descaling bath regime.

In the metallurgical and mechanical engineering industry, a reduction melt system NaH-Na ₂ O-NaOH-Na ₂ CO ₃ is used for the removal of scale formed during the heat treatment of sheets, strips, wires and other products, especially of stainless steel. Effective components are sodium hydride and sodium oxide, the concentrations of which and the suitably selected relative ratio guarantee a sufficient descaling function of the bath and affect its thermal and chemical stability. During the process, the stability of the bath is occasionally impaired, metal dissolution is increased and the descaling ability of the melt is reduced.

The behavior is caused by an increase in the concentration of sodium oxide, which (below 2% by weight) could not be determined yet.

For the descaling system NaH-Na ₂ O-NaOH-Na ₂ CO ₃ , the most promising oxidation method appears, based on the oxidation of the system to form Na ₂ O ₂ (NaO 3) -NaOH-Na ₂ CO ₃ followed by determination of the peroxide formed. The uncontrolled degree of oxidation of sodium oxide is a significant source of errors.

The method according to the invention, applied to the apparatus (Fig. 1), removes these drawbacks by the fact that the dried inert gas with a constant flow and a constant amount of oxygen is fed into the heated reaction vessel 6 and introduced over the sample crucible 8. , proceeds through an opening in the ground-glass cap 2 o of a measuring flow sensor 11, e.g. ZrO ₂ (stab.) which registers a change in the oxygen concentration in the inert gas, proportional to the concentration of the component capable of increasing the oxygen tension in the inert gas.

The method makes it possible to determine the oxygen content corresponding to the initial sodium oxide content of the melt below 0.3% by weight, the concentration of which must be known to regulate the descaling melt mode. The chosen variant of indirect measurement of oxygen tension is based on the finding that said melt system disrupts practically all oxides and the ionic conductivity of the oxygen solid electrolyte is insufficient at the melt utilization temperatures of about 400 ° C. In addition, the experimental arrangement allows the melt behavior to be assessed over a wide temperature range. The method provides reproducible results repeatedly for individual measured samples of pure substances and combinations thereof. The areas below the imaginary line of the constant electromotive voltage of the inert gas for the same samples are proportional to the amount of oxygen excreted.

Fig. 1 shows a schematic diagram of the experimental arrangement of the apparatus.

The reference marks represent:

- cylinder with inert gas

- reducing valve ·

- flowmeter

4, 5 - drying columns

- reaction vessel

- sample oven

- crucible with sample

- opening in the ground-glass cap

- gas cleaning from moss. drift

- measuring flow sensor

- a constant temperature furnace

- washer

- hydraulic closure

He did

A Na ₂ O ₂ sample weighing 0.009 6 g was measured over a temperature range of 20 to 720 ° C.

Fig. 2 shows a graph of measured dependence. On the left side of the y-coordinate is the value of the electromotive voltage (E, in mV, on the right side the value of oxygen partial pressure (Pa), recalculated to the sensor temperature. sodium, part of the curve from 160 ° C to 400 ° C decomposition of sodium hyperoxide to form solid solutions of type ^N and ₂ ° 2 + x ^{and from 400} ° ^{c decomposition <Ju Na} 2 ° 2 *

Example 2

A sample of 0.184 2 g NaOH-Na ₂ O containing 0.007 4 g Na 2 O in a temperature range of 20 to 660 ° C was measured. NaOB pre-annealed to 500 ° C was used for sample preparation. Giant. 3 shows the measured dependence. At temperatures between 280 and 505 ° C, the prepared mixture is reacted with oxygen of an inert gas, the maximum E being about 390 ° C.

Example 3

A sample of oxidized NaOH-Na ₂ O weighing 0.148 4 g was measured with an initial content of 0.011 2 g Na ₂ O over a temperature range of 20 to 660 ° C. The sample was pre-oxidized with dry air at 400 ° C for 30 minutes after mixing the ingredients. Giant. 4 shows the measured dependence.

Sodium hyperoxide is formed in the mixture under these conditions, which decomposes in the temperature range of 70 to 240 ° C and decomposes sodium peroxide above 340 ° C.

Example 4

Samples of pure NaOH weighing 0.099 1 g and 0.1 g were measured. 0.157 5 g, calcined at 700 ° C and 70 ° C, respectively. 500 ° C for 45 minutes. Giant. No. 5 shows the obtained dependencies.

Sodium hydroxide annealed up to 500 ° C reacts with the oxygen of an inert gas in the regions of 270 to 550 ° C, while a higher temperature annealed sample produces a peroxide which decomposes in the heat range of 330 to 400 ° C.

The method of the invention can be used to determine the concentration of sodium oxide in an operating descaling bath, for pure substances and mixtures, to determine the temperature range at which oxygen is released.

Claims (1)

PftEASE OF THE INVENTION Method for determining the content of sodium peroxide and hyperoxide in a system with sodium hydroxide and carbonate, characterized in that the dried inert gas with constant flow and constant amount of oxygen is fed into a heated reaction vessel, introduced in it above the sample crucible, a cap into a measuring flow sensor which continuously registers changes in the oxygen concentration in the inert gas, proportional to the concentration of the sample component capable of increasing the oxygen tension in the inert gas under the given conditions.