Iron Disc Research Articles

Vortex and double-vortex nucleation during magnetization reversal in Fe nanodots of different dimensions

Abstract Magnetic nanodots are of high technological importance in diverse storage and spintronics applications, especially in bit patterned media. Magnetization reversal in such nanodots typically occurs either by coherent rotation of the magnetization or along a vortex state. Other mechanisms of magnetization reversal are scarcely described in the literature. Understanding and predicting the magnetization reversal processes, however, is of utmost importance due to the varying stray fields in the different states under evolution, influencing neighboring nanodots in an array or matrix-like structure. Besides, the stability of vortex states against magnetic field changes – which corresponds to typically broad field ranges with reversible modifications of the magnetic state – influences the robustness of magnetically stored information as well as the necessary external fields for writing new information. Here we report on micromagnetic simulations on nanodots with 10 different, representative diameters and 10 dot thicknesses, respectively, giving rise to 8 possible magnetization reversal processes and suggesting the preconditions for the nucleation and propagation of one or two vortices in cylindrical iron disks. We show the impact of the dimensions and aspect ratios on all phases of magnetization reversal. This study results in a phase diagram of the different magnetization reversal processes.

A novel approach of fluorescent porous graphite carbon nitride based silica gel powder for latent fingerprint detection

Porous graphitic carbon nitride (pg-C3N4) was synthesized from bulk g-C3N4 (Bg-C3N4). First, bulk g-C3N4 was prepared by a thermal method with poly-condensation of melamine as a precursor. The pg-C3N4 was synthesized from Bg-C3N4 under ultrasonic treatment in a sulphuric acid medium. Thereafter, pg-C3N4 was combined with commercial silica gel (Slg) to give a fluorescent Slg/pg-C3N4 powder. These prepared materials were characterized by means of distinctive instrumental techniques consisting of UV–visible spectroscopy (UV–visible), fluorescence spectroscopy (FL), Fourier transform infrared spectroscopy (FT-IR) X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), transmission electron microscopy (TEM) and live cell microscopy. The fluorescent Slg/pg-C3N4 powder was used as a labeling agent for the development of latent fingerprints (LFP) on different surfaces such as glass slides, aluminum foil, aluminum sheets, aluminum rods, a compact disc (CD), iron discs, coins, a tea cup and spoon. The LFP images were additionally captured through the use of ultraviolet radiation at 365 nm due to the fluorescent nature of the Slg/pg-C3N4 powder. The LFP images have been also investigated using different commercial powders such as ZnSO4, TiO2 and Iodine vapor for comparison with fluorescent Slg/pg-C3N4 powder. The Slg/pg-C3N4 powder was used to investigate the LFP images submerged in fresh water. Ultimately, the different fluorescent backgrounds of LFP images had been demonstrated using live cell microscopy with pg-C3N4 and Bg-C3N4. The fluorescent Slg/pg-C3N4 powder exhibited potential as a good labeling agent with excessive sensitivity, rapid detection and an eco-friendly nature. This fluorescent Slg/pg-C3N4 powder was also used to develop the LFP images under conditions that are likely to simulate real crime scenes to establish whether this material can be used in real forensic investigations.

Finite element solution of the three-dimensional system of equations of heat dynamics of friction and wear during single braking

A three-dimensional numerical model of a disk brake to study temperature on a discrete contact of rough surfaces has been developed. It includes the system of equations formulated based on thermotribological postulates of heat dynamics of friction and wear with mutual influence of contact pressure, velocity, properties of materials, and temperature. Two approaches of calculation of the flash temperature and its influence on the maximum temperature during a single braking application were studied. Changes in the contact temperature, sliding velocity, and the thermomechanical wear during braking were shown and discussed. It was found that two of the examined variants of calculation of the flash temperature agree well for the three considered materials of the brake pads combined with the cast iron disk, at each initial sliding velocity in the range from 5 to 20 m s−1.

