Dielectric Powders Research Articles

Performance Analysis on Eco-friendly Machining of Ti6Al4V using Powder Mixed with Different Dielectrics in WEDM

The recent scenario of modern manufacturing is tremendously improved in the sense of precision machining and abstaining from environmental pollution and hazard issues. In the present work, Ti6Al4V is machined through wire EDM (WEDM) process with powder mixed dielectric and analyzed the influence of input parameters and inherent hazard issues. WEDM has different parameters such as peak current, pulse on time, pulse off time, gap voltage, wire speed, wire tension and so on, as well as dielectrics with powder mixed. These are playing an essential role in WEDM performances to improve the process efficiency by developing the surface texture, microhardness, and metal removal rate. Even though the parameter’s influencing, the study of environmental effect in the WEDM process is very essential during the machining process due to the high emission of toxic vapour by the high discharge energy. In the present study, three different dielectric fluids were used, including deionised water, kerosene, and surfactant added deionised water and analysed the data by taking one factor at a time (OFAT) approach. From this study, it is established that dielectric types and powder significantly improve performances with proper set of machining parameters and find out the risk factor associated with the PMWEDM process.

An Investigation on Surfactant Added PMWEDM of Inconel 718

This paper shows the impact of different process parameters and powder characteristics on the material removal rate and surface roughness obtained in surfactant added Powder Mixed Wire Electric Discharge Machining (PMWEDM). Inconel-718 is selected as the workpiece material, which has ample application in the industries handling environment of extreme stress, pressure and temperature. It has high work hardening properties along with high rupture strength, fatigue, and creep, making it extremely difficult to machine. So, additives having different thermo-physical properties are studied to improve the machining efficiency. The additives experimented includes aluminium, silicon carbide, graphite, and aluminium oxide. It is found that the electrostatic force present creates an agglomeration effect with dielectric additive powders, causing inhomogeneity in the mixture. So, a surfactant SPAN20 is used here to maintain the homogeneity of the mixture. The obtained MRR and SR are then modelled and optimised through Particle Swarm Optimization technique (PSO). It is observed that the addition of SPAN20 has improved the MRR by 13.56% and, SR by 45.05%. Also, it has been found that due to the combined abrasive action, abrasive powders increase MRR significantly than others. Furthermore, it is found that low grit size powders with lower density produces better machined surfaces.

Synthesis of micro- and nanostructured materials via oscillating reactions initiated by high-power microwave pulses

Herein we describe the results of our study of plasma chemical process initiated by high-power microwave pulses generated by 75/0.8 gyrotron (frequency 75 GHz, pulse duration up to 12 ms, power up to 550 kW) in mixtures of metal (Mg, Ti, Mo) and dielectric (Al2O3, AlN, B) powders. The process leads to formation of micro- and nanostructured materials and the yield is strongly affected by hydrogen-containing additives (C2B10H12, H3BO3, NaBH4) in the mixture. It was found that the process occurs in three main stages. The first initiation stage is very short (just slightly exceeds the pulse duration) and includes the absorption of microwave irradiation and the discharge proceeded as coulombic explosion. The main stage is much longer and includes decomposition of starting materials and reactions between all the components. All the tested additives prolong the main stage, in some cases by an order of magnitude or even more, and turn it into self-sustaining oscillating mode. The last one is realized most likely due to autothermic effect. As a result, the yield increases sufficiently. Finally, the decay stage is relatively short stage (up to 200 ms) following the main stage and includes irreversible cooling down of the reaction zone and deposition of the particles. The decay stage is not affected by additives. Owing to use the additives we were able to decrease the energy consumption for preparation of the materials below 1 kJ/g, which is 2–3 times lower compared to our previous results. The prepared materials were characterized by SEM, EDS and X-ray diffraction analysis and found to be mainly oxides, nitrides and borides.

