Silicone Grease Research Articles

Highly thermally conductive and anti-corrosive silicone grease enabled using unique hexagonal boron nitride nanosheet/alumina microsphere-based hierarchical structure for heat dissipation in a humid environment

Electronic devices operating in the marine environment often face severe corrosion. In addition, highly integrated and powerful devices generate a notable amount of heat, which may lead to a deterioration in performance and reliability. Therefore, it is essential to develop thermal interface materials (TIMs) with high thermal conductivity and outstanding corrosion resistance for efficient and stable heat dissipation. Herein, a novel hierarchical three-dimensional structure comprising hexagonal boron nitride sheet wrapped alumina microsphere/hexagonal boron nitride flakes (Al2O3@BNNS-BNFs) has been fabricated, which can simultaneously improve the thermal conductivity and corrosion resistance of silicone grease (SG). The dispersibility of BNFs in SG is enhanced by the uniform distribution of Al2O3@BNNSs, while the BNNSs attached to the surface of Al2O3 microspheres improves the compatibility of BNFs and Al2O3 microspheres, thereby effectively enhancing the thermal conductivity of SGs. The thermal conductivity of the Al2O3@BNNS-BNFs/SG can reach up to 1.98 W/(m·K) when the content of Al2O3@BNNS-BNFs is 20 wt%, which is ∼13 times that of ordinary SG. Meanwhile, the Al2O3@BNNS-BNFs/SGs also demonstrate excellent electrical insulation (1.50 × 1013 Ω cm) and corrosion resistance compared to some commercial products. Furthermore, subsequent tests indicate that the Al2O3@BNNS-BNFs/SGs can effectively dissipate heat for electronic devices in various humid environments. These unique properties make the Al2O3@BNNS-BNFs/SGs promising as multifunctional TIMs for thermal management in complex environments, especially in humid or corrosive conditions.

Technical note: Optimization of the preparation of cascade impactors collection substrates for airborne metallic ultrafine particle sampling

The characterization of workers’ exposure to airborne metallic ultrafine particles (UFP) has been an increasing issue because of their effects on health, and as many activities are potentially concerned such as welding, oxy-cutting or 3D printing. Determining the particle size distribution of such an aerosol provides a real contribution to the understanding of UFP exposures and associated health effects, as it is directly related to their penetration in the respiratory tract. In this context, it is proposed to optimize the preparation of collection substrates of cascade impactors of airborne metallic UFP. The experimental results confirm that the collection substrates have to be prepared beforehand by coating them with a high-vacuum-resistant silicone grease. The results highlight that this grease has to be preliminarily dissolved in a heptane-based solution with a mass ratio grease-solvent of 7.5%, and then deposited on the substrate with a target height of 9 μm. Applying this protocol ensures a reproducible and representative determination of the particle size distribution, allowing the phenomena of particle bouncing and reentrainment to be significantly reduced. It is also shown that coated collection substrates remain stable for several months in terms of mass, and that the samples collected remain stable during transport thanks to the improvement of particle cohesion on the coated membrane.

Comparative analysis of thermal interface materials for effective thermal management of electronic devices

ABSTRACT Thermal interface materials (TIM) employed to electronic devices enhances interfacial heat dissipation and thermal contact conductance (TCC). This study compares the performance of TIMs (silicon grease, phase change material (PCM) and composite PCM) on a copper-aluminum contact pair under varying range of contact pressure (0.1 to 0.4 MPa) and interface temperature (35 to 65 °C). Composite PCM is prepared by mixing aluminum powder to PCM in different mass concentrations (4, 8 and 25 wt.%). Result shows that addition of aluminum powder > 8 wt.% to PCM reduces its heat storage capacity and delays heat transfer. Moreover, TCC with silicon grease outperforms PCM by 108%, while CPCM (8 wt. %) is 144% more efficient but costlier than others.

