Microwave-induced Plasma Research Articles

Evaluation of the Use of Diluted Formic Acid in Sample Preparation for Elemental Determination in Crustacean Samples by MIP OES.

A simple procedure for determination of Al, Cr, K, Mg, Mn, and Zn using diluted organic acid in the preparation of shrimp (Macrobrachium amazonicum) and crab samples (Ucides cordatus) was proposed in this study. Determinations were performed using microwave-induced plasma optical emission spectrometer (MIP OES). The contents of elements were evaluated after solubilization of samples in 50% formic acid (v v-1) and subsequent heating in bath with stirring and heating at 90°C. The accuracy of the proposed procedure was assessed using certified fish protein reference material (DORM-4) and the recovery percentages ranged from 91 to 117%. Microwave-assisted acid decomposition was used for a comparison of results with the procedure proposed using diluted formic acid, and the values obtained for all analytes were statistically equal at 95% confidence level. Cr levels were below the limit of detection. Potassium (7917-19,644mgkg-1), Mg (1319-5376mgkg-1), and Zn (43-307mgkg-1) were the most abundant elements in the crustacean species studied can be considered good sources of these constituents for human diet. The proposed procedure using diluted formic acid was considered simple and suitable to determine Al, Cr, K, Mg, Mn, and Zn concentrations in crustaceans using MIP OES.

Aluminium corrosion in power semiconductor devices

In this study, insulated gate bipolar transistor (IGBT) power modules were exposed to high voltage, high humidity, high temperature and reverse bias (HV-H3TRB) conditions until end-of-life (EoL). The limited lifetime of power semiconductor devices when used in demanding applications involving high relative humidity during operation is commonly reported to be associated with the design of the edge termination in power transistor or diode chips. A physics-of-failure (PoF) oriented methodology was adopted in failure analysis, including using lock-in thermography (LiT) for failure localisation and using an advanced microwave-induced plasma (MIP) decapsulation technique for the selective etching of the edge termination polyimide passivation film. A focused ion beam (FIB) was utilised to create a cross-section of the samples for both scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis. The evidence gathered using the physics-of-failure methodology were compared with the results from advanced statistical analysis of the failure distributions in Weibull plots, including comparison of α and β parameters. This analysis revealed correlation with the Weibull distributions and the results from the physics-of-failure. Aluminium corrosion products were systematically observed on guard rings (GR) and field plates (FP) showing that the migration of these corrosion products forming an electrical path between the guard rings that seems to be a major failure mechanism in high humidity environments when reverse bias voltage is applied.

Effect of argon flow rate and direct current bias on the growth of boron nitride coating in low-temperature plasma

A microwave plasma chemical vapor deposition system was used to synthesize cubic boron nitride (cBN) coatings on diamond seeded silicon substrates using direct current (DC) bias. Effects of the argon (Ar) flow rate and bias voltage on the growth of the cBN coatings were investigated. Hydrogen (H2), argon (Ar), a mixture of diborane in H2 (95% H2, 5% B2H6), and N2 were used in the feed gas. A DC bias system was used for external biasing of the sample, which facilitates the goal of achieving sp3 bonded cBN. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) revealed the existence of sp3-bonded BN in the produced samples. With increasing Ar flow, the cBN content in the coating increases and reaches a maximum at the maximum Ar flow of 400 SCCM used in this study. High-resolution XPS scans for B1s and N1s indicate that the deposited coating contains more than 70% cBN. This study demonstrates that energetic argon ions generated in a microwave-induced plasma significantly increase cBN content in the coating.

