Convective drying of onion: Kinetics and nutritional evaluation

The present work aimed, on one hand, to study of the drying of onions in terms of drying kinetics, which was evaluated at 30 °C, 50 °C and 60 °C. The experimental data was fitted to different empirical kinetic models from the literature, and this kinetic study was then complemented with the modelling if terms of Fick's diffusion equation, for estimation of the diffusion coefficients. On the other hand, the chemical characterization in fresh and dried onions at different temperatures (varying from 30 °C to 70 °C) was analysed, to evaluate the effect of drying and drying temperature on the chemical composition of the product. In this way, the analyses of moisture content, sugar content, crude protein, ash, fat, crude fibre, acidity and vitamin C were made and reported in this paper.From the results obtained it was verified that some chemical components of the onions are not affected by drying (ash, fat, protein and fibre) whereas some others are considerably influenced by drying (sugars, acidity and vitamin C). The present work allowed concluding that the three empirical models tested (Newton, Modified Page and Logarithmic) all describe relatively well the dehydration kinetics at the three temperatures analysed. Moreover, from the experimental data it was possible to estimate the diffusivities, which range between 3.33 × 10^?09 m²/s at 30 °C and 8.55 × 10^?09 m²/s at 60 °C.     

Thin Layer Modelling of Recirculatory Convective Air Drying of Curd (Indian Yoghurt)

Dahi is one of the most popular fermented milk products consumed in India with excellent therapeutic properties. The initial moisture content of dahi is approximately 5.7 kg water kg dry solid⁻¹. The shelf life of dahi is limited and hence the long term storage is possible in the form of dahi powder which can further be used as a base for formulation of health drink mix. Dahi was dried in a laboratory scale recirculatory convective air dryer to a final moisture content of 0.04 kg water kg dry solid⁻¹. Drying characteristics of dahi were investigated under varying conditions of dahi thickness (0.003 m, 0.004 m and 0.005 m) and drying air temperatures (45°C, 50°C and 55°C) and velocities (1.5 m s⁻¹, 2.0 m s⁻¹ and 2.5 m s⁻¹). Different drying models were used to simulate the observed drying data. The mathematical models were compared based on R-square and reduced chi-square values. The drying characteristics were satisfactorily described by Page, modified page, logarithmic and Midilli et al. models. The Midilli et al. model followed by modified page model provided the best representation of data. Effective moisture diffusivity computed on the basis of Fick's law varied between 2.52 × 10⁻¹⁰ m² s⁻¹ and 1.3 × 10⁻⁹ m² s⁻¹ under experimental drying air temperatures and sample thicknesses at air velocity 2.5 m s⁻¹. The temperature and thickness dependence of effective moisture diffusivity was expressed by an Arrhenius type of equation. The equation showed best fit for diffusivity data at 2.5 m s⁻¹ and varying temperatures and sample thickness.     

Study of kinetics in the biosorption of lead onto native and chemically treated olive stone

In this research, olive stone was used as precursor for the development of new biosorbents for lead ions. Chemical treatments were analyzed in terms of their effects on physical–chemical properties and kinetics of lead removal. A kinetic study of the biosorption of lead ions by olive stone was analyzed according to six different kinetic models (pseudo first, pseudo second, pseudo n-order, Elovich, solid diffusion and double exponential models). The biosorption kinetic data were successfully described with pseudo-nth order and double exponential models for all biosorbents. The double exponential model allowed estimating the values of external and internal mass transfer coefficients. The values of external mass transfer coefficient (k_e) ranged from 42.62 × 10⁻⁶ to 508.3 × 10⁻⁶ m min⁻¹ and the internal mass transfer coefficient (k_i) from 3.76 × 10⁻⁶ to 73.4 × 10⁻⁶ m min⁻¹. On the other hand, the analysis of experimental data showed that chemical treatments of the biomass led to increase biosorption capacity of the native biomass.     

A new physical pretreatment of plum for drying

In this paper a new physical pretreatment of plums, consists of piercing them by a thin needle, is proposed to increase the rate of drying. The effect of physical pretreatment on drying time was compared with chemical pretreatment that consists of dipping of plums in hot NaOH solution (1%). Drying experiments were carried out in a convective laboratory dryer at 85 °C and 0.81 m/s air velocity. It was observed that pierced plums were dried faster than chemically pretreated plums. After 480 min moisture ratio of pierced sample was 0.07 while for the chemical method it was 0.25. The moisture ratio at any time was compared with seven different mathematical models and the best model was determined according to the best agreement. Accordingly, two-term exponential model for moisture ratio is found to be superior to the other proposed models. The effective diffusivity was found to be 5.471 × 10^?9 m²/s for chemically pretreated and 1.016 × 10^?8 m²/s for physically pretreated plums.     

