Mixture Of Silicon Research Articles

Evaluation of composite fiber-plastics biomass clinkering under the gasification conditions

Cross contamination and non-recyclables remain after the separation of valuables in the recycling process, especially with commingled or single stream recycling systems. Therefore, some carbonaceous fractions of recyclables, such as plastics and fibers, are left as a potential biomass feedstock for the thermochemical or thermal conversion processes. However, this fraction of waste is more likely to be highly contaminated and challenging, or may become unpredictable during its reuse in the thermal conversion process for heat and power applications. The current study aims to find how the increase in plastic specifically in the recycled fiber stream may affect the performance of a downdraft gasifier. Therefore, the effect of plastic combined with fiber feedstock during gasification has been investigated. For this purpose, three different plastic percentages of 2%, 5%, and 10% mixed with fiber were studied. The results showed that higher plastic-containing feedstock has higher energy content; however, the higher plastic content causes mechanical performance issues inside the reactor and does not necessarily guarantee greater biomass heating value. Furthermore, gasifying the higher plastic percentage results in a temperature drop across the reactor. This change in temperature is the result of thermal reactions of fiber material mixed with plastic that generates firm clinkers and interrupts the normal conditions in the reactor. The clinker predominantly contains aluminum, silicon, calcium and sodium that originate from the source of fiber and plastic. This research has shown that a mixture of silicon with aluminum, calcium and sodium under high temperatures result in the generation of a solid clinker that ultimately moves through the reactor and deposits at the bottom of the reactor.

Polycrystalline silicon films obtained by crystallization of amorphous silicon on aluminium based substrates for photovoltaic applications

The fabrication of crystalline silicon thin films on foreign substrates is an attractive and alternative approach to the ingot casting aiming to the reduction of the total costs of photovoltaic cells and modules. The purpose of this work is to describe the CRYSTALSI process which aims at forming polycrystalline silicon films thanks to the thermal crystallization of amorphous silicon layer deposited on aluminium based substrates. The latest are used as a catalyzer for silicon crystallization but also as a back metal contact and reflector for photovoltaic solar cells. Two types of aluminium substrates were applied in these studies: a pure aluminium substrate (99.7% purity) and a silicon rich aluminium substrate containing about 12% of silicon. Silicon thicknesses between 1 and 10μm were deposited and then annealed at temperatures of 490°C, 520°C and 550°C and for duration times from 5min to 12h. The crystallized silicon films were then characterized by Raman spectroscopy, by scanning electron microscopy and by electron backscatter diffraction. The analyses show that the resulting annealed film is composed of two distinct layers: a thin polycrystalline silicon film located just above the substrate and a thicker layer made of a mixture of silicon and aluminium. Contrary to the case of the pure aluminium substrate, the silicon rich aluminium substrate allow to obtain thick and continuous polycrystalline silicon layers due to a controlled diffusion of the silicon within the substrate. As a result, the crystallization at 550°C of 5μm thick amorphous silicon on silicon rich aluminium substrate led to the formation of a thick polycrystalline silicon layer composed of grains of few micrometers in size. A low activation energy of about 2eV is extracted suggesting that the silicon rich aluminium substrate is a catalyzer for the crystallization of amorphous silicon. As for the AIC process, it can be noticed that the limiting step of the CRYSTALSI process is the diffusion of the silicon in the aluminium. A chemical etching using a HNO3, HF, H2O (72.5ml/1.5ml/28ml) solution is found to be appropriate to remove the residual top layer, in order to have access to the polycrystalline silicon layer. This work demonstrates that the CRYSTALSI process can lead to the formation of polysilicon films that can serve as a seed layer for the growth of a thicker absorbing silicon film for photovoltaic applications.