Experimental Study of Thermal Contacts for the Enhancement of Interfacial Heat Transfer

Abstract The thermal management in high-performance electronic devices demands the enhanced rate of heat dissipation for controlling operational temperatures and achieving optimal functioning. There are many interfaces in the heat dissipation circuit where thermal interface materials are applied to enhance heat transfer rate. An experimental investigation is presented on metallic contacts to study the interfacial heat transfer with and without a thermal interface material. Thermal contact conductance is known to be an important parameter estimated for the analysis of interfacial heat transfer across the thermal contacts. Therefore, the thermal contact conductance has been evaluated to identify an effective thermal interface material suitable for the present range of contact pressure and heat flux conditions. Silicone grease is a widely used thermal interface material in electronic industry. Thus, commercially available Silicone grease is evaluated in different boundary line thicknesses for a range of contact pressure and mean interface temperatures. Further, a novel composite thermal paste has been prepared by mixing cupric oxide nanopowder and Silicone grease in three different mass concentrations. Eventually, the results for the new thermal paste showed improved thermal contact conductance and lower interfacial temperature drops as compared to Silicone grease for similar test conditions with few limitations.

Enhancement of thermal conductivity and insulation of silicone thermal interface material through surface modification and synergistic effects of nanofillers for thermal management of electronic devices

Thermal interface materials (TIMs) play an irreplaceable role in highly integrated microelectronic devices. In this work, the addition of acidified carbon nanotubes modified by 3-aminopropyl triethoxysilane (KH550) had an effective enhancement to the thermal conductivity, thermal stability, and electrical insulation performance of silicone grease. On this basis, multi-filled silicone grease composites with better thermal conductivity and electrical insulation were prepared by introducing zinc oxide (ZnO) and Graphene nanoflakes (GNFs). The thermal conductivity of silicone grease achieved 1.438 W m−1 K−1, while the volume resistivity still exceeded 1013 Ω·cm. Additionally, the study explored the impact of varying filler parameters, temperature, and contact pressure on the interface thermal contact resistance of silicone grease. The best performance silicone grease applied to the cooling of the high-power LED exhibited excellent heat dissipation. This work presented a reference for the design and development of low cost, high performance TIMs.

Thermal conformance parameters for assessment of heat transfer between similar and dissimilar metal contacts

AbstractA novel approach to assess the thermal conformance between two metallic materials under transient conditions was proposed in the present investigation. Thermal conformance parameters (ƞ, ϴ, tg) were defined to quantify the contact condition between a metal–metal interface. To assess the effect of load and thermophysical properties of the sink and source materials on the degree of thermal conformance, a thermal conformance assessment parameter (TCAP) was proposed. Heat flux transients at the thermal interface was estimated by using an inverse heat conduction approach for various similar and dissimilar metallic surfaces in contact such as Cu─Cu, Al─Al, Al─Cu, and Cu─Al under both load and no load conditions. Commercially available silicone grease (SG) and thermal grease (CTG) were used as thermal interface materials (TIMs). The thermal conformance parameters increased with the increase in load for all the combinations of interfaces with and without TIMs. It was observed that, except for the copper–copper combination, thermal conformance parameters showed a linear relation with the TCAP. The enhancement in the heat transfer due to the application of load and TIM was validated by determining the maximum temperature difference (∆Tmax) across the interface. The experimental study revealed that the ∆Tmax decreases with the application of load and application of TIM leading to enhanced heat transfer. For the copper–copper combination, the thermal conformance depended solely on the load applied. Due to the lower thermal resistance offered by copper source/sink materials, the interfacial resistance between them becomes a dominant factor. The effect of TIM on heat absorbed by the sink was significant for the Cu/Cu interface.

Exploration and optimization on thermoelectric conversion of waste heat of blast furnace slag

