RU2830677C1 - Composition of radiation-protective plaster dry mixture, method of its production and use - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to the field of construction materials science, in particular to the development of dry mixtures, which can be used as plaster products providing protection from radiation on employees. Composition of the radiation-protective dry plaster mixture includes: gypsum plaster – 15-35 wt. %; bismuth oxide Bi₂O₃ – 50-60 wt. %; tungsten carbide WC – 15-25 wt. %. Method for producing a radiation-protective dry plaster mix includes comprises dry mixing of gypsum plaster with fillers. Dosing of components, loading of components into jet-vortex mill, mixing and dispersion of coarse particles in jet-vortex mill during two starts, unloading of dry mixture and packing into protected paper bags. Method of using the radiation-protective dry plaster mixture involves mixing the dry mixture with water at a water-solid ratio of 0.21-0.29, with continuous mixing for 1-2 minutes.

EFFECT: invention is aimed at obtaining a plaster dry mixture with high strength and high degree of radiation protection in relation to gamma radiation.

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Description

The invention relates to the field of construction materials science, in particular to the development of dry mixtures that can be used as plaster products (as well as putties, blocks, plasterboard sheets, etc.), providing protection from the effects of radiation on employees working with ionizing radiation and surrounding people in industry, medicine and everyday life, with high physical and mechanical characteristics.

A composite material is known with the following composition, wt.%: construction gypsum binder or a mixture of construction and high-strength gypsum binders - 18-38, calcium hydroxide - 0.5-1.0, plasticizer - sodium polycarboxylate - 0.5-0.8, setting retarder - amidox - 0.2-0.5, natural shungite crushed stone of 5-20 mm size - 51-74 and water - the rest. Which is obtained by mixing shungite crushed stone with a solution of sodium polycarboxylate and amidox in water, followed by the introduction of powdered calcium hydroxide and gypsum binder into the resulting mass while stirring until a uniformly coated suspension of shungite crushed stone is obtained (Patent RU 2 405 749, published 10.12.2010, Bulletin No. 34). This composition has high physical and mechanical characteristics, but its disadvantage is that it can only be used to create blocks, panels and tiles and cannot be used as a dry building mixture, while the radiation-protective properties of this composition are insufficient.

Close to the proposed one in its technical essence and achievable result, adopted as a prototype, is a composite material and a method for its production, including beta-hemihydrate or water-soluble anhydrite, and as an additive - a natural carbon-containing mineral - shungite with a dispersion from 1 to 200 μm with the following ratio of components, wt.%: the said gypsum binder - 50-90; the said shungite - 10-50 (Patent RU No. 2232733, published 20.07.2004, Bulletin No. 20).

A method for producing a composite material that includes crushing gypsum rock, calcining it at elevated temperatures, and dry mixing the resulting gypsum binder with an additive for 30-60 minutes.

The following prototype feature coincides with the essential feature of the invention in terms of substance: gypsum binder in the form of beta-hemihydrate. In terms of the method: dry mixing of gypsum binder with fillers.

The disadvantages of the composition and method include the low strength of the resulting material, especially with a shungite content of 40 to 50%, an insufficiently high reduction in the radiation level, the method of obtaining it itself is energy-intensive in terms of obtaining the binder - anhydrite, which requires significant energy consumption during the firing of gypsum, when mixing it with finely ground shungite for 30-60 minutes and when drying products containing a large amount of water (up to 50% humidity).

The invention is aimed at developing the technology and compositions of a radiation-protective plaster dry mix with increased strength and a high degree of radiation protection in relation to gamma radiation (hereinafter referred to as a dry mix).

This is achieved by the fact that the radiation-protective plaster dry mix includes building gypsum (beta-hemihydrate, hereinafter SG) and fillers: bismuth oxide Bi ₂ O ₃ , tungsten carbide WC in the following ratio of components, wt.%: building gypsum - 15-35; bismuth oxide Bi ₂ O ₃ - 50-60; tungsten carbide WC - 15-25.

