CN115584135B - Preparation of soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material - Google Patents

Preparation of soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material Download PDF

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CN115584135B
CN115584135B CN202211183702.9A CN202211183702A CN115584135B CN 115584135 B CN115584135 B CN 115584135B CN 202211183702 A CN202211183702 A CN 202211183702A CN 115584135 B CN115584135 B CN 115584135B
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CN115584135A (en
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汪嘉恒
魏鑫
吴玉程
宫新宇
陈志远
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Hefei University of Technology
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Abstract

The invention discloses a preparation method of a soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material, which enables the material to still realize electromagnetic shielding at the particle level through eddy current by controlling the particle size of biomass carbon to be near the critical size and combining with the cladding of an insulating outer layer, but macroscopically forms an insulator material without a conductive path. By introducing soft magnetic ferrite solid waste to be compounded with biomass carbon, the rotation of magnetic moment in electromagnetic waves can be utilized to cover electromagnetic wave absorption of decimeter wave frequency bands, so that a part of electromagnetic energy is converted into other forms of energy, and the temperature rise of the material caused by microwaves is controlled.

Description

Preparation of soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material
Technical Field
The invention relates to preparation of a soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material, which has good electromagnetic shielding and electromagnetic wave absorption performance, is an insulating electromagnetic shielding material with high resistivity, and belongs to the field of electromagnetic functional materials.
Background
Electromagnetic pollution has become one of the most serious environmental pollution problems in this century. At present, technologies such as electronic communication, 5G, internet of things, wireless charging and the like are vigorously developed, and high-level electronic integration in the aspects of new energy automobiles, unmanned, intelligent networking, aviation, aerospace and the like all enable human space to be filled with electromagnetic waves in various frequency bands, and the electromagnetic waves are mutually overlapped to seriously interfere with the operation of devices, so that the physical health of surrounding people is also seriously threatened. Electromagnetic compatibility (EMC) properties of electrical products, covering the electromagnetic radiation (EMR) and anti-external electromagnetic interference (EMI) capabilities of the device itself, have become a necessity for the industry. The world is also competing to formulate relevant mandatory standards, which have become a future trend of the industry. As a key to solving this problem, research and application of high-efficiency electromagnetic shielding materials are imperative.
The electromagnetic shielding of the currently applied products mostly adopts a metal or conductive nonmetallic shell and a coating, and the electromagnetic shielding is in an integral cladding type shielding form to prevent the emergence of internal electromagnetic waves and the entry of external electromagnetic interference. However, with the characteristics of multiple devices, multiple sensors, multiple control units, multiple chips, complex wiring harnesses and the like of products such as mobile phones, smart home, new energy automobiles and the like, the micro-type and special-shaped parts are difficult to realize integral electromagnetic shielding. Furthermore, the constant reflection of electromagnetic waves in the shield case makes the internal temperature difficult to control, which is detrimental to the heat dissipation of the device. Therefore, a high-resistivity high-impedance material which can be uniformly fused with a base material of a device, a connector, a controller, etc., and has electromagnetic wave absorption and loss, and electromagnetic shielding properties without affecting the electrical properties of the connector therein, will be an important trend for future miniaturization and improvement of EMC of integrated devices.
Disclosure of Invention
The invention aims to provide a preparation method of a soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material. According to the invention, by controlling the particle size of biomass carbon to be near the critical size and combining the cladding of the insulating outer layer, the electromagnetic shielding of the material can still be realized by eddy current at the particle level, but the insulator material without a conductive path is macroscopically formed. By introducing soft magnetic ferrite solid waste to be compounded with biomass carbon, the rotation of magnetic moment in electromagnetic waves can be utilized to cover electromagnetic wave absorption of decimeter wave frequency bands, so that a part of electromagnetic energy is converted into other forms of energy, and the temperature rise of the material caused by microwaves is controlled.
The invention discloses a preparation method of a soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material, which comprises the following steps:
step 1: fully drying and dehydrating biomass raw materials, heating to 600-2000 ℃ at a speed of 2-5 ℃/min in inert protective atmosphere or vacuum, preserving heat for 1-8h for high-temperature carbonization, naturally cooling, grinding the obtained product into biomass carbon powder with a particle size of 20-200 mu m, and separating biomass carbon powder with different particle sizes through screens with different meshes.
