The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anod...The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309 L/308 L SS DMW.展开更多
We report a facile method of synthesizing graphene quantum dots（GQDs） with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photol...We report a facile method of synthesizing graphene quantum dots（GQDs） with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π –π ＊ gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.展开更多
The processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. In order to improve the handling properties, the fine-grained particles, i.e...The processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. In order to improve the handling properties, the fine-grained particles, i.e. host-particles, are coated with various nanoparticles, i.e. vip-particles. The mixing of fine-grained powders is influenced by particle-particle interactions. If these forces are distinctively used, both interactive and ordered mixtures can be produced. These particle mixtures consist of composite-particles that have new physical properties. These modified properties depend strongly on the coating process, the diameter- and mass-relationship of the vip- and the host-particles. The properties of the composite-particles can systematically be adjusted to the requirements of industrial applications. For example, a laboratory bubbling fluidized bed can be used to describe the conveying behavior of the functionalized host-particles. Applications for the functionalized particles are in the pharmaceutical and the powder coating industries, e.g. enhanced dry powder inhalers and thin lacquer films. The present research compares three different mixing/coating processes. The composite-particles are characterized by TEM, SEM and with their fluidization characteristics. The coating process itself is monitored by the electrostatic charge of the particles.展开更多
To predict the particle size and layer-thickness distributions(LTDs)in a continuously operated horizontal fluidized-bed granulation process,two alternative models were considered.A one-dimensional two-zone model was p...To predict the particle size and layer-thickness distributions(LTDs)in a continuously operated horizontal fluidized-bed granulation process,two alternative models were considered.A one-dimensional two-zone model was proposed,which describes with population-balance equations the particle growth in a spraying zone that is separated from the drying zone.The residence-time distribution(RTD)was calculated from a literature correlation and was coupled with a population-balance model via a tank-in-series model with reflux.A two-dimensional,one-zone population-balance model,which was based directly on the RTD and the feed particle-size distribution(PSD)was also used.Granulation experiments were conducted and analyzed microscopically and with a camera optical device to determine the sample PSDs.LTDs over the particle population were derived from the PSDs and were analyzed directly by micro-computer-tomography.To compare the simulated data with the experimentally determined distributions,the PSDs were converted to LTDs.The good agreement shows that both methods are suitable to determine the PSD from an RTD of an arbitrary granulation process in a horizontal fluidized bed.Improvement appears necessary with regards to the LTD spread.展开更多
In order to improve the efficiency of reducing fine dust emissions from diffuse sources,the commonly used water mist can be electrostatically charged.Thus,the attraction between particles and droplets increases due to...In order to improve the efficiency of reducing fine dust emissions from diffuse sources,the commonly used water mist can be electrostatically charged.Thus,the attraction between particles and droplets increases due to electrostatic field forces.In the experimental investigations carried out,an electrostatic two-fluid nozzle was used to generate a charged spray mist according to the principle of charging by induction.In a chamber,dispersed dust was precipitated with the spray mist,while detecting the laser light attenuation.By means of comparative measurements it could be shown that faster sedimentation and separation takes place through electrostatic attraction.Parameter variations regarding the use of compressed air and water were investigated and the sedimentation time of the particle-droplet mixture in the chamber was shown.A size distribution was then calculated from the laser light attenuation,which shows that the proportion of small particles decreases with spray application.Furthermore,the influence of the polarity of droplets and solid particles on the reduction measure was determined.展开更多
Particle interactions are of crucial importance in many applications including fluidized beds and other powder handling systems. The present contribution discusses how surface properties of the particles can be determ...Particle interactions are of crucial importance in many applications including fluidized beds and other powder handling systems. The present contribution discusses how surface properties of the particles can be determined in order to get quantitative information on particle interactions. For instance, we apply adsorption experiments in order to get information on dispersive and polar interactions. These measurements are complemented by careful roughness measurements as well as FTIR-spectroscopy and TG-MS analysis. Adhesion force measurements with AFM and ultra-centrifuge on well defined ideal as well as heterogeneous surfaces led to the introduction of three generic types of adhesion force distributions: monomodal Weibull, bimodal Weibull and lognormal. The influence of roughness and adsorbed layers on adhesion are shown. In addition, we discuss important aspects of the dynamic nature of the adhesion/detachment process by means of MD-simulations.展开更多
