Rapid Local Heating Research Articles

Guidelines for element size and type selection for the finite element simulation of laser-induced elastic waves in thermoelastic laser ultrasonic testing

This paper explores spatial discretization within finite element simulations of laser-induced elastic waves within the context of Laser Ultrasonic Testing (LUT). Motivated by discrepancies and oscillations detected in temperature and displacement results in the literature, we traced these issues back to spatial discretization challenges. These challenges originate from rapid localized heating and the generation and propagation of high-frequency waves across a relatively large domain. This study effectively addresses and rectifies these inaccuracies, offering guidance for selecting the appropriate element size and type. We examined two element types: four-node quadrilaterals (Q4) employing first-order Lagrange and nine-node quadrilaterals (Q9) using second-order Lagrange shape functions. Our analysis encompasses mesh refinement strategies, exploration of time and frequency domain plots for temperature and displacement, as well as an evaluation of different pulse durations. Our findings demonstrate that Q9 elements attain accuracy with grids four times larger than Q4 elements for temperature and wave propagation analyses. Furthermore, we observe that lower frequency waves exhibit reduced sensitivity to element size, emphasizing the relationship between element size and elastic wave frequency. Pulse durations in the 6 to 30 ns range affect the required element size in the heat-affected zone but exert minimal influence on wave frequency and spatial discretization in the remainder of the domain. Finally, we present a new formula for element size selection based on the dominant frequency. This study provides a comprehensive guideline for selecting element size and type, enabling the attainment of accurate results while effectively managing computational costs.

Effect of Local Rapid Cooling Heat Treatment on Residual Stress of Pressure Vessel Inner Wall Welding Layer

Effect of Local Rapid Cooling Heat Treatment on Residual Stress of Pressure Vessel Inner Wall Welding Layer

Temperature driven transformations of glycine molecules embedded in interstellar ice.

The formation of glycine amino acid on ice grains in space raises fundamental questions about glycine chemistry in interstellar media. In this work, we studied glycine conformational space and the related tautomerization mechanisms in water media by means of QM/MM molecular dynamics simulations of four glycine conformational isomers (cc, ct, tc, and tt). Interstellar low density amorphous (LDA) ice and T = 20 K were considered as representative for a cold interstellar ice environment, while temperatures of 250 and 450 K were included to model rapid local heating in the ice. In addition to the LDA environment, water clusters with 4, 17, and 27 H2O molecules were subjected to QM/MM dynamics simulations that allowed glycine tautomerization behaviour to be evaluated in water surface-like environments. The tautomerization processes were found to be strongly dependent on the number of water molecules and specific isomer structure. All the glycine isomers mostly preserve their canonical "neutral" conformations under interstellar conditions.

Preparation of hygroscopic fabric with a uniform and slow exothermic effect and its thermoregulation evaluation

Hygroscopic-exothermic textiles dissipate heat by absorbing moisture around the skin, which makes humans feel warm in a cold environment. However, the local rapid temperature rising and heat concentration due to uneven sweat distribution can cause a heat sensation that is unfavorable to personal thermal comfort in a relatively short period of time. Herein, hygroscopic fabric with a uniform and slow exothermic effect was prepared to achieve thermal-wet comfort of garments. The hierarchical structure textile consists of an inner layer with moisture diffusion and transport performance, a middle layer with moisture absorption and storage properties and an outer layer with moisture absorption and heat generation characteristics, which achieved the effect of slow and uniform heat dissipation during the moisture absorption by controlling the moisture transmission within the fabric. Based on the study of the uniform and slow exothermic effect of fabrics, five indexes, namely the average temperature value, the maximum temperature value, the temperature distribution uniformity index, the percentage of the heating area distribution at the maximum temperature point on the fabric surface and the initial heating rate, were proposed to evaluate the uniformity and the slowness of moisture absorption and heat dissipation in textiles. The result showed that the initial heating rate of multi-layer fabric could be reduced by 0.11–0.25°C/min compared to the single-layer hygroscopic-exothermic fabric and there was an up to 29.93% increase in the heat dissipation area at the maximum temperature point. The uniformity of temperature distribution after moisture absorption of fabrics increased by 41.6–58%.

