Single-pulse Experiments Research Articles

A Study of the Materials Removal Mechanism of Grinding-Aided Electrochemical Discharge Machining of Metal Matrix Composites

In order to research the workpiece materials removal mechanism of Grinding-assisted Electro-chemical Discharge Machining(G-ECDM) of Metal Matrix Composites (MMCs), a good deal of single pulse experiments has been performed in this paper. The crater volume, convex edge, debris, machined surface of G-ECDM have been taken into considerationand it turns out to be that the grinding effect removes the convex edge of the Electro-chemical Discharge Machining (ECDM) crater during the machining of MMCs, the result show that the material removal rate (MRR) of G-ECDM is much higher than that of ECDM and Electrical Discharge Machining (EDM). When compared to the normal ECDM process, it is found that though the Al4C3 phase can be detected in this ECDM condition, no Al4C3 are observed in the processed surface, which indicates a better surface quality. The reason of this phenomenonhas been analyzed theoretically and experimentally. Based on these results, mechanism of the G-ECDM of MMCs was disclosed in this study.

Direct Measurement of High-Temperature Rate Constants of the Thermal Decomposition of Dimethoxymethane, a Shock Tube and Modeling Study.

Shock-tube experiments have been performed to investigate the thermal decomposition of the oxygenated hydrocarbon dimethoxymethane (DMM; CH3OCH2OCH3). The primary initial reaction channels of DMM decomposition are considered to be the two bond fissions: CH3OCH2OCH3 → CH3O + CH2OCH3 (1) and CH3OCH2OCH3 → CH3 + OCH2OCH3 (2). In the present work, two shock-tube facilities and three different detection techniques have been combined: Behind reflected shock waves, we have carried out time-resolved measurements of (i) the formation of H atoms using the highly sensitive H-ARAS (Atomic Resonance Absorption Spectrometry) technique and (ii) the depletion of the DMM reactant by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS). In addition, (iii) the temperature-dependent composition of stable reaction products was measured in single-pulse shock-tube experiments via gas chromatography (GC/MS). The experiments span a temperature range of 1100-1430 K, a pressure range of 1.2-2.5 bar, and initial reactant mole fractions from 0.5 ppm (for H-ARAS experiments) up to 10 000 ppm (for HRR-TOF-MS experiments). Experimental rate constants ktotal, ktotal = k1 + k2, obtained from these three completely different methods were in excellent agreement among each other, i.e., deviations are within ±30-40%, and they can be well represented by the Arrhenius expression ktotal( T) = 1013.28±0.27 exp(-247.90 ± 6.36 kJ mol-1/ RT) s-1 (valid over the 1100-1400 K temperature and the 1.2-2.5 bar pressure range). By replacing the respective ktotal values used in a recently published DMM chemical kinetics combustion mechanism (Vermeire et al. Combust. Flame 2018, 190, 270-283), it was also possible to successfully reproduce measured product distributions.

Study on the characteristics of plasma channel based on multi-spark pulse discharge machining effect

Plasma channel characteristics and energy distribution in electrical discharge machining (EDM) were mostly studied by analyzing the geometry parameters of craters caused by a single pulse discharge in previous studies. However, single pulse experiments cannot provide us insights into superposition, migration, abruption, interruption, and other phenomena of the plasma channel which have significant effects on EDM. Besides, EDM itself is a consecutive pulse discharge process. Thus, this paper focuses on the characteristics of plasma channel and the mechanism of material removal based on experimental data from multi-spark pulse discharge machining. The contrastive milling experiments of different parameters in multi-spark pulse discharge machining in high-speed dry EDM by using nickel-based superalloy as workpiece were conducted. The effects of peak current, dielectric type, breakdown voltage, air pressure, and electrode rotation speed on the crater number, crater distance, crater depth, and crater removal volume were studied. The plasma channel characteristics and material removal mechanism in continuous machining of high-speed dry EDM were revealed.