We describe the development of a T-mixer based continuous flow process for the coating of 86-500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth.After establis...We describe the development of a T-mixer based continuous flow process for the coating of 86-500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth.After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters.This reveals a considerable tunability of the patch morphology and,by virtue of the localized surface plasmon resonance of gold,the optical properties of the product dispersions.In order to further widen the range of nanostructures accessible by our process,a second T-mixer was added.This introduced new gold precursor,leading to further growth of the patches that were formed after the first mixer.By this approach,nearly-complete gold nanoshells could be produced in high yield on both small and large core particles,without the unwanted production of free-standing gold nanoparticles.Due to the pronounced optical properties of nearly-complete gold nanoshells on small core particles,we could estimate from electrodynamic sim-ulations the equivalent shell thickness to be as low as 8.6 nm.This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells.Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical properties.展开更多
Particle distribution in the cross-section of the flighted rotating drum(FRD)is critical to the analysis of heat and mass transfer between gas and solids.In this work,the particle tracking velocimetry(PTV)method is ap...Particle distribution in the cross-section of the flighted rotating drum(FRD)is critical to the analysis of heat and mass transfer between gas and solids.In this work,the particle tracking velocimetry(PTV)method is applied to study the influence of the number of flights on the particle motion in FRDs.The drum,installed with 1,4,8,or 12 rectangular flights,is filled with plastic balls to 15%and operated at various rotating speeds ranging from 10 rpm to 30 rpm.The results show that the number of flights has different effects on the holdup ratio and cascading rate of single flight and active flights.With 8 and 12 flights,the FRD produces a larger and more stable particle ratio of the dilute phase.Moreover,DEM simulations agree with PTV measurements,whereas literature models show significant deviations.展开更多
The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent aff...The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent affect the suspension properties and thus the layer morphology.We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics.Highly branched carbon blacks with a high surface area tend to form less cracked layers.As less branched carbons can pack together more closely,a smaller pore size results in a larger capillary pressure during drying and thus more cracks.The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles.The carbon black aggregates are thus smaller,resulting in closer packing and thinner layers.Moreover,the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer,preventing crack formation.An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.展开更多
Dynamic image analysis provides an automated evaluation method to determine the size and shape of multiple particles. This method represents a common application for ordinary bulk material. The latest draft of ISO 13...Dynamic image analysis provides an automated evaluation method to determine the size and shape of multiple particles. This method represents a common application for ordinary bulk material. The latest draft of ISO 13322–2:2021 describes the state of the art, but lacks instructions for handling fibrous bulk material. Interlocking fibres complicate the measurement conditions and require a disentanglement of fibrous samples during a pre-dispersion step. A further error source includes the fibre orientation inside the measurement zone of the device. If the thresholding algorithm fails to differentiate between the fibre projection area and the background, a subsequent image optimisation solves the problem. This article addresses the mentioned problems by analysing cotton cellulose and polyacrylonitrile fibres. Besides the execution of a pre-dispersion step, the experiments compare the discrepancies between dry and wet dispersion. Here, the software packages PAQXOS and ImageJ perform the image evaluation. In this case, the wet dispersion setup with a subsequent image evaluation by ImageJ provides comprehensible results.展开更多
A scalable method for graphene and few-layer graphene （FLG） production by graphite delamination in aqueous solutions of the nonionic surfactant TWEEN 80 （TW80） using stirred-media mills is presented. Delaminated p...A scalable method for graphene and few-layer graphene （FLG） production by graphite delamination in aqueous solutions of the nonionic surfactant TWEEN 80 （TW80） using stirred-media mills is presented. Delaminated product analysis using statistical Raman spectroscopy yielded extensive processing-structure-property relationships that revealed how stress intensity and specific energy input, i.e., the process parameters, govern the yield of graphene production and defect formation. The dispersed carbon concentration increased but the content and the quality of the FLG product decreased sharply with higher specific energy input. The FLG content of the product was up to 90%, especially for low specific energy input. Moreover, Raman analyses revealed that stress intensities greater than about I nJ were related to significant defect formation in the product particles. Another key parameter for graphene production is solvent viscosity. The FLG concentration in the product increased by a factor of 10 when the solvent＇s viscosity was increased from 1 to 6 mPa-s because shear- and friction-induced delamination was enhanced and in-plane fracture was reduced due to dampening of bead motion. Based on the processing-structure-property relationships found, we propose that the delamination process can be designed in such way that the product consists, almost totally, of FLG and that single-layer graphene is produced. The scalability of graphene production by stirred-media delamination was demonstrated when an increase in the batch size from 0.2 to 2 L had no significant effect on product quality.展开更多