The technology of manufacturing the dry mix includes: dosing of components, loading of components into a jet-vortex mill (for example, VSM-01, OOO Agrotekhkomplekt, Belgorod), mixing and dispersion of large particles in the jet-vortex mill during two starts, unloading of the dry mix and packaging into protected paper bags. The method of using radiation-protective plaster dry mix in the construction materials industry consists of mixing the dry mix with water, at a water-solid ratio of 0.21-0.29, with continuous stirring until the required rigidity and homogeneous mass are obtained within 1-2 minutes.

A comparative analysis with the prototype shows that the declared dry mixture differs in that a mixture of bismuth oxide Bi ₂ O ₃ and tungsten carbide WC is used as a filler (additive).

In terms of the method, it differs in that the method for producing radiation-protective plaster dry mix includes dry mixing of gypsum binder with fillers. The components are dosed, loaded into a jet-vortex mill, mixed and dispersed by large particles in the jet-vortex mill during two starts, unloaded, and packaged in protected paper bags. During preparation and use, the dry mix is mixed with water. radiation protective plaster mixtures at 0.21-0.29 W/T, with continuous stirring until the required rigidity and homogeneous mass are obtained within 1-2 minutes.

Thus, the claimed technical solutions meet the invention criterion of “novelty”.

Comparison of the claimed solutions not only with the prototype, but also with other known technical solutions in this area did not confirm the presence in the latter of features that coincide with their distinctive features, or features that affect the achievement of the specified technical result. This allowed us to conclude that the invention complies with the criterion of "inventive step".

Characteristics of the components used

Gypsum G-5 was used as construction gypsum (for example, OOO Unistrom-Trading, Moscow Region, Zhukovsky). Gypsum characteristics: R _compress = 5.0 MPa; setting time 8-13 min.; R _ig = 2.5 MPa.

Bismuth oxide (α-Bi ₂ O ₃ ) according to GOST 10216-75 (for example, OOO ORT "Khimreaktivy", Yekaterinburg, Russia). Bismuth oxide is a lemon-yellow powder (long needle-shaped crystals), insoluble in water, soluble in acids. The density of α-Bi ₂ O ₃ is 8900 kg/m ³ . Particle size from 0.09 μm to 43.27 μm, modal particle diameter is 12.12 μm.

Tungsten carbide (WC) is a black nanopowder (earthy fine-crystalline mass). The density of WC is 15630 kg/ ^m3 . It is sintered by producing nanopowders of refractory metals and their carbides using a unique technology from scrap of hard-alloy products manufactured by [Pat. EP 3138932 A1 Method and device for obtaining a powder from particles of tungsten or tungsten compounds with a size in the nano-, micron or submicron range; Publication EP 3138932 A1 20170308 (DE); Application; EP 15002564 A 20150901; Priority EP 15002564 A 20150901]. Particle size from 0.08 μm to 25.9 μm, modal particle diameter is 0.09 μm.

The optimal ratio of components, expressed in their percentage content, was determined experimentally. Five compositions were created to study the properties of the dry mixture. The quantitative content of the components of the proposed dry mixture and the prototype is given in Table 1.

Table 1

Compositions of dry mix radiation-protective plaster
Researched
compositions Component content, wt. % H/T SG(beta hemihydrate) Bismuth oxide Bi ₂ O ₃ Tungsten carbide (WC) Shungite 1 35 50 15 - 0.29 2 30 52.5 17.5 - 0.27 3 25 55 20 - 0.25 4 20 57.5 22.5 - 0.23 5 15 60 25 - 0.21 Prototype 50-90 (or 70 for anhydrite) - - 10-50 0.50

