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Preparation and characterization of a new magnetic fluid with good low temperature resistance

Nano Research 2025年第1期18卷 477-486页

作者： Shilin Nie decai li ✉1 Department of Mechanical Engineering Tsinghua UniversityBeijing 100084China State Key Laboratory of Tribology in advanced equipment Tsinghua UniversityBeijing 100084China

Magnetic fluids are a type of novel functionalmaterial that has emerged over the past two decades, whichhave found applications in various aspects of production anddaily life. However, the application of conventional magneticfluids in low-temperature environments is severely limited andoften unsatisfactory. To address this issue, we havedeveloped a new magnetic fluid with excellent low-temperatureresistance. Initially, bare Fe_(3)O_(4) magnetic nanoparticles(FMNPs) were synthesized via co-precipitation without aprotective gas. Subsequently, these particles were modified using polyethylene glycol (PEG)-4000 as a surfactant. Thebare and modified FMNPs (MFMNPs) were characterized using X-ray diffraction (XRD), vibrating sample magnetometer(VSM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetricanalysis-differential thermal gravimetric (TGA-DTG) analysis. The rheological properties, low-temperature resistance of themagnetic fluid were also evaluated. The characterization results indicate that the MFMNPs are spherical andmonodisperse, with a narrow size distribution and a mean particle size of approximately 12 nm. Furthermore, the FTIRspectra and TGA-DTA results suggest that PEG-4000 is linked to the bare Fe_(3)O_(4) particles via hydrogen bonding, indicatingsuccessful modification of the Fe_(3)O_(4) magnetic nanoparticles using PEG. VSM measurements demonstrate that surfacemodification does not alter the crystal morphology or superparamagnetic of Fe_(3)O_(4). However, it does reduce the saturationmagnetization from 68.17 to 54.75 emu/g. Additionally, the prepared magnetic fluid exhibits shear thinning and magneticviscosity effects. It also exhibits excellent low-temperature resistance, maintaining good fluidity without freezing even at -60 ℃. In summary, these results collectively indicate that the new low-temperature resistant magnetic fluid developed in thisstudy is stable and has broad application prospects.

关键词： magnetic fluid low-temperature resistance polyethylene glycol ethylene glycol aqueous solution superparamagnetic

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Control of Magnetic Particle Size in Ferrofluid and Its Effect on Rheological Properties

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Chinese Journal of Mechanical Engineering 2022年第3期35卷 227-235页

作者： Siyu Chen decai li State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China

Rheological properties are the theoretical basis and the key to common problems in ferrofluid applications,therefore they are expected to be adjustable to satisfy different technical requirements through altering the microstructure of ferrofluid during the process of *** this paper,Four ferrofluid samples with different magnetic particle size were prepared by controlling the concentration of precursor solution during co-precipitation process and the rheological properties of these samples were *** samples exhibited field-controlled rheological *** magnetic field would enhance the formation of microstructures,resulting in an increase of *** with the increase of shear rate,microstructures tended to be destroyed,causing viscosity to *** were two opposing mechanisms of the influence of precursor solution *** one hand,the reduction of the precursor solution concentration would produce primary magnetic particles of smaller *** on the other hand,the surfactant became insufficient to completely coat the magnetic particles because of an increased specific surface area,causing the magnetic particles to aggregate and form secondary clustering structures which strongly enhanced the magnetoviscous effect and weakened the viscoelastic effect.

关键词： Ferrofluid Rheology Magnetoviscous effect Viscoelastic effect

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Theory analyses and applications of magnetic fluids in sealing

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Friction 2023年第10期11卷 1771-1793页

作者： decai li Yanwen li Zixian li Yuming WANG State Key Laboratory of Tribology Tsinghua UniversityBeijing100084China

Magnetic fluids are the suspensions composed of magnetic nanoparticles,surfactants,and non-magnetic carrier *** fluids are widely used in various fields,especially in sealing,because of their excellent features,including rapid magnetic response,flexible flow ability,tunable magneto-viscous effect,and reliable self-repairing ***,we provide an in-depth,comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories:static sealing,rotary sealing,and reciprocating *** summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present,particularly focusing on the recent progress of magnetic fluid *** magnetic fluid sealing technology has been commercialized and industrialized,many difficulties still exist in its *** the end of the review,the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.

