Thermal Treatment Of Samples Research Articles

A simple model for vacancy order and disorder in defective half-Heusler systems.

Defective half-Heusler systems X 1-x YZ with large amounts of intrinsic vacancies, such as Nb1-x CoSb, Ti1-x NiSb and V1-x CoSb, are a group of promising thermoelectric materials. Even with high vacancy concentrations they maintain the average half-Heusler crystal structure. These systems show high electrical conductivity but low thermal conductivity arising from an ordered YZ substructure, which conducts electrons, while the large amounts of vacancies in the X substructure effectively scatters phonons. Using electron scattering, it was recently observed that, in addition to Bragg diffraction from the average cubic half-Heusler structure, some of these samples show broad diffuse scattering indicating short-range vacancy order, while other samples show sharp additional peaks indicating long-range vacancy ordering. Here it is shown that both the short- and long-range ordering can be explained using the same simple model, which assumes that vacancies in the X substructure avoid each other. The samples showing long-range vacancy order are in agreement with the predicted ground state of the model, while short-range order samples are quenched high-temperature states of the system. A previous study showed that changes in sample stoichiometry affect whether the short- or long-range vacancy structure is obtained, but the present model suggests that thermal treatment of samples should allow controlling the degree of vacancy order, and thereby the thermal conductivity, without changes in composition. This is important as the composition also dictates the amount of electrical carriers. Independent control of electrical carrier concentration and degree of vacancy order should allow further improvements in the thermoelectric properties of these systems.

Effect of T6 Treatment on Wear Behavior of Al-7Si/ ZrSiO4 Composites

The effect of thermal treatment on microstructure and tribological behavior of Al-7Si/ZrSiO4 reinforced composites has been investigated. Composites with 5, 10 and 15 vol.% of ZrSiO4 particles were produced using stir casting process. Produced composite samples were then further subjected to T6 heat-treatment by subjecting the cast samples for solution treatment for 4 h at 540 °C followed quenching in water and artificial ageing at 170 °C for 5 h. Microstructure of the composite samples revealed uniform distribution of ZrSiO4 particles. Hardness of the T6 thermal treated samples was found to be superior to that of Al-7Si alloy and hardness of the composite samples increased with increase in wt.% of ZrSiO4 particles. Non heat treated alloy and composite reinforced with 15 wt% of ZrSiO4 possessed a maximum hardness of 68 BHN and 110 BHN respectively. Whereas T6 heat treated Al-7Si alloy and composite reinforced with 15 wt% of ZrSiO4 exhibited a maximum hardness of 84 BHN and 146 BHN respectively. T6 treated composites exhibited superior resistance to wear, when compared to the base alloy. As cast Al-7Si alloy exhibited maximum wear rate of 14.3 × 10−3 mm3/m, where as non heat treated 15 wt.% ZrSiO4 reinforced composites exhibited a wear rate of 7.6 × 10−3 mm3/m and wear rate was found to further reduce to 4.0 × 10−3 mm3/m by T6 treatment. SEM images of the wear tested samples showed the adhesive wear and abrasive wear as the dominant wear mechanisms.

Electron-microscope investigations of the Pt-Si system during its rapid thermal treatment

The paper is dedicated to investigation of the influence of rapid thermal treatment on the microstructure of platinum silicide. The Pt films 43.7 nm thick were applied on the substrates of the monocrystal silicon by means of the magnetronic sputtering of platinum with the purity of 99.95 % on the МРС 603 set-up with the cryogenic pumping to the pressure not worse than 5*10-5 Pa. As an operating medium, argon was used with the purity of 99.933 %. Rapid thermal treatment of samples was performed in the thermal balance conditions by irradiating the non-working side of the wafer with the incoherent light flow in the nitrogen atmosphere during 7 s at the temperatures of 200-550 °C. The irradiation source in the set-up was represented by the quartz halogen incandescent lamps. The comparative analysis was done through the traditional long thermal treatment of the platinum films at a temperature of 550 о С for 30 min in the nitrogen atmosphere. Investigations of the platinum silicide microstructure were performed by means of the transmission electron microscopy which demonstrated that the increase in the RTT temperature initiates first the annealing of defects on the inter-grain boundaries, which is evident from the more distinct contrast from the grains, and then one can observe their growth reflecting the forming of the new phase (silicide one). Such progress of changes of the platinum silicide microstructure and of the size of the grains with the increase in treatment temperature is determined by the heat of its forming. As the Pt2Si phase forming heat is minimum and constitutes 10.4-16.8 Kkal/atom of metal, and for PtSi - 15.7-25.5 Kkal/atom of metal, then the forming of a stable PtSi structure requires a higher temperature. The authors carried out calculations of the activation energy of the diffusion synthesis of platinum silicide during rapid thermal treatment. The calculations show that it is 0.37 eV smaller, than during the long thermal treatment. This means that in this case this process is subject to acceleration related to the rupture of the silicon-silicon bonds and electron excitation in silicon under the influence of the photon flow.