Thermal cycling induced capacity enhancement of graphite anodes in lithium-ion cells

Graphite electrodes were electrochemically cycled in Li-ion cells at 50 and 60 °C in order to determine the changes in their surface properties in comparison to the electrodes tested at 25 °C. A 17% drop in planar capacity occurred during the first cycle at 60 °C compared to a 40% at 25 °C and reduced the amount of damage that occurred to graphite due to a rapidly formed solid electrolyte interphase (SEI). During the following cycles, a planar capacity of 3.11 ± 0.12 mAh cm⁻² was attained at 60 °C rather than 0.53 ± 0.03 mAh cm⁻² at 25 °C. The SEI layer formed at 60 °C predominantly consisted of Li₂CO₃ and was devoid of residual LiClO₄ detected at 25 °C. At 25 °C, the diffusion coefficient of Li⁺ (D_Li⁺) was calculated as 1.07 × 10⁻⁸ cm² s⁻¹, whereas at 60 °C, D_Li⁺ increased to 3.25 × 10⁻⁸ cm² s⁻¹. A pre-treatment conducted at 60 °C enhanced the cyclic performance of graphite subsequently cycled at 25 °C; a Li₂CO₃-enriched SEI, generated during the 60 °C pre-treatment, covered the graphite surface uniformly and resulted in a 28% increase in battery capacity at 25 °C.     

SPS processing of bismuth-layer structured ferroelectric ceramics yielding highly textured microstructures

The spark plasma sintering (SPS) behaviour of nano-sized Bi₄Ti₃O₁₂ (BIT) and micron-sized CaBi₂Nb₂O₉ (CBNO) powders is described. The densification process of both powders is very rapid, i.e. the densification occurs within a very narrow time interval (2–3 min using a heating rate of 100 °C min⁻¹ and a pressure of 50 MPa). The BIT powder exhibits a lower densification onset temperature (∼650 °C) and higher maximum shrinkage rate (8.9 × 10⁻³ s⁻¹ at 780 °C) than that of the CBNO powder (∼825 °C and 4.5 × 10⁻³ s⁻¹ at 950 °C). Isothermal compaction studies revealed that fully dense nano-sized BIT compacts could be obtained within the temperature region 750 °C < T_iso < 850 °C while for T_iso > 850 °C compacts containing elongated platelet grains are formed. A new preparation route to produce highly textured compacts is described in detail. Appropriate pre-forms are prepared by spark plasma sintering (SPS) and these fully dense compacts are subject to superplastic deformation in the SPS unit to achieve a total compressive strain of ∼60%. This strain was achieved within a period of 1.5 min and with a maximum strain rates of 1.1 × 10⁻² s⁻¹ achieved at ∼840 °C and 1.3 × 10⁻² s⁻¹ at 1020 °C for the BIT and CBNO compacts, respectively. The X-ray studies showed that the Lotgering orientation factors of grains in the deformed BIT and CBNO compacts are 99% and 70%. The formation of highly textured compacts is suggested to be governed by a superplastic deformation-induced directional dynamic ripening mechanism.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Deformation behavior and joining of a MgF2 optical ceramic

Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF₂) ceramic was investigated at temperatures ranging from 760 to 830 °C in an argon atmosphere at strain rates between 2 × 10⁻⁶ and 4 × 10⁻⁵ s⁻¹. Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38 MPa. Stress exponents of ≈1.4 ± 0.2 were determined at temperatures >760 °C, indicative of a viscous diffusion-controlled deformation mechanism. Activation energy, determined from flow stress as a function of temperature, at a constant strain rate, was ≈476 ± 60 kJ/mol. Self-joining by plastic deformation of MgF₂ was demonstrated at 830 °C at a strain rate of 5 × 10⁻⁶ s⁻¹. The joined samples were characterized by optical transmission measurements and their transmittivity was ≈80% of the unjoined sample in the 2.5–8 μm wavelength range.     