Bonding with brazing alloys as high-temperature interconnection filler through self-propagating exothermic reaction

There has been growing interest in wide bandgap (WBG) semiconductors including SiC and GaN due to the increasing demands for electronic devices serving at high temperatures. However, to maximise the potential capacity of WBG devices, new high-temperature interconnection materials and processes are indispensable as the current existing Sn-based solder alloys and bonding processes developed for Si devices are unable to meet the reliability requirements. In the present work, reactive brazing alloys including Cu-15Ag-5P and Incusil (Ag-27.25Cu-12.5In-1.25Ti) with melting points above 600°C have been utilized as the interconnection materials which offer excellent properties under high operation temperature. The self-propagating exothermic reaction (SPER) was applied for the bonding process via an intense rapid local heating and cooling at a millisecond scale. The strong Cu/Cu-15Ag-5P/Cu and Cu/Incusil/Cu sandwich bonded structures have been created with the assistance of SPER, where the nanofoil was applied from the outside of stacked structures as an external heat source and the bonding process was conducted in the ambient atmosphere without using flux. It has been found that the P element in Cu-15Ag-P alloy has the self-flux effect, which is beneficial for the ultra-fast interfacial reaction process. The experiments where the nanofoil was placed inside of stacked structures between two sheets of brazing alloys have also been conducted, which exhibited the well-bonded interface microstructures between nanofoil and brazing alloys. The outlook on the design for practicality and industrial uses for SPER-assisted bonding with brazing alloys has also been discussed, as a potential viable assembly route for the high-temperature and high-power electronics packaging.

Двумерное моделирование воздействия импульсного локального нагрева на отрывное сверхзвуковое течение, вызванное его поворотом

Двумерное моделирование воздействия импульсного локального нагрева на отрывное сверхзвуковое течение, вызванное его поворотом

Investigating the effect of laser modulation and input energy on bending mechanism and bending angle in the multi-pass laser forming process through real-time monitoring

Laser forming is a non-contact type process used for bending, spatial forming, and alignment of metallic components through a controlled application of laser energy. The process involves localized rapid heating and cooling, inducing thermal strains exceeding the elastic strain of the material resulting in plastic deformation. The process is broadly governed by the temperature gradient mechanism (TGM), buckling mechanism (BM), and upsetting mechanism (UM). However, in the case of multi-pass laser forming process, heat accumulation and variation in the flow stress because of consecutive thermal cycles and strain hardening due to multiple bending cycles makes the process highly complicated. While operating laser in modulated mode may be a wise choice to handle the heat accumulation, inter-pulse cooling cycles along with variation in peak and average power with change in duty cycle affects the bending mechanism and angle significantly. Therefore, in the present study, a real-time monitoring system was developed to investigate the bending mechanism for a multi-pass laser forming process carried out in laser modulated mode. Also, the effect of average power, peak power, heat accumulation, strain hardening on bending mechanism and bending angle were investigated. Keeping the peak power constant, variation in duty cycle from 100% to 40% resulted in reduced average energy and strain hardening was found to be dominant, decreasing bending angle per pass. On contrast, variation in duty cycle by keeping the average power constant resulted in heat accumulation dominating the bending mechanism.

Atomization of High Viscous Liquids Using a MEMS Vibrating Mesh With Integrated Microheater

Aerosol generation is important for a wide range of applications including drug delivery, additive manufacturing, spray cooling, and numerous other applications. However, current aerosol generation devices often have poor droplet uniformity or are limited to low viscosity liquids ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 2 cp). This work presents the development of a Microelectromechanical systems vibrating mesh atomizer capable of atomizing higher viscosity fluids while maintaining high droplet size uniformity. The overall system consists of microfabricated silicon vibrating mesh atomizer, a piezoelectric film, and a flexible thin film microheater. The Si vibrating mesh atomizer was designed to increase atomization thresholds, while the microheater is designed to reduce liquid viscosity to meet the atomization threshold. Atomizers with varying nozzle dimensions were experimentally validated using liquids with varying viscosity and physiochemical properties, such as water, glycerol, propylene glycol, and vegetable glycerin. The microheater was designed to provide local rapid heating with low power consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 1 W. The droplet size distribution results show that when fluid viscosity increases, the volume median diameter of droplets increases, and the spray angle decreases. The Si-vibrating mesh atomizer was able to atomize liquids up to 49.73 cP at room temperature compared to normal metallic vibrating mesh atomizers which have a threshold of approximately 2 cP. The integrated heater enabled atomization of liquids with viscosities as high as 111 cP with low heating ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C). 2023-0042

