Graphene and MnO2 decorated graphene filled composites for electromagnetic shielding applications having excellent dielectric properties

Graphene nanoplatelets (GnP) and α-MnO₂ decorated GnP were integrated into an ethylene vinyl acetate (EVA) matrix using the dual mixing method (solution followed by melt mixing). GnP was added in 1, 3, 5, 8, 10 and 15 phr loadings into an EVA matrix to obtain composites and evaluate their various properties suitable for mechanical and electrical applications. The graphene nanoplatelets were further decorated with α-MnO₂ which was subsequently integrated into EVA at an 8 phr loading to form composites. It was observed in the GnP-EVA composites, that with an increasing GnP content, a substantial increase in the tensile strength (188%) over the neat polymer was observed at a 10 phr loading but reduced thereafter at a 15 phr loading. Dielectric permittivity of the composites were observed to increase with an increasing filler loading, the addition of α-MnO₂ also having a beneficial effect. Conductivity as well as the electromagnetic interference shielding performance were improved with increasing GnP concentrations. A maximum 28 dB of shielding was observed in the 15 phr loaded GnP-EVA composite whereas the α-MnO₂ decorated GnP-EVA composite showed a shielding efficiency of 22 dB at a concentration of 8 phr for a thickness of 2 mm with excellent thermal and mechanical properties. Overall, the composite material will find its application as a flexible EMI shielding material.     

In situ Reaction and Radiation Protection Properties of Gd(AA)3/NR Composites

Summary: For the first time, a series of Gd(AA)₃/NR (natural rubber) composites for X‐ray shielding were prepared by an in situ reaction method. Occurrence of the in situ polymerization of Gd(AA)₃ in composites during vulcanization of NR with peroxide greatly improves the dispersion level of the shielding phase by the remarkable reduction of Gd(AA)₃ particle size and the formation of small sized poly‐Gd(AA)₃ from the matrix. As expected and assumed, the X‐ray shielding properties of all composites apparently increase with the increase of the degree of dispersion of Gd(AA)₃ in composites.

The ability of the composites to shield X‐ray radiation increases with an increase in Gd(AA)₃ content and as the degree of in situ polymerization of Gd(AA)₃ increases (i.e., as t tends towards t₁₀₀).     

Compounding,mechanical and morphological properties of carbon-black-filled natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) blends

Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M_H), minimum torque (S′M_L), torque difference (S′M_H?M_L), scorch time (ts₂) and cure time (tc₉₀) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.     

Gamma ray attenuation coefficient measurement for neutron-absorbent materials

The compounds Na₂B₄O₇, H₃BO₃, CdCl₂ and NaCl and their solutions attenuate gamma rays in addition to neutron absorption. These compounds are widely used in the shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to the four compounds aforementioned, in energies 662, 778.9, 867.38, 964.1, 1085.9, 1173, 1212.9, 1299.1,1332 and 1408 keV, have been determined by the γ rays transmission method in a good geometry setup; also, these coefficients were calculated by MCNP code. A comparison between experiments, simulations and Xcom code has shown that the study has potential application for determining the attenuation coefficient of various compound materials. Experiment and computation show that H₃BO₃ with the lowest average Z has the highest gamma ray attenuation coefficient among the aforementioned compounds.     

Styrenated phenol modified nanosilica for improved thermo-oxidative and mechanical properties of natural rubber