Step 2: dispersing 0.5-3g of biomass carbon powder obtained in the step 1 in 20ml of water or absolute ethyl alcohol, adding a certain amount of dispersing agent, and carrying out continuous ultrasonic treatment or high-speed stirring for 0.5-10h at normal temperature (25 ℃) to modify and modify interface functional groups, so that the powder is uniformly dispersed, and agglomeration among particles is reduced; carrying out suction filtration or centrifugal separation on the obtained product to obtain modified biomass carbon powder with good water solubility and dispersibility;
step 3: crushing ferrite solid waste powder to 50-1000 nm by using a mechanical ball milling mode, and purifying and homogenizing the particle size (less than 1 um) by magnetic separation and sieving; dispersing 0.1-5g ferrite powder in 20ml distilled water, adding silane coupling agent with the mass ratio of 5-45%, carrying out ultrasonic treatment for 15-60 min, and stirring in a water bath at 70 ℃ for 3-8 h; washing with water and ethanol respectively after the reaction is finished, and centrifugally separating to obtain the surface modified ferrite;
step 4: dispersing the surface modified ferrite powder obtained in the step 3 into 30ml of distilled water, and carrying out ultrasonic oscillation for 10-30 min; adding the modified biomass carbon powder obtained in the step 2 into the dispersion liquid, stirring the system in a water bath at 70 ℃ for 3-10 hours, washing with water and ethanol in sequence after the reaction is finished, and centrifugally separating to obtain ferrite modified biomass carbon powder;
step 5: and (3) coating the ferrite modified biomass carbon powder obtained in the step (4) on the particles by adopting the method of the step (5 a) or the step (5 b) respectively to coat the particles with insulating amorphous silicon oxide or insulating polymer shells:
5a: uniformly dispersing ferrite modified biomass carbon powder in a mixed solution consisting of water, alcohol and ammonia water, stirring for 0.5-2h at room temperature, slowly dripping tetraethyl orthosilicate (TEOS) into the system, keeping the room temperature, continuously stirring for 1-20h, washing the reaction product with water and ethanol, and performing suction filtration or centrifugal separation and drying to obtain the insulating amorphous SiO 2 Coated biomass carbon-based shielding material powder;
5b: uniformly dispersing ferrite modified biomass carbon powder in an insulating polymer monomer aqueous solution with the concentration of 0.05-8 mol/L, stirring for 0.5-5h at room temperature, slowly adding an initiator into the solution, continuously stirring for 1-20h at the temperature of 0-90 ℃, washing a reaction product by water and ethanol, and carrying out suction filtration or centrifugal separation and drying to obtain insulating polymer coated biomass carbon-based shielding material powder;
step 6: and (3) mixing the powder material obtained in the step (5) with a device matrix raw material, and forming to obtain the particle-level coated insulating electromagnetic shielding material with high resistivity.
The device matrix comprises resin, rubber, paint, colloid or paraffin wax and the like.
The addition mass of the insulating coated biomass carbon-based powder is 10-40% of the mass of the device matrix material.
The mixing mode comprises direct mixing, banburying or open milling.
The molding method includes injection molding, extrusion molding, compression molding, blow molding, extrusion, rotational molding, coating, and the like.
In the step 1, the biomass raw materials comprise various plants such as straw, trees, rhizomes, pericarps, fibers, seeds and the like or agricultural and forestry wastes. The screen mesh number is 900 mesh, 1600 mesh and 1800 mesh.
In the step 2, the dispersing agent may be one or more of polyvinylpyrrolidone (PVP), sodium dodecyl benzene sulfonate (SDS), sodium Dodecyl Benzene Sulfonate (SDBS), KH550, cetyl Trimethyl Ammonium Bromide (CTAB), oleic acid, tween, sodium citrate, etc., or may be other species that are compatible with the surface of biomass carbon; the addition ratio of the dispersing agent is 0.001-3mol/L.
In the step 4, the mass ratio of the modified biomass carbon powder to the surface modified ferrite powder is 1:2-10.
