Electrostatic Charge Build-up Research Articles

Atomic Layer Deposition Coating on the Surface of Active Pharmaceutical Ingredients to Reduce Surface Charge Build-Up.

Active pharmaceutical ingredients (APIs) typically consist of solid therapeutic particles that may acquire electrostatic charge during milling and grinding operations. This may result in the agglomeration of particles, thereby reducing the flowability and affecting the homogeneity of the drug formulation. Electrostatic charge build-up may also lead to fire explosions. To avoid charge build-up, APIs are often coated with polymers. In this paper, atomic layer deposition (ALD) using metal oxides such as Al2O3 and TiO2 on APIs, namely, palbociclib and pazopanib HCl, has been utilized to demonstrate a uniform coating that results in a significant reduction in the surface charge of the drug particles. Kelvin probe force microscopy (KPFM) shows a 4-fold decrease in the surface contact potential of uncoated pazopanib HCl (2.3 V) to 0.52 and 0.82 V in TiO2-and Al2O3-coated APIs, respectively. Also, the ζ potential indicated a 4-fold decrease in the surface charge on coating pazopanib HCl, i.e., from -32.9 mV to -7.51 and -8.51 mV in Al2O3 and TiO2, respectively. Surface morphology, thermal stability, dissolution studies, and cytotoxicity of the drug particles after coating were also examined. Thermal analysis indicated no change in the melting temperature (Tm) after coating. ALD coating was found to be uniform and conformal as observed in images obtained from scanning electron microscopy (SEM) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). The rate of dissolution was found to be delayed by the coating, and thus ALD offers slower drug release. Coating APIs with TiO2 and Al2O3 did not induce statistically significant cytotoxicity compared to the uncoated samples. The results presented in this study demonstrate that ALD coating can be used to reduce surface charge build-up and enhance the bulk properties of the drug particles without affecting their physicochemical properties.

Operando observation of magnetism in HDD writing heads by spin-polarized scanning electron microscopy.

Operando observation using spin-polarized scanning electron microscopy (spin SEM) has been demonstrated by detecting changes in the magnetization in the writing head of a hard disk drive (HDD) during operation. A current-applying system developed for use in the sample stage of a spin SEM enables imaging of the magnetization changes in the writing head of an HDD while the writing head is activated. Focused ion beam (FIB) technology is used to fabricate electric contacts between the head terminals and the sample holder electrodes. Tungsten film is deposited by FIB technology on the insulator around the writing head to prevent electrostatic charge buildup in the insulators during SEM measurement. This system is well suited for studying the characteristics of writing heads in HDDs in an activated state.

Analysis of Tribo-Charging during Powder Spreading in Selective Laser Sintering: Assessment of Polyamide 12 Powder Ageing Effects on Charging Behavior.

Powder flowability is key to achieving high process stability and part quality by application of smooth and dense layers in selective laser sintering (SLS). This study sheds light on the rarely investigated effect of tribo-electric charge build-up during powder delivery in the SLS process. This is achieved by a novel approach to quantify electrostatic potentials during doctor blading. The presented model setup is used in combination with charge spectrometry and impedance spectroscopy to investigate the alterations in tribo-electric charging behavior for the most commonly used laser sintering material polyamide 12 in its virgin and aged, c.f. reused, states. We show that the electrostatic charge build-up is significantly enhanced for aged polymer powder material, likely contributing to altered performance in SLS processing.

Computational modeling of the electrostatic charge build-up in fluidized beds

Coupled computational fluid dynamics and discrete element method was used to investigate the electrostatic charge build-up in fluidized beds. The charge transfer among particles and particles-wall collision was considered. The repulsive electrostatic force among particles increases the bed voidage and bubble size decreases. The average charge of particles linearly increases with time and the slope of this line increases at higher gas velocities. There is a lack of experimental data on charge transfer and effect of electrostatic charge of particles on the hydrodynamics of fluidized beds and this work provides a first insight into the charge transfer on bubble behaviors.