The present work aims to prepare thermal and oxidation resistant Natural Rubber (NR) composites using antioxidant-modified nanosilica (MNS). The thermo-oxidative aging performance of the composites was evaluated by the variations in mechanical properties after aging at 100 °C for 24 h. The performance was further monitored through Scanning Electron Microscopy, Fourier Transform Infrared spectroscopy, Thermogravimetric Analysis, and Dynamic Mechanical Analysis. NR nanocomposite with 1–7.5 phr nanosilica (NS) and 3 phr MNS were prepared and its rheological properties were studied. A comparative study of the theoretical models yielded that modified Guth-Gold equation predicted Young's modulus better than other models. Thermal stability of natural rubber MNS composite was improved by 10 °C with pre-eminent mechanical properties like tensile strength and heat build-up. A linear relationship of compression set with modulus of all composites were also established. Equilibrium swelling test revealed improved crosslink density in NR MNS composite. The strong interaction between antioxidant and nanosilica enabled low migration of antioxidant in NR MNS composite. Hence its protective function after aging showed more effective than NR NS composites. These versatile functional properties of NR MNS composite suggest its potential application in electrical, electronic and high performance rubber products.     

Effect of high temperature on reduction-controlling reaction rate of agricultural waste chars and coke with steelmaking slag

In the present research, mechanical and thermal properties of high-density polyethylene/wood flour were improved by incorporating nanoclay (Cloisite 30B) and antioxidant (Irganox B225) in the compound. Design of experiments was carried out to optimize composition among nine compounds and to investigate the effect of nanoclay and antioxidant (0–5 phr) and (0–0.4 phr), respectively. The results of mechanical tests showed approximately 24% increase in the tensile strength of compounds containing 2.5 and 5.0 part per hundred (phr) of the nanoclay in the composite compared with the same samples without nanoclay. The tensile modulus of composites increased 7.3% by increasing the level of nanoclay from 0 to 2.5 phr. However, a further increase in the nanoclay content led to a 4.3% decrease in tensile modulus. Evaluation of the thermal oxidation stability of samples confirmed that the thermal oxidation of composites decreased with increasing nanoclay from 0 to 5.0 phr and increased significantly with the addition of the antioxidant.

     

A New Sodium Borate: Na[B6O8(OH)3]·6H2O·H3BO3

The structure of [B₆H₉NaO₁₄, H₃BO₃, 6H₂O] was determined by single‐crystal X‐ray diffraction and further analyzed by FTIR spectroscopy and differential thermal/thermogravimetric analysis. The asymmetric unit contains Na–O polyhedra (distorted octahedron), [B₆O₈(OH)₃]^– fundamental building blocks, one free water molecule and one free H₃BO₃ molecule. In the hexaborate anion, three B₃O₃ rings are linked by a common oxygen atom with five trigonal and one tetrahedral boron atoms. The hexaborate group is also linked to the oxygenated environment of the sodium atom by three other six‐membered rings, each of which involve two boron atoms, three oxygen atoms, and sodium as the joint atom.     

Improved pechini sol-gel fabrication of Li2B4O7/NiO/Ni3(BO3)2 nanocomposites to advanced photocatalytic performance

In current research, nano-scaled Li₂B₄O₇/NiO/Ni₃(BO₃)₂ (LiBNi) composites were fabricated through improved pechini sol–gel method for advanced photocatalytic applications to remove dye contaminations of drinking water under UV/Visible irradiation. To optimize LiBNi nanocomposites properties, different complexing agents including ethylenediaminetetraacetic acid (EDTA), citric acid, tannic acid, tartaric acid and phthalic acid were utilized in pechini sol–gel process. Various sizes and morphologies of Li₂B₄O₇/NiO/Ni₃(BO₃)₂ nanocomposites obtained that were characterized by SEM and TEM techniques. Also, to confirm crystalline and structural features of nano-sized LiBNi samples, analyses of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and energy dispersive X-ray (EDX) were performed. By consideration of UV–Vis data, band-gap of LiBNi nanocomposites premeditated is 3.35 eV. Moreover, photocatalytic degradation of Li₂B₄O₇/NiO/Ni₃(BO₃)₂ nanocomposites was examined via UV/visible waves in aqueous solution for degradation acid red 88 pollutant after 90 min. Some operative factors such as nanocatalyst concentration and irradiation type for optimized LiBNi nanocomposites were assessed for removal of drinking water contaminant.     

