Breakdown Power Research Articles

Microbial degradation of cellulose extracted from wheat bran for bioelectricity production using microbial fuel cell

A successful agro-waste management system may recover energy and stabilize waste, among other benefits. The purpose of this research was to analyze the microbiological decomposition of cellulose that has been alkaline extracted and bleached from wheat bran byproducts. The waste lignin stream was used to synthesize biochar for anode modification. Fourier transform infrared spectroscopy showed that O-H and C-H functional groups predominated in extracted cellulose, whereas scanning electron microscopy, X-ray diffraction, and Raman microscopy characterized lignin-derived biochar and cellulose. Pantoea dispersa, isolated from cow dung, was identified as a cellulose-degrading bacteria using 16 S rRNA sequencing. Cellulose-degrading efficiency was measured by hydrolysis zone size around bacterial colonies. To facilitate cellulose breakdown and sustained power production in a microbial fuel cell, the cellulose-degrading bacteria were co-cultured with the Pseudomonas aeruginosa strain at a 1:1 ratio. Cyclic voltammetry, electrochemical impedance spectroscopy, power density, and current density have been investigated under ideal conditions. At a substrate concentration of 2.5 gm/L and internal resistance of 69.5Ω, a modified anode achieved the maximum power density of 9.1 W/m3. Using agro-waste for waste-to-energy is a step toward a circular bioeconomy.

Improved β-Ga2O3 Schottky Barrier Diodes via thermal oxidation of titanium insertion layer

In realm of β-Ga2O3 Schottky Barrier Diodes (SBDs), insertion layer appeared as an effective strategy for enhancing breakdown voltage. Presently, insertion layer techniques typically employed atomic layer deposition (ALD) to grow insulators with low electron affinity (e.g., Al2O3, HfO2). Although these insertion layers enhanced the reverse break-down characteristics, substantially degraded forward con-duction was also induced. In this study, a TiO2 thin layer by thermally oxidized Titanium metal was inserted to elevate the breakdown voltage and power figure of merit (PFOM) of β-Ga2O3 SBDs, while maintaining the on-resistance nearly unchanged. In comparison with the conventional met-al/semiconductor-SBD (MS-SBD), the thermally oxidized metal/insulator/semiconductor-SBD (MIS-SBD) exhibited 2.75 times elevation of breakdown voltage with only 11.6% reduction of forward current at +5V. The PFOM of the thermally oxidized MIS-SBD was enhanced by 7.6-fold compared to conventional MS-SBD, and by 15.7-fold com-pared to the counterpart ALD MIS-SBD. Analysis of the TiO2/β-Ga2O3 interface characteristics through X-ray photo-electron spectroscopy (XPS) and capacitance-voltage (C–V) measurements revealed that the thermally oxidized TiO2-SBD possesses smaller band offset and larger interface trap density (Dit) compared to the ALD counterpart, which contribute to the higher PFOM of the thermally oxidized TiO2-SBD. This novel TiO2/β-Ga2O3 structure exhibited superior electrical properties, providing potential solution for high performed SBD.

Electrical Activity and Extremes of Individual Suspended ZnO Nanowires for 3D Nanoelectronic Applications.

We explored the electrical activity and extremes inside individual suspended zinc oxide (ZnO) nanowires (NWs) (diameter: 50-550 nm, length: 5-50 μm) subjected to high forward bias-induced Joule heating using two-terminal current-voltage measurements. NWs were isolated using a reproducible nanometrology technique, employing a nanomanipulator inside a scanning electron microscope. Schottky behavior is observed between installed tips and ZnO NW. The suspended ZnO NWs exhibited an average electrical resistivity ρ (approximately 2.3 × 10-2 Ω cm) and a high electron density n (exceeding 1.89 × 1018 cm-3), comparable to that of InP NWs, GaN NWs, and InAs NWs (1018∼1019 cm-3), suggesting the potential to drive advancements in high-performance NW devices. A maximum breakdown current density (JBD) of ∼0.14 MA/cm2 and a maximum breakdown power density (PBD) of 6.93 mW/μm3 were obtained, both of which are higher than substrate-bound ZnO NWs and consistent with previously reported results obtained from probed ZnO NWs grown vertically on the substrate. Moreover, we discovered that NWs experienced thermal breakdown due to Joule heating and exploited this breakdown mechanism to further investigate the temperature distribution along the ZnO NWs, as well as its dependence on the electrical properties and thermal conductance of contact electrodes. Thermal conductance was determined to be ∼0.4 nW K-1 and ∼1.66 pW K-1 at the tungsten(W)-ZnO NW and platinum(Pt)-ZnO NW contacts, respectively. In addition, we measured the elastic modulus (130-171 GPa), which closely approximated bulk values. We also estimated the nanoindentation hardness to be between 5 and 10 GPa. This work provides valuable insights into the electrical activity and extreme mechanisms, thus providing a better understanding of the potentials and limitations associated with utilizing suspended NWs in 3D nanodevices.

