RU2522673C2 - Paste-like material for protection against neutron radiation and method of preparing paste-like material for protection against neutron radiation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to technology of manufacturing materials for protection against neutron radiation. A paste-like material for protection against neutron radiation includes solid grease VNIINP-293 and amorphous powder boron as a filling agent with a weight component ratio (%) 91-97 and 3-19 respectively, and a specific surface of amorphous boron powder constitutes not less than 15 m²/g. A method of preparing the claimed material includes mixing solid grease VNIINP-293 and the filling agent - amorphous powder boron in a weight ratio (%) respectively 91-97 and 3-9.

EFFECT: providing a section of absorption of thermal electrons from 7 to 21 cm^-1 depending on the weight content of boron (3-9% respectively); a temperature of dropping not lower than 170°C; viscosity, determined by a capillary viscometer at plus 50°C and an average gradient of deformation rate 1000 s^-1, within 0,3-1,4 Pa·s, and at minus 50°C and an average gradient of deformation rate 100 s^-1 - not more than 19 Pa·s; a colloidal stability under load 3H (percent of recovered oil) not more than 25%; water content less than 0,01%; as well as providing possibility by means of the claimed composition to fill volumes of different configuration, including long channels of small section (diameter less than 4 mm), in the range of temperatures from minus 50°C to plus 50°C.

3 cl, 4 dwg, 2 tbl

Description

The invention relates to a technology for the manufacture of boron-containing composite materials designed to protect against neutron radiation.

Known boron-containing composition for protection against neutron radiation based on polypropylene, containing amorphous boron and boron nitride as a filler in the following ratio of components, wt.%: Amorphous boron 4-6; boron nitride 9-11; polypropylene 83-87. The technology for preparing this composition includes mixing all the components in a ball mixer with further extruding the resulting mixture. The resulting composition is used as a structural material from which products are manufactured according to the established technology (RF Patent No. 2096431, publ. 20.11.97., IPC C08L 23/12).

Known boron-containing composition for protection against neutron radiation, including an olefin polymer, which is polypropylene or polyethylene, with a filler - boron nitride in the following ratio, wt.%: Polypropylene or polyethylene 30-50, boron nitride 50-70. The method for preparing this composition consists in mixing boron nitride with a part of an olefin polymer in a ball mixer, followed by adding the remaining olefin polymer and continuing mixing in a ball mixer (RF Patent No. 2148062, publ. 04/27/2000., IPC S08K 3/38).

The above boron-containing compositions are used in the manufacture of structural materials designed to protect against radioactive radiation.

As a prototype, a pasty material is selected, intended for protection against radioactive radiation based on plastic synthetic mass, filler, plasticizer and surfactant, obtained by mixing plastic mass, plasticizer and surfactant in a paddle mixer at an elevated temperature of the mixture with the addition of filler and further mixing to obtain a homogeneous pasty mass (RF Patent No. 2111558, publ. 05/20/98, IPC G21F 1/10).

As a plastic synthetic mass for a paste-like protective material from radioactive radiation, butadiene, or nitrile butadiene, or butyl rubber or butyl nitrile or divinyl styrene rubbers are used. As a filler, lithium-6 fluoride, or boron, or its compounds, or titanium hydride, or powdered lead, or bismuth oxide, or uranium dioxide, or thorium dioxide, or tungsten, or tungsten trioxide, or rare earth oxides are used. Dibutyl phthalate, or dibutyl sebacinate, or dioctyl sebacinate, or transformer oil, or industrial oils are used as a plasticizer. As a surfactant - lecithin or cationate-7 in the following ratio of components, wt.%:

Plastic synthetic mass mixed with plasticizer with a ratio of rubber of 8-20%, a plasticizer of 80-92% 4-40 Filler 60-96 Surfactant 0.1-0.5 (over 100%)

Introduction to the composition of the material to protect against radiation from fillers ensures in each case its effectiveness against various types of ionizing radiation. The ratio of the components of the polymer base and filler allows you to get pasty materials with the desired viscosity and flowability.

The disadvantage of the prototype is the high viscosity value of 9000 Pz (900 Pa · s) at 20 ° C, which is due to the high percentage of filler (60-96%). High viscosity makes it difficult to fill the claimed composition with volumes with a small internal cross-section (for example, channels), especially at low temperatures.

The objective of the invention is the creation of a paste-like material with a high protective ability against neutron radiation, which would have a low viscosity in a wide temperature range.