Prediction of transverse welding residual stress considering transverse and bending constraints in butt welding

Welding residual stress is generated by the thermal stress caused by rapid local heating and cooling during welding using a welding heat source. The distribution and size of the residual welding stress are affected by the joint type, welding conditions, constraints, etc., which also affect the fatigue, fracture, and buckling strengths. Therefore, because the magnitude and distribution of residual stress are very important for the safety evaluation of structures, guidelines for structural integrity evaluation suggest a method for deriving the welding residual stress. However, the welding residual stress presented in the guidelines is in a state without constraint; if a constraint exists, it is suggested to use the yield stress of the base material. This can lead to a very conservative design using the yield stress as the welding residual stress in the recent trend of the increasing use of high-strength steels with increased yield stress. Therefore, it is very important to investigate the relationship between constraint and residual stress during welding and to predict the residual stress according to the degree of constraint. In this study, the effects of member thickness, yield stress, lateral constraint, and bending constraint on the welding residual stress in butt welding were investigated, and predictive factors for welding residual stress were established. To this end, a thermal elastic–plastic analysis was performed by changing the thickness, yield strength, lateral constraint, and bending constraint size of the member. Subsequently, the analysis results were used to train a deep neural network (DNN) to predict the residual stress at the center of the weld and toe. In addition, the influence of input factors that affect the prediction accuracy during DNN learning was considered.

Endothelin A receptor inhibition increases nitric oxide-dependent vasodilation independent of superoxide in non-Hispanic Black young adults.

Young non-Hispanic Black adults have reduced microvascular endothelial function compared with non-Hispanic White counterparts, but the mechanisms are not fully elucidated. The purpose of this study was to investigate the effect of endothelin-1 A receptor (ETAR) and superoxide on cutaneous microvascular function in young non-Hispanic Black (n = 10) and White (n = 10) adults. Participants were instrumented with four intradermal microdialysis fibers: 1) lactated Ringer's (control), 2) 500 nM BQ-123 (ETAR antagonist), 3) 10 μM tempol (superoxide dismutase mimetic), and 4) BQ-123 + tempol. Skin blood flow was assessed via laser-Doppler flowmetry (LDF), and each site underwent rapid local heating from 33°C to 39°C. At the plateau of local heating, 20 mM l-NAME [nitric oxide (NO) synthase inhibitor] was infused to quantify NO-dependent vasodilation. Data are means ± standard deviation. NO-dependent vasodilation was decreased in non-Hispanic Black compared with non-Hispanic White young adults (P < 0.01). NO-dependent vasodilation was increased at BQ-123 sites (73 ± 10% NO) and at BQ-123 + tempol sites (71 ± 10%NO) in non-Hispanic Black young adults compared with control (53 ± 13%NO, P = 0.01). Tempol alone had no effect on NO-dependent vasodilation in non-Hispanic Black young adults (63 ± 14%NO, P = 0.18). NO-dependent vasodilation at BQ-123 sites was not statistically different between non-Hispanic Black and White (80 ± 7%NO) young adults (P = 0.15). ETAR contributes to reduced NO-dependent vasodilation in non-Hispanic Black young adults independent of superoxide, suggesting a greater effect on NO synthesis rather than NO scavenging via superoxide.NEW & NOTEWORTHY Endothelin-1 A receptors (ETARs) have been shown to reduce endothelial function independently and through increased production of superoxide. We show that independent ETAR inhibition increases microvascular endothelial function in non-Hispanic Black young adults. However, administration of a superoxide dismutase mimetic alone and in combination with ETAR inhibition had no effect on microvascular endothelial function suggesting that, in the cutaneous microvasculature, the negative effects of ETAR in non-Hispanic Black young adults are independent of superoxide production.