Advanced Friction–Wear Behavior of Organic Brake Pads Using a Newly Developed System

The objective of this study was to investigate the influence of an advanced performance system on the tribological behavior of brake pad material using a specially designed brake pad tester system following standard SAE J-661. The tribological behavior and friction and wear characteristics of the organic brake pad samples were evaluated. During braking tests, the samples, in contact with a cast iron disk, were studied at different disc speeds, temperatures, and braking cycles under a constant pressure. In order to understand the friction and wear behavior, the unworn surfaces, worn surfaces, and wear debris were characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). Furthermore, the surface characteristics and differences in the wear modes of the brake pad samples were examined. Wear debris was permitted to deform the brake pad surfaces, leading to friction layers and enabling the estimation of the friction behavior of the brake pads. The results showed that the best friction–wear behavior was obtained with lower braking cycles at low speeds and temperature. Thus, the newly developed brake pad tester system proved very effective in evaluating the performance of the brake pad samples.

Analytical model to investigate distributions of the thermal stresses in the pad and disk for different temporal profiles of friction power

The friction power is a key parameter that largely determines the value and distribution of temperature and corresponding thermal stresses in friction elements of a braking system. In this article, the influence of this parameter on the thermal stresses is under consideration. For this purpose, the exact formula was obtained to determine the normal thermal stresses, arisen due to frictional heating during relative sliding of the pad on the surface of a brake disk, for 10 selected temporal profiles of the specific friction power. Numerical analysis was carried out for a frictional couple consisting of a cast iron disk and a pad made of retinax. It is established that some temporal profiles of the specific friction power can cause the generation of the tensile stresses on the friction surface of a brake disk in a radial direction. The change of compressive stresses into tensile may indicate the initiation of the microcracks on this surface.

Tribometric Device for Determining Friction Forces and Friction Coefficients in the Case of Dry Friction of Materials

Abstract The aim of the paper was to develop a device (“pin-on-disc” type) for the measurement of friction in plane friction couplings with sliding movement. On tribometric device (made in our laboratory) we can measure the friction force, friction coefficient and wear, for different loading conditions, speeds, time and material coupling. For the measurement of the frictional force as well as of the coefficients of friction, mainly the method with a resistive tensiometric transducer is used. With a DataQ DI 245 data acquisition board it is possible to record up to 2 kHz frequencies in the range of -10 ÷ +10 mV with a resolution of 13 bits. To test the functionality of the device, a preliminary test was carried out for a steel pin- on- cast iron disc, for different values of the normal pushing force. The device was calibrated and the measurement results were recorded and processed on the computer.

Effects of Cr3C2 content and temperature on sliding friction and wear behaviors of Cr3C2/Ni3Al composite materials

Chromium carbide (Cr3C2)-reinforced Ni3Al matrix composites, which possess excellent high-temperature strength and wear resistance, are considered as potential high-temperature wear-resistant materials. In this study, effects of Cr3C2 content on the friction and wear properties of Cr3C2/Ni3Al composites and their counterpart gray cast iron disks were investigated at different temperatures. The worn surface morphologies of the Cr3C2/Ni3Al composites and gray cast iron disks were analyzed to understand their wear mechanisms. The analysis results showed that in the Ni3Al matrix composites, a combination of abrasive wear and adhesive wear occurred at room temperature, whereas adhesive wear was severer at 200 °C. Furthermore, the optimum Cr3C2 contents of the Cr3C2/Ni3Al composites were found to be 18 vol% and 12 vol% at room temperature and 200 °C, respectively. The volume loss of the composites increased with an increase in the fraction of the Cr3C2 strengthening phase at 350 °C. The wear resistance of the gray cast iron disks decreased with an increase in temperature. In contrast, the wear resistance of the Ni3Al matrix composites increased with an increase in temperature. This increased wear resistance of the composites is attributed to the transformation of their wear mechanism with increasing temperature.

