Double-layer Composites Research Articles

Single- and Double-Layer Microwave Absorbers of Cobalt Ferrite and Graphite Composite at Gigahertz Frequency

Microwave absorbers of cobalt ferrite and graphite composite have been fabricated to investigate the broadening of absorption frequency by mixing small and large particles and comparing single- and double-layer composites in order to broaden the absorption frequency and to enhance multireflection and scattering of electromagnetic wave. CoO and Fe2O3 precursors were mechanically alloyed and sintered at 800, 900, 1000 and 1100 ∘C in order to synthesise various particle sizes and shapes. A mixed sample of powders sintered at the above mentioned temperatures was also formed. The morphological, phase, and magnetic properties of these samples were studied. Two series of samples have been synthesised which were single- and double-layer composites. Single-layer composite consisted of mixed particles, and their thickness parameters were varied. Double-layer composite was also prepared with various particle sizes of CoFe2O4 as a layer and graphene as another layer. The effect of these layers as matching and absorbing layer was studied. The degree of crystallinity of CoFe2O4 was increased with increase of sintering temperature. Microstructural study showed the evolution of particle size and shape subjected to sintering temperature. Arrhenius plot showed two stages of growth process with activation energy calculated at 26.85 and 83.091 kJ/mol. The critical size of single domain of this sample plotted from the coercivity against particle size was 63.44 nm. Single-layer composite with mixed particle size was not able to show good electromagnetic (EM)-wave absorption; however double-layer composite showed good return loss. The mechanism of the EM-wave absorption of double-layer composite was discussed in this paper.

Dielectric and microwave absorption properties of CB doped SiO2f/PI double-layer composites

Carbon black (CB) with contents of 5.5 wt% and 15 wt% filled quartz glass fiber reinforced polyimide (SiO2f/PI) composite were designed and prepared. A double-layer absorbing material was designed using the two composites materials as a matching layer and an absorption layer, respectively. The microwave absorption property of single-layer and double-layer composites is calculated according to transmission line theory. The results show that the microwave absorbing property of double-layer composite is better than that of single-layer at the same thickness. When the 5.5 wt%CB doped SiO2f/PI composite is used as the matching layer with a thickness of 0.7 mm and 15 wt%CB doped SiO2f/PI composite is used as the absorption layer with a thickness of 0.9 mm, the RL (reflection loss) of the composite reaches a minimum value of −46.18 dB at 16.07 GHz. Meanwhile, the bandwidth of RL ≤ −5 dB is 5.87 GHz and the bandwidth of RL ≤ −10 dB is 3.95 GHz.

Highly oriented flake carbonyl iron/carbon fiber composite as thin-thickness and wide-bandwidth microwave absorber

Oriented flake carbonyl iron/carbon fibers (FCI/CF) composite with enhanced microwave absorption properties were prepared. The effects of orientation, the addition of CF, and the orientation direction of CF on the microwave absorption properties were investigated, respectively. Compared with the un-oriented FCI composites, higher permeability was obtained due to the FCI orientation. Anisotropic electrical properties of FCI/CF composite were achieved by changing the arranged orientation of CF. A novel double-layer microwave absorber by combining FCI/CF absorbers with different orientation of CF was designed to achieve absorbers with wide absorption band and optimal microwave absorption. The calculated absorption properties indicated that wider absorption bandwidth and thinner thickness were obtained by the single-layer oriented composites, and the absorption properties were further enhanced by the double-layer composites. The double-layer FCI/CF composites show a wider absorption frequency range of 12.0 GHz from 6 to 18 GHz with reflection loss (RL) below −5 dB at thickness of 0.8 mm.

Evaluation of Bending Strength of Abaca Reinforced Polymer Composites

Utilisation of natural fibres is a key step in fabrication of various structural (natural fibre) composites. Abaca has found its place as the most widely used natural fibre ever since it was used in combination with polypropylene to fabricate a natural fibre composite and was subsequently patented by the Daimler Chrysler for use in under floor protection in automobiles. In the present study bending strength of abaca-epoxy (polymer) composites is evaluated and analysed. Abaca-epoxy single and double layered composites were fabricated utilising hand layup technique. Prior to fabrication, abaca fibres were chemically treated with 5% wt. alkali solution (NaOH) to improve interfacial adhesion property between fibre and matrix. Flexural strengths of single and double layer composites were determined by 3-point bend tests. Thereafter a comparison is made between the flexural properties of single and double layered composites to analyse the variation in bending strength of abaca polymer composites. This study reveals that fibre loading and chemical treatment of the abaca fibres result in significant improvement of flexural strength of abaca-epoxy composites.