In the step 5a, in the mixed solution consisting of water, alcohol and ammonia water, the volume ratio of the ammonia water (the concentration is 25-28%) to the water and the alcohol is 1:2-30:25 to 60.
In the step 5a, the proportion of the ferrite modified biomass carbon powder dispersed in the mixed solution is 0.01-0.075 g/mL.
In the step 5a, the adding proportion of the tetraethyl orthosilicate accounts for 2-20% of the total solution volume.
In step 5b, the insulating polymer monomer is selected from monomers constituting a polymer having a high resistivity such as Polystyrene (PS), polymethyl methacrylate (PMMA), polyphenylene sulfide (PPS), polyamide (PA), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), polycarbonate (PC), polyoxymethylene (POM), polyethylene (PE), polyvinyl chloride (PVC), polylactic acid (PLA), and precursor monomers of doped or derivative thereof.
In the step 5b, the proportion of the ferrite modified biomass carbon powder dispersed in the insulating polymer monomer aqueous solution is 0.01-0.075 g/mL.
In the step 5b, the initiator is persulfate and a reagent for polymerizing the monomers, and the adding proportion is 1-12% of the total solution volume.
The material can be directly applied to electromagnetic shielding of various devices in the fields of new energy automobiles, electrical communication, aerospace, intelligent Internet of things, 5G and the like, can be directly applied to modes of injection molding, hot pressing, coating and the like, and is suitable for the frequency band of 1 Hz-40 GHz.
The beneficial effects of the invention are as follows:
1. according to the invention, the insulating shell is used for particle-level cladding to block conductive connection among particles, and the whole body is not insulated;
2. the invention uses common ferrite solid waste in soft magnetic production as magnetic modification, has electromagnetic wave absorption capacity of low frequency band while electromagnetic shielding, is favorable for transferring and losing electromagnetic energy and avoids temperature rise;
3. the insulating shielding material and the matrix material such as polymer can be directly used as raw materials such as injection molding, hot pressing, coating and the like, and can be directly used for molding parts and products such as connectors, switches, controllers, motors and the like, the insulating property of the insulating shielding material does not influence the electrical safety of an internal circuit, and the insulating shielding material can completely replace the existing metal conductive shielding shell;
4. the biomass raw material adopted by the invention widely exists in the nature, the cost is low, expensive equipment and energy consumption are not needed, the ferrite solid waste is an accessory of the soft magnetic industry, the recovery value is extremely low, and the environment pollution exists.
Drawings
FIG. 1 is an SEM image of biomass carbon/ferrite/PMMA prepared in example 1; SEM morphology images show that biomass carbon/ferrite/PMMA particles are irregularly shaped, ferrite small grains are tightly inlaid on the surface of the biomass carbon, and the surface of the biomass carbon/ferrite is covered with a compact coating layer, so that the compact insulating coating of PMMA on the biomass carbon/ferrite composite is proved, the dispersibility among the particles is good, and no obvious agglomeration exists.
FIG. 2 is a biomass carbon/ferrite/SiO prepared in example 2 2 SEM images of (2); SEM morphology image shows that biomass carbon/ferrite/SiO 2 The particles are irregularly shaped, ferrite/SiO 2 The particles are uniformly distributed on the biomass carbon, and the surface roughness of the particles is increased, which indicates that SiO 2 The biomass carbon/ferrite composite is densely and insulatively coated, and ferrite is aggregated in a small scale in recesses on the surface of the biomass carbon.
FIG. 3 shows the real parts of dielectric constants of samples in the frequency bands of (a) 1 to 18GHz, (b) 18 to 26.5GHz, and (c) 26.5 to 40GHz, respectively, in examples 1-3; examples 1-3 correspond to samples where epsilon' is at a higher level at 1-40GHz, where a partial band of frequencies above 5 at 1-18GHz, indicating that there are more dielectric dipoles in the biomass carbon and biomass carbon/ferrite conductive cores despite the coating of the insulating shell.
FIG. 4 shows the imaginary parts of dielectric constants of the samples in the frequency bands of (a) 1 to 18GHz, (b) 18 to 26.5GHz, and (c) 26.5 to 40GHz, respectively, in examples 1-3; examples 1-3 correspond to samples having epsilon "values up to 4 at 1-40GHz, indicating that the biomass carbon and biomass carbon/ferrite conductive cores have dielectric loss properties despite the coating of the insulating shell.