Simple and low-cost tabletop NMR system for chemical-shift-resolution spectra measurements

We have been working on developing a low-cost tabletop NMR system. We reported that a field homogeneity as high as 50 ppm was achieved with a simple NMR magnet by employing two facing ferrite magnets with iron disks in between (Chonlathep et al., 2017). In this paper, we report two improvements added to our previous system: (1) an FPGA based signal processing unit to improve the S/N ratio and (2) a simple shimming mechanism to improve the field homogeneity. We obtained as high as 1 ppm field homogeneity in the best case. The signals from hydrogen nuclear spins in a methyl and carboxy group in acetic acid were resolved in NMR spectra.

Effect of the size on the friction characteristics of brake friction materials: a case study with Al2O3

PurposeThe purpose of this paper is to study the potential of alumina (Al2O3) in nanometer size in automotive brake friction materials.Design/methodology/approachFour brake linings containing alumina differing in particle size (355 µm and 80 nm) and various amount (5 and 10 Wt.%) were designed and produced. The hardness, density and porosity of the samples were measured. All samples were tested on a full-scale brake dynamometer with gray cast iron disc to determine the tribological properties. Detailed examinations on the worn surface were analyzed using a scanning electron microscopy.FindingsIt was concluded that all performance parameters were beneficially affected because of nano alumina.Originality/valueThis paper emphasizes the importance of nano-composites in the automotive industry and helps industrial firms and academicians working on wear of materials.

Experimental comparative study of chrome steel pin with and without chrome plated cast iron disc in situ fully flooded interface lubrication

This paper reports the findings of an experimental study pertaining to the tribo dynamic investigations of contacts formed between chrome base pin and cast iron/chrome plated cast iron discs in situ conditions. Pin on disc geometrical configurations were employed for conducting the experiments at different operating parameters using SAE-15W40 lubricating oil. The fully flooded lubricating condition was insured by directed supply of lubricant at the interface. The friction coefficient, wear rate, vibration amplitude, temperature rise and sound intensity were measured at different loads (varying in the range of contact pressure 1.9–3.1 MPa) and sliding speeds (2–10 m s−1) for the travelling distances between 1000–5000 m. Based on experimental investigations, reductions in the friction coefficient and wear rate were recorded for the chrome steel pin/chrome plated cast iron disc in comparison to chrome steel pin/cast iron disc contact. However, increases in the temperature rise, vibration, and noise were recorded with chrome steel pin/chrome plated cast iron disc contact.

Amorphization of Graphite Flakes in Gray Cast Iron Under Tribological Load

A gray cast iron disc, which had been submitted to a heavy duty automotive brake test, was examined with energy filtered transmission electron microscopy. A graphite flake in a convenient angular position showed the shear interaction of graphite layers with the iron matrix in nano-scale resolution. Atomic layers of graphite were wedged into the ferritic bulk, allowing the entrance of oxygen and the subsequent formation of magnetite. The exfoliated few-layer graphene batches deformed heavily when forced into the matrix. When Raman spectra from the disc surface, which show distinctive carbonaceous bands, were compared with Raman spectra from graphite subjected to deformation in a shaker mill with different milling times, it could be seen that the shear stress on the brake surface was much more effective to induce disorder than the milling, where compressive and impact forces had been additionally exerted on the sample. During shear load the high anisotropy of elastic modulus in the graphite crystalline structure and the low adhesion between graphite basal planes allowed the exfoliation of wrinkled few-layer grapheme batches, causing the formation of more defect related Raman bands than the mechanical stress during high-energy milling.

Plasmonic Nanowires for Wide Wavelength Range Molecular Sensing.

In this paper, we propose the use of a standing nanowires array, constituted by plasmonic active gold wires grown on iron disks, and partially immersed in a supporting alumina matrix, for surface-enhanced Raman spectroscopy applications. The galvanic process was used to fabricate nanowires in pores of anodized alumina template, making this device cost-effective. This fabrication method allows for the selection of size, diameter, and spatial arrangement of nanowires. The proposed device, thanks to a detailed design analysis, demonstrates a broadband plasmonic enhancement effect useful for many standard excitation wavelengths in the visible and NIR. The trigonal pores arrangement gives an efficiency weakly dependent on polarization. The devices, tested with 633 and 830 nm laser lines, show a significant Raman enhancement factor, up to around 6 × 104, with respect to the flat gold surface, used as a reference for the measurements of the investigated molecules.