Structure-Stability Relationships for Fuel Cell Catalysts

Our control over the catalytic activity for the Oxygen Reduction Reaction (ORR) is greater than our present understanding of the factors affecting the stability of catalyst surface atoms. Despite the significant progress in imaging the overall changes at the nanoscale that takes place during advanced degradation test (ADT) protocols, little is known about structure-stability relationships. Nonetheless, recent developments in combining in situ electrochemical methods to inductively coupled plasma with mass spectrometry (ICP-MS) allowed identification of element specific dissolution processes. Specifically, the development of a Stationary Probe Rotating Disk Electrode (SPRDE) system provided insights on Pt dissolution and how it is structure sensitive, highly dependent on electrolyte and double layer composition, as well as influenced by the nature of the electrocatalytic reaction. This serves as a baseline to understand the functional links between structure, activity and stability for a variety of Pt-Metal alloys, how their atomic scale morphology controls stability and activity, its implications for nanoparticle systems, and what strategies can be successfully employed to improve both activity and stability of these surfaces.

Double-layer Electromagnetic Wave Absorber Based on Carbon Nanotubes Doped with La(NO3)3 and Fe3O4 Nanoparticles

Double-layer structure absorbing materials based on the impedance matching principle and transmission line theory can effectively improve the electromagnetic wave absorbing properties. In this paper, the electro-magnetic wave absorbing properties of double-layer absorbers (2 mm thickness), where multiwall carbon nanotube (MWCNT)-La(NO 3 ) 3 /polyvinyl chloride (PVC) and MWCNT-Fe 3 O 4 /PVC composites had been taken turns as the absorption layer and matching layer, were investigated in 2 – 18 GHz range. The absorbing properties of single- and double-layer structure and different each-layer thickness with two types of combinations were compared. The results showed that the design of double-layer structure for composites could effectively broaden the absorption frequency area, and increase the absorption intensity. When MWCNT-La(NO 3 ) 3 /PVC composite were used as absorption layers with 0.6 mm thickness, the absorption bandwidth ( 97 %) of double-layer composite was the widest, reaching a maximum of about 3.36 GHz, and the absorption peak value was also the lowest about – 46.02 dB at 16.24 GHz. DOI: http://dx.doi.org/10.5755/j01.ms.23.3.16279

Microwave absorption and mechanical properties of double-layer cement-based composites containing different replacement levels of fly ash

Abstract Double-layer absorbing cement-based composites with the thickness of 10 mm were prepared, including different replacement levels of fly ash (FA) in the absorbing layer as well as the matching layer for impedance matching. Waste polyethylene terephthalate bottle fragment was introduced as electromagnetic transparent reinforcement aggregate. Carbon black was used to be original absorbent in the absorbing layer. The microstructure and electromagnetic parameters of FA were closely looked at through scanning electron microscope, X-ray diffraction, and analyzer of vector network. The absorption and mechanical properties of cement-based composites were tested. It turned out that when the optimal replacement ratio of FA in the absorbing layer and matching layer gets to 50%:30%, the minimum value of reflection loss achieves −22.3 dB at 13.2 GHz; also, the value of absorption bandwidth that is effective (<−8 dB) is 6.4 GHz. Ni-Zn ferrite proves to be a feasible absorbent that is additional for the matching layer compared to what is added to the absorbing layer. The compressive strength of all the mixtures decreased, while the flexural strength decreased first and then increased with the rise of the FA replacement level.

Reduced-graphene-oxide-and-strontium-titanate-based double-layered composite: an efficient microwave-absorbing material

Microwave-absorbing materials based on reduced graphene oxide (r-GO)/strontium titanate were prepared by embedding in epoxy matrix. R-GO and strontium titanate were synthesized and characterized before composite fabrication. Microstructures of the constituent elements were studied by scanning electron microscopy and X-ray diffraction (XRD). Microwave absorption capabilities of the composite absorbers were investigated using a Vector Network Analyser in the range 8–12 GHz. A maximum reflection loss of −7.5 and −16.4 dB was obtained at 9.3 and 12.08 GHz, respectively, for 2% (w/w) r-GO-loaded epoxy composites. A maximum attenuation of −12.8 dB at 9.3 GHz was obtained for the strontium titanate/epoxy composite. However, double-layer composite with r-GO/strontium titanate/epoxy composition showed the maximum reflection loss of −15.1 dB at 9.47 GHz and −9.65 dB at 12.3 GHz. All the results are discussed in terms of complex permeability and permittivity. The study revealed that intrinsic conductivity and polarization of the r-GO particles and dielectric polarization of the strontium titanate within epoxy matrix contribute to the microwave absorption.