The iron and steel industry involves processes that generate abundant waste heat resources. The energy utilization rate can be improved by using thermoelectric conversion technology to directly convert waste heat into electric energy through the Seebeck effect. In this study, a special waste heat recovery device, designed according to the production environment characteristics of blast furnace (BF) slag, is proposed. The heat transfer process between the BF slag and thermoelectric generator (TEG) is analyzed, and the heat source temperature field model is constructed. Based on the temperature distribution, the size of the TEG is determined. The heat transfer behavior of the thermoelectric module (TEM) is optimized using a non-contact heat collection mode and a water-cooling device, which improves the temperature gradient. A thermal conductive silicone grease is introduced as the thermal conductive layer to achieve uniform distribution of the hot end temperature and improve the heat transfer capacity of the collector plate. After design optimization, the temperature gradient of the TEM increased by 15.3 °C and 38 % on average. The experimental results show that a single TEM can generate about 3.084 J of electric energy. Using 70 kg of BF slag with an initial temperature of 600 °C, the TEG per unit installed area can generate about 1.23 kJ of electric energy in 1 h. This study provides an important foundation for research in thermoelectric conversion, utilization of BF slag waste heat and sustainable development of the iron and steel industry.

Characterization of Distillation and Redistillation Product of Coconut Shell Liquid Smoke at Various Temperatures

This study investigates the impact of distillation temperature on phenol content in coconut shell liquid smoke, a product derived from pyrolysis and subsequent condensation processes. Liquid smoke, renowned for its versatile applications including preservation, antioxidation, antiseptic, and antibacterial properties, necessitates distillation for both quality enhancement and safety. The research comprises a two-stage distillation, featuring 11 temperature variations (100-150°C) in the first stage and 9 variations (75-155°C) in the second stage. Characterization involves pH assessment and Gas Chromatography-Mass Spectrometry (GC-MS) analysis to identify chemical components. The pH range in the initial distillation stage spans 1.18-1.30, and the second stage ranges from 1.11-1.39. GC-MS analysis of raw coconut shell liquid smoke reveals 25 components, including phenol, furan, ketone, acid, alcohol, benzenediol and derivatives, alkyl aryl ether, deoxycytidine, and silicone grease. GC-MS evaluation is conducted on products of the first stage at 125 and 135°C, and the second stage products at 145 and 155°C. In the first distillation stage, liquid smoke contains phenol and assorted compounds. Conversely, the second stage yields purer phenol compounds. The findings suggest potential applications of the redistillation product as raw material in food preservation, antiseptics, and insecticides.

Experimental studies on selected thermal interface materials

The current work is an experimental study, with the primary goal of investigating and exploring ways to improve thermal contact conductance through a detailed examination and analysis of metallic contacts and discovering opportunities for enhancement, increased efficiency, and thus heat dissipation using thermal interface materials. The steady-state experiments have been carried out on a simple and calibrated experimental set-up. A comprehensive investigation was conducted to assess the thermal performance of Cu-Al contacts for the selected range of contact pressures and temperatures to suit the electronic industry?s distinctive characteristics and technical requirements. As a thermal interface material, graphene paste has been tested under various combinations of interface pressure and heating circumstances against the bare metallic contacts. Error analysis has also been performed for the current experimental investigation. It has been demonstrated that using graphene paste as a thermal interface material thermal contact conductance is improved, significantly enhancing heat dissipation. The results of thermal contact conductance for graphene paste have been compared with the same for silicon grease from literature. The present results thus demonstrate the application and suitability of the selected thermal interface material in the specified range of heating and contact pressure conditions in the context of particularly thermal management applications.

Study of the effect of laser textured rotors on the starting performance of metal–rubber mating pairs under different lubricating media environments

To solve the problem of premature failure of the rubber stator of the screw pump due to wear, reduce the frictional resistance torque of the screw pump to solve the problem of difficulty in starting after the shutdown of the screw pump production system in Daqing Oilfield. The effects of micron dot texture and lubricating medium on the tribological properties of 42CrMo metal and acrylonitrile–butadiene rubber mating surfaces were studied by theoretical analysis and tribological tests. The friction coefficient, wear amount, and rubber wear morphology were used as the measurement indexes of drag reduction, wear resistance, and wear degree, respectively. The results showed that the best combination of texture area ratio and the lubricating medium was 10% silicone grease, the friction coefficient and wear amount were reduced by 11% and 10.7%, respectively, compared with untextured, and the main order of chip storage and oil supply effect was 10% > 5% > 15%.