H/T for SG – 0.55, for fillers – 0.15

Construction gypsum was used as a binder, which is due to the scope of application of the dry mix, chemical neutrality (environmental friendliness), ease of use and plasticity. Bismuth oxide and tungsten carbide were used as fillers (additives), which, due to their high density and large atomic numbers, provide good protection against gamma radiation, in addition, this choice is due to the fact that bismuth oxide interacts well with CG due to the acidic environment of CaSO ₄ , as a result of which the structure of CG changes, instead of bundles of thin elongated crystals randomly located in space with a large number of voids, elongated prismatic crystals of gypsum are formed partially fused with bismuth oxide particles, and tungsten carbide in the form of an earthy fine-crystalline mass effectively fills the voids and pores between the crystals, this increases the physical, mechanical and radiation-protective characteristics in relation to gamma radiation. The use of these fillers allows to reduce the W/T ratio to 0.21-0.29, which helps to increase the strength characteristics by reducing the number of voids.

To mix the components of the dry mixture of SG, bismuth oxide and tungsten carbide, a VSM-01 jet-vortex mill was used in two runs.

The loading section was loaded with 15-35 wt.% SG, 50-60 wt.% bismuth oxide Bi ₂ O _3, 15-25 wt.% tungsten carbide WC. The use of the VSM-01 jet-vortex mill for mixing is due to the fact that the components are mixed in an air stream, due to which uniform and complete mixing occurs, with other mixing methods, heavier small particles are mixed downwards, disrupting the uniformity of the distribution of components, in addition, with this method, the components themselves act as grinding media and there is no interaction with the mill walls, this is important when using abrasive particles such as tungsten carbide, as a result of which high purity of the resulting composition is achieved (absence of foreign impurities that are formed when using individual grinding media in other types of mills or when interacting with the surface material of devices for mechanical mixing), which helps to increase the strength characteristics. This method of mixing also allows to significantly increase the specific surface area of the component particles, which increases the probability of a chemical reaction between SG and bismuth oxide, in addition, it increases adhesion, which will contribute to an increase in strength characteristics and radiation-protective properties in relation to gamma radiation. Mixing during two starts allows to break up the agglomerates of tungsten carbide particles. Mixing in one start does not break up all the agglomerates of tungsten carbide particles, as a result of which the components of the dry mixture are distributed unevenly throughout the volume. The third start creates excessive abrasion and grinding of the components, which negatively affects the strength characteristics.

After mixing, the dry mixture was unloaded and then packaged into protected paper bags.

To use the radiation-protective plaster dry mix, mixing was carried out by adding the dry mix to a container with water with continuous stirring until the required rigidity and homogeneous mass were obtained for 1-2 minutes. The amount of water for hydration is 0.21-0.29 W/T. With a decrease in W/T, complete hydration of the dry mix did not occur, and with an increase in W/T, the number of voids increased, which significantly reduced the strength characteristics. After that, a mass ready for use was obtained.

Let us consider the implementation of the method for obtaining a dry mixture using composition 3 as an example (Table 1).

250 g of construction gypsum, 550 g of bismuth oxide and 200 g of tungsten carbide were loaded into the loading section. The VSM-01 jet-vortex mill was started, after which the dry mixture was unloaded. The resulting mixture was reloaded into the loading section, the VSM-01 jet-vortex mill was started and the dry mixture was unloaded. Then the dry mixture was added to the container with 250 g of water with continuous stirring for two minutes. The resulting mass was unloaded into the mold of test samples and compacted.

To prepare the prototype composition, 1000 g of calcium sulfate dihydrate were taken, crushed to obtain a fraction of 0-8 mm with further calcination at a temperature in the product layer of - 170 ° C to obtain 843 g of beta-hemihydrate gypsum, which was mixed with 168.6 g (20 wt.%) of shungite with a dispersion of 1-200 μm. The mixture was homogenized and mixed with 506 g of water to obtain the product.

