Calorimetric Techniques Research Articles

Structural and thermal investigations of CaU(PO4)2; phase diagram study of MO−UO2–P2O5 systems (M = Ca, Sr, Ba)

Structure of monoclinic CaU(PO4)2, synthesized in argon atmosphere at 1473 K, was derived from powder X−ray diffraction (XRD) data using Rietveld refinement method. Thermogravimetric (TG) Curve recorded up to 1573 K in argon atmosphere showed thermal as well as structural stability of CaU(PO4)2. When heated in air, TG curve of CaU(PO4)2 showed weight gain between 1100–1673 K due to oxidation of U(IV) to U(VI). Molar heat capacity of CaU(PO4)2 as well as some ternary alkaline earth phosphates were calculated using differential scanning calorimeter technique. Phase diagrams of pseudo ternary alkaline earth metal−uranium (IV)−phosphates were derived and phase boundaries were established. All the ternary and quaternary compounds used for deriving the phase diagrams were synthesized in an argon atmosphere at 1473 K. X-ray diffraction (XRD) was used as a prime analytical tool to investigate the phase mixtures and draw phase boundaries. Phase diagram of SrO–UO2–P2O5 and BaO–UO2–P2O5 systems confirm the existence two quaternary compounds, (Sr/Ba)U(PO4)2 and (Sr/Ba)7U(PO4)6 in the systems whereas in CaO–UO2–P2O5 system only one quaternary compound, CaU(PO4)2, was identified.

Revealing the dynamics and energetics of interaction of a cationic biological photosensitizer within a bile salt aggregate.

The present investigation reports a detailed characterization of the interaction of a cationic photosensitizer, phenosafranin (PSF) with sodium deoxycholate (NaDC) bile salt aggregates based on spectroscopic and calorimetric techniques. Our explicit spectroscopic results not only establish the occurrence of PSF-NaDC binding interaction, but also reveal marked lowering of micropolarity at the interaction site (ET(30) = 55.97 kcal mol-1 in the presence of NaDC as compared to ET(30) = 63.1 kcal mol-1 in bulk aqueous buffer). A thorough mathematical analysis of the fluorescence depolarization results based on the two-step and wobbling in cone model yields critical insight into the complex rotational relaxation dynamics of the bound drug. The impartation of motional restriction on the PSF molecules within the bile salt aggregates is evidenced from enhancement of average rotational correlation time from <τr> = 136 ps in aqueous buffer to 1.11 ns with added NaDC (8.0 mM). This is further supported from a high value of the generalized order parameter (S = 0.81) as well as the diffusion coefficient (Dw = 1.40 × 1012 s-1). Furthermore, our extensive calorimetric investigation unveils the complicated thermodynamics of the interaction process in terms of predominant entropic contribution over the enthalpic part in the lower temperature regime (TΔS = 18.84 ± 1.13 kJ mol-1, ΔH = -5.82 ± 0.35 kJ mol-1 at 288 K) with subsequent reversal of the relative contributions with increasing temperature (TΔS = 7.54 ± 0.39 kJ mol-1, ΔH = - 17.09 ± 0.90 kJ mol-1 at 318 K). The instrumental role of the hydrophobic effect underlying the PSF-NaDC interaction is characterized by a negative heat capacity change (ΔCp = -364 J mol-1 K-1). An intriguing thermodynamic feature in terms of enthalpy-entropy compensation (with increasing temperature ΔG remains almost constant while ΔH and TΔS vary significantly) aptly corroborates the aforesaid argument and establishes an appreciable hydrophobic contribution to the overall binding energies.