关键词： magnetic fluid sealing mechanism static sealing rotary sealing reciprocating sealing

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An Experimental Validation Study on Ferrofuid Evaporation

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Chinese Journal of Mechanical Engineering 2022年第4期35卷 159-168页

作者： Wenjuan Yu decai li Sifang Niu School of Mechanical Electronic and Control Engineering Beijing Jiaotong UniversityBeijing 100044China State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China

The current research on the evaporation of ferrofuids mainly focuses on the characterization of ultra-low vapor pressure ferrofuids in vacuum and the theoretical analysis of the evaporation *** studies have focused on the experimental validation of the proposed evaporation rate equations and on the comparison of the diferences in ferrofuid *** this study,based on the Bolotov’s model,an evaporation rate equation is deduced from the experimental *** experimental study included a comparison of the evaporation,magnetic particle volume fraction,temperature,height of the fuid surface from the outlet,and magnetic feld of a kerosene-based ferrofuid and its base carrier *** prepared sample was evaporated in a test tube,and the evaporation rate was calculated by measuring the weight loss of the *** experimental results show that the evaporation rate of the base carrier liquid is higher than that of the *** smaller the volume fraction of the magnetic particles,the greater the evaporation *** magnetic particles play a key role in preventing evaporation of the base *** higher the temperature,the smaller the deviation of the evaporation rate from the predicted *** evaporation rates obtained by the two control groups at the height of the fuid surface from the outlet were lower than the predict *** magnetic feld had a certain promotional efect on the evaporation of the *** experimental results were consistent with the results obtained using Bolotov’s *** research validates Bolotov’s model and shows that the model is somewhat biased but still responds well to diferent variables.

关键词： Evaporation rate Experimental study Ferrofuid Kerosene Magnetic feld Validation

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Magnetic and luminescent properties of bifunctional composite Fe_(3)O_(4)@Y_(2)O_(2)S:Eu^(3+)

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Journal of Rare Earths 2024年第8期42卷 1568-1576,I0006页

作者： Zhiqi liang Zhili Zhang liu li Wen Xu decai li School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing100044China Beijing Key Laboratory of Flow and Heat Transfer of Phase Changing in Micro and Small Scale Beijing100044China State Key Laboratory of Tribology Tsinghua UniversityBeijing100084China

As a kind of non-destructive testing method,magnetic particle inspection is widely used in the fields of aviation and high-speed *** properties of magnetic fluorescent bifunctional composites,such as fluorescence intensity and magnetic properties,have increasing demands in magnetic particle *** earth compounds offer potential as novel materials for fluorescent magnetic bifunctional composites due to their excellent optical properties and extremely narrow emission *** this work,the rare earth fluorescent material Y_(2)O_(2)S:Eu^(3+) was synthesized by solid-state reaction ***_(3)O_(4)nanoparticles prepared by hydrothermal method were uniformly coated on the Y_(2)O_(2)S:Eu^(3+) particles through physical adsorption of *** obtained Fe_(3)O_(4)@Y_(2)O_(2)S:Eu^(3+) exhibits dark red color under the ultraviolet *** additio n,X-ray diffractio n,morphology,photoluminescence and hyste resis loop of Fe_(3)O_(4)@Y_(2)O_(2)S:Cu^(3+) were *** luminescence mechanism of Y_(2)O_(2)S:Eu^(3+) is described in detail Fe_(3)O_(4)@Y_(2)O_(2)S:Cu^(3+) displays good paramagnetism and has a good controllability under a magnetic *** magnetic particle inspection of Fe_(3)O_(4)@Y_(2)O_(2)S:Eu^(3+) was performed using a 4-pole electromagnet and a test piece *** magnetic fluorescent bifunctional composite presented in this work can be applied for non-destructive testing.

关键词： Bifunctional material Fe_(3)O_(4) Y_(2)O_(2)S:Eu^(3+) Luminescence Solid-state reaction Rare earths

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Typical dampers and energy harvesters based on characteristics of ferrofluids

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Friction 2023年第2期11卷 165-186页

作者： Yanwen li Pengdong HAN decai li Siyu CHEN Yuming WANG State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China School of Mechanical Engineering North China University of Water Resources and Electric PowerZhengzhou 450045China

Ferrofluids are a type of nanometer-scale functional material with fluidity and *** are composed of ferromagnetic particles,surfactants,and base *** main characteristics of ferrofluids include magnetization,the magnetoviscous effect,and levitation *** are many mature commercial ferrofluid damping applications based on these characteristics that are widely used in numerous ***,some ferrofluid damping studies such as those related to vibration energy harvesters and biomedical devices are still in the laboratory *** review paper summarizes typical ferrofluid dampers and energy harvesting systems from the 1960s to the present,including ferrofluid viscous dampers,ferrofluid inertia dampers,tuned magnetic fluid dampers(TMFDs),and vibration energy *** particular,it focuses on TMFDs and vibration energy harvesters because they have been the hottest research topics in the ferrofluid damping field in recent *** review also proposes a novel magnetic fluid damper that achieves energy conversion and improves the efficiency of vibration ***,we discuss the potential challenges and development of ferrofluid damping in future research.