Gate-mesa trench enables enhanced β-Ga2O3 MOSFET with higher power figure of merit

In this article, a gate-mesa trench (GMT) β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET) device with enhanced performance and breakdown voltage improvement is proposed. Compared with the gate-field plate trench (GFPT), the breakdown voltage and power figure of merit (PFOM) of the GMT device are 2566 V and 680.53 MW cm−2 respectively, which are 1.56 times and 2.25 times higher than those of the GFPT, demonstrating excellent device performance. When the etch depth is 200 nm, the specific on-resistance of the GFPT and the GMT is 8.84 mΩ cm−2 and 9.76 mΩ cm−2, respectively, with the peak transconductance of the GFPT being 61.56 mS mm−1 when the epitaxial layer doping concentration is 3 × 1017 cm-3, which is 1.22 times that of the GMT. The high dielectric constant HfO2 dielectric can significantly improve the PFOM of the device, while the gate oxide Al2O3 drifts the threshold voltage to the right. This article presents a novel approach for designing high-performance enhanced β-Ga2O3 MOSFETs.

500 V breakdown voltage in β‐Ga2O3 laterally diffused metal‐oxide‐semiconductor field‐effect transistor with 108 MW/cm2 power figure of merit

AbstractThe authors’ present a silicon‐on‐insulator (SOI) laterally diffused metal‐oxide‐semiconductor field‐effect transistor (LDMOSFET) with β‐Ga2O3 , which is a large bandgap semiconductor (β‐LDMOSFET), for increasing breakdown voltage (VBR) and power figure of merit. The fundamental purpose is to use a β‐Ga2O3 semiconductor instead of silicon material due to its large breakdown field. The characteristics of β‐LDMOSFET are analysed to those of standard LDMOSFET, such as VBR, ON‐resistance (RON), power figure of merit (PFOM), and radio frequency (RF) performances. The effects of RF, such as gate‐drain capacitance (CGD), gate‐source capacitance (CGS), transit frequency (fT), and maximum frequency of oscillation (fMAX) have been investigated. The β‐LDMOSFET structure outperforms performance in the VBR by increasing it to 500 versus 84.4 V in standard LDMOSFET design. The suggested β‐LDMOSFET has RON ~ 2.3 mΩ.cm−2 and increased the PFOM (VBR2/RON) to 108.6 MW/cm2. All the simulations are done with TCAD and simulation models are calibrated with the experimental data.

Simulation Study to Enhance the Efficiency of Switching Devices using the Combinations of Diodes in Various Networks

AbstractIn this communication, PSpice simulation software is used to design and characterize reverse biasing modes in series and parallel combinations. Using multiple diodes of similar types, how the breakdown voltage and power dissipation vary in parallel and series modes in reverse bias is investigated. In this paper, correlation equations and correlation factors between voltage and current in both series and parallel combinations using n = 1‐5 diodes in reverse bias are also found. The second‐order correlation equation between voltage and current provides a new way for designing new networks of PN junction diodes for better power gain. The mathematical formulation for applied voltage and average current of n = 1‐10 diodes in parallel and series combinations is also calculated, which can help researchers to design new network circuits for switching devices in the electronics industry.

Exploring the efficacy of implementing field plate design with air gap on β-Ga2O3 MOSFET for high power & RF applications

In the present work, source field plate design with an air gap has been studied on lateral β – Ga2O3 MOSFET with the objective of achieving improvement in high power as well as RF performance by employing exhaustive TCAD simulations. A comprehensive investigation of various analog Figure of Merits (FoMs) and RF Figure of merits (FoMs) have been carried out and a thorough comparison has been drawn between the proposed device β-Ga2O3 MOSFET with source field plate and air gap, the β-Ga2O3 MOSFET with gate field plate and the conventional β-Ga2O3 MOSFET. It can be noted that the proposed design yields significantly higher breakdown voltage and Power Figure of Merit (PFoM) as compared to gate field plate design and conventional device without any of these designs and also, the proposed design demonstrates improvement in RF performance as compared to gate field plate design.

