Ceramic-inorganic polymer composites for protection against electromagnetic radiation mechanical properties designing

The possibility of designing mechanical properties of ceramic-inorganic polymer composites for protection against electromagnetic radiation is considered. As a result, the mechanical properties of polymer composite based on polyamide, modified with ceramic-inorganic graphite-ferromagnetic fillers (silicon carbide, chromium oxide Cr2O3 and graphite) was received and optimized. The strength characteristics complex of ceramic-inorganic polymer composites with silicon carbide SiC, chromium oxide Cr2O3 and graphite content in diapason 5-15 % wt. were studied. It was established that the optimal strength characteristics can be received using binary modification of polyamide with ceramic-inorganic graphite-ferromagnetic fillers: polyamide 6 – SiC 10% wt. – Cr2O3 10% wt. and polyamide 6 – SiC 10% wt. – graphite 10% wt. Using mathematical modeling, it was established that the polyamide 6 – SiC 10% wt system is the most optimal for three-component complex modification with ceramic-inorganic graphite-ferromagnetic fillers – Cr2O3 10% wt. – graphite 10% wt. By design experimental-statistical mathematical models in equal regressions, mathematical optimization of mechanical properties of polymeric ceramic-inorganic composites contains for protection against electromagnetic radiation was carried out. Designed polymer ceramic-inorganic composites for protection against electromagnetic radiation according to their strength characteristics can be used for modern radio absorbing materials production.


Introduction
Nowadays, the production of various radio-electronic equipment is actively expanding.The main direction is radio-electronic equipment improving properties: reducing the size and energy losses, better accuracy and speed, etc.Many technologies are already transit to a higher frequency range.So there is a need for materials with appropriate electromagnetic characteristics, which are necessary for matching and protecting various electromagnetic ranges components.
As now there is no single-component material that could achieve a high absorption capacity in a wide frequency band.Such composite materials are used for: biological objects protection, the electromagnetic devices compatibility [1], electromagnetic waves reflection reducing [2].
Composite materials of various nature are actively used to ensure protection against electromagnetic radiation.It is also correspond the sustainable development conception.The main feature of composite materials is that they represent a combination of two or more 1254 (2023) 012010 IOP Publishing doi:10.1088/1755-1315/1254/1/012010 2 constituent components and have new properties different from the components separately properties.Composites are easy to production and provide new, unattainable for traditional materials, physico-chemical properties, such as flexibility, high strength, elasticity, as well as unique new characteristics [3].
In modern scientific literature, many compositions of ferrite components for absorbers of various ranges are described [11].These materials are intended for the electromagnetic radiation range of 0.5-12 GHz.The size of particles of ferrite powders that effectively absorb electromagnetic radiation at frequencies of 0.5-1.5 GHz is 1.65-0.7 mm, and in the range of 2.5-12 GHz -0.1 mm.The advantage of ferrite absorbers is their small thickness (several millimeters).However, they are time-consuming to manufacture and non-technological, as it is necessary to stick ferrite plates on the surface of the metal part being protected.In addition, such absorbers have an insufficiently wide band of operating frequencies [5].
By varying fillers concentration it is possible to achieve the required electromagnetic properties: high absorption coefficient, complex dielectric and magnetic permeability, and shielding level.In modern scientific sources, there is a lot of research on receiving materials for protection against electromagnetic radiation.Most research concerns the design effective materials for protection against electromagnetic radiation based on mixtures and composites of fillers with magnetic properties (such as ferrites [3], metals [6]) and various dielectrics -ceramic, polymer and other matrices [7].As an active phase (filler) of composites, carbon-containing materials (carbon nanotubes [7], graphite [12], carbonyl iron, fullerenes, etc.) [8], ferrite powders [9] are used widly.The composite materials research based on ferroelectrics [10] and multiferroics is actively developing [11].The material absorbing high-frequency electromagnetic radiation based on barium hexaferrite substituted with diamagnetic ions are demonstrated [13].It is shown that absorbing high-frequency electromagnetic radiation in such barium hexaferrite substituted to higher frequencies due to an increase in the magnetocrystal anisotropy [14].
Thermoreactive polymer composites containing silicon carbide [12], carbon fibers [15], carbon black [16] and carbon nanotubes [17] are also effective.They provide protection as radio shielding materials and coatings due to the absorption mechanisms combination [18]: natural ferromagnetic resonance, resonance of domain boundaries movement, eddy current losses and repolarization, multiple imprints and etc.
Such materials effectively provide protection against electromagnetic radiation, but their disadvantages include the complexity synthesis and high cost.
Therefore, polymer composites for protection against electromagnetic radiation based on various thermoplastic matrices (polyvinylbutyral [19], polypropylene [20], polyvinylidene chloride [21], etc.) have been recently designed.In such polymer composites, inorganic ferromagnetic fillers are used.They have better technological, operational and economic characteristics.
In our previous work [22], polymer composites for protection against the electromagnetic radiation absorption based on thermoplastic polyamide 6 and silicon carbide were received.This polymer composites are transparent in the millimeter frequency range (approximately 3 dB, this is a 2-fold attenuation), have a small absorption coefficient but low mechanical properties.
Overall efficiency electromagnetic radiation absorption for received compositions was insufficient.So further research in the framework of complex ceramic-inorganic graphiteferromagnetic fillers application was carried out as expedient.
The aim of the article is ceramic-inorganic polymer composites mechanical properties designing for protection against electromagnetic radiation.
After analysis, the graphite sample was additionally crushed to 100% to the class content less than 0.075 mm using a cylindrical mill on elastic hangers and scattered on a mechanical disperser on 0.02 mm grids.
Quality indicators of carbon graphite sample and scattering results (2 samples) are given in table 1 and table 2.
Polymer composites were production by extruding.Strength characteristics determination was carried out according to ISO 180 and ISO 178.Complex strength characteristics determination of polymeric ceramic-inorganic composites for electromagnetic radiation absorption was carried out on pendulum copra at a temperature of 20 °C.For each composition, 20 parallel measurements were made.Optimization experimental-statistical mathematical models construction in equal regressions form was carried out using the STATISTICA software.