Excellent dielectric and actuated strain properties in CCTOx@BT(1−x)@KH560/NR system via a tunable BaTiO3 interfacial buffer layer

Dielectric elastomers (DEs) require high drive voltages to obtain large actuated strain, which limits their application in the biological field. In this work, we enhanced the dielectric properties of natural rubber (NR) composites by using core–shell structured (CaCu₃Ti₄O₁₂)_x@(BaTiO₃)_(1−x) (CCTO_x@BT_(1−x)) high-dielectric particles with an buffer layer, and adjusted the thickness of the BT buffer layer by adjusting the addition of titanate during the preparation process, and then observed the relationship between the dielectric properties of NR composites and the thickness of the BT buffer layer. In addition, we modified the CCTO_0.75@BT_0.25 fillers surface with silane coupling agent KH560 to enhance the interfacial interaction between the inorganic fillers and polymeric matrix to obtain better dispersion and greater dielectric properties. As a result of the optimization of the CCTO_0.75@BT_0.25@KH560 structure, the actuated strain performance is greatly improved. The actuated strain of 5 per hundred rubber (phr) CCTO_0.75@BT_0.25@KH560/NR is 16.3% at 74.03 kV/mm, which is 6.52 times higher than the actuated strain obtained by NR (2.5%) at 50.28 kV/mm. This work presents a method to optimize the structure of core–shell fillers by modulating the buffer layer, and provides a new idea for further preparation of dielectric elastomer materials with large actuated strain at low voltage.     

The new high-pressure borate Co7B24O42(OH)2·2 H2O—Formation of edge-sharing BO4 tetrahedra in a hydrated borate

The new borate hydrate Co₇B₂₄O₄₂(OH)₂·2 H₂O was synthesized under high-pressure/high-temperature conditions of 6 GPa and 880 °C in a Walker-type multianvil apparatus. The compound crystallizes in the orthorhombic space group Pbam (Z=2) with the lattice parameters a=819.0(2), b=2016.9(4), c=769.9(2) pm, V=1.2717(4) nm³, R₁=0.0758, wR₂=0.0836 (all data). The new structure type of Co₇B₂₄O₄₂(OH)₂·2 H₂O is built up from corner-sharing BO₄ tetrahedra forming corrugated layers, that are interconnected among each other by two edge-sharing BO₄ tetrahedra (B₂O₆ units) forming Z-shaped channels. Interestingly, the here presented structure of Co₇B₂₄O₄₂(OH)₂·2 H₂O is closely related to the structures of M₆B₂₂O₃₉·H₂O (M=Fe, Co), which exhibit BO₄ tetrahedra in an intermediate state on the way to edge-sharing BO₄ tetrahedra.     

Natural rubber composites reinforced with basic magnesium oxysulfate whiskers: Processing and ultraviolet resistance/flame retardant properties

The Magnesium sulfate whiskers (MOSw) were first modified by Stearic acid or Si69, and Natural rubber (NR)/modified-MOSw composites were prepared by blending the modified-MOSw with natural rubber latex. By adding modified-MOS_W into NR, the mechanical properties, the anti-ultraviolet aging property, flammability, and thermal stability of composites were improved obviously. The mechanical properties, crosslink density and thermal stability of composites reach the highest value at 4 wt% Si69-MOS_W. The composite with MOS_W addtion had a higher retention rate after ultraviolet irradiation and the MOS_W could improve the anti-ultraviolet aging property of rubber matrix. The modified MOS_W can effectively improve the oxygen index and the flame retardant grade of rubber composites.     

