Paraffin Wax Matrix Research Articles

Reactive MnO2 template-assisted synthesis of double-shelled PPy hollow nanotubes to boost microwave absorption

Microwave absorbing materials (MAMs) with wide effective absorption bandwidth (EAB) and low filling ratio are highly desirable for practical applications. Rational design in components and structures is one of the effective strategies to achieve MAMs with high performance. Herein, double-shelled hollow (DSH) polypyrrole (PPy) nanotubes were synthesized with hydrochloric acid (HCl) and sodium p-styrene sulfonate (SS) co-doping polymerization process using manganese dioxide (MnO2) nanorods as a self-sacrifice template. With the increase of HCl concentration, the 1D MnO2 core diminishes gradually to form the MnO2@PPy coaxial nanostructures and finally the DSH PPy nanotube, which tunes the microwave absorption performance. Importantly, the DSH PPy nanotubes exhibit excellent microwave absorption of an optimal reflection loss of –50.4 dB and a wide EAB of 7.7 GHz with a low filling ratio of 5 wt% in a paraffin wax matrix. The excellent microwave absorption is believed to be mainly attributed to the enhanced synergistic effects of interfacial polarization and conduction loss arising from the unique DSH structure and the co-doping polymerization.

Influence of physical characteristics of graphene/Al2O3 composites employing nano particles based organic phase changing materials

In the field of energy conservation and management, PCMs are increasingly being used to store latent heat. PCMs have been infused with nanoparticles to enhance their thermal conductivity. This work presents the results of a study on the thermo-physical characteristics of an Al2O3-Graphene (Al2O3: Gr) binary composite (1 wt% Al2O3:0.5, 1, 1.5, and 2 wt% of Graphene (Gr)) with Paraffin wax (PW) as a surfactant. Thermo-gravimetric analyzer (TGA), Thermal property analyzer (TEMPOS), and UV–VIS spectrometer (UV–VIS) were all employed to characterize the materials. The latent heat capability of Paraffin Wax/Al2O3 Gr and PW/Al2O3 Graphene binary composites increased by 8.62 % and 10.02 %, as compared to Phase change material. Al2O3-1.0 and Al2O3Gr-1.0% PCMs exhibit thermal conductivities that are 130 and 180 %more than base paraffin wax. According to the Fourier Transform Infrared spectra, there was no chemical connection between the paraffin wax and nanoparticles. Thermal stability was raised by including Al2O3-Graphene particles into the paraffin wax matrix, according to TGA measurements. The produced composite's light transmission was lowered by 60.2% compared to the base PW, resulting in higher light absorption and, as a result, increased photothermal transformation. Thermal conductivity and enthalpy of the composite generate a great choice of solar photovoltaic thermal and TES systems.

Tunable high-performance microwave absorption of cobalt nanoparticles wrapped in N-self-doped carbon nanofibers at ultralow filler loadings

Manufacturing lightweight, ultralow filler loading, broad bandwidth and highly efficient microwave absorbers is still a challenge. Herein, we have synthesized Co nanoparticles decorated N-self-doped carbon nanofibers (Co@NCNFs) composite by electrospinning followed by a two-step heat treatment and investigated its electromagnetic (EM) and microwave absorption performances under different filler contents (from 2.5 to 7.5 wt%) in paraffin wax matrix. It is found that the Co@NCNFs composite has strong ferromagnetism and moderate graphitization degree as well as abundant polar groups and defects, and Co nanoparticles encapsulated by graphitic carbon layers with sizes around 45–115 nm are uniformly dispersed in the NCNFs. With increasing the filler loading, the EM attenuation ability is gradually strengthened while the impedance matching level is just the opposite. The EM absorbing properties of the composites are more superior within 5.0 wt% Co@NCNFs loading owing to the synergy of improved impedance matching and satisfactory EM dissipation ability. Under an ultralow filler loading of 2.5 wt%, the optimal reflection loss (RL) can reach as strong as −49.3 dB at 17.83 GHz with a thin thickness of 1.61 mm and the maximum effective absorption bandwidth (EAB, RL<−10.0 dB) is as wide as 5.44 GHz (12.56–16.99 GHz) at 1.92 mm. When the filler loading is only 5.0 wt%, a minimum RL value of −52.3 dB is achieved at 6.36 GHz with the thickness of 3.03 mm and the maximum EAB is 4.64 GHz (13.36–18.00 GHz) at 1.42 mm. Compared to other Co/C composite absorbers, the as-prepared Co@NCNFs composite with well-designed constitute and structure demonstrates the better comprehensive absorption performance at a much lower filler loading. Therefore, the present Co@NCNFs may be more promising for practical applications as lightweight and high-performance EM wave absorbers especially in the medium and high frequency range.

