Decrease In Hydrogen Content Research Articles

Hydrothermal carbonization of tobacco stalk for fuel application

Tobacco stalks are an abundant biomass resource which are otherwise treated as waste. In this work, the effect of hydrothermal carbonization temperature and time on the structures, chemical compositions and combustion characteristics of hydrochars obtained from tobacco stalks were evaluated. The carbon content, higher heating value, and energy yield increased with accompanying decrease in hydrogen and oxygen contents with the increase of treatment temperature and time. The evolution of the H/C and O/C atomic ratios indicated dehydration and devolatilization processes occurred during hydrothermal carbonization. The weight loss, combustion range and characteristic temperatures of tobacco stalks were significantly modified after hydrothermal carbonization, resulting in higher ignition temperatures and higher energy density. The kinetics model, Coats–Redfern method revealed the activation energy of hydrochars in zone 2 and 3 were among 43.7–74.8kJ/mol and 46.7–85.8kJ/mol, respectively. Our results show that hydrothermal carbonization reaction can facilitate transforming tobacco stalks into energy-rich solid fuel.

Energetic Characteristics of Syngas Obtained from Gasification of Hazelnut Prunings

The aim of the study concerns the energy recovery of chips, derived from hazelnut prunings, by means of gasification through air. The gasifier is a downdraft fixed bed reactor, the biomass used is characterized by a moisture of about 16% and a LHV of 15MJ/kg. The composition of syngas is characterized by a high amount of nitrogen, more than 50% in volume, that is due to use of air as oxidant agent. Results of syngas analysis show that the increase of air flow causes a decrease in hydrogen content but a more marked increase in carbon monoxide and methane contents. The LHV of syngas obtained ranges from 3.2 to 3.6MJ/Nm3 and it is suitable to obtain thermal energy that can be used to provide heat for small farms, especially for greenhouses. The gasification system presented is also able to obtain as output flow, in addition to syngas, a solid residue or biochar which can be used in agronomic sector to improve soil characteristics.

Hot wire chemical vapor deposited multiphase silicon carbide (SiC) thin films at various filament temperatures

Influence of filament temperature (TFil) on the structural, morphology, optical and electrical properties of silicon carbide (SiC) films deposited by using hot wire chemical vapor deposition technique has been investigated. Characterization of these films by low angle XRD, Raman scattering, XPS and TEM revealed the multiphase structure SiC films consisting of 3C–SiC and graphide oxide embedded in amorphous matrix. FTIR spectroscopy analysis show an increase in Si–C, Si–H, and C–H bond densities and decrease in hydrogen content with increase in TFil. The C–H bond density was found higher than the of Si–H and Si–C bond densities suggesting that H preferably get attached to C than Si. AFM investigations show decrease in rms surface roughness and grain size with increase in TFil. SEM studies show that films deposited at low TFil has spherulites-like morphology while at high TFil has cauliflower-like structure. Band gap values ETauc and E04 increases from 1.76 to 2.10 eV and from 1.80 to 2.21 eV respectively, when TFil was increased from 1500 to 2000 °C. These result show increase in band tail width (E04–ETauc) of multiphase SiC films. Electrical properties revealed that σDark increases from ~7.87 × 10−10 to 1.54 × 10−5 S/cm and Eact decreases from 0.67 to 0.41 eV, which implies possible increase in unintentional doping of oxygen or nitrogen due to improved crystallinity and Si–C bond density with increase in TFil. The deposition rate for the films was found moderately high (21 < rdep < 30 A/s) over the entire range of TFil studied.

Comparative study of torrefaction of empty fruit bunches and palm kernel shell

This paper describes the effect of torrefaction on the characteristics of empty fruit bunches (EFB) and palm kernel shell (PKS). The torrefaction of EFB and PKS was investigated in a horizontal tubular reactor at a temperature ranging from 150 to 600 °C, for torrefaction residence time varying from 0 to 50 min. The torrefied products were characterized in terms of their elemental composition, energy yield, ash content and volatile fraction. The present study developed the torrefaction kinetics of EFB and PKS in a thermogravimetric analyzer to obtain the kinetic parameters. EFB and PKS exhibited excellent energy yield values. The gaseous products from torrefaction of EFB and PKS were also analyzed. Furthermore, the study reveals that the carbon content increases with an increasing torrefaction temperature but the O/C ratio, hydrogen and oxygen content decrease for both EFB and PKS. The energy yield and mass yield were found to decrease with an increase in the torrefaction temperature while the higher heating value (HHV) increased. From this study, torrefaction temperature between 290 and 320 °C is the optimum torrefaction temperature for EFB while torrefaction temperature between 300 and 320 °C is the optimum torrefaction temperature for PKS.

Structural, chemical and nanomechanical investigations of SiC/polymeric a-C:H films deposited by reactive RF unbalanced magnetron sputtering

Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C2H2 precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C2H2 concentration during deposition. A higher C2H2 flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H3/E2. The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp3 bond content shows the highest elastic recovery during scratching.

Collision-Induced Dissociation Ion Mobility Mass Spectrometry for the Elucidation of Unknown Structures in Strained Polycyclic Aromatic Hydrocarbon Macrocycles.

Structure determination of unexpected products obtained during synthesis of large carbon nanotube sidewall segments with more than 200 carbon atoms represents a challenging task for traditional analytical methods. Herein, we investigate a homologous series of four products having the same number of carbon atoms but slightly different hydrogen numbers ranging from 168 to 162. We demonstrate that the combination of mass spectrometry, ion mobility separation, and collision-induced dissociation (CID) can be used to finally elucidate the complete structures with high certainty. The postulated 1,2-phenyl shift as origin for the side reaction could be proven by changes in the minimum fragment sizes. A combination of CID and ion mobility spectrometry was applied for the first time to prove the cyclic nature of all molecules by the significant size increase upon ring opening. Thereby, also, more compact molecules were discovered in the gas phase with thus far unknown structures. Finally, the potential presence of numerous isomers could be ruled out by drift time measurements and molecular modeling together with theoretical collision cross-section (CCS) calculations. Surprisingly, only one defined structure could be assigned to each macrocycle in the homologous series, most likely as a result of natural selection rules driven by ring strain and steric hindrance. With a decreasing hydrogen content, the macrocycles undergo a stepwise transition from a cylindrical to conical shape. Overall, ion mobility mass spectrometry together with molecular modeling shows great potential to analyze unknown structures, especially in cases where structure determination by X-ray single-crystal analysis is not applicable.

Effects of deposition rate and ion bombardment on properties of a-C:H films deposited by H-assisted plasma CVD method

In our previous study, we realized conformal, subconformal, and anisotropic deposition profiles of hydrogenated amorphous carbon (a-C:H) films formed on trench substrates by plasma CVD using toluene. To obtain information on the film structures, we investigated the effects of deposition rate and ion bombardment on hydrogen bonding configurations and hydrogen content in the a-C:H films deposited by plasma CVD using toluene. The structure of a-C:H films transforms from polymer-like a-C:H (PLCH) for the ion energy <75 eV to diamond-like a-C:H (DLCH) for the ion energy ≥75 eV. The hydrogen bonding configurations in a-C:H films are closely related to the ion energy, whereas they are less dependent on ion flux and deposition rate. The mass density increases gradually with decreasing hydrogen content in the PLCH region, and it increases sharply with decreasing hydrogen content in the DLCH region. This difference is due to the different C–C sp3 concentration in PLCH and DLCH films.

High Rate of Hydrogen Incorporation in Vertically Aligned Carbon Nanotubes during Initial Stages of Growth Quantified by Elastic Recoil Detection

We quantified the amount of hydrogen in as-grown vertically aligned multiwall CNTs at different stages of growth using elastic recoil detection analysis (ERDA). We suggest that hydrogen is associated with atomic defects and/or amorphous carbon impurities formed at earlier deposition stages. We found that the highest amount of hydrogen (2.3 wt %) was incorporated during the initial growth stage (15–20 s). Our results show a decrease of hydrogen content with increasing deposition time and/or with decreasing growth rate, which points to dynamical self-annealing of hydrogen-saturated defects. Consequently, the decrease of hydrogen-related defects leads to a higher quality of MWCNTs, which can be easily detected by ERDA. This research provides new insight into the nanotube growth mechanism and provides a new characterization approach for quantifying hydrogen-saturated atomic defects in MWCNTs.

Water Quality Trends in the Blackwater River Watershed, West Virginia

Abstract An understanding of historic and current water quality is needed to manage and improve aquatic communities within the Blackwater River watershed, WV. The Blackwater River, which historically offered an excellent Salvelinus fontinalis (Brook Trout) fishery, has been affected by logging, coal mining, use of off-road vehicles, and land development. Using information-theoretic methods, we examined trends in water quality at 12 sites in the watershed for the 14 years of 1980–1993. Except for Beaver Creek, downward trends in acidity and upward trends in alkalinity, conductivity, and hardness were consistent with decreases in hydrogen ion concentration. Water-quality trends for Beaver Creek were inconsistent with the other sites and reflect ongoing coal-mining influences. Dissolved oxygen trended downward, possibly due to natural conditions, but remained above thresholds that would be detrimental to aquatic life. Water quality changed only slightly within the watershed from 1980–1993, possibly reflectin...

Hydrothermal carbonization of oil palm shell

Palm shell is one of the most plentiful wastes of the palm oil mill industry. This study identifies the capability of hydrothermal carbonization process (HTC) to convert palm shell into high energy hydrochar. The influence of reaction time and reaction temperature of the HTC process was investigated. The process parameters selected were temperature 200 °C to 240 °C, time 10 to 60min, and water to biomass ratio was fixed at 10 : 1 by weight %. Fourier transform infrared (FTIR), elemental, proximate, Burner Emmett and Teller (BET), thermo-gravimetric (TGA) analyses were performed to characterize the product and the feed. The heating value (HHV) was increased from 12.24 MJ/ kg (raw palm shell) to 22.11 MJ/kg (hydrochar produced at 240 °C and 60 min). The hydrochar yield exhibited a higher degree inverse proportionality with temperature and reaction time. Elemental analysis revealed an increase in carbon percentage and a proportional decrease in hydrogen and oxygen contents which caused higher value of HHV. The dehydration and decarboxylation reactions take place at higher temperatures during HTC resulting in the increase of carbon and decrease in oxygen values of hydrochar. The FESEM results reveal that the structure of raw palm shell was decomposed by HTC process. The pores on the surface of hydrochar increased as compared to the raw palm shell.

Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

A novel approach to determine post mortem interval using neutron radiography

One of the most difficult challenges in forensic research is to objectively determine the post-mortem interval (PMI). The accuracy of PMI is critical for determining the timeline of events surrounding a death. Most PMI techniques rely on gross morphological changes of cadavers that are highly sensitive to taphonomic factors. Recent studies have demonstrated that even exhumed individuals exposed to the same environmental conditions with similar PMIs can present different stages of decomposition.After death, tissue undergoes sequential changes consisting of organic and inorganic phase variations, as well as a gradual reduction of tissue water content. Hydrogen (H) is the primary contributor to neutron radiography (NR) contrast in biological specimens because (1) it is the most abundant element in biological tissues and (2) its nucleus scatters thermal and cold neutrons more strongly than any other atomic nucleus. These contrast differences can be advantageous in a forensic context to determine small changes in hydrogen concentrations.Neutron radiography of decaying canine tissues was performed to evaluate the PMI by measuring the changes in H content. In this study, dog cadavers were used as a model for human cadavers. Canine tissues and cadavers were exposed to controlled (laboratory settings, at the University of Tennessee, College of Veterinary Medicine) and uncontrolled (University of Tennessee Anthropology Research Facility) environmental conditions, respectively. Neutron radiographs were supplemented with photographs and histology data to assess the decompositional stages of cadavers. Results demonstrated that the increase in neutron transmission likely corresponded to a decrease in hydrogen content in the tissue, which was correlated with the decay time of the tissue. Tissues depleted in hydrogen were brighter in the neutron transmission radiographs of skeletal muscles, lung, and bone, under controlled conditions. Over a period of 10 days, changes in neutron transmission through lung and muscle were found to be higher than bone by 8.3%, 7.0%, and 2.0%, respectively. Results measured during uncontrolled conditions were more difficult to assess and further studies are necessary. In conclusion, neutron radiography may be used to detect changes in hydrogen abundance that can be correlated with the post-mortem interval.

Bio-oil from Fast Pyrolysis of Empty Fruit Bunch at Various Temperature

Abstract World concern about depletion of fossil fuel and energy security supply has driven into increasing awareness about biomass derived energy. Empty fruit bunch (EFB), one of the major palm oil-derived biomass available in Indonesia, is a potential source for fuel production. Pyrolitic conversion of EFB to bio-fuels is being considered for national energy security and environmental advantages. The objective of the work is to determine the effect of reaction temperature and time on the EFB fast pyrolysis optimization. Elemental analysis composition and physical properties of bio-oil show increase in carbon content, decrease in oxygen, hydrogen, and nitrogen content with increases the pyrolysis temperature.

Molecular dynamics simulations on the growth of thin amorphous hydrogenated carbon films on diamond surface

The growth of thin amorphous hydrogenated carbon films (a-C:H) on diamond (111) surface from the bombardment of CH2 radicals is studied using molecular dynamics simulations. Structural analysis shows that the local structure (e.g., the first coordination number of C atoms) of a-C:H depends critically on the content of hydrogen. The increase in kinetic energy of incident radicals leads to the decrease of hydrogen content, which subsequently changes the proportion of sp3 bonded C atoms in a-C:H.

Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures

Two new absorber coatings for mid-temperature operation (300–350°C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measurements. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350°C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350°C in vacuum for up to 1500h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.

Effect of tetramethylsilane flow on the deposition and tribological behaviors of silicon doped diamond-like carbon rubbed against poly(oxymethylene)

In this study, silicon doped diamond-like carbon (Si-DLC) was deposited on stainless steel (JIS SUS304) by using surface wave-excited plasma (SWP). The effects of tetramethylsilane (TMS) flow on the composition, topography, mechanical properties and tribological behavior were investigated. Pin-on-disc tribo-meter was used to investigate the tribological behavior of the Si-DLC coating rubbed against poly(oxymethylene) (POM). The results show that the deposition rate, roughness of Si-DLC increased and the hardness of Si-DLC decreased with the increase of TMS flow rate from 2 to 4 sccm; the roughness increase therein led to the increase of ploughing term of friction. The increase of adhesion term was also seen with the increase of TMS flow rate, being attributed to the decrease of hydrogen concentration in the coating. It was considered that more POM transferred onto the Si-DLC deposited at higher TMS flow rate due to larger heat generation by friction.

Synthesis and Hydrogen Gas Sensing Performance of Pd-Functionalized Nanostructures

In this work, palladium surface-functionalized single-walled carbon nanotubes (SWNTs) hydrogen gas sensor was fabricated by electrodeposition and its sensing properties were systematically studied under various conditions. The diameter and density of the Pd nanoparticles were optimized by tuning the deposition voltage and time. Using a microfabricated chip consisting of a circular array of 16 individually addressable Pd-functionalised nanosensors, the gas sensing performance for each nanosensor was evaluated sequentially via a customized multiplexer-coupled electronic measurement system with Labview program control. The sensing properties were optimized for high sensitivity and short response time with respect to hydrogen detection. Sensor formed from non-connected chains of Pd particles was found to exhibit excellent sensing properties with resistance change exceeding 60% in 2000 ppm of hydrogen and lowest detection limit of 30 ppm hydrogen. The response time increased from a few minutes to tens of minutes with decreasing hydrogen concentrations.

A low temperature hydrogen sensor based on palladium nanoparticles

Palladium nanoparticles were synthesized by employing Polyol solution chemistry technique. In this method ethylene glycol was used to reduce sodium tetrachloropalladate at 100°C in presence of polyvinylpyrrolidone (PVP) to yield ∼10nm sized particles, which was confirmed by transmission electron microscopy (TEM) studies. Thin films of the synthesized nanoparticles on glass substrates were characterized by glancing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM) to check crystallinity and surface morphology, respectively. Both TEM and GIXRD results support the faceted geometry of nanoparticles. Resistive sensor devices were fabricated with palladium films on glass substrates by laying fine silver paste lines in the form of interdigitated fingers. The hydrogen sensor studies at different temperatures (35–75°C) with gas concentrations (0.1–1%) in nitrogen revealed a dual response trend. The device resistance increased slightly and then decreased sharply upon exposure to hydrogen in nitrogen. Optimum response was obtained at 50°C, with response time (t90) of 3s in 1000ppm hydrogen in nitrogen. Similar studies in air showed only increase in resistance. The data reveal the decrease in response time with the decrease in hydrogen concentration, which is an optimistic result from application viewpoint. Detailed analysis of the results along with the selectivity studies has been presented.

Gas phase hydrogen absorption and electrochemical performance of La2(Ni,Co,Mg,M)10 based alloys

The effect of M = In or Al on the hydrogenation behavior of the La2(Ni,Co,Mg,M)10 alloys at room temperature is presented. The ceramic like samples have been prepared by powder metallurgy route using pure Mg- and the La2Ni9−xMx alloy powder precursors. XRD analysis revealed predominantly the CaCu5-type structure for all final alloys. Partial substitution of Co by In in La2Ni8MgCo causes a slight decrease of hydrogen concentration whereas Al addition increases this parameter. The highest hydrogen concentration of 1.87 wt.% has been reached for La2(Ni8Co0.8Al0.2)Mg composition at hydrogen pressure of 10 bar. Indium addition dramatically decreases the middle-plateau hydrogen equilibrium pressure from peq = 0.37 bar (In-free alloy) to peq = 0.06 bar (1.7 at.% In). The electrochemical performance of the studied materials has been characterized using chronoamperometric and chronopotentiometric techniques. The galvanostatic hydrogenation experiments at 185 mA/g discharge rate revealed the largest discharge current capacity of 355 mAh/g for La2(Ni8Co0.8Al0.2)Mg alloy. The relative diffusivity factor of hydrogen (D¯H/a2) varies for the tested materials in the range of (2.0–5.4)·10−5 s−1.

The Influence of Fluorinated Silicon Nitride Gate Insulator on Positive Bias Stability toward Highly Reliable Amorphous InGaZnO Thin-Film Transistors

For gate insulator of amorphous InGaZnO thin-film transistor, we fabricated fluorinated silicon nitride (SiN:F) film formed by an inductively-coupled plasma enhanced chemical vapor deposition method by utilizing SiF4/N2 as source gases. Threshold voltage shift against electrical stress was successfully suppressed. Chemical analysis revealed that the hydrogen concentration was reduced to 1/10 of conventional SiN film and fluorine was introduced into the interface between the SiN:F film and channel layer. We conclude that the decrease of hydrogen content and introduction of fluorine lead to decrease of electron trap density at the interface and/or the SiN:F film.