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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Synthesis, characterization, and catalytic application of ordered mesoporous carbon–niobium oxide composites

Graphical abstract: The ordered mesoporous carbon–niobium oxide composites have been synthesized by a multi-component co-assembly method associated with a carbonization process. - Highlights: • Ordered mesoporous carbon–niobium oxide composites were synthesized. • The content of Nb{sub 2}O{sub 5} in the composites could be tuned from 38 to 75%. • Niobium species were highly dispersed in amorphous carbon framework walls. • The composites exhibited good catalytic performance in the dehydration of fructose. - Abstract: Ordered mesoporous carbon–niobium oxide composites have been synthesized by a multi-component co-assembly method associated with a carbonization process using phenolic resol as carbon source, niobium chloride as precursor and amphiphilic triblock copolymer Pluronic F127 as template. The resulting materials were characterized using a combination of techniques including differential scanning calorimetry–thermogravimetric analysis, N{sub 2} physical adsorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results show that with increasing the content of Nb{sub 2}O{sub 5} from 38 to 75% the specific surface area decreases from 306.4 to 124.5 m{sup 2} g{sup −1}, while the ordered mesoporous structure is remained. Niobium species is well dispersed in the amorphous carbon framework. The mesoporous carbon–niobium oxide composites exhibit high catalytic activity in the dehydration of fructose to 5-hydroxymethylfurfural. A 100% conversion of fructose and a 76.5% selectivity of 5-hydroxymethylfurfural were obtained over the carbon–niobium oxide composite containing 75% Nb{sub 2}O{sub 5} under the investigated reaction conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of Zn on magnetocaloric effect in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} ceramic composites

Highlights: • Synthesis of magnetic ceramic composites. • Magnetization of dual phase ceramics. • Magnetic entropy change in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} solid solution. - Abstract: We report the magnetic and magnetocaloric properties of (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x = 0.0, 0.1, 0.3, and 0.5) ceramic composites. The composite samples with nominal compositions were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order of magnetic phase transition in the composite samples. A maximum in magnetic entropy change of ∼0.75 J/kg K at 1 T has been observed in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)NiFe{sub 2}O{sub 4} sample. The values of magnetic entropy change of these composites make them attractive for potential applications. These composite samples may consider as potential material for magnetic refrigeration near room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Significant enhancement in structural, dielectric, piezoelectric and ferromagnetic properties of Ba0.9Sr0.1Zr0.1Ti0.9O3-CoFe2O4 multiferroic composites

Highlights: • (1-x)Ba{sub 0.9}Sr{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3}-(x)CoFe{sub 2}O{sub 4} multiferroic composite has been synthesized using mechano-chemical activation technique. • An improvement in dielectric, ferroelectric and piezoelectric properties over the pristine BSZT sample has been observed. • The composite samples also show a substantial enhancement in ferromagnetic characteristics compare to bare BSZT sample. - Abstract: Multiferroic composites (1 − x)Ba{sub 0.9}Sr{sub 0.1}Zr{sub 0.1}Ti{sub 0.9}O{sub 3}-(x)CoFe{sub 2}O{sub 4} (x = 0.0, 0.05, 0.10, 0.20 & 0.30) were prepared using mechanochemical activation method. Rietveld refined XRD patterns confirm the diphasic nature of composite samples. All of the diffraction peaks of (1 − x)BSZT-(x)CFO can be identified for the separate perovskite (BSZT) and inverse spinal (CFO) phases and no other impurity phase were observed for the composites. (1 − x)BSZT-(x)CFO sample with x = 0.05 have shown significant improvement in microstructural, dielectric, ferroelectric and piezoelectric properties over the pristine BSZT sample. Such an improvement in electrical properties can be attributed to larger grain size, improved density and easier ferroelectric domain wall motion inside the grain. Dielectric breakdown strength of the composites also shows a similar trend and is observed to be maximum for the sample with x = 0.05 CFO concentration. The composite samples also show a substantial enhancement in ferromagnetic characteristics and increases progressively with increase in ferrite (CFO) content.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Controllable synthesis of CNT@ZnO composites with enhanced electrochemical properties for lithium-ion battery