Design and development of broadband gap waveguide‐based 0‐dB couplers for Ka‐band applications

The design and fabrication of a wideband millimetre-wave 0-dB coupler is proposed in this paper using gap waveguide technology for low-loss and high-power applications in 30-GHz frequency band. To overcome the fabrication challenges in millimetre-wave frequencies, the gap waveguide technique is utilised. Two gap waveguide-based coaxial- and waveguide-fed 0-dB couplers are designed with broadband performance, high return loss, acceptable coupling flatness and high isolation. For verifying the performance of the proposed structures, a prototype of the waveguide-fed 0-dB coupler is manufactured and measured. The measurement results show that the return and insertion losses and the isolation of the fabricated 0-dB coupler is better than 18 dB, 0.5 and 18 dB, respectively, in the specified frequency range from 26.2 to 34 GHz. Moreover, the breakdown power level of the proposed millimetre-wave structures is in kW orders to satisfy the high-power requirements.

A Cavity Balun for High-Power Shortwave Transmission

Compared with conventional systems, high power puts forward more requirements on the balun: the materials and structures should be more reliable, able to withstand high power, and have extremely high transmission efficiency. Based on the electromagnetic field theory and the visual optimization method by CST MW Studio, a parallel-connected coaxial cavity balun is proposed in this article that can realize the balance–unbalance conversion in almost the entire shortwave frequency band (4.4–27 MHz). For further improvement of the transmission efficiency and the reduction of voltage standing wave ratio (VSWR), an antenna tuning unit (ATU) was added to the unbalanced port of the cavity, which lowered the VSWR from 1.5 to 1.1. The theoretical value of the breakdown power of the balun is also calculated, and it is much larger than the transmit power. The results of the scaled mode measurement are consistent with the simulation results: the amplitude imbalance of the balanced port is within ±0.5 dB, the phase difference is 180° ± 5°, and the withstand power is at least three times the transmit power, which fully demonstrates that the proposed balun is suitable for high-power shortwave transmitting systems.

Study of the Multipactor Effect in Groove Gap Waveguide Technology

This article presents a theoretical and experimental comparative study of the different multipactor threshold values obtained in the rectangular waveguide (RW) and the groove gap waveguide (GGW). To this end, the multipactor effect has been first analyzed in an RW with a recently developed theoretical model. Then, the multipactor breakdown power levels in the equivalent GGW have been predicted with an accurate electron tracking code, showing a significant increment compared with the RW case. In order to validate these results, two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -plane WR-90 RW transformers have been designed with a full-wave electromagnetic simulation tool. The central sections of these transformers have been implemented in RW and GGW, respectively, and their multipactor breakdown power levels have also been predicted. The two designed transformers have been fabricated in aluminum and then measured in terms of electrical response (scattering parameters) and RF multipactor effect (power threshold values). All the experimental results agree well with the set of simulated data, thus fully validating the performed study.

Implementing variable doping and work function engineering in β-Ga2O3 MOSFET to realize high breakdown voltage and PfoM

In this paper, the impact of workfunction engineering and lightly doped region near drain has been studied on lateral β-Ga2O3 metal oxide semiconductor field effect transistor (MOSFET) by employing exhaustive technology computer aided design simulations. The theoretically predicted value of breakdown voltage and power figure of merit (PFoM) for Ga2O3 based devices has not been achieved yet, and hence in order to improve these parameters, variable channel doping and work function engineering have been implemented on lateral β-Ga2O3 MOSFET for the first time in the present work. A thorough comparative assessment has been drawn by comparing the characteristics of the proposed device which incorporates work function engineering along with a variable doping in channel such that higher doping is near the source side and a lower doping region is near the drain end with conventional, doping engineered and work function engineered β-Ga2O3 devices and it is demonstrated that the proposed device offers significant improvement in breakdown voltage and PFoM. Furthermore, the performance of all devices under consideration has been evaluated at high temperatures as well and it is demonstrated that the proposed device offers superior performance in comparison to other devices, and hence is a suitable contender for high voltage and high temperature applications.

