Formation Of Reaction Products Research Articles

Ab initio study of the reactivity of ultracold RbSr + RbSr collisions

We performed ab initio calculations in order to assess the reactivity of ultracold RbSr + RbSr collisions occurring on the singlet as well as the triplet potential. At ultracold energies reactions are energetically possible if they release energy, i.e., they are exoergic. The exoergicity of reactions between RbSr molecules producing diatomic molecules are known experimentally. We extend this to reactions producing triatomic molecules by calculating the binding energy of the triatomic reaction products. We find that, in addition to the formation of Rb2 + 2Sr and Rb2 + Sr2 in singlet collisions, also the formation of Sr2Rb + Rb and Rb2Sr + Sr in both singlet and triplet collisions is exoergic. Hence, the formation of these reaction products is energetically possible in ultracold collisions. For all exoergic reactions the exoergicity is larger than 1000 cm−1. We also find barrierless qualitative reaction paths leading to the formation of singlet Rb2 + 2Sr and both singlet and triplet Rb2Sr + Sr and Sr2Rb + Rb reaction products and show that a reaction path with at most a submerged barrier exists for the creation of the singlet Rb2 + Sr2 reaction product. Because of the existence of these reactions we expect ultracold RbSr collisions to result in almost-universal loss even on the triplet potential. Our results can be contrasted with collisions between alkali-diatoms, where the formation of triatomic reaction products is endoergic, and with collisions between ultracold SrF molecules, where during triplet collisions only the spin-forbidden formation of singlet SrF2 is exoergic.

Rheology and structural build-up of sodium silicate- and sodium hydroxide-activated GGBFS mixtures

Alkali-activated slag cements (AAS) are considered as an alternative to portland cement (PC) in many studies. A significant number of studies have focused on their mechanical and durability properties, but very few studies have concentrated on their rheological behavior. In this study, the effects of sodium silicate and sodium hydroxide on the rheological properties and structural build-up of alkali-activated GGBFS mixtures have been investigated. The sodium silicate-activated GGBFS mixtures exhibited a lower yield stress and a higher plastic viscosity than sodium hydroxide-activated GGBFS mixtures. The small-amplitude oscillatory shear (SAOS) tests indicated a negligible colloidal interaction between GGBFS particles in sodium silicate-activated system; therefore, the early increase in structuration was associated with the formation of reaction products due to the interaction between the dissolved calcium ions and the silicates originated from the activator solution. On the other hand, the stiffness and the early increase in structural build-up of sodium hydroxide-activated GGBFS system were attributed to the formation of well-percolated network.

Investigation of ultrasound-assisted soldering of SiC ceramics by using Zn-Al-In solder for high-temperature applications

PurposeThis study aims to investigate soldering of SiC ceramics by using Zn-Al-In-based solders and ultrasonic soldering. The focus was on the quality of soldered joints, examining the boundary of the solder/substrate joint and the strength of the fabricated joints. Moreover, the fractured surfaces of joints were assessed.Design/methodology/approachThe Zn-5Al base, which is considered for eutectic solder, was used in experiments. When manufacturing this solder, In was also added to at 1 Wt.%. The soldering of SiC substrates on a hot plate with ultrasonic assistance was performed.FindingsThe solder at room temperature consists of a primary segregated solid solution (Zn) and the binary eutectics (Zn) + (Al) with a high Al content and binary lamellar eutectic with a high Zn and In content non-uniformly distributed on the grain boundaries. The average tensile strength of the Zn5Al1In solder was 52 MPa. The ceramic material was wetted during soldering via reaction between the solder and the SiC substrate, with the formation of Al-Si reaction products. The thickness of the reaction layer on the boundary was 0.5–1.1 µm. The average strength of the soldered joint was 59 MPa. The obtained results confirmed the high efficiency of ultrasonic soldering in air.Originality/valueThis work has characterised Zn5Al1In soldering alloy and examining soldering SiC ceramics by a flux-less ultrasonic process. The analyses were oriented to assess the strength and structure of the solder and the soldered joints. Based on the achieved results, it is possible to predict the suitability of the solder alloy for flux-free soldering of SiC ceramics.

