@misc{EfimovaHubrigSchmidt, author = {Efimova, Anastasia and Hubrig, Grit and Schmidt, Peer}, title = {Thermal stability and crystallization behavior of imidazolium halide ionic liquids}, series = {Thermochimica Acta}, volume = {Vol. 573}, journal = {Thermochimica Acta}, issn = {0040-6031}, doi = {10.1016/j.tca.2013.09.023}, pages = {162 -- 169}, abstract = {The 1-butyl-3-methylimidazolium halide ionic liquids are stable up to temperatures of 246(1) °C ([BMIm]Cl), 260(1) °C ([BMIm]Br), and 238(1) °C ([BMIm]I). The thermal decomposition proceeds in thermogravimetric measurements with a total mass loss of 100\%. Using evolved gas analysis (EGA) a complete degradation of [BMIm]X ionic liquids under formation of characteristic fragments CH3+, NHn+, C4Hn+, and CH3X+ (X = Cl, Br, I) has been observed. [BMIm]Cl shows enantiotropic polymorphism with a phase transition temperature at 30(1) °C, and melts at 74(1) °C (ΔHfus = 18 ± 0.5 kJ mol-1). Spontaneous e-crystallization and reversible phase transition have been found for cooling of the substance.[BMIm]Br melts at 78(1) °C (ΔHfus = 29 ± 0.5 kJ mol-1). The re-crystallization fails and thus a glassy solid is formed. The glass transition temperature is about -65 °C, the cold crystallization occurs between -30 and -20 °C. The application of both homogeneous and heterogeneous nucleation agents does not interfere the glassy state. [BMIm]I undergo solidification without crystallization. The melting effect for the amorphous substance arise at -70(5) °C with ΔHfus = 0.4 ± 0.2 kJ mol-1.}, language = {en} } @misc{EfimovaPinnauMischkeetal., author = {Efimova, Anastasia and Pinnau, Sebastian and Mischke, Matthias and Breitkopf, Cornelia and Ruck, Michael and Schmidt, Peer}, title = {Development of salt hydrate eutectics as latent heat storage for air conditioning and cooling}, series = {Thermochimica Acta}, volume = {45}, journal = {Thermochimica Acta}, number = {575}, issn = {0040-6031}, doi = {10.1016/j.tca.2013.11.011}, pages = {276 -- 278}, abstract = {Sustainable air conditioning systems require heat reservoirs that operate between 4 and 20 ◦C. A systematic search for binary and ternary eutectics of inorganic salts and salt hydrates with melting temperatures in this temperature regime and with high enthalpies of fusion has been performed by means of differential scanning calorimetry (DSC). Promising results were obtained for the pseudo-ternary system Zn(NO3)2·6H2O, Mn(NO3)2·4H2O, and KNO3 with the melting temperature range 18-21 ◦C and the enthalpy of fusion of about 110 kJ kg-1. Suitable nucleating and thickening agents have been found and tested to prevent the mixture from supercooling and phase separation.}, language = {en} } @misc{EfimovaPfuetznerSchmidt, author = {Efimova, Anastasia and Pf{\"u}tzner, Linda and Schmidt, Peer}, title = {Thermal Stability and Decomposition Mechanism of 1-Ethyl-3-Methylimidazolium Halides}, series = {Thermochimica Acta}, volume = {604}, journal = {Thermochimica Acta}, doi = {10.1016/j.tca.2015.02.001}, pages = {129 -- 136}, abstract = {The thermochemical behavior of 1-ethyl-3-methylimidazolium [EMIm] halides (Cl, Br and I) has been investigated for their crystalline and liquid states in the temperature range from -90 °C to 600 °C using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The temperatures and enthalpies of phase transitions have been determined: Tfus = 86(1) °C, ΔHfus = 14.2(0.7) kJ mol-1 ([EMIm]Cl); Tfus = 67(1) °C, ΔHfus = 19.3(0.7) kJ mol-1 ([EMIm]Br); and Tfus = 74(1) °C, ΔHfus = 16.9(0.6) kJ mol-1 ([EMIm]I). The decomposition temperatures, determined by onset of DTG at 1 K min-1 are 233(5) °C ([EMIm]Cl), 246(5) °C ([EMIm]Br), and 249(5) °C ([EMIm]I). The maximum operation temperature (MOT) has been estimated based on dynamic TGA for an operation time of 24 h: 132 °C ([EMIm]Cl), 149 °C ([EMIm]Br), 139 °C ([EMIm]I) and 8000 h: 76 °C ([EMIm]Cl), 90 °C ([EMIm]Br), 77 °C ([EMIm]I). The decomposition products of the investigated ionic liquids (ILs) after heating experiments were identified by means of TGA complemented with mass spectrometry (MS), for establishment of the mechanism of thermal decomposition of the ILs. Complete degradation of [EMIm]X ionic liquids occurs under formation of characteristic molecule fragments CH3+, NH+, and X+, CH3X+, C2H5X+ (X = Cl, Br, I).