When using the claimed invention, the following technical result is achieved:

- absorption cross sections of thermal electrons from 7 to 21 cm ^-1 depending on the mass content of boron (3-9%, respectively),

- dropping point not lower than 170 ° C;

- viscosity determined by a capillary viscometer:

a) at plus 50 ° C and an average gradient of the strain rate of 1000 s ^-1 , in the range of 0.3-1.4 Pa · s;

b) at minus 50 ° C and an average strain rate gradient of 100 s ^-1 , not more than 19 Pa · s;

- colloidal stability at a load of 3N (percentage of oil recovered), not more than 25%;

- water content is less than 0.01%;

- the developed composition allows filling volumes of various configurations, including long channels of small cross section (less than ⌀4 mm), in the temperature range from minus 50 ° С to plus 50 ° С.

To solve this problem and achieve a technical result, a paste-like material for protection against neutron radiation, including a plastic synthetic mass and a filler - powdered boron amorphous, according to the invention contains VNIINP-293 grease as a plastic synthetic mass in the following ratio of components, wt.%:

grease VNIINP-293 91-97 amorphous boron powder 3-9,

wherein the specific surface area of amorphous boron powder is at least 15 m ² / g.

To solve this problem and achieve a technical result, there is also proposed a method of preparing a paste-like material for protection against neutron radiation, comprising mixing a plastic synthetic mass and a filler in a paddle mixer, in which, according to the invention, VNIINP-293 grease is used with the ratio amorphous boron, wt.%: 91-97 / 3-9; mixing is carried out in a mixer for highly viscous materials at a temperature of not more than 20 ° C for at least 1.5 hours and a residual pressure in the mixer chamber of not more than 10 ⁴ Pa until a homogeneous mass is obtained, followed by homogenization of the resulting mass.

For mixing the starting components, a mixer for highly viscous materials with Z-shaped blades is used.

Features of the claimed composite material, specified in the "technical effect" achieved by the use as a plastic synthetic mass grease VNIINP-293, and as a filler - powdered boron amorphous with a specific surface area of at least 15 m ² / g and experimentally matched their percentage ratio. In addition, in the method of preparing a paste-like material, a technology has been developed for the manufacture of the material indicating the technological parameters of mixing with the subsequent operation of the homogenization of the material.

Homogenization (intensive mechanical action) is necessary to obtain a homogeneous material with a smoother texture and to improve the mechanical and colloidal stability of the finished material, which is achieved due to better distribution of the filler in the volume of the finished paste-like material.

Figure 1 shows the dependence of the effective viscosity on the mass content of the filler at a temperature of minus 50 ° C and an average strain rate gradient of 100 s ^-1 .

Figure 2 shows the dependence of the effective viscosity on the mass content of the filler at a temperature of plus 50 ° C and an average strain rate gradient of 1000 s ^-1 .

Figure 3 shows the dependence of colloidal stability on the mass content of boron.

Figure 4 presents the dependence of the dropping temperature on the mass content of boron.

The essence of the claimed invention is that in the finished grease VNIINP-293 add amorphous powdery boron with a specific surface area of at least 15 m ² / g in the following ratio, wt.% VNIINP-293 grease - 91-97; amorphous boron powder - 3-9.

VNIINP-293 grease is a grease, which is a pasty material of light gray color, which includes PMS-100 polymethylsiloxane liquid as a liquid base, thickened with lithium soap of stearic acid - lithium stearate.

The technology for preparing the claimed composition included preliminary mixing of the starting components and further homogenization of the resulting composition. Before use, amorphous boron powder was previously dried to constant weight at a temperature of 120 ° C. Premixing was carried out on a paddle mixer with Z-shaped blades designed for processing highly viscous media. Mixing of the material was achieved due to the intense exposure to broad-blade kneading elements. In this case, the mixed material moved inside both horizontally and vertically, due to which boron powder was evenly distributed in the lubricant volume. The maximum loading of the initial components of the composite material into the kneading tank was 300 g. The bottom of the kneading chamber, equipped with double walls, could be heated or cooled. The kneading machine was operated under reduced pressure in order to eliminate the negative effects of air and residual moisture on the quality of the material.

The development of various technological modes of preliminary mixing of the starting components (VNIINP-293 grease and boron) was carried out in order to assess the influence of the time and temperature of the filler mixing on the rheological and physicochemical characteristics of the finished filler. To test the filler technology, VNIINP-293 grease of various technological batches and amorphous powder boron B-99A grade with a specific surface area in the range S _beats = 11-17 m ² / g determined by the Deryagin method were used.

The results of the experiments showed that to obtain a homogeneous system by the claimed method of mixing, the specific surface area of amorphous boron powder should be at least 15 m ² / g.

The physical and rheological parameters of the VNIINP-293 lubricant of some used technological batches are presented in Table 1. It should be noted that individual batches of lubricant have a wide range of viscosity values at minus 50 ° C.