The interaction of evaporating droplets and hot catalyst particles plays a major role in heterogeneously catalysed reactions. The liquid feed is injected into a gas-solid flow and is mixed with the catalyst. The inter...The interaction of evaporating droplets and hot catalyst particles plays a major role in heterogeneously catalysed reactions. The liquid feed is injected into a gas-solid flow and is mixed with the catalyst. The interaction phenomena determine the evaporation time which should be minimised to keep the reactor vessel small. First measurements with a bed of fixed hot FCC-particles （fluid catalytic cracking） and two model fluids have been conducted. The interactions of ethanol and water droplets with the hot bed surface were captured via a high-speed camera. While the ethanol droplet developed a stable steam cushion due to Leidenfrost phenomena, water showed intense interaction and steam explosions which induced repulsion and atomisation of the droplet.展开更多
Dust emissions during storage of non-moving bulk materials are studied with a numerical method.The model relies on a contact-model-free Discrete Element Method(DEM)to model the bulk particle-fluid interaction and the ...Dust emissions during storage of non-moving bulk materials are studied with a numerical method.The model relies on a contact-model-free Discrete Element Method(DEM)to model the bulk particle-fluid interaction and the dust removal coupled with Computational Fluid Dynamics(CFD)to model the gas and the dust phase in a multiphase framework.Here,two storage scenarios are considered:a flown through packed bed and a flown over stockpile.For the first,the performed simulations reveal that the dust discharge can be correlated with the passing fluid pressure drop.For the second,a parameter study of factors influencing the dust emissions is performed.The parameters discussed are the stockpile size,the gas velocity,the slope angle,the particle diameter and the shape of the stockpile,taking into account conical and truncated conical stockpiles.Dust release correlations are obtained for both scenarios,which reflect very well the obtained numerical results.展开更多
For most particle-based applications, formulation in the liquid phase is a decisive step, and thus, particle interactions and stability in liquid media are of major importance. The concept of Hansen solubility paramet...For most particle-based applications, formulation in the liquid phase is a decisive step, and thus, particle interactions and stability in liquid media are of major importance. The concept of Hansen solubility parameters (HSP) was initially invented to describe the interactions of (polymer) molecules and their solubility in different liquids and is increasingly being used in particle technology to describe dispersibility. Because dispersions are not thermodynamically stable, the term Hansen dispersibility parameters (HDP) is used instead of HSP (SiiE, Sobisch, Peukert, Lerche,& Segets, 2018). Herein, we extend a previously developed standardized and non-subjective method for determination of Hansen parameters based on analytical centrifugation to the important class of quantum materials. As a technically relevant model system, zinc oxide quantum dots (QDs) were used to transfer our methodology to nanoparticles (NPs) with sizes below lOnm. The results obtained using the standard procedure starting from a dried powder were compared with those obtained through redispersion from the wet sediment produced during the typical washing procedure of QDs, and drying was observed to play an important role. In conclusion, our study reveals the high potential of HDP for quantifying the interfacial properties of NPs as well as their link to dispersibility.展开更多
Molecular dynamics （MD） simulations of the consecutive compression-decompression cycles ot hexagonal zinc sulfide （wurtzite） nanoparticles predict an irreversible phase transformation to the cubic polymorph.The ph...Molecular dynamics （MD） simulations of the consecutive compression-decompression cycles ot hexagonal zinc sulfide （wurtzite） nanoparticles predict an irreversible phase transformation to the cubic polymorph.The phase transformation commences at the contact area between the particle and the inden- ter and proceeds with the number of compression cycles. Dislocations are visible for a particle size above 5nm. Results from wet grinding and dry powder compression experiments on a commercial wurtzite pigment agree qualitatively with MD simulation predictions. X-ray diffraction patterns reveal that the amount of cubic polymorph in the compressed samples increases with pressure applied to the powder. In comparison with powder compression, wet milling leads to a more pronounced phase transformation. This occurs because the particles are exposed to a large number of stress events by collision with the grinding media, which leads to the formation of defects and new surface crystallites by particle fracture. According to the MD simulations, phase transformation is expected to occur preferentially in surface crystallites because they experience the highest mechanical load. Because of the phase transformation, the wet ground and compressed samples exhibit a lower photo- luminescence intensity than the feed material. In comparison with powder compression, milling reduces the photoluminescence intensity more substantially. This occurs because a higher defect concentration is formed. The defects contribute to the phase transformation and photoluminescence quenching.展开更多