Performance and reliability improvement in intercalated MLGNR interconnects using optimized aspect ratio

In this work, aspect ratio of various intercalation doped MLGNR interconnects are optimized using a numerical approach to achieve improved performance and reliability. A numerical optimization method is presented to estimate optimized aspect ratio considering combined effects of performance, noise and reliability metrics for any arbitrary nano interconnect system. This approach is cost effective and will be extremely useful to industry for selection of aspect ratio of interconnects as it is a non-SPICE method and reduces fabrication iterations for achieving desired performance and reliability. Our numerical method suggests that by minimizing the figure of merit (i.e. Noise Delay Power Product / Breakdown Power P_{BD} ratio), aspect ratio of FeCl3 doped MLGNR interconnect is optimized at 0.987, 0.61 and 0.579 for local, intermediate and global level, respectively at 7 nm node. Comparing the optimized performance metrics in this work with the estimated metrics at prescribed aspect ratio by IRDS roadmap, delay, noise delay product (NDP), power delay product (PDP), PDP/ P_{BD} ratio and figure of merit are improved by (sim2% and sim25%), (sim44% and sim50%), (sim9% and sim48%), (sim6% and sim48%) and (sim49% and sim68%) for 10 mu m and 1 mm long Fecl3 doped MLGNR interconnect, respectively at 7 nm node. Increase in contact resistance leads to significant decrease in performance and increase in optimized aspect ratio of local Fecl3 doped MLGNR interconnect. Scaling down from 10 to 7 nm node results in increase of optimized aspect ratio in all levels of interconnects. Even though the performance of MLGNR degrades with scaling down but when compared to copper, the performance improves with technology scaling. Finally, this study provides circuit designers a detailed guideline for selecting an optimized aspect ratio for achieving better performance, power efficiency and reliability in doped MLGNR interconnects.

Strontium-deficient SrxCoO2-CoO2 nanotubes as a high ampacity and high conductivity material.

Continuous miniaturization of electronics demands the development of interconnectors with high ampacity and high conductivity, which conventional conductors such as copper and gold cannot offer. Here we report the synthesis of Sr-deficient misfit SrxCoO2-CoO2 nanotubes by a novel crystal conversion method and investigate their electrical properties. Bulk Sr6Co5O15 having a quasi-one-dimensional CoO6 polyhedral structure (face-sharing octahedron and trigonal prismatic CoO6 arranged in one-dimension) is converted to SrxCoO2-CoO2 nanotubes where CoO2 adopts a two-dimensional edge-sharing CoO2 layered structure in a basic hydrothermal process. Electrical properties measured on individual nanotubes demonstrate that these nanotubes are semiconducting with a conductivity of 1.28 × 104 S cm-1 and an ampacity of 109 A cm-2, which is the highest reported ampacity value to date of any inorganic oxide-based material. The nanotubes also show a breakdown power per unit channel length (P/L) of ∼38.3 W cm-1, the highest among the regularly used interconnect materials. The above results demonstrate that SrxCoO2-CoO2 nanotubes are potential building blocks for high-power electronic applications.

Thermal-Aware Modeling and Analysis of Cu-Mixed CNT Nanocomposite Interconnects

Growing only single-walled carbon nanotube (SWCNT) or only multi-walled carbon nanotube (MWCNT) in a bundle is not feasible practically. Thus, a random number of SWCNTs and MWCNTs whose diameters are also varied randomly (following a Gaussian distribution) should be considered in a bundle of mixed carbon nanotubes. A thermal aware electrical modeling of copper-mixed carbon nanotube (Cu-MCNT) composite interconnect is proposed here and its performance and reliability has been studied and compared with copper interconnect at 7 nm and 11 nm technology nodes. An increase in filling fraction (F_MCNT) of mixed carbon nanotubes in Cu-MCNT composites leads to a decrease in delay. But in some cases, if the fraction of SWCNTs is greater than that of MWCNTs in a bundle, then it leads to a higher delay. Variation in delay with respect to F_MCNT is more at higher temperature by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 10%. Cu-MCNT composite interconnects with F_MCNT = 0.5 have <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 52% higher breakdown power than copper interconnects and are thermally more efficient. Scaling down the dimensions leads to degradation in performance and reliability combined but this degradation is more in copper interconnect when compared to Cu-MCNT composite interconnect by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 14% Cu-MCNT composite interconnects attain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 39% less temperature rise at steady state when compared to copper interconnects. The performance of Cu-MCNT composite interconnects in terms of meantime to failure at higher current densities is phenomenal as compared to copper interconnects. Our study promotes Cu-MCNT composite interconnects as an alternate candidate to copper interconnects considering their superior electro-thermal performance.

