WO2008020782A1

WO2008020782A1 - Powder mixture for carrying out an exothermic reaction

Info

Publication number: WO2008020782A1
Application number: PCT/RU2006/000577
Authority: WO
Inventors: Dmitry Viktorovich Petunin; Aleksei Vyacheslavovich Druzhkov
Original assignee: Dmitry Viktorovich Petunin; Druzhkov Aleksei Vyacheslavovi
Priority date: 2006-08-11
Filing date: 2006-11-07
Publication date: 2008-02-21
Also published as: RU2330868C2; RU2006129036A

Abstract

The invention relates to chemical heat sources applied for self-contained heating devices and containers which are used for flameless cooking and heating foods, in particular to materials for heat transmission by using magnesium oxidation. The inventive powder mixture for carrying out an exothermic reaction comprises a magnesium alloy powder and a metallic catalyst and a controller of the reaction rate of the mixture with an electrolyte aqueous solution and is characterised in that iron and/or silicon are used in the form of a metallic catalyst and the mixture comprises a reaction rate controller in the form of a fraction of magnesium alloy powder exhibiting a relatively low dispersibility at the following component ratio (mass %): 65-90 mass % magnesium alloy powder having particle size ranging from 200-500 mkm and 10-35 mass % magnesium alloy powder having particle size ranging from 501 to 800 mkm. The powder mixture can also contain a fraction of magnesium alloy powder which exhibits a relatively high dispersibility and the particle size of which ranges from 100 to 199 mkm in a quantity of 5-15 mass %. The iron content in a magnesium-iron alloy is of 5-10 mass % and the silicon content ranges from 0.5 to 2.0 mass %. The powder mixture can also contain 3-7 mass % sodium chloride. Said invention makes it possible to exclude the presence of inert, in terms of heat liberation, reaction rate controllers and to increase a specific amount of heat released by the weight unit of the mixture during the reaction of magnesium with electrolyte aqueous solution.

Description

Powder mixture for an exothermic reaction

The invention relates to the field of chemical heat sources used to equip autonomous heating devices and vessels for flameless cooking or heating of food, specifically to materials for heat transfer based on the oxidation of magnesium.

Known compositions for exothermic redox reactions between a metal from the group of Fe, Mg, Al, Zn and metal oxides of variable valency MnO ₂ , PbO ₂ , Ni ₂ O ₃ [RU 2019 160, Bull. N ° 17, 1994], as well as between magnesium and copper chloride [US 5517981, 1996].

The compositions are characterized by uneven heat release, intense only in the initial stage of redox reactions, which is a significant drawback for the heat exchange process with a heated object, for example, food rations. Another disadvantage is that the nature of the redox reactions does not allow contact of the components of the mixture under storage conditions and predetermines the complex multi-chamber design of heating pads, compresses and other products. To start the reaction, the components must be thoroughly mixed, which determines the inconvenience of their use. The property of magnesium to interact with water with the release of heat is known.

[Glinka N.L. General chemistry. Ed. 16. L .: Chemistry, 1974, C.601] ._ The reaction takes place at a pH below 8.5. Raising the pH leads to passivation of the surface, which prevents interaction, and magnesium ceases to displace hydrogen from water.

The practical use of this interaction is hindered by the fact that in order to control the reaction rate of magnesium with water, it is necessary to introduce additional compounds that affect the pH of the medium. Acid anhydrides and free acids can be used as accelerators of the process, and salts of strong bases and weak acids, for example, bicarbonates, carbonates, phosphates and polyphosphates of alkali metals, calcium hydroxide, etc. can be used as inhibitors of the reaction.

The disadvantage is the low specific heat transfer of the reaction, less than 5 kJ / g (magnesium), and the presence of additional compounds, which in a mixture with magnesium are ballast, which reduces the content of the main heat-generating component. To increase the effect of heat release, magnesium alloys are used with a metal catalyst forming a micro galvanic cell with it. In the presence of an electrolyte, the reaction of magnesium with water is electrochemical in nature. A known alloy of magnesium and iron by type ((mechanical mixture) and methods for their preparation [US 3942511, 1976; US 3993577, 1976]. The alloy is prepared in a ball mill from a mixture of magnesium sawdust and iron powder in an inert solvent. After evaporation of the solvent and separation of the excess The iron obtained residue is a magnesium alloy containing up to 10 mass% of iron.The alloy actively interacts with water in the presence of a small amount of sodium chloride with a specific heat of reaction of up to 5.6 kJ / g (Mg).