Fabrication and oxidation behavior of Al4SiC4 powders

AbstractAl4SiC4 powders with high purity were synthesized by heating the powder mixture of aluminum (Al), silicon (Si), and carbon (C) at 1800°C in argon. The microstructure is characterized as platelike single grain. Both the nonisothermal and isothermal oxidation behavior of Al4SiC4 was investigated at 800°C‐1500°C in air by means of thermogravimetry method. It is demonstrated that Al4SiC4 powder possesses good oxidation resistance up to 1200°C and is almost completely oxidized at 1400°C. At 800°C‐1100°C, the oxide scales consist of an Al2O3 outer layer and a transition layer. Al4SiC4 remains the main phase. At 1200°C, some spallation resulting from the increment of Al2O3 and the mismatch of thermal expansion coefficient between different product layers can be observed. Above 1300°C, the oxide layer is composed of two part, i.e., large‐scale Al2O3 crystals (outer layer) and mullite with less amount of SiO2 (inner layer). The oxidation behavior changes due to the different oxide products. For the reaction kinetics, a new kind of real physical picture model is adopted and obtains a good agreement with the experimental data. The apparent activation energy is calculated to be 176.9 kJ/mol (800°C‐1100°C) and 267.1 kJ/mol (1300°C‐1400°C).

A new method for in vitro feeding of Rhipicephalus australis (formerly Rhipicephalus microplus) larvae: a valuable tool for tick vaccine development

BackgroundRhipicephalus microplus is a hard tick that has a major impact on cattle health in tropical and subtropical regions because it feeds on cattle and is implicated in the transmission of pathogens that cause diseases such as bovine anaplasmosis and babesiosis. Presently, acaricides are used to control tick infestation but this is becoming increasingly less effective due to the emergence of tick strains that are resistant to one or more classes of acaricides. Anti-tick vaccines are a promising alternative to control tick infestation in cattle. The life-cycle and host preference of R. microplus, however, makes vaccine research in cattle costly and would therefore greatly benefit from an in vitro screening system.MethodsTo this aim, a stacked 24-well in vitro feeding system was designed in which the blood meal was administered in a chamber on top of the compartment containing the ticks, exploiting their anti-gravitational tendency. Both compartments were separated by a special feeding membrane, which was made by applying a silicone mixture to a gold beater’s skin (baudruche membrane) with a paint roller to create a slightly uneven surface of 17–40 μm variable thickness. To further stimulate feeding, the membrane was treated with bovine hair extract and the unit was placed at 37 °C with 90% RH and 5% CO2.ResultsUsing this set-up with Rhipicephalus australis (formerly Rhipicephalus microplus), a larval engorgement rate of up to 71% could be achieved. The larvae could successfully feed on blood, but also on serum. The latter allows easy screening of the effect of sera that are raised against tick proteins on feeding. As an example, serum from cattle that were vaccinated with the Bm86 midgut protein of R. microplus significantly reduced larval engorgement rates by 42%.ConclusionThe in vitro feeding system’s high throughput design and its ability to measure statistically significant anti-tick effects in sera from immunized cattle enables screening of multiple vaccine candidates in a cost-effective manner.

Elucidating the process of hydrogen generation from the reaction of sodium hydroxide solution and ferrosilicon

For the first time, the process of hydrogen evolution from ferrosilicon 75 using sodium hydroxide solution has been investigated as a function of temperature using a combination of X-ray photoelectron spectroscopy, X-ray diffraction and physical measurements. Ferrosilicon 75, a mixture of silicon (~50wt.%) and iron disilicide (~50wt.%), has been shown to produce hydrogen by the action of sodium hydroxide solution on the silicon only, with the iron disilicide acting in the role of spectator/protector species for the silicon. Neither iron disilicide alone nor ferrosilicon 45, which does not contain a pure metallic silicon phase, was found to generate hydrogen under similar reaction conditions, further indicating that the presence of a pure metallic silicon phase is essential for hydrogen generation. As the iron disilicide acts as a diluent for the active silicon, it is hypothesized that this would result in a slower release of hydrogen than that which would be obtained from the reaction of silicon alone, which may be useful for applications which require a long-term, sustained release of hydrogen. A hydrogen yield of 462.5mL/g and a maximum hydrogen generation rate of 83mL/min g were obtained within 10min of reaction with 40wt.% NaOH at 348K.