Performance evaluation of various diagnostics developed for a negative ion based neutral beam injector program in IPR

The characteristics of a negative hydrogen ion (H-) source and its neutralization efficiency determine the performance of a negative ion based neutral beam injector (NNBI). Therefore, for the safe operation of an NNBI system, it is necessary to monitor the performance of the ion source and its beam through a systematic characterization process. A judicious selection of different diagnostics based on electrical, optical and thermal types and including calorimetric techniques are required. In this regard, a number of diagnostics are being developed under the NNBI R&D program in the Indian Test Facility (INTF). These diagnostics are versatile in nature in terms of their working principles and independent prototype experimental efforts have been carried out to establish them and prepare them for operational use. Electrical probes (EP), optical emission spectroscopy and cavity ring down spectroscopy (CRDS) are mainly envisaged for ion source plasma characterization. Additionally, standard electrical measurements in RF and DC power supply circuits are already in regular use in the operational experimental setups, ROBIN and HELEN-I, for monitoring the power supplies. Doppler shift spectroscopy (DSS) and optical emission tomography (TOMO) are developed for beam characterization in terms of divergence, stripping and beam profile. Some of these are characterized on separate prototype experiments and are already integrated and have been tested in the available operational plasma experimental setups: ROBIN and HELEN-I. The DSS system, with multiple lines of sight (LOS) (blue-shifted and red-shifted), is integrated in the ROBIN setup and CRDS is arranged in HELEN-I. The TOMO technique is used to find the beam power density profile from the hydrogen beam emitted Balmer line intensity. The optical brightness profile of a neutral beam due to beam emission radiation is proportional to the beam power density. In this regard, a tomography code based on maximum entropy is developed to reconstruct the 2D optical emissivity profile of the INTF beam by inverting the LOS integral of the brightness of the beam. The code has been validated with the simulated INTF beam power density profile, in terms of the mathematical functions representing it. In the present manuscript, the performance evaluations of these diagnostics are presented.

Process hazard evaluation for catalytic oxidation of 2-octanol with hydrogen peroxide using calorimetry techniques

In this work, various calorimetric and analytical techniques were implemented to identify reaction pathways and safety issues associated with the 2-octanol to 2-octanone two liquid phase catalytic reaction oxidative using aqueous hydrogen peroxide as oxidant, sodium tungstate (Na2WO4) as catalyst and methyltri-n-octylammonium hydrogen sulfate [CH3(n-C8H17)3N+HSO4−] as phase transfer catalyst. Differential scanning calorimetry (DSC) was employed to measure the temperature and heat flux of the reactant mixtures under dynamic scanning. Phi-TEC II adiabatic calorimeter was used to track temperature and pressure under worst runaway scenario. Isothermal reaction calorimeter (RC1e) was used to assess conditions relevant to normal process operations. Gas chromatography-mass spectrometry (GC–MS) was utilized to analyze final products of all measurements qualitatively and quantitatively. Data from both DSC and Phi-TEC II show that two highly exothermic reactions were detected with “onset” temperature at ~50 and ~220 °C, respectively. In all cases, only 2-octanol and 2-octanone were the identifiable compounds via GC–MS. 2-Octanol conversion was in the range of 15–50% and it reveals a linear correlation with overall heat generation. Data obtained verify that both exothermic peaks result from alcohol oxidation, thus indicating that in the conditions of the reaction and with the employed catalysts, hydrogen peroxide did not fully decompose at lower temperatures. Non-condensable gas generation measurements validated this argument. Based on those results, possible macroscopic reaction pathway was proposed. Furthermore, pressure and temperature profiles by PHI-TEC II indicated a potential transition to a homogeneous liquid phase at higher temperatures. The RC1e results verified that 2-octanol conversion was higher at higher stirring rates, while evaporative cooling of solvents tempered the reaction by removing the heat generated, thus improving safety. These findings can be further used to propose safer operating measures for design and scale-up of this reaction process to avert a potential runaway and to probe in the reaction pathways so as to increase inherently safer conditions for its performance.

Thermal stability and crystallization kinetics of Ge13In8Se79 chalcogenide glass

ABSTRACTGe-In-Se system, similar to many other chalcogenide glasses, has attracted much attention due to its interesting physical properties and applications. This article reports thermal analysis and estimation of activation energies of the glass transition and amorphous-crystallization transformation of Ge13In8Se79 chalcogenide glass. The kinetic parameters were investigated under a non-isothermal condition at different heating rates (7–40 K/min) using differential scanning calorimetric (DSC) technique. The amorphous nature of the samples was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The activation energy was calculated from DSC data using five isoconversional methods: Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Vyazovkin. The results confirm that the activation energy of crystallization varies and depends on the degree of crystallization as well as temperature. It was also observed that the transformation from amorphous to the crystalline structure is complex involving different mechanisms of nucleation, diffusion, and growth.