Synthesis of new materials through microwave discharge initiated by pulses of high power gyrotron in the mixtures of metal and dielectric powders

Herein we describe a new plasma chemical method for synthesis of new materials. Plasma was generated as a result of microwave discharge initiated by pulses of high power gyrotron in the mixtures of metal and dielectric powders. The gyrotron operates at frequency of 75 GHz giving pulses with duration of 2-12 ms and power up to 550 kW. Mixtures of Al with Al2O3, AlN, melamine and NH4Cl were treated with the pulses in the specially constructed plasma chemical reactor, which allowed to collect products of the process and to carry out real time monitoring of the process with low- and high-speed cameras and spectrometers. We observed a complicate oscillating process, which led to formation of micro dispersed materials containing phases usually formed at high temperatures. It was shown that plasma temperature in all the experiments was at least 2500 K in all reaction areas and above 3500 K in main reaction zone. We also realized that addition of hydrogen-containing substances (e.g. C2B10H12) resulted in a noticeable intensification of the process – highly likely due to the change of reactions pathways through an involvement of hydrogen into the intermediate stages. Obtained data confirm that microwave discharge is a promising method for synthesis of new materials including fine structure materials, e.g. consisting of major phase micro particles covered with a thin layer of minor phase.

Absorption and Remission Characterization of Pure, Dielectric (Nano-)Powders Using Diffuse Reflectance Spectroscopy: An End-To-End Instruction

This paper addresses the challenging task of optical characterization of pure, dielectric (nano-)powders with the aim to provide an end-to-end instruction from appropriate sample preparation up to the determination of material remission and absorption spectra. We succeeded in establishing an innovative preparation procedure to reproducibly obtain powder pellet samples with an ideal Lambertian scattering behavior. As a result, a procedure based on diffuse reflectance spectroscopy was developed that allows for (i) performing reproducible and artifact-free, high-quality measurements as well as (ii) a thorough optical analysis using Monte Carlo and Mie scattering simulations yielding the absorption spectrum in the visible spectral range. The procedure is valid for the particular case of powders that can be compressed into thick, non-translucent pellets and neither requires embedding of the dielectric (nano-)powders within an appropriate host matrix for measurements nor the use of integrating spheres. The reduced spectroscopic procedure minimizes the large number of sources for errors, enables an in-depth understanding of non-avoidable artifacts and is of particular advantage in the field of material sciences, i.e., for getting first insights to the optical features of a newly synthesized, pure dielectric powder, but also as an inline inspection tool for massively parallelised material characterization.

Study on electric field distribution in cylindrical metal silo considering particle segregation

The cylindrical metal silo plays an important role in the industry for storing the product, while the undesired of electrostatic charge on the dielectric powder leads to dangerous electrostatic discharge and threatening human safety and causing a great economic loss. The aim of the study was to investigate the effect of the particle segregation on the electric field in the silo base on the electric field simulation. Three parameters were studied: large particle layer thickness fraction, small particle space charge density (ρS) and large particle space charge density (ρL). The effect of the particle segregation on the electric field in the silo was evaluated through comparing the electric field in the segregation case to that in the uniform case. The results showed that the particle segregation significantly affected the electric field in the silo. The space charge density of the small particle mainly influenced the electric field in the small particle layer, while that of the large particle had a significant effect on the electric field in the large particle layer. The particle segregation not only could increase the electric field strength but also could decrease the electric field, which was dependent on the relative magnitude of the large (|ρL|) and small (|ρS|) particle space charge density. Additionally, the relative growth rate (absolute value) of the maximum electric field strength increased with the increase of |ρL-ρS|.

On the Dust Structures and Chain Reactions Induced over the Regolith by Gyrotron Radiation

Dust structures formed in exothermic chain plasma chemical processes initiated by pulsed gyrotron radiation in mixtures of metal and dielectric powders are studied. The composition of the powder mixture corresponds to the composition of the lunar regolith. Experiments at the energy of the gyrotron microwave pulse of 1–3 kJ and a pulse duration of 1.5–4 ms reveal an explosive process caused by the Coulomb repulsion of charged particles from the surface of the regolith into the reactor volume. The explosion is followed by the development of chain self-propagating high-temperature synthesis reactions. During these reactions lasting for tens of seconds, the suspension of dust particles rises tens of centimeters above the powder surface. The energy release is more than two orders of magnitude higher than the energy of initiation of a chain reaction. Regolith spheroids with diameters from 1 to 1000 µm precipitate on the side surfaces of the reactor. An analogy of the possible contribution of the Coulomb repulsion between charged particles and plasma exothermic processes to the dispersion of regolith dust when the Moon surface is bombarded by micrometeorites is considered.