Effect of pulsed electric field and thermal treatments on the bioactive compounds, enzymes, microbial, and physical stability of almond milk during storage

This study was designed to examine the impact of thermal treatment (TT) and pulsed electric field (PEF) on the overall quality of almond milk. The storage study showed a reduction in bioactive compounds and antioxidant activities with periods, while PEF-treated almond milk exhibited a higher amount than untreated and TT samples. PEF and TT improved the product microbial shelf-life during storage. Lipoxygenase and peroxidase of the PEF-treated sample at 28 kV/cm were inactivated by 50% and 45%, respectively; whereas TT achieved 59% and 68%, respectively. The less color variation was observed in PEF-treated samples than TT. The colloidal stability was significantly increased as a result of particle size and sedimentation index reduction after the PEF treatment. Results showed an increase in free amino acid production with increasing after PEF processing, while the fatty acids profile did not change significantly. Furthermore, the processing treatments did not significantly change the pH, soluble solids, and acidity values. Practical applications Nowadays, different non-thermal techniques are used to enhance the nutritional quality and stability of different fruits and vegetable juices. The present research showed that pulsed electric field (PEF) could enhance the bioactive compounds, antioxidant activities, colloidal stability, and free amino acid, while reducing the activity of the enzyme and microbial load. The results of this research proposed that the PEF can enhance the quality of almond milk and may be applied at an industrial scale.

Effect of Temperature on the Composition of a Synthetic Hydrocarbon Aviation Lubricating Oil.

Synthetic hydrocarbon aviation lubricating oils (SHALOs) gradually degrade over time when subjected to high temperatures, resulting in their composition and properties varying over the operation lifetime. Therefore, understanding the SHALO degradation properties by elucidating the mechanism on a molecular level, as a function of high temperature, is of interest. A SHALO was subjected to thermal treatment (TT) at 180, 200, 230, 250, 270, or 300 °C for 2 h. The chemical compositions of six TT samples and one fresh oil were analyzed by fourier transform infrared F spectroscopy, advanced polymer chromatography, and gas chromatography/mass spectrometry. Furthermore, the physicochemical properties, such as kinematic viscosity, pour point, and acid number, of seven samples were determined. The oil samples were grouped by cluster analysis (CA) using a statistical method. The SHALO was identified to comprise 20 functional groups, including comb-like alkanes, long-chain diesters, amines, phenols, and other compounds. TT at <230 °C caused partial cracking of the SHALO base oils, with a concomitant change in the antioxidant content and type, and the polycondensation reactions were dominant. The observed antioxidant changes were not obvious from TT at >230 °C. A large number of small-molecule compounds were detected, including n-alkanes and olefins. TT at 250 °C was shown to be an important threshold for the kinematic viscosity, pour point, and acid number of the samples. Below 250 °C, the sample properties were relatively stable; but at elevated TT temperatures (>250 °C), the properties were observed to dramatically degrade. As the sample color was highly sensitive to temperature, the TT temperature induced rapid and significant color changes. The CA analysis results for the oil compounds at the molecular level were in good agreement with observed changes in the physicochemical properties at the macro level.

