High-temperature Form Research Articles

High-Temperature Forming of a Vehicle Closure Component in Fine-Grained Aluminum Alloy AA5083: Finite Element Simulations and Experiments

Fine-grained AA5083 aluminum-magnesium alloy sheet can be formed into complex closure components with the Quick Plastic Forming process at high temperature (450oC). Material models that account for both the deformation mechanisms active during forming and the effect of stress state on material response are required to accurately predict final sheet thickness profiles, the locations of potential forming defects and forming cycle time. This study compares Finite Element (FE) predictions for forming of an automobile decklid inner panel in fine-grained AA5083 using two different material models. These are: the no-threshold, two-mechanism (NTTM) model and the Zhao. The effect of sheet/die friction is evaluated with five different sheet/die friction coefficients. Comparisons of predicted sheet thickness profiles with those obtained from a formed AA5083 panel shows that the NTTM model provides the most accurate predictions.

Concentration effect of cerium in (Y 0.9− xGd 0.1Ce x) 2SiO 5 blue phosphor

(Y 0.9− x Gd 0.1Ce x ) 2SiO 5 with various Ce concentration, x, was prepared by calcination of spray pyrolysis precursor obtained from a mixture of nitrates and TEOS under H 2/N 2 atmosphere. Cerium could be doped up to 3 at.% into the high-temperature form (X2) of Y 2SiO 5. The unit cell volume linearly expanded with the x-value. Its structural refinement suggested that the doped Ce 3+ ions were almost equally distributed into two kinds of rare earth sites in the X2 phase. The PL spectra showed a peak shift toward significantly longer wavelength (red-shift) with increasing x-value. The PL red-shift might be caused by an energy transfer among the Ce 3+ ions distributed in the two sites having slightly different 5d excited energy levels with different coordination numbers.

Monazite structure from dehydrated CaSeO4·2H2O

AbstractThe structure of the high-temperature form of CaSeO4, formed by dehydration of the gyspum-type structure dihydrate is presented. The material is equivalent to that described previously as a P212121 form, but is however, a monazite with unit cell a = 6.85661(16) Å, b = 7.04962(15) Å, c = 6.68817(15) Å and β = 104.2675(21)° in space group P121/n1. Also presented is evidence for two intermediate trigonal and pseudo-trigonal phases related to the structurally similar minerals rhabdophane, bassanite, and γ-CaSO4. This result permits closer comparisons between intermediate-temperature structures of the selenate with related sulphates, and orthophosphates with a view to extending structural stability via synthesis of solid-solutions.

New approach to gas pressure profile prediction for high temperature AA5083 sheet forming

A new theoretical approach to the prediction of gas pressure profiles that vary smoothly with time in high temperature forming of fine-grained AA5083 sheet is presented. The required pressure-flow stress relationship, which couples the gas pressure profile and the material constitutive model, was implemented in ABAQUS implicit. Forming of a rectangular pan in a die with variable entry radii was simulated with a single creep mechanism model that accounts for hardening/softening in AA5083. Predicted sheet thickness and thinning in a die entry radius region at the end of forming are examined in detail. Results are compared with those from two additional gas pressure schemes. One of these is taken directly from experiments and the other is based upon an algorithm that is internal to ABAQUS. The effect of friction on forming time is explored in the absence of a stability criterion for necking.

Structures and negative thermal expansion properties of the one-dimensional cyanides, CuCN, AgCN and AuCN

The behaviour of the lattice parameters of HT-CuCN (high-temperature form), AgCN and AuCN have been investigated as a function of temperature over the temperature range 90-490 K. All materials show one-dimensional negative thermal expansion (NTE) along the -(M-C≡N)- chain direction c (α c (HT-CuCN) = -32.1 × 10- 6 K -1 , α c (AgCN) = -23.9 x 10- 6 K -1 and α c (AuCN) = -9.3 x 10- 6 K -1 over the temperature range 90-490 K). The origin of this behaviour has been studied using RMC modelling of Bragg and total neutron diffraction data from AgCN and AuCN at 10 and 300 K. These analyses yield details of the local motions within the chains responsible for NTE. The low-temperature form of CuCN, LT-CuCN, has been studied using single-crystal X-ray diffraction. In this form of CuCN, wavelike distortions of the -(Cu-C≡N)-chains occur in the static structure, which are reminiscent of the motions seen in the RMC modelling of AgCN and AuCN, which are responsible for the NTE behaviour.

