RU2830745C1 - High temperature resistant radiotransparent composite material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of composite materials, namely monolithic, radio-transparent structures for protection of antenna equipment during their operation in modes of one-sided heating up to 1400 °C. High temperature resistant radiotransparent composite material obtained by autoclave moulding from a reinforcing filler in the form of a silica thread woven into a knitted fabric and impregnated with powdered phthalonitrile binder “ФНИ 350”. Radiotransparent material at temperature of 20 °C and frequency 10⁶ Hz has a dielectric constant of 4.23, dielectric loss angle tangent is 0.02, at temperature of 20 °C and frequency 10⁸ Hz its dielectric constant is equal to 4.14, dielectric loss angle tangent is 0.002, and after exposure to high-speed heat flow with temperature of 1800 °C and holding time of 250 s at temperature of 1400 °C on the surface of the material at frequency 10⁶ Hz the dielectric constant of material is 2.71, and the tangent of the dielectric loss angle is 0.0018.

EFFECT: possibility of making high temperature resistant radiotransparent composite material and complex shaped articles from it without mechanical treatment and destruction of reinforcing components operating at temperatures up to 1400 °C on their outer surfaces without loss or reduction of values of dielectric characteristics for 60–250 seconds.

1 cl, 1 dwg, 3 tbl

Description

The invention relates to the field of composite materials, namely monolithic, radio-transparent structures for protecting antenna equipment during their operation in one-sided heating modes up to 1400°C.

Known from Russian patent 2784939 IPC C086 6/00 published 01.12.2022 A method for producing a high-temperature composite material, in which a silica thread woven into a knitted fabric is used as a reinforced silica filler, and to maintain its woven state, arselon yarn is integrated into the latter, removed by heating to 400-600 ° C for 2-12 hours in an air atmosphere, after which the silica filler is impregnated with a powdered phthalonitrile binder, laying out the calculated amount of binder between the filler layers so that the lowest and highest layers of the binder make up the masses of the inner layers, and sintering the powder at 50 ° C for 10 minutes after laying out each layer. The high-temperature composite material obtained by the specified method cannot be classified as a radio-transparent material, since the patent does not provide radio-transparency parameters - dielectric constant and dielectric loss tangent.

Known from the Russian Federation patent 2211201 IPC C04B 28/00, C04B 28/34 published on 27.08.2003 is a glass fiber laminate composition and a method for its manufacture, including glass fabric with a SiO ₂ content of at least 98% - 20 ÷ 22%, an aluminophosphate binder - 38 ÷ 40% and aluminum oxide powder - 38 ÷ 40%. The method for manufacturing glass fiber laminate includes impregnating the glass fabric with a 15% solution of organosilicon resin, applying a slip from a suspension of an aluminophosphate binder and powder to the glass fabric blanks, laying out a stack of blanks of a given thickness and, after drying at 20 ÷ 25 °C for 24 hours, heat pressing is performed at a pressure of 7.0-9.0 MPa and a final temperature of 270 °C.

The main disadvantage of the specified analogue is the presence of an organic component in the structure of the material - a finishing film of organosilicon resin on the surface of the fiberglass, which decomposes at temperatures above 400 ° C with the release of carbon (carbonization process), which worsens the radiotechnical properties of the material, especially the tangent of the dielectric loss angle. At the same time, the strength of the material decreases, since after the finishing film burns out, the effect of the acidic phosphate binder on the quartz fabric increases and destroys it. At the same time, products from such textolite are manufactured using mechanical processing methods, which leads to rupture of the reinforcing material and a decrease in the strength of the products.

The closest to the claimed invention is a highly heat-resistant radio-transparent fiberglass and a method for producing it according to Russian Federation Patent No. 2610048 IPC C04B 35/80, published on 07.02.2017, made on the basis of a phosphate binder and a finished fibrous filler with a protective coating applied to the fabric using the sol-gel technology from saturated aqueous solutions of aluminum and chromium salts. At the same time, the specified material has stable characteristics in terms of dielectric constant (3.48 ÷ 3.62) and dielectric loss tangent (0.0021 ÷ 0.0071) at 10 ¹⁰ Hz with an increase in indicators depending on an increase in temperature in the range from 20 ° C to 1200 ° C.

At the same time, a number of technical objects with antenna equipment must maintain their operability at temperatures of 1400°C, including in emergency and fire conditions. Therefore, the use of the above invention in such conditions is either impossible or requires additional testing.

The task of the authors of the claimed invention is to develop a structure and technology for producing a highly heat-resistant radio-transparent composite material (hereinafter referred to as HRCM) for use in technical objects with antenna equipment, maintaining its operability under conditions of temperature effects up to 1400°C for a specified time.

The new technical result provided by the use of the proposed invention consists in the possibility of manufacturing VRKM and complex profile products from it without mechanical processing and destruction of reinforcing components operating at temperatures of 1400°C÷1500°C on their outer surfaces without loss or reduction of dielectric characteristics for 60-250 seconds.

