Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.     

The strength of glass fibre reinforcement after exposure to elevated composite processing temperatures

The results of a study on the properties of glass fibres after thermal conditioning at typical engineering thermoplastic processing temperatures are presented. The mechanical performance of rovings and single fibres of well-defined silane- and water-sized E-glass fibre samples was investigated at room temperature after thermal conditioning at temperatures up to 400 °C. Thermal conditioning for 15 min led to strength degradation of >50 % at higher temperatures. The tensile strength of silane-coated fibres was relatively stable up to 300 °C but exhibited a precipitous drop at higher conditioning temperatures. The water-sized fibres exhibited an approximately linear decrease in strength with increasing conditioning temperature. The strength distribution of the water-sized fibres could be well represented by a unimodal three-parameter Weibull distribution. The strength distributions of the sized fibres were more complicated and required the use of a bimodal Weibull distribution. The results are discussed in terms of the changes in surface coating and bulk glass structure during heat conditioning.     

Investigation of Thermophysical Properties of Thermal Degraded Biodiesels

Biofuels are an alternative to fossil fuels and can be made from many different raw materials. The use of distinct catalyst and production processes, feedstocks, and types of alcohol results in biofuels with different physical and chemical properties. Even though these diverse options for biodiesel production are considered advantageous, they may pose a setback when quality specifications are considered, since different properties are subject to different reactions during usage, storage and handling. In this work, we present a systematic characterization of biodiesels to investigate how accelerated thermal degradation affects fuel properties. Two different types of biodiesel, commercially obtained from distinct feedstocks, were tested. The thermal degradation process was performed by maintaining the temperature of the sample at \(140 \,^{\circ }\hbox {C}\) under constant air flux for different times: 0 h, 3 h, 6 h, 9 h, 12 h, 24 h and 36 h. Properties such as density, viscosity, activation energy, volumetric thermal expansion coefficient, gross caloric value, acid value, infrared absorption, and temperature coefficient of the refractive index were used to study the thermal degradation of the biodiesel samples. The results show a significant difference in fuel properties before and after the thermal degradation process suggesting the formation of undesirable compounds. All the properties mentioned above were found to be useful to determine whether a biodiesel sample underwent thermal degradation. Moreover, viscosity and acid value were found to be the most sensitive characteristics to detect the thermal degradation process.     

Thermometry in Normal Liquid 3He Using a Quartz Tuning Fork Viscometer

We have developed the use of quartz tuning forks for thermometry in normal liquid ³He. We have used a standard 32 kHz tuning fork to measure the viscosity of liquid ³He over a wide temperature range, 6 mK<T<1.8 K, at SVP. For thermometry above 40 mK we used a calibrated ruthenium oxide resistor. At lower temperatures we used vibrating wire thermometry. Our data compare well with previous viscosity measurements, and we give a simple empirical formula which fits the viscosity data over the full temperature range. We discuss how tuning forks can be used as convenient thermometers in this range of temperatures with just a single parameter needed for calibration.     

Experimental investigations and optimization of forming force in incremental sheet forming

Incremental sheet forming process has been proved to be quiet suitable and economical for job and batch type production, which exempts expensive and complex tooling for sheet forming. Investigation of forming forces becomes important for selecting the appropriate hardware and optimal process parameters in order to assure perfection and precision of process. Moreover, lack of available knowledge regarding the process parameters makes the process limited for industrial applications. This research paper aims at finding out effects of different input factors on forming forces in single-point incremental forming (SPIF) process. For operation sustainability and hardware safety, it becomes critical to optimize forming forces for a given set of factors to form a particular shape. In this study, optimization of input factors has been performed to produce conical frustums with helical tool path using Taguchi analysis as design of experiment (DOE) and analysis of variance (ANOVA). The optimal experimental conditions for forming forces have been calculated as sheet thickness (0.8 mm), step size (0.2 mm), tool diameter (7.52 mm), tool shape (hemispherical), spindle speed (1000 rpm), feed rate (1000 mm/min) and wall angle (50^o). Effects of tool shape and viscosity of lubricants have also been investigated. An intensive understanding of the mechanism of forming forces has been presented, which shows that force trend after peak values depends upon instant input factors that can be categorized as a safe, severe and crucial set of parameters.     

