RU2303204C2 - Exothermal composition for fuel element - Google Patents

Abstract

FIELD: chemical heat sources.

SUBSTANCE: exothermal composition comprises ferrum, initiator of oxidation reaction, moisture collecting sorbent, potassium chloride, and water. The oxidation reaction initiator is made of activated carbon the specific surface and specific volume of microscopic pores of which is equal to 500-700 m²/g and 0.15-0.25 cm³/g, respectively. The moisture-collecting sorbent is made of activated carbon the specific surface and specific volume of micro-pores of which is 1400-1600 m²/g and 0.7-1.0 cm³/g.

EFFECT: enhanced stability of composition.

1 dwg

Description

The invention relates to the field of chemical heat sources operating on the basis of the use of thermal effects of chemical reactions, in particular to the field of autonomous heat sources (AIT), capable of providing rapid local heating to a given temperature and maintaining it for a required period of time.

Environmentally friendly and fireproof AIT have already found application in various fields: temperature stabilization of electronic devices; curing of sealants and other materials (when the use of heaters of other types is excluded); assistance in natural disasters and catastrophes; in medicine; when working in the cold (lumberjacks, aircraft, oilmen, military personnel); drying clothes and shoes in the field, heating food and much more.

For these purposes, compositions are used whose heat release is based on the exothermic oxidation of powdered iron by atmospheric oxygen. Such a process takes place in the presence of an electrolyte, which destroys the oxide film formed on the surface of iron. Before oxygen is opened, the aqueous electrolyte solution is in the water-retaining sorbent and the initiator of the reaction. The initiator of the oxidation process, as a rule, is activated carbon, the process of desorption of the electrolyte from which occurs already at the initial stage of heat release.

The known composition of the exothermic composition of a heating pad for the body [US No. 5046479, 1991], including iron powder 55-65 wt.%, Activated carbon 3.5-4.5%, water-retaining sorbent 9-11%, sodium chloride 4.5-6 % and water 18-22% (electrolyte). The heater works stably in the temperature range 38-41 ° C for 20-24 hours. The disadvantages of this composition include the fact that satisfactory temperature-time indicators are achieved due to the design features of a medical heating pad. The use of this composition in a widely used fuel element [US No. 4516564, 1985], consisting of an airtight film with holes in it and a shutter that closes and opens these holes, leads to significant overheating at the initial stage of the iron oxidation reaction and, as a result, to stop reactions due to the intense release of sorbed moisture that floods the surface of the composition.

The known composition of the charge for the fuel element [Ru No. 2179005, 2002.02.10], in which activated carbon, as the initiator of the oxidation process, is replaced by silica gel with a limited pore volume of 0.75-1.15 cm ³ / g, which makes it possible to choose the conditions for stable operation of the fuel element at the initial stage of the oxidation of iron.

The main disadvantage of this composition is the instability of heat generation, expressed in the reduction of a given operating temperature.

This is due to the fact that, in the absence of activated carbon, the electrochemical component of the reaction, which, in turn, is due to the difference in electric potentials between iron and carbon, is excluded from the oxidation of iron, which provides heat.

The technical task is to find an exothermic composition for a fuel element that provides fast heating to operating temperature, stable and continuous heat release in the temperature range 40-60 ° C. Since for a given composition of the exothermic composition, the working temperature directly depends on the area of the holes of the aforementioned airtight film, the technical problem reduces to the requirement of maintaining the working temperature at a constant level in a certain period of time.

The closest effect and composition to be achieved is the exothermic thermal compress composition described in US patent No. 5233981, 1993, A61F 7/00 (prototype), including iron powder 40-75 wt.%, The initiator of the oxidation reaction (activated carbon) 1- 10%, water-retaining sorbent 1-40%, sodium chloride 1-10% and water 1-40%. Compress steadily works in the temperature ranges 38-44 ° С. Time to reach operating temperature is more than 30 minutes.

The disadvantage of the composition is that the effect of stability of heat dissipation is achieved due to the structural restriction of oxygen access, which in turn does not allow to reach operating temperatures above 50 ° C.

The temperature characteristics of the composition of the prototype wt.%: Iron powder - 60, activated carbon - 7, water-retaining sorbent (perlite sand) - 15, sodium chloride - 3, water - 15 - shows that when removing restrictions on the access of oxygen, the main disadvantage of the composition of the prototype is a significant overheating in the initial stage of the oxidation reaction and a short duration of stable operation (see drawing, curve "prototype").

The claimed invention is aimed at finding an exothermic composition for a fuel element that provides quick, up to 20 minutes, output at the operating temperature and stable long-term operation in the range of operating temperatures of 40-60 ° C. Stability is understood as the absence of an overheating phenomenon at the initial stage of the iron oxidation process and the constancy of the working temperature for a certain time.

The technical result is achieved by the fact that an exothermic composition for a fuel element is proposed, including iron powder, an oxidation reaction initiator, a water-retaining sorbent, sodium chloride and water, characterized in that activated carbon with a specific surface area of 500-700 m ² / is used as an initiator of the oxidation reaction g and a specific micropore volume of 0.15-0.25 cm ³ / g, and activated carbon with a specific surface area of 1400-1600 m ² / g and a specific micropore volume of 0.70-1.00 cm ³ / g is used as a water-retaining sorbent when following proportions of their components, wt.%:

iron powder 50-65; activated carbon with specific surface of 500-700 m ² / g and specific micropore volume 0.15-0.25 cm ³ / g 5-15; activated carbon with specific surface of 1400-1600 m ² / g and specific micropore volume 0.70-1.00 cm ³ / g 10-30; sodium chloride 0.2-1.5; water 10-25.

