The Interaction of γ-Glycidoxypropyltrimethoxysilane with Oxidised Aluminium Substrates: The Effect of Drying Temperature

The interaction of γ-glycidoxypropyltrimethoxysilane (GPS) with oxidised aluminium substrates has been investigated in terms of the effect of the drying, or curing, temperature. Samples treated with aqueous solutions of GPS at concentrations of 1,4 and 8% v/v were cured at 25, 50, 93 and 120°C. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to construct adsorption isotherms and determine the thicknesses of the various GPS coatings. A temperature effect induces subtle changes in the structure of the resulting films. The uptake of GPS is increasing with increasing concentration of GPS. The structure of the films changes at a threshold temperature between 50 to 93°C. XPS and ToF-SIMS data both indicate that the interaction of the GPS film on aluminium is different for low and high temperatures drying regimes. Using the Beer-Lambert equation, it was found that increasing the curing temperature leads to the variation of the thickness of silane films. This is interpreted in terms of changes in the crosslink density of the films and in their state of hydration and/or degradation.     

Degradation of Interfacial Chemistry of Epoxy/Silane/Aluminium Interfaces as a Result of Aqueous Attack

The degradation of a thin layer of adhesive on a grit-blasted aluminium substrate, as a result of aqueous attack, was investigated and compared with the behavior of the adhesive on a grit-blasted aluminium substrate treated with γ-glycidoxypropyl trimethoxy silane (GPS). The degradation study was achieved by examining aluminium coupons treated with adhesive that had been immersed in water at 25°C and an elevated temperature (50°C) for various treatment times ranging between 10 min and 1 day. All samples were characterized using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS and ToF-SIMS data indicated that the adhesive layer on both types of substrate was readily displaced by water. This is shown to be a two-stage process with bond rupture being identified by ToF-SIMS analysis and the displacement of the organic phase occurring at a later stage, as indicated by the XPS analysis, which showed a reduction in surface carbon concentration. When the substrates were directly in contact with water, a hydration process occurred and hydrated oxide species were formed on the surfaces. The results indicated that the hydration process was a postfailure event.     

Influence of Temperature on Aminosilane Thin Films Deposited on Aluminium Substrates: A Study by Surface Analysis

Thin films of aminopropyltriethoxysilane (APS) have been deposited on grit-blasted aluminium and dried at four different temperatures: room temperature (RT), 50, 93, and 120°C. These specimens were prepared in order to assess the occurrence of the three important reactions known to take place when using silanes as films and/or primers: hydrolysis in the absence of water, condensation with the substrate, i.e., covalent bond formation, and crosslinking or self-condensation.

Analyses performed using X-ray photoelectron spectroscopy (XPS) indicate that the films reduce in thickness with temperature and that the type of silicon bonding changes mostly above 50°C. Time of flight secondary ion mass spectrometry (ToF-SIMS) reveals that covalent bonding of APS on aluminium occurs at all temperatures used in this study as well as showing that the films are close to being fully hydrolysed. It is also possible to assess the presence of crosslinking within the films.     

Degradation of Interfacial Chemistry of Epoxy/Silane/Aluminium Interfaces as a Result of Aqueous Attack

The degradation of a thin layer of adhesive on a grit-blasted aluminium substrate, as a result of aqueous attack, was investigated and compared with the behavior of the adhesive on a grit-blasted aluminium substrate treated with γ-glycidoxypropyl trimethoxy silane (GPS). The degradation study was achieved by examining aluminium coupons treated with adhesive that had been immersed in water at 25°C and an elevated temperature (50°C) for various treatment times ranging between 10 min and 1 day. All samples were characterized using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS and ToF-SIMS data indicated that the adhesive layer on both types of substrate was readily displaced by water. This is shown to be a two-stage process with bond rupture being identified by ToF-SIMS analysis and the displacement of the organic phase occurring at a later stage, as indicated by the XPS analysis, which showed a reduction in surface carbon concentration. When the substrates were directly in contact with water, a hydration process occurred and hydrated oxide species were formed on the surfaces. The results indicated that the hydration process was a postfailure event.     