Improvement of heat sink performance using paraffin/graphite/hydrogel phase change composite coating

Phase-change materials offer high latent heat and are widely used for energy storage applications. Paraffin wax is usually used as a phase-change material. However, its application in energy storage is restricted due to its low thermal conductivity. In the present work, graphite and graphite-hydrogel are used to enhance the thermal conductivity and heat release properties of paraffin wax. Wax-graphite (W-G) and wax-graphite-hydrogel (W-G-H) composites were synthesized by the dispersion of graphite and graphite-hydrogel in paraffin wax above its melting temperature. Scanning electron microscope (SEM) analysis was used to investigate the graphite and graphite-hydrogel distribution in the paraffin wax matrix. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) characterization were performed to measure the thermal stability and phase transition properties, respectively. DSC revealed that all composites have a similar melting temperature. The W-G-H composite displayed nearly 12 folds more thermal conductivity compared to the pure paraffin wax. High temperature brings adverse impacts on energy efficiency, and even destroys a semiconductor device. The synthesized W-G-H composite is proposed to decrease the working temperature of semiconductor devices. As an applicative demonstration, the W-G-H composite film was coated at the back of the solar panel. The W-G-H composite coated solar panel displayed a surface temperature that was near ∼4 °C lower than the bare solar panel while operating. The real-time experiment indicates that the W-G-H composite has high thermal conductivity and heat release properties. The study reports fundamentally new low-cost, simple, scalable, and self-adaptive, passive cooling technology to the semiconductor industry. The proposed material can further be developed in the form of paint and its heat sink properties can be improved by introducing hydrogels doped with Li+ and Br− ions.

Electromagnetic Interference Shielding Properties of (Ni0.5Zn0.5Fe2 O4 /CI/CB) Ternary Composites-Filled Paraffin Wax Matrix

In this work, Ternary composites of NiZn ferrite/carbonyl iron/carbon black (Ni0.5Zn0.5Fe2 O4 /CI/CB) are prepared via two stages: Firstly, Ni0.5Zn0.5Fe2 O4 is prepared using a self-combustion method. After that, the process is continued via mixing CB, CI, and Ni0.5Zn0.5Fe2 O4 through the grinding balls. Three various weight ratios of Ni0.5Zn0.5Fe2 O4 /CI/CB (1:1:1, 1:1:2, and 2:1:1) with various thicknesses (2–4–6 mm) are prepared. The absorbers are prepared by dispersing (Ni0.5Zn0.5Fe2 O4 /CI/CB) composites with a weight ratio of 40% w/w within a paraffin wax matrix. X-ray diffractometry and FTIR spectroscopy are utilized in order to characterize the samples. The morphology of the powders is investigated by SEM. The electromagnetic interference (EMI) shielding properties are measured in the frequency band of 8.8–12 GHz to investigate microwave characterization. Microwave absorption materials (MAMs) show wide absorption bandwidths and reasonable surface density. The maximum shielding efficiency is 21.7 dB at 11.0 GHz for 4 mm thickness of the F/CI/CB-111 composite sample.