An important development in Particle Technology is directed towards tailored product properties, i.e. product engineering. Product properties are strongly related to the disperse properties of the particles, i.e. thei...An important development in Particle Technology is directed towards tailored product properties, i.e. product engineering. Product properties are strongly related to the disperse properties of the particles, i.e. their size, shape, morphology and surface. We discuss some general applicable principles in product engineering and give various examples. Strongly related to this approach are methods to characterize and to tailor product and particle properties. For systems which are controlled by the interfaces (e.g. particles in the micron size range and below) we apply a multi-scale approach from the particulate interfaces over particle interactions to the macroscopic properties. Thus, we tailor macroscopic product properties through microscopic control of the interfaces. This approach must be complemented by methods to characterize particle and product properties. It is shown that by careful consideration of the underlying physical processes considerable progress can be achieved.展开更多
Humanity has been facing the threat of a variety of ifectious diseases.Airborne microorganisms can cause airbome infectious diseases,which spread rapidly and extensively,causing huge losscs to human society on a globa...Humanity has been facing the threat of a variety of ifectious diseases.Airborne microorganisms can cause airbome infectious diseases,which spread rapidly and extensively,causing huge losscs to human society on a global scale.In recent years,the detection technology for airbome microorganisms has developed rapidly;it can be roughly divided into biochemical,immune,and molecular technologies.However,these technologies still have some shortcomings;they are time consuming and have low sensitivity and poor stability.Most of them need to be used in the ideal environment of a laboratory,which limits their applications.A biosensor is a device that converts biological signals into detectable signals.As an interdisciplinary feld,biosensors have successfully introduced a variety of technologies for bio-detection.Given their fast analysis speed,high sensitivity good portability,strong specifcity,and low cost,biosensors have been widely uised in cnvironmental monitoring,medical research,food and agricultural safety,military.medicine and other fields.In recent years,the performance of biosensors has greatly improved,becoming.a promising techmology for airborne microorganism detection.This review introduces the detection principle of biosensors from the three aspects of component identification,energy conversion principle,and signal amplification.It also summarizes its research and application in airborne microorganism detection.The new progress and future development trend of the biosensor detection of airbormne microorganisms are analyzed.展开更多
Fluidized bed opposed jet mills are capable of meeting the continuously growing dema nd for contamination-free fine particles.In this type of jet mill,the solid material is entrained and accelerated by expanding gas j...Fluidized bed opposed jet mills are capable of meeting the continuously growing dema nd for contamination-free fine particles.In this type of jet mill,the solid material is entrained and accelerated by expanding gas jets that are focused onto a focal point in side a fluidized bed.The resulting particle collisions induce breakage.The process is affected by the relative particle velocities and the number of particle-particle collisions.Clearly,both quantities are distributed.However,to date,neither relative particle velocities nor collision frequencies in such units have been determined.The present work introduces an innovative method to assess the stressing conditions in jet mills experimentally.To this end,mixtures of glass and ductile metal microspheres were used,with the latter employed in small amounts.Inter-particle collisions between the aluminum and glass spheres lead to the formation of dents on the microparticles.The size and number of these dents are associated with the individual collision velocities and overall collision frequencies.The correlation between dent size and collision velocity was obtained from finite element calculations based on empirical data.The proposed approach was validated using particle image velocimetry during secondary gas injection into a fluidized bed reactor.In this case the effect of the distance between two opposed nozzles was examined.For a lab-scaled fluidized bed opposed jet mill the effects of gas pressure and hold-up were investigated.Relative particle velocities were found to be sign ificantly lower tha n the gas velocities,while the nu mber of contacts per particle was determined to be extremely high.展开更多
基金the National Natural Science Foundation of China(No.51771211)Key Research Program of Frontier Sciences,CAS(QYZDY-SSW-JSC012)the Key Program of the Chinese Academy of Sciences(ZDRW-CN-2017-1)。
文摘The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309 L/308 L SS DMW.
