Fabrication and properties of CTBN/Si3N4/cyanate ester nanocomposites

Hybrid fillers of carboxyl‐terminated liquid butadiene‐acrylonitrile/silicon nitride (CTBN/Si₃N₄) are performed to regulate the mechanical properties, heat resistance properties, dielectric properties and thermal conductivities of the bisphenol A dicyanate ester (BADCY) resins. With the 10 wt% addition of CTBN/Si₃N₄ hybrid fillers, the maximum impact, and flexural strength of the CTBN/Si₃N₄/BADCY nanocomposite is increased to 15.4 kJ/m² and 144.3 MPa, respectively. And the corresponding thermal conductivity value of the CTBN/Si₃N₄/BADCY nanocomposite is increased to 0.622 W/mK with 18 wt% addition of CTBN/Si₃N₄ hybrid fillers. Moreover, with the addition of CTBN/Si₃N₄ hybrid fillers, the heat resistance properties of the CTBN/Si₃N₄/BADCY nanocomposites are increased, but the dielectric properties get worse slightly. POLYM. COMPOS., 37:2522–2526, 2016. © 2015 Society of Plastics Engineers     

Aluminum oxide particles/silicon carbide whiskers’ synergistic effect on thermal conductivity of high-density polyethylene composites

Aluminum oxide (Al₂O₃) particles and silicon carbide (SiC) whiskers improved the thermal conductivity of high-density polyethylene (HDPE). To improve the dispersion of inorganic fillers in the matrix, 5 wt% of maleic anhydride-modified polyethylene was added into HDPE as a compatibilizer, and the hybrid matrix was denoted as mHDPE. The thermal conductivity, heat resistance, and tensile properties of resulting HDPE composites were characterized. The results showed that the thermal conductivity reached its maximum value of 0.8876 W/(m K) at 1/4 weight ratio of Al₂O₃/SiC, which was 110.3, 54.8, and 8.8% higher than that of pure HDPE, mHDPE/Al₂O₃, and mHDPE/SiC composites, in the order given, indicating that hybrid fillers have synergistic effect on the thermal conductivity of HDPE composites. Moreover, they also have a synergistic effect on the heat resistance and Young’s modulus. As the SiC content increases, the heat resistance of the composites increases at first and then falls, and the maximum VST is reached at an Al₂O₃/SiC weight ratio of 3/2, which is 5.4 °C higher than that of HDPE. The maximum Young’s modulus of the composites (1160 MPa) is obtained at an Al₂O₃/SiC weight ratio of 1/4, and the yield strength increases gradually as the SiC whiskers’ content increases.     

The effect of noncondensable gas on heat transfer in the preheater of the sewage sludge drying system

We used a shell-and-tube type preheater to investigate the effect of noncondensable gas on heat transfer. In the preheater of the drying system, heat is exchanged between steam-air mixed gas which is dryer outlet gas and sewage sludge. To evaluate the performances of the preheater, water was first used in the tube-side material instead of sewage sludge and steam-air mixed gas in the shell-side material. The test variables were as follows: mixed gas inlet temperatures range from 95 to 120 °C; inlet air content, m _air /m _steam from 55 to 83%; tube-side water flow rate from 42 to 62 kg/h. The shell-side heat transfer coefficient varied from 150 to 550W/m²K, which corresponds to the amount of noncondensable gas in the steam-air mixed gas and the overall heat transfer coefficient varied from 60 to 210W/m²K. Using sewage sludge as a tube-side material the overall heat transfer coefficient varied from 60 to 130W/m2K and the outlet temperature of sewage sludge was above 90 °C, which is high enough for reducing energy consumption in the dryer by preheating the sewage sludge.     

Microporous Materials Derived from the Thermal Decomposition of the Titania/PDMS Hybrid Particles

A microporous material containing titania nano-particles was obtained by thermal decomposition of the titania/silicone hybrid spherical particles. The titania/silicone hybrid spherical particles were converted to porous silica with the BET surface area of about 360 m²/g by heat treatment at 400^∘C in air, while the spherical morphology of the particles was retained. The thermal decomposition of the organic groups of the hybrid particles was accompanied with the generation of the micropores and the transformation of the silicone to silica. The thermal decomposition of the organic groups and the micro-structural change of the hybrid particles were investigated by XRD, N₂ adsorption/desorption isotherm, CHN elemental analysis, FT-IR, and solid-state ²⁹Si magic angle spinning (MAS) NMR.     