关键词： ferrofluid characteristics damping applications ferrofluid viscous dampers ferrofluid inertia dampers tuned magnetic fluid dampers(TMFDs) vibration energy harvesters

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Theoretical Analysis and Experimental Study on Breakaway Torque of Large-diameter Magnetic liquid Seal at Low Temperature

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Chinese Journal of Mechanical Engineering 2013年第4期26卷 695-700页

作者： ZHANG Haina li decai WANG Qinglei ZHANG Zhili School of Mechanical Electronic and Control EngineeringBeijing Jiao Tong University

The existing researches of the magnetic liquid rotation seal have been mainly oriented to the seal at normal temperature and the seal with the smaller shaft diameter less than 100 mm. However, the large-diameter magnetic liquid rotation seal at low temperature has not been reported both in theory and in application up to now. A key factor restricting the application of the large-diameter magnetic liquid rotation seal at low temperature is the high breakaway torque. In this paper, the factors that influence the breakaway torque including the number of seal stages, the injected quantity of magnetic liquid and the standing time at normal temperature are studied. Two kinds of magnetic liquid with variable content of large particles are prepared first, and a seal feedthrough with 140 mm shaft diameter is used in the experiments. All experiments are carried out in a low temperature chamber with a temperature range from 200℃ to -100℃. Different numbers of seal stages are tested under the same condition to study the relation between the breakaway torque and the number of seal stages. Variable quantity of magnetic liquid is injected in the seal gap to get the relation curve of the breakaway torque and the injecting quantity of magnetic liquid. In the experiment for studying the relation between the breakaway torque and the standing time at the normal temperature, the seal feedtrough is laid at normal temperature for different period of time before it is put in the low temperature chamber. The experimental results show that the breakaway torque is proportional to the number of seal stages, the injected quantity of magnetic liquid and the standing time at the normal temperature. Meanwhile, the experimental results are analyzed and the torque formula of magnetic liquid rotation seal at low temperature is deduced from the Navier-Stokes equation on the base of the model of magnetic liquid rotation seal. The presented research can make wider application of the magnetic liquid seal

关键词： magnetic liquid breakaway torque low temperature large-diameter

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Theoretical and experimental study on magnetic-fluid-based flow sensors

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Chinese Science Bulletin 2011年第17期56卷 1844-1847页

作者： HAO RuiCan li decai School of Mechanical Electronic and Control Engineering Beijing Jiaotong University Beijing 100044 China

The dependence of flow volume on the pressure difference between the ports of a U-tube was determined for both laminar and turbulent flows of a magnetic *** results showed that the dependence was linear in the case of laminar flow but was non-linear in the case of turbulent *** addition,the inductance and the voltage difference across two coils around the arms of the U-tube were *** voltage difference was proportional to the flow volume and inversely proportional to the square of the coil *** theoretical and experimental results demonstrate that the design of magnetic-fluid-based flow sensors is feasible.

关键词：流量传感器磁流体实验线圈长度 U型管非线性电压差压力差

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Numerical and experimental study of magnetic fluid seal with large sealing gap and multiple magnetic sources

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Science China(Technological Sciences) 2013年第11期56卷 2865-2869页

作者： YANG XiaoLong ZHANG Zhili li decai School of Mechanical Electronic and Control EngineeringBeijing Jiaotong University

To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was *** field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid *** effects of sealing gap height and magnetic source amount on the sealing capability were investigated *** theoretical and experimental results were compared,analyzed and *** results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large *** theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 ***,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.

关键词： experimental study magnetic fluid multiple magnetic sources numerical simulation seals

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Discriminative Features of Abnormities in a Spiral Groove Gas Face Seal Based on Dynamic Model Considering Contact

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Chinese Journal of Mechanical Engineering 2022年第2期35卷 135-149页

作者： Yuan Yin Weifeng Huang decai li Songtao Hu Xiangfeng liu Ying liu State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong UniversityShanghai 200240China

It is a difficult task to root the cause of the failure of a gas face seal because different causes may result in similar *** the work being presented,the discrimination of multiple types of abnormities in a spiral groove gas face seal is studied.A dynamic model is employed to analyze groups of cases in order to uncover the dynamic behaviors when the face contact is induced by different mixtures of abnormities,whose discriminative features when motion and contact are monitored are studied and uncovered.A circumferential-pattern-related oscillation phenomenon is discovered,which is extracted from contact information and implies the relative magnitude of the moment on stator and the rotor *** experimental observation shows consistent *** means that the grooves(or other circumferential patterns)generate useful informative features for *** results provide guidance for designing a monitored gas face seal system.

关键词： Gas face seals Dynamics Tribology Nonlinear system

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