Proton beam induced dynamics of tungsten granules

This paper reports the results from single-pulse experiments of a $440\text{ }\text{ }\mathrm{GeV}/c$ proton beam interacting with granular tungsten samples in both vacuum and helium environments. Remote high-speed photography and laser Doppler vibrometry were used to observe the effect of the beam on the sample grains. The majority of the results were derived from a trough containing $\ensuremath{\sim}45\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ diameter spheres (not compacted) reset between experiments to maintain the same initial conditions. Experiments were also carried out on other open and contained samples for the purposes of comparison both with the $45\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ grain results and with a previous experiment carried out with sub-$250\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ mixed crystalline tungsten powder in helium [Phys. Rev. ST Accel. Beams 17, 101005 (2014)]. The experiments demonstrate that a greater dynamic response is produced in a vacuum than in a helium environment and in smaller grains compared with larger grains. The examination of the dynamics of the grains after a beam impact leads to the hypothesis that the grain response is primarily the result of a charge interaction of the proton beam with the granular medium.

Damage in a Thin Metal Film by High-Power Terahertz Radiation

We report on the experimental observation of high-power terahertz-radiation-induced damage in a thin aluminum film with a thickness less than a terahertz skin depth. Damage in a thin metal film produced by a single terahertz pulse is observed for the first time. The damage mechanism induced by a single terahertz pulse could be attributed to thermal expansion of the film causing debonding of the film from the substrate, film cracking, and ablation. The damage pattern induced by multiple terahertz pulses at fluences below the damage threshold is quite different from that observed in single-pulse experiments. The observed damage pattern resembles an array of microcracks elongated perpendicular to the in-plane field direction. A mechanism related to microcracks' generation and based on a new phenomenon of electrostriction in thin metal films is proposed.

Influence of electrode temperature on electric erosion pit morphology during cool electrode EDM

The mechanism of material removal through cool electrode electrical discharge machining (EDM) was investigated in this study by using single pulse discharge method. The influence of electrode temperature on the electric erosion pit morphology on the surface of the electrode and workpiece was analyzed. Finite element simulation was conducted on the temperature field between the electrode and workpiece under different electrode temperatures, and the simulation results were verified through a single pulse experiment. Under the same single pulse discharge parameters, when the electrode temperature was −20, 20, and 60 °C, the electric erosion pit diameter on the electrode surface increased to 290, 350, and 403 μm, respectively; the change in electric erosion pit diameter on the workpiece surface was small, and the corresponding values were 690, 705, and 718 μm. However, the bulge of the electric erosion pit on the surface of the workpiece became increasingly obvious, and the surface became unsmooth. The results of the single pulse experiment and the finite element simulation were identical. A comparative experiment involving the machining of Ti-6Al-4V titanium alloy was conducted with cool electrode and conventional EDM. Electrode wear, surface roughness, and machining efficiency were analyzed. Compared with that in conventional EDM, electrode wear decreased by 24.5%, the material removal rate increased by 14.16%, and surface roughness decreased by 14.14% in cool electrode EDM. Reducing the electrode temperature changed the electric erosion pit morphology on the electrode and workpiece surface, reduced electrode wear, improved surface processing quality, and increased processing efficiency.

Application of 1H and 27Al magic angle spinning solid state NMR at 60 kHz for studies of Au and Au-Ni catalysts supported on boehmite/alumina

In this work for the first time we show the power of solid state NMR spectroscopy in structural analysis of alumina and catalysts supported on the alumina surface employing very fast (60kHz) magic angle spinning (MAS) technique. In the methodological part we demonstrate that under such MAS condition, cross-polarization (CP) from proton to aluminum is an efficient process when a very weak 27Al RF field is applied. The mechanism of CP transfer and the Hartmann-Hahn (H-H) matching conditions were tested for 27Al RF fields equal to 3.3 and 8.3kHz. It has been found that double quantum (DQ) CP/MAS is the best choice for H-H set with RF =3.3kHz. It has been also proved that the quality of 1H-27Al CP/MAS spectra strongly depends on 27Al carrier offset. Applied to γ-alumina, this method revealed that 1H-27Al CP/MAS at 60kHz is extremely useful for mapping the distribution of hydroxyl groups on the surface. Indeed, the AlV sites, which are not easily detected with Single Pulse Experiment (SPE), are clearly seen when 1H-27Al CP/MAS is applied. Utilizing 2D 1H-27Al CP/MAS HETCOR experiment it was possible to assign the proton positions and to correlate them with aluminum centers. Studies of mono- (Au) and bi- (Au-Ni) metallic catalysts supported on boehmite/alumina carrier employing 1D and 2D HETCOR experiments clearly show that distributions of hydroxyl groups for both systems are dramatically different.