Synthesis and Microwave Absorption Properties of Ni0.5Zn0.5Fe2O4/CI Composite Coated with Polyaniline within Paraffin Wax Matrix

Ternary composites of polyaniline/Ni0.5Zn0.5Fe2O4/carbonyl iron (PANI/F/CI) are prepared via two stages. Firstly, Ni0.5Zn0.5Fe2O4 is prepared using a sol-gel method. After that, PANI/F/CI composites are prepared us-ing an in-situ polymerization technique of PANI in the existence of the Ni0.5Zn0.5Fe2O4 and CI. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, Ultraviolet-visible (UV-vis) spectros-copy, and Thermogravimetric analysis (TGA) are utilized to characterize samples. The morphology of the powders is investigated by Scanning electron microscope (SEM). The electromagnetic interference (EMI) shielding and microwave absorption (MA) properties are measured in the frequency band of 8.8–12 GHz to investigate the microwave characterization. The results refer those microwave absorption properties are relat-ed to the absorber thickness and the loading ratio of the absorber within a paraffin matrix. Minimal reflection loss of –30.8 dB at the matching frequency (fm) of 10.3 GHz and the absorption bandwidth under –10 dB (BW–10dB) of 2.8 GHz for 3.4 mm thickness with a surface density (SD) of 3.38 kg/m2 are noticed for the PANI/F/CI composite sample. The maximum shielding efficiency (SE) of 30.12 dB at 11.0 GHz for 3.2 mm thickness is observed for the PANI/F/CI composite sample.

Synthesis and Microwave Absorption Properties of (Ni0.5Zn0.5Fe2O4/CI/CB) Ternary Composites

In this work, ternary composites of NiZn ferrite/carbonyl iron/carbon black (Ni0.5Zn0.5Fe2O4/CI/CB) were prepared via two stages. Firstly, Ni0.5Zn0.5Fe2O4 was prepared by a self-combustion method using sucrose as a fuel. After that, the operation was continued via mixing CB, CI, and Ni0.5Zn0.5Fe2O4 through grinding balls. Three various weight ratios of Ni0.5Zn0.5Fe2O4/CI/CB (1:1:1, 1:1:2, and 2:1:1) with various thicknesses (2–4–6 mm) were prepared. The absorbers were prepared by dispersing (Ni0.5Zn0.5Fe2O4/CI/CB) composites with a weight ratio within a paraffin wax matrix of 40 % w/w. X-ray diffractometry and FTIR spectroscopy were used in order to characterize the samples. The morphology of the powders was investigated by SEM. The functional characterization was accomplished by measuring the microwave absorption properties in the fre-quency band of 8.8–12 GHz. The microwave absorption materials (MAMs) showed wide bandwidths under –10 dB in the range of 2.81–3.20 GHz and reasonable surface density in the range of 3.625–4.041 kg/m2. The absorber of 3.20 GHz bandwidth had a minimal reflection loss of –19.4 dB at the matching frequency of 9.92 GHz with a thickness of 6 mm.

Synthesis of porous Fe3O4-SnO2 core-void-shell nanocomposites as high-performance microwave absorbers

Porous Fe3O4-SnO2 core-void-shell nanocomposites with a porous Fe3O4 core and urchin-like SnO2 shell have been fabricated through the combined processes of modified stobber method with hydrothermal deposition technique. These nanocomposites can be maximize the interface areas between the core and shell that consume higher microwave energy, with the goal of improving the microwave absorption performance, i.e., of achieving strong reflection loss and wide effective bandwidth. The surface area and pore width distribution confirmed the mesoporous morphology of the porous Fe3O4-SnO2 core-void-shell nanocomposites. The microwave absorption analysis shows that the present porous Fe3O4-SnO2 core-void-shell nanocomposites with lower amount (30 wt%) in paraffin wax matrix exhibit very strong reflection loss peak of −66.5 dB (6.8 GHz) with the 3 mm absorber thickness, and have a wide effective absorbing bandwidth of 5.6 GHz (10.2–15.8 GHz). The high performance of nanocomposites can be attributed to the porous core-shell structure together with the void space. The interspace between the core and the shell can induce multiple reflections, interfacial polarization and even microwave plasma. Thus, we believe that a controlled porous structure in Fe3O4-SnO2 core-void-shell nanocomposites constitutes a novel approach to attain high-performance microwave absorbers in the field of electromagnetic wave absorption.

Deposition of a SiO2 Shell of Variable Thickness and Chemical Composition to Carbonyl Iron: Synthesis and Microwave Measurements.

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment.