Innovative mitigation measures for electrostatic charge build-up on surfaces of dry-type air-core reactors for HVDC application

Equipment installed in the d.c. yards of HVDC converter stations is subject to the electrostatic charge build-up phenomenon. This can result in pollution accumulation on the surfaces of the high voltage equipment operating at high d.c. potential. The charge build-up on the reactor surface may cause discharges across the surface and through the encapsulation of the winding packages. In case of dry-type air-core HVDC reactors the observed pollution build-up takes the form of an irregular pattern of varying sized black spots.

Insight into multifunctional polyester fabrics finished by one-step eco-friendly strategy

Polyethylene terephthalate (PET) has been widely used in fabrics owing to its great mechanical properties, easy processability and quick drying. However, PET-based products always suffer from uncomfortable low sweat uptake and electrostatic charge buildup mainly due to its bad surface wettability. Moreover, porous fabrics may induce unfavorable mite and microorganism reproduction. Due to lack of reactive groups on the PET skeleton, it was very difficult to endow its surface hydrophilicity, antistatic properties, perdurable antimicrobial and anti-mite properties by conventional methods. In this work, we develop a one-step eco-friendly finishing strategy for PET fabrics through photochemical reaction using benzophenone group terminated quaternary ammonium salt (BP-QAS) as the finishing reagent. The as-finished PET fibers changed from incompact state to compact state due to the increased cohesive forces within individual fibers, resulting in improved tearing strength. The PET fabrics show significantly improved hydrophilicity, and antistatic properties. Furthermore, the as-finished PET fabrics exhibit excellent, durable broad-spectrum antimicrobial activities against gram-negative, gram-positive, drug-resistant bacteria and fungi. Moreover, our fabric shows long-lasting antimicrobial properties above AAA requirements after 50 laundering cycles. Usual PET fabrics generally have difficulty achieving AAA standards after 10 laundering cycles. In addition, our as-prepared fabrics showed excellent anti-mite activities against house dust mites based on disruption of the microbial and mite membrane due to oxidation stress, while no negative effects were observed for mouse and rabbit. The finished PET fabrics can be applied to multiple industries to prevent infectious diseases and improve public health, including but not limited to packaging, clothes, water treatment, and medical appliances.

Dynamic gas flow effects on the ESD of aerospace vehicle surfaces

An aerospace vehicle traveling through the atmosphere is subject to triboelectrically induced electrostatic charge build-up caused by dust and ice crystal impingement. Electrostatic discharges between an antenna housing and the exterior of the vehicle may interfere with system operation. Paschen's Law, derived for stationary, charged surfaces, fails to account for the loss of electron-ion pairs with high gas velocity between the electrodes. The purpose of this work is to develop a version of Paschen's Law that takes into account the flow of ambient gas past electrode surfaces. The basic hypothesis of this work is that the number of electron-ion pairs created per unit distance between electrode surfaces is mitigated by the electron-ion pairs removed per unit distance by the flow of gas. The revised theoretical model must be a function of the mean velocity, vxm, of the ambient gas and reduce to Paschen's law when the gas mean velocity, vxm = 0. This model has been evaluated by wind tunnel experimentation. Initial data of the baseline wind tunnel experiments show results consistent with the hypothesis. Based on the results of this work, it is hoped that the safety of aerospace vehicles will be enhanced with a redefinition of electrostatic launch commit criteria. It is also possible that new products, such as anti-static coatings, may be formulated from this data.

Numerical study of the influence of the powder and pipe properties on electrical charging during pneumatic conveying

During pneumatic transport, powders often experience the build-up of electrostatic charge due to collisions of the particles with the pipe. Since this can lead to hazardous spark discharges with unwanted implications, such as accidental explosions, there is a strong interest in exploring various options to limit this electrification process. In this paper we present the results of numerical simulations that we performed in order to evaluate the influence of the material properties of the powder and pipe, respectively, on this process. In our study, the turbulent flow of the carrier gaseous phase was treated numerically via Large Eddy Simulations while the particles were tracked individually in Lagrangian framework. Four-way coupling between the powder and the gaseous phase was also assumed. Our numerical simulations predicted that the particle Poisson ratio and Young's modulus, its electrical resistivity, as well as the permittivity represent promising measures to control the charge of the powder. More specifically, an increase of each of these quantities by 50% may lead to a decrease of the powder charge of up to 40%.