Satellite and central transitions selective 1H/{27Al} D-HMQC experiments at very fast MAS for quadrupolar couplings determination

Recent study has demonstrated the application of the proton-detected heteronuclear multi-quantum coherence (HMQC) at ultrafast Magic Angle Spinning (MAS) to probe quadrupolar nuclei including 14N and 35Cl. In addition, for half-integer quadrupolar nucleus like 35Cl, the quadrupolar product can be calculated based on the shift difference between the center band of satellite transition (ST) and the central transition (CT) peaks. The applicability of this technique is further investigated on spin I=5/2, namely 27Al nucleus, and kaolin is chosen as the testing sample. However this study is not straightforward owing to a spin quantum number I=5/2 of 27Al nucleus and a small quadrupolar coupling of kaolin. Furthermore, very fast MAS, which is mandatory for proton-detected experiment to suppress 1H–1H homonuclear dipolar interactions, introduces additional complexities. It induces the partial overlap of CT and the center band of inner ST (ST1) resonance in addition to the insufficiency of CT-selective excitation by soft-pulse irradiation. In the current work, we employ the constant-time D-HMQC experiment, in which the duration between two recoupling blocks is fixed to a constant value and the arbitrary t1 increment can be used within this duration. This constant-time D-HMQC enables the precise determination of CT and ST resonance shifts through CT- and ST-selective observations by the indirect spectral width (i) with asynchronized sampling to the top of rotational-echoes for STs and (ii) three times larger than the spinning frequency, respectively. We also numerically and experimentally develop a satellite-selective excitation technique, in which the radio frequency field is applied to the first spinning sideband of ST1 resonance. The satellite-selective 1D single pulse and 2D conventional D-HMQC experiments are demonstrated. The quadrupolar product of 27Al nucleus extracted from the resulting spectra is in good agreement with the literature.

The effect of pulse energy on the removal form of silicon crystal in electrical discharge machining

A single-pulse discharge system for semiconductors was designed and produced. Single-pulse discharge experiments with single-crystal silicon were conducted, and the morphology of the electric erosion pit under different discharge energy levels was observed. Three removal forms, namely, heat removal, stress removal, and secondary crushing in electrical discharge machining (EDM) of single-crystal silicon, were discovered, and the mechanisms of semiconductor discharge processing were described. Finally, the role of different removal forms in single-crystal silicon EDM was explained and verified.

Reversible Phase Change Characteristics of Cr-Doped Sb2Te3 Films with Different Initial States Induced by Femtosecond Pulses

As a kind of chalcogenide alloy, phase change material has been widely used as novel storage medium in optical disk or electrical memory. In this paper, femtosecond pulses are used to study the reversible phase transition processes of Cr-doped Sb2Te3 films with different initial states. The SET processes are all induced by multiple pulses and relate to the increase of crystallized partial in the irradiated spot. When the Cr concentration is 5.3 at % or 10.5 at %, the crystallization mechanism is still growth-dominated as Sb2Te3, which is beneficial for high speed and high density storage, whereas the necessary crystallization energy increases with more Cr-dopants, leading to higher amorphous thermal stability. RESET results by multiple pulses show that Cr-dopants will not increase the power consumption, and the increase in Cr-dopants could greatly increase the antioxidant capacity. Single-pulse experiments show that the RESET process involves the competition of melting/amorphization and recrystallization. The reversible SET/RESET results on different initial states are quite different from each other, which is mainly due to the different surroundings around the irradiated spot. Crystalline surroundings provide higher thermal conductivity and lead to easier crystallization, whereas amorphous surroundings were the reverse. All in all, Cr-doped Sb2Te3 films with suitable composition have advantages for storage with high density, better thermal stability, and lower power consumption; and the suitable initial states could ensure better reversible phase transition performances.

Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

Optimization of liquid jet system for laser-induced breakdown spectroscopy analysis

A complex optimization of geometrical and temporal parameters of a jet system (developed in Laser-induced breakdown spectroscopy (LIBS) laboratory of Brno University of Technology) for direct elemental analysis of samples in a liquid state of matter using LIBS was carried out. First, the peristaltic pump was synchronized with the flashlamp of the ablation laser, which reduced variation of the ablated sample amount. Also, the fluctuation of the laser ray angle incident on the jet surface was diminished. Such synchronization reduced signal standard deviations and thus increased repeatability of the measurements. Then, laser energy and distance of the focusing lens from the sample were optimized. The gate delay time and the gate width were optimized for single pulse (SP) experiments; the gate delay time and the inter-pulse delay were optimized for the use of double pulse (DP) variant. Results were assessed according to the highest signal to noise ratios and the lowest relative standard deviations of the signal. The sensitivity of the single pulse and the double pulse LIBS for the detection of heavy metals traces, copper (Cu i at 324.754 nm) and lead (Pb i at 405.781 nm), in aqueous solution of copper (ii) sulfate and lead (ii) acetate, was estimated in terms of limits of detection (LODs). As a result, sensitivity improvement of DP LIBS system was observed, the LOD of Cu obtained with DP was calculated 40% lower than LOD gained from SP technique.

Reaction Pathways Involved in CH4 Conversion on Pd/Al2O3 Catalysts: TAP as a Powerful Tool for the Elucidation of the Effective Role of the Metal/Support Interface.

Temporal Analysis of Products (TAP) investigation on Natural Gas-fueled Vehicle (NGV) catalysts provides information related to the nature of reaction steps involved over noble metals and at the metal-support interface. The determination of accurate kinetic parameters for methane adsorption from single pulse experiments and subsequent investigation of sequential surface reactions from alternative CH4/O2 pulse experiments is the first step toward the establishment of relevant structure/activity relationships which can highlight the importance of the metal/support interface on freshly-prepared and aged single palladium based catalysts.

Core@shell Poly(n-butylacrylate)@polystyrene Nanoparticles: Baroplastic Force-Responsiveness in Presence of Strong Phase Separation.

Poly(n-butylacrylate)@polystyrene nanoparticles behaving as a capsule-based sealing nanoadditive are synthesized through an optimized semicontinuous emulsion polymerization protocol. Solid state time-domain (1)H-NMR and (13)C magic angle spinning (MAS) NMR analysis suggest strong phase separation. Line width of (13)C resonances in cross polarization and single pulse experiment MAS-NMR spectra indicates that the peculiar mobility of each phase is preserved at the nanoscale. Atomic force spectroscopy (AFM) shows the permanence of spherical shape in absence of solvent (i.e., subsequent to strong capillary and surface forces) up to moderate external load, as well as the possibility of plastically deforming the polystyrene shell and ultimately triggering the nanoparticle flow at higher force loads. The breakdown characteristic of the nanoparticle shows for the first time baroplastic behavior on a single particle with precise biphasic core@shell morphology.

Characterization of pseudosingle bunch kick-and-cancel operational mode

Author(s): Sun, C; Robin, DS; Steier, C; Portmann, G | Abstract: Pseudosingle-bunch kick-and-cancel (PSB-KAC) is a new operational mode at the Advanced Light Source of Lawrence Berkeley National Laboratory that provides full timing and repetition rate control for single x-ray pulse users while being fully transparent to other users of synchrotron radiation light. In this operational mode, a single electron bunch is periodically displaced from a main bunch train by a fast kicker magnet with a user-on-demand repetition rate, creating a single x-ray pulse to be matched to a typical laser excitation pulse rate. This operational mode can significantly improve the signal to noise ratio of single x-ray pulse experiments and drastically reduce dose-induced sample damage rate. It greatly expands the capabilities of synchrotron light sources to carry out dynamics and time-of-flight experiments. In this paper, we carry out extensive characterizations of this PSB-KAC mode both numerically and experimentally. This includes the working principle of this mode, resonance conditions and beam stability, experimental setups, and diagnostic tools and measurements.

Interelectrode discharge mechanism in high-speed wire electrical discharge machining

Different from conventional electrical discharge machining (EDM), given that the dielectric fluid utilized in high-speed wire EDM (HSWEDM) has a certain conductivity, a passive film can form on the workpiece surface because of the electrochemical reaction during processing. Such formation affects the interelectrode discharge characteristics. The formation mechanism of the passive film was analyzed in this study. The effect of the passive film on the discharge gap was evaluated through single-pulse discharge experiments. Results show that the density and thickness of the passive film increase with the increase in dielectric fluid conductivity or the accumulation of leakage energy; the discharge gap is thus reduced. However, in actual processing, the existence probability of open-circuit voltages is very small, and the high temperature produced by spark discharge has an erosion effect on the passive film. Consequently, forming a dense passive film on a workpiece surface is difficult, and spark discharge still occurs in an interelectrode gap in HSWEDM. A multi-cutting experiment was conducted to study the effect of the passive film on dimensional accuracy. Results indicate that the passive film affects the discharge gap because of the difference in dielectric fluid conductivity. A size error of approximately 2 μm was generated when the initial conductivity difference was roughly 2000 μS/cm.