Preparation of novel silica/poly(butylene succinate-co-adipate) organic–inorganic hybrid biodegradable material via sol–gel method

Silica/poly(butylene succinate-co-adipate) organic–inorganic hybrid biodegradable materials were prepared by the sol–gel method. Fourier-transform infrared spectroscopy (FT-IR) and Thermogravimetry/differential thermal analysis (TG/DTA) indicated that the inorganic (SiO₂, C₆H₅SiO_3/2) and organic (PBSA) components were well dispersed in the hybrid material. Heat resistant test shows that the hybrid material was both heat resistant and flexible. The presence of phenyl groups and siloxane network was responsible for the flexibility and heat resistance.     

Experimental investigation on the mechanical,structural and thermal properties of Cu–ZrO2 nanocomposites hybridized by graphene nanoplatelets

Hybrid Cu–ZrO₂/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on the mechanical and electrical properties of the produced hybrid nanocomposite was investigated while maintaining ZrO₂ mass fraction constant at 5%. High-energy ball milling was applied for mixing powders followed by compaction and sintering. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO₂/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO₂ nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. The compressive strength increased with the GNPs content and reached 504.6 MPa at 0.5%, 31% higher than the Cu-5%ZO₂. The thermal conductivity had the maximum value at 0.5 wt%GNPs and reached 345 W/m k. The results provide efficient manufacturing process for high strength and good conductivity hybrid nanocomposites, which is applicable in many structural applications such as heat exchange purposes.     

Pool boiling of water-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and water-Cu nanofluids on horizontal smooth tubes

Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e., water-Al₂O₃ and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth copper and stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed test heater. The experiments have been performed to establish the influence of nanofluids concentration as well as tube surface material on heat transfer characteristics at atmospheric pressure. The results indicate that independent of concentration nanoparticle material (Al₂O₃ and Cu) has almost no influence on heat transfer coefficient while boiling of water-Al₂O₃ or water-Cu nanofluids on smooth copper tube. It seems that heater material did not affect the boiling heat transfer in 0.1 wt.% water-Cu nanofluid, nevertheless independent of concentration, distinctly higher heat transfer coefficient was recorded for stainless steel tube than for copper tube for the same heat flux density.     

Hybrid solar still by heat pump compression

Our study is related to an experimental work and modelling of a simple solar still (SSS), green house type, asymmetrical and a hybrid system of a solar still connected to a heat pump (SSSHP). Simple solar stills have in general very low efficiency and our study aims in improving that incorporation by heat pump. This will increase vapor condensation, improve efficiency and consequently the output per m² of still surface area. Data obtained from our experimental research are used to determine convective and evaporative heat transfer coefficients such as the experimental and theoretical efficiencies. The nom of the hybrid system is HSSHP. Daily output increased from 2 l/m² for the SSS up to 12 l/m² for the HSSHP and average efficiency increased from 20% to 80%.     

Catalytic Cracking of Heavy Olefins into Propylene, Ethylene and Other Light Olefins

Hybrid catalysts developed for the thermo-catalytic cracking of liquid hydrocarbons were found to be capable of cracking C₄ ⁺ olefins into light olefins with very high combined yields of product ethylene and propylene (more than 60 wt%) and C₂–C₄ olefins (more than 80 wt%) at 610–640 °C, and also with a propylene/ethylene weight ratio being much higher than 2.4. The olefins tested were heavier than butenes such as 1-hexene, C₁₀ ⁺ linear alpha-olefins (LAO) or a mixture of LAO. The hydrogen spillover effect promoted by the Ni bearing co-catalyst, contributed to significantly enhancing the product yield of light olefins and the on-stream stability of the hybrid catalyst.     

