Etching Research Articles

Evaluation of Etching Time Effect on Shear Bond Strength of Orthodontic Brackets Bonded with Self-Adhesive Composite: An in-Vitro Study

Introduction: Precise acid etching of the tooth surface is a significant factor in the strength of the bracket bond. The current study aimed to determine the effect of different application times of acid etching on the shear bond strength of metallic orthodontic brackets under controlled laboratory conditions. Methods: Sixty intact premolar teeth were selected for this in-vitro study. The samples were divided into four groups based on the different acid etching times: 20, 25, 30, and 35 seconds. The teeth surfaces were etched with 37% phosphoric acid according to the specified times, and brackets were bonded to the enamel surface using GC Ortho connect composite. Shear bond strength values of the brackets was measured using a Universal Testing Machine. The amount of Adhesive Remnant Index was also observed using a stereomicroscope. Additionally, the surface roughness of the tooth enamel after bracket bonding was examined using SEM. The results related to shear bond strength were analyzed with one-way ANOVA statistical test and using SPSS version 16 software. The non-parametric Kruskal Wallis (Wallis-Kruskal) test was also used to check the frequency of ARI index. Results: The highest shear bond strength was observed at 25 seconds, and the lowest at 30 seconds. However, there was no significant difference in the shear bond strength of brackets was observed among the four groups (p=0.186). The highest ARI score was observed at 35 seconds, and the lowest at 20 seconds. No statistically significant difference was observed in the ARI scores in different groups. SEM images revealed that the enamel surface porosity was highest at 20 seconds. Conclusion: The results indicate that the shear bond strength and ARI at different acid etching times do not significantly differ. Therefore, orthodontic bracket bonding can be performed with less acid etching time.

Surface preparation before chemical copper plating of printed circuit board holes. Part II. Activation

Surface preparation before chemical copper plating of printed circuit board holes. Part II. Activation

Shear bond strength of a composite resin restoration in primary teeth following cavity preparation using laser- an in-vitro study.

To evaluate and compare the shear bond strength of composite resin restorations in primary teeth, following cavity preparation with both traditional dental burs and laser irradiation. One hundred primary molars extracted from the children visiting our department were collected and randomly divided into five groups (A-E) with 20 teeth in each group. In groups A, B, C, D, and E the teeth samples were etched with phosphoric acid, Er; YAG laser followed by acid etching, Er, Cr: YSGG laser followed by acid etching, Er; YAG laser etching only and Er, Cr: YSGG laser etching only, respectively. Following, all the samples were restored with composite resin and subjected to 500 cycles of thermocycling. The shear bond strength of the resin composite was analyzed. The type of fractures was also noted. Data obtained were subjected to statistical analysis. The mean value of shear bond strength of Group A, B, C, D, and E was 17.562 ± 0.810, 15.928 ± 0.415, 14.964 ± 0.566, 11.833 ± 0.533 and 11.187 ± 0.517, respectively. Adhesive failure was most commonly seen in all the groups. The phosphoric acid etching remains a highly effective technique for pre-treating dentin in composite resin restorations. The shear strength of composite resin to the dentin of laser-prepared cavity in primary teeth can be improved by the addition of acid etching.

Study on the combustion of toluene by acid etching assisted ultrasonic supported low content Pt catalyst

Catalytic combustion technology is an effective method for the treatment of volatile organic compounds (VOCs). However, the catalytic activity of loaded noble metal catalysts is limited by factors such as high noble metal dosage and poor stability. In this study, a method for the preparation of acid etching assisted ultrasonic loaded low-content Pt-cordierite catalysts was proposed. By comparing with the 0.5 % Pt/cordierite catalyst prepared without acid etching, it was found that the catalytic activity of toluene of the 0.5 % Pt/cordierite-HNO3 catalyst was significantly improved, and the T90 of toluene combustion was only 201 ℃, which indicated that the acid etching effectively promoted the interfacial bonding between the active component Pt and the carrier. Finally, it was confirmed by XPS that the active component Pt in the 0.5 % Pt/cordierite-HNO3 catalyst existed in multiple valence states, which effectively promoted the catalytic combustion of toluene.