A review of performance optimization and current research in PMEDM

Abstract The EDM method is non-conventional in machining for machining of geometrically unpredictable or hard materials and electrically conductive materials that cannot be machined with ordinary forms of machining. With latest strategies, research has emphasized EDM's increased machining efficiency. PMEDM is an ongoing method where a Mixed conductive powder with the dielectric liquid to improve EDM machining capabilities in this direction. This paper introduces the review work done to improve the performance characteristics of machining like MRR, SR and TWR for different Machining parameters like Ip, Duty factor, Ton, Toff, Work piece material, powder type, concentrated powder with different dielectric liquids and powder materials. Also in the paper reports and summaries Current trends in the research, PMEDM using various powders such as Nano powders mixed in dielectric fluids and examined the current challenges, future scope of research and impediments of the PMEDM process.

Broadband emission from Er-contained yttrium orthophosphate and orthovanadate nanopowders excited by near infrared radiation

Spectral-luminescent properties of nanosized dielectric powders Y(1-x)ErxPO4 and Y(1-x)ErxVO4 (x = 0, 0.25, 0.5, 0.75, 1) excited to levels 4I13/2, 4I11/2, 4I9/2, 4S3/2 of Er3+ ions were investigated. For the above concentration series of nanosized powders the regularities of the appearance of anti-Stokes luminescence from 4S3/2, 4F9/2 and 4I9/2 levels of Er3+ ions, as well as broadband emission registered in the visible spectral range, are revealed. The mechanism of occurrence of this broadband radiation is refined and discussed.

Plasma-chemical processes under high-power gyrotron’s discharge in the mixtures of metal and dielectric powders

Synthesis of nano- and microstructured materials is a field of high activity in material science. Plasma-chemical processes are effective and versatile tools for this purpose. Plasma can be generated in different ways, in this work we use pulses of high-power gyrotron (75 GHz/550 kW) to initiate a discharge in mixtures of metal and dielectric powders. Depending on the starting composition of mixture it is possible to obtain new materials. It was shown earlier that MgAl2O4 can be prepared from Mg/Al2O3 mixture. Now we demonstrate that organic compounds can also be introduced into the mixture. Using melamine as a source of nitrogen we prepared aluminum oxynitrides (Al11O15N, Al27O39N) starting from Al/Al2O3. An addition of small amount of carborane C2B10H12 makes the process even more intensive, since in this case hydrogen is involved. Proposals on possible mechanism was made basing on observations during the process and composition and morphology of final products.

3-D Printed Structures by Microdispensing Materials Loaded With Dielectric and Magnetic Powders

In this paper, we develop processes for printing 3-D structures by microdispensing materials loaded with dielectric and magnetic powders. Manufacturing with these materials is demonstrated by 3-D printing simple tower and bridge structures. The dielectric and magnetic properties are adjusted by loading different amounts of powder into a host silicone material. The long-term goal of the research is to print larger and more complex structures while also realizing a range of electromagnetic properties for applications in 3-D printed electromagnetics.

Study of Material Removal Rate in Powder Mixed EDM of AA7075/B4C Composite

In the present study, AA7075/B4C composite is fabricated by mechanical stir casting process taking 5% boron carbide particles of average size 20-40 µm. In order to achieve improved surface properties and enhanced material removal rate, chromium particles are added in the dielectric fluid and powder mixed EDM of the composite is performed using copper electrode. Four process parameters namely current, pulse on time, pulse off time and gap voltage are considered for investigating the material removal rate (MRR). Design of experiment (DOE) has been set as per central composite rotatable design using response surface methodology (RSM). Surface characteristic such as recast layer is assessed by SEM. Comparative study of recast layer is carried out at intermediate and higher setting of process parameters. MRR is found to be a function of current, pulse on time and gap voltage. MRR is optimized using desirability approach. Confirmatory experiment is found with 8.65% deviation from predicted value of MRR.