Experimental determination of the enthalpies of formation of the lithium silicides Li7Si3 and Li12Si7 based on hydrogen sorption measurements

Abstract This work focuses on the determination of the standard molar enthalpies of formation Δ f H °(298) of the lithium silicides Li 7 Si 3 and Li 12 Si 7 . For this purpose the hydrogenation/dehydrogenation equilibria in the system Li-Si-H were investigated at three different temperatures (450 °C, 475 °C, 500 °C) using a Sieverts type apparatus. The measurements are based on two different sample types: (i) pure silicide Li 7 Si 3 (Li 2.33 Si) and (ii) a stoichiometric mixture of lithium hydride and silicon in the ratio of Li:Si = 2.33:1. The calculation of the standard enthalpies of formation by using the slopes of the classical Van't Hoff plot results in uncertainties of at least 10%. Due to this relatively large error, an alternative evaluation method based on the linking of the hydrogen equilibrium pressures p eq (H 2 ) from the sorption measurements with recently published precise heat capacity and entropy data of the lithium silicides was applied. The obtained values for the standard enthalpy of formation amount to Δ f H °(298) = (−25.3 ± 0.3) kJ/(mol atom) for Li 7 Si 3 and Δ f H °(298) = (−23.5 ± 0.3) kJ/(mol atom) for Li 12 Si 7 exhibiting strongly reduced uncertainties.

Structural and optoelectronic properties of p-type SiO:H films deposited in transition zone

P-type hydrogenated silicon oxide (p-SiOx:H) films are prepared by radio frequency plasma enhanced chemical deposition with various CO2 flow rates. We use gas mixtures of carbon dioxide (CO2), hydrogen (H2), silane (SiH4) and diborane (B2H6) as reaction source gases. For all experiments the substrate temperature, pressure and power density are fixed at 200 oC, 200 Pa and 200 mW/cm2, respectively. The films are deposited on Corning Eagle 2000 glass substrates for optoelectronic measurements and on crystalline Si wafers for Fourier transform infrared (FTIR) measurement. The structural, optical and electronic properties of the films are systematically studied as a function of CO2 flow rate. The CO2 flow rate is varied from 0 to 1.2 cm3 min-1, with all other parameters kept constant. It is shown that with the CO2 flow rate increasing from 0 to 1.2 cm3 min-1, the Raman peak shifts from 520 cm-1 to 480 cm-1 and corresponding crystalline volume fraction decreases from 70% to 0. In addition, the FTIR spectrum shows that the oxygen content increases from 0 to 17% and the hydrogen bond configuration gradually shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H2) and (Si-H2)n complexes in the film. What is more, with the incorporation of oxygen, the optical band gap of each of all p-type SiO:H films increases from 1.8 eV to 2.13 eV, while the dark conductivity decreases from 3 S/cm (nc-Si:H phase) to 8.310-6 S/cm (a-SiOx:H phase). Furthermore, the oxygen incorporation tends to disrupt the growth of silicon nanocrystals due to the created dangling bonds that arises from an increased structural disorder. This leads to microstructural evolution of SiO:H film from a single nanocrystalline phase into first a mixed amorphous-nanocrystalline and subsequently into an amorphous phase. At a certain threshold of CO2 flow rate, a transition from nanocrystalline to amorphous growth takes place. The transition from nanocrystalline to amorphous silicon is confirmed by Raman and FTIR spectra. In the transition region or crystalline volume fraction of about 45%, Raman spectrum also reveals that the a mixture of nanocrystalline silicon and amorphous silicon oxide (a-SiOx:H) phase exists in the film. This means that nanocrystalline silicon oxide (nc-SiO:H) is a two-phase structural material consisting of a dispersion of silicon nanocrystals (nc-Si) embedded in the amorphous SiOx network. As is well known, the oxygen-rich amorphous phase can help enhance the optical band gap, while the nc-Si phase contributes to high conductivity. Finally, it is the SiO:H film deposited at phase transition that can realize a relatively high dark conductivity (about S/cm) with a wide optical band gap of 2.01 eV in the film. By using the transition p-layer as the window layer in conjunction with a suitable buffer thickness, we obtain a thin film solar cell with an open-circuit voltage of 890 mV, a short-circuit current density of 12.77 mAcm-2, fill factor of 0.73, and efficiency of 8.27% without using any back reflector.