Large Eddy simulation of triboelectric charging in pneumatic powder transport

The triboelectric charging of powders and hoses during pneumatic transport can cause hazardous spark discharges. In this work we employ numerical simulations to gain a deeper understanding in the physical processes involved in the build-up of electrostatic charge. To this end, Large Eddy Simulations are performed to simulate the turbulent flow of the gaseous phase while the particulate phase is described in Lagrangian framework. Dynamic models accounting for the particle-wall and particle-particle charge exchange are implemented and a model describing the charge distribution in an insulating hose is also developed. Our numerical results are in good agreement with available experimental data, while our simulations provide additional physical insight and information about the charging process. The results presented herein can be used to improve the safety of operation of many pneumatic components in process engineering.

Understanding electrostatic charge behaviour in aircraft fuel systems

This paper presents work on the simulation of electrostatic charge build-up and decay in aircraft fuel systems. A model (EC-Flow) has been developed by BAE Systems under contract to Airbus, to allow the user to assess the effects of changes in design or in refuel conditions. Some of the principles behind the model are outlined. The model allows for a range of system components, including metallic and non-metallic pipes, valves, filters, junctions, bends and orifices. A purpose-built experimental rig was built at the Health and Safety Laboratory in Buxton, UK, to provide comparison data. The rig comprises a fuel delivery system, a test section where different components may be introduced into the system, and a Faraday Pail for measuring generated charge. Diagnostics include wall currents, charge densities and pressure losses. This paper shows sample results from the fitting of model predictions to measurement data and shows how analysis may be used to explain some of the observed trends.

A Hygroscopic Sensor Electrode for Fast Stabilized Non-Contact ECG Signal Acquisition.

A capacitive electrocardiography (cECG) technique using a non-invasive ECG measuring technology that does not require direct contact between the sensor and the skin has attracted much interest. The system encounters several challenges when the sensor electrode and subject’s skin are weakly coupled. Because there is no direct physical contact between the subject and any grounding point, there is no discharge path for the built-up electrostatic charge. Subsequently, the electrostatic charge build-up can temporarily contaminate the ECG signal from being clearly visible; a stabilization period (3–15 min) is required for the measurement of a clean, stable ECG signal at low humidity levels (below 55% relative humidity). Therefore, to obtain a clear ECG signal without noise and to reduce the ECG signal stabilization time to within 2 min in a dry ambient environment, we have developed a fabric electrode with embedded polymer (FEEP). The designed hygroscopic FEEP has an embedded superabsorbent polymer layer. The principle of FEEP as a conductive electrode is to provide humidity to the capacitive coupling to ensure strong coupling and to allow for the measurement of a stable, clear biomedical signal. The evaluation results show that hygroscopic FEEP is capable of rapidly measuring high-accuracy ECG signals with a higher SNR ratio.

Study of Charged Frame ESD Immunity Testing Specified in ISO 7176-21

The EMC product standard for electrically powered wheelchairs is ISO 7176-21, which requires charged frame electrostatic discharge (ESD) immunity testing. When a moving wheelchair carrying a buildup of electrostatic charge due to triboelectrification of the wheels and floor comes into contact with a grounded metal object, the resulting air-gap discharge may cause the wheelchair to malfunction. Since the IEC 61000-4 series does not cover immunity testing that simulates such ESD events, ISO 7176-21 independently provides the test method. Currently, many companies are developing personal care robots to assist human in daily activities. Considering the risk presented by such robots that involve physical contact with humans, the charged frame ESD test will be a test item for the safety validation of personal care robots that are mobile and battery powered. In practice, however, when charged frame ESD tests are conducted according to the test procedure specified in ISO 7176-21, some issues and questions arise in regard to such matters as the means of charging the robot under test, the material of the insulating support on which to place the robot, and simulation of discharge from a robot rider or wearer. This paper investigates the test procedure of ISO 7176-21 and proposes modifications for enabling charged frame ESD testing to be properly carried out for personal care robots.

