Type Apparatus Research Articles

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.

Characterization of a nanocrystalline Mg–Ni alloy processed by high-pressure torsion during hydrogenation and dehydrogenation

Ball-milled Mg-Ni powder has been cold-compacted and subsequently processed by severe shear deformation under high-pressure torsion. The effect of high pressure torsion on morphology and microstructure of the disk-shape samples has been characterized by scanning electron microscopy and X-ray diffraction, respectively. In order to achieve partially hydrogenated and dehydrogenated states of deformed samples, the hydrogen uptake or release was interrupted at 25%, 50% and 75% hydrogen contents in a Sieverts' type apparatus. In this paper we present the characterization of the microstructure during a full absorption-desorption cycle of the nanocrystalline Mg–Ni alloy.

Pulsating flow type apparatus: Energy dissipation rate and droplets dispersion

Hydrodynamics of pulsating flow type apparatus (PFA), namely droplet disintegration, was investigated by use of theoretical approach and experimentally. Impact of several mechanisms on droplet sizes: Kelvin–Helmholtz instabilities, turbulence in the bulk of liquid and near walls of apparatus, dynamic and inertial mechanisms as well as high shear stresses are studied. It was found that oil droplet sizes in water in PFA (mean diameter of 20μm and the maximum diameter of 35μm) are 1.8 times smaller than in the stirred tank with Rushton turbine (maximum diameter about 70μm) at the same level of energy dissipation rate. By other words, according to the Kolmogorov theory the stirred tank with Rushton turbine needs 4.5 times more dissipated energy to get the same sizes of droplets (1800W/kg for Rushton turbine and 400W/kg for PFA). Comparison of PFA with tubular turbulent apparatus (baffled pipe) has shown similar advantages of PFA.It has been revealed that these effects attributed to the generally other mechanisms of droplet dispersion in PFA compared with usual apparatuses like stirred tanks, where the turbulence plays the main role in the droplet disintegration. Among these mechanisms are pulsations of velocity, acceleration and pressure, high shear stresses rate, and some instabilities.

Composition and biological activities of the essential oil of Piper corcovadensis (Miq.) C. DC (Piperaceae)

Essential oil from fresh leaves of the shrub Piper corcovadensis (Miq.) C. DC was obtained in 0.21% (w/w) yield by hydrodistillation in a Clevenger type apparatus. Thirty-one components, accounting for 96.61% of the leaf oil, were identified by gas chromatography-mass spectrometry. The major constituents of the oil were 1-butyl-3,4-methylenedioxybenzene (30.62%), terpinolene (17.44%), trans -caryophyllene (6.27%), α-pinene (5.92%), δ-cadinene (4.92%), and Limonene (4.46%). Bioassays against larvae of the Dengue mosquito (Aedes aegypti) revealed that leaf oil (LC50 = 30.52 ppm), terpinolene (LC50 = 31.16 ppm), and pure 1-butyl-3,4-methylenedioxybenzene (LC50 = 22.1 ppm) possessed larvicidal activities and are able to interfere with the activity of proteases from L4 gut enzymes. Additionally, the essential oil exhibited a strong oviposition deterrent activity at 50 and 5 ppm. This paper constitutes the first report of biological activities associated with the essential oil of leaves of P. corcovadensis.

Dry Sliding Wear Behavior of Tic-AA7075 Metal Matrix Composites

ABSTRACT The AA7075 matrix reinforced with 2 to 10 weight % of TiC particles were made by stir casting. Effects of load on the wear and friction of the worn surfaces of matrix and composite pins sliding against a rotating disc have been investigated under dry condition. The wear tests were carried out using a pin-on-disc type apparatus at three different loads (10, 20 and 30N) under a constant velocity of 2m/s for a sliding distance of 2Km. The coefficient of friction was recorded and wear rate of the Aluminum metal matrix composite (AMMC) pins calculated from mass loss measurement. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was used to investigated the worn surface. It is observed that higher load leads to higher wear rate and lower coefficient of friction for matrix as well as composites. The hardness was found to increase with the increase in wt. % of the reinforcement.