Synthesis of oxide and nitride ceramics in high-power gyrotron discharge

Synthesis of oxides, nitrides, and oxynitrides of silicon and aluminium by a pulsed microwave discharge in the mixtures of metal and dielectric powders is described. The microwave pulses were generated by high-power gyrotron (frequency 75 GHz, power up to 550 kW, pulse duration from 0.1 to 15ms). SiO2 + β-Si3N4 (1:1 by molar) and α-Al2O3 + AlN (2:1 by molar) mixtures with Mg (1 and 5wt%) were treated in air with microwave pulses with power of 250÷400 kW and duration of 2÷8 ms. It was found that the discharge cannot be initiated for both mixtures in absence of Mg at any pulse power and duration. When 1% of Mg was added, the discharge was observed for both mixtures under 8 ms pulses of 400 kW; however, the amounts of materials produced were not enough for analysis. With 5% of Mg the discharge was observed for both mixtures under 8 ms pulses of 350 kW, and products of the plasma-chemical processes in the Al2O3 + AlN mixture were analyzed.

Multifunctional graded dielectrics fabricated using dry powder printing**This paper was submitted for review on 15 February 2017. The project is funded by the Office of Naval Research, Code 331.

The ability to fabricate multifunctional devices that combine good structural properties with embedded electromagnetic functionality has many practical applications, including antireflective surfaces for structural radomes, load bearing conformal antennas, integrated RF transmission lines and passive beam forming networks. We describe here a custom made 3D printer that can print high dielectric constant ceramic powders within a low-loss structural composite substrate to produce mechanically robust parts with integrated graded dielectric properties. We fabricated a number of these parts and evaluated their anisotropic dielectric properties by determining the complete permittivity tensor of the printed samples as a function of local powder weight. This data was then experimentally validated using two practical examples: a Chebyshev antireflective stack and a 2D passive beamsteering network. The results of both electromagnetic systems displayed acceptable agreement between the simulated and measured results. This agreement shows that powder printing is a potential approach for fabricating spatially graded dielectric electromagnetic systems.

Considering the possibility of bonding utilizing cold sintering for ceramic adhesives

AbstractHere, we introduce a new bonding technique that enables the joining of different materials at low temperatures and provides a bond superior to that of polymer adhesives at high temperatures, in temperature ranges between 250°C and 500°C. This technique involves a low temperature sintering process that is termed the “Cold Sintering Process,” where a dielectric composite powder material is sintered to function as the adhesive between two other materials being bonded. In order to characterize and further discuss the potential of this new bonding methodology, which we call Cold Sintering Ceramic Bonding (CSCB), we demonstrate the initial mechanical characteristics of samples with sandwich structures of mesh/CSCB/mesh, including four‐point bending, micro‐indentation, and adhesion pull tests. Where appropriate, we compare mechanical properties against low and high temperature epoxies and demonstrate that the CSCB matches up competitively with the epoxies at low temperatures and remains strong at temperatures well above those where standard polymer adhesives fail. Transmission electron microscopy show a high quality interface between a stainless steel plate and the ceramic after the CSCB.

Initiation of dusty structures in chain reactions under the action of gyrotron radiation on a mixture of metal and dielectric powders with an open boundary

A dusty plasma formed in chain exothermal reactions initiated by radiation of a high-power gyrotron in mixtures of metal and dielectric powders has been described. An oscillatory character of such chain reactions, as well as the appearance of dust particles at the first (explosive) stage, has been detected. The tracks, velocities, and sizes of dust particles have been measured. It has been revealed that ensembles of dust particles appear in a reactor after switching-off of the gyrotron against the background of development of chemical reactions. The time of existence of these ensembles is three or four orders of magnitude larger than the duration of a microwave radiation pulse. The quasistationary state of the low-temperature plasma with charged macroparticles appears because of both the chemical heating of the mixture in the reactor and thermophoresis. It has been shown that dust particles are necessary as crystallization nuclei for the creation (or deposition) of complex composites of nano- and micromaterials produced in secondary plasma chemical synthesis.