FIG. 5 shows the shielding effectiveness of the samples in the frequency bands of (a) 1 to 18GHz, (b) 18 to 26.5GHz, and (c) 26.5 to 40GHz, respectively, in examples 1 to 3. SE of the high resistivity insulating samples of examples 1-3 was mostly in the 18-26.5GHz bandAnd the SE in the 18-26.5GHz frequency band can reach 7dB at most after the SE exceeds 4 dB. Higher resistivity (greater than 10) in combination with the samples of examples 1-5 9 Omega.m), it shows that the biomass carbon and the biomass carbon/ferrite conductive core have higher dielectric characteristics, so that effective shielding of electromagnetic waves in the frequency range of 1-40GHz can be formed under the condition that the insulating shell is coated and no conductive connection exists between particles.
Detailed Description
Example 1:
(1) The dehydrated and dried biomass raw material is treated by N 2 Carbonizing at 800 ℃ in the atmosphere, grinding and sieving the product to obtain biomass carbon powder with the average particle size of 9 mu m;
(2) Dispersing 0.15g of biomass carbon powder obtained in the step (1) in 20mL of absolute ethyl alcohol, adding 1g of PVP, and continuing ultrasonic treatment for 1h until the powder is uniformly dispersed, and carrying out suction filtration and separation on the product to obtain biomass carbon powder with better dispersibility;
(3) Crushing ferrite solid waste powder to an average particle size of about 200nm by using a mechanical ball milling mode, and magnetically separating and sieving; dispersing 0.4g ferrite powder in 20mL distilled water, adding KH550 with a solution mass ratio of 30%, and ultrasonically treating at 70deg.C and N after 15min 2 Stirring in a water bath under protection for 5h; washing with water and ethanol respectively after the reaction is finished, and centrifugally separating to obtain surface modified ferrite powder;
(4) Dispersing the ferrite powder obtained in the step (3) into 30mL of distilled water, and carrying out ultrasonic oscillation for 15min; adding the biomass carbon powder obtained in the step (2) into the dispersion liquid, stirring the system in a water bath at 70 ℃ for 4 hours, washing the system with water and ethanol for three times after the reaction is finished, and centrifugally separating to obtain a ferrite modified biomass carbon powder material;
(5) Dispersing the biomass carbon/ferrite powder obtained in the step (4) in a mixed solution composed of 2ml of MMA, 18ml of deionized water and 55ml of absolute ethyl alcohol, then adding 0.02g of ammonium persulfate, stirring in a water bath at 70 ℃ for 10 hours, washing the product with water and absolute ethyl alcohol, and drying for 8 hours to obtain a biomass carbon/ferrite/PMMA composite material;
(6) Uniformly mixing and molding the biomass carbon/ferrite/PMMA powder obtained in the step (5) with paraffin wax according to the proportion of 30%, and respectively testing electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz and 26.5-40 GHz.
Example 2:
(1) The dehydrated and dried biomass raw material is treated by N 2 Carbonizing at 800 ℃ in the atmosphere, grinding and sieving the product to obtain biomass carbon powder with the average particle size of 9 mu m;
(2) Dispersing 0.15g of biomass carbon powder obtained in the step (1) in 20mL of absolute ethyl alcohol, adding 1g of PVP, and continuing ultrasonic treatment for 1h until the powder is uniformly dispersed, and carrying out suction filtration and separation on the product to obtain biomass carbon powder with better dispersibility;
(3) Crushing ferrite solid waste powder to an average particle size of about 200nm by using a mechanical ball milling mode, and magnetically separating and sieving; dispersing 0.6g ferrite powder in 20mL distilled water, adding KH550 with a solution mass ratio of 30%, and performing ultrasonic treatment at 70deg.C and N after 15min 2 Stirring in a water bath under protection for 5h; washing with water and ethanol respectively after the reaction is finished, and centrifugally separating to obtain surface modified ferrite powder;
(4) Dispersing the ferrite powder obtained in the step (3) into 30mL of distilled water, and carrying out ultrasonic oscillation for 15min; adding the biomass carbon powder obtained in the step (2) into the dispersion liquid, stirring the system in a water bath at 70 ℃ for 4 hours, washing the system with water and ethanol for three times after the reaction is finished, and centrifugally separating to obtain a ferrite modified biomass carbon powder material;
(5) Dispersing the biomass carbon/ferrite powder obtained in the step (4) in 20mL of absolute ethyl alcohol, then adding 0.1g PVP and 0.5mL ammonia water, dropwise adding 0.1mL tetraethyl orthosilicate (TEOS) under high-speed stirring, continuously stirring the solution for reacting for 8 hours, washing the product with water and absolute ethyl alcohol, and drying for 8 hours to obtain the biomass carbon/ferrite/SiO 2 A composite material;
(6) Biomass carbon/ferrite/SiO obtained in the step (5) 2 The powder is uniformly mixed with paraffin wax in a proportion of 30%, and electromagnetic parameters and shielding effectiveness of the powder at 1-18GHz, 18-26.5GHz and 26.5-40 GHz are tested respectively.