Microwave Cooled Microbolometers Based on Cermet Si–Cr Films

We present the results of creating a cooled microbolometer based on the cermet films of the silicon and chromium mixture. This material is used for manufacturing the freely hanging high-resistive microbolometers for the first time. The details of fabricating such microbolometers and the prospects for using cermet films to construct microbolometers are discussed. The first estimates of sensitivity of the fabricated microbolometers are given.

Surface alloying of A2618 aluminum with silicon and iron by TIG process

In this study, surface alloying of A2618 aluminum was carried out by pre-placing powder mixture of silicon and iron followed by subsequent tungsten inert gas (TIG) surface melting. This process resulted in the formation of 1.4 to 2.1mm thick alloyed layers containing Al-Fe-Si intermetallic compounds on aluminum substrate. The fabricated layers were then studied using optical and scanning electron microscopes equipped with energy dispersive X-ray spectroscopy (EDS) analyzer, X-ray diffractometer, microhardness tester and pin on disc wear testing machine. The hardness of the alloyed layer reached values as high as 210HV0.2, as compared with 60HV0.2 for A2618 aluminum base material, due to the formation of Al13Fe4, Fe5Si3, Al8Fe2Si, and Al5FeSi compounds in the alloyed region. The wear rate of the surface alloyed specimen was almost half of the wear rate of the untreated base material due to the presence of the aforementioned hard intermetallic compounds in the alloyed layer.

Industrial waste silica preparation of silicon carbide composites and their applications in lithium-ion battery anode

Silicon particles with uniform sizes were formed by cleaning solid organic wastes from the silicon industry with ether and nitric acid and ball milling the products. The resulting silicon was then used to prepare anode materials for lithium-ion batteries by mixing the silicon with graphite microspheres (GMs) and sintering the mixture in the presence of sucrose. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermo-gravimetric analysis were used to characterize the composites. The silicon and GM mixtures contained tightly bound amorphous carbon and ball-like composites. These P-Si/C composites had high capacities (520 mAh/g at 50 mA/g and 320 mAh/g at 500 mA/g) and excellent charge-discharge cycling stabilities, displaying only a 8.8% loss after 100 cycles at 50 mA/g).

ChemInform Abstract: Low Temperature Synthesis of LiSi2N3 Nanobelts via Molten Salt Nitridation and Their Photoluminescence Properties.

AbstractThe title nanobelts are synthesized from a mixture of silicon, melamine, LiCl, and NaF powders (alumina crucible, N2, 900—1200 °C, 3 h).

Investigation of radiation detection properties of CRY-018 and CRY-019 scintillators for medical imaging