The disadvantage of this mixture is the high reaction rate with water, which leads to its use in a device for producing hydrogen [US 4017414, 1977] and does not allow its effective use in heat exchange devices. Of interest are methods for producing magnesium alloys [US 4072514,

1978] with iron, iron oxide, zinc, chromium, aluminum, and manganese with a phase interface with magnesium alloy and said metal. In one case, alloys are produced by mechanically pressing small metal particles into larger magnesium particles, in the other case, by introducing solid metal particles into molten magnesium and subsequent cooling, which ensures uniform distribution of the catalyst in the volume of magnesium. Both methods are aimed at the formation of microelectrochemical cells.

The technical task for instruments and devices using heat generated as a result of exothermic chemical reactions is to equip them with compositions characterized by:

- on the one hand, high heat dissipation, which is achieved by using in an exothermic mixture only those ingredients that produce heat as a result of the reaction;

- on the other hand, stable and prolonged heat release in the range of predetermined temperatures, which is achieved by introducing additional ingredients that regulate the reaction rate, usually in the direction of its slowdown.

A device for producing high temperature for heating a diver according to the patent is known [US 4223661, 1980], for which magnesium alloys are proposed, formed mechanically in a ball mill from powders of magnesium and metals, including copper, titanium, chromium, nickel, as well as from carbon powder (graphite).

The disadvantage is that, in order to prevent burns to the body, alloys with extremely low specific heat release characteristics are proposed.

Known exothermic composition for flameless heater [US

5117809, 1992], which contains a powder of an alloy of magnesium with iron, prepared in a ball mill, NaCl salt, a surfactant, and food acid anhydride or free food acid as a pH regulator. The porous packaging in which the exothermic composition is contained may also be impregnated with acid. The acid controls the pH between 4 and 7 so that the reaction of magnesium with water does not proceed too vigorously at low pH and too slowly at high pH.

The disadvantage of this composition is the presence of surfactants, acid anhydrides or free acids, which reduces the content of the main component - magnesium alloy, therefore, reduces the overall heat release of the proposed composition.

The closest technical solution is a powder mixture, which enters into an exothermic reaction with water in a flameless heater [US 5611329, F 24 J 1/00, 1997] (prototype), consisting of two non-woven sheets of polyester forming many pockets. Each pocket is filled with a powder mixture of the composition, wt.%: An alloy of magnesium and iron (5 atom%) - 80 - 85 NaCl - 5 - 7 chemical antifoam - 3 - 4 inert filler - 7 - 9

The disadvantage is the presence of a large number of components of the exothermic mixture, in particular, antifoam, inert filler and optional NaCl in the powder mixture. An inert filler is included in the mixture as a regulator of the reaction rate of magnesium with water. As a result, the composition of the mixture is not characterized by a sufficiently high content of the main component, the magnesium alloy, and this reduces the overall heat release of the composition. The present invention is aimed at finding the composition of the powder mixture for the implementation of an exothermic reaction, providing an increase in the amount of heat generated by the exothermic mixture in the reaction of magnesium with an aqueous electrolyte solution. Among the tasks is also the regulation of heat dissipation power, which ensures the stable operation of heating devices in the temperature range of 50 - 6O ⁰ C for 8 - 15 minutes.

The technical result is achieved by the fact that a powder mixture is proposed for carrying out an exothermic reaction, including a magnesium alloy powder with a metal catalyst and a reaction rate regulator of the mixture with an aqueous electrolyte solution, characterized in that iron and / or silicon is used as a metal catalyst, and as a regulator the reaction rate, the mixture contains a fraction of a relatively low dispersion magnesium alloy powder with the following component ratios (mass%): magnesium alloy powder with size mi particles 200 - 500 microns - 65 - 90; magnesium alloy powder with particle sizes of 501 - 800 microns - 10 - 35.

It is advisable that the powder mixture additionally contains a fraction of the magnesium alloy powder of relatively high dispersion, with the following component ratios (mass%): magnesium alloy powder with a particle size of 200 - 500 microns - 65 - 85; magnesium alloy powder with a particle size of 501 - 800 microns - 10 - 25; magnesium alloy powder with a particle size of 100 - 199 microns - 5 - 15.

Preferably, in the magnesium-iron alloy, the iron content is 5 to 10 mass%, and in the magnesium-silicon alloy the silicon content is 0.5 to 2.0 mass%.

It is possible that the powder mixture additionally contains sodium chloride in an amount of 3 to 7 mass%. The presence in the powder mixture of various fractions of a magnesium alloy is due to the fact that the chemical reaction of electrolytic oxidation of a magnesium alloy powder with a particle size of 200 - 500 μm has a maximum specific heat dissipation in the first 1 to 4 minutes (Figure 1, curve 1) and the amount of heat released significantly exceeds the amount of heat that can be absorbed by the heated object, for example, food rations, during this period.

Therefore, to ensure efficient heat transfer, the composition contains a fraction of a relatively low dispersion magnesium alloy powder with particle sizes of 501-800 microns, characterized by a maximum specific heat release power from 2 to 12 minutes of the reaction (Fig. L, curve 2). The total effect ensures stable operation in the temperature range of the heating of food soldering to 50 - 6O ⁰ C for 12 minutes.

In cases where a quick exit to operating temperature is required, it is advisable to include a small amount of a relatively high dispersion fraction of magnesium alloy powder with a particle size of 100 - 199 μm, with a maximum specific heat output in the first minute of the reaction (Fig. L, curve 3 )

The quantitative content of the fractions was established experimentally and controls the reaction rate to ensure stable heat release for heating food rations (canned food) weighing 250 g in the temperature range 50 - 6O ⁰ C for 12 minutes.

The claimed content of iron in the alloy of magnesium with iron and the silicon content in the alloy of magnesium with silicon provides the maximum value of the specific heat of the exothermic reaction, which is illustrated in Fig.2.

In special cases, solely for ease of operation, the powder mixture may contain sodium chloride in an amount sufficient to obtain ~ 3% electrolyte solution after the mixture has reacted with water.

All alloy powders are prepared by pressing particles of a metal catalyst into a magnesium surface using a ball mill and then separating the finished powders into fractions. The proposed powder mixture for the exothermic reaction works as follows: when in contact with an aqueous electrolyte solution, the magnesium alloy powder is oxidized with heat. In the presence of an electrolyte, the surface of the magnesium alloy is cleaned of the formed oxide film, which ensures its further oxidation, while the electrolyte performs another function, namely, it eliminates the possible adhesion of reagent particles.

The specified result is achieved by the fact that in the proposed powder mixture it is possible to increase the content of the main component for the implementation of the exothermic reaction - magnesium by at least 10%. This allows you to either reduce the mass and dimensions of the heating device based on the developed composition, or to increase its technical characteristics: increase the amount of heat generated by the unit weight of the mixture to 6.18 kJ / g (mixture) compared to the prototype (~ 5 kJ / g), increase the heating temperature.

The invention is illustrated by the following accompanying diagrams:

Figure 1. Change in specific heat dissipation power W _yд . (W / g) in time for magnesium alloys with iron 6.5 mass% for various fractions of alloy particles: particle fraction 200-500 μm (curve 1), particle fraction 501-800 μm (curve 2), particle fraction 100 - 199 μm (curve 3);

Figure 2. The dependence of the specific heat Q _yd. (kJ / g) reactions from the content of metal catalysts in the magnesium alloy: silicon (curve 1) and iron (curve X).

The achievement of the technical result is illustrated in Fig.Z and Fig.4.

Fig.Z. Relative, per minute interval, heat release Q _0111. (kJ / last minute) of a mixture weighing 10 g in time during the reaction of a magnesium alloy with an aqueous electrolyte solution: Example 3 (curve 1); Example 8 (curve 2); Example 21 (curve 3); Example 29 is a prototype (curve 4).

Figure 4. The amount of emitted 10 g of a mixture of heat Q (kJ) in time: Example 3 (curve 1); Example 8 (curve 2); Example 21 (curve 3); Example 29 is a prototype (curve 4).

As can be seen from Fig.Z for the claimed composition of the powder mixture there is a more uniform distribution of heat over time. From figure 4 it follows that the amount of heat generated by the claimed mixture to 12 minutes ~ 15% higher than that of the prototype.

The following are examples of achieving a technical result when using the proposed powder mixture for carrying out an exothermic reaction in a heating device. All Examples are summarized in the Table. Examples 1-3.

To 10 g of a powder mixture of an alloy of magnesium with iron (6.5 mass%) of the following composition of fractions (mass%),

JVa of Example in Table 1 2 3 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 58.09 kJ of heat is released within 12 minutes with a specific heat of 5.81 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 48-53 ⁰ C.

Examples 4 to 6. To 10 g of a powder mixture of an alloy of magnesium with iron (10 mass%) of the following composition of fractions (mass%),

JVa of Example in Table 4 5 6 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 55.91 kJ of heat is generated within 12 minutes with a specific heat of 5.59 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 45-50 ⁰ C. Examples 7 - 9. To 10 g of a powder mixture of an alloy of magnesium with silicon (0.5 mass%) of the following composition of fractions (mass%),

N ° of the Example in Table 7 8 9 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 61.82 kJ of heat is released within 12 minutes with a specific heat of 6.18 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 55-60 ⁰ C. Examples 10 - 12.