Compositional Analysis of Lavandula pinnata Essential Oils

The genus Lavandula includes about thirty species plus a number of intraspecific taxa and hybrids, which are distributed in the Mediterranean area. The traditional use of lavender both as perfume or medicinal plant is known since antiquity. Nowadays several species are extensively cultivated for the extraction of their essential oils (EOs) which are used in manufactured products like cosmetics and perfumes or in phytotherapy. Lavandula pinnata L. f. (syn L. pinnata Lundmark) is a rare species native to the Canary Islands used in folk medicine as relaxant and also a valuable remedy against bites. To the best of our knowledge, EOs from L. pinnata have been very little studied. The present paper reports on the quali- and quantitative compositional profile of the EOs distilled (by a Spring type apparatus) from the aerial parts (flowers and leaves) of this species cultivated in soilless conditions. Chemical analyses by means of GC and GC-MS techniques have indicated that oxygenated monoterpenes are the main constituents of both the flowers (68.30%) and the leaves (83.65%). Carvacrol is the main compound which characterizes the EOs of this species. In addition, discrete amounts of spathulenol (12.22%) and caryophyllene oxide (14.62%) have been detected in flowers EOs, while leaves EOs contained small amounts of carvacrol methyl ether (2.52%).

Volatile Composition of Underground Parts of Tanacetum longifolium Wallich ex DC.

Tanacetum longifolium is a perennial, aromatic herb (Asteraceae), growing between 3300-5000 msl in the Himalaya. Essential oil of this genus was imported in India for use in Homeopathy and western medicine. Plants were collected at flowering stage, essential oil was extracted using Clevenger type apparatus and analyzed by GC-MS and GC-FID. Eleven compounds have been identified from volatile oil constituting 83.0 % of the total essential oil, out of which major component was β-pinene (>55.37%).

Isothermal vapor–liquid equilibrium data for the trifluoromethane (R23) + 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) system at temperatures from 254 to 348 K

In this study, we present new experimental data of vapor–liquid equilibrium for the binary system trifluoromethane (R23) + 2,3,3,3-tetrafluoropropene (R1234yf), measured at 254.10, 273.43, 293.24, 303.17, 318.08, 332.97, and 348.40 K and at pressure ranging from 0.1568 to 4.3553 MPa. A “static-analytic”-type apparatus is used to do the measurements, with sampling of the equilibrium phases via capillary sampler (ROLSI™). We used two different methods to model the obtained isothermal P-x-y data: 1) the Peng-Robison cubic equation of state, incorporating the Mathias-Copeman alpha function, combined with the NRTL excess free energy model and Wong-Sandler mixing rules, and 2) the PC-SAFT equation of state. Both models show a very good agreement with the experimental data.

A structural study of the hydrogen absorption properties by replacing vanadium with zirconium in metal alloys

Hydrogen storage and microstructure the TiCrV0.9, TiCrV0.9Zr0.2 and TiCrV0.7Zr0.4 alloys were investigated. The alloys were melted in arc furnace, the structure was analysed by X- ray diffraction and hydrogen absorption times were analysed by Sievert's type apparatus. The results showed that the addition of Zr replacing the V decreases in the absorption capacity passing of 3.8%wt to 2.0%wt in contrast the speed of hydrogen absorption increases considerably.

MATHEMATICAL MODELING OF THE SULFURIC ACID DROPS EVAPORATION

The evaporation process of sulfuric acid solution has been analyzed in the hollow apparatus of column type under direct contact between acid drops and hot gas. On the basis of the mathematical model the main parameters have been calculated: evaporation time, distance passed by a drop and its evaporation temperature. The mathematic dependencies of evaporation time of water and sulfuric acid drops on their initial diameters and air temperature have been developed. The drop diameter of ≤ 0.5∙10-3 m was found to be necessary to carry out the evaporation with the rate sufficient for the industrial columns. The obtained results are proposed to be used to determine the effect of intensifying parameters on the evaporation process of sulfuric acid waste solutions and development of their recycling technology.

Chemical profiling of leaf essential oil, Antioxidant potential and Antibacterial activity of Syzygium lanceolatum (Lam.) Wt. & Arn. (Myrtaceae)

Introduction: The present study was aimed to analyse the chemical composition, antioxidant potential and antibacterial activity in the leaf essential oil of Syzygium lanceolatum Methods: The essential oil was isolated by hydrodistillation method using a Clevenger type apparatus. The chemical composition of leaf essential oil was analysed by GC-MS. Antioxidant activity was determined by DPPH and ABTS radical scavenging assay. Antibacterial potential was tested against six bacterial strains. Results: GC-MS analysis revealed 2,8-Dimethyl-7-methylene-1,8-nonadien-3-yne (9.77%), Germacrene D (7.45%) as the major constituents and Linalool, β-Selinene (0.03%), Santalol (0.02%) were present in trace amounts. Maximum free-radical scavenging activity (69.97%) was observed at 500 ppm by the essential oil of S. lanceolatum, while the synthetic antioxidant Gallic acid showed 90.93% inhibition at the same concentration. The IC 50 value of leaf essential oil and standard gallic acid were 219.24 ± 5.82 ppm and 159.84 ± 2.7 ppm respectively. In ABTS analysis, the oil showed the percentage inhibition in concentration dependent manner. 500 ppm concentration of oil showed 73.01% free-radical inhibition while the gallic acid exhibited 90.4% inhibition. The IC 50 value of leaf essential oil and standard were 169.68 ± 3.09 ppm and 217.09 ± 0.70 ppm respectively. Antibacterial activity of leaf essential oil was tested against six bacterial strains and it was effective against all the strains. Conclusion: A total of 106 compounds were identified from the leaf essential oil and alkynes were the major class of compound, followed by the sesquiterpenes. The DPPH radical scavenging assay confirmed the antioxidant potential of the essential oil. Antibacterial activity tests proved that it is a potent growth inhibitor of pathogenic microbes. The present study throws light on the bioactive composition of S. lancoelatum essential oil and further studies will confirm the mode of action of these compounds.

Sliding Wear Analysis of Ultra High Strength Steel Using Full Factorial Design Approach

This study describes multi-factor-based experiments that were applied to investigate the sliding wear behaviour of quenched and tempered wear resistant steel. This study was aimed to evaluate the effect of input parameters (such as applied load, sliding velocity and sliding time) on wear rate. Full factorial design through design of experiments approach was used for investigation by establishing an empirical relationship between wear loss and input parameters and determining the optimal combination of testing parameters for minimum and maximum wear losses. Sliding wear tests were carried out using pin-on-disc type apparatus at room temperature under dry sliding wear conditions. Detailed investigation revealed that applied load was the most significant factor affecting the wear performance followed by sliding velocity and sliding time. The maximum weight loss due to wear was found to be 33.48 mg when experimentation was conducted at maximum levels of input variables and minimum wear loss of 3.12 mg was obtained at the minimum levels of load, sliding velocity and sliding time. The scanning electron microscopy of the worn pin surfaces shows that adhesion and plastic deformation were the dominating mechanisms involved during experimentation that resulted in maximum wear of the pins, and on the other hand no such mechanism persisted when the pins were worn under minimum sliding wear conditions.

TO PHYSICAL MODEL OF THE VACANCY CLUSTER TUBES FORMATION AND METAL PROPERTIES CHANGES AFTER DYNAMIC CENTRIFUGAL CASTING

The experimental results on crystallization of Pb in dynamic centrifugal casting apparatus of a new type, with a rotor speed 3000 rev/min have considered. In the crystallized Pb, vacancy clusters with an average tube diameter 39 nm have revealed by scanning electron microscopy (SEM). After the dynamic centrifugal casting process, two Pb melting temperatures have been recorded by DSC method. A remarkable enhancement of the mechanical properties of recrystallized Pb have established by dynamic mechanical analysis (DMA). The paper is devoted to the physical model of the vacancy clusters conversion to nanopipes and possible change of physical properties of metals after dynamic centrifugal casting at speeds of the order 3000 rev/min.