Identification and Quantitation of Reaction Products from Chlorogenic Acid, Caffeic Acid, and Their Thermal Degradation Products with Odor-Active Thiols in Coffee Beverages.

A holistic ultraperformance liquid chromatography (UPLC)-time of flight (TOF)-mass spectrometry-based approach was used to screen for storage-induced reaction products consisting of the volatile key coffee thiols methanethiol, 2-furfurylthiol, 2-methyl-3-furanthiol, 3-mercapto-3-methylbutanol, and 3-mercapto-2-butanone and low-molecular weight phenolic constituents of coffee beverages including chlorogenic acid, caffeic acid, and their thermal degradation products hydroxyhydroquinone, catechol, and 4-ethylcatechol. Multiple marker compounds could be detected in thiol-enriched coffee brews after UPLC-TOF-MS profiling and statistical data analysis. Subsequently, marker compounds were synthesized and structurally characterized via high-resolution mass spectrometry and 1D- and 2D-NMR experiments. Quantification of these reaction products in fresh and stored coffee beverages was realized in native coffee and after stir bar sorptive extraction with liquid desorption by means of UHPLC-MS/MS. The quantitative data revealed the biggest influence of storage time on the formation of reaction products between hydroxyhydroquinone and methanethiol and 2-furfurylthiol, while other reaction products were only slightly affected by storage and thus most likely formed during the roasting process.

Effects of sprouting and fermentation on the formation of Maillard reaction products in different cereals heated as wholemeal

The concentration and composition of reducing sugars and free amino acids as Maillard reaction (MR) precursors change with grain sprouting. The formation of early and advanced glycation products, and α-dicarbonyl compounds as intermediates were monitored during heating native and sprouted wholemeals, as well as during heating of yeast and sourdough fermented native and sprouted wholemeals. Sprouting increased the concentration of all MR products because of an increase in reducing sugar concentrations. Although reducing sugars were lowered due to their consumption by yeasts, fermentation did not lower the furosine concentration. Sourdough fermentation unexpectedly increased furosine because the low pH caused glucose release from polysaccharides. Glyoxal, methylglyoxal and diacetyl were found to be formed as metabolites during yeast and sourdough fermentation. Another factor affecting the MR in sprouted/fermented wholemeals was revealed to be the increased amount of total free amino acids that compete with bound lysine to react with reducing sugars.

Variation in mineral composition by hydration and carbonation in calcium hydroxide matrix containing zeolite

Natural zeolite can modify the mechanical properties of concrete as a supplementary cementitious material based on pozzolanic activity . However, the pozzolanic reaction is difficult to explain because of the formation of amorphous reaction products and the complexity of concrete systems. In this study, the mineral, amorphpus phase compositions and pozzolanic reaction mechanism of zeolite were further investigated by performing X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS NMR) analysis. Additionally, the pozzolanic activity of Ca(OH) 2 (CH)/zeolite (CHZ, 0–50 wt% proportions of zeolite) specimens was investigated after 1, 3, 7, and 28 d of hydration. The pozzolanic products were identified as C-(A)-S-H gel and monocarboaluminate (AFmc) mineral. Zeolite, having a 5 wt% proportion of CHZ specimens, completely reacted after 3 d of hydration. The optimal zeolite proportion for forming AFmc minerals in CHZ specimens after hydration (HCHZ) was 5 wt%. As the zeolite proportion increased beyond 20 wt%, [Al(OH) 4 ] - tended to react with [SiO(OH) 3 ] - to form aluminosilicate gel instead of AFmc. After carbonation curing (CO 2 concentration, 99%; gas pressure, 0.2 MPa; curing time, 2 h), the compressive strength of CHZ specimens (CCHZ) improved by 14–34% compared with that of pure CH specimens. An amorphous phase/calcite ratio of approximately 0.21 might produce an optimum strength resistance property in CCHZ. The heat released from the carbonation was beneficial for the polycondensation reaction of amorphous aluminosilicate to partially form Si[OSi] 4 or Al[OSi] 4 structures. • Pozzolanic products were identified as AFmc mineral and C-(A)-S-H gel by XRD and MAS NMR analysis. • The suitable zeolite proportion to form AFmc minerals in HCHZ specimens was 5 wt%. • In HCHZ20 to HCHZ50 specimens, [Al(OH) 4 ] - reacts with [SiO(OH) 3 ] - to form aluminosilicate gel. • Compressive strength of CCHZ specimens was 14–34% higher than that of pure CH specimens. • Minerals evolution of HCHZ and CCHZ specimens were quantified by QXRD and TGA techniques.