Structure and conductivity of NiO/YSZ composite prepared via modified glycine-nitrate process at varying sintering temperatures

Nickel oxide and Yttria-stabilized zirconia (NiO/YSZ) composite is one of the most promising mixed conducting electrode materials in both solid oxide electrolysis cell and solid oxide fuel cell applications. In this study, 50 wt% NiO and 50 wt% YSZ composite was synthesized via a modified glycine-nitrate combustion process (GNP) and the effect of sintering temperatures (1100 °C, 1300 °C and 1500 °C) on its microstructure and electrical properties were investigated. TG/DTA and in-situ high temperature XRD revealed the thermal property behavior and the structural changes of the as-combusted precursor material. For all the samples sintered at different temperatures, room temperature XRD patterns revealed a distinct cubic phases of both YSZ and NiO while SEM images showed a porous microstructure. The total conductivities at 700 °C are 9.87 × 10⁻³, 5.26 × 10⁻³, 4.02 × 10⁻³ S/cm for the 1100, 1300, and 1500 °C with activation energies of 0.1722, 0.3555, and 0.3768 eV, respectively. Conductivity measurements of the different sintered samples revealed that the total conductivities as well as the activation energies are greatly affected by different sintering temperatures.     

Characterisation of industrial tomato by-products from infrared drying process

The thin-layer infrared drying behaviour of industrial tomato residues, peels and seeds, was experimentally investigated in the temperature range from 100 °C to 160 °C. The drying rate was found to increase with temperature, hence reducing the total drying time. In particular, as drying temperature was raised from 100 °C up to 160 °C, the time period needed to reduce the moisture content of the sample from 236.70 wt% down to 5.26 wt% (dry basis) was observed to decrease from 99.5 min to 35 min.Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer infrared drying process of industrial tomato residues was proposed. The effective moisture diffusivity is dependent on moisture content; the average values for the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion, and varied from 5.179 × 10^?9 m²/s to 1.429 × 10^?8 m²/s over the temperature range. The temperature dependence of the effective diffusivity coefficient was described following an Arrhenius-type relationship. Activation energy for the moisture diffusion was determined as 22.23 kJ/mol.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Experimental modelling of infrared drying of industrial grape by-products

The thin-layer infrared drying behaviour of industrial grape by-products was experimentally investigated in the temperature range from 100 to 160 °C. The drying rate was found to increase with temperature, thus reducing the total drying time. In particular, as drying temperature was raised from 100 °C up to 160 °C, the time period needed to reduce the moisture content of the sample from 204.32% down to 38.89% by weight (dry basis) decreased from 60.5 to 21 min.Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer infrared drying process of wet grape residues was proposed. The values for the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion. They varied from 11.013 × 10^?9 to 26.050 × 10^?9 m²/s along the temperature range. The temperature dependence of the effective diffusivity coefficient was expressed by an Arrhenius type relationship. Activation energy for the moisture diffusion was determined as 19.27 kJ/mol.     

Silicon carbide films from polycarbosilane and their usage as buffer layers for diamond deposition

Thin films of polycarbosilane (PCS) were coated on a Si (100) wafer and converted to silicon carbide (SiC) by pyrolyzing them between 800 and 1150 °C. Granular SiC films were derived between 900 and 1100 °C whereas smooth SiC films were developed at 800 and 1150 °C. Enhancement of diamond nucleation was exhibited on the Si (100) wafer with the smooth SiC layer generated at 1150 °C, and a nucleation density of 2 × 10¹¹ cm^− 2 was obtained. Nucleation density reduced to 3 × 10¹⁰ cm^− 2 when a bias voltage of − 100 V was applied on the SiC-coated Si substrate. A uniform diamond film with random orientations was deposited to the PCS-derived SiC layer. Selective growth of diamond film on top of the SiC buffer layer was demonstrated.     

Correction of moisture and sucrose effective diffusivities for shrinkage during osmotic dehydration of apple in sucrose solution

Shrinkage, moisture and sucrose effective diffusivities were correlated for infinite slab shape samples of apple during osmotic dehydration in sucrose solution. Experiments were carried out in the sucrose solutions of different concentrations (30%, 40% and 50%) and temperatures (30 °C, 40 °C and 50 °C). The two parameter model, developed by Azuara et al. (1992), was used to predict water loss and solid gain at equilibrium condition. Moisture and sucrose diffusivities were estimated by fitting the experimental moisture loss and solid gain data to the modified form of Fick's second law of diffusion, considering the shrinkage of the apples during osmotic dehydration. Results showed that the volume of the samples decreased linearly with water loss (WL) and weight reduction (WR). For above conditions of osmotic dehydration, effective diffusivities without considering the shrinkage were found to be in the range of 1.36 × 10⁻¹⁰ m²/s–2.00 × 10⁻¹⁰ m²/s, and those with considering the shrinkage were in the range of 0.87 × 10⁻¹⁰ m²/s–1.27 × 10⁻¹⁰ m²/s. The values of the effective diffusivities estimated by considering the shrinkage were smaller than those without considering this phenomenon.     