Evaluation of X-Ray Microanalysis for Characterization of Dental Enamel

Elemental analysis of dental hard tissues is of importance. The aim of this study is to evaluate X-ray microanalysis (XRMA) of bovine enamel in a scanning electron microscope (SEM) with different coatings. The buccal surface of bovine incisors was polished flat, one-third was coated with carbon, one-third with gold, leaving one-third uncoated for XRMA in an SEM equipped with an energy-dispersive microanalysis system. The elements oxygen, sodium, magnesium, phosphorous, chlorine, potassium, and calcium were analyzed using their respective characteristic K X-ray series. Comparisons were made with analyses of glass produced by fusion of the bovine enamel, showing that oxygen analyses using the K X-ray series are reliable and preferable to calculating oxygen by stoichiometry for natural enamel. For the gold-coated and uncoated analyses, carbon was also measured using the K X-ray series. Small area Analyses in small areas (80 × 80 μm) in variable pressure-SEM mode with low vacuum (20 Pa), without any coating, midway between 40 μm wide gold lines 140 μm apart to avoid build-up of electrostatic charge is the preferred method, especially if carbon is included in the analysis. The analyses of bovine enamel are sufficiently reproducible to be regarded as quantitative for all elements except carbon.

Cation–π induced aggregation of water-soluble [PtII(diimine)(Ln-S,O)]+complexes studied by1H DOSY NMR and TEM: from ‘dimer aggregates’ in acetonitrile to nano-aggregates (‘metallogels’) in water

(1)H NMR chemical shift concentration dependence as well as the diffusion coefficients from DOSY NMR of mixed ligand [Pt(II)(1,10-phenanthroline)(N-pyrrolidyl-N-(2,2-dimethylpropanoyl)thiourea)]Cl ([Pt(II)(phen)(L(1)-S,O)]Cl) dissolved in mixtures of acetonitrile-water in the range 0-30% (v/v) D(2)O-CD(3)CN shows that the complex cation (M(+) = [Pt(II)(phen)(L(1)-S,O)](+)) aggregates to form dimers, 2M(+) ⇌ {M(+)}(2), with association constants ranging from K(D)(CD(3)CN) = 17 ± 2 M(-1) to K(D)(30% (v/v) D(2)O-CD(3)CN) = 71 ± 8 M(-1) at 299.3 K, presumably via non-covalent cation-π interactions. Experimental data are consistent with an 'offset' face-to-face cation-π stacking arrangement of the planar cation. However in water-rich solvent mixtures from >30% (v/v) D(2)O-CD(3)CN to pure D(2)O, the extent of aggregation significantly increases until a critical aggregation concentration (CAC) is reached, estimated to be 9.6 and 10.3 mM from (1)H NMR chemical shift concentration dependence and DOSY NMR measurements respectively. Above the CAC the formation of nano-structures formulated as {[Pt(II)(phen)(L(1)-S,O)](+)}(n)Cl(-)(y) (n, y > 2) is indicated. DOSY studies show a significant decrease of the average diffusion coefficient D(obs) as a function of increasing concentration of [Pt(II)(phen)(L(1)-S,O)]Cl in D(2)O. The aggregation number (N) estimated from hydrodynamic volumes of the mononuclear [Pt(II)(phen)(L(1)-S,O)](+) cation (V(H)(0)), and those V(H) estimated from D(obs) (N = V(H)/V(H)(0)) as a function of total complex concentration, ranges from ~2 to ~735 in pure D(2)O. Above the CAC well defined nano-structures which may be loosely termed "metallogels" could be characterized by means of transmission electron microscopy. As expected the addition of NaCl appears to increase the extent of aggregate formation, by presumably stabilizing the formation of nano-sized {[Pt(II)(phen)(L(1)-S,O)](+)}(n)Cl(-)(y) aggregates preventing excessive positive electrostatic charge build-up.