Investigation of pure sliding and sliding/rolling contacts in a DLC/Cast iron system when lubricated in oils containing MoDTC-Type friction modifier

Abstract Diamond-like carbon (DLC)/cast iron (CI) systems have been widely investigated due to their important application in engine components such as cylinders, pistons and more specifically for the cam/follower interface. The pure sliding contact of the DLC/CI system has traditionally been the focus of research; consequently less is understood about sliding/rolling contact systems. In addition, the tribological and tribochemical characteristics of the Molybdenum Dialkyl Dithiocarbamate (MoDTC) as a lubricant additive in such sliding/rolling contacts are not fully understood. In this study, a Mini Traction Machine (MTM) was used to run the experiments using alloy steel balls coated with 15 atomic percent (at. %) hydrogenated DLC (a-C: 15H) rubbing against uncoated cast iron discs. Results showed that the sliding/rolling ratio affects friction, wear and tribochemistry in CI/DLC systems; pure sliding enhances MoDTC activation. MoDTC decomposes to form MoS2, FeMoO4 and not MoO3. In addition, it was observed that MoS2/FeMoO4 ratio depends on test conditions and affects to the friction performance.

Friction instability induced by iron and iron oxides on friction material surface

This study analyzed the effect of ferrous wear particles, which can be transferred from gray iron brake discs to the friction material surface during brake applications, on friction instability. To simulate the chemical change of the sliding surfaces, ferrous particles, such as pure iron, Fe2O3, and Fe3O4 particles, were embedded on the sliding surface of a friction material, and their friction characteristics were investigated using a scale dynamometer. The results showed that the ferrous particles aggravated friction instability, showing larger stick-slip amplitudes and wider velocity ranges for friction instability than the bare specimen. The embedded ferrous particles increased the static coefficient of friction and produced larger stick-slip amplitudes in the order of Fe2O3, iron, and Fe3O4, while the friction material without ferrous particles showed the least instability. The surface energy and amount of high-pressure contact plateaus on the sliding surface were attributed to the high friction instability caused by the interfacial adhesion increased by ferrous particles at the sliding interface. This explained the frequent friction-induced noise and vibrations found with a corroded or relatively soft gray iron disc.

Movement characteristics of magnetic wheel type magnetic actuator

This paper proposes a new magnetic actuator that operates on the resonance energy of a one-degree-of-freedom model by using an electromagnetic force. The actuator is moved by the difference in inertia force during one period of vibration. A magnetic wheel type movement system using two electromagnetic vibration components and combining two iron disks and electromagnets was prototyped. Experimental results show that the system can move at 18.5 mm/s in a vertical direction when the system has load mass of 90 g. It has been shown that the system can move over 360 degrees on an iron structure.

Fe-Ti alloy layer plasma deposition – Monitoring of plasma parameters and properties of deposited alloys, anodization and photoelectrochemical characterization

Metallic Fe-Ti alloy thin films were deposited by high-power impulse magnetron sputtering (HiPIMS) on a glass substrate with an FTO electrode. Two-component alloys were prepared by sputtering of a single target, which was composed from two sectors made from different elements: iron disc and titanium ring. Chemical composition of alloy thin films was controlled by the width of titanium ring that partially covered iron target. These alloy thin films were anodized in fluorine-containing electrolyte with the aim to create mixed oxide nanostructures. Anodized layers were amorphous and transparent. After calcination, the layers consisted of crystalline Fe2O3 although TiO2 was still amorphous. Photoelectrochemical characterization show that increasing amount of titanium in the alloy results in the fabrication of Fe2O3/TiO2 nanostructures with higher photocurrent compared to those prepared from pure iron by the same anodization technique.