Elucidation of formation mechanism responsible for charge-transfer reagent ions in microwave induced plasma desorption ionization (MIPDI) source

Charge transfer reagent ions NO+ and O2+ were major observed in microwave-induced plasma desorption ionization (MIPDI) source. Ions NO+ was prosperous in the discharge region while ions O2+ generated in the afterglow region. Fundamental aspects of conditions that controlled MIPDI were addressed here to help understand the specific role of atmospheric components for charge transfer reagent ions formation. In the presence of trace nitrogen in Ar-MIPDI plasma, the production of NO+ ions increased significantly, while ions N2+ were not observed. The controlled afterglow environment obtained by connecting the plasma source to the mass spectrometer using a quartz reaction chamber found that ions O2+ produced from the interaction between plasma-generated energy particles and oxygen molecules. With the aid of mass spectra and optical emissions spectra, the ionization capacity of Ar-MIPDI plasma was revealed. Both the discharge region and afterglow region are not energetic enough to ionize N2 molecules. Charge transfer reagent ions in the MIPDI source have vital ionization ability for aromatic compounds. A deeper understanding of fundamental aspects, especially of condition-controlled ionization in a MIPDI source, will be vital for future practical applications, particularly with regard to difficult to ionize (e.g., nonpolar) species.

Properties of high entropy borides synthesized via microwave-induced plasma

Microwave-induced plasma was used to anneal precursor powders containing five metal oxides with carbon and boron carbide as reducing agents, resulting in high entropy boride ceramics. Measurements of hardness, phase structure, and oxidation resistance were investigated. Plasma annealing for 45 min in the range of 1500–2000 °C led to the formation of predominantly single-phase (Hf, Zr, Ti, Ta, Mo)B2 or (Hf, Zr, Nb, Ta, Mo)B2 hexagonal structures characteristic of high entropy borides. Oxidation resistance for these borides was improved by as much as a factor of ten when compared to conventional commercial diborides. Vickers and nanoindentation hardness measurements show the indentation size effect and were found to be as much as 50% higher than that reported for the same high entropy boride configuration made by other methods, with average values reaching up to 38 GPa (for the highest Vickers load of 200 gf). Density functional theory calculations with a partial occupation method showed that (Hf, Zr, Ti, Ta, Mo)B2 has a higher hardness but a lower entropy forming ability compared to (Hf, Zr, Nb, Ta, Mo)B2, which agrees with the experiments. Overall, these results indicate the strong potential of using microwave-induced plasma as a novel approach for synthesizing high entropy borides.

Determination of elemental impurities Cd, Pb, As, Hg, Co, V, Ni, Pd, Ru, Ag, Pt, Mo, Al, and Fe in highly potent analgesic activity agent by microwave-induced plasma optical emission spectrometry (MIP OES)

Determination of elemental impurities Cd, Pb, As, Hg, Co, V, Ni, Pd, Ru, Ag, Pt, Mo, Al, and Fe in highly potent analgesic activity agent by microwave-induced plasma optical emission spectrometry (MIP OES)

Adsorption of Cu (II) Ions Present in the Distilled Beverage (Sugar Cane Spirit) Using Chitosan Derived from the Shrimp Shell.

Cachaça (sugar cane spirit) is a typically Brazilian distilled beverage. Copper ions can be present in craft beverages despite their acceptance in the national and international market. This study aims to evaluate the efficiency of chitosan as an adsorbent in removing copper (II) from cachaça. The structural characteristics of the obtained chitosan and the effect of adsorbed copper were evaluated by Fourier Transform Infrared Spectroscopy (ATR-FTIR), viscosimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The deacetylation reaction from chitin (shrimp shell) resulted in chitosan with a deacetylation degree of 88.9% (potentiometric titration) and 86.9% (FTIR), low crystallinity, and an estimated molecular weight of 162.96 kDa. The copper reduction rate was 84.09% evaluated by spectrophotometric titration and microwave-induced plasma optical emission spectrometry (MIP–OES). The amine groups of chitosan had adsorption affinity with copper ions, and the kinetic analysis showed a better fit of the data by the Elovich equation, suggesting that the chemosorption mechanism controlled the kinetic process. The results suggest that chitosan has the potential to improve the quality and safety of cachaça.

Hierarchical nanoporous Ge anodes for lithium-ion batteries via plasma-phase-fabricated Mg2Ge

Microwave-induced Mg plasma rapidly “deep reduces” GeO2 to Mg2Ge, a precursor to bespoke hierarchical nanoporous Ge, which acts as a high-performance anode in lithium-ion cells.

Greening Ultrasound-Assisted Extraction for Sorghum Flour Multielemental Determination by Microwave-Induced Plasma Optical Emission Spectrometry.

Sorghum is the fourth most important cereal produced in Argentina and the fifth worldwide. It has good agronomic characteristics and could be developed in arid areas, allowing a wide geographic distribution. Its starch content, higher than 70%, makes it possible to obtain a good yield of flours. Nutritionally, it should be noted that the grain does not have the protein fraction called prolamins, which makes it suitable for consumption by people with celiac disease. The multielemental composition constitutes an important indicator of the nutritional profile of the grains and allows, together with other parameters, to select the most suitable varieties for human consumption. In its determination, the preanalytical stage is decisive to obtain a reliable result. Organic samples are a challenge for sample introduction systems that use plasma-based techniques. As an alternative to conventional pretreatment with a microwave-assisted digestion (MWAD), a greener, quick, and simple treatment is proposed, using ultrasound-assisted extraction (UAE) in diluted acid media. The UAE method accelerates analysis times, improves performance and productivity, and was applied to sorghum samples cultivated in the province of La Pampa (Argentina). Microwave-induced plasma optical emission spectrometry (MIP OES) was employed for the determination of Cu, K, Mg, Mn, P, and Zn. The detection limits found ranged from 0.6 (Cu) to 89 (P) mg kg−1, and the precision expressed by the relative standard deviation (RSD) was ≤7.7% (Zn). For validation, a maize reference material (NCS ZC 73010) was evaluated. The principal component analysis revealed three different groupings related to the sorghum varieties' mineral profile.

Methods to Enable Fault Isolation on 2.5D Molded Interposer Packages

Abstract This article discusses the failure analysis challenges associated with large overmolded 2.5D packages and explains how laser decapsulation followed by microwave-induced plasma (MIP) spot etching removes overmold while keeping everything else intact. It also describes a defect isolation procedure in which the sample is analyzed in a large chamber environmental SEM with its ball grid array directly wired to an EBAC amplifier.

A Microwave-Induced Atmospheric-Pressure Low-Temperature Linear Plasma Source Based on Parallel Plate Transmission Lines

This article presents a new type of microwave-induced atmospheric-pressure low-temperature dielectric barrier discharge source, based on the principle of parallel plate transmission lines (PPTLs). This source is a simple structure with small size, large plasma discharge area, and low discharge temperature. Experiments show that linear plasma discharge with width of 15 mm can be obtained with input power of only 25 W at 2.45 GHz. The temperature of sample placed 1 mm vertically away from the nozzle and treated for 3 min is about 45 °C even with 60-W microwave input power, which proved its thermal safety even for the biomedical applications. Emission spectroscopy diagnosis indicates that the electron density of plasma can be controlled easily by adjusting the discharge gap and the dielectric thickness. It makes this source available for various applications. This work provides a new approach to obtain uniform linear plasma.

Photochemical vapor generation combined with headspace solid phase microextraction for determining mercury species by microwave-induced plasma optical emission spectrometry

A new and simple photochemical vapor generation (PCVG) technique utilizing UVC irradiation combined with headspace solid phase microextraction (HS SPME) is developed for the unified separation and preconcentration of mercury species followed by their determination through miniaturized thermal desorption argon microwave-induced plasma optical emission spectrometry (TD–MIP–OES). Inorganic mercury (Hg2+), methylmercury, and ethylmercury are decomposed and reduced to mercury cold vapor in 2% formic acid through combined UVC irradiation and thermochemical reduction. The mercury vapor is subsequently liberated from the liquid phase and transported to the headspace. Without any tedious sample pretreatments, HS SPME using DVB/CAR/PDMS fiber affords clean and convenient one-step extraction followed by direct desorption into the injection port of the detection system. The 15 min-long UVC irradiation, thermal reduction of mercury species, and preconcentration of mercury vapor resulted in low limits of detection between 0.08 and 0.10 ng mL−1 for all mercury species. The method performance was validated by determining the total mercury and MeHg concentration in a tuna fish certified reference material (ERM CE464) and total mercury in sediment ERM CC580, and the results agreed well with the certified values.

Multiple response optimization of ultrasound-assisted procedure for multi-element determination in Brazilian wine samples by microwave-induced plasma optical emission spectrometry

In the present work, a method was developed, optimized, and validated for the determination of aluminum, manganese, lead, copper, cadmium, and zinc by microwave-induced plasma optical emission spectrometry of wine samples from the São Francisco Valley, northeastern Brazil. The samples were subjected to a sonochemical treatment aiming at the degradation of the sample matrix. To optimize the analytical procedure, initially, a two-level fractional factorial design was used to study five experimental variables and determine which ones significantly affected the analytical response. In a second step, the significant variables were optimized using the Doehlert matrix as the response surface methodology and the desirability function as a strategy to optimize multiple responses. The optimum conditions established were concentrations of nitric acid (2.3 mol L−1) and hydrogen peroxide (9%). The developed method is simple, fast, and precise, has a low operational cost and low limits of detection and quantification. The accuracy confirmed by spike tests with recoveries ranging from 104 to 118% and comparative analysis of the results obtained using the proposed method and digestion total procedure. The method was applied for multi-element determination in three wine samples.

Preparation of low molecular chitosan by microwave-induced plasma desorption/ionization technology

Compared with high molecular weight chitosan (HMWC), low molecular weight chitosan (LMWC) has better solubility and biological activity. However, there is no quick and environmentally friendly to prepare low molecular chitosan. In this study, microwave induced plasma desorption/ionization (MIPDI) was used for the first time to prepare LMWC through the degradation processes of HMWC. The results showed that MIPDI has the most abundant ∙OH content at the gas-liquid interface, and the active particles represented by ∙OH can degrade chitosan with a molecular weight of 540 KDa into soluble chitosan (≤ 10 KDa), and the yield of soluble chitosan can reach 61% in 60 min. Moreover, a series of characterization results showed that the chain structure and crystal structure gradually degraded as the treatment time increased while the chemical structure of chitosan did not change significantly. Antibacterial experiments also indicated that the antimicrobial property of LMWC obtained by MIPDI degradation was improved. In short, this method has proven to be a new, fast and green processing method for the preparation of low molecular chitosan.

CFD Modeling of a Lab-Scale Microwave Plasma Reactor for Waste-to-Energy Applications: A Review

Rapidly increasing solid waste generation and energy demand are two critical issues of the current century. Plasma gasification, a type of waste-to-energy (WtE) technology, has the potential to produce clean energy from waste and safely destroy hazardous waste. Among plasma gasification technologies, microwave (MW)-driven plasma offers numerous potential advantages to be scaled as a leading WtE technology if its processes are well understood and optimized. This paper reviews studies on modeling experimental microwave-induced plasma gasification systems. The system characterization requires developing mathematical models to describe the multiphysics phenomena within the reactor. The injection of plasma-forming gases and carrier gases, the rate of the waste stream, and the operational power heavily influence the initiation of various chemical reactions that produce syngas. The type and kinetics of the chemical reactions taking place are primarily influenced by either the turbulence or temperature. Navier–Stokes equations are used to describe the mass, momentum, and energy transfer, and the k-epsilon model is often used to describe the turbulence within the reactor. Computational fluid dynamics software offers the ability to solve these multiphysics mathematical models efficiently and accurately.

In vitro bioaccessibility of Cu and Zn in cooked beef cuts

Cu and Zn bioaccessibility was studied in two different beef cuts (rib plate and top sirloin), through the development of an in vitro assay. Samples were cooked at two degrees of doneness (medium and well-done) as usually consumed locally, to establish the contribution to the recommended daily allowance (RDA). Simulated gastrointestinal conditions were optimized and trueness of the method was evaluated by performing mass balances. Analytical determinations were performed by atomic absorption spectrometry and microwave-induced plasma optical emission spectrometry. No significant differences were found between the studied cuts nor between the degrees of doneness evaluated. Mean bioaccessible fraction (BF) of Zn was 83%, for both cuts and both degrees of doneness. In the case of Cu, rib plate presented a mean BF of 20%, while for top sirloin was of 38%. However, these differences found between cuts and degrees of doneness were not statistically significant. The contribution of Cu and Zn to the RDA for adults over 19 years was estimated, as an example, considering a 200 g portion. Results showed that the RDA of Zn would be completely covered, while the contribution to the RDA of Cu would be up to 33%.

