RU2250245C2 - Heat-accumulating composition based on octohydrate of barium hydroxide and used to fill copper capsules - Google Patents

Abstract

FIELD: heat-accumulating compositions.

SUBSTANCE: the invention is dealt with substances used for a heat transportation at the expense of a change of a phase state of heat-accumulating composition in the devices receiving the heat at its irregular delivery or consumption, in particular, in the system of a pre-starting preparation of transportation means and their power installations. The heat-accumulating composition contains (in mass %): 99 - 99.5 of octohydrate of barium hydroxide, 0.5-1.0 of sodium sulfite. Use of the composition decreases action of corrosion and considerably improves operational characteristics of the heat accumulator.

EFFECT: the invention ensures reduction of action of corrosion and considerable improvement of operational characteristics of the heat accumulator.

1 cl, 1 ex, 1 tbl

Description

The invention relates to substances for heat transfer due to a change in the phase state and can be used in devices that consume heat when it is unevenly received or consumed, in particular in the pre-start preparation system for vehicles and power plants.

Known heat accumulator containing heat-accumulating metal capsules that are filled with barium hydroxide octahydrate, which changes its state of aggregation at a melting point of 78 ° C in the range of operating temperatures of the heat accumulator (see RF Patent No. 2052734, class F 24 H 7/00 // Bull Inventory No. 2, 01/20/1996).

The disadvantages of barium hydroxide octahydrate when used as a heat storage composition in the known heat accumulator are increased corrosion activity in relation to the metal walls of the capsule, which significantly reduces the service life and reliability of the product, as well as the increased toxicity of dissolved barium compounds, which is manifested during depressurization of metal capsules as a result corrosion, which negatively affects the environment and the health of staff.

It is also known that dilution of barium hydroxide octahydrate with potassium nitrates (the stoichiometric mixture contains 61% octahydrate) slightly reduces corrosion (see Reznitsky LA Thermal batteries. M., 1996, 93 S.). However, at the same time, the total heat of fusion of the solution also decreases significantly (by about 33.5%), which makes it economically disadvantageous to use these mixtures as a heat storage composition.

The closest to the proposed composition in terms of technical nature and the achieved result is barium hydroxide octahydrate, which is used to fill copper sealed plates of a car’s heat accumulator (see. Heat accumulator. Tolyatti: VAZ. Scientific and Technical Center. Express information No. 4, 02.23.1993).

Copper has better thermal conductivity than steel and is more resistant to corrosion. However, the use of copper for the manufacture of heat storage capsules does not completely eliminate corrosion in the environment of barium hydroxide octahydrate and saves the risk of capsule depressurization during operation of the heat accumulator.

The aim of the invention is to reduce the corrosion activity of a heat storage device based on barium hydroxide octahydrate with respect to the copper walls of the heat accumulator.

This goal is achieved due to the fact that the heat storage composition based on barium hydroxide octahydrate, which fills the copper capsules of the heat accumulator, additionally contains sodium sulfite in the following ratio of ingredients, wt.%:

Barium Hydroxide Octahydrate 99.0-99.5

Sodium sulfite 0.5-1.0

When solving this problem, a result is created, which consists in the fact that the proposed heat storage composition (TAS) for filling copper capsules contains sodium sulfite, which acts as a corrosion inhibitor.

Corrosion of copper as an electropositive metal in alkaline solutions proceeds in accordance with the reactions (see Tomashov ND, Chernov GP. Theory of corrosion and corrosion-resistant structural alloys. M. - L .: Chemistry, 1993, 329 p.) :

with further oxidation

or directly

The resulting copper compounds can dissolve in hot alkali to form cuprates:

Copper corrodes in an alkaline medium according to the scheme with oxygen depolarization:

moreover, the molecular oxygen of air dissolved in the heat storage composition is the depolarizer.

The total corrosion electrochemical process can be described in the form of the following coupled reactions:

(анодный процесс)

(anode process)

(катодный процесс)

(cathodic process)

The speed of the cathodic process in a sealed enclosed space of the capsule is low due to the low concentration of oxygen in the solution (~ 10 ^-4 mol / l) and the absence of its entry from the air. This limits the rate of corrosion as a conjugate reaction.