Example 3:
(1) The dehydrated and dried biomass raw material is treated by N 2 Carbonizing at 800 ℃ in the atmosphere, grinding and sieving the product to obtain biomass carbon powder with the average particle size of 9 mu m;
(2) Dispersing 0.15g of biomass carbon powder obtained in the step (1) in 20mL of absolute ethyl alcohol, adding 1g of PVP, and continuing ultrasonic treatment for 1h until the powder is uniformly dispersed, and carrying out suction filtration and separation on the product to obtain biomass carbon powder with better dispersibility;
(3) Crushing ferrite solid waste powder to an average particle size of about 200nm by using a mechanical ball milling mode, and magnetically separating and sieving; dispersing 0.8g ferrite powder in 20mL distilled water, adding KH550 with a solution mass ratio of 30%, and performing ultrasonic treatment at 70deg.C and N after 15min 2 Stirring in a water bath under protection for 5h; washing with water and ethanol respectively after the reaction is finished, and centrifugally separating to obtain surface modified ferrite powder;
(4) Dispersing the ferrite powder obtained in the step (3) into 30mL of distilled water, and carrying out ultrasonic oscillation for 15min; adding the biomass carbon powder obtained in the step (2) into the dispersion liquid, stirring the system in a water bath at 70 ℃ for 4 hours, washing the system with water and ethanol for three times after the reaction is finished, and centrifugally separating to obtain a ferrite modified biomass carbon powder material;
(5) Dispersing the biomass carbon/ferrite powder obtained in the step (4) in 20ml of styrene aqueous solution with the concentration of 5mol/L, mixing, carrying out ultrasonic treatment, stirring in a water bath at 70 ℃ for 3 hours, washing the product with water and absolute ethyl alcohol, and drying for 8 hours to obtain a biomass carbon/ferrite/PS composite material;
(6) Uniformly mixing and molding the biomass carbon/ferrite/PS powder obtained in the step (5) with paraffin wax according to the proportion of 30%, and respectively testing electromagnetic parameters and shielding effectiveness at 1-18GHz, 18-26.5GHz and 26.5-40 GHz.