Facile synthesis of lightweight 3D hierarchical NiCo2O4 nanoflowers/reduced graphene oxide composite foams with excellent electromagnetic wave absorption performance

Considering the high filling ratios, high densities, and narrow absorbing bandwidths of the current electromagnetic wave (EMW) absorbers, in this work, we successfully synthesized a 3D hierarchical NiCo2O4 nanoflowers/reduced graphene oxide (NiCo2O4/RGO) composite foam by a simple method under gentle condition. The NiCo2O4 nanoflowers and unique 3D foam structure are beneficial to the refraction and scattering of EMW, which endows the prepared 3D foam with highly efficient EMW absorption performance. When the ratio between NiCo2O4 and RGO in the foam is 1:1, 5% mass fraction of NiCo2O4/RGO foam in paraffin wax can reach a minimum reflection loss (RLmin) value of -52.2 dB with a thin thickness merely 2.6 mm. Simultaneously, the effective absorption bandwidth (EAB, RL exceeding -10 dB) is 7.04 GHz that covers the whole Ku band (10.96-18 GHz). Moreover, the effects of the thickness of the absorber and the loading ratios of the foam in paraffin wax matrix on the EMW absorption properties are also carefully investigated. The results indicate that the optimum EMW absorption performance of NiCo2O4/RGO can be tuned in different bands. The EMW absorption mechanism is ascribed to the proper impedance matching and larger dielectric and magnetic loss produced by the synergy of NiCo2O4 and RGO. Therefore, the NiCo2O4/RGO hybrid foam is ideal candidate to be used as high-efficient EMW absorbers with low filling ratio, light weight, and broad frequency bandwidths.

Hydrophobic nanosilica-stabilized graphite particles for improving thermal conductivity of paraffin wax-based phase-change materials

Phase change materials based on paraffin wax are characterized with low thermal conductivity, which could be improved by the addition of particles of a heat-conducting material, for example, graphite. However, graphite particles agglomerate in molten paraffin wax matrix and settle. In this study, the use of hydrophobic nano-sized silicon dioxide as a stabilizer was considered to obtain stable dispersions of graphite in paraffin wax. Rheological and thermophysical properties of paraffin-based mixtures containing from 1 to 5 vol. % of hydrophobic silica and from 1 to 15 vol. % of graphite were investigated. At the concentration of 3 vol. %, silica nanoparticles form a percolation structure, which is expressed in the emergence of the yield stress that is capable to prevent the sedimentation of graphite particles introduced into the mixture. It allows obtaining dispersions that are stable both in time and at passage of cooling–heating cycles. The joint influence of silica and graphite fillers on the ability of paraffin wax to accumulate and conduct heat was investigated. Thermal conductivity of dispersions at the introduction of graphite increases according to the Maxwell's model, which allows improving the thermal conductivity on 33 % from initial value at the introduction of 15 vol. % of graphite.

A study on the fabrication and microwave shielding properties of PANI/C60 heterostructures

AbstractThe in‐situ chemical oxidative polymerization was introduced to prepare the composites of polyaniline/fullerene (PANI/C60) in this work. The effects of different reaction conditions such as the concentration of C60, the concentration of doping acids, the concentration of aniline (ANI), and the reaction temperature were investigated. The composites were characterized by FTIR, scanning electron microscopy, transmission electron microscope, X‐ray diffraction, TGA, X‐ray photoelectron spectroscopy, and vector network analyzer measurements. The electromagnetic interference (EMI) shielding properties were evaluated over the frequency range of 1.0–4.5 GHz, and it was found that the average total EMI SE was 23.01 dB with additional content of 50 wt% the optimized PANI/C60 composite powder, which contains ~97.26 wt% of PANI (mainly nanorods) and ~2.74 wt% of C60 in the paraffin wax matrix. The possible composites formation mechanism and EMI shielding mechanism for PANI/C60 composites were discussed. The relationship between the conductivities of the samples and the EM shielding performance was also investigated.