Adhesion and Scratch Resistance of Polycarbonate Films on Ferroplate Substrates: Effect of γ-APS Primers

The influence of γ-aminopropyltriethoxysilane (γ-APS) primers on the adhesion and scratch resistance of polycarbonate (PC) films on ferroplate substrates was determined from the critical normal loads at which debonding of the films from the substrates occurred during scratch testing. The critical load was a strong function of the concentration of the aqueous solutions from which the γ-APS primers were adsorbed and of the thickness of the primer films. Thus, the critical normal load increased from 0.09 ± 0.02 N to 0.31 ± 0.07 N as the concentration of the γ-APS solutions increased from 0.05% to 0.2%, respectively. However, the critical load increased only slightly as the solution concentration increased beyond 0.2%. The increase in critical load as concentration of γ-APS solutions increased was related to the formation of an interphase involving chemical reaction and physical entanglement of PC and γ-APS molecules. The critical load for debonding of PC films from the substrates also depended strongly on the temperature at which the γ-APS films were dried before application of the PC films. Thus, the critical normal loads for debonding were 0.31 ± 0.07, 0.20 ± 0.02, and 0.05 ± 0.01 N for γ-APS films that were dried for 15 min at room temperature, 60°C, or 110°C, respectively. The decrease in critical load with increasing drying temperature was attributed to the greater cross-link density in γ-APS films that were dried at elevated temperatures, which limited interdiffusion and physical entanglement of PC and γ-APS molecules. High reaction temperature of γ-APS and PC induced a fragmentation of amine. However, it also increased the probability of amines to react with carbonate because of increasing mobility of PC chains. Optimization of these two factors was required to obtain the greatest adhesion and scratch resistance. Chemical reactions occurring between PC films and γ-APS primers were investigated by reflection-absorption infrared spectroscopy (RAIR) and X-ray photoelectron spectroscopy (XPS) using diphenyl carbonate (DPC) as a model compound. The carbonyl absorption band of neat DPC was observed at 1780 cm^-1. However, two carbonyl bands were observed at 1738 and 1652 cm^-1 in RAIR spectra of γ-APS films that were reacted with DPC and were assigned to urethane and urea groups, respectively. XPS results revealed that urethane was the main reaction product between DPC and γ-APS. It was concluded that urethane groups formed by the reaction of PC with γ-APS were responsible for adhesion and scratch resistance of PC to ferroplate substrates that were primed with γ-APS.     

Evaluation of the Interaction and Adsorption of γ-Glycidoxy propyl trimethoxy silane with Grit-Blasted Aluminium: A ToF-SIMS and XPS Study

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) have been employed to study the adsorption and interaction of γ-glycidoxy propyl trimethoxy silane (GPS) with grit-blasted aluminium.

GPS displaces adventitious hydrocarbon either by covalent bond formation between GPS and aluminium, or adsorption, when GPS is deposited on the aluminium. ToF-SIMS fragments present at a nominal mass m/z = 71 were peak-fitted to seven peaks by using CasaXPS Software. AlOSi⁺ and Si⁺ were used to establish a relationship between covalent bond formation and the adsorption process. It is found that the adsorption isotherms of Si⁺ relating to the adsorption of GPS were of the Langmuir type. The interfacial bonding between GPS and aluminium is mainly covalent at low solution concentrations. At higher concentrations (greater than 4.5 × 10^?4 M) all the sites for the covalent bond formation appear to be occupied while these for the acid-base interaction are still available and then become fully occupied at solution concentrations of 4.5 × 10^?2 M and above.     

Comparative Evaluation of Physical Properties of Edible Chitosan Films Prepared by Different Drying Methods

Edible films are alternative packaging, which have recently received much attention due mainly to environmental reasons. Edible films may be formed from edible biomaterials such as polysaccharides, proteins, or lipids. Among these biopolymers, chitosan is of interest because it has a good film-forming property and is biodegradable, biocompatible, and nontoxic. Several techniques have been used to prepare edible chitosan films with various degrees of success. However, it is always interesting to find an alternative technique to produce films of superior quality at shorter processing (drying) time. In this study, the influences of different drying methods and conditions on the drying kinetics and various properties of chitosan films were investigated. Drying at control conditions (ambient air drying and hot air drying at 40°C) as well as vacuum drying and low-pressure superheated steam drying (LPSSD) at an absolute pressure of 10 kPa were carried out at different drying temperatures (70, 80, and 90°C). The properties of chitosan films, in terms of color, tensile strength, percent elongation, water vapor permeability (WVP), glass transition temperature (T_g), and crystallinity, were also determined. Based on the results of both the drying behavior and film properties, LPSSD at 70°C was proposed as the most favorable conditions for drying chitosan films.     