Highlights: • The optimized CNT@ZnO composites deliver 709.2 mAh g{sup −1} at 100 mA g{sup −1} after 50 cycles. • The structure of CNT@ZnO composites has the advantages of both ZnO and MWCNTs. • The optimized CNT@ZnO composites are promising anode materials for LIBs. - Abstract: The design and synthesis of anode materials with novel structures are one of crucial issues for developing next-generation lithium-ion battery. In this work, carbon nanotube@zinc oxide (CNT@ZnO) composites are synthesized by a liquid-phase method using CNTs as a conductive support. The design of CNT@ZnO composites combines the advantages of both ZnO nanoparticles and CNTs. The optimized CNT@ZnO composite exhibits the superior cycling and rate performance. It could deliver a discharge capacity of 709.2 mAh g{sup −1} at 100 mA g{sup −1} after 50 cycles. The electrochemical results indicate that the as-synthesized CNT@ZnO composite is superior in enhancing the electrochemical performance of ZnO-based anode materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Enhanced visible-light-driven photocatalytic activities of Bi2Fe4O9/g-C3N4 composite photocatalysts

Highlights: • The novel Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} composite photocatalysts have been designed and prepared. • Combination of Bi{sub 2}Fe{sub 4}O{sub 9} and g-C{sub 3}N{sub 4} could enhance the visible-light-driven photocatalytic degradation for RhB. • The effects of Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} weight ratios on photocatalytic performance in the composite have been discussed. • The Z-scheme photocatalytic mechanism was proposed and discussed in detail. - Abstract: A series of Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} composite photocatalysts are prepared via a facile mixing-calcination method. The crystal structures of composites are investigated by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR). The Field Emission Scanning Electron Microscope (FE-SEM) in combination with Energy Dispersive X-ray Spectroscopy (EDS) mapping analysis and Transmission Electron Microcopy (TEM) images illustrate the uniform distribution of constituent elements and clear interface between Bi{sub 2}Fe{sub 4}O{sub 9} and g-C{sub 3}N{sub 4} component. The visible-light-driven photocatalytic rates of Rhodamine B over Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} composites increase and then decrease with the increase of g-C{sub 3}N{sub 4} content. The effects of Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} weight ratios on photocatalytic performance are thoroughly discussed. Meanwhile, the active species trapping experiments and the electrochemical impedance spectra as well as the electronic energy-band structure estimation analysis demonstrate that the photocatalytic mechanism for Bi{sub 2}Fe{sub 4}O{sub 9}/g-C{sub 3}N{sub 4} composites is ascribed to the Z-scheme. In addition, the recyclability and stability experiments of the composite are also studied.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Recyclable magnetic Fe3O4@SiO2/β-NaYF4:Yb3+,Tm3+/TiO2 composites with NIR enhanced photocatalytic activity