Experimental research on thermoelectric characteristics of a thermoelectric generator with external influencing factors optimization

The external influencing factors, the thermal interface material, load-bearing brick weight, and temperature difference, of a thermoelectric generator (TEG) device were experimentally examined. The micro heat pipe array (MHPA), as one novel thermal interface material, was investigated. The multi-variable coupling approach is used to analyze the intrinsic coupling correlation of the external influencing factors. The dimensionless synthesis economic factor index was proposed to analyze the improvement of thermoelectric characteristics, which can quickly assess the contact thermal resistance of different thermal interface materials. The results showed that the load power and load voltage generally increase with increased temperature differences. The contact thermal resistance decreases with increased load-bearing brick weight, but the decrement gradually decreases. The thermal interface material plays an important role in thermoelectric characteristics. The load-bearing brick weight performs little impact on the non-thermal interface material (NTIM) scheme. The two thermal conductive silicone grease schemes noticeably reveal better thermoelectric characteristics than those of the graphite paper schemes, although the thermal conductivity of thermal conductive silicone grease are much lower than that of graphite paper. The MHPA scheme exhibit the best thermoelectric characteristics, and its dimensionless synthesis economic factor index can be up to 371.81 %.

Fabrication and application of graphene-based silicone grease

With the increasing power requirements of integrated circuits, the demand for efficient cooling has followed suit. Silicone grease is commonly used due to its thermal stability and ability to fill in airgaps between the electronic components and radiators. Previous works attempted to increase the grease’s thermal conductivity by adding various additives such as boron nitride or functionalized carbon nanotubes. Functionalized graphene was chosen in this study due to its exceptional physical and chemical properties. Results show that the functionalization with several acid mixtures combined with ball milling resulted in a compound chemically equivalent to graphene and thoroughly dispersed in silicone grease. An optimal grease was produced, containing 1 wt% Gr-COOH and possessing a thermal conductivity of 6.534 W mK−1. The resulting grease’s performance in thermal dissipation and approximated lifespan improvements was compared to a commercially available silicone grease using a 200 W LED. Results indicated a 4.5 °C decrease in saturation temperature of LED chip along with a 257% increase in thermal conductivity.

Experimental study of ice melting of concrete permeable brick sidewalks using embedded carbon fibre heating wire

Electric heating methods have been proven to be effective means to melt ice on sidewalks and bridge decks. However, sidewalks are covered with permeable concrete bricks separated by gaps, which differ from surfaces of roads and bridge decks. Therefore, it is necessary to study methods of melting ice on sidewalks. In this paper, a method for melting ice on sidewalks based on carbon fibre heating wire (CFHW) is proposed. The experiments compare the effects of various environment temperatures, wind speeds, and energising voltages and spacings of CFHW on the surface temperature and melting of ice on sidewalk specimens. The transfer law of heat energy produced by CFHW inside the specimen and the effect of sealing concrete brick holes with a thermal conductive silicone grease in ice melting sidewalks are analysed. The results show that the proposed method has good ice melting performance on sidewalks.

Effect of various nanoparticle fillers on the thermal contact resistance (TCR) between crystals and aluminium alloys materials

This study fills a gap in how various nanoparticle fillers affect the thermal contact resistance (TCR) of the thermal material interface between different materials. Thermal interface materials (TIMs) provide a vital method for the reduction of thermal contact resistance and can greatly improve thermal conductivity between surfaces in contact. This study investigates the working characteristics of ammonium dihydrogen phosphate (ADP) crystals and aluminium alloy (5A06) in an inertial confinement fusion (ICF) device, where TIMs with a thermally conductive silicone grease QM850 as the base was prepared and doped with five different types of nanoparticles. The effects of nanoparticle type, volume ratio, and surface roughness of the aluminium alloy on TCR were determined through experimental analysis. The results demonstrate that, when the volume ratio of nanoparticles in TIMs is held constant, TCR decreases as the thermal conductivity of nanoparticles increases. TCR reaches its lowest value at a volume ratio of 30% but increases significantly due to agglomeration effects when the ratio exceeds this point. The aluminium alloy's surface roughness also impacts TCR, but the addition of nanocomposites with varying volume content as TIMs can effectively mitigate this effect. This study provides valuable theoretical support for reductions in TCR between metal and crystal materials, which can significantly affect the thermal structural design of crystal modules.