Oxidation and ablation behaviour of multiphase ultra-high-temperature ceramic Ta0·5Zr0·5B2–Si–SiC protective coating for graphite

To provide reliable oxidation protection for carbon materials under harsh high-temperature aerobic environments, a dense monolayer-multiphase ultra-high-temperature ceramic Ta_0·5Zr_0·5B₂–Si–SiC (TZSS) coating was fabricated by a combination of dipping and in-situ reaction. The oxidation resistance of the TZSS coating was investigated at 1923 K in air. The results indicated that the TZSS coating could offer at least 70 h of oxidation protection for the matrix material. The synergistic oxygen-blocking effect of the thick oxide layer formed during the oxidation test and the inner coating, played a key role in the oxidation protection process. These were responsible for the excellent oxidation resistance ability of the TZSS coating. Additionally, the ablation performance of the TZSS coating was also investigated under increased heat flux from 2.4 MW/m² to 4.2 MW/m². The ablation behaviours changed from the oxidation and evaporation of coating materials to mechanical scouring, corresponding to increased mass and linear ablation rates. Interestingly, after ablation for 40 s under a heat flux of 4.2 MW/m², a new microstructure composed of “lath-like” Ta₄Zr₁₁O₃₂ solid solution grains was found in the ablation center. This oxide layer possessed few micropores, which could provide reliable protection for the matrix material under ultra-high-temperature oxygen-containing airflow erosion, thus preventing further damage to the composite.     

Structural,mechanical and tribological properties of Cu–ZrO2/GNPs hybrid nanocomposites

Hybrid Cu–ZrO₂/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on mechanical and tribological properties of the produced hybrid nanocomposite was studied while maintaining ZrO₂ mass fraction constant at 5%. High energy ball milling was applied for mixing powders and compaction and sintering were applied for consolidation. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO₂/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO₂ nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. This improved nano and micro structure of Cu–5%ZrO₂/0.5%GNPs nanocomposites revealed higher hardness, 169.3 HV, compared to 65.5 HV for Cu–5%ZrO₂ nanocomposite. The wear rate is decreased in this composite while it increased with increasing GNPs content more than 0.5%. The coefficient of friction is decreased as well for this hybrid nanocomposite and remain constant with increasing GNPs content more than 0.5%.     

Field emission characteristics of CNFB-CNT hybrid material grown by one-step MPCVD

A hybrid material consisting of carbon nanotubes (CNTs) and carbon nanoflake balls (CNFBs) was successfully synthesized by microwave-plasma-assisted chemical vapor deposition using a H₂/CH₄/N₂ ratio of 4:1:2 at 80 Torr for 30 min. The precursor used was a sol-gel solution containing ferric nitrate, tetrabutyl titanate, and n-propanol. The carbon hybrid material (CNFB-CNT) exhibited excellent field emission properties, with its turn-on field being 1.77 V/μm. It also showed two field enhancement factors (1536 and 7932) for different electric fields. The emission current density of the hybrid remained higher than 0.65 mA/cm² for more than 50 h and was 0.82 mA/cm² even after 50 h of continuous emission. Further, the field emission properties of the CNFB-CNT hybrid were better than those of other single-structured carbon nanomaterials (CNTs, CNFs, or CNFBs). Therefore, the CNFB-CNT hybrid material should be a promising candidate for use in high-performance field emitters.     

Ca-based sorbent looping combustion for CO2 capture in pilot-scale dual fluidized beds

To demonstrate process feasibility of in situ CO₂ capture from combustion of fossil fuels using Ca-based sorbent looping technology, a flexible atmospheric dual fluidized bed combustion system has been constructed. Both reactors have an ID of 100 mm and can be operated at up to 1000 °C at atmospheric pressure. This paper presents preliminary results for a variety of operating conditions, including sorbent looping rate, flue gas stream volume, CaO/CO₂ ratio and combustion mode for supplying heat to the sorbent regenerator, including oxy-fuel combustion of biomass and coal with flue gas recirculation to achieve high-concentration CO₂ in the off-gas. It is the authors' belief that this study is the first demonstration of this technology using a pilot-scale dual fluidized bed system, with continuous sorbent looping for in situ CO₂ capture, albeit at atmospheric pressure. A multi-cycle test was conducted and a high CO₂ capture efficiency (> 90%) was achieved for the first several cycles, which decreased to a still acceptable level (> 75%) even after more than 25 cycles. The cyclic sorbent was sampled on-line and showed general agreement with the features observed using a lab-scale thermogravimetric analysis (TGA) apparatus. CO₂ capture efficiency decreased with increasing number of sorbent looping cycles as expected, and sorbent attrition was found to be another significant factor to be limiting sorbent performance.     