Highlights: • Fe{sub 3}O{sub 4}@SiO{sub 2}/β-NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+}/TiO{sub 2} composites have been successfully fabricated. • The upconversion of energy transfer from β-NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} to TiO{sub 2} was confirmed. • Fe{sub 3}O{sub 4}@SiO{sub 2}/β-NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+}/TiO{sub 2} composites exhibit photocatalytic activity in NIR. • The composites can be easily magnetic separated from water after application. • The composites show good stability indicated from four recycled tests. - Abstract: To extend the activities of TiO{sub 2} to the near infrared (NIR) region and to separate and recycle photocatalysts easily is vital for the high harvest of solar energy for sustainable society. The magnetic NIR activated Fe{sub 3}O{sub 4}@SiO{sub 2}/β-NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+}/TiO{sub 2} (FS/UC/T) composites have been synthesized by using the solvothermal method by adding Fe{sub 3}O{sub 4}@SiO{sub 2} and Degussa P25 into the mixed solution of NaOH, ethanol, oleic acid, Re(NO{sub 3}){sub 3} and NH{sub 4}F. Moreover, the obtained composites were explored for photocatalytic applications. It was found that FS/UC/T emit UV–vis light under irradiation of 980 nm laser and efficient energy transfer from β-NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} to TiO{sub 2} was verified. The photodegradation experiments for treating methylene blue (MB), rhodamine B (RhB), methyl orange (MO) and colorless phenol were carried out to evaluate the photocatalytic activities of the samples. The photodegradation rates reach 76.62%, 68.48%, 30.05% and 27.16% for MB, RhB, MO and phenol under irradiation of 980 nm laser, respectively, which suggested magnetic FS/UC/T composite is an advanced NIR-driven photocatalyst. Moreover, the magnetic photocatalyst showed easy separation and good stability in the recycled tests. It suggested a promising system to utilize the NIR energy for photocatalysis based on TiO{sub 2} and to utilize the magnetic for separation of photocatalysts, which will contribute to practical environmental remediation in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Multifunctional transition metal doped titanium dioxide reduced graphene oxide composites as highly efficient adsorbents and photocatalysts

A series of novel, mesoporous transition metal doped titanium dioxide-reduced graphene oxide composites are synthesized where the dopants were Mn, Co, Ni, Mo, and W. An in-situ synthesis method was used which involves a green, economic, hydrothermal process which can be scaled up easily. The composites show high surface areas (165–245 m 2 /g) and monomodal pore size distributions with average pore diameters in the range of 3–5 nm. The homogeneous distributions of the dopants are seen in SEM-EDX mapping data. The indirect band gaps of the composite materials are in the range of 2.20–2.48 eV. The composites show excellent dye adsorption activities where 100% adsorption of Rhodamine B occurs within 5 min when Mo–TiO 2 /rGO composite is used. Furthermore, the adsorbed dye can either be desorbed or photocatalytically degraded and the composite is reusable up to 10 cycles without losing significant activity. Mo–TiO 2 /rGO composite showed excellent adsorption of both cationic and anionic dyes at neutral pH.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fatigue and fracture behavior of bulk metallic glasses and their composites

A fundamental understanding of the fatigue and fracture behavior of bulk metallic glasses (BMGs) and their composites is of critical significance for designing new BMG systems and developing new manufacturing and processing techniques so as to broaden the scope of applications of BMGs and their composites. However, the fatigue and fracture studies on BMGs are limited so far, compared to other mechanical properties. The present work reviews the fatigue and fracture behavior of BMGs and their composites, as well as that of metallic-glass films, ribbons, and wires. The grand challenge for the fatigue and fracture performance of BMGs is: What produces a large difference among the fatigue and fracture results of BMGs? According to the fatigue and fracture investigations of crystalline alloys including recently invented high entropy alloys, many factors could be involved, such as the composition, material quality, specimen geometry, chemical environment, surface condition, temperature, cyclic frequency, mean stress, and residual stress, etc. Based on this challenge, the present work will review and address the factors affecting the fatigue and fracture behavior of BMGs and their composites. Here, the mechanisms of fatigue-crack initiation, propagation, and fracture of BMGs and their composites in different loading conditions and environments will be outlined, analyzed, and discussed. Future research directions of fatigue and fracture of BMGs and their composites are provided for reference.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reduced de-doping and enhanced electrical conductivity of polyaniline filled phenol-divinylbenzene composite for potential lightning strike protection application