Feasibility of Hydrogen Production from Cellulose and Prediction of the Product Distribution: Thermodynamics Analysis

High carbon emissions, depleting fossil energy reserves have become a global problem. It is necessary to develop renewable energy sources that are environmentally friendly. Hydrogen (H2) is one of the energy sources and carriers that can be developed. This gas can be produced from renewable, sustainable, and economical resource such as biomass that contains cellulose as the main ingredient. This thermodynamic analysis of H2 production from cellulose is necessary as a theoretical study to determine the feasibility of the reaction. The computational thermodynamic was analyzed using Microsoft Excel 2019 and Matlab Program R2013a. Prediction of the equilibrium composition of the substances involved in the reaction was attempted by minimization Gibbs free energy change with Lagrange undetermined multipliers methods. As a result, the value of ΔHr0; ΔSr0 and ΔGr0 are +624,7500 kJ/mol; +2,1491 kJ/mol.K and; -26,1540 kJ/mol, respectively. Analysis of equilibrium constant of this conversion has a large ln K value (> 1). A negative ΔGr0 value and large ln K indicates that the formation of H2 from (C6H10O5)n is plausible and feasible and reaction product formation is strongly favored at equilibrium. The composition of the substances involved at 298 K from the largest to the smallest is CH4 (4.5 mol), H2O (3 mol), CO2 (1.5 mol), H2 (1.28×10-5 mol), HCOOH (5.85×10-10 mol), C6H12O6 (3.72×10-10 mol) and C6H12O5 (1.35×10-10 mol). Interestingly, H2 yield will rise significantly with the increase of reaction temperature. This preliminary study provides an overview of reaction conditions so that H2 production from biomass can be produced maximally.

Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash

This study presents the results of an experimental campaign on the use of municipal solid waste incinerator bottom ash (MIBA) and fly ash (FA) as precursors for the production of alkali-activated materials. MIBA was subjected to a pre-treatment stage in response to two issues: high metallic aluminum content, which reacts in a high pH solution, releasing hydrogen; and low amorphous content of silica-, aluminum- and calcium-bearing phases, which translates into a limited formation of reaction products. The proposed pre-treatment stage oxidizes most of the metallic aluminum fraction and compensates for the low reactivity of the material via the formation of additional reactants. Different combinations of MIBA and FA were tried—mass-based ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 for MIBA/FA. Two mix designs of the alkaline activator with sodium hydroxide and sodium silicate were evaluated by varying the Na2O/binder and SiO2/Na2O ratios. These mortars were tested in the fresh and hardened state. The results showed that the pre-treatment stage was effective at stabilizing the dimensional variation of MIBA. Despite the lower reactivity of MIBA, mortars with 50/50 of MIBA/FA presented a maximum 28-day compressive strength of 25.2 MPa, higher than the 5.7 MPa of mortars made with MIBA only.

