NOx and N2O precursors (NH3 and HCN) from biomass pyrolysis: Co-pyrolysis of amino acids and cellulose, hemicellulose and lignin

Nitrogen in biomass is mainly in forms of proteins (amino acids). Glycine, glutamic acid, aspartic acid, leucine, phenylalanine and proline are the major amino acids in agricultural straw. The six amino acids were pyrolyzed individually at 800 °C in a tubular reactor in an argon atmosphere. Each amino acid sample was then pyrolyzed individually with cellulose, hemicellulose or lignin with 1:1 mixing ratio by weight under the same condition. The emissions of HCN and NH₃ were detected with a Fourier transform infrared (FTIR) spectrometer. The extent of interaction between the amino acids with cellulose, hemicellulose or lignin was determined by comparing the yields of HCN and NH₃ from co-pyrolysis with those from single amino acid pyrolysis under the same condition. The results indicate that the structure of the amino acid has a significant effect on the nitrogen transformation during pyrolysis. The mixtures undergo solid-state decomposition reactions during co-pyrolysis. The extent of interaction between the amino acids with cellulose, hemicellulose or lignin depends on the amino acid types and the components in biomass. Although single proline and leucine form no char, they give a significant amount of nitrogen-containing char when co-pyrolyzed with cellulose, hemicellulose and lignin. HCN and NH₃ yields and nitrogen conversion pathway from amino acid pyrolysis are influenced by cellulose, hemicellulose and lignin.     

Secondary ion mass spectrometry and X-ray photoelectron spectroscopy studies on TiO2 and nitrogen doped TiO2 thin films

Anatase phase TiO₂ and nitrogen (N) doped TiO₂ thin films were synthesized by an ultrasonic spray pyrolysis technique on c-Si (100) substrates in the temperature range 300-550 °C. The former used a precursor solution of titanium oxy acetylacetonate in methanol whereas the later used a titanium oxy acetylacetonate hexamine mixture in methanol. Homogeneity across the film’s thickness and the nature of the film-substrate interface were studied by dynamic depth profiling acquired using secondary ion mass spectrometry SIMS. The stoichiometry and bonding state of various species present in the films were studied using X-ray photoelectron spectroscopy (XPS). N-doping was confirmed by both SIMS and XPS. XPS studies revealed that the nitrogen content of the films synthesized at 300 °C (3.2%) is high compared to that of films made at 350 °C (1.3%).     

Influence of TaCl5 partial pressure on texture structure of TaC coating deposited by chemical vapor deposition

TaC was deposited on graphite substrate with different TaCl₅ partial pressure at 800 °C and 1200 °C by chemical vapor deposition. Microstructures and texture structures of the prepared coatings were researched with X-ray diffraction and scanning electronic microscopy. When the coating deposition process is controlled by surface reaction kinetics (800 °C), TaCl₅ partial pressure had little influence on the microstructure and texture structure of the coating. When the coating formation process is controlled by diffusion kinetics (1200 °C), the microstructure, texture structure of the prepared TaC grains vary greatly with TaCl₅ partial pressure. In the diffusion controlled process, the increasing of TaCl₅ partial pressure will result in the changing of gas supersaturation, and then the occurrence of secondary nucleation, which is the main reason for the changing of coating morphology and texture structure. With the help of competitive growth in (1 0 0) and (1 1 1) directions, the formation mechanism of the different texture coatings are discussed in detail. In addition, a diffusion model of deposition species around step-edge-corner was also proposed to explain the growth mechanism of the texture coatings.     

Adsorption and desorption of dibenzothiophene on Ag-titania studied by the complementary temperature-programmed XPS and ESR

Adsorption, desorption and structure of the surface chemical compounds formed upon interaction of dibenzothiophene (DBT) in solution of n-octane with the sulfur-selective Ag/Titania sorbent for the ultradeep desulfurization of liquid fuels was characterized by the temperature-programmed X-ray photoemission spectroscopy (XPS) and Electron Spin Resonance. Adsorption of DBT proceeds via chemisorption via the oxygen-containing surface groups. Desorption of DBT and thermal regeneration of the “spent” Ag/Titania were studied by the complementary temperature-programmed XPS and ESR from 25 °C to 525 °C, in the high vacuum vs. air. The XPS spectrum of the pure DBT is reported for the first time.     