Results and discussion
Primary studies were directed at studying the SiC, Cr 2 O 3 and graphite impact on strength properties complex of polyamide 6 compositions.From previous work [22], it was found that increasing the content of SiC in polyamide 6 led to an increase in both IR and BSDB.
Optimal content of fillers for those was found at level 5%wt.But overall efficiency of received compositions protection against electromagnetic radiation was insufficient, this article researched compositions with a higher content of SiC -10% wt., and optimized the content of Cr 2 O 3 and graphite in the range of 5-15 % wt.Also, to establish the synergistic effect the three different ceramic-inorganic graphite-ferromagnetic fillers integrated effect, polyamide 6 -SiC -Cr 2 O 3graphite systems were studied.In the table 3 shown the filler's level impact of polymer ceramicinorganic composites based on the polyamide 6 -SiC -Cr 2 O 3 -graphite system on the IR and BSDB.From the data in table 3, it can be seen that the introduction of polyamide 6 -SiC 10% wt.into the system of chromium oxide Cr 2 O 3 and graphite increases their IR and BSDB.The maximum level of the studied strength characteristics is typical for the systems of polyamide 6 -SiC 10% wt.-graphite 10% wt.Also high level of strength is also observed in the triple complex system of ceramic-inorganic fillers polyamide 6 -SiC 10% wt.-Cr 2 O 3 10% wt.-graphite 10 % wt.It can be concluded that binary modification with ceramic-inorganic graphite-ferromagnetic fillers of composites based on the systems polyamide 6 -SiC 10% wt.-Cr 2 O 3 10% wt. and polyamide 6 -SiC 10% wt.-graphite 10% wt. is optimal for increasing its strength characteristics.For three-component complex modification with ceramic-inorganic graphite-ferromagnetic fillers, the polyamide 6-SiC 10% wt.-Cr 2 O 3 10 % wt.-graphite 10 % wt.system is the most optimal.Also, while studying the spectral characteristics of the polymeric ceramic-inorganic composites, it was established that the highest level of reflection coefficient over 23 % is typical for polyamide 6 systems of 6-10% wt.silicon carbide -10% wt.chromium oxide Cr 2 O 3 -10% wt.graphite, which is related to the complex nature of the action of various ceramic-inorganic graphite-ferromagnetic fillers.This system is almost 2.5 times superior to previously obtained composites [20] in level of spectral characteristics.
For building a mathematical model to optimize mechanical properties of ceramic-inorganic polymer composites for protection against electromagnetic radiation, an analysis datas given in the table 3 was carried out.Ninth experiments were made, the composition of the composite varied within the following limits: polyamide 6 + SiC 10 % wt.-from 83.32 to 100 % wt.; graphite -from 0 to 13.04 % wt.; Cr 2 O 3 -from 0 to 13.04 % wt.At the same time, the IS values ranged from 38 to 52.5 MPa, and the BSDB values ranged from 175 to 190 MPa.Table 4 shows the pairwise correlation coefficients between indicators.It can be concluded that the indicators of IS and BSDB are interrelated, which is confirmed by the high value of the pairwise correlation coefficient between them (0.860).Table 5 shows the calculated mathematical equations that describe content of polyamide 6 + 10%wt.SiC, graphite and Cr 2 O 3 impact on the IR and BSDB, as well as statistical indicators.Multiple correlation indicators R and R 2 of the developed models are high enough (R = 0.792 − 0.838; R 2 = 0.627 − 0.702), and level of standard error 2.921-3.115MPa allow to use built equations for the IR and BSDB prediction of designed ceramic-inorganic polymer composites for protection against electromagnetic radiation.