A new strategy for the reinforcement of paraffin-based fuels based on cellular structures: The armored grain — Mechanical characterization

Paraffin waxes have been identified as promising hybrid rocket fuels. Though attractive from the ballistic point of view, these materials feature poor mechanical properties and, in particular, a brittle behavior making them unsuitable for application in operating systems. This study introduces a new strategy to enhance the mechanical properties of paraffin-based fuel grains manufactured at lab-scale. The implemented technique is based on the use of a 3D printed reinforcing structure embedded in the paraffin wax matrix and providing mechanical properties to the grain. This is named armored grain. The gyroid, a triply periodic cellular structure, is selected as a suitable reinforcing structure and its mechanical behavior is assessed by experimental and numerical investigations. Different 3D printable materials are considered, focusing the analysis on the differences due to their structural properties, compatibility and wettability with the paraffin fuel. In this paper, the mechanical properties of the gyroid-reinforced grains are evaluated by compression tests. The armored grains performance is compared to the mechanical behavior of fuel formulations in which reinforcement is pursued by blending the paraffin with thermoplastic polymers. The strength of the paraffin wax can be slightly enhanced by the addition of thermoplastic polymers. Under the investigated conditions (polymer mass fraction ≤10%), this reinforcing strategy yields blends with brittle behavior, while the armored grain provides a ductile behavior. The structural response of the armored grain can be tuned by exploiting different 3D printer polymers and relative densities (7%, 10%, 15%) for the gyroid reinforcement. Under the investigated conditions, the higher the relative density the stronger the mechanical properties. Albeit all the investigated polymers for gyroid reinforcement enhance the structural behavior of the paraffin wax, the nylon-based armored grain seems the most promising solution, featuring a 35% yield stress and a 296% yield strain increase over the paraffin baseline.

Expanded Graphite/Paraffin/Silicone Rubber as High Temperature Form-stabilized Phase Change Materials for Thermal Energy Storage and Thermal Interface Materials.

In this work, expanded graphite/paraffin/silicone rubber composite phase-change materials (PCMs) were prepared by blending the expanded graphite (EG), paraffin wax (PW) and silicone rubber (SR) matrix. It has been shown that PW fully penetrates into the three dimensional (3D) pores of EG to form the EG/PW particles, which are sealed by SR and evenly embedded in the SR matrix. As a result of the excellent thermal stability of SR and the capillary force from the 3D pores of EG, the EG/PW/SR PCMs are found to have good shape stability and high reliability. After being baked in an oven at 150 °C for 24 h, the shape of the EG/PW/SR PCMs is virtually unchanged, and their weight loss and latent heat drop are only 7.91 wt % and 11.3 J/g, respectively. The latent heat of the EG/PW/SR composites can reach up to 43.6 and 41.8 J/g for the melting and crystallizing processes, respectively. The super cooling of PW decreased from 4.2 to 2.4 due to the heterogeneous nucleation on the large surface of EG and the sealing effect of the SR. Meanwhile, the thermal conductivity of the EG/PW/SR PCMs reaches 0.56 W·m−1·K−1, which is about 2.8 times and 3.73 times of pure PW and pristine SR, respectively. The novel EG/PW/SR PCMs with superior shape and thermal stabilities will have a potential application in heat energy storage and thermal interface materials (TIM) for electronic devices.

Preparation and characterization of a flexible microwave absorber based on MnNiZn ferrite (Mn0.1Ni0.45Zn0.45Fe2O4) in a thermoset polyurethane matrix

In this work, spinel nanoMnNiZn ferrite (Mn0.1Ni0.45Zn0.45Fe2O4) was hosted by a thermoset polyurethane matrix (PU), to produce flexible thin nanocomposite sheets as efficient microwave absorbers. The microwave absorbers of polyurethane nanocomposites were prepared using different loading ratios of MnNiZn ferrite (70%, 75%, and 80wt%). Microwave absorption properties of the nanocomposites were characterized in the range of S- and C-band (2–8 GHz) frequency. Structural and morphological characterizations were performed using X-ray diffractometry (XRD), Fourier-transform infrared spectrophotometer (FTIR), and scanning electron microscopy (SEM). The tensile test was performed to examine the mechanical properties of the molded nanocomposites. The surface hardness was measured using Shore (A) hardness tool. The nanocomposite with 80 wt% loading percent of ferrite in PU at thickness of 5 mm exhibits the best absorption properties and has effective absorption bandwidth (≥ − 10 dB) of 4.28 GHz, with − 29.7 dB minimum reflection loss (RL) at the matching frequency (5.86 GHz) with density of only 2.403 g/cm3. The experimental results reveal that the microwave absorption properties of the synthesized nanocomposites were improved and reinforced in the case of polyurethane matrix compared to the paraffin wax matrix, through polar–polar interactions and adhesion between the filler and elastomeric matrix depending on their chemical nature. Also, the effect of thermal aging on the performance of the microwave absorption properties of PU–ferrite nanocomposite has been studied. To the best of our knowledge, the use of this cost-effective thermoset polyurethane matrix prepared from PPG, TDI, and castor oil and loaded with ferrite has not been reported before. The effect of polar–polar interactions between the matrix and the ferrite on the microwave absorption characteristics has also been investigated. The high value of reflection loss makes the obtained lightweight and flexible nanocomposite a promising microwave-absorbing material.