基金Project supported by the National Basic Research Program of China(Grant Nos.2011CB932700 and 2011CB932703)the National Natural Science Foundation of China(Grant Nos.61335006,61378073,and 61077044)the Beijing Natural Science Foundation,China(Grant No.4132031)
文摘We report a facile method of synthesizing graphene quantum dots（GQDs） with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π –π ＊ gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.
文摘The processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. In order to improve the handling properties, the fine-grained particles, i.e. host-particles, are coated with various nanoparticles, i.e. vip-particles. The mixing of fine-grained powders is influenced by particle-particle interactions. If these forces are distinctively used, both interactive and ordered mixtures can be produced. These particle mixtures consist of composite-particles that have new physical properties. These modified properties depend strongly on the coating process, the diameter- and mass-relationship of the vip- and the host-particles. The properties of the composite-particles can systematically be adjusted to the requirements of industrial applications. For example, a laboratory bubbling fluidized bed can be used to describe the conveying behavior of the functionalized host-particles. Applications for the functionalized particles are in the pharmaceutical and the powder coating industries, e.g. enhanced dry powder inhalers and thin lacquer films. The present research compares three different mixing/coating processes. The composite-particles are characterized by TEM, SEM and with their fluidization characteristics. The coating process itself is monitored by the electrostatic charge of the particles.
基金the Forschungs-Gellschaft Verfahrens-Technik(GVT-IGF project no.17633 N)the German Federal Ministry of Science and Education(BMBF,WIGRATEC+project No.03WKCI4B).
文摘To predict the particle size and layer-thickness distributions(LTDs)in a continuously operated horizontal fluidized-bed granulation process,two alternative models were considered.A one-dimensional two-zone model was proposed,which describes with population-balance equations the particle growth in a spraying zone that is separated from the drying zone.The residence-time distribution(RTD)was calculated from a literature correlation and was coupled with a population-balance model via a tank-in-series model with reflux.A two-dimensional,one-zone population-balance model,which was based directly on the RTD and the feed particle-size distribution(PSD)was also used.Granulation experiments were conducted and analyzed microscopically and with a camera optical device to determine the sample PSDs.LTDs over the particle population were derived from the PSDs and were analyzed directly by micro-computer-tomography.To compare the simulated data with the experimentally determined distributions,the PSDs were converted to LTDs.The good agreement shows that both methods are suitable to determine the PSD from an RTD of an arbitrary granulation process in a horizontal fluidized bed.Improvement appears necessary with regards to the LTD spread.
文摘In order to improve the efficiency of reducing fine dust emissions from diffuse sources,the commonly used water mist can be electrostatically charged.Thus,the attraction between particles and droplets increases due to electrostatic field forces.In the experimental investigations carried out,an electrostatic two-fluid nozzle was used to generate a charged spray mist according to the principle of charging by induction.In a chamber,dispersed dust was precipitated with the spray mist,while detecting the laser light attenuation.By means of comparative measurements it could be shown that faster sedimentation and separation takes place through electrostatic attraction.Parameter variations regarding the use of compressed air and water were investigated and the sedimentation time of the particle-droplet mixture in the chamber was shown.A size distribution was then calculated from the laser light attenuation,which shows that the proportion of small particles decreases with spray application.Furthermore,the influence of the polarity of droplets and solid particles on the reduction measure was determined.