To prepare the prototype composition with water-soluble anhydrite, 1000 g of calcium sulfate dihydrate were taken, crushed to obtain a fraction of 0-10 mm with subsequent calcination at a temperature in the product layer of 335 ° C. At the output, 791 g of water-soluble calcium sulfate anhydrite was obtained, after which it was mixed with 237.3 g (30 wt.%) of shungite with a dispersion of 1.0 mm. The mixture was ground in a mill for 60 minutes to obtain shungite in it with a dispersion of 1-200 μm and mixed with 475 g of water to obtain the product.

The study of compressive strength R _сж was carried out in accordance with GOST R 58276-2018 "Dry building mixtures on gypsum binder. Test methods".

Determination of radiation protection characteristics with respect to gamma radiation was carried out using a dosimeter-radiometer DKS-96 with a detection unit BDKS-96b. First, the background was measured, which is stored in the device's memory, then gamma radiation sources were lowered into a lead container, the exposure dose was measured without using a protective screen, after which the container was hermetically sealed with a sample of the test material made of a dry mixture 10 mm thick using a special groove, creating a protective screen, and then the exposure dose was measured. The following sources were used: E( ²⁰⁷ Bi) = 0.570 MeV, E( ¹³⁷ Cs) = 0.662 MeV, E( ⁶⁰ Co) = 1.252 MeV. Each source is made in the OSGI 4 geometry and is a ∅25 mm disk, in the center of which there is an active spot of ∅2.5 mm of radionuclide, sealed with a polymer material with a total thickness of 3 mm. The sources are manufactured at JSC "V.G. Khlopin Radium Institute", St. Petersburg.

Linear attenuation coefficient , cm ^–1 was calculated using formula (1)

where I ₀ is the exposure dose rate in the absence of protection, µSv/h;

I – exposure dose rate in the presence of protection, µSv/h;

d – material thickness, m.

The results of the study of the obtained mixture for compressive strength and radiation-protective characteristics in relation to gamma radiation are presented in Table 2.

Table 2

Physical, mechanical and radiation-protective properties of a composite based on a dry mixture in relation to gamma radiation

Compound Linear attenuation coefficient, cm ^-1 R _compression, MPa E( ^207Bi ) =0.570 MeV E( ¹³⁷ Cs) = 0.662 MeV E( ⁶⁰ Co) = 1.252 MeV 1 0.298 0.259 0.176 18.1 2 0.309 0.266 0.182 16.7 3 0.322 0.274 0.189 15.2 4 0.334 0.283 0.196 13.5 5 0.346 0.291 0.203 11.4 Prototype 0.114-0.142 0.102-0.129 0.063-0.086 8.6-4.9

As a result of the experiments, it was established that in order to achieve the set technical result, the proposed radiation-protective plaster dry mix should contain components in the following ratio: CG - 20-30 wt. %; bismuth oxide Bi ₂ O ₃ - 52.5-57.5 wt. %; tungsten carbide WC - 17.5-22.5 wt. % (compositions No. 2, 3, 4). At 20 wt. % and less (composition 5) CG in the composition of the radiation-protective plaster dry mix significantly worsened its physical and mechanical properties, assessed by compressive strength (Table 2), since at a low CG content the fillers are not bonded into a single material, and at more than 30 wt. % its radiation-protective characteristics with respect to gamma radiation significantly worsen. Reducing the bismuth oxide content in the radiation-protective plaster dry mix to less than 52.5 wt. % significantly reduces the linear gamma-ray attenuation coefficient and the SG structure does not change completely, and with an increase of more than 57.5 wt. %, the structure of the radiation-protective plaster dry mix was destabilized, which led to deterioration of the physical and mechanical properties. The tungsten carbide content in the polymer composite in the range of 17.5-22.5 wt. % imparts improved surface properties to the radiation-protective plaster dry mix and sufficient filling of the pores with an earthy fine-crystalline mass; with a smaller amount of the additive (composition 5), the pores of the finished radiation-protective plaster dry mix are not completely filled, and with its increase (composition 1), excessive filling occurs, which leads to the destruction of the material structure and a decrease in compressive strength.