1,2-Indanedione — A winning ticket for developing fingermarks: A validation study

1,2-Indanedione has been extensively researched since the discovery of its fluorogenic reaction with amino acids in 1997 by Joullié et al. [1]. This current study compares the development of fingermarks on used train tickets by the three leading reagents for amino acids—ninhydrin, DFO and 1,2-indanedione. The train tickets are ideal for the task due to their high abundance and frequent use by a diverse population. However, their unique double-layer composition of a cellulose-based regular paper on one side and a thermally sensitive layer on the other requires an adjustment of the traditional development procedures. Heat, which is normally applied after dipping the specimens in the reagents solutions, had to be avoided due to darkening of the sensitive thermal layer. Instead, it has been replaced by air-drying in a fume-hood 24h prior to the recording of the results. Three groups, each containing 500 used train tickets had been treated by each of the three reagents. The results were expressed in terms of percentage of both comparable and partial fingermarks. In this study we controlled neither the quality of the fingerprint donors nor the conditions under which the latent fingermarks had been deposited or stored. However, the large number of similar exhibits which are randomly chosen allows tentative conclusions on the potential of each reagent, hence, a new criterion for the potential of fingermark development (PFD) is proposed. The PFD combines all the partial fingermarks and identifiable fingermarks (graded 1 and 2) thus, highlighting the sensitivity of the reagents. In this work, the superiority of 1,2-indanedione is demonstrated using both the traditional comparison tests as well as the suggested “PFD”.

Effects of reinforcing arrangement of kenaf fibres into unsaturated polyester for improved properties

In this current study, the mechanical, structural and morphological properties of kenaf fibre based polyester composites based on reinforcing arrangement were investigated. Fibres were placed in layers into the resin to enhance reinforcement. A hand lay-up technique was used to prepare the sandwich composite. Composites were characterized by tensile, flexural and impact testing. The structural properties as well as crystalline behaviour were observed by X-ray diffraction analysis. Additionally, the surface of the fractured samples was also examined using scanning electron microscopy to understand the interaction behaviour between the fibres and matrix. Results of the analyses revealed that single layered kenaf mat enhanced the tensile strength by 80%, whereas the double layered improved by 156%, in the presence of a fixed amount of curing agent. The thermal properties of the composites based on double layered kenaf mat were also found to improve compared to the others. The double layered composites can be used as high temperature-sustained roofing materials to replace traditional products.

Critical Assessment on Modeling and Design of Nonfaradaic CMOS Electrochemical Sensing

To assist the design process of nonfaradaic electrochemical sensors in realistic biological media, we examine multiple types of sensing operations in polyelectrolytes. By comparing the quasi-static transconductance, impedance spectroscopy, and capacitance–voltage measurements, we assess the physical contributions from the double-layer composition, overall solution resistance, and sensing surface potential under various polyelectrolytic molarities. The mixture of NaCl and MgCl2 is chosen for illustration to provide insight into circuit model parameters for nonfaradaic sensing. Our finding also shed light on the dynamics of double-layer competition and correlation, which is critical for understanding the physical phenomena occurring at the sensing interface, and accurately interpreting sensor data.

Nitrate sensing based on Pd‐Sn bimetallic composite: a comparison between a bulk electrode and a microband electrode array

This work presents a bulk electrode and a microband electrode array for electrochemical nitrate sensing in acidic medium. The microelectrode array is fabricated on silicon wafer by micro electro-mechanical system technique. Electrodepostion was carried out to modify tin onto the bulk palladium electrode and thus formed Pd-Sn bimetallic composite. On the microelectrode array, Pd and Sn were successively deposited to obtain a double-layer composite. The performance of the two kinds of electrodes towards nitrate sensing was investigated and compared. The microelectrode array showed better sensitivity and repeatability than the bulk electrode. The results are consistent with the unique properties of the microelectrode array in electrochemical analysis such as high current density and low background noise.

Development of quick-hardening infilling materials for composite railroad tracks to strengthen existing ballasted track

Abstract A composite railroad track is a rigid track system that is developed using quick-hardening infilling materials, and has the advantages of a reduced maintenance cost compared to a conventional ballasted track. Quick-hardening infilling materials were developed in this study, which does not require the processes of cleaning the aggregates crushed due to the repeated load imposed by rolling stock, and thus the materials can strengthen existing ballasted tracks with an enhanced level of efficiency and speed. Theoretical reviews of pore size, permeability, pore channel length and tortuosity depending on the size of the aggregate in ballasted tracks were conducted first to predict the influence of filling parameters of infilling materials for composite railroad tracks. Based on the theoretical filling performance analysis of ballasted tracks, a thermosetting polymer was developed, which is a 3D cross linking agent that performs redox radical polymerization reaction at room temperature. The polymer was used as a primary filling material to fill the lower ballast layer, which could not be filled by conventional cement-based filling materials. A double-layered composite was formed by filling the upper ballast layer with the ceramic-based secondary filling material using the reaction between dead-burned magnesia and acid ammonium phosphate. The performance of infilling materials was validated through strength measurement and microscopic analysis.

Ag/CNT nanocomposites and their single- and double-layer electromagnetic wave absorption properties

The electromagnetic wave absorption properties of single- and double-layer silver nanoparticle/carbon nanotube (Ag/CNT) nanocomposites were evaluated. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The double-layer composites constructed from CNT 30wt.% and Ag/CNT 30wt.% with total thickness of 3.3mm showed a minimum R.L. of ∼−52.9dB (over 99.999% absorption) at 6.3GHz. The bandwidth of reflection loss less than −10dB was observed at 3 regions, with wideness of 3.5, 0.8, and 1.5GHz. Thin absorber with large R.L. and wide response bandwidth at low and high frequency regions can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.

Double-layer electromagnetic wave absorber based on barium titanate/carbon nanotube nanocomposites

The electromagnetic wave absorption properties of double-layer barium titanate/carbon nanotube (BTO/CNT) nanocomposites were evaluated. The BTO/CNT nanomaterials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The minimum R.L. of single-layer BTO/CNT 30wt% nanocomposites sample with a thickness of 1.1mm reached ~−30.3dB (over 99.9% absorption) at 13.8GHz, and the bandwidth of the reflection loss less than −10dB (over 90% absorption) was 1.5GHz. The double-layer composites consist of BTO/CNT 30wt% (absorption layer) with thickness of 1.0mm and BTO 30wt% (matching layer) with thickness of 0.3mm showed a minimum R.L. of ~−63.7dB (over 99.9999% absorption) at 13.7GHz, and the bandwidth of the reflection loss less than −10dB was 1.7GHz. Wider response bandwidth, >1.7GHz also can be achieved with different designs of double-layer absorbers. The R.L. significantly improved and wider response bandwidth can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.

Risk zones for coke drum shell produced by explosive welding

The resulting explosive welding double-layer composite (steel 12CrMo+steel 08Cr13) was used in the manufacture of coke drum shell. The transition zone in this composite consists of several layers: recrystallization zones, local melted zones and zones containing different types of carbides. A segregation zone was found near the local melted zone. Eutectoid decomposition resulting in the formation of colonies of rod-shaped carbides occurs in this zone. Both melted and segregation zones are possible risk zones for coke drum shell. To avoid such risks it was proposed to lower the temperature down to 500°C and to increase the duration of tempering process up to 10h.

Study of the light losses in glass composites with nanosize coatings

The light losses have been studied in composites of glass with a single- or double-layer coating of composition SiO2 and/or TiO2 obtained by sol–gel technology. The measured absorption of the composite always differs from the theoretically calculated value as a consequence of the inhomogeneity and the different degree of porosity of the nanosize film and the diffusion of oxides from the substrate. The barrier properties of the SiO2 layer in double-layer composites largely depend on the rheological characteristics of the film-forming solution and the deposition regime.

Double-Layered Cement Composites with Superior Electromagnetic Wave Absorbing Properties Containing Carbon Black and Expanded Polystyrene

This paper reported that, using the method of double layer composite successfully prepared high performance of electromagnetic wave absorption materials. Such a composite is composed of a cement matching layer filled with expanded polystyrene (EPS) beads and an absorbing cement layer made of EPS beads and carbon black. The samples were tested by arching method in the frequency range of 8~18GHz. The reflectivities were revealed to be excellent, the lowest being-17dB. The new material can be used for building indoor electromagnetic radiation protection.

Electrode/Electrolyte Interface in Sulfolane-Based Electrolytes for Li Ion Batteries: A Molecular Dynamics Simulation Study

The double layer composition and structure of the mixed-solvent electrolyte tetramethylene sulfone/dimethyl carbonate (TMS/DMC) doped with LiPF6 near the graphite surface have been investigated usi...

Fire retardancy effects in single and double layered sol–gel derived TiO2 and SiO2-wood composites

Sol–gel derived TiO2 and SiO2-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites.