Residual Carbon Concentration Research Articles

Co-Fermentation of Chlorella vulgaris with Oleaginous Yeast in Starch Processing Effluent as a Carbon-Reducing Strategy for Wastewater Treatment and Biofuel Feedstock Production

Low biomass yield and nutrient removal efficiency are problems challenging the employment of microorganisms for wastewater remediation. Starch processing effluent (SPE) was used as a fermentation substrate to co-culture Chlorella vulgaris and Rhodotorula glutinis for biofuel feedstock production. Co-culture options were compared, and the optimal conditions were identified. The result shows that microalgae and yeast should be inoculated simultaneously at the beginning of SPE-based fermentation to achieve high biomass yield and the optimal inoculation ratio, light intensity, and temperature should be 2:1, 150 μmol/m2/s, and 25 °C, respectively. Under the optimal conditions, the lipid yield of microorganisms was 1.81 g/L and the carbon–conversion ratio reached 82.53% while lipid yield and the carbon–conversion ratio in a monoculture fell in the range of 0.79–0.81 g/L and 55.93–62.61%, respectively. Therefore, compared to the monoculture model, the co-fermentation of Chlorella vulgaris and Rhodotorula glutinis in starch processing effluent could convert nutrients to single-cell oil in a more efficient way. It should be noted that with the reduced concentration of residual organic carbon in effluent and the increased carbon–conversion ratio, co-fermentation of microalgae and yeast can be regarded as a promising and applicable strategy for starch processing effluent remediation and low-cost biofuel feedstock production.

Austenite Formation and Manganese Partitioning during Double Soaking of an Ultralow Carbon Medium‐Manganese Steel

Double soaking (DS) is a thermal processing route intended to produce austenite–martensite microstructures in steels containing austenite‐stabilizing additions and consists of intercritical annealing (primary soaking), followed by heating and brief isothermal holding at an increased temperature (secondary soaking), and quenching. Herein, experimental dilatometry during DS of a medium‐manganese (Mn) steel with nominally 7 wt% Mn and an ultralow residual carbon concentration, in combination with phase‐field simulations of austenite formation during secondary soaking, is presented. The feasibility of maintaining heterogeneous Mn distributions during DS is demonstrated and insight is provided on the effects of the secondary soaking temperature and prior Mn distribution on the ferrite‐to‐austenite phase transformation during the secondary soaking portion of the DS treatment.

Synthesis and Sintering of Tungsten and Titanium Carbide: A Parametric Study

The three primary steps in the production of tungsten carbide WC and titanium carbide TiC powders are the preparation of the green mixture, carbidization by furnace annealing, and ball milling of the annealed products. This work performed a comprehensive parametric investigation of these three steps. The impact of several factors was examined including the carbon precursor, the mass and diameter of the milling bodies (balls), the milling time and speed, the temperature and length of the annealing process, the height of the powder in the furnace boats, and the rate at which the furnace boats move. Regression models for every stage of the process were verified by 10-fold validation and used to optimize the synthesis sequence, resulting in high-quality WC and TiC with a grain size below 2 microns and a content of free carbon below 0.1%. Additionally, solid solution (W,Ti)C was fabricated by mechanochemical synthesis from the elemental mixtures; however, further modification of this technique is necessary because of the observed relatively high concentration of residual free carbon (0.2–0.8%) and contamination by Fe.

Substantial and simultaneous reduction of major electron traps and residual carbon in homoepitaxial GaN layers

The presence of large amounts of electron traps together with residual carbon, as well as their trade-off relationship, is an obstacle to fabricating next-generation GaN-based power devices using the metal-organic chemical vapor deposition (MOCVD) method. Using the hydride vapor phase epitaxy (HVPE) method, we have overcome all of the aforementioned obstacles. In a previous study, we realized GaN homoepitaxial layers with greater purity than the best MOCVD-grown layers by removing quartz components from the high-temperature region of the HVPE apparatus. In the present study, the concentration of residual carbon was further reduced to less than 3 × 1014 cm−3 by removing carbon components near the wafer. In addition, the concentrations of major electron traps widely observed in homoepitaxial GaN layers were substantially reduced to the 1012–1013 cm−3 range via further modification of the HVPE conditions/apparatus to suppress etching of a stainless-steel flange of the HVPE reactor. The results imply that stainless-steel-related impurities such as Fe and Cr are the most likely cause of the major electron traps although native point defects have long been considered their origin. The resultant GaN layers, which showed substantially improved optical and electrical properties, did not exhibit a trade-off relationship between the concentrations of carbon and electron traps.

Stray particles as the source of residuals in sand filtrate: Behavior of superfine powdered activated carbon particles in water treatment processes

Although superfine powdered activated carbon has excellent adsorption properties, it is not used in conventional water treatment processes comprising coagulation–flocculation, sedimentation, and sand filtration (CSF) due to concerns about its residual in treated water. Here, we examined the production and fate of very fine carbon particles with lacking in charge neutralization as a source of the residual in sand filtrate after CSF treatment. Almost all of the carbon particles in the water were charge-neutralized by coagulation treatment with rapid mixing, but a very small amount (≤0.4% of the initial concentration) of very fine carbon particles with a lesser degree of charge neutralization were left behind in coagulation process. Such carbon particles, defined as stray carbon particles, were hardly removed by subsequent flocculation and sedimentation processes, and some of them remained in the sand filtrate. The concentration of residual carbon particles in the sand filtrate varied similarly with that of the stray carbon particles. The stray and residual carbon particles were similarly smaller than the particles before coagulation treatment, but the residual carbon particles had less charge neutralization than the stray carbon particles. The turbidity of water samples collected after sedimentation was not correlated with the residual carbon concentration in the sand filtrate, even though it is often used as an indicator of treatment performance with respect to the removal of suspended matter. Based on these findings, we suggest that reduction of the amount of stray particles should be a performance goal of the CSF treatment. Examining this concept further, we confirmed that the residence time distributions in the coagulation and flocculation reactors influenced the concentration of stray carbon particles and then the residual carbon particle concentration in sand filtrate, but found that the effect was dependent on coagulant type. A multi-chambered-reactor configuration lowered both the stray carbon particle concentration after coagulation treatment and the residual carbon particle concentration in sand filtrate compared with a single-chambered reactor configuration. When a normal basicity PACl that consisted mainly of monomeric Al species was used, the stray carbon particle concentration was decreased during coagulation process and then gradually decreased during subsequent flocculation process because the monomeric Al species were transformed to colloidal Al species via polymeric Al species. In contrast, when a high-basicity PACl that consisted mostly of colloidal Al species was used, coagulation treatment largely decreased the stray carbon particle concentration, which did not decrease further during subsequent flocculation process. These findings will be valuable for controlling residual carbon particles after the CSF treatment.

Impact of Residual Carbon on Avalanche Voltage and Stability of Polarization-Induced Vertical GaN p-n Junction

We demonstrate that the residual carbon concentration in the drift region can have a significant impact on the reverse leakage, breakdown voltage, and breakdown stability of GaN-on-GaN vertical diodes. Two generations (Gen1, Gen2) of polarization-doped p-n junctions with different C concentrations were compared, in terms of avalanche voltage, avalanche instability, and deep-level concentration. The original results collected within this paper show that: 1) both generations of devices can safely reach the avalanche regime; diodes with a lower residual CN have a higher reverse leakage and a lower avalanche voltage, due to an uneven distribution of the electric field; 2) the presence of residual carbon can lead to breakdown walkout, i.e. a recoverable increase in breakdown voltage under reverse-bias stress. Specifically, devices with higher C concentration show a fully-recoverable breakdown walkout, whereas the breakdown voltage is stable in devices with lower C concentration; and 3) steady-state photocapacitance measurements confirm the presence of CN in both generations, and are used to assess the relative difference in concentration between Gen1 and Gen2, even for levels below secondary ion mass spectroscopy (SIMS) sensitivity. The results described in this paper indicate the existence of a trade-off between breakdown voltage (increasing by improving compensation) and breakdown stability (improving by reducing CN concentration) and are of fundamental importance for the optimization of GaN power devices.

A novel strategy for medical foods digestion and subsequent elemental determination using inductively coupled plasma optical emission spectrometry

A sample preparation method using only H2O2 in the single reaction chamber system (SRC-H2O2) for medical foods (MFs) digestion and further elemental determination by inductively coupled plasma optical emission spectrometry (ICP OES) was proposed. Digestion of some refractory substances (RS), such as, histidine, linoleic acid, phenylalanine and tryptophan, was also investigated. For the method development important parameters, such as, maximum temperature and pressure of SRC system, volume of H2O2 and sample mass were evaluated. Digestion efficiency was evaluated based on the concentration of residual carbon (RC) of final digests. The optimized method conditions were 1 g of sample, 6 mL of 50% H2O2 and maximum temperature and pressure of 250 °C and 160 bar, respectively. The digests obtained using the optimized conditions presented concentration of RC lower than 720 mg L−1. The accuracy of SRC-H2O2 method was evaluated by analysis of reference material (RM) NIST 8435 (whole milk powder) and by comparison between results obtained using the proposed method and those obtained by digestion with concentrated HNO3 (SRC-HNO3). Significant differences were not observed comparing the results of SRC-H2O2 with reference values of RM and SRC-HNO3. Limits of detection obtained by the proposed method ranged from 0.01 to 88 μg g−1 for all elements determined by ICP OES. SRC-H2O2 method provided digests of individual constituents (sodium caseinate, corn syrup and sunflower oil) of MFs and RS with residual carbon content (RCC) lower than 10% (calculated based on molar and sample masses), except for linoleic acid (RCC of 17%). These same compounds were also digested using SRC-HNO3 method and the RCC values were significantly lower than than those found by SRC-H2O2, except for aromatic amino acids (tryptophan and phenylalanine). The final acidity of digests obtained using SRC-H2O2 was negligible that is convenient for elemental determination using ICP-based techniques and agrees with green analytical chemistry requirements.

Atomic layer deposition of stoichiometric In2O3 films using liquid ethylcyclopentadienyl indium and combinations of H2O and O2 plasma

Liquid ethylcyclopentadienyl indium (InEtCp) was synthesized, and this compound exhibited superior characteristics, including a relatively high vapor pressure and thermal stability up to 250 °C. In2O3 thin films were subsequently deposited by atomic layer deposition (ALD) using the InEtCp as a precursor together with combinations of oxidants: H2O followed by O2 plasma (WpO), H2O followed by O2 (WO), O2 plasma alone (pO), and O2 plasma followed by H2O (pOW). The growth rates for In2O3 thin films using the pO and pOW processes were much smaller than those using the WO and WpO processes. A self-limiting surface reaction during the WpO process was observed with no delay in nucleation when the pulse times for InEtCp, H2O, and O2 plasma were 0.1, 2.0, and 14 s, respectively, at a growth temperature of 200 °C. For the WO and WpO processes, the In2O3 films are considered to be formed by quite different mechanisms, due to oxidation or lack thereof in the presence or absence of the -O-In-OH* intermediate product. This is due to the difference in the oxidation strength of O2 gas and O2 plasma during the oxidation step in the ALD process. As a result, In2O3 thin films deposited by WpO were obtained with a stoichiometric O/In ratio of 1.5 and a negligibly low residual carbon concentration of around TOF-SIMS detection limit, below 1 ppm. Therefore, InEtCp is one of the promising candidate precursors to form a high quality In2O3 film.

Comparison of plasma-enhanced atomic layer deposition AlN films prepared with different plasma sources

A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 Å/cycle, contain residual oxygen and carbon concentrations of about 10% and 4%, respectively, and possess a refractive index of 2.07 (at 632.8 nm).

Study on reduction of iron ore concentrate in rotary kiln to produce direct reduced iron

A direct reduced iron (DRI) was prepared using iron concentrate pellets and a coal as a reductant through three stages, namely, the first: iron concentrate pellets were dried by slow heating at 150 ° C to remove water content, the second: they were heated at 1,200°C to reduce magnetite into hematite which was treated in two different conditions, namely by oxygen and without oxygen injections; and the third: they were reduced in an atmosphere of CO/CO 2 at various temperatures of 950-1,200°C. In this reduction process of iron oxide would be reduced by CO to metallic iron (Fe). The experimental results showed that the metallization without oxygen injection produced the best metallization at 1,100°C and the ratio of carbon/iron (FC/Fe) of 0.52 to result 84.54%, contained 74.68% Fe and 88.34% Fe total . The metallization by oxygen injection produced the best metallization at 1,100°C, providing result of 96.81%, Fe metal of 87.88% and 90.78% of Fe total . The iron oxides on the DRI were relatively low, namely 2.9%. In this research, prior pellets preparation a magnetic oxidation process on iron ore concentrate was also conducted and changed the magnetite into hematite. The reduction process on its pellets produced 94.15% metallization at 1,100°C, and the DRI contained 97.85% of Fe total , 85.32% of Fe metal and 5.35% of Fe oxides. Furthermore, analyzing a remained carbon of the DRI using microscopy to seek the metal structure formed. The remained carbon was reported around 1-6% C. Next smelting process, it is suggested to have a high residual carbon concentration as there will be a carbon boil mechanism to reduce iron oxides that are still lagging on the DRI.

Determining the Severity of Torrefaction for Multiple Biomass Types Using Carbon Content

This research concerns the investigation of an alternative measurement to directly indicate the severity of torrefaction. Composition and process data from both batch and continuous torrefaction experiments using willow, wheat straw, and cattail biomass were combined and analyzed. The mass yield, which is an indication of torrefaction severity was correlated to the net change in residual carbon concentration (ΔC), and second the total change in mass (ΔMt) was correlated to net change in mass of carbon per 100 g of feedstock (ΔMc). Analysis of the experimental data show a polynomial relationship between the dry mass yield (Ym) and the change residual carbon concentration (ΔC). This relationship is Ym = 5.05ΔC2 – 3.96ΔC + 0.98 (R2 = 0.89). The uncertainty in this correlation is ±7.3% (w/w). The relation between total change in mass (ΔMt) and change in carbon mass (ΔMc) meanwhile was found to fit a linear model by ΔMc = 0.36ΔMt + 1.04 with a coefficient of determination of 0.96. Each of these models was then...

Influence of dislocation density and carbon impurities in i-GaN layer on the performance of Schottky barrier ultraviolet photodetectors

The influences of dislocation density and carbon impurities in i-GaN layer on the performance of Schottky barrier ultraviolet photodetectors are investigated. It is found that an increase in dislocation density leads to a decrease in the responsivity, mainly because that the dislocation defects act as charge traps in GaN which can increase the recombination probability of photo-generated electron-hole pairs. On the other hand, it is shown that high carbon impurity content in the i-GaN layer also causes a decrease of the responsivity, mainly because the fact that the photo-generated carriers can’t be effectively collected due to the effect of C-induced deep level centers related to carbon impurities.To fabricate high performance GaN based ultraviolet photodetectors, it is important to reduce dislocation density and keep a relatively low concentration of residual carbon during the material growth.