In this study, phenolic resin was mixed with a cross-linking agent divinylbenzene (DVB) to prepare a polyaniline-based electrically-conductive thermosetting polymer composite. It has been shown that this Phenol-DVB mixture can undergo cationic polymerization in the presence of the dodecylbenzene sulfonic acid (DBSA)-doped polyaniline (PANI). Composites with different weight ratios of phenolic resin and DVB were mixed with a fixed weight of DBSA-PANI (i.e. 30 wt. %). Increasing the phenol content in the resin system was found to improve the electrical conductivity of the composite to almost 2700%. This improvement has been assigned to the reduced de-doping of polyaniline in phenol-DVB resin. Active sites of phenol effectively attached to the β carbon of DVB and reduced the proton subtracting species of DVB, leading to reduced de-doping of PANI. This behavior was studied through various characterization techniques including differential scanning calorimetry (DSC), FT-IR spectroscopy and Scanning Electron Microscopy (SEM). Electrical conductivity measurement, mechanical properties, and in-situ electrical conductivity measurements were performed to find the optimized properties of the composite. Optimized composites prepared with the composition of 30 wt. % DBSA-PANI and 70 wt. % of phenol-DVB (50 wt. % each), have shown electrical conductivity of 0.20 S/cm and a flexural modulus of 2.1 GPa, which is a significant improvement in the flexural properties of polymer based-thermosetting composites with similar electrical conductivity. Lastly, this material can be a potential candidate for the lightning strike protection of fiber reinforced plastics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Pathway to High Rate Capability in Interconnected Composite Electrolytes: A Case Study with a Single-Ion-Conducting Polymer

In a three-dimensional interconnected polymer/ceramic composite electrolyte (3D composite), both the polymer and ceramic electrolyte phases are individually connected with a polymer-rich surface layer to provide conformal contact with the electrodes. This work investigates how the transference number of the polymer phase affects the electrochemical properties of the 3D composite. Here, we fabricate a 3D composite using a “single-ion” conducting polymer electrolyte (PE), Li 1+x+y Al x Ti 2–x Si y P 3–y O 12 (LICGC) ceramic, and compare its electrochemical properties with the neat polymer, and with a 3D composite made with a dual-ion-conducting PE (we reported previously). Our results reveal that changing the polymer phase from a dual-ion-conducting PE to a single-ion-conducting PE results in a 9-fold increase in the limiting current density, although the interfacial impedance between the polymer and LICGC ceramic remains high (and contributes significantly to the total impedance of the 3D composite). Further, the limiting current density of the 3D composite is dictated by the PE and minimally affected by the ceramic scaffold. The ceramic scaffold, however, helps to ease the concentration gradient buildup within the PE and moderately improves the overall transference number. The LICGC scaffold does not provide any additional Li dendrite resistance due to its high reactivity with Li.

25 ENERGY STORAGE↗
DOE OSTI2021

Effect of the Segmental Structure of Thermoplastic Polyurethane (Hardness) on the Interfacial Adhesion of Textile-Grade Carbon Fiber Composites

In polymer composites, the fiber–matrix interface is primarily influenced by the surface treatment of the fibers and polymer morphology. Previous studies have investigated the effect of surface treatment of carbon fiber on the mechanical properties of the resulting composites. However, very few studies have explored the chemical structural modification of polymer effect on the fiber–matrix adhesion. In this work, the interfaces of soft thermoplastic polyurethane (S-TPU) and hard-segmented TPU (H-TPU) were investigated through surface, thermal, and mechanical characterization. A textile-grade carbon fiber (TCF) with 1% concentration of epoxy sizing (an emerging material for nonaerospace applications with 450 K filament tows) was used as a reinforcement to investigate the structure–property relationship at the interface. Atomic force microscopy results showed 39% higher surface roughness for S-TPU than for H-TPU. X-ray photoelectron spectroscopy results revealed a 550% increase in C=O content, which can provide multiple hydrogen bonding networks in H-TPU, and these C=O bonds can produce a strong chemical bond at the fiber–matrix interface. Additionally, dynamic mechanical analysis and differential scanning calorimetry results confirmed the presence of hydrogen bonding that enhances the cross-linked density by 232% in H-TPU compared to S-TPU. The improved mechanical properties of H-TPU composites, such as flexural, impact and tensile by 30, 50, and 130% compared to S-TPU composites, prove that the crystallinity and hydrogen bonding significantly increase the load bearing capacity due to the strong interface. The mechanical properties of TCF–TPU composites validate the formation of chemical bonds through a nucleophilic addition reaction at the interface and improve the bond strength of the composites. Thus, tailoring the polyurethane structure broadens the performance of segmented TPU in conjunction with TCF reinforcement, which has implications for cost-effective, high-strength composites.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Engineering Calcium-Bearing Mineral/Hydrogel Composites for Effective Phosphate Recovery