Table 1 Physical and rheological indicators of various batches of grease VNIINP-293 VNIINP-293 grease lot number Viscosity η _eff , Pa · s Colloidal stability of the COP,% Drop point T _cap , ° C plus 50 ° C at speed defor. 1000 s ^-1 minus 40 ° C at speed defor. 100 s ^-1 four 0.54 15.85 12.72 207 3 0.87 8.9 15.70 215 228 1,02 10.0 13.21 210 6 0.72 8.7 15.6 178 TU norms for VNIINP-293 greasing 0.3-1.4 No more than 19 no more than 25 not lower than 170

The mixture of the starting components was tested at temperatures: 25 ° C, 40 ° C, 55 ° C, 80 ° C. According to the results of the experiments, it was shown that the achievement of the claimed technical result is possible at a minimum mixing temperature (25 ° C), as a result of which mixing at higher temperatures is impractical. The result obtained is consistent with the literature data, according to which, in the production of greases, the modifying agent is introduced into the finished grease at room temperature, since at this temperature of introduction it does not participate in the initial stage of the formation of the grease and almost does not change its rheological properties.

It is known that powdered fillers are difficult to evenly distribute in the volume of highly viscous material. In this regard, to determine the mixing time of the starting components required for a fairly uniform distribution of the powdered filler in the lubricant, the corresponding experiments were carried out with the following ratio of the starting components wt.%: VNIINP grease - 293-95, boron - 5. The mixing time was from 1 to 5 h; temperature 25 ° C, pressure - 1 · 10 ⁴ Pa. In the course of the experiment, 3-5 samples of material in an amount of 60 g were taken after each hour of mixing in order to track the dynamics of changes in the values of colloidal stability, dropping temperature and viscosity of the material. The experimental results showed that the values of the indicated parameters of the material remain constant at mixing times of at least 1.5 hours. Similar experiments conducted for other ratios of the starting components at 25 ° C confirmed the conclusions about the need to mix them for at least 1.5 hours.

Further work related to the selection of the percentage of the lubricant to boron amorphous was carried out at the previously selected optimal mixing mode: temperature 25 ° C and a mixing time of at least 1.5 hours. This ratio varied in the range from 85 to 97 wt.% VNIINP- lubricant 293 and from 3 to 15 wt.% Amorphous boron (see table 2 and figure 1 - figure 4). As a result of the work, it was found that an increase in the mass content of boron in the lubricant of more than 9 wt.% Leads to a significant increase in the viscosity of the resulting compositions at low temperatures, which is therefore impractical (see table 2 and figure 1 - figure 4) .

The complex of studies showed that the introduction of amorphous boron into the VNIINP-293 lubricant (see Table 1) in the general case leads to a significant increase in the viscosity of the material at low temperatures (up to 40% or more of the viscosity value of a clean lubricant at minus 50 ° C) , a slight increase in the dropping point (not more than 2% of the dropping point of a pure lubricant), while the value of colloidal stability remains unchanged.

table 2 Characteristics of the finished material at various wt.% Boron content in the lubricant. Mass fraction of boron in VNIINP-293 lubricant,% T _cap , ° C COP,% η _eff , Pa · s plus 50 ° C, (1000 s ^-1 ) minus 40 ° C, (100 s ^-1 ) 0 209.3 15.25 0.45 5.86 3 210.0 14.66 0.58 8.81 four 209.3 18.06 0.58 9.11 5 212.7 18.92 0.61 9.07 6 214.3 14.81 0.71 13.21 7 211.5 16.40 0.76 13.18 8 217.0 16.15 0.71 16.65 9 218.5 15.24 0.85 17.39 10 219.3 15.22 1.01 20.80 fifteen 230,0 8.70 - - Technical result No less than 170 No more than 25 0.3 to 1.4 No more than 19

After mixing on a paddle mixer, the pasty material was homogenized in order to achieve a better distribution of powdered boron amorphous in the volume of the finished material. Homogenization of the material was carried out on an IKA magic LAB machine using the appropriate module included in the machine package. The module, consisting of three pairs of rotor-stator systems, installed one after another, provided a three-stage homogenization of the material. The multi-stage placement of the rotor-stator systems made it possible to achieve maximum mechanical impact on the material in a short time of its passage through the module. In this case, shear rates ranged from 42,000 to 100,000 s ^-1 .

As a result of homogenization, a pasty material was obtained that had a smooth, uniform texture, the required viscosity and was colloidal and mechanically stable.

Next, an analysis was determined for the water content in the finished material. As an example, we studied a sample of the finished material containing wt%: VNIINP-293 grease - 95, boron - 5. The mass fraction of water in the sample was less than 0.01%, which meant the absence of water in the finished sample. A similar analysis was determined for samples of the finished material with other ratios of the starting components. The results were consistent with the claimed technical result.