The obtained data show that the claimed radiation-protective plaster dry mix has higher strength indicators and radiation-protective characteristics in relation to gamma radiation, represented by compressive strength and linear coefficient of gamma radiation attenuation.

Thus, the proposed solution allows for protection against gamma radiation with high physical and mechanical characteristics (compressive strength) due to the proposed composition and method: using bismuth oxide Bi ₂ O ₃ and tungsten carbide WC as fillers, which, due to their high density and large atomic numbers, provide good protection against gamma radiation; in addition, in the presence of bismuth oxide, the structure of the gypsum plaster changes: instead of bundles of thin elongated crystals randomly located in space with a large number of voids, elongated prismatic gypsum crystals are formed, partially fused with bismuth oxide particles, and tungsten carbide in the form of an earthy fine-crystalline mass effectively fills the voids and pores between the crystals; the use of a VSM-01 jet-vortex mill in two starts for mixing and dispersing the components of a dry mixture in an air flow produces uniform and complete mixing, with this method the components themselves act as grinding bodies and there is no interaction with the walls of the mill, thereby achieving high purity of the resulting composition, this mixing method also allows to significantly increase the specific surface area of the component particles, which increases the likelihood of a chemical reaction between SG and bismuth oxide, in addition, it increases adhesion; for mixing, compliance with B/T 0.21-0.29 increases strength characteristics by reducing the number of voids.

The advantages of the proposed radiation-protective plaster dry mix are as follows:

- the dry mixture has improved radiation-protective characteristics, in contrast to the prototype, namely: linear gamma radiation attenuation coefficient (for E( ^207Bi ) =0.570 MeV) 0.298-0.346 cm ^-1 ; (for E( ^137Cs ) =0.662 MeV) 0.259-0.291 cm ^-1 ; (E( ^60Co ) =1.252 MeV) 0.176-0.203 cm ^-1 , which is two to three times higher than that of the prototype.

- the dry mixture has higher physical and mechanical characteristics in terms of _Rc than the prototype: 11.4-18.1 MPa for the dry mixture and 4.9-8.6 MPa for the prototype; in maximum and minimum values, the prototype is two times smaller.

- the production of a dry mix does not require the use of calcination to obtain a binder, including water-soluble anhydrite, which significantly simplifies the production technology compared to the prototype, and the use of a VSM-01 jet-vortex mill for mixing the components ensures uniform and complete mixing, high purity of the resulting composition, increases the likelihood of a chemical reaction between SG and bismuth oxide, increases adhesion, in addition, a decrease in W/T from 0.5 (in the prototype) to 0.21-0.29 W/T in a dry mix increases compressive strength by reducing the number of voids.

Thus, the use of the proposed composition of the radiation-protective plaster dry mix and the proposed method of its production and use allows obtaining high radiation-protective characteristics in relation to gamma radiation with high physical and mechanical characteristics.

Claims (6)

1. The composition of the radiation-protective plaster dry mix, including, building gypsum and fillers, characterized in that a mixture of bismuth oxide Bi ₂ O ₃ and tungsten carbide WC is used as fillers in the following ratio of components, wt.%: building gypsum – 15-35; bismuth oxide Bi ₂ O ₃ – 50-60; tungsten carbide WC – 15-25. 2. A method for producing a radiation-protective dry plaster mix according to paragraph 1, including dry mixing of building gypsum with fillers, characterized in that the components are dosed, the components are loaded into a jet-vortex mill, large particles are mixed and dispersed in the jet-vortex mill during two starts, the dry mix is unloaded and packaged into protected paper bags. 3. A method for using a radiation-protective plaster dry mix according to item 1, which includes mixing the dry mix with water at a water-solid ratio of 0.21-0.29, with continuous stirring until the required rigidity and homogeneous mass are obtained within 1-2 minutes.