Straw Application Strategy to Optimize Nutrient Release in a Southeastern China Rice Cropland

The management and improvement of paddy soils fertility are key factors for the future capacity of rice production. The return of rice straw to paddy soils is the best alternative to the application of industrial fertilizers for rice production sustainability. The best strategy for applying rice straw to improve soil nutritional capacity during rice growth has not yet been investigated. We compared straw decomposition in the ditches and ridges in paddy fields subjected to a typical crop management in southeastern China. Straw spread on the ridges provided lower residual straw carbon (C) concentration and mass, lower nitrogen:phosphorus ratio N:P, C:N, and C:P ratios, and lower soil salinity, as well as higher temperature, and higher N- and P-release capacity during the rice crop in comparison to the straw spread in the ditches. Therefore, applying rice straw to the ridges is better strategy than applying it to ditches to enhance rice production.

Multivariate Optimization of Conditions for Digestion of Wet Feeds for Dogs and Cats Using a Closed Digester Block and Multielement Determination by ICP-OES

A full 24 factorial design was applied to find the best combination of diluted reagents (HNO3 and H2O2), time, and temperature for the digestion of samples of wet feed for dogs and cats using a closed digestion block. The residual carbon concentration (RCC) was used as the response in the factorial design. All variables and their interactions significantly influenced the digestion of the feed samples, as indicated by the RCC. The conditions established for the digestion of 0.05 g (dry mass) wet feed samples were the addition of 3.0 mol/L HNO3 and 5.0% m/m H2O2 in a final volume of 10 mL, followed by heating in a closed digestion block at a temperature of 170°C for 120 min. Analyses were performed by inductively coupled plasma (ICP) optical emission spectrometry (OES). LOQs ranged from 0.2 μg/g (Mg and Sr) to 51 μg/g (P). Accuracy of the analytical method was confirmed through the analysis of the Standard Reference Materials Tomato Leaves (NIST 1573), Apple Leaves (NIST 1515), and Peach Leaves (NIST 1547). The agreement values achieved ranged from 80.2 ± 0.3% for Ba to 113.8 ± 7.1% for Zn (n = 3). Addition and recovery tests were carried out by adding the analytes to a feed sample at two concentration levels, and the recoveries were between 84 ± 6 and 114 ± 10% for macroelements (Ca, K, Mg, and P; n = 3) and between 88 ± 3 and 113 ± 7% for microelements and trace elements (B, Cu, Fe, Sr, and Zn; n = 3). The precision values achieved for the different elements, expressed as RSDs, were better than 7.3% (Zn; n = 3) except for Cu determination, that was 14.6% (n=3). The optimized analytical method was applied to 10 commercial samples of wet feed for cats and dogs, with the concentrations of Al, B, Ba, Ca, Cu, Fe, K, Mg, Mn, P, Sr, and Zn determined by ICP-OES.

Green microwave-assisted wet digestion method of carbohydrate-rich foods with hydrogen peroxide using single reaction chamber and further elemental determination using ICP-OES and ICP-MS

A sample preparation method using only H2O2 in the single reaction chamber system (SRC-UltraWave™) was proposed for carbohydrate-rich foods (CRFs) digestion and further elemental determination by inductively coupled plasma (ICP) based techniques. The greenness of the proposed method was evaluated based on the Analytical Eco-Scale. Additionally, the digestion efficiency, obtained under different conditions (temperature and volume of H2O2), was evaluated based on the concentration of residual carbon (RC). Determination of RC and major elements (Ca, Fe, Mg and Na) were carried out using inductively coupled plasma optical emission spectrometry (ICP-OES), while the minor and toxic elements (As, Ba, Cd, Co, Cu, Mn, Mo, Pb, Sr and Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS). Digests with lower RC were obtained using 8mL of 50% H2O2, 250°C and 199bar. Residual carbon lower than 250 and 400mgL−1 were obtained for honey and different flours (wheat, corn, cassava and potato), respectively. Maxima sample masses of 0.75g and 1.25g were efficiently digested (without insoluble residues) for different flours and honey, respectively. Reference materials (RMs) and certified reference material (CRM) with carbohydrate-rich matrices: corn bran (RM NIST 8433), cotton cellulose (RM IAEA V9) and rice flour (CRM NIST 1568a) were used to evaluate the accuracy of the proposed method. Additionally, accuracy was also evaluated by comparison between results obtained using proposed method and those obtained by microwave-assisted wet digestion (MAWD) with concentrated HNO3. Significant differences were not observed when comparing the results of the proposed method with reference values of RMs, CRM and MAWD. Limits of detection obtained by the proposed method were suitable for the quality control analysis of CRFs and ranging from 0.0001μgg−1 to 30μgg−1. As water and oxygen are the main products of H2O2 with CRFs, final digests are suitable for ICP-based techniques analysis due to its low acidity and consequent reduction of physical interferences on nebulization devices. Finally, according to the Analytical Eco-Scale, the proposed method was considered an excellent green analysis with final score of 85.