A Thermodynamic Analysis of Glycerol Monostearate Production by Glycerolysis

Thermodynamic analysis was performed on the reaction producing glycerol monostearate (GMS) from glycerol and stearic acid to examine the reaction's feasibility. Generation of GMS by glycerolysis of glycerol with stearic acid or fatty acids is thermodynamically advantageous in accordance with the equilibrium constant, K. Thermodynamic analysis was carried out to determine the parameters that affect the glycerolysis reaction using MATLAB 2014A and Microsoft Excel 2013. The obtained values of ΔHro; ΔSroand ΔGro were + 45.69 kJ/mol; +1.144 kJ/mol.K and –1.074 kJ/mol. Equilibrium constants at 433.15 K, 453.15 K, and 473.15 K for this synthesis were favourable, at 5.76 x 1024, 1.43 x 1027 and 2.23 x 1029, respectively. The higher the temperature, the greater the value of ln K, which suggests a limitless equilibrium. The largest yield of the substances involved in the reaction was obtained at 473 K with C3H8O3 (0.2286 mol), C18H36O2 (0.0620 mol), C21H42O4 (0.4379 mol) and H2O (0.27131 mol). Negative ΔGro values for this reaction suggest that formation of glycerol monostearate (C21H42O4) was plausible and feasible, and the formation of reaction products at equilibrium was highly favoured. This prediction provides an overview of the reaction to ensure an optimal yield of glycerol monostearate.

Degradation and lifetime of self-healing thermal barrier coatings containing MoSi2 as self-healing particles in thermo-cycling testing

Yttria-stabilized zirconia (YSZ) is the state-of-the-art top coat material for thermal barrier coatings (TBCs) applied on highly loaded gas turbine parts. During operation at high temperatures, stresses are induced by the thermal expansion coefficient mismatch between the ceramic TBC and the metallic substrate. As a consequence cracks can grow, propagate and finally lead to a spallation of the top coat. Using atmospheric plasma spraying (APS), so-called self-healing MoSi2 particles can be incorporated into the YSZ matrix to mitigate the propagation of cracks leading to a lifetime gain and possibly higher temperature capability of the TBC. In the present work, the healing process is realized by the oxidation of the self-healing particles, which introduces a volume expansion by a formation of reaction products, which can seal the cracks. The self-healing particles were introduced within the first 150 μm of the YSZ coating matrix immediately on top of the bond coat. The degradation and lifetime of such systems were studied in furnace cycling and in burner rig tests, in which a temperature gradient through the sample was applied. The lifetime of the self-healing coatings was then compared to the lifetime of an YSZ coating without self-healing particles. In burner rig tests a clear lifetime extension of the self-healing TBCs was observed. The origin of this different behavior was investigated by microstructural analysis in scanning electron microscopy. A further insight into the failure mechanisms was gained by the analysis of a self-healing TBC cycled in a furnace cycling test only for about 55% of its expected lifetime.

Weathered bottom ash from municipal solid waste incineration: Alkaline activation for sustainable binders

• Alkali-activation of weathered bottom ash (WBA) and metakaolin (MK) was evaluated. • The increase in MK content leads to a generalised upward trend in porosity. • The synergistic combination of WBA and MK reduce the heavy metal(loid)s release. • The encapsulation effect increases as increase the curing period. Alkali-activated binders (AABs) stand out as promising candidates to replace ordinary Portland cement (OPC) since waste can be used as raw material for their manufacture. This study addresses the environmental feasibility of using weathered bottom ash (WBA) and metakaolin (MK) as alkali-activated binder precursors (AA-WBA/MK). Different proportions of WBA and MK were mixed (100/0, 75/25, 50/50, 25/75, and 0/100 wt%) with a mixture of waterglass (WG) and NaOH 8 M as an alkaline activator solution. The effect of increasing MK content was assessed from a chemical, physical, mechanical, and environmental perspective. The results revealed the formation of secondary reaction products of C-(A)-S-H, (C,N)-A-S-H, and N-A-S-H gels. The compressive strength of AA-WBA/MK binders decreased (from 61.6 MPa to 12.6 MPa) as the MK content increased. The monolithic tank test validated the use of AA-WBA/MK binders for construction purposes, although with some restrictions due to their content in As, Sb, and V. Finally, the encapsulation efficiency and mechanical performance of AA-WBA/MK binders was enhanced as the curing period increased.