Effect of gas–liquid phase change of axial rotating heat pipe on fluid-thermal-solid behaviors of high-speed spindle

The thermal deformation control (TDC) of the high-speed spindle (HSS) is difficult to be realized because the nonlinear, non-steady, and varying influencing factors, and traditional cooling system cannot effectively dissipate the internal heat and realize TDC. It is expected to effectively export the internal heat of HSS with a reasonable design and manufacturing. To effectively realize HSS cooling and TDC, the effect of gas–liquid phase change of axially rotating heat pipe (ARHP) on fluid-thermal-solid behaviors of HSS is investigated. The ARHP, which is suitable for HSS cooling and TDC, is designed. Then an experimental platform is constructed to study the operation performance and heat dissipation performance (HDP) of the designed ARHP under different working conditions. The effects of the rotational speed, heat flux, and cooling air flow rate on HDP of ARHP are investigated. The designed ARHP is embedded into the original HSS (O-HSS) to dissipate the internal heat, and the silicone grease (SG) is used to fill the gap between the ARHP and shaft core of HSS, increasing the contact area and enhancing heat transfer. Then the fluid-thermal-solid coupling behavior of HSS is simulated and experimentally studied. To verify the effectiveness of the designed ARHP and the proposed heat dissipation scheme, the fluid-thermal-solid coupling behaviors of O-HSS, HSS with ARHP (ARHP-HSS), and HSS with ARHP and SG (ARHP-SG-HSS) are compared. The results show that the maximum temperatures of ARHP-SG-HSS and ARHP-HSS are reduced by 50% and 43.5% compared with that of O-HSS, respectively. Moreover, the maximum thermal balance time of O-HSS, ARHP-HSS, and ARHP-SG-HSS is 1450 s, 800 s, 500 s, respectively. The maximum thermal deformation (TD) ranges of O-HSS, ARHP-HSS, and ARHP-SG-HSS are [-35 μm, 25 μm], [-20 μm, 10 μm], and [-20 μm, 10 μm], respectively. The maximum TDs of ARHP-SG-HSS and ARHP-HSS are reduced by 76.5% and 58.8% compared with maximum TD of O-HSS, respectively.

Thermal Management System of Vapor Compression for Downhole Instrument

Abstract As the depth of oil and gas exploration increases, downhole electronics face the threat of high-temperature failure. At present, passive cooling technology has the problem of short working time, while active cooling technology has low energy utilization. This paper presents a thermal management system of vapor compression with a combination of active and passive cooling. The system uses insulation materials to isolate the high-temperature environment, thermally conductive silicone grease to strengthen the heat exchange in the evaporator, and vapor compression refrigeration cycles to absorb internal heat. The coefficient of performance (COP), exergy destruction and exergy efficiency of octane, nonane, and cyclohexane as refrigerants were examined, and the effects of different insulation materials on refrigeration performance were studied from both theoretical and numerical perspectives. The results showed that cyclohexane exhibited the best cooling capacity with a COP of 1.296 and a exergy efficiency of 49.21%. The thermal management system cooling performance is optimal when the insulation material is a vacuum flask, with an effective cooling capacity of 121.7 W.

Monolithic scintillator PET detector by using light sharing between adjacent detector modules