The inventive paste-like material was made by the claimed method, its rheological and physicochemical parameters were determined (see table 3, table 4, figure 1 - figure 4). As a result of the analysis of experimental indicators, the optimal percentage ratio of the starting components was selected:

VNIINP-293 greasing 91-97% Amorphous Boron 3-9%

The essence of the invention is illustrated by the example of the preparation of a paste-like material.

Due to the insignificant difference in the properties between boron isotopes, with the exception of neutron-absorbing ability, the study was conducted on a natural mixture of isotopes.

Example 1. Before the preparation of the paste-like material was carried out the input control of the starting components.

1.1 Input control of lubrication indicators VNIINP-293:

a) appearance - visually;

b) determination of viscosity - the measurement of this value was carried out on a capillary viscometer "AKV-2" according to GOST 7163-84;

c) determination of dropping point - the measurement of this value was carried out on the apparatus "Drop - 20-02" according to GOST 6793-74;

d) determination of colloidal stability - the measurement of this value was carried out on the apparatus "AKS-20" GOST 78142-74;

1.2. Determination of amorphous boron powder indicators

a) mass fraction of boron - measurement of the mass fraction of boron in the initial powder was carried out by chemical analysis in accordance with TU (normative document);

b) specific surface area was measured by the method of Deryagin

To prepare a paste-like material, 285 g of VNIINP-293 grease and 15 g of amorphous boron powder, dried at a temperature of 120 ° C to constant weight with an accuracy of ± 0.001 g, were taken and pre-mixed in a laboratory kneading machine HKD-T 0.6 at a temperature of 25 ° C for 2 hours and a residual pressure of 1 · 10 ⁴ Pa until a homogeneous mass is obtained. Then the resulting paste-like material was unloaded and loaded into the feeder of the IKA magic LAB machine for further homogenization using the DISPAX-REACTOR module and the F6 generator (rotor-stator system). Shear rates at a machine rotor speed of 10,000 rpm and 16,000 rpm were 42000-63000 s ^-1 and 68000-100000 s ^-1, respectively. The pressure was limited by the maximum allowable working pressure in IKA magicLAB and amounted to 2 · 10 ⁵ Pa. The working chamber of the machine was cooled with a CF3 thermostat to a temperature of 25 ° C. The homogenization time was 10 minutes.

After homogenization, the finished paste-like material was unloaded and its physicochemical and rheological parameters were determined.

Viscosity, colloidal stability and dropping point were determined according to paragraph 1.1.

Determination of chemical indicators of the finished paste-like material:

a) water content — this value was measured on a DL-39X titrator by coulometric titration.

Thus, it is experimentally shown (see table 2, table 3, figure 1 - figure 4) that the developed pasty material for protection against neutron radiation has rheological and physico-chemical parameters according to the technical result, namely:

- absorption cross sections of thermal electrons from 7 to 21 cm ^-1 depending on the mass content of boron (3-9%, respectively),

- dropping point not lower than 170 ° C;

- viscosity determined by a capillary viscometer:

a) at plus 50 ° C and an average strain rate gradient of 1000 s ^-1 , in the range of 0.3-1.4 Pa · s;

b) at minus 50 ° C and an average strain rate gradient of 100 s ^-1 , not more than 19 Pa · s;

- colloidal stability at a load of 3H (% percentage of oil recovered), not more than 25;

- water content,% - less than 0.01.

The characteristics of the claimed pasty material are obtained using the claimed method for producing this material.

Claims (3)

1. A paste-like material for protection against neutron radiation, including plastic synthetic mass and filler - amorphous powdery boron, characterized in that VNIINP-293 grease is used as plastic synthetic mass in the following ratio of components, wt.%:
grease VNIINP-293 91-97 amorphous boron powder 3-9,
wherein the specific surface area of amorphous boron powder is at least 15 m ² / g. 2. A method of preparing a paste-like material for protection against neutron radiation, comprising mixing in a paddle mixer a plastic synthetic mass and a filler — powdered boron amorphous, characterized in that VNIINP-293 grease is used as a plastic synthetic mass in relation to amorphous boron, wt. %: 91-97 / 3-9, mixing is carried out in a mixer for highly viscous materials at a temperature of not more than 20 ° C for at least 1.5 hours and a residual pressure in the mixer chamber of not more than 10 ⁴ Pa to obtaining a homogeneous mass followed by homogenization. 3. The method according to claim 2, characterized in that the mixing is carried out in a high viscosity mixer with Z-shaped blades

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