A binder prepared by low-reactivity blast furnace slags for cemented paste backfill: Influence of super-fine fly ash and chemical additives

• SFA, AlS and CC were used to modify the properties of binder for CPB. • The hydration mechanism of the binder was found to be ‘NG-I-D’. • Enhanced property was due to refined pore structure and increased reaction gels. • Excess AlS delayed binder hydration. Alternative binders for cemented paste backfill (CPB) are necessary to be prepared considering the high cost and environmental footprint of ordinary Portland cement (OPC). This study focuses on the preparation of a binder using low-reactivity blast furnace slag (BFS). Superfine fly ash (SFA) and chemical additives (aluminum sulfate, AlS and carbide slag, CC) are used to modify the binder properties. Both SFA and chemical additives could promote the binder reaction with the formation of more reaction products. The pore structure was then refined; thereby higher compressive strength was observed. Krstulovic-Dabic (K-D) model was used to characterize the hydration process and all binders hydration mechanism was ‘NG-I-D’. The synergistic effect of SFA, AlS, and CC showed the best performance, the compressive strength of the CPB samples could reach 0.24 MPa and 2.73 MPa at 3 and 28 days using the optimal proportion. The excellent performance can be attributed to the physical and chemical effects of the coupling actions of SFA and chemical additives.

Contribution of Hydrolysis and Drying Conditions to Whey Protein Hydrolysate Characteristics and In Vitro Antioxidative Properties.

During the generation of functional food ingredients by enzymatic hydrolysis, parameters such as choice of enzyme, reaction pH and the drying process employed may contribute to the physicochemical and bio-functional properties of the resultant protein hydrolysate ingredients. This study characterised the properties of spray- (SD) and freeze-dried (FD) whey protein hydrolysates (WPHs) generated using Alcalase® and Prolyve® under pH-stat and free-fall pH conditions. The enzyme preparation used affected the physicochemical and antioxidative properties but had no impact on powder composition, morphology or colour. SD resulted in spherical particles with higher moisture content (~6%) compared to the FD powders (~1%), which had a glass shard-like structure. The SD-WPHs exhibited higher antioxidative properties compared to the FD-WPHs, which may be linked to a higher proportion of peptides <1 kDa in the SD-WPHs. Furthermore, the SD- and FD-WPHs had similar peptide profiles, and no evidence of Maillard reaction product formation during the SD processing was evident. The most potent in vitro antioxidative WPH was generated using Alcalase® under free-fall pH conditions, followed by SD, which had oxygen radical absorbance capacity and Trolox equivalent (TE) antioxidant capacity values of 1132 and 686 µmol TE/g, respectively. These results demonstrate that both the hydrolysis and the drying process impact the biofunctional (antioxidant) activity of WPHs.

On-line Electrode Dissolution Monitoring during Organic Electrosynthesis: Direct Evidence of Electrode Dissolution during Kolbe Electrolysis.

Electrode dissolution was monitored in real‐time during Kolbe electrolysis along with the characteristic products. The fast determination of appropriate reaction conditions in electro‐organic chemistry enables the minimization of electrode degradation while keeping an eye on the optimal formation rate and distribution of products. Herein, essential parameters influencing the dissolution of the electrode material platinum in a Kolbe electrolysis were pinpointed. The formation of reaction products and soluble platinum species were monitored during potentiodynamic and potentiostatic experiments using an electroanalytical flow cell coupled to two different mass spectrometers. The approach opens new vistas in the field of electro‐organic chemistry because it enables precise and quick quantification of dissolved metals during electrosynthesis, also involving electrode materials other than platinum. Furthermore, it draws attention to the vital topic of electrode stability in electro‐organic synthesis, which becomes increasingly important for the implementation of green chemical processes utilizing renewable energy.