Electrical conductivity and electromagnetic interference shielding properties of polymer/carbon composites

Ferrocene-based polythiophene (PT) composites containing different carbon fillers like multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO) and carbon black (CB) were prepared through in situ chemical oxidative polymerization method. The prepared PT composites were characterized by employing SEM, TEM, FTIR, XRD and XPS techniques. The thermal stability of the PT composites was investigated by TG analysis. It was found that the thermal stability of PT composites was highly improved as compared with pure PT. The electrical conductivity of the composites was measured by a typical four-probe method. Electrical conductivity measurements indicated that the PT composites showed excellent electrical conductivity. Electromagnetic interference shielding effectiveness (EMI SE) of the composites was measured by using coaxial method in the frequency range of 1–4.5 GHz. The total shielding effectiveness (SET) achieved for PT composites along with MWCNT, RGO and CB was − 24 dB, − 11.27 dB, and − 10.46 dB at 50 wt% composite sample loading in the paraffin wax matrix, respectively. Therefore, the PT-MWCNT composite can be used for the EMI shielding applications.

Effect of Microstructure and Magnetic Properties of Ba-Pb-Hexaferrite Particles on EMI Shielding Behavior of Ba-Pb-Hexaferrite-Polyaniline-Wax Nanocomposites

We report that the microstructure, electrical and magnetic properties of the fillers play a very crucial role in synergistically enhancing absorption dominated electromagnetic interference (EMI) shielding in nanocomposites. We prepared nanocomposites by dispersing of varying microstructure and magnetic properties Barium-Lead hexaferrite (BaxPb1−xFe12O19; x = 0.0, 0.4, 0.8 and 1.0) particles and polyaniline (PANI) (light weight conducting species) a in microwave transparent paraffin wax matrix. The EMI shielding behavior of the nanocomposites was studied in the 8–18 GHz frequency band. The hexaferrite powder samples used in the nanocomposites were synthesized by the sol–gel method followed by calcination at 1000°C. The electron micrographs confirm that the pure Pb-hexaferrite sample (x = 0) contains well defined hexagonal plate-like particles. With increase in Ba-content in the samples, the hexagonal particles transform to smaller spherical particles, and the magnetic properties such as coercivity and saturation magnetization change. These modifications in the morphology and magnetic properties of the samples facilitate high attenuation of microwave radiation in our developed nanocomposites. The conducting species (PANI) reflects the microwave from its surface but absorbs it through conduction-loss (Ohmic absorption), whereas the (non-conducting) magnetic Ba-Pb hexaferrite particles absorb the microwave through ferromagnetic resonance but scatter it from their surface due to impedance mismatch. The scattered waves normally increase the electromagnetic smog outside the specimen. To reduce this EM-smog, the Ba-Pb hexaferrite-PANI-Wax nanocomposites provide a synergy among all the electrical and magnetic properties, which leads to very high attenuation through absorption of the scattered electromagnetic wave. Our work demonstrates that the nanocomposites containing Ba-Pb hexaferrite particles are not only efficient in shielding microwave radiation but also help in controlling the electromagnetic-smog.