Effect of cellulose–lignin interactions on char structural changes during fast pyrolysis at 100–350 °C

This study investigates the cellulose–lignin interactions during fast pyrolysis at 100–350 °C for better understanding fundamental pyrolysis mechanism of lignocellulosic biomass. The results show that co-pyrolysis of cellulose and lignin (with a mass ratio of 1:1) at temperatures < 300 °C leads to a char yield lower than the calculated char yield based on the addition of individual cellulose and lignin pyrolysis. The difference between the experimental and calculated char yields increases with temperature, from ～2% 150 °C to ～6% at 250 °C. Such differences in char yields provide direct evidences on the existence of cellulose–lignin interactions during co-pyrolysis of cellulose and lignin. At temperatures below 300 °C, the reductions in both lignin functional groups and sugar structures within the char indicate that co-pyrolysis of cellulose and lignin enhances the release of volatiles from both cellulose and lignin. Such an observation could be attributed to two possible reasons: (1) the stabilization of lignin-derived reactive species by cellulose-derived reaction intermediates as hydrogen donors, and (2) the thermal ejection of cellulose-derived species due to micro-explosion of liquid intermediates from lignin. In contrast, at temperatures ≥ 300 °C, co-pyrolysis of cellulose and lignin increases char yields, i.e., with the difference between the experimental and calculated char yields increasing from ～1% at 300 °C to ～8% at 350 °C. The results indicate that the cellulose-derived volatiles are difficult to diffuse through the lignin-derived liquid intermediates into the vapor phase, leading to increased char formation from co-pyrolysis of cellulose and lignin as temperature increases. Such an observation is further supported by the increased retention of cellulose functional groups in the char from co-pyrolysis of cellulose and lignin.     

Surface analysis of heat-treated Mong Hsu rubies

Mong Hsu rubies have been heat treated in air at 1100, 1200, 1300, 1400, 1500 and 1600 °C. Their visual appearance and surface analysis (XPS) after each stage of heating have been monitored. The characteristic blue core regions of untreated ruby become slightly faded at 1100 °C and completely disappear at temperatures above 1500 °C. Trace amounts of Na, Ca, Si and Fe were found on the surface of untreated stones. Ti was first detected after heating to 1100 °C. Plots of detected surface concentrations of elements versus temperature show that the highest concentration of Fe occurred at 1300 °C while surface concentrations of Ti appeared to show two maxima near 1300 and 1500 °C. The results suggest that both the changing oxidation state of Fe²⁺ to Fe³⁺ and the diffusion of the Fe and Ti ions with temperature are responsible for the color changes through decreasing Fe²⁺ to Ti⁴⁺ charge transfer.     

The sodium diffusion in aluminium-oxide

The transport of Na through the polycrystalline ceramic arc tube of high intensity discharge lamps has been investigated. This complex process consists of several steps: solution in the ceramics, diffusion through the ceramics, leaving the bulk phase, evaporation from the surface. Among the listed processes the kinetics of the diffusion was examined in the temperature range 400-1200 °C, separately from other disturbing effects. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used to determine the concentration depth profiles. The obtained results confirmed that the grain boundary diffusion plays an important role in the transport process of sodium through the ceramic wall. The bulk and the grain boundary diffusion coefficients and the temperature dependencies of these transport processes have been determined. The activation energy of Na bulk diffusion is 56.5 ± 6.7 kJ/mol at 900-1200 °C, respectively the activation energies of Na grain boundary diffusion amount to 97.5 ± 21.6 kJ/mol in the temperature range 700-1100 °C and 7.7 ± 4.0 × 10⁻² kJ/mol at 400-700 °C. The preexponential factor of the bulk diffusion was found to be D_o = 5.1 × 10⁻¹⁵ ± 9.5 × 10⁻¹⁷ cm²/s in the temperature range 900-1200°C, whereas the preexponential factors of grain boundary diffusion are D_o = 1.1 × 10⁻¹⁰ ± 1.1 × 10⁻¹¹ cm²/s at 700-1100 °C and D_o = 7.5 × 10^-15 ± 1.5 × 10⁻¹⁷ cm²/s at 400-700 °C.     