Dual-readout calorimetry

We summarize the fundamental aspects of dual-readout calorimetry, a calorimetric technique able to overcome the non-compensation problem by means of two independent scintillation and Cherenkov light signals detection. The expected ultimate energy resolution for single-hadron detection, together with the excellent particle identification capability, makes a dual-readout fiber calorimeter one of the most promising options for future leptonic colliders. In this paper, we include the main benefits of a new silicon photomultiplier-based readout system that allows to sample showers with an unprecedented spatial resolution.

Direct determination of anaerobe contributions to the energy metabolism of Trypanosoma cruzi by chip calorimetry.

We describe a chip calorimetric technique that allows the investigation of biological material under anoxic conditions in a micro-scale and in real time. Due to the fast oxygen exchange through the sample flow channel wall, the oxygen concentration inside the samples could be switched between atmospheric oxygen partial pressure to an oxygen concentration of 0.5% within less than 2h. Using this technique, anaerobic processes in the energy metabolism of Trypanosoma cruzi could be studied directly. The comparison of the calorimetric and respirometric response of T. cruzi cells to the treatment with the mitochondrial inhibitors oligomycin and antimycin A and the uncoupler FCCP revealed that the respiration-related heat rate is superimposed by strong anaerobic contributions. Calorimetric measurements under anoxic conditions and with glycolytic inhibitors showed that anaerobic metabolic processes contribute from 30 to 40% to the overall heat production rate. Similar basal and antimycin A heat rates with cells under anoxic conditions indicated that the glycolytic rates are independent of the oxygen concentration which confirms the absence of the "Pasteur effect" in Trypanosomes. Graphical abstract.

Differential Scanning Calorimetric Study of the Effect of Cholesterol on the Thermotropic Phase Behavior of the Phospholipid 1‐Stearoyl‐2‐Oleoyl‐sn‐Glycero‐3‐Phosphocholine

AbstractUsing the differential scanning calorimetric (DSC) technique, the thermal properties of 1‐stearoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (SOPC) phospholipid and its mixture with cholesterol (Chol), in the range between 10 and 50 mol.%, were investigated. A considerable modification of the structural conformation and the biophysical properties of the bilayer of the phospholipid system after the Chol incorporation were detected. Concentrations below 30 mol.%, and especially in the range 10–20 mol.%, were found to be optimal in the effective miscibility of SOPC and Chol components. The effective miscibility completeness, mainly in the gel and liquid crystal phases, was indicated. It was discovered that Chol mixed with SOPC slightly shifts its gel (L β) to liquid crystal (L α) phase transition temperature, decreases cooperativity, expressed by the van't Hoff enthalpy, and markedly and progressively reduces the transition enthalpy to almost zero at 50 mol.%. By deep incubation of the cholesteric phospholipid mixture, it was revealed that the endothermic peak associated with laminar crystal to gel phase transition does not exist in conventional pure SOPC bilayer systems.

Copper chromite decorated on nitrogen-doped graphene aerogel as an efficient catalyst for thermal decomposition of ammonium perchlorate particles

In this study, CuCr2O4 spinel (CCO) nanoparticles decorated on three-dimensional graphene networks were synthesized using hydrothermal method followed by a calcination process. The as-prepared material was characterized by different analysis methods and used for catalytic thermal decomposition of ammonium perchlorate particles (AP). For this purpose, CuCr2O4@GA/AP composites were fabricated by solvent/non-solvent (composite processing) and simple mixing methods. The catalytic effect of the as-prepared composites was investigated by differential scanning calorimetric and thermogravimetric (TG) analysis techniques. Owing to the synergistic effect of the spinel-structured copper chromite nanoparticles, high surface area of graphene aerogel and composite processing of AP, the high-temperature decomposition of AP in the presence of 4 mass% CuCr2O4@GA nanocomposite prepared by solvent/non-solvent method was reduced from 432 to 323 °C and the heat released (∆H) from decomposition of AP was increased from 590 to 1760 J g−1.