MEMS microphone arrays for quench detection in superconducting cables

An acoustic array is proposed as a quench detection method in superconducting magnets. A quench occurs when the current density in the superconductor exceeds a critical value, resulting in a loss of superconductivity and rapid local heating. This event is destructive and must be rapidly detected. It is thought that the quench may act as an acoustic source (Takayasu, 2019), which could be detected and localized by a microphone array inserted into the cryogenic coolant. A main advantage of this method is that acoustics propagate 1000 times faster than the normal zone propagation velocity in HTS conductors, providing for fast detection times. To demonstrate this concept, we first characterized the performance of a piezoelectric MEMS microphone and several potential preamplifiers under cryogenic conditions. An acoustic sense node was then constructed that operates down to 10 K. A cryogenic probe incorporating the MEMS array was used to study a quench event in a segment of a 2 mm wide REBCO tape. Quench experiments were carried out in a 7.6 cm diameter, 111 cm tall cryostat in Helium gas at 20 to 50 K. The MEMS array clearly detects a quench induced failure. Other observed acoustic features of unknown origin will be described.

Acute impact of aerobic exercise on local cutaneous thermal hyperaemia.

Little is known about the acute changes in cutaneous microvascular function that occur in response to exercise, the accumulation of which may provide the basis for beneficial chronic cutaneous vascular adaptations. Therefore, we examined the effects of acute exercise on cutaneous thermal hyperaemia. Twelve healthy, recreationally active participants (11 male, 1 female) performed 30-minute cycling at 50% (low-intensity exercise, LOW) or 75% (high-intensity exercise, HIGH) maximum heart rate. Laser Doppler flowmetry (LDF) and rapid local skin heating were used to quantify cutaneous thermal hyperaemia before (PRE), immediately following (IMM) and 1-h (1HR) after exercise. Baseline, axon reflex peak, axon reflex nadir, plateau, maximum skin blood flow responses to rapid local heating (42°C for 30-min followed by 44°C for 15-min) at each stage were assessed and indexed as cutaneous vascular conductance [CVC=flux/mean arterial blood pressure (MAP), PU·mmHg-1], and expressed as a percentage of maximum (%CVCmax). Exercise increased heart rate (HR), MAP and skin blood flow (all P<0.001), and to a greater extent during HIGH (all P<0.001). The axon reflex peak and nadir were increased immediately and 1-h after exercise (all comparisons P<0.01 vs. PRE), which did not differ between intensities (peak: P=0.34, axon reflex nadir: P=0.91). The endothelium-dependent plateau response was slightly elevated after exercise (P=0.06), with no effect of intensity (P=0.58) nor any interaction effect (P=0.55). CONCLUSION: Exercise increases cutaneous microvascular axonal responses to local heating for up to 1-h, suggesting an augmented sensory afferent function post-exercise. Acute exercise may only modestly affect endothelial function in cutaneous microcirculation.

Freezing-induced wetting transitions on superhydrophobic surfaces

Supercooled droplet freezing on surfaces occurs frequently in nature and industry, often adversely affecting the efficiency and reliability of technological processes. The ability of superhydrophobic surfaces to rapidly shed water and reduce ice adhesion make them promising candidates for resistance to icing. However, the effect of supercooled droplet freezing—with its inherent rapid local heating and explosive vaporization—on the evolution of droplet–substrate interactions, and the resulting implications for the design of icephobic surfaces, are little explored. Here we investigate the freezing of supercooled droplets resting on engineered textured surfaces. On the basis of investigations in which freezing is induced by evacuation of the atmosphere, we determine the surface properties required to promote ice self-expulsion and, simultaneously, identify two mechanisms through which repellency falters. We elucidate these outcomes by balancing (anti-)wetting surface forces with those triggered by recalescent freezing phenomena and demonstrate rationally designed textures to promote ice expulsion. Finally, we consider the complementary case of freezing at atmospheric pressure and subzero temperature, where we observe bottom-up ice suffusion within the surface texture. We then assemble a rational framework for the phenomenology of ice adhesion of supercooled droplets throughout freezing, informing ice-repellent surface design across the phase diagram.