Y(BH4)3—an old–new ternary hydrogen store akalearning from a multitude of failures

Fourteen different synthetic approaches towards pure solvent-free Y(BH(4))(3) have been tested, thirteen of which have failed. Attempted reactions of YCl(3) or Y(OC(4)H(9))(3) with LiBH(4) in THF, those of YCl(3) with (C(4)H(9))(4)N(+) BH(4)(-), as well as between YH(x approximately 3) and R(4)NBH(3) (R = CH(3), C(2)H(5)) in the presence or absence of a solvent (n-hexane or CH(2)Cl(2)) did not lead to the expected product. The mechanochemical solid/solid reactions (MBH(4) + 3 YX(3)--> Y(BH(4))(3) + 3 LiCl, where M = Li, Na; X = F, Cl) have succeeded only for the LiBH(4) and YCl(3) reagents, but the separation of the crystalline reaction products (Y(BH(4))(3) in its Pa3 phase and LiCl) by dissolution or flotation in various solvents has not been successful. The thermal decomposition process of Y(BH(4))(3) in a mixture with LiCl has been investigated with thermogravimetric (TGA) and calorimetric analysis (DSC) combined with spectroscopic evolved gas analysis (EGA). Three major endothermic steps could be distinguished in the DSC profile at ca. 232, 282, 475 degrees C (heating rate 10 K min(-1)) corresponding to a phase transition and two steps of thermal decomposition. Solid decomposition products are amorphous except for the new cubic polymorph of Y(BH(4))(3) overlooked in previous work. The high-temperature phase forms at the onset of thermal decomposition and it may be prepared by heating of the low-temperature phase up to a narrow temperature range (194-210 degrees C) followed by rapid quenching. Y(BH(4))(3) constitutes a novel highly efficient hydrogen storage material (theor. 9.0 wt% H) but, unfortunately, the evolved H(2) is contaminated by toxic boron hydrides and products of their pyrolysis.

Nodes to the grindstone

Materials become superconductors when charge carriers pair up; this pairing is stabilized by an energy gap, the energy cost for creating single-particle excitations. In any new class of superconductors, the momentumspace structure of this energy gap (or superconducting order parameter) is generally considered to be one of the most important clues to the nature of the pairing mechanism. Determining the order parameter is rarely straightforward, and historically, e.g., in the hightemperature cuprate superconductors, many different types of experiments had to be analyzed and compared before a consensus was achieved. It is therefore not surprising that, nearly two years after the discovery of the high-temperature iron-pnictide superconductors, the symmetry and form of the order parameter in these systems are still controversial. However, the degree of apparent disagreement among different experiments on similar samples [1] has raised the question: can the superconducting state of these materials be extraordinarily sensitive to either disorder or other aspects of electronic structure that “tune” the pairing interaction? In a recent article published in Physical Review B[2], B. Muschler and collaborators from the Walther Meissner Institute in Germany, along with Tom Devereaux, Ian Fisher, and collaborators from Stanford in the US provide important clues using Raman spectroscopy.

Simulation of High-Temperature AA5083 Bulge Forming with a Hardening/Softening Material Model

High-temperature bulge forming of AA5083 aluminum sheet was simulated with the commercial finite element (FE) code ABAQUS™. A material model that is strain rate sensitive and accounts for strain hardening and softening was used. Results were compared with data from AA5083 bulge forming experiments at 450 °C where the gas pressure was a prescribed constant value. The results show that the material model is capable of predicting the deformation and thinning behavior at different constant pressure levels. In ancillary simulations, time-varying pressure profiles were computed (rather than prescribed) with an internal ABAQUS™ routine that attempts to maintain the strain rate at the bulge dome pole within a specified range. The time-varying profiles, for which no experimental AA5083 bulge forming data exist, can be programmed into existing bulge testing instrumentation to validate the associated predictions of bulge dome height and thinning. The present effort represents a necessary step toward predicting gas pressure profiles by coupling the pressure profile with a desired sheet deformation rate.

Anomalous Out-Diffusion Profiles of Nitrogen in Silicon

Out-diffusion nitrogen profiles measured by SIMS after annealing at 850 and 800oC, have a peculiar minimum at a depth of about 5 m. The profiles are well reproduced by simulations assuming that there is a considerable fraction of nitrogen stored in substitutional clusters VN4. Upon annealing, these clusters lose nitrogen and convert into a stable high-temperature form VN1. This reaction involves a preliminary attachment of a fast-diffusing interstitial trimer, N3. Accordingly, the conversion occurs only in the bulk but not at the surface (due to out-diffusion loss of N3), and the substitutional component decreases from the surface towards the bulk. By fitting the profiles, the two basic parameters of the N2/N1 transport are deduced: P = D1K1/2 (a combination of the monomeric diffusivity D1 and the dissociation constant of dimers, K), and the dissociation time of dimers. With these data, D1(T) and K(T) are specified.

Nitrate-Melt Synthesized HT-LiCoO2 as a Superior Cathode-Material for Lithium-Ion Batteries

An electrochemically-active high-temperature form of LiCoO2 (HT-LiCoO2) is prepared by thermally decomposing its constituent metal-nitrates at 700 ºC. The synthetic conditions have been optimized to achieve improved performance with the HT-LiCoO2 cathode in Li-ion batteries. For this purpose, the synthesized materials have been characterized by powder X-ray diffraction, scanning electron microscopy, and galvanostatic charge-discharge cycling. Cathodes comprising HT-LiCoO2 exhibit a specific capacity of 140 mAhg-1 with good capacity-retention over several charge-discharge cycles in the voltage range between 3.5 V and 4.2 V, and can sustain improved rate capability in contrast to a cathode constituting LiCoO2 prepared by conventional ceramic method. The nitrate-melt-decomposition method is also found effective for synthesizing Mg-/Al- doped HT-LiCoO2; these also are investigated as cathode materials for Li-ion batteries.

The incommensurately modulated crystal structure of β-Pb2BiVO6: interpretation of the phase transition α → β → δ and conduction properties of related materials

A new polymorph of Pb(2)BiVO(6) was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions alpha --> beta and beta --> delta were identified in the mother phase; the high-temperature form delta-Pb(2)BiVO(6) eventually decomposes at 753 K to a mixture of Pb(4)BiVO(8) and the high-temperature form of PbBiVO(5) before showing recombination at 923 K. beta-Pb(2)BiVO(6) has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of beta-Pb(2)BiVO(6) by TEM diffraction studies confirmed the lattice and incommensurate modulation character. Log sigma = f(T(-1)) dependences for Pb(2)BiVO(6)-related materials (6% M-for-V-substituted compositions; M = Cr, Mn, P) are reported, which allow the characterization (E(a) and isothermal sigma values) of the beta- as well as the delta- and alpha-Pb(2)BiVO(6) varieties.

Conformational polymorphism in aripiprazole: Preparation, stability and structure of five modifications

Five phase-pure modifications of the antipsychotic drug aripiprazole were prepared and characterized by thermal analysis, vibrational spectroscopy and X-ray diffractometry. All modifications can be produced from solvents, form I additionally by heating of form X degrees to approximately 120 degrees C (solid-solid transformation) and form III by crystallization from the melt. Thermodynamic relationships between the polymorphs were evaluated on the basis of thermochemical data and visualized in a semi-schematic energy/temperature diagram. At least six of the ten polymorphic pairs are enantiotropically and two monotropically related. Form X degrees is the thermodynamically stable modification at 20 degrees C, form II is stable in a window from about 62-77 degrees C, and form I above 80 degrees C (high-temperature form). Forms III and IV are triclinic ($P\overline 1$), I and X degrees are monoclinic (P2(1)) and form II orthorhombic (Pna2(1)). Each polymorph exhibits a distinct molecular conformation, and there are two fundamental N-H$\cdots$O hydrogen bond synthons (catemers and dimers). Hirshfeld surface analysis was employed to display differences in intermolecular short contacts. A high kinetic stability was observed for three metastable polymorphs which can be categorized as suitable candidates for the development of solid dosage forms.