Application of BaO–CaO–Al2O3–B2O3–SiO2 glass–ceramic seals in large size planar IT-SOFC

BaO–CaO–Al₂O₃–B₂O₃–SiO₂ (BCAS) glass–ceramics can be used as sealant for large size planar anode-supported solid oxide fuel cells (SOFCs). BCAS glass–ceramics after heat treatment for different times were characterized by means of thermal dilatometer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the coefficients of thermal expansion (CTE) of BCAS glass–ceramics are 11.4×10⁻⁶ K⁻¹, 11.3×10⁻⁶ K⁻¹ and 11.2×10⁻⁶ K⁻¹ after heated at 750 °C for 0 h, 50 h, and 100 h, respectively. The CTE of BCAS matches that of YSZ, Ni–YSZ and the interconnection of SOFC. Needle-like barium silicate, barium calcium silicate and hexacelsian are crystallized in the BCAS glass after heat-treatment for above 50 h at 750 °C. The glass–ceramics green tape prepared by aqueous tape casting can be directly applied in sealing the cell of SOFCs with 10 cm×10 cm. The open circuit voltage (OCV) of the cell keeps 1.19 V after running for 280 h at 750 °C and thermal cycling 10 times from 750 °C to room temperature. The maximum power density is 0.42 W/cm² using pure H₂ as fuel and air as oxidation gas. SEM images show no cracks or pores exist in the interface of BCAS glass–ceramics and the cell.     

Effect of moisture on the thermoelectric properties in expanded graphite/carbon fiber cement composites

A kind of dry mixing and pressing process was introduced to prepare expanded graphite/carbon fiber cement composites (EG-CFRC). Significant effect of moisture on the thermoelectric properties of EG-CFRC was observed. The higher the moisture content is, the greater the absolute Seebeck coefficient. The maximum of absolute Seebeck coefficient 11.59 μV/°C was obtained with moisture of 14.98% at 33 °C. Simultaneously, the maximum of electrical conductivity 0.78 S cm⁻¹ was got with moisture of 11.44%. Furthermore, the largest power factor 7.85×10⁻⁴ µW m⁻¹ K⁻² was calculated at 33 °C with moisture of 11.44%. The carrier scattering, polarization effects and high density defects interface of EG-CFRC are attributed to the enhancement of thermoelectric properties in the case of higher moisture content.     

Dielectric and thermal properties of AlN ceramics

The effects of slow-cooling and annealing conditions on dielectric loss, thermal conductivity and microstructure of AlN ceramics were investigated. Y₂O₃ from 0.5 to 1.25 mol% at 0.25% increments was added as a sintering additive to AlN powder and pressureless sintering was carried out at 1900 °C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 °C min⁻¹ from 1900 to 1750 °C, subsequently cooled to 970 °C at a rate of 10 °C min⁻¹ and then annealed at the same temperature for 4 h. AlN and YAG (5Al₂O₃/3Y₂O₃) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y₂O₃ had a low loss of <2.0 × 10⁻³ and a high thermal conductivity of >160 W m⁻¹ °C⁻¹.     

Spouted bed and microwave-assisted spouted bed drying of parboiled wheat

The effect of spouted bed and microwave-assisted spouted bed drying on drying rates of parboiled wheat was investigated. In addition, the effective moisture diffusivities of parboiled wheat were calculated. The drying experiments were performed using 200 g of parboiled wheat, at three different air temperatures (50, 70, 90 °C) and at two different microwave powers (3.5 W/g (db), 7.5 W/g (db)). Microwave-assisted spouted bed drying at microwave power of 3.5 W/g and 7.5 W/g reduced drying time by at least 60% and 85%, respectively compared to spouted bed drying. The effective diffusivity values were in the range of 1.44 × 10^?10–3.32 × 10^?10 in spouted bed drying while they were between 5.06 × 10^?10 and 11.3 × 10^?10 in microwave-assisted spouted bed drying at different experimental conditions.     

Absence of superconductivity in boron-implanted diamond

Recently, superconductivity has been found in heavily boron-doped diamond prepared by high temperature/high pressure synthesis or chemical vapour deposition. An alternative doping method of technological relevance is ion implantation. It is an open question whether superconductivity can also be obtained in boron-implanted diamond. Here we report on the transport and magnetic properties of high dose (2.3 × 10¹⁶–1.7 × 10¹⁷ cm^− 2) boron-implanted natural IIa diamond samples doped at elevated temperature of 900 °C and subsequently annealed at 1500 °C and 1700 °C. For comparison implantation at room temperature was also carried out. The samples were further characterized by Raman and infrared spectroscopy. No superconductivity could be detected in the samples at temperatures down to 40 mK. We discuss the possible origin for the absence of superconductivity.