A study on pore formation of high surface area activated carbon prepared by microwave-induced plasma with KOH (MiWP-KOH) activation: Effect of temperature-elevation rate

The activation using microwave-induced plasma with KOH (MiWP-KOH activation) can realize extremely fast synthesis of activated carbon (AC), which needed only several minutes. The present work focusses the effect of temperature-elevation rate on pore formation. For the discussion, AC was prepared using a conventional heat conduction method with various temperature-elevation programs, and the structural analysis results from these experiments were compared with those observed in AC prepared by the MiWP-KOH activation. As a feature in the pore structure of AC induced by the MiWP-KOH activation, micropore volume highly dominates over mesopore volume with (micropore/mesopore) ratio = 4.3–4.9. This property can be explained by the experiments with the controlled temperature-elevation rate, suggesting that rapid temperature-elevation rate is the key factor for such micropore-dominating structure. Additionally, it was suggested that the temperature of the feed material in the MiWP-KOH activation can become about 800 °C within 75 s. MiWP-KOH activation can generate significantly higher surface area than the conventional heating with the similar temperature changing program, suggesting the effect of microwave irradiation to enhance the pore formation. Based on these investigations, a characteristic pore formation model in the MiWP-KOH activation is considered.

Single-Step Synthesis Process for High-Entropy Transition Metal Boride Powders Using Microwave Plasma

A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B2 using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B4C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB2-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials.

Hydrogen-rich syngas production from biomass in a steam microwave-induced plasma gasification reactor

Substitution of fossil fuels by sustainable practices must be rapidly implemented to mitigate the impacts of climate change. The conversion of biomass into combustible gas is investigated in a microwave-induced plasma reactor using pure steam as the plasma working gas for the first time. The optimum results are achieved at the highest forward microwave power of 6 kW with biomass carbon conversion efficiency over 98% and complete biomass energy recovery in syngas. Unreacted steam is simply condensed out, leading to the production of a syngas with low inert dilution and high calorific value in the range 10.5–12 MJ/Nm3. The syngas produced is rich in hydrogen, exceeding 60% by volume. The proposed process could aid in the transition to a carbon neutral economy as it has the potential to efficiently convert biomass to syngas that can be used for the sustainable generation of fuels, chemicals and energy.

Propulsive effect of microwave-induced plasma jet on spark ignition of CO2-diluted CH4-air mixture

To explore the application potential of microwave-assisted spark ignition (MAI) under exhaust gas recirculation conditions, the ignition performance of MAI under CO2 dilution is tested with CH4-air premixed spherical flames. Experiments are carried out in a constant volume combustion chamber with CO2 dilution ratio of 0–20% and equivalence ratio varied from 0.5–1.0. The microwave pulse repetition frequency (PRF) and trigger delay are altered to evaluate the interaction time window between microwave and flame kernel according to the occurrence of bright spot. Results show that MAI extended the lean limit from 0.7 to 0.6 when the mixture is diluted with 8% CO2. At equivalence ratio 1.0, the CO2 dilution limit is extended from 8% in SI mode to 20% in MAI mode. Delaying the microwave trigger beyond 1 ms, the bright spot no longer occurs implying that the time window is about 1 ms. The time window is extended to 2 ms with 1 kHz microwave triggered synchronously with spark, and increasing the microwave PRF to 10 kHz prolongs the time window to 3 ms. However, as CO2 added, the time window is obviously shortened and no more than 1 ms, indicating that CO2 dilution accelerates the decay of electron density in the flame kernel, so that the enhancement is mainly reflected in the first microwave pulse with 1 kHz PRF. The single microwave pulse of 1 kHz induces stronger plasma jet propelling the flame front, and its direction directly decides the ignition success rate near ignitable limit. On the whole, under high ratio of CO2 dilution, increasing the intensity and controlling the direction of microwave-induced plasma jet is beneficial to MAI performance.