Thermodynamic properties of two zinc borates: 3ZnO·3B2O3·3.5H2O and 6ZnO·5B2O3·3H2O

Two pure zinc borates with microporous structure 3ZnO·3B₂O₃·3.5H₂O and 6ZnO·5B₂O₃·3H₂O have been synthesized and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of 3ZnO·3B₂O₃·3.5H₂O(s) and 6ZnO·5B₂O₃·3H₂O(s) in 1 mol · dm⁻³ HCl(aq) were measured by microcalorimeter at T = 298.15 K, respectively. The molar enthalpies of solution of ZnO(s) in the mixture solvent of 2.00 cm³ of 1 mol · dm⁻³ HCl(aq) in which 5.30 mg of H₃BO₃ were added were also measured. With the incorporation of the previously determined enthalpy of solution of H₃BO₃(s) in 1 mol · dm⁻³ HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(6115.3 ± 5.0) kJ · mol⁻¹ for 3ZnO·3B₂O₃·3.5H₂O and −(9606.6 ± 8.5) kJ · mol⁻¹ for 6ZnO·5B₂O₃·3H₂O at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles.     

Synthesis and Characterization of Magnesium Pyroborate by Solution Combustion and Conventional Ceramic Methods: A Comparative Study

Solution Combustion Synthesis (SCS) and ConventionalCeramic Process (CCP) were applied for the preparation of magnesium pyroborate (Mg₂B₂O₅) from Mg(NO₃)₂ · 6H₂O and H₃BO₃. Structural and morphological properties of the products were comparatively examined by XRD and FT‐IR spectroscopic measurements as well as SEM and BET techniques. The effects of synthesis conditions on the properties of products were investigated throughly by optimizing the B/Mg molar ratio and reaction duration in CCP and by optimizing the fuel (carbohydrazide) quantity in SCS. Pure Mg₂B₂O₅ (triclinicsuanite) was obtained by thermal treatment in CCP employing a B/Mg molar ratio of 3:1. It was found that the fuel must be in close proximity to the stoichiometric requirements in order to obtain the desired product in highly crystalline form from SCS. The Mg₂B₂O₅ samples obtained by both methods exhibited similar structural properties but different morphologies.     

A new polymorph of Cu3B2O6

A new polymorph of nonacopper(II) bis(orthoborate) bis(hexaoxodiborate), Cu₉(BO₃)₂(B₂O₆)₂, or Cu₃B₂O₆ with Z′ = 3, has a pseudo‐layered monoclinic structure containing BO₃ triangles and B₂O₆ units consisting of corner‐sharing BO₃ triangles and BO₄ tetrahedra. The compound was obtained during an investigation of the Li–Cu–B–O system. In contrast to the triclinic form of Cu₃B₂O₆, the layers are linked to one another by BO₄ tetrahedra.     

Room-temperature vulcanized silicone rubber/barium titanate–based high-performance nanocomposite for energy harvesting

Rubber composites were prepared for elastomer slab by mixing barium titanate (BaTiO₃), carbon nanotube (CNT), carbon black (CB), and room-temperature vulcanized (RTV) silicone rubber. An electrode was prepared from composite for energy harvesting with fillers such as CB and CNT, and RTV thinner was used to improve the processing of the specimen. At 50 phr of BaTiO₃, there is an increase in compressive modulus by 180%. There was a correlation between prestrain and biaxial strain in enhancing the energy generation. After poling of the rubber composite containing 50 phr of BaTiO₃ at 11 kV/mm, the energy harvesting was increased at all strains. In durability test at 70 phr of BaTiO₃ for 60% cyclic biaxial strain, the drop in voltage from the piezoelectric energy harvesting was almost zero for 3000 cycles.     

Design and preparation of high-aspect-ratio zinc borate whiskers and their effects on mechanical properties of PP nanocomposite

Well-dispersed, high-aspect-ratio 4ZnO·B₂O₃·H₂O whiskers (4ZnO·B₂O₃·H₂O_HARw) were synthesized by a facile hydrothermal method with the aid of ZnSO₄·7H₂O. The formation mechanism was investigated, and the results showed that Zn²⁺ and SO ₄ ^2? ions played a crucial role in the control of 4ZnO·B₂O₃·H₂O_HARw extended along [010] direction. X-ray diffraction (XRD) analysis, high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry (TG)-differential scanning calorimetry (DSC) results confirmed that the powder was 4ZnO·B₂O₃·H₂O. Scanning electron microscopy (SEM) and TEM showed that the average aspect ratio of the product was about 100. Nanocomposites of surface-modified 4ZnO·B₂O₃·H₂O_SM-HARw/PP were prepared and their mechanical properties measured. The results suggested that the mechanical properties of 4ZnO·B₂O₃·H₂O_SM-HARw/PP composites were superior to composites made with low-aspect-ratio whiskers (4ZnO·B₂O₃·H₂O_SM-LARw), which displayed poorer mechanical properties even at low addition.     