The content of the main reagent, iron powder, in the mixture is due to the fact that when the amount is less than 50%, the heat-generating ability is significantly reduced and it is not possible to achieve stable operating temperatures above 40 ° C, and when the amount is more than 65%, heat dissipation is observed due to a deficiency of the remaining components of the claimed exothermic composition.

Characteristics of activated carbons are selected on the basis of a study of the reaction of oxygen oxidation of air with iron-containing mixtures, which include active carbons of various grades [Drobot NF, Gavrichev KS, Noskova OA et al. Physical Chemistry, 2002, v. 76, No. 1, pp. 94-97]. It was found that the heating rate and the amount of heat generated, i.e. the duration of heat release is determined by the specific surface area of the coals, the volume of their micropores, the ratio of the dynamics of sorption and desorption of water by coals.

So, activated carbons with a specific surface <700 m ² / g, micropore volume ≤0.25 cm ³ / g, sorbing> 25% of water and easily giving it away (water desorption at 50 ° С> 35%), provide the maximum heating rate .

Active carbons with a specific surface> 1400 m ² / g, micropore volume> 0.7 cm ³ / g, sorbing> 80% of water and holding it firmly (water desorption at 50 ° C <5%), provide the maximum amount of heat generated or duration of heat release.

The lower limits of the content of activated carbons in the composition are due to the fact that with a relative amount of activated carbon with a micropore volume of 0.15-0.25 cm ³ / g less than 5 wt.%, A quick exit to operating temperatures above 50 ° C is not provided (the trend is given in Example 2), and with a relative amount of activated carbon with a micropore volume of 0.70-1.00 cm ³ / g less than 10 wt.%, The duration of heat generation is insignificant (the trend is shown in Example 1).

An exothermic composition for a fuel element is prepared as follows: a mixed composition of iron powder and two types of activated carbons is impregnated in an inert medium with an aqueous solution of sodium chloride at t = 20-25 ° C, then the mixture is placed in an airtight film of the fuel element.

The proposed exothermic composition works as follows: when air oxygen is opened, iron powder is oxidized with heat. At the same time, an intensive process of desorption of an aqueous solution of sodium chloride from coal, which serves as the initiator of the reaction, begins, as a result of which the iron surface is cleaned of the formed oxide film, which ensures its further oxidation. As the temperature rises, the process of slow desorption of the electrolyte from coal begins, which performs the function of a water-retaining sorbent.

The temperature of the mixture quickly enough, in 5-20 minutes, reaches the required value of 40-60 ° C, after which there is a uniform process of heat release.

The achievement of the technical result is illustrated in the drawing "Temperature-time characteristic of an exothermic composition for a fuel element".

The following are examples of compositions of the proposed exothermic composition for a fuel element

Example 1. Composition, wt.%:

iron powder 60; activated carbon with specific surface of 500-700 m ² / g and specific micropore volume 0.15-0.25 cm ³ / g fifteen; activated carbon with specific surface of 1400-1600 m ² / g and specific micropore volume 0.70-1.00 cm ³ / g 10; sodium chloride 1.0; water fourteen.

The temperature characteristic is shown in the drawing of curve 1.

The time to reach the operating temperature is 5 minutes, the duration of stable operation is 150 minutes.

Example 2. Composition, wt.%:

iron powder fifty; activated carbon with specific surface of 500-700 m ² / g and specific micropore volume 0.15-0.25 cm ³ / g 5; activated carbon with specific surface of 1400-1600 m ² / g and specific micropore volume 0.70-1.00 cm ³ / g thirty; sodium chloride 1.5; water 13.5.

The temperature characteristic is shown in the drawing of curve 2.

The time to reach the operating temperature is 20 minutes, the duration of stable operation is up to 400 minutes.

Example 3 (the best option to achieve a technical result).

Composition, wt.%:

iron powder 60; activated carbon with specific surface of 500-700 m ² / g and specific micropore volume 0.15-0.25 cm ³ / g 7; activated carbon with specific surface of 1400-1600 m ² / g and specific micropore volume 0.70-1.00 cm ³ / g fifteen; sodium chloride 1,2; water 16.8.

The temperature characteristic is shown in the drawing of curve 3.

The time to reach the operating temperature is 10 minutes, the duration of stable operation is 720 minutes.

The proposed exothermic composition provides a quick, up to 20 minutes, output at operating temperature, stable and long-term operation of the fuel element in the temperature range 40-60 ° C.

Claims (1)

An exothermic composition for a fuel element, comprising iron powder, an oxidation reaction initiator, a water-retaining sorbent, sodium chloride and water, characterized in that activated carbon with a specific surface area of 500-700 m ² / g and a specific micropore volume of 0 is used as an initiator of the oxidation reaction 15-0.25 cm ³ / g, and activated carbon with a specific surface area of 1400-1600 m ² / g and a specific micropore volume of 0.70-1.00 cm ³ / g is used as a moisture-retaining sorbent with the following ratios of components, weight. %: iron powder 50-65 activated carbon with specific surface of 500-700 m ² / g and specific micropore volume 0.15-0.25 cm ³ / g 5-15 activated carbon with specific surface of 1400-1600 m ² / g and specific micropore volume 0.70-1.00 cm ³ / g 10-30 sodium chloride 0.2-1.5 water 10-25