High-Pressure Processing of Sugarcane Juice (Saccharum officinarum) for Shelf-Life Extension During Ambient Storage

Freshly extracted sugarcane juice was subjected to high-pressure treatment (HPP) at 523 MPa/50 °C/11 min and thermal treatment at 90 °C/5 min and studied for changes in physicochemical, enzymatic, nutritional qualities and microbial load during 30 days of storage at ambient temperature. Results showed that significant changes were recorded in HPP treated juice in terms of color, antioxidants and phenolic content; however, the change was substantially low when compared to thermal treated samples, thus indicating that HPP treated sugarcane juice can better retain quality parameters. During storage, the total color difference increased significantly in both HPP and TP samples. HPP of sugarcane juice resulted in inactivation of 64% of polyphenol oxidase and 58% of peroxidase enzyme, whereas the corresponding values recorded for thermal were 85% and 75%, respectively. The residual activity of these enzymes decreased during storage. The loss in ascorbic acid was observed to be 11% in HPP treated samples, whereas it was 25% in TP samples. The vegetative microorganism present in the juice was below the detection limit (1 log CFU/mL) up to 25 days. The study indicated that the shelf-life of HPP and TP samples stored at 25 °C was estimated to be 25 and 10 days, respectively, based on sensory qualities, ascorbic acid retention and total color difference. Thus, HPP has a potential to develop packed ready-to-drink sugarcane juice and enhances for its commercialization.

Polymorphism in Sulfanilamide: 14N Nuclear Quadrupole Resonance Study

To demonstrate the selectivity of 14N nuclear quadrupole resonance (14N NQR) spectroscopy in chemistry and pharmacy, a study of sulfanilamide polymorphism was undertaken. We studied 3 known polymorphs of sulfanilamide by 14N NQR. We found at room temperature 2 sets of 3 14N NQR transition frequencies, corresponding to 2 different nitrogen sites in the crystal structure for each of 3 polymorphs. We measured the temperature dependence of all quadrupole frequencies ν+, ν−. In each set, only 1 of the 3 14N NQR frequencies is enough to characterize the polymorph. Spin-lattice relaxation time (T1) measurement is supplemental information. We also measured the transition temperature between polymorphs and estimated the ratio of polymorphs after thermal treatment of sample.

Effective Strategy for Improving the Dielectric Strength and Insulation Lifetime of LLDPE

The voltage stabilizers can effectively improve DC breakdown strength of polyolefin, but its precipitation from polymer matrix inhibits its application. To address this problem, we prepared a reactive voltage stabilizer 4-acryloxy acetophenone (AAP) and employed a simple strategy of grafting it onto the LLDPE backbone to maintain polyolefin at a high DC breakdown strength level for a long time. The DC breakdown strength of thermal-treated samples at 60 °C for different periods was measured. It was found that the grafting samples performed much higher DC breakdown strength than that of neat LLDPE and blending samples after accelerated migration at 60 °C. SEM images demonstrated lower AAP precipitation on the surface of grafting samples. The purified grafting samples also exhibited high DC breakdown strength, which means the AAP can be maintained via grafting onto strategy. Meanwhile, the rheological results showed good processability of the grafting samples.

Thermoanalytical study and crystallization of Ba(PO3)2–WO3 glasses

Barium phosphate glasses of the composition (100 − x)Ba(PO3)2–xWO3 with 0–60 mol% WO3 were prepared and studied. Thermal studies of the glasses were carried out with DTA, dilatometry and hot-stage microscopy. Glass transition temperature in this glass series increases with increasing WO3 content from 461 °C (x = 0) to 623 °C (x = 60). Most glasses containing WO3 crystallize on heating within the range of 650–750 °C with the exception of glasses with 20–30 mol% WO3, which are thermally stable. Very high chemical durability of these glasses with dissolution rate of 1.4 × 10−8–6.2 × 10−9 g cm−2 min−1 was also revealed. Crystallization of glasses revealed the existence of a new compound Ba(WO2)2(PO4)2 in the studied compositional series. The compound Ba(WO2)2(PO4)2 possess hexagonal unit cell of dimensions a = 11.5191(1) A and c = 6.3437(1) A, and its melting point is 936 °C. Raman spectra of crystallized glasses confirmed the formation of crystalline compound in this glass series and revealed the presence of glass phase in some thermal-treated samples. 31P MAS NMR showed on only one coordination of phosphorus atoms in the Ba(WO2)2(PO4)2 compound.

Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO₂ under Various Atmospheres.

