RU2314062C2 - Method of preparing aerosol forming fire-extinguishing compositions having elevated moisture resistance - Google Patents

Abstract

FIELD: fire-extinguishing materials.

SUBSTANCE: invention relates to an area of preparing aerosol forming fire-extinguishing compositions containing potassium or sodium nitrate as oxidant. Method according to invention comprises mixing appropriate components and molding samples. When samples are removed from mold, their surface is moistened with liquid mixture consisting of 20-50% epoxide resin, 2-5% dibutyl phthalate, 5-8% polyethylene-polyamine, and acetone (to 100%). Thereafter, samples are partially dried for 1-2 h at room temperature and then dried for 1-5 h at 60-100°C.

EFFECT: enhanced moisture resistance of compositions.

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Description

The invention relates to extinguishing agents and preventing the combustion of flammable liquids, combustible substances and materials in confined spaces.

Aerosol forming fire extinguishing compositions (AOC) containing potassium or sodium nitrates as an oxidizing agent (WO 92/17244, application, class A62D 1/00, A62C 5/02, 1992) were widely used as effective means of volumetric fire extinguishing in confined volumes. The increased hygroscopicity and water solubility of these oxidizing agents determine the insufficiently reliable performance of charges from similar AOS during their operation in conditions of high humidity or as a result of even short-term contact with water. This circumstance necessitates the use of pressurized equipment, as well as providing special conditions to prevent humidification of AOS and reduces the reliability of the use of such fire extinguishing means in conditions of high humidity (storage and basement rooms, ship compartments, etc.). The higher the hygroscopicity and the content used in the composition of such oxidizing agents, the higher its ability to absorb moisture and the lower the survivability of the samples during their operation in conditions of high humidity. So, a composition containing 70% potassium nitrate (KNO ₃ ), 11% phenol-formaldehyde resin (PFS) and 19% dicyandiamide (DCDA), at a relative humidity of φ = 92.5% for 10 days, sorb 1.74 wt.% Water . Under the same conditions, when sodium nitrate (NaNO ₃ ) is used as an oxidizing agent, about 4.2 wt.% Of water is adsorbed. 20 minutes after immersion of samples with KNO ₃ in water, their surface is destroyed, and if NaNO _{3 is} present, the integrity of the samples is observed in the first minutes of contact with water. The noted differences correspond to the hygroscopicity and water solubility of these oxidizing agents: relative humidity over a saturated KNO ₃ solution is 92.5%, and its solubility in water is 24%, while for NaNO ₃ these values are 77% and 42%, respectively (Shidlovsky A.A. Fundamentals of pyrotechnics, GIOP, M., 1954).

It is known that, along with the physicochemical nature of the components used, the moisture resistance of the composition can also be affected by the method of manufacturing products from AOS. For example, AOS samples manufactured by injection technology, ceteris paribus, have a lower tendency to moisture compared to samples obtained by the method of "deaf" pressing, primarily due to the increased porosity of the latter. This may be indicated by their lower density in comparison with the calculated one (by 3-5% or more) even at extremely high pressing pressures (Ore> 300 MPa). The density of the samples made by free casting is close to theoretical.

The porosity of pressed samples from AOS helps to reduce their moisture resistance, including due to the significant contribution of capillary sorption of water in conditions of high humidity.

One of the known methods for the manufacture of aerosol forming compositions includes the method described in the patent (RU, 2095104, CL A62D 1/00, 1/06, 1996). It was chosen by us as a prototype and consists of sequentially performed technological operations for dosing and mixing the components for 1 hour, followed by molding of products of the necessary geometric shape by the method of pressure pressing at specific pressure Rud = 150 MPa.

According to the obtained experimental data, none of these methods for the manufacture of AOS can significantly increase the moisture resistance of the samples. So, regardless of the indicated preparation methods, samples of the same formulation (74% KNO ₃ , 16% DCDA and 10% PFS) had hygroscopicity at the level of 1.62 ... 1.88% (φ = 92.5%, exposure time τ = 10 days) and began to collapse in 2-3 minutes after immersion in water. As the samples were moistened at φ = 92.5%, a decrease in speed (from 2.6 to 1.1 mm / s), stability and full burning were noted. The completeness of combustion was estimated by the amount of slag residues in the model chamber after the combustion of the sample.

As follows from the foregoing, insufficient moisture resistance of products from AOS reduces their operational reliability and limits the range of application of aerosol-forming fire extinguishing agents, necessitating the adoption of special measures to exclude their moistening.

The technical result of the present invention is to develop a method for the manufacture of aerosol-forming fire extinguishing compositions having increased moisture resistance, based on such traditional oxidizing agents as potassium or sodium nitrates to expand their fields of application, including under conditions of exposure to adverse factors caused by high humidity.