Self-Heating and Reliability-Aware “Intrinsic” Safe Operating Area of Wide Bandgap Semiconductors—An Analytical Approach

The emergence of several technology options and the ever-broadening range of applications (e.g., automotive, smart grids, solar/wind farms) for power electronic devices suggest both a need and an opportunity to develop unifying principles to guide the development of wide bandgap (WBG) semiconductors. Unfortunately, power electronic devices are typically evaluated with a variety of elementary figure of merits (FOMs), which offer inconsistent/contradictory projections regarding the relative merits of emerging technologies. Indeed, one relies on the empirical (extrinsic) safe-operating area (SOA) of a packaged device to ultimately assess the performance potential of a technology option. Unfortunately, extrinsic SOA can only be calculated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a posteriori, i.e.,</i> after precise measurement of the fabricated device parameters, making it suitable only for relatively mature technologies. Based on the insights of material-device-circuit-system performance analysis of a variety of idealized WBG power electronic devices (e.g., GaN HEMT, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\beta }$ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MOSFET), in this paper, we analytically derive a comprehensive, substrate-, self-heating-, and reliability-aware “intrinsic/limiting” safe operating area (SOA) that establishes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> , i.e., before device fabrication, the optimum and self-consistent trade-off among breakdown voltage, power consumption, operating frequency, heat dissipation, and reliability. We establish the relevance of the intrinsic-SOA by comparing its prediction with a broad range of experimental data available in the literature. In between the traditional FOMs and extrinsic SOA, the intrinsic SOA allows fundamental/intuitive re-evaluation of intrinsic technology potential for power electronic devices and identifies specific performance bottlenecks and suggests strategies to circumvent them.

Effects of gas adsorbed on solid surface during gas breakdown in electron cyclotron resonance discharges

The microwave breakdown power (P wb) in an ECR plasma source was not merely determined by pressure (gas flow rate), but found to vary with the time interval between two successive breakdowns. The measured P wb dropped rapidly from a high value at a short time interval to a low level at a long time interval. The obtained dependence of P wb on pressure (gas flow rate) exhibited distinct features: the normal monotonicity and abnormal non-monotonicity at the short and long time intervals, respectively. The effective zone in the antenna’s surface, bombarded by hot electrons heated in the ECR layer, was validated by (1) masking the antenna with a film having a variable radius; (2) calculating the distribution of the vertical component of the microwave electric field with respect to the static magnetic field; and (3) imaging glows of transient breakdown discharges with a fast camera. The reduction in P wb was mainly attributed to the enhanced emission of δ-electrons from the gas-adsorbed antenna under the bombardment of energetic electrons coming from the ECR layer. The correlation between the dynamic gas coverage and the emission coefficient of δ-electrons was established to understand the abnormal ECR breakdown features.

Regulation of electron depletion layer in polymer-based nanocomposites for superior energy storage capability

Polymer-based dielectrics trigger great interests in advanced electric systems due to their high breakdown strength and power density. However, a major drawback is that excessive addition of high-εr ceramic nanofillers may deteriorate their breakdown strength and further reduce energy density. Herein, a general strategy is provided to dramatically enhance the breakdown strength by introducing a small amount of core–shell structured Al2O3@BiFeO3 nanofibers into PVDF/PMMA polymer matrix. The thickness of BiFeO3 shell is regulated by controlling its molar concentration. A significantly enhanced breakdown strength (759 kV mm−1) and an ultrahigh energy density (22.7 J cm−3) with an energy efficiency of 72% are observed. The greatly improved breakdown strength is ascribed to the regulation of electron depletion layer. When the width of heterojunction region gradually approaches to the scale of electron depletion layer, more annihilation of electrons happens and thus contributes to the enhancement of the breakdown strength. The results suggest that our designed structure can help to address the issue of both enhancing the breakdown strength and energy density for diverse nanocomposites over a broad application.