Calculation of predominant drug release mechanism using Peppas-Sahlin model, Part-I (substitution method): A linear regression approach

The objective of this study was to develop Nicorandil controlled release floating tablets using combination of hydrophilic and hydrophobic polymers by melt granulation technique. The in vitro drug release characteristics were determined using USP XXII type 2 (paddle type) apparatus, in a medium of 0.1N HCL. The dissolution profile of all the batches were extended up to 24 hrs. To study and model the drug delivery from polymeric floating tablets, the dissolution data was fitted to a pioneered method Korsmeyer-Peppas equation. The results indicate that, all the formulations followed super Case-II release mechanism, except MCS4 which followed non- Fickian or anomalous release mechanism. In order to determine the predominant mechanism (diffusion/ relaxation model), drug release data was incorporated into Peppas-Sahlin model. The results revealed that, Fickian release contribution was preponderance than corresponding Case-II relaxational contribution in all the formulations. In addition to this, the relaxational contribution was observed with negative sign in all the formulations but, only at specific time intervals. Relaxational contribution with negative values indicates the Fickian release mechanism was more pronounced than relaxation i.e. almost the relaxational mechanism was absent.

Effects of topical and systemic administration of Eugenia caryophyllata buds essential oil on corneal anesthesia and analgesia.

Clinical studies suggest that essential oil of Eugenia caryophyllata (Clove) buds (EOEC) is efficacious in the treatment of dental pain. In the present study, we investigated the analgesic and local anesthetic effects of EOEC and its possible mechanisms of action in acute corneal pain in rats. EOEC was extracted by hydro-distillation in a Clevenger type apparatus from clove buds. The acute corneal pain was induced by applying a drop (40 µl) of 5 M NaCl solution on the corneal surface, and the numbers of eye wipes were counted during the first 30 s. The mechanical sensation of the cornea was evaluated by calibrated Von Frey filaments. Systemic administration of EOEC (100 and 200 mg/kg, SC) and morphine (2.5 and 5 mg/kg, IP) produced a significant antinociceptive effect in acute corneal pain. Pretreatment with naloxone or atropine prevented the EOEC-induced analgesia. However, L-arginine and methylene blue did not change the suppressive effect of EOEC on corneal pain response. Topical application of EOEC, eugenol and lidocaine significantly decreased corneal sensitivity. Combination treatments of eugenol (25 µg) with lidocaine (0.5%) and EOEC (50 µg) with lidocaine (0.5%) also significantly suppressed corneal sensitivity. Systemic administration of EOEC produced analgesia in the acute corneal pain through mechanisms that involved both opioidergic and cholinergic systems. In addition, topical instillation of EOEC, eugenol, and lidocaine produced local anesthesia in the rat cornea. Sub-anesthetic doses of EOEC or eugenol produced a significant local anesthetic effect when concurrently used with the sub-anesthetic dose of lidocaine.

Chemical Composition of the essential oil of Morella parvifolia (Benth.) Parra-O. from the Venezuelan Andes

Venezuela is a country with high biodiversity. The specie Morella parvifolia belongs to the Myricaceae family, which is rich in essential oils. The study of M. pubescens essential oil is the only reported in this genus. Its major component is germacrene - B (~ 32%). The present work reports the chemical composition of the essential oil of Morella parvifolia (Benth.) Parra -O. collected in Venezuela. The essential oil (0.3 - 0.5 % yield) of the fresh leaves of M. parvifolia from three different plants, from the same location, were obtained by hydrodistillation using a Clevenger type apparatus. The chemical constituents were identified by GC-MS analysis. From twenty three to twenty nine compounds (96.06 – 97.31 % of the samples) were identified. The major constituents found were α - bisabolol (50.56 - 58.9 %) and α - pinene (12.88 - 16.79%). Analysis of antimicrobial activity on Gram (+) and Gram (-) strains was performed but no antibacterial activity was observed. .