Conclusions
The article considers the possibility to receive polymeric ceramic-inorganic composites for protection against electromagnetic radiation.As a result the polymer polyamide composites modified with ceramic-inorganic graphite-ferromagnetic fillers: SiC, Cr 2 O 3 and graphite were received.
The strength complex characteristics of compositions with carbide SiC -10%wt .were studied.For them content of Cr 2 O 3 and graphite in range 5-15%wt.was optimized.It was found that the optimal strength characteristics shows composites based on the systems polyamide 6 -SiC 10%wt.-Cr 2 O 3 10%wt.and polyamide 6 -SiC 10%wt.-graphite 10%wt.when it is binary modification with ceramic-inorganic graphite-ferromagnetic fillers.For threecomponent complex modification with ceramic-inorganic graphite-ferromagnetic fillers, the most optimal system is polyamide 6 -SiC 10%wt.-Cr 2 O 3 10%wt.-graphite 10%wt with highest mechanical and spectral properties.By design experimental-statistical mathematical models in equal regressions, mathematical optimization of polymeric ceramic-inorganic composites mechanical properties for protection against electromagnetic radiation was carried out.Received polymeric ceramic-inorganic composites for absorbing electromagnetic radiation can be used for radio-absorbing materials production according to their strength and spectral characteristics.

Table 1 .
Quality indicators of carbon graphite sample.

Table 3 .
Filler's level impact of polymer ceramic-inorganic composites based on the polyamide 6 -SiC -Cr 2 O 3 -graphite system on the IR and BSDB.

Table 4 .
Pairwise correlation coefficients of mathematical model for composition mechanical properties optimization.SiC 10 % wt.content increasing leads IR and BSDB decreasing.The same time, graphite content increasing leads IS and BSDB increasing.The Cr 2 O 3 content impact on mechanical properties is insignificant.

Table 5 .
Mathematical equations and statistical indicators of mathematical model for composition IR and BSDB optimization.