文摘Particle interactions are of crucial importance in many applications including fluidized beds and other powder handling systems. The present contribution discusses how surface properties of the particles can be determined in order to get quantitative information on particle interactions. For instance, we apply adsorption experiments in order to get information on dispersive and polar interactions. These measurements are complemented by careful roughness measurements as well as FTIR-spectroscopy and TG-MS analysis. Adhesion force measurements with AFM and ultra-centrifuge on well defined ideal as well as heterogeneous surfaces led to the introduction of three generic types of adhesion force distributions: monomodal Weibull, bimodal Weibull and lognormal. The influence of roughness and adsorbed layers on adhesion are shown. In addition, we discuss important aspects of the dynamic nature of the adhesion/detachment process by means of MD-simulations.
基金The authors gratefully acknowledge the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)for funding of the Cluster of Excellence"Engineering of Advanced Materials"(Project-ID 53244630).
文摘We describe the development of a T-mixer based continuous flow process for the coating of 86-500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth.After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters.This reveals a considerable tunability of the patch morphology and,by virtue of the localized surface plasmon resonance of gold,the optical properties of the product dispersions.In order to further widen the range of nanostructures accessible by our process,a second T-mixer was added.This introduced new gold precursor,leading to further growth of the patches that were formed after the first mixer.By this approach,nearly-complete gold nanoshells could be produced in high yield on both small and large core particles,without the unwanted production of free-standing gold nanoparticles.Due to the pronounced optical properties of nearly-complete gold nanoshells on small core particles,we could estimate from electrodynamic sim-ulations the equivalent shell thickness to be as low as 8.6 nm.This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells.Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical properties.
文摘Particle distribution in the cross-section of the flighted rotating drum(FRD)is critical to the analysis of heat and mass transfer between gas and solids.In this work,the particle tracking velocimetry(PTV)method is applied to study the influence of the number of flights on the particle motion in FRDs.The drum,installed with 1,4,8,or 12 rectangular flights,is filled with plastic balls to 15%and operated at various rotating speeds ranging from 10 rpm to 30 rpm.The results show that the number of flights has different effects on the holdup ratio and cascading rate of single flight and active flights.With 8 and 12 flights,the FRD produces a larger and more stable particle ratio of the dilute phase.Moreover,DEM simulations agree with PTV measurements,whereas literature models show significant deviations.
文摘The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer.The interactions between the ionomer,carbon black particles,and solvent affect the suspension properties and thus the layer morphology.We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics.Highly branched carbon blacks with a high surface area tend to form less cracked layers.As less branched carbons can pack together more closely,a smaller pore size results in a larger capillary pressure during drying and thus more cracks.The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles.The carbon black aggregates are thus smaller,resulting in closer packing and thinner layers.Moreover,the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer,preventing crack formation.An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.
文摘Dynamic image analysis provides an automated evaluation method to determine the size and shape of multiple particles. This method represents a common application for ordinary bulk material. The latest draft of ISO 13322–2:2021 describes the state of the art, but lacks instructions for handling fibrous bulk material. Interlocking fibres complicate the measurement conditions and require a disentanglement of fibrous samples during a pre-dispersion step. A further error source includes the fibre orientation inside the measurement zone of the device. If the thresholding algorithm fails to differentiate between the fibre projection area and the background, a subsequent image optimisation solves the problem. This article addresses the mentioned problems by analysing cotton cellulose and polyacrylonitrile fibres. Besides the execution of a pre-dispersion step, the experiments compare the discrepancies between dry and wet dispersion. Here, the software packages PAQXOS and ImageJ perform the image evaluation. In this case, the wet dispersion setup with a subsequent image evaluation by ImageJ provides comprehensible results.
基金This work was supported financially by the German Science Foundation （DFG）, Collaborative Research Centre SFB953： ＂Synthetic Carbon Allotropes＇. The authors would like to thank S. Romeis and C. Konnerth for interesting and profound discussions
文摘A scalable method for graphene and few-layer graphene （FLG） production by graphite delamination in aqueous solutions of the nonionic surfactant TWEEN 80 （TW80） using stirred-media mills is presented. Delaminated product analysis using statistical Raman spectroscopy yielded extensive processing-structure-property relationships that revealed how stress intensity and specific energy input, i.e., the process parameters, govern the yield of graphene production and defect formation. The dispersed carbon concentration increased but the content and the quality of the FLG product decreased sharply with higher specific energy input. The FLG content of the product was up to 90%, especially for low specific energy input. Moreover, Raman analyses revealed that stress intensities greater than about I nJ were related to significant defect formation in the product particles. Another key parameter for graphene production is solvent viscosity. The FLG concentration in the product increased by a factor of 10 when the solvent＇s viscosity was increased from 1 to 6 mPa-s because shear- and friction-induced delamination was enhanced and in-plane fracture was reduced due to dampening of bead motion. Based on the processing-structure-property relationships found, we propose that the delamination process can be designed in such way that the product consists, almost totally, of FLG and that single-layer graphene is produced. The scalability of graphene production by stirred-media delamination was demonstrated when an increase in the batch size from 0.2 to 2 L had no significant effect on product quality.