Study on interactions of vitamin B1 with sodium dodecyl sulfate for potential food applications: Conductometric, volumetric, calorimetric and spectroscopic approach

As vitamin B1 (thiamine hydrochloride, THC) is being oxidized by food preservatives and light, therefore the advantages of surfactant micelles as protecting agent are taken into consideration in the present study. Keeping this in mind the impact of THC on the SDS micellar system has been studied by using conductance, volumetric, calorimetric and spectroscopic techniques. From conductance measurements, various parameters like critical micellization concentration (CMC), degree of dissociation (α) and thermodynamics of micellization (ΔGᴼm, ΔHᴼm and ΔSᴼm) have been calculated. Apparent molar volume (VΦ) and apparent molar compressibility (Ks,2,Φ) have been calculated from density and sound velocity measurements which have been discussed in terms of solute-solute and solute-solvent interactions. The binding and partitioning of THC into SDS micelles have been studied by using UV–visible spectroscopy and calorimetric studies. Calorimetric studies have also been used to address the interactions of THC with monomers of SDS. The values of binding/partitioning constant (K), enthalpy, entropy, free energy and stoichiometry of binding have been determined in the pre-micellar and post-micellar regions from isothermal titration calorimetery (ITC). In addition, proton (1H) NMR studies have been performed to determine the locus and orientation of THC within SDS micelles.

Cadmium association with DREAM promotes DREAM interactions with intracellular partners in a similar manner to its physiological ligand, calcium.

Cd2+ exposure has been associated with neurodegenerative diseases and other pathologies, but the underlying mechanism through which it exerts toxic effects remain unresolved. Using calorimetric and spectroscopic techniques, we show that Cd2+ binds to EF-hands in DREAM (downstream regulatory element antagonist modulator) with an equilibrium dissociation constant of 89 ± 10 nM, which is superior to that determined for Ca2+ (Kd = 1000 nM). Analogous to Ca2+ binding, Cd2+ binding triggers changes in the protein secondary and tertiary structure, including increased exposure of the hydrophobic cavities, as determined using a fluorescent probe, 1-anilinonaphthalene-8-sulfonic acid. In addition, we demonstrate that Cd2+ binding modulates DREAM interactions with FITC-labeled peptides that mimic binding sites of DREAM effector proteins; helix-9 of presenilin-1, and site-1 and site 2 of potassium voltage channel 4.3 (residues 2-22 and 70-90, respectively). Cd2+ association with DREAM increases its affinity for helix 9 of presenilin roughly 30-times compared to metal-free DREAM. The DREAM affinity for site-1 and site 2 is elevated approximately 7 and 15 times, respectively, in the presence of Cd2+. The above results suggest that DREAM and probably other members of the neuronal calcium sensor family bind Cd2+ with an affinity that is superior to that for Ca2+ and the interactions between toxic Cd2+ and DREAM and other neuronal calcium sensors provide novel insight into the molecular mechanism of Cd2+ neurotoxicity.

Thermodynamics of protein folding: methodology, data analysis and interpretation of data

Thermodynamics of protein folding refers to the stability measurements where structural changes of a given protein in the presence of a denaturing agent are monitored by spectroscopic or calorimetric techniques. In macroscopic point of view, protein stability represents the ratio of the population of its unfolded state to that of folded one in equilibrium condition, while in microscopic point of view, the stability is actually a net value from a combination of favorable and unfavorable contributions that affect the structural integrity of a protein molecule. In this manuscript, the principles and methodological aspects of thermodynamic studies and methods of data analysis as well as interpretation of the results are presented.