A mononuclear ruthenium complex showing multiple proton-coupled electron transfer toward multi-electron transfer reactions

Two new ruthenium(II) complexes bearing dissociable protons, [Ru(trpy)(H(2)bim)Cl]PF(6) (1) and [Ru(trpy)(H(2)bim)(OH(2))](PF(6))(2) (2) (H(2)bim = 2,2'-biimidazole and trpy = 2,2':6',2''-terpyridine), were synthesized and characterized, where the H(2)bim and M-OH(2) moieties are expected to serve as proton-dissociation sites. Single crystal X-ray diffraction analyses revealed that the H(2)bim and M-OH(2) moieties act as proton donors in intermolecular hydrogen bonds. Two pK(a) values of 2 (pK(a1) = 9.0 and pK(a2) = 11.3) were spectrophotometrically determined, where the first proton dissociation is assigned to that from H(2)bim and the second is from M-OH(2). This assignment was supported by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations for two sets of conjugated bases, [Ru(trpy)(Hbim)(OH(2))](+) and [Ru(trpy)(H(2)bim)(OH)](+) for the first proton dissociation, and [Ru(trpy)(Hbim)(OH)](+) and [Ru(trpy)(bim)(OH(2))](+) for the second dissociation. Electrochemical studies in aqueous solutions under various pH conditions afforded the Pourbaix diagram (potential versus pH diagram) of 2, where the pK(a) values found from the diagram agree well with those determined spectrophotometrically. It was also found that demonstrates four-step proton-coupled electron transfer (PCET) reactions to give the four-electron oxidized species, [Ru(IV)(trpy)(bim)(O)](2+), without electrostatic charge buildup during the reactions. The multiple PCET ability of 2 would be applicable to various multi-electron oxidation reactions. Catalysis of electrochemical water oxidation was indeed evaluated in the initial attempt to demonstrate multi-electron oxidation reactions, revealing that the water oxidation potential for 2 is lower than that for other ruthenium catalysts, [Ru(trpy)(bpy)(OH(2))](2+), [Ru(trpy)(bpm)(OH(2))](2+) and [Ru(tmtacn)(bpy)(OH(2))](2+) (bpy = 2,2'-bipyridine, bpm = 2,2'-bipyrimidine, and tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), which are known to be active catalysts for water oxidation.

Preparation and characterization of polyimide/silane coupling agent modified multiwall carbon nanotubes composites

AbstractPolymer/carbon nanotube (CNT) nanocomposites have received much attention recently. In this study, we attempt to enhance the electrical conductivity of polyimide (PI) by variously modifying multiwall carbon nanotube (MWNT). We report the successful synthesis of PI/MWNT composite films using a blending process, and examine their properties and morphology. We modified MWNT by three different methods: thermal purification (U‐CNT), oxidation with HNO3 (N‐CNT) and modification with a silane coupling agent (G‐CNT). We confirmed the successful preparation of the modified MWNTs by Fourier transform infrared (FTIR) and Raman spectroscopy, and transmission electron microscopy (TEM). The low amorphous surface characteristics of N‐CNT produced low surface resistance in the range of 105–106 Ω/cm2 for the PI/N‐CNT composites, which dispersed the buildup of electrostatic charge and improved dispersion. On the other hand, the better miscibility and interaction between G‐CNT and PI, for the PI/G‐CNT composites present superior thermal stability and mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Deployment Experiment for Ultralarge Solar Sail System (UltraSail)

UltraSail is a next-generation high-payoff system with very large (kilometers-squared class) solar sails enabling high payload mass fractions for high Delta-V. One of the primary innovations is the near elimination of sail supporting structures by attaching each blade tip to a formation-flying tip satellite. To design the deployment of kilometers-long blades by centrifugal force provided by tip satellites, the peel force of the blade material must be known. In this research, an experiment to determine the force necessary to deploy a stowed film in a vacuum was designed, fabricated, and operated for various CP-1 polyimide film samples, including uncoated, aluminum-coated, and uncoated but conductive film. Results for uncoated film samples were heavily dependent on vacuum levels, with very high forces observed at low pressures due to electrostatic charge buildup. However, for the coated film and conductive film samples, the types most likely to be used on an UltraSail mission, preliminary results show that the peel forces are negligibly small. This small peel force is critical for the successful, simple, and efficient deployment of the UltraSail system. A potential problem associated with trapped air between film layers was identified by the experiment, and a future winding scheme will guard against this issue.