During the last years the research for new scintillation crystals has been crucial for the improvement of imaging performance in nuclear medicine applications. Crytur company has recently released two new scintillators named CRY-018 and CRY-019 which are non hygroscopic, have short decay time and low refraction index. They represent the ideal candidates to substitute NaI:Tl and BGO crystals in future PET ad SPECT applications. The purpose of this work is to characterize this unknown crystals, look for possible applications in imaging for nuclear medicine. The results of this work were compared with the results obtained with a LaBr3:ce scintillation crystal. This particular crystal is used as a comparison benchmark because of its strong linear pulse height uniformity response and high energy resolution. Measurements have been performed with a high count rate which is typical for medical applications. Irradiation of the crystals have been performed in three different geometries and in a photon energy range suitable with SPECT and PET applications. The experimental results identify the CRY-018 as an Yttrium and Silicon mixture and the CRY-019 with as Lutetium and Silicon one. Moreover a light yield of about 45% of LaBr3 one, was obtained for both the CRY-018 and CRY-019. This is one of the higher light yield between most of the scintillation crystals usually used in nuclear medicine. Both crystals are characterized by a non-proportionality in the pulse height linearity response. Energy resolutions of 7.4% for CRY-018 and 8.4% for CRY-019 at 661 keV, have been measured. The intrinsic component of the energy resolution has been esteemed for all three scintillators. An intrinsic detection efficiency of about 45% at 122 keV for CRY-018 and 14% at 661 keV for CRY-019 has been measured. Compared with LaBr3:Ce efficiency, which is highly deteriorated by the coating required by the hygroscopicity, CRY-018 and CRY-019 are really interesting considering that these two samples are only 6 mm thick. Crytur's crystals seem to be suitable for nuclear medicine applications.

The role of aluminium as an additive element in the synthesis of porous 4H-silicon carbide

Addition of 5 at.% aluminium to silicon and carbon in the process of forming SiC monoliths for use as diesel particle filters and catalyst supports, creates mechanically stable, well connected, and highly porous 4H-SiC structures. These monoliths have 65% accessible porosity with pore diameters of 17−20μm. Mixtures of silicon, graphite, aluminium and water, are extruded into honeycomb structures and heated under nitrogen and argon. The 2H-AlN crystalline assembly formed during initial heating under nitrogen at 850°C acts as a template for the subsequent reaction between silicon and graphite under argon to yield 3C-SiC. During a final high temperature step under argon at 1950°C, Al-vapour/liquid is crucial for the transformation of 3C-SiC to 4H-SiC. This final step also alters the SiC crystal morphology significantly and produces large by-product crystals of Al4C3·mSiC·nAlN. The polytypic conversion and recrystallization mechanism were found, in this case, to be independent phenomena.

Thermodynamic Characterization of the Hydrogen Sorption Reaction of Lithium Silicides

In the modern society new energy storage systems have become a basic need not only as a mobile energy source but also in the context of the global energy transition. Currently, the dominating anode material in lithium ion batteries is Graphite. It´s main drawback is the limited storage capacity and the low energy density (372 mAh g-1). Therefore, Silicon seems to be an attractive alternative for the next generation anode material. It offers an extremely large theoretical specific energy density (Li17Si4: 4054 mAh g-1) and low discharge potentials. Furthermore, lithium silicides show high reversible hydrogen storage capacity and may be used as safe hydrogen storage material [1,2]. For the application of lithium silicides in lithium ion batteries fundamental knowledge of the physicochemical properties of the various phases is essential. Especially accurate thermodynamic data is crucial for the understanding of the Li-Si phase diagram, phase transitions and electrochemical equilibria as well as for any rational design of materials for battery applications. Numerous investigations of the binary Li-Si system were reported in literature, however, only few of them provided reliable thermodynamic data. Therefore, we recently reported experimental heat capacities and entropies of the five lithium silicides Li17Si4, Li16.42Si4, Li13Si4, Li7Si3 and Li12Si7 [1,3]. For thermodynamic calculations the enthalpies of formation are also required but the uncertainty of available data in literature is about 10 %, which is unacceptable for reliable equilibrium calculations. Motivated by this situation we recently focused our activity on the accurate determination of the standard enthalpies of formation ΔFH°(298K) of the lithium silicides Li17Si4, Li13Si4, Li7Si3 and Li12Si7. For this purpose, the hydrogen absorption and desorption equilibria at three different temperatures (450°C, 475°C and 500°C) were investigated using a Sieverts type apparatus. Two different sample types were used for the measurements: (i) a stoichiometric mixture of lithium hydride and silicon and (ii) pure silicide. The determination of the enthalpy of formation was performed by applying the van´t Hoff relation. This approach resulted in uncertainties of at least 10 %. This unsatisfying result directed our attention to an alternative evaluation method. Combining the hydrogen equilibrium pressure peq(H2) from the sorption measurements with our precise heat capacity and entropy data of the lithium silicides finally provided values for the standard enthalpies of formation with an error of less than 2 %. Utilizing the complete set of experimental thermodynamic data, the Li-Si phase diagram can now be calculated (CALPHAD) with excellent accuracy. [1] D. Thomas, M. Zeilinger, D. Gruner, R. Hüttl, J. Seidel, A. U. Wolter, T. F. Fässler, F. Mertens, The Journal of Chemical Thermodynamics 2015, 178–190. [2] M. T. McDowell, S. W. Lee, W. D. Nix, Y. Cui, Adv. Mater. 2013, 25, 4966–4985. [3] D. Thomas, M. Abdel-Hafiez, T. Gruber, R. Hüttl, J. Seidel, A. U. B. Wolter, B. Büchner, J. Kortus, F. Mertens, J. Chem. Thermodyn. 2013, 64, 205–225.