In this report, the photocatalytic activity of P25 has been explored and the influence of thermal treatment under various atmospheres (air, vacuum and hydrogen) were discussed. The samples’ characteristics were disclosed by means of various instruments including X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and UV–vis. This study also accentuates various states of the oxygen vacancy density formed inside the samples as well as the colour turning observed in treated P25 under various atmospheres. Produced coloured TiO2 samples were then exploited for their photocatalytic capability concerning photodegradation of methylene blue (MB) using air mass (AM) 1.5 G solar light irradiation. Our findings revealed that exceptional photocatalytic activity of P25 is related to the thermal treatment. Neither oxygen vacancy formation nor photocatalytic activity enhancement was observed in the air-treated sample. H2-treated samples have shown better photoactivity which even could be further improved by optimizing treatment conditions to achieve the advantages of the positive role of oxygen vacancy (O-vacancy at higher concentration than optimum acts as electron trapping sites). The chemical structure and stability of the samples were also studied. There was no sign of deteriorating of O2-vacancies inside the samples after 6 months. High stability of thermal treated samples in terms of both long and short-term time intervals is another significant feature of the produced photocatalyst.

FTIR analysis of thermal and plasma treatments on riceberry brown rice

Riceberry brown rice (RB) is known as source for valuable nutrients. Recently our group has used plasma treatment on RB to effectively shorten their cooking time and soften their texture. During the plasma treatment, rice was also subject to elevated temperature. This sometimes has led to confusion whether the thermal effect dominate. In this study, we have carried on these issues by using Fourier Transform Infrared spectroscopy (FTIR) to follow changes in vibrational characteristics of RB after being plasma treated. The plasma treatment was performed using a low-pressure inductively coupling argon plasma system. This is done in comparison to conventional thermal treatment at 45°, 60°, and 75°C for 120 minutes. The O-H stretching group was found to increase in the plasma treated samples; while decreasing in all the other thermal treated samples. The decrement has varied monotonically with temperature. There is also significantly increasing of C-O-C skeletal mode of α-glycosidic linkage, C-O-H bonding, and C-O-C asymmetric stretching glycosidic bonds in the plasma treated samples; while the decrement was observed in the thermal treated samples. This is understood as a consequence of cross-linking effect; leading to increase in glycosidic bonds along with H2O abstraction during the plasma treatment. It can be concluded that the plasma treatment has caused more inclusive effects which cannot be accounted for by the action of the thermal treatment alone.

INFLUENCE OF MICROSPHERIC CATALYST HEAT TREATMENT ON THE STRUCTURE AND CATALYTIC PROPERTIES

Oktifine 480P catalyst, containing catalytic additives, is used on refineries in Ufa to boost light olefin production and increase gasoline octanes in the Fluid Catalytic Cracking (FCC) process. Under the hydrothermal conditions present in the FCC regenerator (typically > 700 oC and > 8 % steam), FCC catalysts partly deactivates. Zeolite undergoes to dealumination and partial structural collapse, thereby losing activity, micropore surface area, and has changes in selectivity. Fresh catalyst are added at appropriate respective levels to the FCC unit to keep overall targeted steady state activity and selectivity. To pin down change rate of the structure and catalytic properties of the catalyst after heat treatment a number of studies were done. For research, microspheric catalyst Oktifine 480P, produced on Ishimbay Specialized Chemical Plant of Catalysts, was exposed to thermal treatment under 700 oС, 760 oС, 800 oС temperatures. ASTM D3907 standard feed was used for micro-activity cracking testing at 480 oС. Fresh catalyst Oktifine 480P was very active at vacuum gasoil cracking, micro-activity was estimated to 90,3 %. The micro-activity of heat treated samples were slowly decreasing by temperature increasing but still very high to compare with micro-activity of equilibrated sample of catalyst. So micro-activities for thermal treated samples under 700 oС, 760 oС, 800 oС were respectively 87,5 %, 85,2 %, 84 %, 85 % and micro-activity of equilibrated sample of catalyst was 42,4 %.