Enhancing hydrogen evolution reaction of confined monodispersed NiSe2−X nanoparticles by high-frequency alternating magnetic fields

Introduction of alternating magnetic field (AMF) to electrocatalytic process has been proved an effective strategy for significantly enhancing catalytic performance of magnetic nanoparticles (NPs) electrocatalysts. Coupling AMF with currently highly promising monodispersed NPs electrocatalysts could be an interesting tactics. However, magnetic heating effect under AMF may cause agglomeration and even falloff of NPs, and how to efficiently and stably utilize AMF in monodispersed NPs electrocatalysts to enhance the catalytic performance is an urgent issue. In this work, room-temperature ferromagnetism is introduced into NiSe2−X nanoparticle by vacancy engineering, and proposes a feasible design to confine monodispersed ultra-small NiSe2−X NPs in an amorphous carbon matrix. Under AMF, the spin flips of the magnetic domains in confined NiSe2−X NPs generate magnetic heating related to Néel relaxation, which achieve rapid local heating of NiSe2−X NPs electrocatalyst and greatly improves hydrogen evolution reaction performance (a significantly increase of current density by ∼400 %). This work provides new ideas for the preparation of ultra-small monodispersed NPs electrocatalysts that can utilize AMF to enhance catalytic performance, and has an important significance in accelerating clean energy production.

Temperature gradient control of frequency conversion heating for a thick-walled pipe based on energy transfer

Characterized by energy concentration, electromagnetic heating technology has a significant advantage in achieving local rapid heating of a workpiece. However, electromagnetic heating may create a great temperature gradient in the wall thickness direction for a workpiece with a thick wall that requires penetrating heating. To improve the evenness of the temperature between the internal and external surfaces, a frequency conversion heating method is proposed. An electric–magnetic–thermal coupling model for frequency conversion heating of welded pipes is established and verified by temperature measurement experiments, thereby revealing the distribution characteristics of the induced current, temperature, and magnetic flux intensity. On this basis, a new concept—the energy surface—is defined. An induction heating schedule suitable for thick-walled pipes is formulated with the energy surface transfer characteristics. The electromagnetic distribution resembles the topology of an underwater lake. There is a "demagnetization region" with a magnetic flux intensity of < 0.321 T. The field width varies with the frequency. The temperature difference along the wall thickness of the welded pipe reaches its maximum after the critical demagnetization surface manifests. By controlling the frequency conversion heating, the temperature difference can be decreased to 88.82%, thus improving the induction heating quality of the welded pipe. This study provides a measurable theoretical reference basis for investigating the change in the internal heat source caused by the change of electromagnetic characteristics to accurately control the temperature gradient.

The Role of Endothelin Receptors on Sensory Nerve Mediated Dilation in Postmenopausal Women

Rapid local heating of the skin elicits biphasic vasodilation. The initial peak in skin blood flow (SkBF) is mediated by sensory nerves (i.e., the axon reflex). Both endothelin (ETA and ETB) receptors are located on axon terminals on nociceptor fibers, and therefore may be involved in the sensory nerve mediated vasodilation. Although prior work shows a blunted axon reflex with aging, this has yet to be examined in women, and the role of ETA and ETB receptors in this initial sensory nerve‐mediated vasodilatory response remains unclear.PURPOSEWe tested the hypothesis that the initial peak is blunted in postmenopausal women (POST) compared to young women (YW), and that blockade of ETA and ETB receptors would improve sensory nerve‐mediated dilation in POST.METHODSWe retrospectively analyzed data in 25 healthy YW (27±10 yr) and 16 healthy POST (56±1 yr). Cutaneous vasodilation to local heating was measured using laser doppler flowmetry during microdialysis perfusions of lactated Ringer’s (control), ETA receptor blockade (BQ‐123, 500nM), and ETB receptor blockade (BQ‐788, 300nM). Cutaneous vascular conductance (CVC) was calculated as SkBF/MAP at baseline and during the initial peak of local heating (42°C); CVC were normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C.RESULTSAll women were normotensive (MAP: YW 83±8 mmHg; POST 94±2 mmHg, p &lt; 0.001) and not obese (YW 23±3 kg/m2; POST 24±1 kg/m2, p = 0.153). Sensory nerve‐mediated dilation at the control site was reduced in POST (YW 63 ±14 vs POST 49 ±17 %CVCmax, p=0.004). Blockade of ETA (YW 54 ±10 vs POST 55 ±9 %CVCmax, p=0.579) and ETB (YW 62 ±17 vs POST 59 ±13 %CVCmax, p=0.476) receptors did not impact the initial peak of local heating in either group.CONCLUSIONSThese preliminary data suggest the sensory nerve‐mediated vasodilation during local heating is attenuated with aging in women, but endothelin receptors do not contribute to this age‐related decrease. Additional research is needed to further understand the interactions between sex hormones and aging in regulating sensory nerve mediated vasodilation.