Thermodynamic Assessment of the Hydrogen Sorption Reaction in the System Li-Si-H

Recently, extensive studies using silicon anodes in lithium ion batteries (LiB) have shown that the Li-Si-system is an attractive alternative to the currently dominating graphite anode in view of costs and specific capacity. Currently the main obstacle of silicon is the poor charge/discharge cycling stability and capacity fading due to the large volume variation during charging/discharging. However, remarkable progress has recently been achieved by using thin films of silicon or silicon nanowires to relieve the mechanical stress [1]. It is indisputable that future progress in lithium silicide applications will require fundamental knowledge of the physicochemical properties of the various lithium silicide phases. Especially accurate thermodynamic quantities are crucial for the understanding as well as modelling of phase, reaction and electrochemical equilibria. In contrast to the numerous phase diagram studies reported in the literature, only few reliable thermodynamic quantities were available. Motivated by this situation, we recently reported experimental heat capacities and entropies of the lithium silicides Li17Si4, Li16.42Si4, Li13Si4, Li7Si3 and Li12Si7 [2,3]. Presently, the standard molar enthalpies of formation of the lithium silicides seem to be one of the most unreliable fundamental data because available values scatter by about 10 % which is unacceptable in view of reliable thermodynamic equilibrium calculations. This contribution is focused on the accurate experimental determination of the standard enthalpies of formation DFH°(298) of the lithium silicides Li17Si4, Li13Si4, Li7Si3 and Li12Si7. For this purpose the hydrogenation/dehydrogenation equilibria in the system Li-Si-H were investigated at three different temperatures (450 K, 475 K, 500 K) using a Sievert’s type apparatus. The measurements based on two different sample types: (i) pure silicide and (ii) a stoichiometric mixture of lithium hydride and silicon. The calculation of the standard enthalpies of formation by using the slopes of the classical van’t Hoff plots results in uncertainties of at least 10 %. Due to this unsatisfying large error, an alternative evaluation method is demonstrated linking the hydrogen equilibrium pressures peq(H2) from the sorption measurements with our precise heat capacity and entropy data of the lithium silicides. The obtained values for the standard enthalpies of formation show strongly reduced uncertainties of less than 2%. Finally, it will be shown that the phase diagram of the Li-Si-system can now be calculated (CALPHAD) with excellent quality using a complete set of experimental thermodynamic data. [1] M. T. McDowell, S. W. Lee, W. D. Nix, Y. Cui, Adv. Mater. 2013, 25, 4966–4985. [2] D. Thomas, M. Abdel-Hafiez, T. Gruber, R. Hüttl, J. Seidel, A. U. B. Wolter, B. Büchner, J. Kortus, F. Mertens, J. Chem. Thermodyn. 2013, 64, 205–225. [3] D. Thomas, M. Zeilinger, D. Gruner, R. Hüttl, J. Seidel, A. U. Wolter, T. F. Fässler, F. Mertens, The Journal of Chemical Thermodynamics 2015, 178–190.