Experimental Investigation of Material and Geometry Effects on Microwave Breakdown of Evanescent-Mode Cavity Resonators

This article presents an experimental investigation of microwave breakdown in evanescent-mode cavity resonators with different surface materials and post geometries, aiming at unveiling the role of secondary electron emission (SEE), attachment, and diffusion on microwave breakdown in inhomogeneous electric fields. The breakdown power of six cavities resonating at 2.6 GHz was measured at pressures ranging from 1 to 100 mbar in ambient air. The cavity with lower secondary emission yield surface material has a higher breakdown power on the left side of the breakdown curves, indicating the importance of SEE in microwave breakdown, especially at low pressures. Meanwhile, except for the cavity with hemisphere post, it was found that the quality factor has little effect on the breakdown power since electric field distributions inside these cavities are not significantly linked to post geometry. Two distinct regimes are observed in the breakdown curves with a transition pressure of 10 mbar. Namely, the breakdown curves present an emission-free branch above the transition, where microwave breakdown occurs in the gap, and a diffusion branch below the transition, where the microwave plasma expands out of the gap. We performed a theoretical calculation and found that the transition occurs when the attachment length equals the post radius.

Possibilities of phase-structural engineering and properties of microarc oxide coatings on the AMг3 alloy

Purposeof the work: to establish the regularities of the alkali-silicate electrolyte composition influence and the conditions of electrolysis during microarc oxidation of the AMг3 aluminum alloy on the kinetics of the oxide coating formation, its structure and the conditions for the formation of the α-Al2O3 phase. Results. The possibility of forming high-density MAO coatings on the AMг3 aluminium alloy during electrolysis in alkali-silicate electrolytes has been determined. The regularities of the kinetics of MAO coatings growth at different electrolyte composition and oxidation time were revealed. It was found that the phase composition of MAO coatings consists of the following phases − α-Al2O3, γ-Al2O3, and mullite (3Al2O3•2SiO2), the ratio of which changes with a change in the amount of sodium silicate (Na2SiO3). It was found that addition of an inorganic soluble salt dopant to the electrolyte, which contains oxygen (K2Cr2O7), leads to a qualitative change in the phase composition − an increase in the amount of α-Al2O3 phase in the coating composition and an increase in hardness. In this case, it becomes possible to obtain MAO coatings of small thickness (up to 90 μm) with a high content of the α-Al2O3 phase (up to 40 %), which cannot be carried out in an alkali-silicate electrolyte. Analysis of the effect of high-temperature annealing of MAO coatings on the shape of the diffraction spectrum made it possible to revealthe appearance of tetragonality in the crystal lattice of the γ-А12О3 phase. The structural state with a tetragonally distorted lattice is a stage of γ-А12О3 → α-А12О3 transformation. Scientific novelty. It was found that when using an alkaline-silicate electrolyte for electrolysis, the addition of liquid glass (Na2SiO3) leads to an increase in the growth rate of the coating, but at the same time it stimulates the formation of mullite (3Al2O3 × 2SiO2) as a phase component. An increase in the alkaline (KOH) component leads to a decrease in the growth rate (to 0,6…0,7 μm/min) and stimulates the formation of the γ-Al2O3 phase. The formation of the α-Al2O3 (corundum) phase is stimulated with a long process duration, when the thickness of the dielectric layer and the breakdown power increase. An increase in the amount of α-Al2O3 leads to an increase in the hardness of the coatings. Isothermal annealing at temperatures exceeding 1 000 °C stimulates the γ-Al2O3 → α-Al2O3 polymorphic transformation. The initial stage of such a transformation is the appearance of tetragonality in the crystal lattice of the γ-Al2O3 phase. Practical value. This study allows us to propose an additive to the alkali-silicate electrolyte in the form of a K2Cr2O7 salt, which increases the rate of formation of MAO coatings to 1,4 μm/min and, at the same time, qualitatively and quantitatively changes the phase composition of the coatings, increasing its hardness.

A MATHEMATICAL MODEL FOR DYNAMIC PROJECT SCHEDULING PROBLEM AND REACTIVE SCHEDULING IMPLEMENTATION

In today's real-life implementations, projects are executed under uncertainty in a dynamic environment. In addition to resource constraints, the baseline schedule is affected due to the unpredictability of the dynamic environment. Uncertainty-based dynamic events experienced during project execution may change the baseline schedule partially or substantially and require projects' rescheduling. In this study, a mixed-integer linear programming model is proposed for the dynamic resource-constrained project scheduling problem. Three dynamic situation scenarios are solved with the proposed model, including machine breakdown, worker sickness, and electricity power cut. Finally, generated reactive schedules are completed later than the baseline schedule.