}, language = {en} } @misc{GrohBreternitzAhmedetal., author = {Groh, Matthias F. and Breternitz, Joachim and Ahmed, Ejaz and Isaeva, Anna and Efimova, Anastasia and Schmidt, Peer and Ruck, Michael}, title = {Ionothermal Synthesis, Structure, and Bonding of the Catena-Heteropolycation 1∞[Sb2Se2]+}, series = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie}, volume = {641}, journal = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie}, number = {2}, issn = {1521-3749}, doi = {10.1002/zaac.201400543}, pages = {388 -- 393}, abstract = {The reaction of antimony and selenium in the Lewis-acidic ionic liquid 1-butyl-3-methyl-imidazolium tetrachloridoaluminate, [BMIm]Cl·4.7AlCl3, yielded dark-red crystals of [Sb2Se2]AlCl4. The formation starts above 160 °C; at about 190 °C, irreversible decomposition takes place. The compound crystallizes in the triclinic space group Pequation image with a = 919.39(2) pm, b = 1137.92(3) pm, c = 1152.30(3) pm, α = 68.047(1)°, β = 78.115(1)°, γ = 72.530(1)°, and Z = 4. The structure is similar to that of [Sb2Te2]AlCl4 but has only half the number of crystallographically independent atoms. Polycationic chains 1∞[Sb2Se2]+ form a pseudo-hexagonal arrangement along [01-1], which is interlaced by tetrahedral AlCl4- groups. The catena-heteropolycation 1∞[Sb2Se2]+ is a sequence of three different four-membered [Sb2Se2] rings. The chemical bonding scheme, established from the topological analysis of the real-space bonding indicator ELI-D, includes significantly polar covalent bonding in four-member rings within the polycation. The rings are connected into an infinite chain by homonuclear non-polar Sb-Sb bonds and highly polar Sb-Se bonds. Half of the selenium atoms are three-bonded.}, language = {en} } @misc{PfisterSchaeferOttetal., author = {Pfister, Daniela and Sch{\"a}fer, Konrad and Ott, Claudia and Gerke, Birgit and P{\"o}ttgen, Rainer and Janka, Oliver and Baumgartner, Maximilian and Efimova, Anastasia and Hohmann, Andrea and Schmidt, Peer and Venkatachalam, Sabarinathan and W{\"u}llen, Leo van and Sch{\"u}rmann, Ulrich and Kienle, Lorenz and Duppel, Viola and Parzinger, Eric and Miller, Bastian and Becker, Jonathan and Holleitner, Alexander and Weihrich, Richard and Nilges, Tom}, title = {Inorganic double helices in semiconducting SnIP}, series = {Advanced Materials}, volume = {28}, journal = {Advanced Materials}, number = {44}, issn = {1521-4095}, doi = {10.1002/adma.201603135}, pages = {9783 -- 9791}, abstract = {SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods <20 nm in diameter can be accessed mechanically and chemically within minutes.}, language = {en} } @misc{EfimovaHubrigPfuetzneretal., author = {Efimova, Anastasia and Hubrig, Grit and Pf{\"u}tzner, Linda and Schmidt, Peer}, title = {Thermal Stability of Alkyl-Imidazolium-Ionic Liquids}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {640}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {11}, issn = {1521-3749}, doi = {10.1002/zaac.201490026}, pages = {2391}, abstract = {The thermochemical behavior of two groups of ionic liquids (ILs), 1-ethyl-3-methylimidazolium [EtMeIm] and 1-butyl-3-methylimidazolium [BuMeIm] halides (Cl, Br and I) was investigated for their crystalline and liquid