The specified tasks and new technical result are ensured by the fact that the VRKM, containing as a reinforcing filler a silica thread woven into a knitted fabric, impregnated with a powdered phthalonitrile binder for autoclave molding of the composition obtained in this way, is characterized in that at a temperature of 20 ° C and a frequency of 10 ⁶ Hz its dielectric constant is 4.23, the dielectric loss tangent is 0.02, at a temperature of 20 ° C and a frequency of 10 ⁸ Hz its dielectric constant is 4.14, the dielectric loss tangent is 0.002, and after exposure to a high-speed heat flow with a temperature of 1800 ° C and a holding time of 250 sec at a temperature of 1400 ° C on the surface of the material at a frequency of 10 ⁶ Hz the dielectric constant of the material is 2.71, and the dielectric loss tangent is 0.0018.

The invention is illustrated by drawings:

Fig. 1 shows the frequency dependence of the dielectric loss tangent tgδ.

Implementation of the invention

All reagents and components used are commercially available in the Russian Federation, all procedures not otherwise specified were carried out under normal conditions - at room temperature or ambient temperature in the range from 18 to 25°C.

General scheme for obtaining VRKM

The reinforcing filler used in the specified material and in the products molded from it is the PAT.01 fabric according to TU PAT.1382867.001-2022, woven from silica thread K11S6-170BA and arselon thread. The powdered phthalonitrile binder FNI350 according to TU 20.14.43-002-73047899-2020 is used as a matrix (binder).

The technological process for obtaining highly heat-resistant radio-transparent composite material and products made from it consists of the following main operations:

- cutting the fabric according to cutting maps and the number of layers (depending on the dimensions of the product);

- removal of arselon yarn from the fabric after cutting at a temperature of at least 700°C for 12-16 hours in a thermal oven with forced air blowing (the mode is different in comparison with the analogue according to the Russian Federation patent 2784939);

- laying the calculated number of layers of the web into the matrix with simultaneous, uniform layer-by-layer laying between the layers of the calculated amount of powdered binder with its layer-by-layer sintering at 50°C for 10 minutes for each layer (the mode differs in comparison with the analogue according to the Russian Federation patent 2784939);

- the resulting composition is cured in an autoclave, heating to a temperature of 190°C at a rate of 0.5°C/min with a holding time of 4 hours under a pressure of 8 bar;

- post-curing of the molded material (plates, blanks, etc.) or a product made from it in a thermal furnace at a temperature of 330°C for 8 hours and atmospheric pressure.

The physical and mechanical characteristics of the VRKM after testing of manufactured samples, carried out by an accredited laboratory under normal conditions (at 20°C), are presented in Table 1.

After testing samples of the material under the influence of a high-speed heat flow with a temperature of 1800°C and a holding time of 250 seconds at a temperature of 1400°C on the surface of the material, carried out by an accredited laboratory of the Central Institute of Aviation Materials (CIAM), its mechanical strength was:

- compressive strength - 16 MPa;

- breaking stress in bending - 9.5 MPa.

Tests to determine the permittivity ε' and the dielectric loss tangent tgδ of the VRKM samples were carried out on a Novocontrol BDS-80 measuring complex manufactured by NOVOCONTROL Technologies GmbH & Co. The results of tests to determine the values of the dielectric characteristics of the samples are presented in Table 2.

After determining the dielectric characteristics at frequencies above 10 ⁶ Hz using the Jonscher function on the specified equipment, the results of the dielectric characteristics were obtained (Table 3, Fig. 1).

The curve of the dielectric loss tangent and frequency dependence is shown in Fig. 1. As can be seen from the graphical dependence, the minimum value of the dielectric loss tangent is fixed at frequencies close to 10 ⁸ Hz. This is due to the relaxation processes occurring in the connections of the binder and reinforcing filler at frequencies greater than 10 ⁸ Hz and the increase in the value of the dielectric loss tangent. This feature of the material must be taken into account when installing and operating antenna equipment on products.

At the same time, as can be seen from the presented tables and graphic material, the value of the dielectric constant remains stably constant regardless of the thermal operating conditions of the material.

Claims (1)

A highly heat-resistant radio-transparent composite material intended for the manufacture of monolithic radio-transparent structures for the protection of antenna equipment during their operation in modes of one-sided heating up to 1400°C, obtained by autoclave molding, characterized in that a silica thread woven into a knitted fabric, impregnated with a powdered phthalonitrile binder FNI 350, is used as a reinforcing filler, at a temperature of 20°C and a frequency of 10 ⁶ Hz having a permittivity of 4.23, a dielectric loss tangent of 0.02, at a temperature of 20°C and a frequency of 10 ⁸ Hz - a permittivity of 4.14, a dielectric loss tangent of 0.002, and after exposure to a high-speed heat flow with a temperature of 1800°C and a holding time of 250 sec at a temperature of 1400°C on the surface of the material at a frequency At 10 ⁶ Hz the permittivity of the material is 2.71 and the dielectric loss tangent is 0.0018.