Reaction Kinetics and Characterization of Slag-Based, High Strength, “Just-Add-Water” Type (One-Part) Alkali-Activated Binders

The influence of different levels of alkalinity, expressed using M2O-to-binder ratio (n) and activator SiO2-to-M2O ratio (Ms), (M being the Na+ or K+ cation) on the reaction kinetics, compressive strength development and the reaction product formation in slag-based systems activated using alkali powders are discussed. The fundamental idea is to better understand one-part, “just-add-water” type alkali activated binders that are easy-to-use than the systems that rely on liquid activators. The difference in the behavior of the systems with changes in the cationic species (Na+ or K+) and the overall levels of alkalinity is elucidated. Heat release and its rate, and thermal analysis and Fourier Transform Infrared Spectroscopy (FTIR) are used for the characterization of the reaction and the products formed. The influence of activator alkalinity on the initial dissolution and acceleration phases is examined using isothermal calorimetry. An increase in Ms is found to result in reduced early-age and slightly increased later-age compressive strengths. The activator cationic species influences later-age strengths, with K-silicate activated mortars showing a higher strength. The strength data is related to the C-(A)-S-H gel formation. The study shows that slag-based binders can be proportioned to obtained compressive strengths in excess of 80 MPa at later ages (56 days), and up to 30 MPa within 72 hours. The optimal alkali levels based on n and Ms for both the Na- and K-based activator systems are determined.

Characterization of mechanically activated fly ash-based lightweight geopolymer composite prepared with ultrahigh expanded perlite content

This study focused on the optimization of the production conditions of an ultrahigh expanded perlite lightweight aggregate-filled fly ash-based geopolymer composite and the determination of its product properties. The geopolymer matrix was synthetized using mechanically activated fly ash and an alkaline solution. In a systematic series of experiments, the effect of expanded perlite (EP) content, the compaction pressure and the compaction time on the mechanical properties of the lightweight composite were investigated. In the case of the optimal production conditions, the composites were characterized in terms of physico-mechanical properties, water absorption and microstructure. The composites produced under optimal conditions had an average uniaxial compressive strength of 246 kPa and density of 534 kg/m3 at 80% by volume EP content, and 264 kPa and 221 kg/m3 at 95% by volume EP content. Both the FT-IR spectroscopy and scanning electron microscopy results proved the formation of main geopolymerization reaction products in the matrix of the composite, as well its reaction with the lightweight aggregate.

Sustainable use of waste glass in alkali activated materials against H2SO4 and HCl acid attacks

This study examined the effect of using waste glass powder (GP) as a partial precursor in alkali activated mortars exposed to H2SO4 and HCl acid solutions for one year. The changes in physical appearance, surface alkalinity, mass, compressive strength and microstructure of the hardened samples after immersion in acid solutions were evaluated. The findings of the test program revealed that the inclusion of 10%–20% GP as a replacement of fly ash (FA) substantially reduced the physical, mechanical and microstructural damages of the specimens due to acid attack. This is attributed to the additional Si, Na and Ca ions provided by GP that enhanced the formation of reaction products and introduced a dense microstructure with reduced porosity. However, the use of GP content beyond 20% increase the availability of free Ca and porosity that led to considerable deterioration when exposed to the acid solutions.

Mechanical anisotropy evolution of 3D-printed alkali-activated materials with different GGBFS/FA combinations

The mechanical anisotropy of 3D-printing concrete is a crucial factor limiting the application of this technology. This study focuses on the evolutions of mechanical anisotropy and interlayer pore structure in the 3D-printed alkali-activated materials (3DPAAMs) with different precursors combinations of grounded granulated blast-furnace slag (GGBFS) and fly ash (FA), aiming to elucidate the relationship of mechanical anisotropy evolution and precursor selections. The pores generated by the printing process were quantitatively characterized with X-ray computed tomography (X-CT) tests using image processing methods. Results show that the mechanical anisotropy coefficient (IMechanical) of 3DPAAMs mitigates with the curing age since the formed reaction products fill the pores generated by the printing process. With the curing age extension from 3 to 28 days, the IMechanical of GGBFS-based 3DPAAMs decreased 51.1%, 60.9%, and 71.1% for compressive, flexural and split tensile strengths, respectively. Over-high FA incorporation (50 and 75%) yields lower mechanical strengths and aggravated anisotropy. Compared with GGBFS-based 3DPAAMs, the addition of 75% FA increases the IMechanical at 28 days by 274%, 236% and 274% for compressive, flexural and split tensile strengths, respectively. The low activation reactivity of FA and the higher thixotropy of FA-incorporated mixtures coarsen the interlayer pore structure, contributing to a higher mechanical anisotropy.