Enhancement of beta spectrometry using double scintillators and ML-based unfolding

We present a novel beta spectrometer that consists of two identical plastic scintillators with one scintillator screened by a thin copper plate as a beta shield. The screened scintillator responds only to gamma photons while the other scintillator responds to both beta particles and gamma photons. The spectrometer’s response to beta and gamma radiations was characterized by experiments and Monte Carlo simulations. The gamma responses of the scintillators were in good agreement in most energy region while the screened scintillator showed a notable gamma attenuation in the low energy region below 150 keV. Comparison of the simulated and measured pulse height spectra showed good agreements for both beta and gamma radiations. For beta spectrum analysis, a simple gamma subtraction method and a convolutional neural network (CNN)-based method were investigated for various mixed beta–gamma fields. The subtraction method showed good accuracy in most energy regions while a notable overestimation of beta fluence was observed in the low energy region, which was caused by the gamma attenuation effect of the screened scintillator. The outcomes of the CNN method showed good agreements with the true beta fluence spectra for the validation dataset, however, the CNN model led to a significant overestimation for a dataset produced using the radionuclides that have not been used in the training datasets. To take the advantages of the outperforming features of both unfolding methods, a hybrid algorithm was deduced by applying a tolerance range to the subtraction result.

Synthesis and characterization of the dental adhesive monomer 10-MDP

Many studies have demonstrated the excellent performance of 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate) as a functional monomer for dental adhesive materials and as a primer for ceramic surfaces. Although adhesive performance is affected by the purity level of 10-MDP, this parameter is rarely described, and possible byproducts have been suggested in the literature, but have not been identified to date. The present study aims to present an accessible 10-MDP synthesis strategy with easily handled reagents and address the characterization challenges, especially in identifying byproducts. 10-MDP was synthesized from 10-hydroxydecyl methacrylate and phosphorus pentoxide in acetone. The final product was characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR) and mass spectrometry MALDITOF/TOF. The main chemical groups associated with 10-MDP were identified by 1H, 31P, and 13C NMR analyses. Only mass spectrometry analyses (MALDITOF/TOF) could identify the presence of dimers as byproducts. Its proposed chemical structure indicates that the dimers were formed by the reaction between the phosphate ester groups and others formed by the reaction of the methacrylic group of 10-MDP molecules. Careful adjustment of the synthesis conditions to reduce the formation of these byproducts is also described. The results indicate that the characterization of 10-MDP batches as raw materials is an important task because, depending on the byproduct present, its ability to polymerize or acid etching capacity may be compromised.

Automated High-Throughput Biological Sex Identification from Archeological Human Dental Enamel Using Targeted Proteomics.

Biological sex is key information for archeological and forensic studies, which can be determined by proteomics. However, the lack of a standardized approach for fast and accurate sex identification currently limits the reach of proteomics applications. Here, we introduce a streamlined mass spectrometry (MS)-based workflow for the determination of biological sex using human dental enamel. Our approach builds on a minimally invasive sampling strategy by acid etching, a rapid online liquid chromatography (LC) gradient coupled to a high-resolution parallel reaction monitoring (PRM) assay allowing for a throughput of 200 samples per day (SPD) with high quantitative performance enabling confident identification of both males and females. Additionally, we developed a streamlined data analysis pipeline and integrated it into a Shiny interface for ease of use. The method was first developed and optimized using modern teeth and then validated in an independent set of deciduous teeth of known sex. Finally, the assay was successfully applied to archeological material, enabling the analysis of over 300 individuals. We demonstrate unprecedented performance and scalability, speeding up MS analysis by 10-fold compared to conventional proteomics-based sex identification methods. This work paves the way for large-scale archeological or forensic studies enabling the investigation of entire populations rather than focusing on individual high-profile specimens. Data are available via ProteomeXchange with the identifier PXD049326.

Hydrophobic Interface Engineering for Highly Reversible and Stable Zn Anodes

AbstractRechargeable aqueous zinc batteries (AZIBs) with merits of high safety and high theoretical capacity are regarded as next‐generation energy storage devices. However, their practical application is hindered by the instable Zn anodes associated with the dendrite growth, parasite corrosion and side reactions. Developing a stable solid electrolyte interface is crucial for improving the cycling stability of Zn anodes. Herein, a hydrophobic interface is constructed on Zn anode through a simple heptafluorobutyrate acid etching route. The hydrophobic interface containing organic C─F, O─C═O and inorganic Zn─F bonds effectively address the issues of dendrites growth and parasitic reactions. Consequently, symmetric cells with acid‐treated Zn‐HA anodes achieve a prolonged lifespan of over 2000 h at 4.0 mA cm−2 and 1100 h at 10.0 mA cm−2. When paired with MnO2 cathode, the full cells deliver lower overpotential and outstanding cycling stability. This strategy provides a simple and feasible method to construct stable Zn anode for achieving high performance AZIBs.

Cell Experiment Equipment by Using Ashes as Electrolytes

This article presents information about an experiment on how to create simple galvanic cell experiment equipment by using waste ash from burning as electrolytes, a copper plate as a cathode, and a zinc plate as an anode. The main purpose is to create a set of experimental equipment for teaching physics under the title of electrochemistry, to examine the possibility of generating electricity from ash, to study the change of the mixture ratio between the ashes and water that affects the open circuit voltage (OCV), to compare the value of the open circuit voltage from the sedimentation ashes electrolyte and non-sedimentation ashes electrolyte, and to study the pH value of the ash’s electrolyte within two hours. The research revealed that it can create five sets of galvanic cells by using different quantities of ashes, and it was found that the ashes from burning can generate electricity. The same type of ash with a different quantity will give almost the same OCV values, and changing the mixture ratio between ash and water will not affect the OCV values, which found that the mixing ratio between water and dry ash to become an electrolyte must use a minimum mixing ratio of water equal to ash or use a ratio of water more than ash to mix together. The results of measuring the value of OCV over a period of 2 hours found that the average value is almost constant, equal to 0.7 V. Here, we found that if the ash is allowed to settle, the value of OCV will decrease slightly, and if the ash is not allowed to settle, the value of OCV is constantly unchanged. It was also found that the pH value of the ash in each galvanic cell during the period of 2 hours was the same, with an average high alkalinity of about 13. This shows that alkaline electrolytes can generate electricity and have almost constant electricity. These five devices can be applied as a teaching tool for the Physics and Chemistry subject in the title of electrochemistry for students at the secondary school level and bachelor’s students because of an easy way to fabricate galvanic cells. The materials used are cheap and easy to find. It can also be used to study the characteristics of electrical conductivity in ash’s electrolyte and the characteristics of ash’s electrolyte.

Thioctic Acid-Based Solvent-Free and Recoverable Adhesive for Dry/Wet Environments.

Metal adhesive synthesis typically involves heating and solvents, and the resultant adhesives lack degradability and suffer from recycling and sustainable problems. Herein, we developed a solvent-free and chemically degradable biobased adhesive (p(Elp-TA)+PVP) from thioctic acid (TA), its derivative (Elp), and polyvinylpyrrolidone (PVP). Through a rapid acid-triggered cationic ring-opening polymerization of dithiolane at ambient conditions, p(Elp-TA)+PVP adhesive could build up a strong lap shear strength of 1123 kPa in air and an underwater lap shear strength of 534 kPa to the copper plate. Molecular dynamics simulations show that compared to p(Elp-TA), the presence of an appropriate amount of PVP can significantly enhance the binding energy of the adhesive molecules to the metal substrate, and the rapid adhesion of p(Elp-TA)+PVP molecules to metal substrates was achieved through a synergistically dynamic adaptive network enhanced by hydrogen bonding, reversible dynamic bonding, and metal coordination bonding at 40 ps. More importantly, the applied p(Elp-TA)+PVP adhesive could be easily degraded and reverted to its small-molecular-weight lipoic acid species. Upon exposure to dithiothreitol, a green reducing agent, the average molecular weight of the adhesive could quickly decrease from 1603 kDa to 274 Da. This green adhesive constructed by a simple method provides a promising general strategy for developing a controlled degradable and recoverable adhesive from natural resources.

Boron nitride quantum dots supported hollow NH2-MIL-125 drive photo-Fenton-PMS system for photocatalytic tetracycline degradation: Contribution of tannic acid etching

NH2-MIL-125(Ti) materials had great potential for photocatalytic applications but had low activity due to exciton effect and narrow absorption range of visible light. The surface oxygen-containing negative functional groups of boron nitride quantum dots (BNQDs) could overcome these defects, but due to the low load capacity, a higher specific surface area of the substrate was usually required. In this paper, a hollow Ti-MOF material was developed by etching technology. The hollow structure formed by tannic acid etching broadened the absorption range of visable light and provided more alternative surfaces for loading BNQDs. The 85.2% of high tetracycline (TC) removal efficiency for the best sample (BNQDs-5@20-Ti-MOF + PMS) was obtained, which was about 56.8 and 1.9 times of the 20-Ti-MOF and BNQDs-5@20-Ti-MOF, respectively. BNQDs-5@20-Ti-MOF + PMS system showed a great TC degradation efficiency in a wide pH range (pH = 5–9). In addition, reaction temperature and the inorganic ions did not show significant inhibition effect for TC removal. Both free radical and non-free radical pathways were involved in the TC degration by BNQDs-5@20-Ti-MOF + PMS system, among which O2•− and 1O2 played the key roles. Interestingly, multiple 1O2 production paths contributed to the high efficiency and stability of BNQDs-5@20-Ti-MOF + PMS system. This study revealed a reasonable combination of Ti-MOF and BNQDs, which provided a new efficient photocatalyst for environmental remediation.

PIRANESI'S CIRCUSES AND CARCERES: THE NEWLY DISCOVERED FIRST STATE OF THE CAMPUS MARTIUS PLAN AND ITS ANTIQUARIAN CONTEXT

This essay takes as its starting point the newly discovered first state print of the large topographical plan of the Campus Martius of ancient Rome made by Giovanni Battista Piranesi in the years around 1760. There are significant differences between the first and the more common second state (which was bound into the Campus Martius volume published in 1762) and they concern the form of the circuses, six of which are included by Piranesi in his plan. This essay will investigate those changes and propose a hypothesis regarding the motivations for them by looking at the antiquarian context with which Piranesi was familiar and taking into consideration his enthusiasm for on-site examination of ancient remains. Particularly relevant are the ruins of the circus of Maxentius on the via Appia just outside the city, a site which preoccupied Piranesi at various times throughout his career in Rome. The antiquarian material examined includes earlier writings on circuses, which had a marked effect on the way that Piranesi drew his circuses in the first state of the plan and on the changes he made, clearly visible in the copper plates from which the prints were made. The circus Maximus and circus of Maxentius as described by Pirro Ligorio, Onofrio Panvinio and Raffaele Fabretti are key to the genesis and development of the Campus plan.

A New Process for Efficient Non-Destructive Metal-Activated Composite Plating of Ni-P-Al2O3 on Titanium Base and Its Performance Research

A new high efficient and non-destructive mental activation process of electroless composite plating was proposed. The process utilized electromagnetic induction equipment to heat the titanium alloy substrate and used its energy to complete the activation process, which could successfully attach the nickel nanoparticles firmly to the surface of the titanium alloy; at the same time, the process pre-activated Al2O3 nanoparticles and added the activated nanoparticles to the plating solution. In the process of plating, the activated titanium substrate was used as the catalytic center of electroless nickel plating (ENP) for electroless composite plating. The new activation process avoided complicated traditional processes such as acid etching and zinc dipping. Such traditional processes require huge doses of chemicals, including various strong acids, so improper waste liquid treatment will cause harm to the environment. The important parameters of the process were optimized by orthogonal experiments. A scanning electron microscope (SEM), an X-ray photoelectron spectroscopy (XPS), an energy dispersive spectrometer (EDS), thermal shock experiments and friction and wear experiments were used to characterize and analyze the surface morphology, composition, binding force and friction coefficient of the coating, and analyze the coating quality by measuring the plating rate and the thickness of the coating. The results showed that the rate of electroless composite plating increased with the increase in Al2O3 nanoparticle concentration. When the concentration of Al2O3 nanoparticles reached 1.5 g/L, the ENP rate decreased with the increase in Al2O3 nanoparticle concentration. The adhesion of the sample was evaluated by the scratch test, which showed that the binding grade of the sample was 0, and the Vickers hardness was 688.5 HV. Results showed that the coating produced by this new process has excellent performance. Therefore, the process is an environmentally friendly and fast activation composite plating process.

Fabrication of conductive polyimide/metal composite fibers for high temperature EMI shielding

Surface metallization of high-performance polymer fibers via electroless plating represents a significant advancement in producing lightweight, flexible and durable electromagnetic interference (EMI) shielding fabrics. The conventional process for metallization of polyimide (PI) fibers faces challenges, including complex procedures and insufficient interfacial adhesion between the metal layer and fiber matrix. Herein, carboxylate-containing PI (PIC) fibers were developed to mitigate the mechanical degradation caused by traditional alkaline etching. Conductive composite fibers (PIC/Cu) were successfully produced through a continuous electroless copper plating process. The robust PIC/Cu interfacial bonding achieved based on nanoscale mechanical interlocking through Ni nanoparticles imparts excellent flexibility and durability, evidenced by only a 4 % increase in electrical resistance after 5000 bending cycles. The dense, uniform copper layer provides high conductivity (1.3 × 104 S/cm), resulting in an optimal EMI shielding efficiency of 63.4 dB for the corresponding fabric. Moreover, PIC/Cu-Ni fibers prepared by further electroless plating of nickel layer on the surface of PIC/Cu fibers demonstrate remarkable electrical stability across temperatures ranging from 50 to 350°C, with only a 1.2 % reduction in conductivity after exposure to 350°C for 1 h. These findings advance the development of high-performance conductive PI fibers for applications in aerospace vehicles and high-temperature environments.

Limit Flow Etchant Applicator

White spot lesions (WSLs) have been reported to occur in a majority of orthodontic patients who undergo multibracket appliance treatment. WSL scores are proven to be higher in total-etch techniques as compared to partial etching, with no difference in bond strengths. It is thus very important to prevent unnecessary etching and demineralization of enamel in those areas where it is not needed and to etch only the surface intended for bracket bonding. This article describes a simple method to limit the flow of the acid etchant to the area on the tooth surface receiving the bracket, with the added advantage of a positioning gauge on the etchant applicator.

Cu-MOF derived two-dimensional copper-carbon nanosheets for efficient nitrate reduction

In recent years, the strategy of reducing ammonia (NH3) from nitrate-related sources such as industrial wastewater driven by clean energy sources has garnered significant attention. Previous studies have shown that Cu-based species can effectively catalyze nitrate reduction reaction (NO3RR), but the reaction intermediates tend to aggregate on the surface of catalysts, resulting in low Faraday efficiency. In this study, two-dimensional porous carbon nanosheets were successfully prepared through direct pyrolysis of a mixture of ZnCu-BTC crystal and FeCl3 salt. Interestingly, cube-shaped CuCl nanoparticles were easily precipitated from the MOF-derived carbon surface during acid etching process. The resulting CuCl-CNS exhibited good NO3RR performance, achieving an NH3 yield of 96.9 % and 292.5 µmol h−1 cm−2 at −0.60 V versus reversible hydrogen electrode. Moreover, the assembled zinc-nitrate battery revealed a peak power density of 4.73 mW cm−2 and long-term cycle stability. This work provides valuable insights into the development of MOF-derived Cu-based nanocomposites for effective nitrate reduction.

Direct Composite Restorations on Permanent Teeth in the Anterior and Posterior Region - An Evidence-Based Clinical Practice Guideline - Part 2: Recommendations for Composite Processing.

Part 2 of this German S3 clinical practice guideline provides recommendations for the process of manufacturing composite restorations. It covers key aspects like caries removal, field isolation, matrix and adhesive techniques, as well as light curing and polishing. The outcomes of interest include survival rates and restoration quality. A systematic literature search was conducted by two methodologists using MEDLINE and the Cochrane Library via the OVID platform, including studies up to December 2021. Additionally, the reference lists of relevant manuscripts were manually reviewed. Six PICO questions were developed to guide the search. Consensus-based recommendations were for- mulated by a panel of dental professionals from 20 national societies and organizations based on the collected evidence and ex- pert opinion. The guideline advocates for one-stage selective caries removal near the pulp and underscores the effectiveness of various isolation techniques, adhesive systems, and the crucial role of light polymerization. The use of anatomically pre- formed sectional matrices and phosphoric acid etching is recommended to enhance restoration quality. Additionally, polish- ing composite restorations is advised to improve surface finish. This guideline provides comprehensive recommendations that inform clinicians on optimizing the composite restor- ation manufacturing processes. The adoption of these best practices can improve the quality and longevity of dental restorations.