Study on viscosity of conventional and polymer modified asphalt binders in steady and dynamic shear domain

This study focuses on evaluating the flow behavior of conventional and polymer modified asphalt binders in steady- and dynamic-shear domain, for a temperature range of 20–70 °C, using a Dynamic Shear Rheometer (DSR). Steady-shear viscosity and frequency sweep tests were carried out on two conventional (VG 10 and VG 30) and two polymer (SBS and EVA) modified asphalt binders. Applicability of the Cox–Merz principle was evaluated and complex viscosity master curves were analyzed at five different reference temperatures. Cross model was used to simulate the complex viscosity master curves at different temperatures.It was found that asphalt binders exhibited shear-thinning behavior at all the test temperatures. The critical shear rate increased with increase in temperature and was found to be lowest for plastomeric modified asphalt binder. The Cox–Merz principle was found to be valid in the zero-shear viscosity (ZSV) domain and deviated at higher frequency/shear rate for all the binders. Results from the study indicated that the ratio of ZSV can be successfully used as shift factors for construction of master curves at different reference temperatures. Cross model was found to be suitable in simulating the complex viscosity master curves at all the test temperatures. Analysis of model parameters indicated that a strong relationship exists between ZSV and the critical shear rate. ZSV and critical shear rate varied exponentially with temperature. This relationship was used to propose a simple equation for assessing the shift factors for construction of master curves.     

The study of luminescence properties on Ce:YAG phosphor in glass co-sintered at different temperatures

Ce:YAG phosphor in glass was prepared by co-sintering bismuthate glass frits and Ce:YAG phosphors at different temperatures in the 550–800 °C range. In this work, the effect of co-sintering temperature on the photoluminescence and chromaticity coordinates (CIE) of phosphor in glass was investigated. The results show that the CIE coordinates is tunable with the increase of co-sintering temperature. As temperature increased from 550 to 700 °C, the intensity of emission and excited peak increases until a maximum is reached, after which it rapidly drops off. The degradation of luminescence properties with the higher co-sintering temperature is due to the broken lattice surrounding the Ce³⁺ and oxidation of the Ce³⁺ caused by the reactions between the bismuthate glass and Ce:YAG phosphors.     

GAS HOLDUP IN BAFFLED BUBBLE COLUMNS OF DILUTE SLURRIES OF FINE POWDERS AND VISCOUS LIQUIDS

ABSTRACT

Experimental gas phase holdup data reported by the authors as taken on two baffled bubble columns and involving slurries of fine powders (average particle diameter ≤90 μm) and dilute suspensions (mass fraction ≤ 20 percent) in viscous fluids are re-examined after correction for a small calculation error in superficial gas velocity. The two bubble columns are: a Plexiglas bubble column, 0.108 m in diameter and 2.25 m tall, equipped with seven 19 mm tubes arranged in equilateral triangular configuration with a pitch of 36.5 mm and a Pyrex glass column, 0.305 m in diameter and 3.24 m tall, equipped with thirty-seven 19 mm tubes arranged in the same configuration. Air and nitrogen are used as gas phase, water and Therminol as liquid phase, and iron oxide powders, glass beads and sand as solid phase. The small column data are at ambient temperature while those belonging to the large column extend from ambient to 473K. These data are examined to assess the influence of column diameter (scale-up), temperature, slurry concentration and viscosity, and superficial gas velocity on gas holdup for baffled columns.

It is found that in the 0.108 m diameter column the holdup is about the same for axial probes of different diameters, 19 mm, 31.8 mm and 50.8 mm, for two-phase systems involving liquids of small (water) and large (Therminol) viscosities. However, when a seven-tube bundle is installed, the holdup increases. This is consistent with the bubble dynamics and observed bubble sizes. This qualitative trend is also upheld by three-phase systems involving dilute slurries of fine powders. In the larger column when fully packed with a thirty-seven tube bundle, the holdup is found to be the same as for the small column. A loosely packed bundle gives smaller holdup at temperatures greater than the ambient due to the larger size of bubbles. The gas holdup is greater for a less viscous system and this is again due to the larger size of bubbles in a more viscous system. The influence of temperature is pronounced and is very characteristic of the nature of liquid involved. For example for water and Therminol the variations are in opposite directions with change in temperature. Bubble splitting and foaming control the nature of these dependencies. With the addition of solids the holdup is almost insignificantly altered at all temperatures.     