X-ray photoelectron spectroscopy study of pyrolytically coated graphite platforms submitted to simulated electrothermal atomic absorption spectrometry conditions

The present work is part of an ongoing project aiming to a better understanding of the mechanisms of atomization on graphite furnace platforms used for electrothermal atomic absorption spectrometry (ETAAS). It reports the study of unused pyrolytic graphite coated platforms of commercial origin, as well as platforms thermally or thermo-chemically treated under simulated ETAAS analysis conditions. X-ray photoelectron spectroscopy (XPS) was employed to study the elements present at the surfaces of the platforms. New, unused platforms showed the presence of molybdenum, of unknown origin, in concentrations up to 1 at.%. Species in two different oxidations states (Mo⁶⁺ and Mo²⁺) were detected by analyzing the Mo 3d spectral region with high resolution XPS. The analysis of the C 1s region demonstrated the presence of several signals, one of these at 283.3 eV related to the presence of Mo carbide. The O 1s region showed also various peaks, including a signal that can be attributed to the presence of MoO₃. Some carbon and oxygen signals were consistent with the presence of CO and C-O- (probably C-OH) groups on the platforms surfaces. Upon thermal treatment up to 2900 °C, the intensity of the Mo signal decreased, but peaks due to Mo oxides (Mo⁶⁺ and Mo⁵⁺) and carbide (Mo²⁺) were still apparent. Thermo-chemical treatment with 3 vol.% HCl solutions and heating up to 2900 °C resulted in further diminution of the Mo signal, with complete disappearance of Mo carbide species. Depth profiling of unused platforms by Ar⁺ ion etching at increasing time periods demonstrated that, upon removal of several layers of carbonaceous material, the Mo signal disappears suggesting that this contamination is present only at the surface of the pyrolytic graphite platform.     

Thermal oxidation temperature dependence of 4H-SiC MOS interface

The thermal oxidation temperature dependence of 4H-silicon carbide (SiC) is systematically investigated using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. When SiC is thermally oxidized, silicon oxycarbides (SiC_xO_y) are first grown and then silicon dioxide (SiO₂) is grown. It is identified by XPS that the SiO₂ films fall into two categories, called SiC-oxidized SiO₂ and Si-oxidized SiO₂ in this paper. The products depend on thermal oxidation temperature. The critical temperature is between 1200 and 1300 °C. The interface trap density (D_it) of the sample possessing Si-oxidized SiO₂, at thermal oxidation temperature of 1300 °C, is lower than SiC-oxidized SiO₂ at and below 1200 °C, suggesting that a decrease of the C component in SiO₂ film and SiO₂/SiC interface by higher oxidation temperature improves the metal-oxide-semiconductor (MOS) characteristics.     

Oxidation kinetics of thin copper films and wetting behaviour of copper and Organic Solderability Preservatives (OSP) with lead-free solder

The oxide formation on thin copper films deposited on Si wafer was studied by XPS, SEM and Sequential Electrochemical Reduction Analysis SERA. The surfaces were oxidized in air with a reflow oven as used in electronic assembly at temperatures of 100 °C, 155 °C, 200 °C, 230 °C and 260 °C. The SERA analyses detected only the formation of Cu₂O but the XPS analysis done for the calibration of the SERA equipment proved also the presence of a CuO layer smaller than 2 nm above the Cu₂O oxide. The oxide growth follows a power-law dependence on time within this temperature range and an activation energy of 33.1 kJ/mol was obtained. The wettability of these surfaces was also determined by measuring the contact angle between solder and copper substrate after the soldering process. A correlation between oxide thickness and wetting angle was established. It was found that the wetting is acceptable only when the oxide thickness is smaller than 16 nm. An activation energy of 27 kJ/mol was acquired for the spreading of lead free solder on oxidized copper surfaces.From wetting tests on copper surfaces protected by Organic Solderability Preservatives (OSP), it was possible to calculate the activation energy for the thermal decomposition of these protective layers.