Black etched electroless Ni–P coatings for enhanced efficiency towards alkaline water splitting

Requirements for wider use of water electrolysis for hydrogen production include the development of highly efficient, cheap, and easily made electrodes. Promising properties can be achieved with Ni–P materials. Herein, nitric acid etching (being used for blackening of electroless Ni–P coatings) resulted in enhanced efficiency towards hydrogen and oxygen evolution reactions (HER and OER) in 1.0 M KOH. For etched Ni-7.6 wt%P coating, the potential of HER at −10 mA cm−2 was about −0.20 V vs. RHE, and the potential of OER at 10 mA cm−2 was about 1.67 V, whereas for etched Ni they were −0.40 V and 1.94 V, respectively. Surface layers of etched coatings contained bundles of microrods and were enriched in O and P. Impedance measurements showed that etching caused about a 60-fold increase of CPE which can be ascribed to the development of surface area and pseudocapacitance of redox reactions, involving Ni ⇄ NiO. It is proposed that the electroactivity of Ni–NiO composite is to a large extent associated with the oxide reduction effects, involving high activity of newborn (pristine) Ni nanoparticles, acidification at the metal surface and disclosure of bare metal. Etched Ni–P coatings can be promising for the activation of electrodes for water electrolysis.

Physical properties and microstructural corrosion propertiesof Laser-bent 304 Stainless Steel Sheets

Laser treatment by laser bending is a technique of treating sheet metal by thermal residual stresses generated by laser assisted heating without any externally applied mechanical forces. The advantages of laser assisted bending over conventional bending include flexibility of non-contact processing, amenability to materials with diverse shape/geometry, and high precision/productivity. Up to now, most of previous work on laser bending was concentrated on study of bending angles/shapes with laser operating conditions, and modelling of the thermal process, however, no work has been reported on corrosion behavior of the laser-bended components. Since the laser bending is a thermal process, it is believed that the thermal process could not only alter microstructure, but also affect corrosion performances, such as intergranular corrosion, due to possible sensitisation caused by repeating laser scans. The aim of the present work is to investigate corrosion performance of laser-bent 304 austenitic-steel sheet with thicknesses of 2 mm and 1.5 mm, respectively, using a 2 kW CO2 laser. After laser treatment, the laser-bent samples were characterised in terms of microstructural change within bent zones consisting of melt-zone and heat-affected zone, using optical microscopy and scanning electron microscopy (SEM). Hardness profiles were obtained across the bent zones. Corrosion performances of the laser-bent evaluated by means of electrolytic etching in oxalic acid and double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. Laser bending is a thermal process, it is believed that the thermal process could not only alter microstructure, but also affect corrosion performances, due to possible sensitisation caused by repeating laser scans.

Experimental and numerical study on a multilayer magnetic field rotary eddy current inertial damper

To improve the output damping force of the eddy current damper, a multilayer magnetic field rotary eddy current inertial damper (MMF-RECID) is proposed. The MMF-RECID is an inerter-based eddy current damper. A prototype device of the MMF-RECID is manufactured and tested, and its mechanical properties are systematically investigated. Firstly, the configuration of the MMF-RECID is described, and the calculation formulas of the axial force are derived. Secondly, an MMF-RECID prototype is designed and fabricated, and the apparent mass and energy dissipation performance under recycled axial loading are investigated. Three-dimensional transient numerical simulations of eddy current damping are conducted using the ANSYS Electronics Desktop. The results show that the eddy current damping force exhibits velocity nonlinearity, and the test results are consistent with the simulation results. Next, the study focuses on parameters influencing the maximum eddy current damping torque generated by the copper plate and the corresponding critical rotating speed. These parameters encompass the number and size of the magnets, the thickness of the copper plate, and the air gap. Finally, the earthquake-reduction effect of a six-degree-of-freedom structure equipped with MMF-RECID is analyzed. This study demonstrates that the ball screw system of MMF-RECID achieves a multiplicative effect of apparent mass and eddy current damping force, the eddy current damping force of a multi-layer magnetic field versus a single-layer magnetic field conforms to the law of linear superposition, and the hysteresis curves are stable. The eddy current damping torque can be improved by increasing the number and size of the magnets, and decreasing the air gap. The thickness of the copper plate significantly affects both the maximum damping torque and the critical speed, and the optimal thickness range is between 2 mm and 4 mm.