Hydrogen storage properties of TiFe-based ternary mechanical alloys with cobalt and niobium. A thermochemical approach

Ternary alloys of general composition (TiFe)100-xMx (M = Co, Nb) have been synthesized from pure metals through high-energy ball milling. The maximum concentration of alloying components allowing formation of single phase TiFe-type compounds has been defined as 2 at.%. The hydrogenation behavior of the mechanical alloys in comparison with the arc-melted ones of the same composition has been studied by a combination of volumetric and calorimetric techniques. Influence of the alloy composition and the synthesis mode on the crystal structure of TiFe and its hydrides has been evaluated. It has been shown that the thermochemical method based on calorimetric titration provides more accurate information about phase transformations in the nanocrystalline metal hydride systems. The obtained results show that the third components slightly affect the hydrogen storage performance of non-equilibrium mechanical alloys in contrast with alloys produced by conventional melting.

Binding of Noradrenaline to Native and Intermediate States during the Fibrillation of α-Synuclein Leads to the Formation of Stable and Structured Cytotoxic Species.

Parkinson's disease is characterized by the deterioration of dopaminergic neurons of substantia nigra pars compacta along with a substantial loss of noradrenergic neurons of the locus coeruleus, which is the major source of noradrenaline (NA) in the brain. We have investigated the interaction of NA with α-synuclein (α-syn), the major protein constituent of Lewy bodies that are the pathological hallmark of Parkinson's disease (PD). It is expected that NA, like dopamine, could bind to α-syn and modulate its aggregation propensity and kinetics, which could also contribute to the onset of PD. We have, thus, evaluated the thermodynamic parameters of interaction of NA with α-syn monomer as well as species formed at different stages during its fibrillation pathway and have investigated the conformational and aggregation properties using various spectroscopic and calorimetric techniques. Binding isotherms of NA with α-syn species formed at different time points in the pathway have been observed to be exothermic in nature, suggesting hydrogen bonding interactions and weak affinity with binding constants in the millimolar range in all the cases. The interaction site of NA for α-syn was determined using Förster resonance energy transfer measurements that resulted in its binding in close proximity (23 Å) of an Alexa-labeled A90C mutant of α-syn. Docking studies further suggested binding of NA to the C-terminal as well as the non-amyloid-β component (NAC) region of α-syn. We have shown that α-syn oligomerization into sodium dodecyl sulfate resistant, higher-order, β-sheet-rich species is dependent on the oxidation of NA. Under non-reducing conditions, NA was also found to disaggregate the intermediates, populated during the fibrillation pathway, which are more cytotoxic compared to amyloid fibrils, as observed by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide cytotoxicity assay using a human neuroblastoma cell line. On the basis of these and earlier data, we propose that NA-induced formation of α-syn oligomers may contribute to the progressive loss of the noradrenergic neuronal population and the pronounced Lewy body deposition observed in patients with PD.

Glass transition and crystallization kinetics of a new chalcogenide-alkali metal $$\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}$$ Se 80 Te 8 ( NaCl ) 12 alloy

A new chalcogenide-alkali metal alloy of \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) has been prepared by a melt-quench technique. The crystallized phases due to the thermal annealing are observed by X-ray diffraction of the powdered sample. The glass transition and kinetics of crystallization in the \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) alloy are studied using the differential scanning calorimetric technique under non-isothermal conditions. The activation energy of the glass transition is evaluated by Kissinger and Mahadevan methods. The crystallization activation energy (\(E_{\mathrm{c}}\)) is calculated by isoconversion Friedman methods. The decrease of \(E_{\mathrm{c}}\) with increasing crystallization conversion is attributed to the complex mechanism of the crystallization process. Based on the shape of the characteristic kinetic function, the crystallization growth is found to be a three-dimensional growth from the bulk nuclei. The results show that the conditions of the Sestak–Berggren model are satisfied for describing the crystallization process of the studied \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) alloy. The parameters M and N involved in this model are calculated and related to the crystallization process.