states in the temperature range from -100 °C to 600 °C using DSC and thermogravimetric analysis (TGA). Some investigated ILs exhibit significant subcooling effect and the glass state formation [1]. The decomposition mechanism has been identified by means of TGA with coupled mass spectrometry (MS). All investigated ILs decompose with a total mass loss of about 100 \% in the temperature range of Tonset from 230 to 290 °C (Fig. 1). By complete degradation of IL, dominant fragments CnH2n+1+, CnH2n+, CnHn+, NHn+, and the respective alkyl halides (X = Cl, Br, I) are formed.}, language = {en} } @techreport{PinnauEfimovaSchmidt, author = {Pinnau, Sebastian and Efimova, Anastasia and Schmidt, Peer}, title = {Identifikation technischer Salze als Latentspeichermaterialien im Temperaturbereich von 4 bis 15 °C und deren Verkapselung: Abschlussbericht}, address = {Dresden}, doi = {10.2314/GBV:786966173}, pages = {92}, abstract = {Der Einsatz von thermischen Speichern erlaubt eine bessere Lastanpassung von Erzeugeranlagen zur Geb{\"a}udeklimatisierung sowie eine Optimierung des Betriebsregimes unter energetischen Gesichtspunkten. F{\"u}r solche Anwendungsf{\"a}lle k{\"o}nnen Latentw{\"a}rmespeicher zum Einsatz kommen, bei denen {\"u}blicherweise der Schmelz- und Erstarrungsvorgang sogenannter Phasenwechselmaterialien (Phase Change Materials, PCM) ausgenutzt wird. F{\"u}r die Anwendungstemperaturbereiche der Klimatisierung von etwa 4 °C bis 15 °C und f{\"u}r die K{\"u}hlung bis etwa 25 °C ist die Auswahl an Reinstoffen mit einer passenden Schmelztemperatur sehr begrenzt. Durch die Bildung von eutektischen Gemischen aus zwei oder mehr Komponenten - die {\"a}hnlich wie Reinstoffe einen scharfen Schmelzpunkt aufweisen - kann die Bandbreite an potentiellen PCM's f{\"u}r diesen Temperaturbereich vergr{\"o}ßert werden. F{\"u}r die genannten Temperaturbereiche werden vorzugsweise anorganische Salzhydrate als potentielle Speichermedien betrachtet, da diese gegen{\"u}ber organischen Substanzen h{\"a}ufig gr{\"o}ßere Schmelzenthalpien und geringere Kosten aufweisen.}, language = {de} } @misc{EfimovaVargaMatuscheketal., author = {Efimova, Anastasia and Varga, Janos and Matuschek, Georg and Saraji-Bozorgzad, Mohammad R. and Denner, Thomas and Zimmermann, Ralf and Schmidt, Peer}, title = {Thermal Resilience of Imidazolium-Based Ionic Liquids—Studies on Short- and Long-Term Thermal Stability and Decomposition Mechanism of 1-Alkyl-3-methylimidazolium Halides by Thermal Analysis and Single-Photon Ionization Time-of-Flight Mass Spectrometry}, series = {Journal of Physical Chemistry B}, volume = {122}, journal = {Journal of Physical Chemistry B}, number = {37}, doi = {10.1021/acs.jpcb.8b06416}, pages = {8738 -- 8749}, abstract = {Ionic liquids are often considered as green alternatives of volatile organic solvents. The thermal behavior of the ionic liquids is relevant for a number of emerging large-scale applications at elevated temperature. Knowledge about the degradation products is indispensable for treatment and recycling of the used ionic liquids. The objective of this paper was an investigation of the short- and long-term stability of several 1-alkyl-3-methylimidazolium halides, determination of the degradation products, and the elucidation of their decomposition patterns and structure-stability relations. Short-term stability and mechanism of thermal degradation were investigated by a self-developed, innovative thermal analysis single-photon ionization time-of-flight mass spectrometry device with Skimmer coupling. The applied technology provides real-time monitoring of the forming species and allows tracing their change during the course of the decomposition. Therein, the almost fragment-free soft ionization with vacuum ultraviolet photons plays