Effectively recovering phosphate from wastewater streams and reutilizing it as a nutrient will critically support sustainability. Here, to capture aqueous phosphate, we developed novel mineral-hydrogel composites composed of calcium alginate, calcium phosphate (CaP), and calcium silicate (CSH) (CaP + CSH/Ca-Alg). The CaP + CSH/Ca-Alg composites were synthesized by dripping a sodium alginate (Na-Alg) solution with ionic precursors into a calcium chloride bath. To change the mineral seed’s properties, we varied the calcium bath concentrations and the ionic precursor (sodium dibasic phosphate (NaH 2 PO 4 ) and/or sodium silicate (Na 2 SiO 3 )) amounts and their ratios. The added CSH in the mineral-hydrogel composites resulted in the release of calcium and silicate ions in phosphate-rich solutions, increasing the saturation ratio with respect to calcium phosphate within the mineral-hydrogel composites. The CSH addition to the mineral-hydrogel composites doubled the phosphate removal rate while requiring lesser initial amounts of Ca and P materials for synthesis. Furthermore, by incorporating both CSH and CaP mineral seeds in composites, we achieved a final concentration of 0.25 mg-P/L from an initial 6.20 mg-P/L. Moreover, the mineral-hydrogel composites can remove phosphate even under CaP undersaturated conditions. This suggests their potential to be a widely applicable and environmentally-sustainable treatment and recovery method for nutrient-rich wastewater.

42 ENGINEERING↗
DOE OSTI2019

Stereolithography 3D Printing of Lignin-Reinforced Composites with Enhanced Mechanical Properties

Due to the availability, biodegradability, and biological effects, lignin has emerged as an interesting alternative to petroleum-based compounds for developing sustainable chemicals, materials, and composites. In this study, lignin at various concentrations was incorporated into methacrylate resin via solution blending to fabricate lignin-reinforced composites using stereolithography apparatus three-dimensional printing. Softwood kraft lignin in the amounts of 0.2, 0.4, 0.5, 0.8, and 1.0 wt % in the methacrylate resin was used as a printing ink, and the gel contents and relative contents of the residual resin in the printed samples with various lignin concentrations were measured. The effects of the lignin on the ultimate mechanical properties of the non-postcured and postcured printed composites were determined. The tensile testing results revealed that the incorporation of lignin in the composite increased the tensile strength by 46–64% and Young’s modulus by 13–37% for the postcured printed composites compared with that of the control sample (no lignin added). Employing a 0.4 wt % softwood kraft lignin, the tensile strength of the postcured printed composite reached the highest value of 49.0 MPa, which was a 60% increase in comparison to that of the control sample with 30.7 MPa. Scanning electron microscopy images of the fracture samples illustrated that the lignin-incorporated composites exhibited a rougher fracture surface that can presumably dissipate the stress, which could be a contributing factor for the mechanical enhancement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Scalable and Tunable Carbide-Phosphide Composite Catalyst System for the Thermochemical Conversion of Biomass

We have prepared composite materials of hexagonal nickel phosphide and molybdenum carbide (Mo2C) utilizing a simple and scalable two-stage synthesis method comprised of carbothermic reduction followed by hydrothermal incubation. We observe the monophasic hexagonal phosphide Ni2P in the composite at low phosphide-to-carbide (P:C) ratios. Upon increasing the proportion of P:C, the carbide surface becomes saturated, and we detect the emergence of a second hexagonal nickel phosphide phase (Ni5P4) upon annealing. We demonstrate that vapor-phase upgrading (VPU) of whole biomass via catalytic fast pyrolysis is achievable using the composite material as a catalyst, and we monitor the resulting product slates using pyrolysis gas chromatography/mass spectrometry. Our analysis of the product vapors indicates that variation of the P:C molar ratio in the composite material affords product slates of varying complexity and composition, which is indicated by the number of products and their relative proportions in the product slate. Our results demonstrate that targeted vapor product composition can be obtained, which can potentially be utilized to tune the composition of the bio-oil downstream.