Claims (9)

1. The preparation method of the soft magnetic solid waste composite biomass-based high-resistivity self-loss electromagnetic shielding material is characterized by comprising the following steps of:
step 1: fully drying the biomass raw materialDehydrating, heating to 600-2000 deg.C at 2-5 deg.C/min under inert protective atmosphere or vacuum, maintaining for 1-8 hr for high temperature carbonization, naturally cooling, and grinding into particle size of 20-200μmIs a biomass carbon powder;
step 2: dispersing 0.5-3g of biomass carbon powder obtained in the step 1 in 20ml of water or absolute ethyl alcohol, adding a certain amount of dispersing agent, and carrying out continuous ultrasonic treatment or high-speed stirring for 0.5-10h at normal temperature to modify and modify interface functional groups, so that the powder is uniformly dispersed, and agglomeration among particles is reduced; carrying out suction filtration or centrifugal separation on the obtained product to obtain modified biomass carbon powder with good water solubility and dispersibility;
step 3: crushing ferrite solid waste powder to 50-1000 nm by using a mechanical ball milling mode, and purifying and homogenizing the particle size by magnetic separation and sieving; dispersing 0.1-5g ferrite powder in 20ml distilled water, adding a silane coupling agent, performing ultrasonic treatment for 15-60 min, and stirring in a water bath at 70 ℃ for 3-8 h; washing with water and ethanol respectively after the reaction is finished, and centrifugally separating to obtain the surface modified ferrite;
step 4: dispersing the surface modified ferrite powder obtained in the step 3 into 30ml of distilled water, and carrying out ultrasonic oscillation for 10-30 min; adding the modified biomass carbon powder obtained in the step 2 into the dispersion liquid, stirring the system in a water bath at 70 ℃ for 3-10 h, washing with water and ethanol in sequence after the reaction is finished, and centrifugally separating to obtain ferrite modified biomass carbon powder;
step 5: and (3) coating the ferrite modified biomass carbon powder obtained in the step (4) on the particles by adopting the method of the step (5 a) or the step (5 b) respectively to coat the particles with insulating amorphous silicon oxide or insulating polymer shells:
5a: uniformly dispersing ferrite modified biomass carbon powder in a mixed solution consisting of water, alcohol and ammonia water, stirring at room temperature for 0.5-2h, slowly dripping tetraethyl orthosilicate into the system, keeping the room temperature and continuously stirring for 1-20h, washing the reaction product with water and ethanol, and performing suction filtration or centrifugal separation and drying to obtain the insulating amorphous SiO 2 Coated biomass carbon-based shielding material powder;
5b: uniformly dispersing ferrite modified biomass carbon powder in an insulating polymer monomer aqueous solution with the concentration of 0.05-8 mol/L, stirring for 0.5-5h at room temperature, slowly adding an initiator into the solution, continuously stirring for 1-20h at the temperature of 0-90 ℃, washing a reaction product by water and ethanol, and performing suction filtration or centrifugal separation and drying to obtain insulating polymer coated biomass carbon-based shielding material powder;
step 6: mixing the powder material obtained in the step 5 with a device matrix raw material, and forming to obtain a particle-level coated insulating electromagnetic shielding material with high resistivity;
in the step 2, the dispersing agent is one or more of polyvinylpyrrolidone, sodium dodecyl benzene sulfonate, KH550, cetyltrimethylammonium bromide, oleic acid, tween and sodium citrate; the addition ratio of the dispersing agent is 0.001-3mol/L.
2. The method of manufacturing according to claim 1, characterized in that:
in the step 4, the mass ratio of the modified biomass carbon powder to the surface modified ferrite powder is 1:2-10.
3. The method of manufacturing according to claim 1, characterized in that:
in the step 5a, in the mixed solution consisting of water, alcohol and ammonia water, the volume ratio of the ammonia water to the alcohol is 1:2-30:25-60.
4. The method of manufacturing according to claim 1, characterized in that:
in the step 5a, the proportion of the ferrite modified biomass carbon powder dispersed in the mixed solution is 0.01-0.075 g/mL.
5. The method of manufacturing according to claim 1, characterized in that:
in the step 5a, the adding proportion of the tetraethyl orthosilicate accounts for 2-20% of the total solution volume.
6. The method of manufacturing according to claim 1, characterized in that:
in step 5b, the insulating polymer monomer is selected from monomers constituting a polymer having a high resistivity of polystyrene, polymethyl methacrylate, polyphenylene sulfide, polyamide, polypropylene, polybutylene terephthalate, polyimide, polycarbonate, polyoxymethylene, polyethylene, polyvinyl chloride or polylactic acid, and precursor monomers of doped or derivative thereof.
7. The method of manufacturing according to claim 1, characterized in that:
in the step 5b, the proportion of the ferrite modified biomass carbon powder dispersed in the insulating polymer monomer aqueous solution is 0.01-0.075 g/mL.
8. The method of manufacturing according to claim 1, characterized in that:
in the step 5b, the initiator is persulfate, and the adding proportion is 1-12% of the total solution volume.
9. The method of manufacturing according to claim 1, characterized in that:
the addition mass of the insulating coated biomass carbon-based powder is 10-40% of the mass of the device matrix material.
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