Mechanism of the Key Impact of Residual Carbon Content on the Reliability of Integrated Resistive Random Access Memory Arrays

Resistive random access memories (RRAM) require high density, low power consumption and high reliability. Systematic statistic electrical, material and theoretical studies were demonstrated in this work to point out and clarify a key impact of carbon residues on the resistive switching (RS), particularly the endurance, of the integrated HfO2-based 4 kbit RRAM array. The mechanism of the carbon atoms interacting with oxygen vacancies and serving also as filament was understood in nanoscale by performing density functional theory (DFT) calculations. Under an oxygen-deficient environment, carbon atoms tend to fill in oxygen vacancy (VO··) sites and could form conductive filaments which require higher energy to be broken compared to the original VO·· filaments. By controlling the residual carbon concentration lower than 4%, highly reliable HfO2-based integrated 4 kbit RRAM array was achieved, which is of great interest for future nonvolatile memories.

Improvement of Ohmic contact to p-GaN by controlling the residual carbon concentration in p++-GaN layer

Growth conditions are used to control the residual carbon impurity incorporation in p++-GaN layers. Specific contact resistance (ρc) with various residual carbon concentrations has been investigated through the circular transmission line model (CTLM) method and secondary ion mass spectroscopy (SIMS) analysis. A correlation between residual carbon and ρc indicates that incorporation of proper carbon impurity can be an advantage for Ohmic contact, although carbon can also act as a compensating donor to worsen the Ohmic contact at a very high concentration. Finally, ρc is improved to 6.80×10−5Ω×cm2 with a carbon concentration of 8.3×1017cm−3 in p++-GaN layer, when the growth temperature, pressure and flow rate of CP2Mg and TMGa are 940°C, 100Torr, 3μmol/min and 28μmol/min, respectively.

Numerical simulation of residual stress in low temperature colossal carburised layer on austenitic stainless steel

A numerical model is proposed to quantitatively characterise the residual stress evolutions in low temperature colossal carburised layer on austenitic stainless steel. In this model, on the basis of the consideration of concentration and stress dependent carbon diffusivity, prediction of the carbon concentration distribution and growth regularity of carburised layer is performed. The strain rate is discussed taking the compositive effects of residual stress and carbon concentration gradient. Based on the strain compatibility of carburised layer and substrate, the residual stress is calculated. Meanwhile, a low temperature colossal carburisation experiment is carried out on 316L austenitic stainless steel and the carbon concentration and residual stress are measured to verify the validity of the model. The numerical results of carbon concentration and residual stress distributions agree with the experimental data, indicating that the numerical model established in this paper can be used to investigate the process of low temperature colossal carburisation.

Emission efficiency enhanced by reducing the concentration of residual carbon impurities in InGaN/GaN multiple quantum well light emitting diodes.

A series of samples with varying growth pressure are grown and their optical and structural properties are investigated. It is found that the residual carbon concentration decreases when the reactor pressure increases from 80 to 450 Torr during the InGaN/GaN multiple quantum well growth. It results in an enhanced peak intensity of electroluminescence because carbon impurities can induce deep energy levels and act as non-radiative recombination centers in InGaN layers.

Material insights of HfO2-based integrated 1-transistor-1-resistor resistive random access memory devices processed by batch atomic layer deposition.

With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption.