High-temperature Form Research Articles

Modeling of Failure in Aluminum Alloy Braze for a High Temperature Thermoelectric Assembly

The objective of this work is to design a commercially viable thermoelectric generator (TEG) assembly that can be used in passenger vehicles to be able to withstand extreme environmental conditions. Since the operating temperatures of the TEGs can reach temperature levels higher than 500 °C, aluminum braze alloys offer a good high temperature solution for die attach. However, the evolution of fatigue damage in the aluminum braze must be understood in order to ensure an acceptable reliability of the TEG. In this paper, the proposed design of TEG package assembly was evaluated under extreme temperature conditions. Three-dimensional models of full scale TEG were analyzed using finite element analysis (FEA). The failures of aluminum alloy based braze (high temperature form of solder) material in the TEG application was investigated. Low cycle fatigue using direct cyclic approach was considered for the reliability analysis. Continuum damage mechanics approach was used to study the fatigue failure due to power cycling. Different TEG assembly designs were investigated and compared to determine the best possible solution for the extreme environment application.

Roflumilast – A reversible single-crystal to single-crystal phase transition at 50 °C

Roflumilast is a selective phosphodiesterase type 4 inhibitor and is marketed under the brand names Daxas®, Daliresp® and Libertec®. A phase transition of the drug substance roflumilast was observed at 50°C. The low temperature form, the high temperature form and the phase transition were characterised by differential scanning calorimetry, variable temperature powder X-ray diffraction and single crystal X-ray diffraction, Raman spectroscopy and solid state NMR spectroscopy.The phase transition of roflumilast at 50°C is completely reversible, the high temperature form cannot be stabilised by quench cooling and the phase transition does not influence the quality of the active pharmaceutical ingredient (API) and the drug product. It was observed to be a single crystal to single crystal phase transition.

Crystal structures of the high temperature forms of V8O15 and V9O17 and structural trends in the VnO2n−1 Magnéli series

We report the structure of the metallic high-temperature (ht) form of V9O17, determined from single crystal X-ray diffraction: space group=P-1 a=5.4219(7)Å, b=7.0142(9)Å, c=14.5252(19)Å, α=97.0310(10)°, β=90.9900(10)°, γ=108.9630(10)°, V=517.53(12)Å3, and Z=2. We also report refinement of the structure of metallic ht-V8O15, space group=P-1, a=5.4315(17)Å, b=7.015(2)Å, c=13.147(5)Å, α=100.144(4)°, β=95.776(4)°, γ=108.965(3)°, V=459.6(3)Å3, and Z=2. The structure of metallic V9O17 is interpreted and discussed in the context of the VnO2n−1 Magnéli phases, yielding trends about how the underlying forces contribute to the metal to insulator transition (MIT). The manner in which structural features of the metallic phases change as a function of n supports previous arguments that there is a turnover in the forces leading to the MIT between n=6 and n=8.

Solid-State Phase Transitions of dl-Aminobutyric Acid

Four polymorphs are known for the amino acid racemate DL-aminobutyric acid: one tetragonal form B and three monoclinic forms A, C, and D for which two solid-solid phase transitions take place between 209 and 337 K. The intermediate form A, in space group P2(1)/c, is known to display disorder in the crystalline state with the ethyl side chain occupying three different conformations. The high temperature form D and the low temperature form C have been assumed to display a similar type of disorder in the space group C2/c. The present investigation, on the basis of high quality crystal structures at 100 K (C form), 220 K (A form), 295 K (A form), and 295 K (D form), provides updated results for all three forms and in particular demonstrates that the A → C and A → D transitions in fact involve only a partial space group conversion, so that two monoclinic phases are simultaneously present at high and low temperatures. To the best of our knowledge, such a phenomenon has not been observed previously for an organic molecule. The nonroutine refinement of the crystallographic data was performed with a specially adapted version of the program JANA2006. The observed polymorphs are compared with those found for DL-norvaline, DL-norleucine, and DL-methionine.

Transmission Electron Microscopy Study of Low Mo-content Bi-Mo-O Phases

δ-Bi2O3, a material with a fluorite-type structure, is one of the best solid-state oxygen-ion conductors. It is a high-temperature form that cannot be quenched to room temperature. However, doping with small amounts of transition metal oxides preserves the δ-Bi2O3 structure at low temperature and retains its anionic conduction properties. The Bi2O3–MoO3 materials are interesting because of their functional properties, chiefly as catalysts and as good ionic conductors. All the phases in this system are related to the fluorite structure except Bi2MoO6 which shows an Aurivillius-type structure.

Morpholine sulfur trifluoride: Vibrational spectra, conformational properties and crystal structure

Analysis of the vibrational spectra and quantum chemical calculations for morpholine sulfur trifluoride, SF3N(CH2CH2)2O, demonstrate that the morpholine ring possesses chair conformation and occupies an equatorial position of the trigonal bipyramidal SF3 group. The compound exists in the gas phase as a mixture of two conformers. The conformer with the SF3 group in equatorial orientation relative to the six-membered morpholine ring is slightly more stable than the axial conformer and the equilibrium is surprisingly temperature independent. MP2 and B3LYP calculations with cc-pVTZ basis sets predict free energy differences ΔG°=G°ax−G°eq of +0.18 and +0.40kcal/mol, respectively. At temperatures below 12°C the title compound crystallizes and the structure of the equatorial conformer, which is the only form present in the crystal, was determined by X-ray diffraction. At 131(1)K a phase transition occurs and the low and high temperature forms were studied at 100 and 150K, respectively.

A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene

A series of conformational polymorphs of hexakis(4-fluorophenoxy)cyclotriphosphazene have been identified and characterized. Three of the four polymorphs are previously unreported. Thermal analysis coupled with variable temperature powder X-ray diffraction has shown that conversion between polymorphs occurs at well-defined temperatures. The high temperature form is metastable at room temperature and is never obtained from solution. Two forms are observed in solution crystallization experiments, a monoclinic form and a triclinic form. Slurry experiments revealed that the triclinic form is the most stable at room temperature. The fourth polymorph is observed only at low temperatures. Interconversion between three of the polymorphs occurs in a single-crystal to single-crystal manner.

Magnetic and magnetocaloric properties of the high-temperature modification of TbTiGe

The high-temperature form (HT) of the ternary germanide TbTiGe was prepared by melting. The investigation of HT-TbTiGe by x-ray and neutron powder diffractions shows that the compound crystallizes in the tetragonal CeScSi-type structure (space group I4/mmm; a = 404.84(5) and c = 1530.10(9) pm as unit cell parameters). Magnetization and specific heat measurements as well as neutron powder diffraction performed on HT-TbTiGe reveal a ferromagnet having TC = 300(1) K as the Curie temperature; the Tb-moments are aligned along the c-axis. This magnetic ordering is associated with a modest magnetocaloric effect around room temperature. The isothermal magnetic entropy change ΔSm was determined from the magnetization data; ΔSm reaches, respectively, a maximum value of − 4.3 and − 2.0 J K−1 kg−1 for a magnetic field change of 5 and 2 T.

Mössbauer and X-ray diffraction studies of cubic (ZrO2)0.90(Sc2O3)0.10 − x (Fe2O3) x solid solutions

(ZrO2)0.90(Sc2O3)0.10 − x(Fe2O3)x solid solutions have been studied by X-ray diffraction and Mossbauer spectroscopy. The results demonstrate that heat treatment in the range 1420–1810 K destabilizes the fluorite-type structure (C-ZrO2) of the Fe-free (x = 0) material and stabilizes it in the Fe-containing samples (0.01 ≤ x ≤ 0.05). The increase in the stability of the high-temperature cubic form of zirconia can be accounted for by the influence of ScFeO3 dissolved in C-ZrO2.

A New Partially Deprotonated Mixed-Valence Manganese(II,III) Hydroxide–Arsenate with Electronic Conductivity: Magnetic Properties of High- and Room-Temperature Sarkinite

A new three-dimensional hydroxide-arsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn(2)(OH)AsO(4) (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) Å, b = 7.5220(6) Å, c = 9.8117(6) Å, α = 92.410(4)°, β = 109.840(4)°, γ = 115.946(4)°, P1̅. The unit cell content derived from Rietveld refinement is Mn(8)(O(4)H(x))(AsO(4))(4). Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH(-)/O(2-) inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO(4) groups placed in between. Bond-valence analysis indicates both partial deprotonation (x ≅ 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 °C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn-O-Mn] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic behavior of compound 1. The loss of three-dimensional magnetic ordering by heating of compound 1 could well be based on the presence of Mn(3+) ions (d(4)) in compound 2.

Dipotassium trisodium triphosphate, K2Na3P3O10

The structure of the title compound, K2Na3P3O10, is characterized by open chains of three PO4 tetra­hedra linked by single oxygen bridges. The P3O10 groups have crystallographic twofold symmetry, with the central P atom being located on the twofold rotation axis. One of the sodium ions lies on a centre of inversion, whereas all the remaining atoms are in general positions. The structure is isotypic with that of the high-temperature form of Na5P3O10 phase I.

Demonstration of Thermodynamics and Kinetics Using FriXion Erasable Pens

FriXion erasable pens contain thermochromic inks that have colored low-temperature forms and colorless high-temperature forms. Liquid nitrogen can be used to kinetically trap the high-temperature forms of the ink at temperatures at which ordinarily the low-temperature forms are more thermodynamically stable.

New Insights into an Old Molecule: Interaction Energies of Theophylline Crystal Forms

The asthma therapeutic theophylline exists in at least three anhydrous polymorphs and a monohydrate. The single-crystal X-ray structure of the high-temperature polymorph form I is presented for the first time, and the energetic relationship between forms I and II is investigated using the partial charges and chemical hardness analysis (PACHA) algorithm. It is shown that the interactions in the form I crystal network are stronger, especially the hydrogen bond. The single-crystal neutron structure of the monohydrate demonstrates static disorder of the water molecule as well as dynamic disorder of the methyl groups. PACHA investigations based on the neutron coordinates reveal that the homomeric interactions in this form are stronger than the interaction of the water with the host molecules. The dehydration of the hydrate should thus leave the theophylline network intact, explaining the isomorphic powder X-ray diffractograms of the monohydrate and its dehydrated form III.

Phase equilibria in the Ag2Se-As2Se3-Bi2Se3 system

We have studied phase equilibria in the pseudoternary system Ag2Se-As2Se3-Bi2Se3 and constructed the 300-, 600-, and 800-K isothermal sections, a number of partial phase diagrams, and the liquidus projection of this system. The AgAsSe2-AgBiSe2 and As2Se3-AgBiSe2 joins are shown to be pseudobinary, and the Ag3AsSe3-AgBiSe2 and AgAs3Se5-AgAsSe2 joins are pseudobinary below the liquidus. Several in- and univariant peritectic, eutectic, and eutectoid equilibria and a broad region of AgBiSe2-based solid solutions are identified. The homogeneity region of the AgBiSe2-based phase has the largest extent along the AgAsSe2-AgBiSe2 join: 40 mol % (650 K) for the high-temperature form of AgBiSe2 and 20 mol % (300 K) for its low-temperature form.

Comparison between Finite Element Commercial Codes to Simulate High-Temperature AA5083 Bulge Forming

In this study in order to investigate the behavior of AA5083 aluminum sheet during high-temperature bulge forming a material model was used which accounts for the strain-rate sensitivity, the hardening and the softening of the material, the evolution of the grain growth and the phenomenon of the cavitation. The results obtained from the finite element commercial codes MSC.Marc® and ABAQUSTM were compared.

Comparison between Finite Element Commercial Codes to Simulate High-Temperature AA5083 Bulge Forming

Comparison between Finite Element Commercial Codes to Simulate High-Temperature AA5083 Bulge Forming

Binäre Lanthan‐Stannide mit Sn:La‐Verhältnissen nahe 1:1 – Synthesen, Kristallstrukturen, Chemische Bindung

AbstractFour binary lanthanum stannides close to the 1:1 ratio of Sn:La were synthesized from mixtures of the elements. The structures of the compounds have been determined by means of single‐crystal X‐ray data. The low temperature (α) form of LaSn (CrB‐type, orthorhombic, space group Cmcm, a = 476.33(6), b = 1191.1(2), c = 440.89(6) pm, Z = 4, R1 = 0.0247), crystallizes with the CrB‐type. The structure exhibits planar tin zigzag chains with a Sn–Sn bond length of 299.1 pm. In contrast to the electron precise Zintl compounds of the alkaline earth elements, additional La–Sn bonding contributions become apparent from the results of band structure calculations. In the somewhat tin‐richer region, the new compound La3Sn4 (orthorhombic, space group Cmcm, a = 451.45(4), b = 1190.44(9), c = 1583.8(2) pm, Z = 4, R1 = 0.0674), crystallizing with the Er3Ge4 structure type, exhibits Sn3 segments of the zigzag chains of α‐LaSn together with a further Sn atom in a square planar Sn coordination with increased Sn–Sn bond lengths. In the Lanthanum‐richer region, La11Sn10 (tetragonal, space group I4/mmm, a = 1208.98(5), c = 1816.60(9) pm, Z = 4, R1 = 0.0325) forms the undistorted tetragonal Ho11Ge10 structure type. Its structure, which contains isolated Sn atoms, [Sn2] dumbbells and planar [Sn4] rings is related to the high temperature (β) form of LaSn. The structure of β‐LaSn (space group Cmmm, a = 1766.97(6), b = 1768.28(5), c = 1194.32(3) pm, Z = 60, R1 = 0.0453), which forms a singular structure type, can be derived from that of La11Sn10 by the removal of thin slabs. Due to the different stacking of the remaining layers, planar [Sn4] chain segments and linear [Sn–Sn–Sn] anions are formed as additional structural elements. The chemical bonding (Sn–Sn covalent bonding, Sn–La contributions) is discussed on the basis of the simple Zintl concept and the results of FP‐LAPW calculations (density of states, band structure, valence electron densities and electron localization function).

Lanthan-Triel/Tetrel-ide La(Al,Ga)x(Si,Ge)1-x. Experimentelle und theoretische Studien zur Stabilität intermetallischer 1 : 1-Phasen / Lanthanum Triel/Tetrel-ides La(Al,Ga)x(Si,Ge)1−x. Experimental and Theoretical Studies on the Stability of Intermetallic 1:1 Phases

Systematic studies of the phase formation at the binary sections LaSi - LaGa and LaGe - LaAl have been carried out by means of synthetic, crystallographic and bond theoretical methods. The hightemperature forms of the two binary monotetrelides LaSi and LaGe crystallize with the FeB structure type, whereas LaGa forms the related CrB type and LaAl the significantly different CeAl type. Starting from LaSi/LaGe, the FeB type (orthorhombic, space group Pnma, Z = 4, a = 839.2(1)/842.7(1), b = 399.9(1)/412.3(1), c = 606.2(2)/612.2(1) pm, R1 = 0.0356/0.0298) remains stable only down to a valence electron number per M atom (M = Si, Ge, Al, Ga) of 6.9 (LaGa0.10Si0.90: a = 840.14(7), b = 404.12(12), c = 608.5(2) pm, R1 = 0.0513; LaAl0.15Ge0.85: a = 845.40(7), b = 414.08(13), c = 614.08(14) pm, R1 = 0.0213). In the system LaGaxSi1−x, the stability range of the CrB type (orthorhombic, space group Cmcm, Z = 4) starts at a gallium proportion of 25% (LaGa0.25Si0.75: a = 450.03(8), b = 1140.5(2), c = 406.05(6) pm, R1 = 0.0163) and extends to the border compound LaGa (v. e./M = 6). The CrB type also occurs in the system La-Al-Ge, but is in this case only formed around the 1 : 1 composition in between LaAl0.42Ge0.58 (a = 455.90(12), b = 1161.1(3), c = 418.05(9) pm, R1 = 0.0474) and LaAl0.61Ge0.39 (a = 454.89(10), b = 1168.8(2), c = 420.41(11) pm, R1 = 0.0447). These stability ranges, the variations of several key geometric parameters such as the M-M distances or the heights of the trigonal prisms, and the main aspects of the chemical bonding in these lanthanum monometallides are analyzed using FP-LAPWband structure methods. The structure of the new compound La2Al2Ge (V2B3 structure type, orthorhombic, space group Cmcm, a = 416.69(4), b = 2719.7(4), c = 450.46(5) pm, Z = 2, R1 = 0.0458) combines the structural elements of the CrB/FeB structure family (two-bonded M atoms) with the trigonally planar bonded M atoms of the ThSi2 type in a fully ordered Al and Ge atom distribution and thus without phase width

Synthesis and Structure Determination of the High Temperature Form of La2WO6

This article presents the synthesis, structure determination, and structure analysis of α-La2WO6. This high temperature polymorph was directly observed using laboratory in situ high-temperature X-r...

Thermodynamic modeling of the C–RE (RE=La, Ce and Pr) systems

The phase diagrams and thermodynamic properties of the C–RE (RE=La, Ce and Pr) binary systems were assessed by using the CALPHAD method applied to the experimental data in the literature. In the C–RE (RE=La, Pr) systems, RE2C3 and βREC2 (high-temperature form of REC2 phase) were modeled as non-stoichiometric phases while αREC2 (low-temperature form of REC2 phase) was considered to be stoichiometric phase. For La2C3 phase, enthalpy increment (HT–H298K) information was also considered in the optimization. Due to their negligible homogeneities, intermediate compounds Ce2C3 and CeC2 in the C–Ce system, were treated as stoichiometric phases. One set of self-consistent thermodynamic parameters was finally obtained for each of these binary systems. Comparisons between calculated and measured phase diagrams as well as thermodynamic properties showed that most of the experimental information can be satisfactorily accounted for by the present thermodynamic descriptions.