Caracterização Química do Óleo Essencial de Philodendron sp. no Município de São João da Baliza, Roraima

In the Amazon region of Brazil, the roots of different species of Philodendron sp. are used in traditional medicine. This study aims to characterize the chemical composition of the essential oils of Philodendron genus, native in mountain area in the municipality of Sao Joao da Baliza, from the Roraima state. The essential oils roots were extracted by hydrodistillation in Clevenger type apparatus for a period of three consecutive hours. The identification of chemical constituents was made by comparison of the mass spectra of the substances with the database of the GCMS system and Kovats index. DOI: http://dx.doi.org/10.17807/orbital.v7i4.774

Chloride catalytic effect on hydrogen desorption in NaAlH4

Hydrogen is considered as an environmental friendly energy carrier because it generates no pollution. Chlorides are promising catalyst for the hydrogen desorption in sodium alanate. All reactions and operations were performed under argon atmosphere in glove box. Crystalline NaAlH4 and catalyst TiCl3, Nb2O5 PbCl2 and CeCl3 were mixed in a ratio of (1, 2) wt%. Due to the air sensitivity of the samples they were covered with a kapton tape layer to minimize any contamination for characterization purpose. Structural characterizations and phase compositions of the samples were studied by XRD. The hydrogen storage capacity is measured by seivert type apparatus. Amount of desorbed hydrogen was found to be 3.6 wt % to 5.5 wt% at 250 °C with different type of catalyst. In the present work effect of doping of TiCl3, Nb2O5 PbCl2 and CeCl3 catalysis in NaAlH4 are investigated to understand the hydrogen desorption kinetics. It is concluded that enhanced storage capacity of NaAlH4 can be achieved due to various catalysts with reduction in temperature 285 °C–250 °C for desorption.

Catalytic effect of Nb2O5 on dehydrogenation kinetics of NaAlH4

Sodium alanate is an important hydrogen storage material with high hydrogen content of 7.5 wt%, but it does not release hydrogen easily. In the present work niobium oxide (Nb2O5) and titanium cholride (TiCl3) catalysts are used to dehydrogenate NaAlH4. Structure and morphology of materials are characterized by XRD and SEM techniques. Sodium alanate was found to have tetragonal structure having a = 5.02 Å, b = 5.02 Å and c = 11.34 Å lattice parameters. Dehydrogenation of NaAlH4 at 250 °C converts it to a great extent to Na3AlH6 with lattice parameter a = b = c = 7.755 Å, living behind a very small amount of sodium alanate reflecting in XRD peak. Scanning electron microscopic studies shows reduction in particle size after dehydrogenation. The dehydrogenation kinetics of the samples was studied using dynamic Seivert type apparatus. The amount of desorbed hydrogen was found to be 4.8 and 5.0wt %.

A Study of the Pressure-Composition-Temperature Curve of Mg(BH4)2 by Sievert’s Type Apparatus

The Pressure-Composition-Temperature(PCT) curve of Mg(BH4)2 was studied by Sievert`` type apparatus. In order to understand the slope of the first plateau pressure, a thermal analysis technique was introduced. The PCT curves of the dehydriding reaction for Mg(BH4)2 are measured at 573, 598, 623, and 653 K, respectively. Under every temperature measured, the first plateau pressure shows slope but the second plateau pressure of MgH2 is clearly observed. The apparent enthalpy for the first plateau pressure from Mg(BH4)2 to MgH2 is roughly estimated. The equilibrium pressure at each temperature is determined to be the first plateau pressure where the hydrogen content is -5wt%. The apparent enthalpy for the first reaction from Mg(BH4)2 was estimated to be △H = 51.1 kJ mol-1 H2, and the apparent enthalpy for the dehydriding reaction from MgH2 was estimated to be △H = 90.0 kJ mol-1H2. The result of the thermal analysis shows three peaks. This means that it decomposes at least through the pathway of three reactions.