A monolithic crystal-based positron emission tomography (PET) detector has a low cost and high sensitivity and allows determining 3D positions by scintillation light distribution. However, the edge effect inherent to scintillators deteriorates the position resolution of the detector toward the crystal borders due to the escape and reflection of the scintillation light. An increase in crystal thickness will improve the detection efficiency, but the edge effect becomes severe. To improve the position resolution and detection efficiency of scintillators, the light-sharing technique is developed. Two identical trapezoidal monolithic cerium-doped lutetium yttrium orthosilicate (LYSO) crystals with a bottom size of 25.80 × 25.80 mm2 and a thickness of 20 mm are optically coupled at one lateral face by an optical medium. The scintillation light near the optically coupled interface is jointly collected by two adjacent 8 × 8 SiPM arrays from the bottom faces. The SiPM signals are individually read out and processed by using the multichannel readout application-specific integrated circuits (ASICs) of TOFPET2 to provide a light distribution. The transverse positions and depth of interaction (DOI) are calculated from the measured light distribution. As expected, the optical glue with a refractive index of n = 1.68 shows better light sharing between two LYSO crystals than the coupling media of silicon grease (n = 1.40) and air. For the 20 mm thick monolithic LYSO-based PET detector, the transverse position resolution near the crystal edge is improved by nearly 30% by using the light-sharing method compared with the black-painted treatment. However, the DOI resolution near the edge of the crystal is not significantly improved, which may be attributed to the incomplete collection of scintillation light. The DOI resolution of the detector would be improved by using electronics with lower noise and SiPM arrays with smaller pixel.

Enhanced Thermally Conductive Silicone Grease by Modified Boron Nitride

In this work, a chemical modification method was used to prepare silicone grease with high thermal conductivity. We report two preparation methods for thermal conductive fillers, which are hydroxylated boron nitride-grafted carboxylic silicone oil (h-BN-OH@CS) and amino boron nitride-grafted carboxylic silicone oil (h-BN-NH2@CS). When h-BN-OH@CS and h-BN-NH2@CS were filled with 30 wt% in the base grease, the thermal conductivity was 1.324 W m−1 K−1 and 0.982 W m−1 K−1, which is 6.04 and 4.48 times that of the base grease (0.219 W m−1 K−1), respectively. The interfacial thermal resistance is reduced from 11.699 °C W−1 to 1.889 °C W−1 and 2.514 °C W−1, respectively. Inorganic filler h-BN and organic filler carboxylic silicone oil were chemically grafted to improve the compatibility between h-BN and the base grease. The covalent bond between functionalized h-BN and carboxylic silicone oil is stronger than the van der Waals force, which can reduce the viscosity of the silicone grease.

Research on thermal protection of piezoelectric pressure sensor for shock wave pressure measurement in explosion field

PurposeThe purpose of this study is to clarify the mechanism of ambient and transient temperature effects on piezoelectric pressure sensors, and to propose corresponding compensation measures. The temperature of the explosion field has a significant influence on the piezoelectric sensor used to measure the shock wave pressure. For accurate shock wave pressure measurement, based on the actual piezoelectric pressure sensors used in the explosion field, the effects of ambient and transient temperatures on the sensor should be studied.Design/methodology/approachThe compensation method of the ambient temperature is discussed according to the sensor size and material. The theoretical analysis method of the transient temperature is proposed. For the transient temperature conduction problem of the sensor, the finite element simulation method of structure-temperature coupling is used to solve the temperature distribution of the sensor and the change in the contact force on the quartz crystal surface under the step and triangle temperatures. The simulation results are highly consistent with the theory.FindingsBased on the analysis results, a transient temperature control method is proposed, in which 0.5 mm thick lubricating silicone grease is applied to the sensor diaphragm, and 0.2 mm thick fiberglass cloth is wrapped around the sensor side. Simulation experiments are carried out to verify the feasibility of the control method, and the results show that the control method effectively suppresses the output of the thermal parasitic.Originality/valueThe above thermal protection methods can effectively improve the measurement accuracy of shock wave pressure and provide technical support for the evaluation of the power of explosion damage.

Originating Point of Traveling Waves on a Spherical Field Dependent on the Nature of Substrate Surface

The Belousov–Zhabotinsky (BZ) reaction was investigated to understand how the direction of traveling waves (TWs) is determined in a spherical field. A cation-exchange resin bead loaded with the catalyst of the BZ reaction was placed on a glass plate coated with silicone greases with different surface densities. TWs were generated at the contact point between the bead and glass plate for a lower density silicone grease, and at the upper half of the bead for a higher density silicone grease. In addition, TWs were generated in the middle section of the bead, which was sandwiched between two parallel glass plates coated with a high-density silicone grease. The experimental results were qualitatively reproduced by numerical calculations. These results are discussed in relation to the adsorption of Br2 into the silicone grease as the source of the inhibitor.