Pressure Dependence of Bis(2-ethylhexyl) Sebacate and VG32 Hydraulic Oil Viscosities Using a Quartz Crystal Resonator

Conductances versus sweep frequencies for AT-cut quartz crystal resonators have been measured for bis(2-ethylhexyl) sebacate and several machine oils under high pressure. The frequencies versus viscosities of these liquids appeared on the correlation line between frequency shift and viscosity. The correlation line agreement is essentially a criterion for when quartz resonators may be used because non-Newtonian silicone oils deviated from the correlation line. The responses of resonators immersed in bis(2-ethylhexyl) sebacate were obtained at pressures up to 350 MPa. Viscosities were calculated from the resonance frequencies. The pressure dependence of the bis(2-ethylhexyl) sebacate viscosity agreed well with that obtained with the rolling ball method. By using reference liquids, it was found that resonator responses were independent of temperature over the range 295–372 K. Viscosity measurements for VG32 hydraulic oil were taken at pressures up to 250 MPa and at the temperature at which the commercial viscosity grade was defined [313 K (40 °C)].     

Numerical investigation of an arc inlet structure extrusion die for large hollow sections

This paper aims to improve the working life of extrusion dies by optimal structure design, which plays an important role in mass production. First, an arc-shaped inlet die structure for an aluminum large-hollow-section profile was developed. Second, a three-dimensional finite-element model of the porthole extrusion process was established using an arbitrary Lagrangian-Eulerian method. Third, the comparison of the formability was analyzed and discussed, including the diversity of extrusion forces and uniformity properties between the proposed design and two traditional design schemes using the same extrusion process. A group of square-profile extrusion dies was used to set up a L16_4_3 orthogonal experimental scheme, considering the side length of profiles, L, with four levels, 110, 100, 90, and 80 mm; inlet angles, α, of the porthole bridge of 0°, 10°, 20°, and 30°; and profile wall thicknesses, t, of 1, 1.5, 2, and 2.5 mm. The results of the orthogonal tests were similar to those of the actual production die model. Two different analysis models reached the same conclusion: the inlet angle or the arc inlet structure has a small effect on the metal flow and the forming distribution, but the arc inlet structure can alleviate the stress load of the dies. The die testing and production validation results indicate that the novel structural design of the arc inlet die will have a long working life.     

Prediction of Powder Stickiness along Spray Drying Process in Relation to Agglomeration

The spray drying process consists of a fast convective drying of liquid droplets by hot air. Initially, the water activity (a_w) of a drop is close to 1. During drying, the drop surface a_w decreases while viscosity increases until reaching a sticky rubbery state before further drying. This can be observed for products such as carbohydrates, leading to particles sticking on walls (product losses) or to adhesion between particles leading to agglomeration. In this study, particle stickiness was investigated in a cocurrent pilot spray dryer by measuring drying air properties (temperature and relative humidity) at different positions. This allowed describing the evolution of temperature and mean water content of the drying drops. Two model products (maltodextrin DE12 and DE21) were spray dried varying process parameters liquid flow rate (1.8, 3.6, and 5.4 kg/h), air temperature (144°, 174°, and 200°C), airflow rate (80–110 kg/h), and rotary atomizer speed (22,500–30,000 rpm). The two products exhibit different drying behaviors in relation to their affinity towards water (sorption isotherms) and glass transition temperature evolution with a_w (stickiness). Depending on drying conditions and product, the drop stickiness was observed very rapidly, close to the atomizer, or later, along the chamber. This approach can be used to identify conditions and positions corresponding to sticky particles.     

Effect of warm mix asphalt chemical additives on the mechanical performance of asphalt binders

Warm mix asphalt (WMA) has become very popular in asphalt pavement construction because it allows reducing both energy consumptions and carbon emissions. WMA can be obtained by using different types of additives and can be produced, applied, and compacted at temperatures 20–40 °C lower than hot mix asphalt. WMA additives allow reducing the working temperatures without compromising the final performance of the asphalt concrete. Many WMA additives are available on the worldwide market and some of them reduce the viscosity of asphalts binder (organic additives or foam) whereas others do not act on this sense (chemical additives). This study focuses on the effect of chemical additives on the performance of asphalt binders for WMA production. To this purpose, a neat bitumen, a polymer modified bitumen (PMB) and two different chemical additives were selected. All the binders were characterized through conventional tests, DSR, MSCR, FTIR and microscopic analysis. The result clearly showed that the influence of the chemical additives on the neat bitumen is negligible or non-existent. On the contrary, significant changes were observed in the modified bitumen properties. Specifically, chemical additives reduce the viscosity temperature susceptibility of PMBs in the temperature range between 80 and 140 °C, increase the rutting resistance potential and the elastic response of PMBs at high temperatures. Moreover, a morphological inspection supported the modifications observed in the rheological properties of PMBs.     