Sulfite assisted rotating disc electrocoagulation on cadmium removal: Parameter optimization and response surface methodology

Abstract Redox conditions is an extraordinary parameter as it controlled the generation of functional products in iron–electrocoagulation process. In the present study, a newly designed rotating disc electrocoagulation system (RDEC) on cadmium removal from wastewater assisted by sodium sulfite is investigated. The oxidation and reduction environment are adjusted and controlled with rotate speed and sodium sulfite, respectively. In the first stage, single effect factors such as initial pH (pHi), current density (j), electrode distance (d), rotate speed (n), Na2SO3 dosage (CS), and initial Cd2+ concentration (C0) in RDEC process are evaluated using iron disc as sacrificial electrodes. Results indicate that initial pH, current density, and Na2SO3 dosage have a positive influence on Cd2+ removal, whereas rotate speed and electrode distance exhibit an opposite affect. The increase of Cd2+ removal efficiency at low rotate speed or high Na2SO3 dosage might be attributed to the generation of Fe(II)–Fe(III) layered double hydroxides (LDHs), which is identified to be an vital intermediatein on the removal of cadmium because of an oxygen–free solution environment is maintained. Finally, Response Surface Methodology (RSM) is carried out to investigate the interactional influences between current density, rotate speed, and Na2SO3 dosage and the optimal parameters based on the result of single factor experiments. The actual removal efficiency of Cd2+ and energy consumption (EEC) are respectively calculated as 98.11% and 2.98 kW h/m3 at the optimum operating conditions: C0 25 mg/L, pHi 7, j 10.85 mA/cm2, CCl 1000 mg/L, CS 114.5 mg/L, d 20 mm, and n 44.16 rpm.

Gradient residual strain and stress distributions in a high pressure torsion deformed iron disk revealed by high energy X-ray diffraction

High energy X-ray diffraction is used to investigate for the first time the distribution of residual X-ray elastic stresses inside a high pressure torsion (HPT) deformed iron disk with a diameter and thickness of ~30 and ~8mm, respectively. In the experiment, a dedicated conical slit system restricts the diffraction gauge volume in three dimensions to ~0.45mm3, which is then used to scan the bulk sample cross-section in a non-invasive manner. Pronounced residuals stress gradients with maximal tensile stresses of ~200MPa are observed along radial and tangential directions and are correlated to the deformation gradient arising from HPT.

On the influence of car brake system parameters on particulate matter emissions

The influence of car brake system parameters on particulate matter emissions was investigated using a pin-on-disc tribometer. Samples from a low-steel friction material and a cast iron disc were tested for different sliding velocities, nominal contact pressures and frictional powers. Disc temperatures were also measured. Their impact on total concentration, size distribution, particle coefficient and transition temperature was analysed. Results show that frictional power is the most significant brake system parameter. However, temperature, as a response parameter, is the most influential, inducing a shift towards the ultrafine particulate fraction and raising emissions. A transition temperature, independent of the system parameters, was identified.

Pin-on-Disc Testing of Low-Metallic Friction Material Sliding Against HVOF Coated Cast Iron: Modelling of the Contact Temperature Evolution

Pin-on-disc (PoD) testing is widely used to investigate the sliding behaviour of materials and relevant wear mechanisms under different tribological conditions. The approach has been also profitably applied to the characterization of materials for brake systems to obtain specific information on the wear mechanisms. In the present study, the transient thermal analysis of a pin made with a friction material dry sliding against HVOF coated and uncoated pearlitic cast iron disc in a PoD apparatus was investigated by means of a finite element analysis together with experimental measurements. The aim of the investigation was to model the surface contact temperature in this sliding system to highlight the role of the different surface conditions, i.e., coated and uncoated, on the evolution of the pin and disc temperatures during sliding. In addition, we propose a simplified analytical equation for estimating the average temperature rise in the contact region during sliding, by extending the Kennedy approach in order to be able to provide a quick evaluation of the contact temperature for this kind of couplings, what is very helpful when characterizing a large number of systems in different contact conditions.