Comparative study of dielectric properties of geopolymer matrices using different dielectric powders

Due to their interesting properties, geopolymers have found various applications in different domains. The evaluation of the dielectric properties of a geopolymer matrix for RF applications is innovative. In this context, this paper focuses, first, on the evaluation of the suitability of a geopolymer matrix with dielectric materials, and then on the improvement of the real permittivity value of the obtained material. For this purpose, the precursors either dielectric powder or aluminosilicate powder were first characterized. Then, the feasibility of the geopolymer matrix was investigated. Based on the feasibility test, it was shown that these kinds of materials can be successfully filled with various types of dielectric materials, such as ZrO2, BaTiO3 and Y2O3. Moreover, the optimized parameters of the synthesis process, which included a small amount of water in the formulation, were 20°C for the synthesis temperature, 85% for the humidity level and 7 days for the setting time. The measurement of the dielectric properties evidenced, first, that the real part of the relative permittivity strongly depends on the formulation and storage process. Then, the incorporation of a high percentage of BaTiO3 (60%) induced an increase in the real part of the permittivity value and a decrease in the loss tangent. Finally, the mixing law of Maxwell-Garnet was applied to compare the theoretical and measured values of the permittivity. It was deduced that the small difference detected at low percentages whatever the dielectric materials can be explained by the preponderant effect of the geopolymer matrix compared to ZrO2 or BaTiO3, it seems that the mixing law well functioned with BaTiO3 than ZrO2. This is in accordance with the better dielectric properties for samples containing BaTiO3.

Microwave Measurement System for Detection of Dielectric Objects in Powders

Detection and removal of undesirable objects is an important issue in many material processing industries. This paper presents a microwave-based measurement technique for detection of dielectric objects in powder materials flowing through metal pipes. A nonintrusive microwave sensor is developed, which uses multiple resonant modes to obtain high sensitivity with respect to permittivity variations inside the pipe. Undesirable objects are detected based on the scattering parameters of the sensor, which are measured using a fast-sampling microwave transmitter and receiver unit. We present a detection algorithm derived from the likelihood-ratio test, which includes a parametric model of the local statistical distribution of the measured scattering parameter data. The model involves a set of Mobius transformations that map the measured scattering parameters to a domain where the data are Gaussian distributed. All unknown parameters in the model are estimated from data using maximum likelihood. Based on measurement results from a gravity-fall experimental setup, we conclude that small dielectric objects can be reliably detected in heterogeneous flows of dielectric powder.

Influence of magnetic field-aided filler orientation on structure and transport properties of ferrite filled composites

Epoxy resins are materials commonly used for insulations and encapsulations due to their easy processing process and mechanical strength. For their applications in power industry and electronics the effective heat dissipation is essential, thus their thermal conductivity is one of the most important properties. Introduction of appropriate dielectric powders, preferably in an ordered way, can increase the thermal conductivity of the polymer while keeping its good electrical insulation properties. In this work we used strontium ferrite as a filler to study the evolution of the filler particles distribution in the fluid before curing. Magnetic ferrite particles were dispersed in liquid epoxy resin and formation of chain-like or more complex structures under applied external magnetic field was observed and investigated. Computer simulations made show that with increasing magnetic field these structures are characterized by longer chains, higher speed of particles displacement and stronger structural anisotropy. However, for highly-filled systems, stronger inter-particle interactions make the alignment process less effective. The effective thermal conductivity simulated with FEM methods increases with increasing filler content and the percolation threshold in aligned systems is achieved at lower filler concentrations than for reference isotropic samples. The results are compared with the experimental data and a good qualitative agreement is obtained.

Observation of self-organized square lattice pattern formation in surface barrier discharge plasma

The experimental observation of a two-dimensional self-organized square lattice pattern in a planar surface barrier discharge is reported. The discharge was operated near atmospheric pressure in helium gas. The transition from irregular plasma spot pattern to a square lattice pattern is achieved by reducing the discharge driving frequency. On increasing the driving frequency the regular lattice pattern is destroyed and again transforms to an irregular plasma spot pattern. Dielectric degradation and powder formation is also observed after discharge process. Spatio-temporal behavior of observed plasma pattern is presented.