A corrosion process of this kind almost completely stops when 0.5-1.0 wt.% Sodium sulfite is added to the TAC, binding molecularly dissolved oxygen:

It should be borne in mind that copper must have a high degree of purity, and also you cannot use other metals when welding and gluing capsule seams with TAC. Otherwise, due to the formation of local galvanic cells of the “Cu - metal” type, copper corrosion can sharply increase with all the negative consequences, including the evolution of hydrogen.

Example. Copper cylindrical capsules with a length of 130 mm, an inner diameter of 14 mm and a wall thickness of 1.0 mm are filled with liquid barium hydroxide octahydrate (Ba (OH) ₂ · 8H ₂ O) with the required amount of anticorrosive additive of sodium sulfite (Na ₂ SO ₃ ). Then the ends of the capsules are flattened and brewed. The resulting capsules in an amount of 10 pieces for each composition are subjected to prolonged thermal cycling in a special installation that provides heating of samples to 130 ± 5 ° C and cooling to minus 10 ± 5 ° C according to a given program. Melting point Ba (OH) ₂ · 8H ₂ O , T _PL = 78 ° C. After 500 cycles, the contents of every 10 capsules are mixed and subjected to analysis of the copper content in the heat storage composition (TAS) by the photometric method. In addition, at the installation for low-temperature differential thermal analysis (DTA), the heat of fusion of the studied TACs is determined before and after thermal cycling in the mode of linear temperature increase at a rate of 0.5 ° C / min. In this case, fixed amounts of a TAC sample and a standard substance of comparison with known thermal properties are used. The heat of fusion is determined by the formula

where Δ H ₁ and W ₁ is the heat of fusion and the mass of the investigated TAS;

Δ H ₂ and W ₂ is the heat of fusion and the mass of the standard reference substance (stearic acid Δ H _pl = 199.3 J / g, T _pl = 71.5 ° C);

Q ₁ and Q ₂ are the areas limited by thermograms (temperature change over time) of the studied TAS and stearic acid, respectively.

The composition and properties of the proposed and known technical solutions are presented in the table “Comparative data of the experimental verification of the known and proposed TAS”.

Table Comparative data of experimental verification of the known and proposed TAS Heat storage composition The content of components, wt.% Heat of fusion, J / g The mass of copper in TAS, g Ba (OH) ₂ · 8H ₂ O Na ₂ SO ₃ Before thermal cycling After thermal cycling Proposed 99.5 0.5 296.3 275.3 - 99 1,0 293.6 273.2 - Beyond 99.8 0.2 297.8 276.0 traces 98.5 1.5 288.7 267.1 - Famous 100.0 - 299.2 278.6 3.0310 ^-3

As can be seen from the data in the table, the known heat storage composition contains, after thermal cycling, 3.03 · 10 ^-3 g of copper and, therefore, causes corrosion of the copper walls of the capsule. The addition of 0.5-1.0 wt.% Sodium sulfite to barium hydroxide octahydrate provides an almost complete cessation of corrosion of copper walls with a very slight decrease in heat of fusion (not more than 2.0%) with respect to the known TAC - Ba (OH) ₂ · 8H ₂ O. A decrease in the content of Na ₂ SO ₃ in the TAC is less than 0.5 wt.%, For example, to 0.2 wt.% Is impractical, since it causes corrosion of the capsule walls and the results of the TAC analysis after thermal cycling record the presence of traces of dissolved copper . The increase in the content of Na ₂ SO ₃ in the TAS over 1.0 wt.%, For example up to 1.5 wt.%, Is also impractical, since it leads to a more significant decrease in the heat of fusion of the TAS (more than 4.0%) after thermal cycling.

The use of the proposed heat storage composition based on barium hydroxide octahydrate with the addition of 0.5-1.0 wt.% Sodium sulfite to fill copper capsules of heat accumulators can reduce the corrosion activity of TAC and significantly improve the operational characteristics of the heat accumulator, including the uptime of the product and reduction of toxic TAS emissions from capsule depressurization due to corrosion.

Claims (1)

Heat storage composition for filling copper capsules based on barium hydroxide octahydrate, characterized in that it contains sodium sulfite in the following ratio of ingredients, wt.%: Barium Hydroxide Octahydrate 99-99.5 Sodium sulfite 0.5-1.0