基金supported by the Deutsche Forschungsgemeinschaft(WI 972/20-1)
文摘The interaction of evaporating droplets and hot catalyst particles plays a major role in heterogeneously catalysed reactions. The liquid feed is injected into a gas-solid flow and is mixed with the catalyst. The interaction phenomena determine the evaporation time which should be minimised to keep the reactor vessel small. First measurements with a bed of fixed hot FCC-particles （fluid catalytic cracking） and two model fluids have been conducted. The interactions of ethanol and water droplets with the hot bed surface were captured via a high-speed camera. While the ethanol droplet developed a stable steam cushion due to Leidenfrost phenomena, water showed intense interaction and steam explosions which induced repulsion and atomisation of the droplet.
基金The research projects IGF 19411 N and IGF 20974 N of the research association Forschungs-Gesellschaft Verfahrens-Technik e.V.(GVT)are supported by the Federal Ministry of Economic Affairs and Energy through the German Federation of Industrial Research Associations(AiF)as part of a program for promoting industrial community research(IGF)on the basis of a decision by the German Bundestag.
文摘Dust emissions during storage of non-moving bulk materials are studied with a numerical method.The model relies on a contact-model-free Discrete Element Method(DEM)to model the bulk particle-fluid interaction and the dust removal coupled with Computational Fluid Dynamics(CFD)to model the gas and the dust phase in a multiphase framework.Here,two storage scenarios are considered:a flown through packed bed and a flown over stockpile.For the first,the performed simulations reveal that the dust discharge can be correlated with the passing fluid pressure drop.For the second,a parameter study of factors influencing the dust emissions is performed.The parameters discussed are the stockpile size,the gas velocity,the slope angle,the particle diameter and the shape of the stockpile,taking into account conical and truncated conical stockpiles.Dust release correlations are obtained for both scenarios,which reflect very well the obtained numerical results.
文摘For most particle-based applications, formulation in the liquid phase is a decisive step, and thus, particle interactions and stability in liquid media are of major importance. The concept of Hansen solubility parameters (HSP) was initially invented to describe the interactions of (polymer) molecules and their solubility in different liquids and is increasingly being used in particle technology to describe dispersibility. Because dispersions are not thermodynamically stable, the term Hansen dispersibility parameters (HDP) is used instead of HSP (SiiE, Sobisch, Peukert, Lerche,& Segets, 2018). Herein, we extend a previously developed standardized and non-subjective method for determination of Hansen parameters based on analytical centrifugation to the important class of quantum materials. As a technically relevant model system, zinc oxide quantum dots (QDs) were used to transfer our methodology to nanoparticles (NPs) with sizes below lOnm. The results obtained using the standard procedure starting from a dried powder were compared with those obtained through redispersion from the wet sediment produced during the typical washing procedure of QDs, and drying was observed to play an important role. In conclusion, our study reveals the high potential of HDP for quantifying the interfacial properties of NPs as well as their link to dispersibility.