Synthesis and thermochemistry of MgO·3B2O3·3.5H2O

A new magnesium borate MgO·3B₂O₃·3.5H₂O has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B₆O₉(OH)₂]·2.5H₂O. The enthalpy of solution of MgO·3B₂O₃·3.5H₂O in approximately 1 mol dm⁻³ HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5595.02±4.85) kJ mol⁻¹ of MgO·3B₂O₃3.5H₂O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.     

Infrared,Raman and XPS spectroscopic studies of Bi2O3–B2O3–Ga2O3 glasses

Glasses with compositions 60Bi₂O₃–(40?x)B₂O₃–xGa₂O₃ (x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga₂O₃. The glass transition temperature (T_g), the onset crystallization temperature (T_x), ΔT (T_x?T_g) decrease with the content of Ga₂O₃. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga₂O₃. On the other hand, the addition of Ga₂O₃ causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi⁵⁺ and Bi³⁺ exist in 5 mol% Ga₂O₃ content, while Bi⁵⁺ amounts decrease with the increase of Ga₂O₃ contents. The glass is mainly composed of [BiO₆], [BO₃], [BO₄] and [GaO₄] polyhedra. Glasses are supposed to have layer structure. [BO₃] triangle and [BO₄] tetrahedra may be located between the [GaO₄] tetrahedral and [BiO₆] octahedra to prevent crystallization and to compensate electric charge.     

Flexible poly(dimethyl siloxane) composites enhanced with 3D porous interconnected three-component nanofiller framework for absorption-dominated electromagnetic shielding

A new poly(dimethyl siloxane) (PDMS) composite was developed based on the 3D porous interconnected framework that is fabricated from reduced graphene oxide (rGO) and Dy₂O₃ decorated single-walled carbon nanotube (Dy₂O₃@SWNT). Despite merely containing ~0.6 wt% fillers, the composite prepared by backfilling 3D framework (3D-Dy₂O₃@SWNT-rGO) with PDMS prepolymer acquires as high as 32.9 dB of absorption-dominated (92.3%–96.9%) electromagnetic interference (EMI) shielding effectiveness in X-band, and up to 47% and 52% increments of respective compressive strength and modulus at 50% strain relative to PDMS. These performances result from the excellent combination of electrical conductivity (up to 0.317 S cm⁻¹), magnetism (up to 7.1 × 10⁻⁵ emu g⁻¹ of susceptibility), and mechanical toughness (complete recovery after 80% compression) in a single three-component filler system of 3D-Dy₂O₃@SWNT-rGO. Moreover, the organic integration of mechanical flexibility of PDMS with shape-tunable ability of 3D-Dy₂O₃@SWNT-rGO enables PDMS composites developed here to EMI-shield any shape surfaces.     

Neutron Equivalent Dose Rate Measurements of Gypsum-Waste Tire Rubber Layered Structures

The neutron equivalent dose rates (µSv/h) of gypsum, steel-reinforced rubber waste tire, and gypsum-waste tire rubber sandwich composite samples were investigated. Prepared samples were irradiated with ²⁴¹Am-Be neutrons and transmission values were obtained using dose equivalent rates measured with a BF₃ neutron detector. Results were compared to those of concrete, and as a result of neutron shielding, the performance of gypsum, waste tire, and waste tire (steel-reinforced rubber) embedded gypsum samples was higher than that of concrete. This information may be useful for shielding design of nuclear application areas.