Transient Behavior Analysis for Solar Energy Storage in PCM-CFM Material Using Equivalent Heat Capacity Method as Storage Model

A paraffin wax and copper foam matrix were used as a thermal energy storage material in the double passes air solar chimney (SC) collector to get ventilation effect through daytime and after sunset. Air SC collector was installed in the south wall of an insulated test room and tested with different working angles (30o, 45o and 60o). Different SC types were used; single pass, double passes flat plate collector and double pass thermal energy storage box collector (TESB). A computational model based on the finite volume method for transient tw dimensional domains was carried out to describe the heat transfer and storage in the thermal energy storage material of collector. Also, equivalent specific heat method was employed to describe the heat storage and release in the mushy zone. Experimental results referred to an increase in thermal conductivity of paraffin wax that supported by copper foam matrix more than ten times. While the ventilation effect was still active for hours after the sun set, depending on the heat storage amount. Maximum ventilation mass flow rate with TESB collector was recorded with value equals to 36.651 kg/hr., when the overall discharge coefficient that was calculated for the system equals to 0.371. Experimental results showed that the best working angle range was 45~60o, and the highest air to the collector approaching temperature appeared to the double passes flat plate collector. Results gave greater heat storage efficiency of (47)% when the maximum solar radiation was 780 W/m2 at 12.00pm, while the energy summation through duration charge time was 18460 kJ. Computational results, depending on the equivalent heat capacity method for heat storage or release from phase change material that supported by copper foam matrix, showed the behavior of paraffin wax melting and solidification situation through periodic for charge and released heat from the solar collector. Also, these results gave agreement approaching the experimental results for the heat storage in the combined heat storage material, with standard error of 16.8%.

Effect of Lipid Additives and Drug on the Rheological Properties of Molten Paraffin Wax, Degree of Surface Drug Coating, and Drug Release in Spray-Congealed Microparticles.

Paraffin wax is potentially useful for producing spray-congealed drug-loaded microparticles with sustained-release and taste-masking properties. To date, there is little information about the effects of blending lipids with paraffin wax on the melt viscosity. In addition, drug particles may not be entirely coated by the paraffin wax matrix. In this study, drug-loaded paraffin wax microparticles were produced by spray-congealing, and the effects of lipid additives on the microparticle production were investigated. The influence of lipid additives (stearic acid, cetyl alcohol, or cetyl esters) and drug (paracetamol) on the rheological properties of paraffin wax were elucidated. Fourier transform-infrared spectroscopy was conducted to investigate the interactions between the blend constituents. Selected formulations were spray-congealed, and the microparticles produced were characterized for their size, drug content, degree of surface drug coating, and drug release. The viscosity of wax-lipid blends was found to be mostly lower than the weighted viscosity when interactions occurred between the blend constituents. Molten paraffin wax exhibited Newtonian flow, which was transformed to plastic flow by paracetamol and pseudoplastic flow by the lipid additive. The viscosity was decreased with lipid added. Compared to plain wax, wax-lipid blends produced smaller spray-congealed microparticles. Drug content remained high. Degree of surface drug coating and drug release were also higher. The lipid additives altered the rheological properties and hydrophobicity of the melt and are useful for modifying the microparticle properties.

Microwave absorption by watermelon-like microspheres composed of γ-Fe2O3, microporous silica and polypyrrole

Uniform γ-Fe2O3/microporous SiO2/polypyrrole (Fe/m-SiO2/PPy) microspheres (MSs) with “watermelon-like” structures were successfully fabricated using cetyltrimethylammonium bromide (CTAB) as a pore-directing agent. In the “watermelon-like” microspheres, γ-Fe2O3 nanoparticles represented the seeds, m-SiO2 the pulp, and PPy the rind. Through synergistic harnessing of the magnetic loss properties of γ-Fe2O3 and the dielectric loss properties of the m-SiO2/PPy core/shell structure, the Fe/m-SiO2/PPy MSs displayed outstanding excellent electromagnetic wave absorption (EMWA) properties. The maximum reflection loss (RLmax) of Fe/m-SiO2/PPy was − 51.24 dB (7.44 GHz) with a thickness of 4.0 mm, with an effective absorption bandwidth (EAB) (RL < − 10 dB) of 4.16 GHz at a loading of 14.2 wt% in a paraffin wax matrix. These results conclusively demonstrate that Fe/m-SiO2/PPy MSs-containing composites are very efficient EMWA materials and that porous core/shell/shell structures offer a promising approach for the rational design of lightweight high-performance EMW absorbers.