Effective microstructure unit in control of impact toughness in CGHAZ for high strength bridge steel

The high strength bridge steel was processed with the simulated coarse grain heat affected zone (CGHAZ) thermal cycle with heat input varying from 30 to 60 kJ/cm, the microstructures were investigated by means of optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD) and transmission electron microscope (TEM), and the impact properties were evaluated from the welding thermal cycle treated samples. The results indicate that the microstructure is primarily composed of lath bainite. With decreasing heat input, both bainite packet and block are significantly refined, and the toughness has an increasing tendency due to the grain refinement. The fracture surfaces all present cleavage or fracture for the samples with different heat inputs. Moreover, the average cleavage facet size for the CGHAZ is nearly equal to the average bainite packet size and the bainitic packet boundary can strongly impede the crack propagation, indicating that the bainitic packet is the most effective unit in control of impact toughness in the simulated CGHAZ of high strength bridge steel.

Characterisation of an Al-BN nanocomposite prepared by ball milling and hot extrusion

Aluminium-matrix-nanocomposites were manufactured by ball milling of microscale aluminium powder with BN nanoparticles in air, followed by subsequent consolidation by hot extrusion. The microstructure of the samples was studied using scanning electron microscopy. Vickers microhardness measurements were used to probe the mechanical properties of the samples. The amplitude dependent damping of the nanocomposites was measured at room temperature after thermal treatment of samples, and the linear thermal expansion was measured over a wide temperature range from room temperature up to 670K in the as-extruded state. The experimental results give a comprehensive picture of the behaviour of this nanocomposite system over the range of thermomechanical treatment conditions examined in this study. Based on these experimental data some possible influences of BN nanoparticles on the anelastic, plastic and thermal properties of microcrystalline aluminium are discussed.

Effect of high hydrostatic pressure processing and squeezing pressure on some quality properties of pomegranate juice against thermal treatment

ABSTRACTThe aim of this study was to investigate the effect of high hydrostatic pressure (HHP) treatment (200, 300, 400 MPa; 5°C, 15°C and 25°C; 5 and 10 min) on some quality properties of pomegranate juice. Juice samples are obtained under industrial conditions at two different squeezing pressure levels (100 and 150 psi – 0.689 and 1.033 MPa, respectively). Results are compared against conventional thermal treatment (85°C/10 min) and raw sample. For all three processing temperature, HHP combinations at 400 MPa for 10 min were sufficient to decrease the microbial load around 4.0 log cycles for both squeeze levels. All HHP treatments showed no significant decrease at antioxidant activity, total phenolic content and monomeric anthocyanin pigment concentrations, while there was a significant decrease (p ≤ .05) in thermal-treated samples. Being the highest sugar alcohol in pomegranate juice, mannitol content must be considered for determining the authenticity, and mannitol content increased with squeezing pressure and thermal treatment.

The Role of the Bainitic Packet in Control of Impact Toughness in a Simulated CGHAZ of X90 Pipeline Steel

X90 pipeline steel was processed with the simulated coarse grain heat affect zone (CGHAZ) thermal cycle with heat input varying from 30 kJ/cm to 60 kJ/cm, the microstructures were investigated by means of optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM), and the impact properties were evaluated from the welding thermal cycle treated samples. The results indicate that the microstructure is primarily composed of lath bainite. When decreasing the heat input, both bainite packet and block are significantly refined, and the toughness has an increased tendency due to the grain refinement. The fracture surfaces all present cleavage fracture for the samples with different heat inputs. Moreover, the average cleavage facet size for the CGHAZ is nearly equal to the average bainite packet size, and the bainitic packet boundary can strongly impede the crack propagation, indicating that the bainitic packet is the most effective unit in control of impact toughness in the simulated CGHAZ of X90 pipeline steel.

Preservation of bioactive compounds of a green vegetable smoothie using short time-high temperature mild thermal treatment.