Drying Kinetics and Color Retention of Dehydrated Rosehips

Freshly harvested rosehips (Rosa canina L.) were dehydrated in a parallel flow type air dryer at six air temperatures (30, 40, 50, 60, and 70°C) at air velocities of 0.5, 1.0, and 1.5 m/s. Drying air temperature and velocity significantly influenced drying time and energy requirement. Minimum and maximum energy requirement for drying of rosehips were determined as 6.69 kWh/kg for 70°C at 0.5 m/s, and 42.46 kWh/kg for 50°C, 1.5 m/s. In order to reduce drying energy consumption, it is recommended that the drying air velocity must not be more than 0.5 m/s and drying air temperature should be 70°C. In addition, the influence of drying air temperature and air velocity on the color of dried rosehip has been studied. Hunter L, a, b values were used to evaluate changes in the total color difference (ΔE) on dried rosehips. 70°C drying air temperature and 1 m/s air velocity were found to yield better quality product.     

Electrochemical and time-of-flight secondary ion mass spectrometry analysis of ultra-thin metal oxide (Al2O3 and Ta2O5) coatings deposited by atomic layer deposition on stainless steel

Ultra-thin (5–50 nm) layers of aluminium and tantalum oxides deposited by atomic layer deposition (ALD) on a stainless steel substrate (316L) for corrosion protection have been investigated by electrochemical methods (linear scan voltammetry, LSV, and electrochemical impedance spectroscopy, EIS) and time-of-flight secondary ion mass spectrometry, ToF-SIMS. The effects of the deposition temperature (250 °C and 160 °C) and coating thickness were addressed. ToF-SIMS elemental depth profiling shows a marked effect of the organic and water precursors used for deposition and of the substrate surface contamination on the level of C and OH trace contamination in the coating, and a beneficial effect of increasing the deposition temperature. The polarization data show a decrease of the current density by up to four orders of magnitude with increasing coating thickness from 5 to 50 nm. The 50 nm films block the pitting corrosion in 0.8 M NaCl. The uncoated surface fraction (quantified from the current density and allowing a ranking of the efficiency of the coating, also confirmed by the capacitance and resistance values extracted from the EIS data) was 0.03% with a 50 nm thick Al₂O₃ film deposited at 250 °C. The correlation between the porosity values of the coatings and the level of C and OH traces observed by ToF-SIMS points to a marked effect of the coating contaminants on the sealing performance of the coatings and on the corrosion resistance of the coated systems.     

Improvement of graphitization of isotropic carbon by Al2O3 formed from aluminium chelate compound

For improving the graphitization of isotropic carbon, ethyl acetoacetate aluminium diisopropoxide and aluminium oxide were used as catalysts. Their effect was investigated and the corresponding mechanism was discussed. The results showed that the isotropic carbon was graphitized greatly by the addition of ethyl acetoacetate aluminium diisopropoxide when the heat-treatment temperature was over 1850°C, and slightly by the addition of aluminium oxide at 1900°C. The mechanism is considered to be that the aluminium compound formed from ethyl acetoacetate aluminium diisopropoxide reacted with C to give Al₄C₃ and with increasing temperature the Al₄C₃ decomposed to form Al(g) and C_Gr which was graphitized. Additionally, Al-containing gases and CO₂(g) were the reactants of the reaction between aluminium oxide and C. This showed only a little effect on the graphitization of isotropic carbon when the heat-treating temperature was 1900°C. ©     

Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300-400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.     

Effect of the substrate temperature on the physical characteristics of amorphous carbon films deposited by d.c. magnetron sputtering