基金supported financially by Arbeitsgemeinschaft industrieller Forschungsvereinigungen(AiF)(Grant No.:IGF333ZN)
文摘Molecular dynamics （MD） simulations of the consecutive compression-decompression cycles ot hexagonal zinc sulfide （wurtzite） nanoparticles predict an irreversible phase transformation to the cubic polymorph.The phase transformation commences at the contact area between the particle and the inden- ter and proceeds with the number of compression cycles. Dislocations are visible for a particle size above 5nm. Results from wet grinding and dry powder compression experiments on a commercial wurtzite pigment agree qualitatively with MD simulation predictions. X-ray diffraction patterns reveal that the amount of cubic polymorph in the compressed samples increases with pressure applied to the powder. In comparison with powder compression, wet milling leads to a more pronounced phase transformation. This occurs because the particles are exposed to a large number of stress events by collision with the grinding media, which leads to the formation of defects and new surface crystallites by particle fracture. According to the MD simulations, phase transformation is expected to occur preferentially in surface crystallites because they experience the highest mechanical load. Because of the phase transformation, the wet ground and compressed samples exhibit a lower photo- luminescence intensity than the feed material. In comparison with powder compression, milling reduces the photoluminescence intensity more substantially. This occurs because a higher defect concentration is formed. The defects contribute to the phase transformation and photoluminescence quenching.
文摘An important development in Particle Technology is directed towards tailored product properties, i.e. product engineering. Product properties are strongly related to the disperse properties of the particles, i.e. their size, shape, morphology and surface. We discuss some general applicable principles in product engineering and give various examples. Strongly related to this approach are methods to characterize and to tailor product and particle properties. For systems which are controlled by the interfaces (e.g. particles in the micron size range and below) we apply a multi-scale approach from the particulate interfaces over particle interactions to the macroscopic properties. Thus, we tailor macroscopic product properties through microscopic control of the interfaces. This approach must be complemented by methods to characterize particle and product properties. It is shown that by careful consideration of the underlying physical processes considerable progress can be achieved.
基金by the National Natural Science Foundation of China(Grant No.51678402)the Tianjin New Crown Epidemic Emergency Project(No.20ZXGBSY00100).
文摘Humanity has been facing the threat of a variety of ifectious diseases.Airborne microorganisms can cause airbome infectious diseases,which spread rapidly and extensively,causing huge losscs to human society on a global scale.In recent years,the detection technology for airbome microorganisms has developed rapidly;it can be roughly divided into biochemical,immune,and molecular technologies.However,these technologies still have some shortcomings;they are time consuming and have low sensitivity and poor stability.Most of them need to be used in the ideal environment of a laboratory,which limits their applications.A biosensor is a device that converts biological signals into detectable signals.As an interdisciplinary feld,biosensors have successfully introduced a variety of technologies for bio-detection.Given their fast analysis speed,high sensitivity good portability,strong specifcity,and low cost,biosensors have been widely uised in cnvironmental monitoring,medical research,food and agricultural safety,military.medicine and other fields.In recent years,the performance of biosensors has greatly improved,becoming.a promising techmology for airborne microorganism detection.This review introduces the detection principle of biosensors from the three aspects of component identification,energy conversion principle,and signal amplification.It also summarizes its research and application in airborne microorganism detection.The new progress and future development trend of the biosensor detection of airbormne microorganisms are analyzed.
基金the German Research Foundation through the DFG priority program 1679"Dynamic Simulation of Interconnected Solids Processes".
文摘Fluidized bed opposed jet mills are capable of meeting the continuously growing dema nd for contamination-free fine particles.In this type of jet mill,the solid material is entrained and accelerated by expanding gas jets that are focused onto a focal point in side a fluidized bed.The resulting particle collisions induce breakage.The process is affected by the relative particle velocities and the number of particle-particle collisions.Clearly,both quantities are distributed.However,to date,neither relative particle velocities nor collision frequencies in such units have been determined.The present work introduces an innovative method to assess the stressing conditions in jet mills experimentally.To this end,mixtures of glass and ductile metal microspheres were used,with the latter employed in small amounts.Inter-particle collisions between the aluminum and glass spheres lead to the formation of dents on the microparticles.The size and number of these dents are associated with the individual collision velocities and overall collision frequencies.The correlation between dent size and collision velocity was obtained from finite element calculations based on empirical data.The proposed approach was validated using particle image velocimetry during secondary gas injection into a fluidized bed reactor.In this case the effect of the distance between two opposed nozzles was examined.For a lab-scaled fluidized bed opposed jet mill the effects of gas pressure and hold-up were investigated.Relative particle velocities were found to be sign ificantly lower tha n the gas velocities,while the nu mber of contacts per particle was determined to be extremely high.