Smoothies represent an excellent and convenient alternative to promote the daily consumption of fruit and vegetables in order to obtain their health-promoting benefits. Accordingly, a green fresh vegetables smoothie (77.2% cucumber, 12% broccoli and 6% spinach) rich in health-promoting compounds was developed. Soluble solids content, pH and titratable acidity of the smoothie were 4.3 ± 0.4°Bx, 4.49 ± 0.01 and 0.22 ± 0.02 mg citric acid 100-1 g fw, respectively. Two thermal treatments to reduce microbial loads and preserve quality were assayed: T1 (3 min at 80 ℃) and T2 (45 s at 90 ℃). Fresh blended unheated samples were used as control (CTRL). The smoothie presented a viscoelastic behaviour. T1 and T2 treatments reduced initial microbial loads by 1.3-2.4 and 1.4-3.1 log units, respectively. Samples were stored in darkness at 5 and 15 ℃. Colour and physicochemical changes were reduced in thermal-treated samples throughout storage, which were better preserved at 5 ℃ rather than at 15 ℃. Vitamin C changes during storage were fitted with a Weibullian distribution. Total vitamin C losses of T1 and T2 samples during storage at 15 ℃ were greatly reduced when they were stored at 5 ℃. Initial total phenolic content (151.1 ± 4.04 mg kg-1 fw) was 44 and 36% increased after T1 and T2 treatments, respectively. The 3-p-coumaroyl quinic and chlorogenic acids accounted the 84.7 and 7.1% relative abundance, respectively. Total antioxidant capacity (234.2 ± 20.3 mg Trolox equivalent kg-1 fw) remained constant after the thermal treatments and was better maintained during storage in thermal-treated samples. Glucobrassicin accounted the 81% of the initial total glucosinolates content (117.8 ± 22.2 mg kg-1 fw) of the smoothie. No glucosinolates losses were observed after T2 treatment being better preserved in thermal-treated samples. Conclusively, a short time-high temperature mild thermal treatment (T2) showed better quality and bioactive compounds retention in a green fresh vegetable smoothie during low temperature storage.

Bioactive Titanium Oxide Coatings Fabricated on NiTi SMA via Thermal Treatment for Medical Applications

To enhance the biocompatibility, bioactivity and mechanical properties of NiTi shape memeory alloy (SMA), titanium oxide coatings were fabricated via thermal treatments at 400 and 600°C, respectively. The surface morphology, elemental distribution and phase composition of the untreated and thermal treated samples were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), respectively. The comparative study was carried out for the thermal treated samples at different temperatures in terms of surface Ni content and bioactivity, then the optimal temperature of the thermal treatment was obtained.

INFLUENCE OF SPECIFIC THERMAL TREATMENT ON YOUNG'S MODULUS CHANGES IN A NATURAL RUBBER–BASED COMPOUND: STUDY BY AFM NANOINDENTATION

ABSTRACT The determination and study of Young's modulus at the nanometric scale in an efficient and fast way is carried out using atomic force microscopy (AFM) in contact mode. The aim of this study is to evaluate the impact of a specific thermal treatment on Young's modulus changes from the surface toward the bulk of a cured natural rubber (NR)–based compound. The AFM nanoindentation experiments were conducted on a cross-linked NR sample. Following a depth profiling analysis method, AFM deflection distance curves were measured every 40 μm from the oxygen-exposed surface toward the bulk, and then the Hertz's model was applied to force-indentation curves for the calculation of the Young's modulus. Investigations on the thermal-treated samples revealed an overall increase of the Young's modulus along the samples after heating. Moreover, a decrease of Young's modulus values from the surface exposed to oxygen during heating toward the bulk was observed, indicating a stiffening of the sample at the surface.

Effect of the size of CuBr nanocrystals formed in potassium-aluminum-borate glass on the phase transformation temperature

At thermal treatment of samples of potassium-aluminum-borate glass containing Cu and Br, a heterogeneous nanophase is formed as drops of the liquid containing CuBr and KBr. At room temperature, the phase contains CuBr and K2CuBr3 nanocrystals. The effect of sizes of nanophase areas on the temperatures of phase transformations (liquidus, solidus, and crystallization) at heating and cooling has been investigated. At the sizes of CuBr crystals equal to 10 nm, the solidus temperature is close to that shown on the state diagram of the KBr-CuBr system. The decrease of the sizes of CuBr crystals from 10 to 4.5 nm results in the decrease of the solidus temperature from 170 to 95°C and the liquidus temperature from 208 to 120°C: in other words, the dimensional effect is manifested almost identically on the values of the solidus and liquiddus temperatures. The decrease of the sizes of the liquid drops from 19 to 7 nm results in the decrease of the crystallization temperature from 100 to 70°C.