The growth rate, composition, electrical resistivity, mass density, refractive index and microstructure of amorphous carbon (a-C) films prepared by direct current (d.c.) magnetron sputtering were investigated as functions of the substrate temperature (50–350°C). The hydrogen content determined by elastic recoil detection analysis (ERDA) and the electrical resistivity of films were found to be dependent on both the base pressure in the deposition chamber and substrate temperature. For films deposited below 200°C, the hydrogen content was less than 2 at.% and the substrate temperature was the only parameter which affected their electrical resistivity. The electrical resistivity decreased from 0.2 to 0.03 Ωcm as the substrate temperature increased from 50 to 200°C. The mass density of films evaluated from Rutherford backscattering (RBS) data and film thickness decreased from 2.2 to 1.4 g cm⁻³ with increasing substrate temperature. A linear relationship between the refractive index and the mass density of a-C films was clearly established. From the optical measurements, the decrease in mass density was correlated to an increase in porosity of films with increasing substrate temperature. The decrease in electrical resistivity with increasing substrate temperature was attributed to a graphitization of a-C films. This modification of the microstructure of a-C films as the deposition temperature was varied from 50 to 350°C was observed by examination of the cross-section of samples by transmission electron microscopy and Raman spectroscopic analyses of a-C films.     

EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY ON THE DRYING RATES AND DRYING TIMES OF GREEN BELL PEPPERS (CAPSICUM ANNUUM L)

Green bell pepper dices were dehydrated at different dry bulb air temperatures (55°, 60°, 65°, 70° and 75°C) and relative humidities (15, 20, 25, 30, 35 and 40%). The effects of temperature and relative humidity (RH) on the drying rates and drying period of diced green bell peppers were determined. Drying rate curves were characterized by a short induction (heating) phase followed by a falling rate period. Near constant rate drying was observed only at 55°C at 15% RH and at 65°C (15% RH). Drying rates generally increased with increasing temperatures and decreasing RH. The effect of temperature on the drying rates became less pronounced with increasing RH Drying rate maxima at 70°C and RH of 15, 20 25 and 40% exceeded those at 75°C, possibly due to case-hardening.     

Effects of deposition temperature on the crystallinity of Ba0.5Sr0.5TiO3 epitaxial thin films integrated on Si substrates by pulsed laser deposition method

Epitaxial Ba_0.5Sr_0.5TiO₃ (BSTO) thin films were grown on TiN buffered Si (0 0 1) substrates by PLD method and the effects of deposition temperature on their crystallinity and microstructure were studied. BSTO thin films were prepared with substrate temperature ranging from 350 to 650 °C. The BSTO films grown at below 400 °C showed amorphous phase and the film grown at 450 °C showed mixed phase of crystalline and amorphous, where crystalline phase was observed only at the top surface portion of the film. The BSTO films with fully crystalline phase were obtained in the samples deposited at above 500 °C. The (0 0 l) preferred orientation and the crystallinity of the BSTO films were improved with increasing the temperature. The dielectric constant, measured at 100 kHz and at room temperature, of the BSTO film grown at 650 °C was measured to be as high as 1129.     

Influence of Temperature and Air Velocity on Drying Time and Quality Parameters of Pistachio (Pistacia vera L.)

Drying is one of the important steps in pistachio processing. In this step kernel moisture content is decreased from 50 to less than 5% (d.b.) which will result in suitable condition for storage. Study of effective parameters in pistachio drying is important since these parameters influence drying time and kernel quality. In this research, a mono layer of pistachios was dried at three different temperatures (60, 75, and 90°C), and three levels of drying air velocity (1.5, 2, and 2.5 m/s). Changes of drying time, protein, fat and peroxide value were investigated for two common Iranian pistachio varieties Kalehghouchi and Fandoghi. Sensory tests were also used to check flavor of pistachios dried at the three temperature levels (60, 75, and 90°C). Statistical analysis of the data indicated that increasing the temperature to 90°C reduced drying time down by about 37% and caused a change in pistachio flavour. Taste tests indicated a consumer preference for pistachios dried at 75°C. If the air velocity is increased from 1.5 to 2.5 m/s, drying time reduces about 10 percent. Changes in temperature and air velocity have no significant effects on protein and fat content of pistachios, but if temperature reaches 90°C, peroxide value will increase to 0.55 meq/kg, which is still within the permissible limit for processed pistachios.     

EFFECT OF DRYING MODE ON DRYING KINETICS OF ONION

Onion slices 3 mm thick were dried in different modes. Drying at 60°C by convection was taken as a reference process." reviseddate="It has been shown that increase in air temperature increases the rate of drying. Effective diffusivity increases with increasing temperature, but it is strongly dependent on water content. Energy of activation for diffusion is also strongly affected by water content." acceptdate="Stepwise changes in temperature do not result in beneficial effects which could be expected. Extension of drying time was even observed in respect to that obtained at constant 60°C." printpubdate="Drying with infrared energy or assisting convective drying with microwave energy results in increased drying rates and substantial shortening of the drying time.     