Shock response of filled corrugated sandwich structures under extreme temperatures

Shock tube experiments were performed to investigate the blast response of corrugated steel cellular core sandwich panels filled with a silicone based syntactic foam at room and high temperatures. The syntactic foam filler was prepared by mixing a two-part silicone mixture with glass microspheres; its microstructure, and mechanical properties were also characterized. The syntactic foam-filled sandwich panels were loaded via air shock pressure by using the shock tube with a fixture capable of testing materials at temperatures up to 900℃. High-speed photo-optical methods, digital image correlation techniques, were used in tandem with optical band-pass filters and high intensity light sources for providing sufficient contrast at elevated temperatures. Back-face deformation images were captured using two synchronized high-speed cameras while a third camera captured the side view deformation images. The shock pressure profiles and digital image correlation analysis were used to obtain the impulse imparted to the specimen, transient deflection, in-plane strain and out-of-plane velocity of the back-face sheet. It was observed that using the syntactic foam as a filler material decreased the front face and back face deflections by 42% and 27%, respectively, as compared to the empty sandwich panel. At high temperatures, the silicone-based syntactic foam decomposes into silica, a stable and non-hazardous byproduct. The highest impulse was imparted to the specimen at room temperature and subsequently lower impulses with increasing temperatures were observed. Due to the increased ductility of steel at high temperatures, the specimens demonstrated an increase in back face deflection, in-plane strain and out-of-plane velocity with increased temperatures, with weld failure being the primary form of core damage.

Experimental Study on Foam Properties of Mixed Systems of Silicone and Hydrocarbon Surfactants

AbstractSilicone surfactants are inevitably involved in industrial applications in combination with hydrocarbon surfactants, but properties of the mixtures of silicone and hydrocarbon surfactants have received little attention, especially foam properties of the mixtures. In this study, aqueous solutions of respective binary mixtures of a nonionic silicone surfactant with anionic, cationic, and nonionic hydrocarbon surfactants were prepared for evaluation of their foam properties. Surface tension of aqueous solutions of the mixtures were measured with the maximum bubble pressure method. Foaming ability and foam stability of the mixtures were then evaluated with the standard Ross–Miles method. The findings show that the addition of the silicone surfactant results in a decrease in surface tension for aqueous solutions of the hydrocarbon surfactants. The critical micelle concentration (CMC) of the hydrocarbon surfactants is also changed by the additive silicone surfactant. Additionally, clear foam synergistic effects were observed in the mixtures of silicone and hydrocarbon surfactants, regardless of the ionic types of the hydrocarbon surfactant. The foam stability of the hydrocarbon surfactant was shown to generally improve with the increasing concentration of the silicone surfactant. Even so, aqueous solutions of different ionic hydrocarbon surfactants in the presence of the silicone surfactant will give different foam stabilities. The results of the present study are meant to provide guidance for the practical application of foams generated by the mixtures of the silicone and hydrocarbon surfactants.

The Effect of Additives on the Burning Rate of Silicon‐Calcium Sulfate Pyrotechnic Delay Compositions

AbstractThe effect of fuel particle size as well as the influence of inert and reactive additives on the burning rate of the Si‐CaSO4 composition was evaluated. The burning rate decreased with increase in fuel particle size, while the enthalpy remained constant. Addition of fuels to the base composition increased the burning rate, with an increase from 12.5 mm ⋅ s−1 to 43 mm ⋅ s−1 being recorded upon 10 wt‐% Al addition. Ternary mixtures of silicon, calcium sulfate, and an additional oxidizer generally decreased the burning rate, with the exception of bismuth trioxide, where it increased. The Si‐CaSO4 formulation was found to be sensitive to the presence of inert material, addition of as little as 1 wt‐% fumed silica stifled combustion in the aluminum tubes.