a crucial role. We have detected unfragmented molecules whose formation was only assumed by electron ionization. Nevertheless, the main decomposition products of the selected ionic liquids were alkyl imidazoles, alkenes, alkyl halides, and hydrogen halides. From the decomposition products, we have deduced the fragmentation patterns and discussed their interrelation with the length of the alkyl chain and the type of the halide anion. Our results did not suggest the evaporation of the investigated ionic liquids prior to their decomposition under atmospheric conditions. Long-term thermal stability and applicability were determined based on thermogravimetric analysis evaluated with a kinetic model. Thus, the time-dependent maximum operation temperature (MOT) for the respective ionic liquids has been calculated. As a rule, the short-term stability overestimates the long-term decomposition temperatures; the calculated MOT are significantly lower (at least 100 K) than the standardly obtained decomposition temperatures.}, language = {en} } @misc{KniesKaiserLeAnhetal., author = {Knies, Maximilian and Kaiser, Martin and L{\^e} Anh, Mai and Efimova, Anastasia and Doert, Thomas and Ruck, Michael}, title = {Low-Temperature Ordering in the Cluster Compound (Bi₈)Tl[AlCl₄]₃}, series = {Inorganics}, volume = {7}, journal = {Inorganics}, number = {4}, doi = {10.3390/inorganics7040045}, pages = {1 -- 9}, abstract = {The reaction of Bi, BiCl₃, and TlCl in the ionic liquid [BMIm]Cl·4AlCl₃ (BMIm = 1-n-butyl-3-methylimidazolium) at 180 °C yielded air-sensitive black crystals of (Bi₈)Tl[AlCl₄]₃. X-ray diffraction on single crystals at room temperature revealed a structure containing [Tl(AlCl₄)₃]∞12- strands separated by isolated Bi₈²⁺ square antiprisms. The thallium(I) ion is coordinated by twelve Cl⁻ ions of six [AlCl₄]⁻ groups, resulting in a chain of face-sharing [TlCl₁₂]¹¹⁻ icosahedra. The Bi₈²⁺ polycation is disordered, simulating a threefold axis through its center and overall hexagonal symmetry (space group P6₃/m). Slowly cooling the crystals to 170 K resulted in increased order in the Bi₈ cluster orientations. An ordered structure model in a supercell with a' = 2a, b' = 2b, c' = 3c and the space group P6₅ was refined. The structure resembles a hexagonal perovskite, with complex groups in place of simple ions.}, language = {en} } @misc{MeissnerEfimovaSchmidt, author = {Meißner, Andr{\´e} and Efimova, Anastasia and Schmidt, Peer}, title = {Impacts of TGA furnace parameters for prediction of long-term thermal stability of ionic liquids}, series = {Thermochimica Acta}, volume = {704}, journal = {Thermochimica Acta}, doi = {10.1016/j.tca.2021.178917}, pages = {178917-1 -- 178917-7}, abstract = {The concept of maximum operation temperature is established for the prediction of the time dependent thermal stability of ionic liquids based on kinetic evaluation of thermogravimetric analysis. The influence of the furnace control parameters on the maximum operation temperature (MOT) is shown using the example of 1-methyl-3-propylimidazolium iodide ([C3C1im]I) with respect to three different parameter sets of a programmed proportional integral derivative (PID) controller of the TGA. Kinetics of thermal decomposition of [C3C1im]I have been investigated with the implementation of an improved kinetic model. The activation energy obtained using the Kissinger-Akahira-Sunose equation showed variations apparently due to the decomposition degree. The model compound is decomposed by a one-step kinetics, which results from pseudo zero order relationship of the activation energy to the conversion rate. The activation energy, pre-exponential factor, and the activation energy are strongly dependent on the parameters of TGA furnace controller.}, language = {en} }