Convective Drying Kinetics of Red Chillies

The drying kinetics of four varieties of chillies (Pb-Lal, Pb-Guchhedar, Pb-Surkh, and CH-1) was studied. The chillies (pricked and unpricked) were pretreated in the dip sol solution. The treated chillies were dried in an automatic weighing experimental dryer at selected temperatures (45°, 50°, 55°, 60°, and 65°C). The results indicated that drying took place in the falling rate period. Out of three models considered, Page's model was found to be the most suitable for describing the drying behavior of chillies. The dependence of drying constant on temperature was analyzed using an Arrhenius equation. The variety Pb-Lal has the maximum value of activation energy (42.59 kJ/mol), which is also reflected in the reduced drying time for this variety. The results of quality studies of dried chillies in terms of capsaicin content and coloring matter indicated that the Pb-Lal variety had acceptable capsaicin content of 532.08 µg and coloring matter of 73.8 ASTA.     

MICROFLORA CHANGES IN TUNA MINCE DURING CONVECTION AIR DRV1NG

Microorganisms grow in tuna during drying at low temperatures. The drying temperature of 50°C or below is not lethal to the microflora. The decimal reduction time (D-value) varied from 12.66 to 2.63 hr when drying temperature increased from 60 to 100°C, respectively. These values can be used to estimate the lethal effect of drying on the natural microflora in tuna.     

TiO2 photocatalytic films on stainless steel: The role of Degussa P-25 in modified sol–gel methods

The role of Degussa P-25 loading (0–100 g/L) in the alkoxide sol was investigated for the synthesis of immobilized TiO₂ photocatalytic films on 304 stainless steel using the P-25 powder-modified sol–gel method (PPMSGM). The structural properties of the films (PPMSGFs) obtained after gel drying and calcination at 600 °C were examined using different materials characterization techniques including X-day diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of films with good adherence to the stainless steel support were evaluated using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant and UV-A radiation. The P-25 loading did not have a significant effect on the size of the crystallites in the films. However, increasing the P-25 loading in the sol resulted in an increase in (i) the amount of crystalline material retained on the support (i.e., for both anatase (1 0 1) and rutile (1 1 0) crystal phases); (ii) the number of grains (aggregates of P-25 particles and crystallites formed from the alkoxide sol); (iii) the number of pores in the film (in the range of 0–50 g/L); and (iv) the number of microcracks on the surface of PPMSGFs. On the other hand, increasing the P-25 loading in the sol resulted in a decrease in the size of grains on the surface of PPMSGFs. XPS analysis revealed the presence of Cr³⁺, Mn³⁺ and Fe³⁺ on the surface of PPMSGFs as a result of diffusion of these species from the stainless steel support during film calcination at 600 °C. The concentration of these foreign species on the film surface decreased with an increase in the P-25 loading in the sol. Increasing P-25 loading in the sol yielded films with higher photocatalytic activity but a concentration of 50 g/L P-25 in the sol was found as the maximum for obtaining films with good adherence on the stainless steel support. Increase in the photocatalytic activity of the films with increasing P-25 loading in the sol was mainly attributed to the enhancement of the number of P-25 active sites exposed to the solution due to film morphology and surface characteristics and to the reduction in Cr³⁺ and Fe³⁺ concentrations on the surface of the films.     

NMR Imaging of the Interfaces of Epoxy Adhesive Joints

Nuclear magnetic resonance imaging (NMRI) is used to study epoxy adhesive bonded structures at a proton resonance frequency of 300 MHz. Oligomeric and almost pure monomeric diglycidyl ethers of bisphenol-A, triethylenetetramine and xylene representing typical raw materials of epoxy adhesives are imaged at 25 and 50°C with varying repetition times to optimize measurement conditions for the adhesives. NMR images with good signal-to-noise ratios from the liquid epoxy adhesives are obtained at 50°C using the shortest possible echo times and a repetition time of 1 s. Chemical shift images of the glue-lines are presented and their possible uses in adhesive studies are discussed. The use of NMRI to detect heterogenous resin/resin and resin/curing agent mixtures is demonstrated. A non-invasive glue-line analysis is made of an aluminium/epoxy/aluminium sample with a model debonding by recording cross-sectional NMR images and a proton shadowgram.