Experimental Determination and Assessment of Enthalpies of Formation of Lithium Silicides

Recently, extensive studies using silicon anodes in lithium ion batteries (LiB) have shown that the Li-Si-system is an attractive alternative to the currently dominating graphite anode in view of costs and specific capacity. Currently the main obstacle of silicon is the poor charge/discharge cycling stability and capacity fading due to the large volume variation during charging/discharging. However, remarkable progress has recently been achieved by using thin films of silicon or silicon nanowires to relieve the mechanical stress [1]. It is indisputable that future progress in lithium silicide applications will require fundamental knowledge of the physicochemical properties of the various lithium silicide phases. Especially accurate thermodynamic quantities are crucial for the understanding as well as modelling of phase, reaction and electrochemical equilibria. In contrast to the numerous phase diagram studies reported in the literature, only few reliable thermodynamic quantities were available. Motivated by this situation, we recently reported experimental heat capacities and entropies of the lithium silicides Li17Si4, Li16.42Si4, Li13Si4, Li7Si3 and Li12Si7 [2,3]. Presently, the standard molar enthalpies of formation of the lithium silicides seem to be one of the most unreliable fundamental data because available values scatter by about 10 % which is unacceptable in view of reliable thermodynamic equilibrium calculations. This contribution is focused on the accurate experimental determination of the standard enthalpies of formation ΔFH°(298) of the lithium silicides Li17Si4, Li13Si4, Li7Si3 and Li12Si7. For this purpose the hydrogenation/dehydrogenation equilibria in the system Li-Si-H were investigated at three different temperatures (450 K, 475 K, 500 K) using a Sievert’s type apparatus. The measurements based on two different sample types: (i) pure silicide and (ii) a stoichiometric mixture of lithium hydride and silicon. The calculation of the standard enthalpies of formation by using the slopes of the classical van’t Hoff plots results in uncertainties of at least 10 %. Due to this unsatisfying large error, an alternative evaluation method is demonstrated linking the hydrogen equilibrium pressures peq(H2) from the sorption measurements with our precise heat capacity and entropy data of the lithium silicides. The obtained values for the standard enthalpies of formation show strongly reduced uncertainties of less than 2%. Finally, it will be shown that the phase diagram of the Li-Si-system can now be calculated (CALPHAD) with excellent quality using a complete set of experimental thermodynamic data. [1] M. T. McDowell, S. W. Lee, W. D. Nix, Y. Cui, Adv. Mater. 2013, 25, 4966–4985. [2] D. Thomas, M. Abdel-Hafiez, T. Gruber, R. Hüttl, J. Seidel, A. U. B. Wolter, B. Büchner, J. Kortus, F. Mertens, J. Chem. Thermodyn. 2013, 64, 205–225. [3] D. Thomas, M. Zeilinger, D. Gruner, R. Hüttl, J. Seidel, A. U. Wolter, T. F. Fässler, F. Mertens, The Journal of Chemical Thermodynamics 2015, 178–190.

Structure and optical properties of aSiAl and aSiAlHx magnetron sputtered thin films

Thin films of homogeneous mixture of amorphous silicon and aluminum were produced with magnetron sputtering using 2-phase Al–Si targets. The films exhibited variable compositions, with and without the presence of hydrogen, aSi1−xAlx and aSi1−xAlxHy. The structure and optical properties of the films were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy, UV-VisNIR spectrometry, ellipsometry, and atomistic modeling. We studied the effect of alloying aSi with Al (within the range 0–25 at. %) on the optical band gap, refractive index, transmission, and absorption. Alloying aSi with Al resulted in a non-transparent film with a low band gap (<1 eV). Hydrogenation of the films increased the band gap to values >1 eV. Variations of the Al and hydrogen content allowed for tuning of the optoelectronic properties. The films are stable up to a temperature of 300 °C. At this temperature, we observed Al induced crystallization of the amorphous silicon and the presence of large Al particles in a crystalline Si matrix.