Effects of borosilicate glass additions on microstructures and magnetic properties of low temperature co-fired NiCuZn ferrites

The low temperature co-fired NiCuZn ferrites with different borosilicate glass additions are prepared by a conventional solid-state reaction method. It is found that borosilicate glass additions can enhance densification of specimens based on liquid phase sintering and grain growth promotion. Small amount of borosilicate glass additions do not have a significant effect on forming into the main phase. But too much glass additions will damage the magnetic properties. As the borosilicate glass additions increase from 0 to 0.1 wt%, the permeability measured at 100 kHz decreases from 664 to 555, while the permeability values decrease rapidly from 310 to 169 with the glass additions rising from 0.3 to 0.9 wt%. The 0.1 wt% borosilicate glass can enhance the resistivity from 4.07 × 10¹⁰ Ω cm to 9.81 × 10¹⁰ Ω cm, while 0.9 wt% borosilicate glass addition leads to inhomogeneous grains and intragranular pores, resulting in deterioration of the resistivity to only 1.4 × 10¹⁰ Ω cm.     

Investigations on tailored forming components as tribologically loaded machine elements

To fulfil future trends of machine elements, the surface and part properties need to be enhanced. To advance machine elements, the application of tailored forming technology offers new possibilities. With this approach, it is possible to design and manufacture machine elements consisting of two or more different metallic materials with improved performance and functionality specially adapted to their respective application. The process chain starts with the joining of different materials to multi-metal work pieces, which are subsequently formed close to the final contour. The properties of the joining zone can be improved by thermal and mechanical treatment accompanying the forming process.Exemplary multi-metal components with a boundary zone subjected to rolling contact fatigue were investigated. Thus, an axial bearing, a shaft with an integrated raceway, a bearing bushing/angular contact ball bearing and a bevel gear wheel were in the focus of this research. Here, the highly stressed areas are reinforced with a higher strength material, while the rest of the part consists of a lower grade material. In case of the shaft, the raceway acts like the inner ring of a bearing and should resist rolling contact fatigue and mechanical wear. The process route was set up and simulations regarding the fatigue life in dependence of the layer thickness of the material acting as raceway were performed. First fatigue tests were executed to prove the reliability of the described concept.     

Ab Initio Calculated Results Require New Formulations for Properties in the Limit of Zero Density: The Viscosity of Methane ($$\hbox {CH}_{4}$$)

A wide-ranging formulation for the viscosity of methane in the limit of zero density is presented. Using ab initio calculated data of Hellmann et al. (J Chem Phys 129, 064302, 2008) from 80 K to 1500 K, the functional form was developed by guided symbolic regression with the constraints of correct extrapolation to \(T \rightarrow 0\) and in the high-temperature limit. The formulation was adjusted to the recalibrated experimental data of May et al. (Int J Thermophys 28, 1085–1110, 2007) so that these are represented within their estimated expanded uncertainty of 0.053 % (\(k = 2\)) in their temperature range from 210.756 K to 391.551 K. Based on comparisons with original data and recalibrated viscosity ratio measurements, the expanded uncertainty of the new correlation is estimated outside this temperature range to be 0.2 % to 700 K, 0.5 % to 1100 K, 1 % to 1500 K, and physically correct at higher temperatures. At temperatures below 210 K, the new correlation agrees with recalibrated experimental data within 0.3 % down to 150 K. Hellmann et al. estimated the expanded uncertainty of their calculated data at 1 % to 80 K. The new formulation extrapolates without a singularity to \(T\rightarrow 0\).     