Comparison of influence of fluidization time on electrostatic charge build-up in the bubbling vs. slugging flow regimes in gas–solid fluidized beds

Electrostatic charge generation poses significant problems in some commercial gas–solid fluidized bed reactors such as those in gas-phase polyolefin production. Understanding the contributing factors to charge generation is important in determining the charge generation mechanisms, leading to the development of methods to reduce or prevent this phenomenon. This work focused on determining the effect of fluidization time on particle charging and the amount of particle adhesion on the fluidization column wall in both the bubbling and slugging flow regimes. The charging effect was investigated for particles in three regions of the fluidized bed: elutriated fines, bulk particles inside the bed, and particles adhered to the column wall. The particles size distribution, mass and charge were measured for all three regions. Fluidization was carried out with polyethylene resins from an industrial reactor; times of 15, 30, 60, 120, 180, and 360 min were evaluated. Increased fluidization time decreased the amount of particles mass collected in the bulk region and increased those adhered to the column wall during the velocities tested in the bubbling flow regime. Whereas the quantity of particles in each region was not affected by fluidization time for the velocities examined in the slugging flow regime. Bipolar charging was observed with relatively smaller particles becoming predominately positively charged and larger particles becoming predominately negatively charged. Each region of the bed affected the magnitude of net q/m, with elutriated fines having the largest magnitude, followed by those adhered to the column wall, and finally those in the bulk of the bed. Charge saturation was attained for fluidization times greater than 60 min for particles in the bulk and along the column wall for all gas velocities. However, extended fluidization times were required with the entrained fines in bubbling flow; whereas charge saturation of fines in slugging flow occurred shortly after the onset of fluidization. Mean particle diameter for each measurement region was not impacted by the fluidization time for any of the gas velocities tested. The bed hydrodynamics was found to definitely have an impact on the particle–wall fouling where the particle layer continued to develop on the inner column wall as fluidization time increased for those velocities in the bubbling regime while comparatively less impact on particle layer growth was observed in the slugging flow regime. In addition, the bubbling flow regime resulted in particle layers formed on the column wall to be longer and thinner whereas those formed in the slugging flow regime were shorter and thicker.

Addition of fines for the reduction of powder charging in particle mixers

Experiments were carried out to study the effectiveness of fine powders as an additive on the reduction of electrostatic charge build-up for glass beads, polyethylene resins and starch powders in a mechanical shaking device. Four fine powders, carbon nanotubes (CNTs), Larostat 519, activated carbon and aluminum powders were tested on their effectiveness on charge reduction. It is found that particle size does have a significant effect on charge build-up of the bulk powder. The addition of small fraction of fine glass beads (150–170 μm) into coarse glass beads (210–300 μm) led to observable charge reduction, indicating that small particles added to large bulk powders can help reduce electrostatic charge build-up. Compared to other additives of larger sizes, CNT is a much more effective antistatic agent. Aluminum powder performed poorest among all additives tested. CNTs out-performed the commercial antistatic powder, Larostat 519, in reducing the charge generated by shaking action. Furthermore, better charge dissipation was observed at higher CNT contents. The experiment also revealed that conductivity alone was not a good indicator of antistatic capability because aluminum powder, despite having a good conductivity, performed poorly.

A new mechanism for the electrostatic charge build-up and dissipation in dielectrics

Excess electrostatic charge induction on paper under an electrostatic potential, at different relative humidity (RH) values, was measured using a Kelvin electrostatic voltmeter set-up. Results show that samples under a positive potential accumulate excess negative charges, which are dissipated when the potential is brought down to zero. Rates of charge accumulation and dissipation over the samples are equal under constant RH and both rates decrease markedly at lower RH values. These results are interpreted using a new model for the electrification of insulators, based on the effect of the electric potential on the electrochemical potential (µi=µi° + RTln a + zFV) of H(H2O)n+ and OH(H2O)n- ions within water adsorbed on insulators. Rates of paper electrification and re-neutralization are thus strongly dependent on the amount of water in the atmosphere. This model explains the experimental results presented in this work and also a number of hitherto unexplained reports on electrostatic phenomena.