Structural paradigm of Se-rich Ge–Se glasses by high-resolution x-ray photoelectron spectroscopy

The structure of binary GexSe100−x chalcogenide glass family (0≤x≤30) is determined by high-resolution x-ray photoelectron spectroscopy (XPS). On the basis of compositional dependences of fitting parameters for Ge and Se core level XPS spectra, the ratio between edge- and corner-shared tetrahedra is determined. We find that this ratio for glasses with 20≤x≤30 is almost constant with a value same as for the high-temperature crystalline form of GeSe2.

Microstructure and Crystal Structure in TAGS Compositions

GeTe, a small bandgap semiconductor that has native p-type defects due to Ge vacancies, is an important constituent in the thermoelectric material known as TAGS. TAGS is an acronym for alloys of GeTe with AgSbTe2, and compositions are normally designated as TAGS-x, where x is the fraction of GeTe. TAGS-85 is the most important with regard to applications, and there is also commercial interest in TAGS-80. The crystal structure of GeTe1+δ has a composition-dependent phase transformation at a temperature ranging from 430°C (δ = 0) to ~400°C (δ = 0.02). The high-temperature form is cubic. The low-temperature form is rhombohedral for δ < 0.01, as is the case for good thermoelectric performance. Addition of AgSbTe2 shifts the phase transformation to lower temperatures, and one of the goals of this work is a systematic study of the dependence of transformation temperature on the parameter x. We present results on phase transformations and associated instabilities in TAGS compositions in the range of 70 at.% to 85 at.% GeTe.

Reversible Breaking and Forming of Metal–Ligand Coordination Bonds: Temperature‐Triggered Single‐Crystal to Single‐Crystal Transformation in a Metal–Organic Framework

Yb(C(4)H(4)O(4))(1.5)] undergoes a temperature-triggered single-crystal to single-crystal transformation. Thermal X-ray single-crystal studies showed a reversibly orchestrated rearrangement of the atoms generated by the breaking/formation of coordination bonds, in which the stoichiometry of the compound remains unchanged. The transformation occurs on heating the crystal at approximately 130 degrees C. This uncommon behavior was also studied by thermal methods, FTIR spectroscopy, and thermodiffractometry. Both polymorphs, alpha (room-temperature form) and beta (high-temperature form), are proven to be active heterogeneous catalysts; the higher catalytic activity of beta is owed to a decrease in the Yb coordination number. A mechanism based on spectroscopic evidence and involving formation of the active species Yb-O-OH is proposed for the sulfide oxidation.

Proton transfer in electrochemically active “solid hydroxide proton conductor-hydrogenated metal” heterostructures

The electrochemical activity of solid-state heterostructures containing a hydrogenated metal and a solid proton conductor is investigated in the temperature ranges of 360-458 K, 360-370 K, and 320-420 K. The eutectics KOH/NaOH or KOH / KOH · H 2 O and the chemical compound KOH · H 2 O were chosen as the pro- ton conductor. The conductivity of these electrolytes is higher than 1 mS/cm and their activation energies lower than 0.4 eV. Proton conductivity of the electrolytes is established by the emf method and confirmed by the iso- tope effect (H ⇔ D) in the conductivities of KOH · H 2 O and the high-temperature form of KOH/NaOH (the pro- tium forms are ≈ 1.4 times higher). Anomalies in the temperature dependence of conductivity and heat capacity are characteristic of eutectics in the region of 360 ± 1 K, and this has an effect on the electrochemical properties of the PdH x | KOH / NaOH | PdO y and TiH x | KOH · H 2 O | C heterostructures. Transport of atomic particles of hydro- gen—most likely protons—across ( Pd / Ti )c i | MOH heteroboundaries (where aec = KOH · H 2 O , KOH / NaOH , KOH / KOH · H 2 O has a reversible character, which is shown by isotope and impedance measurements. The importance of the self-organized microheterogeneous solid eutectics KOH/NaOH and KOH / KOH · H 2 O for their high conductivity compared to NaOH, KOH, and KOH · H 2 O taken individually is discussed.