Rapid Actuation of Thermo-Responsive Polymer Networks: Investigation of the Transition Kinetics.

The swelling and collapsing of thermo-responsive poly(N-isopropylacrylamide)-based polymer (pNIPAAm) networks are investigated in order to reveal the dependency on their kinetics and maximum possible actuation speed. The pNIPAAm-based network was attached as thin hydrogel film to lithographically prepared gold nanoparticle arrays to exploit their localized surface plasmon resonance (LSPR) for rapid local heating. The same substrate also served for LSPR-based monitoring of the reversible collapsing and swelling of the pNIPAAm network through its pronounced refractive index changes. The obtained data reveal signatures of multiple phases during the volume transition, which are driven by the diffusion of water molecules into and out of the network structure and by polymer chain re-arrangement. For the micrometer-thick hydrogel film in the swollen state, the layer can respond as fast as several milliseconds depending on the strength of the heating optical pulse and on the tuning of the ambient temperature with respect to the lower critical solution temperature of the polymer. Distinct differences in the time constants of swelling and collapse are observed and attributed to the dependence of the cooperative diffusion coefficient of polymer chains on polymer volume fraction. The reported results may provide guidelines for novel miniature actuator designs and micromachines that take advantages of the non-reciprocal temperature-induced volume transitions in thermo-responsive hydrogel materials.

Synthesis of MnO2 Particles via One Step Localized Heating Method as Catalyst for Dye Degradation

This work demonstrated the synthesis of MnO2 particles via a rapid one-step localized heating method. The heat was transferred directly from the wire into the precursor solution, hence minimized the heat loss to the surrounding. As a result, the precursor solution was heated up rapidly and MnO2 particles with different morphologies were successfully synthesized in short duration within 10 to 15 min. These MnO2 particles were used as catalyst in the degradation of Rhodamine B (RhB) organic dye. Particularly, MnO2 particles synthesized at 10 min possessed outstanding catalytic activity with 99% degradation efficiency of RhB dye in 10 min of reaction time. This was greatly contributed by its 3D nanoflowers morphology that provided more active sites for catalytic activities to occur. The promising catalytic activity, synthesizing by a simple and affordable synthesis setup could provide an alternative in the development of MnO2 catalyst for organic pollutants removal.

Influence of the position and energy of local rapid heating of the supersonic gas flow on the position of the separation point on the surface of airfoil

Using numerical simulation, the study of the process of rapid local energy release in supersonic flow in a two-dimensional unsteady case and the process of separation point shift by a gas-dynamic perturbation caused by the energy input into the flow were carried out. The flow around the airfoil was modeled as laminar, and local heat release as a instantaneous isochoric process without changing the gas density. The value of energy input and the place of gas heating on the surface of the airfoil were varied. The cases of initiation of energy input at a certain distance before and after the initial position of the separation point, as well as immediately before the separation point, were considered. During obtained flow patterns processing, the displacement of the separation point position downstream, the time of this displacement, the position and size of the separation region with reattachment and the lifetime of this flow zone were determined. The obtained data can help to choose a strategy for initiating energy input in a repetitively pulsed regime, as well as in a regime of a variable position of energy release on the surface of a body, streamlined by compressible gas flow.

Microwave-Enabled Size Control of Iron Oxide Nanoparticles on Reduced Graphene Oxide

Nanoparticle-functionalized 2D material networks are promising for a wide range of applications, but in situ formation of nanoparticles is commonly challenged by rapid growth. Here, we demonstrate controlled synthesis of small and dispersed iron oxide nanoparticles on reduced graphene oxide (rGO) networks through rapid localized heating with microwaves with low-cost iron nitrate as the precursor. The strong coupling of the microwave radiation with the rGO network rapidly heats the network locally to decompose the iron nitrate and generate iron oxide nanoparticles, while cessation of microwaves leads to rapid cooling to minimize crystal growth. Small changes in the microwave reaction time (<1 min) led to very large changes in the iron oxide morphology. The solid-state microwave syntheses produced narrower nanoparticle size distribution than conventional heating. These results illustrate the potential of solid-state microwave syntheses to control the nanoparticle size on 2D materials through rapid localized heating under the microwave process conditions, which should be extendable to a variety of transition metal oxide-rGO systems.