Relation between magnetization and Faraday angles produced by ultrafast spin-flip processes within the three-level Λ-type system

Ultrafast magneto-optical (MO) experiments constitute a powerful tool to explore the magnetization dynamics of diverse materials. Over the last decade, there have been many theoretical and experimental developments on this subject. However, the relation between the magnetization dynamics and the transient MO response still remains unclear. In this work, we calculate the magnetization of a material, as well as the magneto-optical rotation and ellipticity angles measured in a single-beam experiment. Then, we compare the magnetization to the MO response. The magnetic material is modeled by a three-level Λ-type system, which represents a simple model to describe MO effects induced by an ultrafast laser pulse. Our calculations use the density matrix formalism, while the dynamics of the system is obtained by solving the Lindblad equation taking into account population relaxation and dephasing processes. Furthermore, we consider the Faraday rotation of the optical waves that simultaneously causes spin-flip. We show that the Faraday angles remain proportional to the magnetization only if the system has reached the equilibrium-state, and that this proportionality is directly related to the population and coherence decay rates. For the non-equilibrium situation, the previous proportionality relation is no longer valid. We show that our model is able to interpret some recent experimental results obtained in a single-pulse experiment. We further show that, after a critical pulse duration, the decrease of the ellipticity as a function of the absorbed energy is a characteristic of the system.

Microcosmic mechanism of electrical discharge machining ablation on titanium alloy

Single-pulse experiment was conducted to study the mechanism of electrical discharge machining (EDM) ablation on titanium alloy. The discharge equivalent model of EDM ablation was established, and changes in the oxide layers between electrodes of EDM ablation was analyzed in this paper. Thermodynamic and kinetic analysis of titanium alloy EDM ablation showed that sufficient discharge energy was available to ignite titanium alloy and that titanium alloy possessed the conditions necessary for sustained combustion. The discharge gap of EDM ablation, the polarity effect, the erosion pit, and the morphology of the surface oxide layer were also studied. Results show that the ablation efficiency of titanium alloy was better than that of conventional EDM and that the morphology of the surface oxide layer was consistent with the interpretation of its ablation mechanism.

Influence of discharge energy on EDM ablation

In the process of electrical discharge machining (EDM) ablation, discharge energy can heat the materials, activate the surface, and eliminate metal corrosion. We study the discharge energy by building an ablation machining energy model. We show that in theory, the magnitude of the discharge energy directly determines the processing speed of ablation milling. Based on single-pulse discharge experiments, we observe an exponential increase in the EDM ablation pit diameter with increasing discharge energy. The ablation pit model is built to study the effect of the discharge energy on the ablation pit depth. The effect of discharge energy on the material removing rate (MRR), electrode wear rate (EWR), and surface roughness rate (Ra) of the EDM ablation was studied in this paper. The results show that, on one hand, the material removing rate (MRR) and surface roughness (Ra) have a direct relationship with the discharge energy. On the other hand, the electrode wear rate (EWR) has an inverse relationship with the discharge energy.

Measuring spin relaxation with standard pulse sequences in the singlet–triplet basis

Pulsed electrically and optically-detected magnetic resonance are extremely sensitive to changes in the permutation symmetry of weakly-coupled spin pairs, and are well-suited for investigating devices with a small number of spins. However, the change in observable from conventional electron spin resonance modifies the results of standard inductively-detected pulse sequences which are routinely used to obtain phase coherence and lifetimes. Whilst these effects have been discussed for single-pulse experiments, their role in multi-pulse sequences is less clear. Here, we investigate this effect in Hahn echo and inversion-recovery sequences, and show a second set of narrower echoes are produced that distort measurement outcomes. We demonstrate that phase cycling is able to deconvolve the additional echo signals, allowing spin relaxation times to be reliably extracted.