Preparation and Thermal Analysis of Blended Nanoaluminum/Fluorinated Polyether-Segmented Urethane Composites

The thermally induced reaction of aluminum fuel and a fluoropolymer oxidizer such as polytetrafluoroethylene (via C-F activation) has been a well-studied thermite event for slow-burning pyrolants among a multitude of energetic applications. Generally, most metallized thermoplastic fluoropolymers suffer from manufacturing limitations using common melt or solvent processing techniques due to the inherent low surface energy and high crystallinity of fluoropolymers. In this report, we prepared an energetic composite utilizing the versatility of urethane-based polymers and provide a comparative thermal characterization study. Specifically, a thermite formulation comprising of nanometer-sized aluminum (nAl) fuel coated with perfluoropolyether (PFPE) oxidizer was solvent-blended with either a polyethylene glycol (PEG) or PFPE-segmented urethane copolymer. Thermal data were collected with calorimetric and thermogravimetric techniques to determine glass transition temperature and decomposition temperature, which showed modest effects upon various loadings of PFPE-coated nAl in the urethane matrix. While our application focus was for energetics, this study also demonstrates the potential to expand the ability to broadly manufacture structural metallized composites to their consideration as coatings, foams, or fibers.

Development of Bright Fluorescent Poly(1-vinyl-2-pyrrolidone-co-acrylonitrile) and Its Polysalts with HCl and HNO3: Materials for Solid State Electrical Applications

Herein, we have reported the synthesis, characterization, and ionic conductivity analysis of fluorescent poly(1-vinyl-2-pyrrolidone-co-acrylonitrile) and its salts with 10% HCl and HNO3 in solid state. The synthesized polymers and their polysalts were characterized using Fourier-transformed infrared spectroscopy, UV-visible, Cyclic Voltammetry, Thermogravimetric analysis, Differential Scanning Calorimetric, X-ray diffraction, and spectrofluorometric techniques. The AC conductivities were measured in the frequency ranging from 42 Hz to 1 MHz and temperature from 30°C to 70°C in solid state. Ionic conductivities of the salts of the copolymer with hydrochloric acid and nitric acid were found to be 2.145×10−5 and 2.349×10−5 S cm −1, respectively, which are nearly 1000 times more than that of poly(1-vinyl-2-pyrrolidone-co-acrylonitrile). The activation energies for the copolymer and the polyelectrolytes were found to be 0.454, 0.6288, and 0.659 eV, respectively. The transport number of the copolymers was found to be 0.0278, and that of the polysalts was found to be 0.7596 and 0.7424, respectively. The copolymer showed distinct fluorescent when irradiated with UV light and can be used as acid vapor sensor in solid state.

Intelligent copolymers based on poly (N-isopropilacrylamide). Part ii: Grafts polysaccharide to obtain new biomaterials for biomedical and pharmacological applications

Biopolymers such as polysaccharides are compounds that have functional groups and they are very susceptible to be used in chemical modifications and also allows them to synthesizer of new copolymers (used as graft-like chains). Poly (N-Isopropylacrylamide) PNIPAm, is a thermosensitive synthetic polymer widely used in the preparation of intelligent gels for the biomedical field, but have some limitations in use as biodegradable matrix or scaffolds. In this research wered the synthesis and characterization of copolymers their PNIPAm grafted with the polysaccharides: chitosan (CS) or hyaluronic acid (HA), were performed to obtain new biodegradable and biocompatible biomaterials that conserve the intelligent character (thermosensitivity).The PNIPAm was in first chemically modified with 3-butenoic acid in order to generate carboxyl end groups on the graft-polymer chain (PNIPAm-co-COOH) which serve as anchor points and then covalently graft the polysaccharides. For the specific case of grafting with hyaluronic acid, it was necessary to perform a second modification using piperazine (PIP) and obtain the graft-polymers PNIPAm-co-COO-g-PIP. All this modification process was previously reported (Carrero et al, 2018). In this case, the polysaccharides used as grafts-like chains were: (1) chitosan oligomers obtained by acid degradation and (2) hyaluronic acid. The characterization of all copolymers obtained was follow by infrared spectroscopic (FT-IR); the differential scanning calorimetric (DSC) technique was used to determine the lower critical solution transition temperature (LCST), resulting in the range of 29-34 °C. Its morphology was studied using scanning electron microscopy (SEM), but previously was simulate an inject process, for the reversible gel character presented by these novel copolymers; resulting a high porosity and interconnection between pores (scaffold-like micrometric structures). Hemocompatibility assays were performed on agar/blood systems, showing non cytotoxicity. All these results give these graftcopolymers a high potentiality of use as scaffolds in tissue engineering and also for pharmacological applications.