Melt compounded polylactic acid-hexagonal boron nitride-aluminum oxide hybrid composites for electronic applications: impact of hybrid fillers on thermophysical,dielectric, optical,and hardness properties

ABSTRACT

The dielectric, thermophysical, optical, and hardness of pure polylactic acid (PLA) and hBN micropowder and Al₂O₃ nanopowder (1% to 30%) reinforced PLA hybrid composites were investigated. Hybrid composites exhibit improved thermal conductivity (k – 0.54 W/mK), permittivity (?? – 4.6720 @ 1 MHz to 1 GHz) with very low loss tangent (tan δ < 0.02). High absorption in UV region was observed for all hybrid composites. Overall, the prepared hybrid composites can be used as a bio-based dielectric substrates, enclosures, thermal interface material for low temperature applications and UV-absorbable coating materials for fabric, packaging, and storage applications.     

Thermal energy storage in inorganic salts

The work involved studying the potential of Na₂SO₄, NaCl, KCl, CaCl₂ and some eutectic mixtures of inorganic salt for storing thermal energy. Heat storage materials have wide application in devices such as “off-peak” space heating furnaces. Data reveal Na₂SO₄ to be a better heat storage material than other salts as well as conventional heat storage materials because of its dimorphic nature and high heat of transition. It is estimated that less than 0.29 m³ of Na₂SO₄ would be required for heating a normal sized house on the Canadian Prairies.     

Thermal shock resistance and mechanical properties of La2Ce2O7 thermal barrier coatings with segmented structure

La₂Ce₂O₇ (LCO) is a promising candidate material for thermal barrier coatings (TBCs) application because of its higher temperature capability and better thermal insulation property relative to yttria stabilized zirconia (YSZ). In this work, La₂Ce₂O₇ TBC with segmentation crack structure was produced by atmospheric plasma spray (APS). The mechanical properties of the sprayed coatings at room temperature including microhardness, Young's modulus, fracture toughness and tensile strength were evaluated. The Young's modulus and microhardness of the segmented coating were measured to be about 25 and 5 GPa, relatively higher than those of the non-segmented coating, respectively. The fracture toughness of the LCO coating is in a range of 1.3–1.5 MPa m^1/2, about 40% lower than that of the YSZ coating. The segmented TBC had a lifetime of more than 700 cycles, improving the lifetime by nearly two times as compared to the non-segmented TBC. The failure of the segmented coating occurred by chipping spallation and delamination cracking within the coating.     

Self-emulsification synthesis of epoxy phosphate ester and its flame-retardant mechanism in flexible poly(vinyl chloride)/magnesium hydroxide composites

A trade-off dilemma exists for simultaneously improving the mechanical properties and flame resistance of flexible polyvinyl chloride (fPVC)/magnesium hydroxide (MH) composites. In this study, epoxy phosphate ester (EPE), a hydrophobic surface modifier of MH, was synthesized using a self-emulsification method. After modification, EPE was bonded to the surface of MH (MHEPE) without altering its morphology. The results of limiting oxygen index and cone calorimetry tests indicated that fPVC/MHEPE exhibited better flame retardancy and smoke suppression effects than did fPVC/MH. The peak of the heat release rate, total heat release, peak of the smoke production rate, and total smoke production of the fPVC/MHEPE composite were 206.0 kJ m⁻², 45.90 MJ m⁻², 0.0729 m² s⁻¹, and 9.88 m², which were 8.64%, 14.00%, 27.61%, and 9.02% lower than those of the fPVC/MH composite, respectively. For the fPVC/MHEPE composite, a compact and continuous char residue formed, which could inhibit heat and flammable volatile migration between the matrix and burning zones. In the gas phase, the dilution effect of H₂O vapor reduced the concentrations of O₂ and flammable volatiles. The free-radical quenching effect of ·PO and ·PO₂ also played a vital role in extinguishing flame and terminating combustion. Further, the introduction of EPE improved the tensile and impact strengths of the fPVC/MH composites because of the excellent interfacial compatibility between MHEPE and the fPVC matrix. This study provides a simple and workable solution for the trade-off dilemma, and the remarkable flame retardancy and mechanical properties of the fPVC/MHEPE composite render it a promising cable material.     