Effect of substrate temperature on properties of Cu(In,Ga, Al)Se<Subscript>2</Subscript> films grown by magnetron sputtering

Cu(In, Ga, Al)Se₂ (CIGAS) thin films were deposited by magnetron sputtering on Si(100) and soda-lime glass substrates at different substrate temperatures, followed by post-deposition annealing at 350 or 520 °C for 5 h in vacuum. Electron probe micro-analysis and secondary ion mass spectroscopy were used to determine the composition of the films and the distribution of Al across the film thickness, respectively. X-ray diffraction analysis showed that the (112) peak of CIGAS films shifts to higher 2θ values with increasing substrate temperature but remains unchanged when the films were annealed at 520 °C for 5 h. Scanning electron microscopy and atomic force microscopy images revealed dense and well-defined grains for both as-deposited and annealed films. However, notable increase in grain size and roughness was observed for films deposited at 500 °C. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as the substrate temperature was increased.     

Effect of calcining temperature on microstructures and electrical properties in modified lead zirconate titanate ceramics

The effect of calcining temperature on microstructures and electrical properties of modified lead zirconate titanate ceramics has been investigated. Specimens of the modified lead zirconate titanate ceramics, formed with different powders calcined over the temperature range from 800 to 950 °C, were prepared by roll forming process. It is observed that the calcining temperature of the powders alters the grain size, which, in turn, modifies the electrical properties of the ceramics. The results also show that dielectric constant, saturated polarization and piezoelectric coefficient tend to increase with increasing calcining temperature up to 900 °C and then to sharply decrease. The best electrical properties were obtained from the samples with the calcining temperature of 900 °C. At the lower calcining temperatures, a small PbO excess seems to result in PbO-rich grain boundaries and anomalous grain growth during sintering process. In addition, when the calcining temperature was increased to 950 °C, a PbO deficiency appears to take place by breaking up the stoichiometry.     

Rutile TiO<Subscript>2</Subscript> films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO₂) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO₂ films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO₂ films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO₂ films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO₂ layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm^?2 for TiO₂ layer heat-treated at 600 °C.     

Determination of the Thermal Diffusivity of Electrically Non-Conductive Solids in the Temperature Range from 80 K to 300 K by Laser-Flash Measurement

The adoption of the popular laser-flash method at temperatures far below 300 K is restricted by the weak signal-to-noise ratio and the limited spectral bandwidth of the commonly used mercury cadmium tellurite (MCT) infrared (IR) detector used as a non-contacting temperature probe. In this work, a different approach to measure the temperature rise in pulse heating experiments is described and evaluated. This method utilizes the change of the temperature-dependent electrical resistance of a thin strip of sputtered gold for the detection of a temperature rise as it was proposed by Kogure et al. The main advantage of this method at lower temperatures is the significantly higher signal-to-noise ratio compared to the commonly used IR detectors. A newly developed laser-flash apparatus using this detection method for the determination of the thermal diffusivity in the temperature range from 80 K to 300 K is presented. To test the accuracy of the new detection method, the thermal diffusivity of a borosilicate crown glass (BK7) specimen at 300 K was determined and compared to results derived with a MCT detector. Good agreement of the derived thermal diffusivity values within 3 % was found. The thermal diffusivity of BK7 and polycrystalline aluminum nitride (AlN) was measured at temperatures between 80 K and 300 K by a laser-flash method to test the functionality of the apparatus. Finally, the thermal conductivity was calculated using values for the specific heat capacity determined by temperature modulated differential scanning calorimetry (MDSC). Comparisons with literature data confirm the reliability of the experimental setup.     

Development of a hot stamped channel section with axially tailored properties – experiments and models

In this work, the in-die heating (IDH) tailored hot stamping (THS) process is considered, in which the forming tool is partitioned into zones that are either cooled or heated. Four configurations of THS rails were formed: a non-tailored configuration using conventional room temperature tooling and three tailored configurations in which one-half of the rail was formed in tooling that was heated at different temperatures (in the range 400–700 °C). Micro-hardness measurements confirmed that THS can be used to form an axial crush member that contains tailored properties along its length. The as-formed parts exhibited a Vickers hardness of 430–484 HV in zones formed in cooled tooling, 235–280 HV in zones formed in tooling that was heated to 400 °C and 190–215 HV in zones that were formed when the die set was heated to 700 °C. Numerical models of the THS process were developed using the Åkerström material model in LS-Dyna. As part of the modelling, the activation energies for each phase were calibrated using an LS-OPT routine. The resulting hardness predictions were compared with experimental data to assess the accuracy of the LS-OPT routine. The predicted hardness distributions in the components were quite accurate (usually within 10%, but as high as 16% in some cases).