Changes in key aroma-active compounds and sensory characteristics of sunflower oils induced by seed roasting.

This study investigated the changes in aroma composition and perception of sunflower oils induced by seed roasting using sensory-oriented flavor analysis. Volatile compounds were extracted by solvent-assisted flavor evaporation and headspace solid-phase microextraction. Odorants were characterized by gas chromatography-olfactometry-mass spectrometry and aroma extract dilution analysis. The cold-pressed and roasted sunflower oils contained 13 and 50 odorants, respectively, with the flavor dilution factors between 1 and 256. Fifty-six odorants were newly identified in sunflower oils. Quantification of 26 important odorants by the external standard method revealed apparent changes induced by seed roasting in loss of terpenes, formation of Maillard reaction products, and the increase in lipid oxidation products. The most important odorants (odor active values, OAVs=1-1857) in the cold-pressed sunflower oil included α-pinene (11,145µg/kg), β-pinene (4068µg/kg), linalool (56µg/kg), hexanal (541µg/kg), octanal (125µg/kg), α-phellandrene (36µg/kg), and (E)-2-octenal (69µg/kg), contributing to the raw sunflower seed, woody, green, earthy, and sweet aromas of the oil. The most important contributors (OAVs=1-884) to the roasted, smoky, and burnt aromas of the roasted sunflower oil were 2- and 3-methylbutanal (6726 and 714µg/kg), 2,6-dimethylpyrazine (2329µg/kg), 2,5-dimethylpyrazine (12,228µg/kg), 2,3-dimethylpyrazine (238µg/kg), 2,3-pentanedione (1456µg/kg), 2-pentylfuran (1332µg/kg), 2,3-dimethyl-5-ethylpyrazine (213µg/kg), and 1-pentanol (693µg/kg). Aroma recombination of the key odorants in odorless sunflower oil adequately mimicked the general aroma profiles of sunflower oils. This study provides an important foundation for understanding the relationship between oil processing and aroma molecules of sunflower oils. PRACTICAL APPLICATION: The clear changes observed in the composition and concentrations of key aroma compounds explained the changes in sensory characteristics of sunflower seed oils induced by seed roasting on a molecular basis. Characterizing the key aroma-active composition of sunflower oil and investigating its relationship with oil processing could provide important practical applications for the sunflower oil industry in flavor regulation, quality control, product development, and process optimization.

Microstructure understanding of high Cr-Ni austenitic steel corrosion in high-temperature steam

The microstructure and microchemistry of the oxide scales formed on Fe-21Cr-32Ni and Fe-17Cr-9Ni steels after exposure to deaerated high-temperature high-pressure steam at 600 °C for 1500 h have been analysed and compared by several advanced characterization techniques. By comparing the oxide scales formed at different-stages of exposure, it is shown that Fe-21Cr-32Ni steel was internally oxidized at the early-stage, and then an external oxide scale was developed together with an inner chromia band under the internal oxidation zone. In comparison, Fe-17Cr-9Ni steel was internally oxidized together with an external Fe-rich oxide scale during the entire experimental period. The thicknesses of the internal oxidation zone of Fe-21Cr-32Ni and Fe-17Cr-9Ni steels were ∼7 and ∼70 µm, respectively. Further characterisation revealed that the internal oxidation zone contained (Cr, Fe, (Ni)) 3 O 4 and nanoscale nickel networks, together with numerous nano-pores. The effects of these structures on mass transfer and reaction product formation were discussed, in connection with the alloy composition and the formation of the chromia layer.