A sustainable bio-adsorbent for thermal energy storage for space heating applications

Thermal energy storage is an emerging technology that allows the storage of heat when it is available, which can be used later. One of the available technologies for thermal energy storage is the adsorption of moisture from air by adsorbents. Several adsorbents have been studied in the literature for this application, but there is a need for a sustainable adsorbent that can be eco-friendly, cost effective, and available for scale-up for commercialization of the technology. The current paper focused on the synthesis of a flax shives-based composite (equal weight percent of flax shives and salt hydrates) prepared by the impregnation method and its application in thermal energy storage. The composite showed durability, stability, and reasonable energy storage density with a very low cost per unit of energy. The structural characterization of the hybrid was performed by scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX). The thermal energy storage density, as well as the charging/discharging characteristics were measured using a laboratory-scale thermal energy storage apparatus. The flax/CaCl₂/LiCl hybrid showed reasonable energy storage density at 74 kWh/m³ for 50% inlet relative humidity after regeneration at 120°C. Although the energy storage density was not high, the flax/CaCl₂ composite was found to be the most cost-effective material, as it showed the lowest cost per energy stored at 0.98 CAD/kWh at 50% relative humidity (RH) after regeneration at 120°C.     

Ablation resistance of SiC‐modified ZrC coating prepared by SAPS for SiC‐coated carbon/carbon composites

This study evaluated the ablation resistance of ZrC/SiC coating for carbon/carbon (C/C) composites at different temperatures and heat fluxes, which improved the researches on ultra‐high temperature oxidation of ZrC/SiC system. Results showed that the protection of coating depended on temperature and heat flux. Ablation test for 120 seconds under heat flux of 2.4 MW/m² at 2270°C revealed a good ablation resistance, with the linear ablation rate reduced by 96.4% and the mass gain rate increased by 383.3% compared with those of pure ZrC coating. The good ablation resistance was attributed to the formation of dense oxide scale surface. SiC could improve the compactness of the oxide scale at this temperature by forming SiO₂. A dense scale could not form at 2105°C after ablation for 120 seconds, resulting in a dissatisfactory ablation resistance of the coating. After ablation for 120 seconds at 1738°C, the coating was integrated due to the protection of glassy SiO₂ encapsulated ZrO₂. The coating could not resist the strong shear force from the flame at heat flux of 4.2 MW/m² and was severely damaged after ablation for 60 seconds.     

Preparation and coagulation performance of hybrid coagulant polyacrylamide–polymeric aluminum ferric chloride

In this study, we synthesized a novel hybrid coagulant, polyacrylamide (PAM)–polymeric aluminum ferric chloride (PAFC), by the polymerization of acrylamide monomer with the redox system (NH₄)₂S₂O₈–NaHSO₃. The factors affecting the PAM–PAFC hybrid coagulant were investigated in an orthogonal experiment. The maximum intrinsic viscosity was observed at an initiator mass fraction of 0.5%, a polymerization temperature of 50 °C, a monomer mass fraction of 20%, and a polymerization time of 4 h, which were the optimum synthesis parameters. The spatial network structure of the PAM–PAFC hybrid coagulant was graphically determined by scanning electron microscopy. Hybrid PAM–PAFC was adopted to treat the kaolin–humic acid suspension and the synthetic dye wastewater. The effect of the coagulant dosage and pH on the coagulant experiments were examined. The coagulant experiment on the kaolin–humic acid suspension showed that the optimum treatment efficiency was achieved at a coagulants dosage of 0.6 mg/L, at which level the turbidity reductions with the inorganic PAFC coagulant, PAM–PAFC composite, and PAM–PAFC hybrid were 95.30%, 95.84%, and 98.38%, respectively. Treatment with the PAM–PAFC hybrid coagulant was also effective in removing Congo Red and Direct Fast Turquoise Blue GL; the color‐removal efficiencies for these dyes were higher than 93% and 94%, respectively. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46355.