09 BIOMASS FUELS↗
DOE OSTI2014

Temperature dependence of gas sensing behaviour of TiO{sub 2} doped PANI composite thin films

In the present work we have reported the effect of temperature on the gas sensing properties of TiO{sub 2} doped PANI composite thin film based chemiresistor type gas sensors for hydrogen gas sensing application. PANI and TiO{sub 2} doped PANI composite were synthesized by in situ chemical oxidative polymerization of aniline at low temperature. The electrical properties of these composite thin films were characterized by I-V measurements as function of temperature. The I-V measurement revealed that conductivity of composite thin films increased as the temperature increased. The changes in resistance of the composite thin film sensor were utilized for detection of hydrogen gas. It was observed that at room temperature TiO{sub 2} doped PANI composite sensor shows higher response value and showed unstable behavior as the temperature increased. The surface morphology of these composite thin films has also been characterized by scanning electron microscopy (SEM) measurement.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Epoxy composites based on inexpensive tire waste filler

Tire waste (TW) was recycled as raw material for the preparation of DGEBA-type epoxy composite materials. The effects of filler amount and epoxy type on the mechanical properties of the composites were investigated. Tensile strength and Young’s modulus of the composites with NPEL were generally higher than composites with NPEF. The appropriate mass level for TW in both type composites was found to be 20 wt%. The equilibrium water sorption of NPEL/TW and NPEF/TW composites for 14-day immersion was determined as 0.10 % and 0.21 %, respectively. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used for characterization of the composites.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Design, fabrication, and properties of 2-2 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution

The laminated 2-2 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were fabricated by employing Lead Zirconium Titanate ceramic as active phase, and mixture of cement powder, epoxy resin, and hardener as matrix phase with a mass proportion of 4:4:1. The dielectric, piezoelectric, and electromechanical coupling properties of the composites were studied. The composites with large total volume fraction of piezoelectric phase have large piezoelectric strain constant and relative permittivity, and the piezoelectric and dielectric properties of the composites are independent of the dimensional variations of the piezoelectric ceramic layer. The composites with small total volume fraction of piezoelectric phase have large piezoelectric voltage constant, but also large dielectric loss. The composite with gradually increased dimension of piezoelectric ceramic layer has the smallest dielectric loss, and that with the gradually increased dimension of matrix layer has the largest piezoelectric voltage constant. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with varied surface vibration amplitude of the transducer.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Evaluation of mechanical properties and durability performance of HDPE-wood composites

The objective of this work is to evaluate the mechanical properties and durability performance of bio-composite materials made from sawdust and thermoplastic polymer (HDPE). For the preparation of the composites, sawdust in different proportions with Maleic Anhydride grafted Polyethylene (MAPE) as the coupling agent was used. The thermal and mechanical properties were successively characterized. The results indicate that adding wood fillers to a polymer matrix increases the degree of crystallinity and improves the tensile strength and ductility of composites. On the contrary, resistance to water absorption decreases as a function of the wood fillers. Scanning electron microscopy (SEM) was used to analyze morphological structure alteration when exposed to intense weathering. The biodegradability of bio-composites up to 97 days was also investigated; the results indicate that, by increasing the filler content, the amount of weight loss increased as well. In other words, even though the addition of sawdust to thermoplastic polymer improves the mechanical performance of a composite material, it also accelerates the biodegradation rate of the composite. An optimum amount of filler content might compromise the effect of biodegradation and mechanical properties of composite materials.

36 MATERIALS SCIENCE↗