The technical result is achieved by introducing into the technological process of manufacturing products from AOS an additional operation to wet their surface after extraction from the mold with a liquid mixture consisting of epoxy resin (20 ... 50 wt.%), Dibutyl phthalate (2 ... 5 wt.%), polyethylene polyamine (5 ... 8 wt.%) and acetone (the rest is up to 100%), followed by drying at room temperature for 1-2 hours and drying at T = 60 ... 100 ° C in within 1-5 hours.

In contrast to the known method of protecting samples by applying a surface coating, when there is a clear difference between the structure and physicochemical properties of the polymer matrix of the main composition and the armor, the proposed manufacturing method from AOS allows you to create a transitional surface layer that is uniform in chemical composition and properties, consisting of interpenetrating vulcanization network of an epoxy resin from an acetone mixture and acetone-extracted polymer components of the AOS combustible-binder. Therefore, the presence of acetone in the proposed method of manufacturing products is necessary, but within certain limits. In the absence of acetone or its low concentration in the mixture (less than 37%), the moisture protective properties of the surface layer of the samples are reduced. Thus, according to the data obtained, the amount of moisture absorbed by samples from AOS with a size of 25/0 is 10 mm (diameter 25 mm, height 10 mm, no channel) containing 70% KHO ₃ , when immersed in water for 1 hour, it was at the level 1.8 wt.% - in the absence of acetone and 0.32 wt.% - at 40% of its content in the mixture. At the same time, when the concentration of acetone decreases, the specific gravity of the inert surface film per 1 cm ^{2 of the} surface increases (from 0.28 to 0.74 g / cm ² for 40 and 10% acetone concentration, respectively), which negatively affects the ignition processes and burning samples. The moisture resistance of the samples also decreases with a high acetone content (more than 73%), as well as with the content of other components of the mixture beyond the above limits, since this leads to a deterioration in the physicomechanical properties of the surface layer or an increase in its defectiveness.

The effectiveness of the proposed method for the manufacture of products from aerosol forming compositions to increase their moisture resistance is illustrated by the following examples.

Cylindrical samples with a size of 67/10 - 40 mm (outer diameter - 67 mm, channel diameter - 10 mm, height - 40 mm) weighing 200 g of the same recipe (74% oxidizing agent KNO ₃ or NaNO ₃ , 16% DCA and 10% FFS) were prepared in two ways: according to the method described in Example 1 of the prototype (RU, 2095104, class A62D 1/00, 1/06, 1996), and according to the proposed method, in which samples were removed from the mold immersed for 10 ... 15 seconds in a pre-prepared homogeneous mixture of epoxy resin, dibutyl phthalate, polyethylene polyamine and acetone. Then, samples were dried and dried according to the temperature-time regimes given in the table.

The obtained results confirm the increased moisture resistance of products from aerosol-forming extinguishing compositions made by the method proposed in the invention, in comparison with products of a similar composition made using previously known methods. This allows us to recommend this method for the production of products from AOS, intended, in particular, for operation in rooms and structures with high humidity.

No. p / p Indicators Composition option one 2 A method of manufacturing samples According to the prototype According to this invention According to the prototype According to this invention one. Type of oxidizing agent Potassium nitrate Sodium nitrate 2. The composition of the epoxy-acetone mixture, wt.%: - epoxy resin 20,0 60.0 - dibutyl phthalate 2.0 5,0 - polyethylene polyamine 8.0 5,0 - acetone 70.0 30,0 3. The drying mode of the samples after wetting with an acetone mixture and dipping: - temperature, ° С - 60.0 - 100.0 - time, τ, hour - 5,0 - 1,0 four. The amount of sorbed moisture, wt.%: - at a relative humidity of 92.5% for 10 days 1.88 0.30 4.8 0.86 - after soaking in water for 1 hour The sample is destroyed 10 minutes after immersion in water 0.25 The sample is destroyed 2 minutes after immersion in water 0.42

Claims (1)

A method of manufacturing aerosol-forming fire extinguishing compositions containing potassium nitrate or sodium nitrate as an oxidizing agent by mixing the constituent components and molding samples, characterized in that after removing the samples from the mold, their surface is wetted with a liquid mixture of epoxy resin, dibutyl phthalate, polyethylene polyamine and acetone in the following ratio of components, wt.%: epoxy resin 20-50 dibutyl phthalate 2-5 polyethylene polyamine 5-8 acetone the rest is up to 100%, followed by calibration at room temperature for 1-2 hours and drying at a temperature of 60-100 ° C for 1-5 hours.