To 10 g of a powder mixture of an alloy of magnesium with silicon (1 mass.%) Of the following composition of fractions (wt.%),

The JVs of Example in Table 10 11 12 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution are added to the calorimeter in a polymer pocket of a heating device. As a result of the exothermic reaction, 61.51 kJ of heat is released within 12 minutes with a specific heat of 6.15 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 54-60 ⁰ C. Examples 13 - fifteen.

To 10 g of a powder mixture of an alloy of magnesium with silicon (2 mass%) of the following composition of fractions (mass%),

Example Na in Table 13 14 15 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 60.89 kJ of heat is released within 12 minutes with a specific heat of 6.09 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 54-59 ⁰ C. Examples 16 - eighteen. To 10 g of a powder mixture of magnesium alloys with silicon (0.5-2 mass%) and iron (5-6 mass%) of the following composition of fractions (mass%),

Na Example in Table 16 17 18 with particle sizes of 200 - 500 μm 90 80 65 with particle sizes of 501 - 800 μm 10 20 35 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 58.09 kJ of heat is released within 12 minutes with a specific heat of 5.81 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 47-50 ⁰ C. Examples 19 - 24.

To 10 g of a powder mixture of an alloy of magnesium with iron (6.5 mass%) of the following composition of fractions (mass%), Example Na in Table 19 20 21 22 23 24 with particle sizes of 200 - 500 μm 85 70 70 75 65 65 s with a particle size of 501 - 800 microns 10 20 15 10 25 20 with a particle size of 100 - 199 microns 5 10 15 15 10 15 500 ml of a 3% aqueous electrolyte solution is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, 58.09 kJ of heat is released within 12 minutes with a specific heat of 5.81 kJ / g (mixture), which is enough to heat a 250 gram soldering from 0 ⁰ C to 49-59 ⁰ C. Examples 25 - 28 .

To 10 g of a powder mixture of fractions of an alloy of magnesium with silicon (0.5 - 2.0 mass%) and NaCl of the following composition (mass%), Example Na in Table 25 26 27 28 with particle sizes of 200 - 500 μm 85 70 65 65 with particle sizes of 501 - 800 μm 10 20 25 20 with particle sizes of 100 - 199 μm 5 10 10 15 NaCl 7 6 4 3 500 ml of water is added to the calorimeter in the polymer pocket of the heating device. As a result of the exothermic reaction, heat is released within 12 minutes 60.52-61.45 kJ with a specific heat of 6.05-6.14 kJ / g (mixture), which is enough to heat a 250-gram food rations from 0 ⁰ C to 55-57 ⁰ C, Example 29 (prototype).

To 10 g of the powder mixture of the prototype, placed in the polymer pocket of the heating device in the calorimeter, 500 ml of water is added. As a result of the exothermic reaction, 49.58 kJ of heat is released within 12 minutes with a specific heat of 4.96 kJ / g (mixture), which is sufficient for heating

250 gram food rations from 0 ⁰ C to 41 ⁰ C.

The advantages of the proposed powder mixture for exothermic reactions are as follows: excludes the presence of components inert from the point of view of heat release - the reaction rate regulators. The specific amount of heat released by a unit weight of the mixture during the reaction of magnesium with an aqueous electrolyte solution increases.

The regulation of the specific power of heat generation ensures stable operation in the temperature range of 50-60 ⁰ C for 8-15 minutes.

Claims

Claim

1. A powder mixture for carrying out an exothermic reaction, comprising a magnesium alloy powder with a metal catalyst and a reaction rate regulator of the mixture with an aqueous electrolyte solution, characterized in that iron and / or silicon is used as a metal catalyst, and the mixture contains a fraction as a reaction rate regulator magnesium alloy powder of relatively low dispersion with the following component ratios (mass%): magnesium alloy powder with a particle size of 200 - 500 microns - 65 - 90; magnesium alloy powder with particle sizes of 501 - 800 microns - 10 - 35.

2. The powder mixture according to claim 1, characterized in that it further comprises a fraction of a magnesium alloy powder of relatively high dispersion, with the following component ratios (mass%): magnesium alloy powder with a particle size of 200 - 500 microns - 65 - 85; magnesium alloy powder with a particle size of 501 - 800 microns - 10 - 25; magnesium alloy powder with a particle size of 100 - 199 microns - 5 - 15.

3. The powder mixture according to claim l. and claim 2., characterized in that in the alloy of magnesium with iron, the iron content is 5 to 10 mass%, and in the alloy of magnesium with silicon, the silicon content is 0.5 to 2.0 mass%.

4. The powder mixture according to claim l. and claim 2., characterized in that it further comprises sodium chloride in an amount of 3 to 7 wt.%.