Origin and Quantification of Increased Core Loss in MnZn Ferrite Plates of a Multi-Gap Inductor

Inductors realized with high permeable MnZn ferrite require, unlike iron-powder cores with an inherent dis-tributed gap, a discrete air gap in the magnetic circuit to prevent saturation of the core material and/or tune the inductance value. This large discrete gap can be divided into several partial gaps in order to reduce the air gap stray field and consequently the proximity losses in the winding. The multi-gap core, realized by stacking several thin ferrite plates and inserting a non-magnetic spacer material between the plates, however, exhibits a substan-tial increase in core losses which cannot be explained from the intrinsic properties of the ferrite. In this paper, a comprehensive overview of the scientific literature regarding machining induced core losses in ferrite, dating back to the early 1970s, is provided which suggests that the observed excess core losses could be attributed to a deterioration of ferrite properties in the surface layer of the plates caused by mechanical stress exerted during machining. However, in a first experimental analysis no structural evidence for a deteriorated layer close to the surface is identified by means of Scanning Electron Microscopy (SEM). Therefore, in a next step, a new calorimetric measurement setup based on temperature rise monitoring is proposed in this paper in order to quantify and differentiate between core losses associated with the bulk and the surface of the ferrite plates and therefore to pinpoint the measured excess core loss to shallow layers of ferrite with deteriorated magnetic performance. Electrical measurement of the surface related core losses utilizing the widely accepted two-winding wattmeter method with reactive power compensation is outlined in the appendix but was not employed in this work due to comparably low measurement accuracy. By means of the proposed measurement technique, the bulk and surface core loss density of the MnZn ferrite material 3F4 from FerroxCube was determined for sinusoidal flux density amplitude varying from 75 mT up to 200 mT and excitation frequencies ranging from 200 kHz to 1 MHz. The measured core loss densities (W/cm 3 ) show good agreement with the Steinmetz model provided by the manufacturer validating the proposed calorimetric core loss measurement technique. The measured surface loss density (W/cm 2 ) can also be well predicted with a Steinmetz model, whereby the frequency exponent α in the surface is slightly smaller and the flux density exponent β is slightly larger compared to the Steinmetz parameter of the bulk ferrite. It is shown that the ratio between surface and bulk core losses of a composite core assembled from individual plates is only a function of plate thickness and does not depend on the actual cross section area. Critical plate thickness is then defined to be reached when the total power loss in the composite core has doubled compared to a solid (single-piece) core sample. This new quantity provides a very helpful figure for multi-gap inductor designs. Besides the deteriorated surface layers, several other mechanisms potentially contributing to increased core losses in multi-gap inductors were identified and are finally discussed in the appendix of this paper: flux crowding in the core due to tolerances and imperfections in machining and assembly; deterioration of ferrite properties due to pressure buildup in the stack of plates during the curing of the employed epoxy resin; ohmic loss in the ferrite associated with the current flowing in the conduction path provided by the low impedance of the ferrite material at high frequencies and the parasitic capacitance between winding and the ferrite core.

Design and building of an isoperibolic calorimeter: measurements of enthalpy of formation for derivatives of glycidol

The enthalpy of formation can be determined indirectly with different calorimetric techniques; one of the most used is combustion calorimetry. During a combustion process, there are multiple energy variables that can significantly influence the overall result of the measurement. One of these variables is the energy exchange that exists between the calorimeter and the surroundings. To reduce this energy contribution and obtain more precise measurements of combustion energies of compounds containing the elements C, H, O and N, a combustion calorimeter in isoperibolic operation was designed, constructed and calibrated. The measurements made with this instrument show good precision; the results obtained for internal energy and the combustion enthalpy of succinic acid (solid sample) and for glycidol, glycidyl isopropyl ether, glycidyl butyrate and glycidyl methacrylate (liquid samples) are presented. The error percentage for the of the calorimetric system proposed was compared with a commercial calorimeter and published results in the literature.