Bistability of Magnetization without Spin-Transition in a High-Spin Cobalt(II) Complex due to Angular Momentum Quenching

[Co(NO(3))(2)L] (L: 2,6-di(pyrazol-1-yl)pyrazine) (1) exhibits an abrupt transition with hysteresis in magnetic susceptibility between 228 and 240 K. The results of spectroscopic and XRD measurements showed that 1 is in the high spin state in the whole temperature range. Therefore the observed hysteresis is not due to a spin transition but corresponds to a partial quenching of the angular momentum contribution to the magnetic susceptibility. Crystallographic measurements on the low- and high-temperature form of 1, combined with DFT calculations, showed that a symmetric twisting of the coordinating nitrate ions upon the transition is the most important factor in the orbital quenching mechanism. Utilizing such quenching to control magnetic properties can be a new approach to engineer transition metal complexes with magnetic functionalities without changing their spin or oxidation state.

Temperature- and Pressure-Induced Proton Transfer in the 1:1 Adduct Formed between Squaric Acid and 4,4′-Bipyridine

We have applied a combination of spectroscopic and diffraction methods to study the adduct formed between squaric acid and bypridine, which has been postulated to exhibit proton transfer associated with a single-crystal to single-crystal phase transition at ca. 450 K. A combination of X-ray single-crystal and very-high flux powder neutron diffraction data confirmed that a proton does transfer from the acid to the base in the high-temperature form. Powder X-ray diffraction measurements demonstrated that the transition was reversible but that a significant kinetic energy barrier must be overcome to revert to the original structure. Computational modeling is consistent with these results. Modeling also revealed that, while the proton transfer event would be strongly discouraged in the gas phase, it occurs in the solid state due to the increase in charge state of the molecular ions and their arrangement inside the lattice. The color change is attributed to a narrowing of the squaric acid to bipyridine charge-transfer energy gap. Finally, evidence for the possible existence of two further phases at high pressure is also presented.

Crystal structure and thermal expansion of the low- and high-temperature forms of Ba MIV(PO 4) 2 compounds ( M=Ti, Zr, Hf and Sn)

The crystal structure of β-BaZr(PO 4) 2, archetype of the high-temperature forms of Ba M(PO 4) 2 phosphates (with M=Ti, Zr, Hf and Sn), has been solved ab initio by Rietveld analysis from synchrotron X-ray powder diffraction data. The phase transition appears as a topotactic modification of the monoclinic (S.G. C 2 / m ) lamellar α-structure into a trigonal one (S.G. P 3 ¯ m 1 ) through a simple mechanism involving the unfolding of the [ Zr ( PO 4 ) 2 ] n 2 - layers. The thermal expansion is very anisotropic (e.g., −4.1< α i <34.0×10 −6 K −1 in the case of α-BaZr(PO 4) 2) and quite different in the two forms, as a consequence of symmetry. It stems from a complex combination of several mechanisms, involving bridging oxygen rocking in M–O–P linkages, and “bond thermal expansion”.

Mechanical properties of textured ceramics from muscovite–kaolinite alternate layers

An organized network of mullite anisotropic crystals embedded in a silico-aluminate matrix material is obtained at interfaces of sintered alternate layers of muscovite and kaolinite minerals. The nucleation and growth of mullite anisotropic crystals occur preferentially along the muscovite basal planes through topotactic reaction with the high temperature form of muscovite. Simultaneously to structural transformations, dehydroxylation of muscovite induces an exfoliation process, which is temperature and time dependent. The kinetics of this process was controlled using an appropriate thermal cycle and uniaxial load. During sintering, the control of mullite size mainly depends in temperature and the addition of a small quantity of low-temperature liquid phase also favors the growth of mullite. But liquid induces the weakening of the organization degree of the mullite network. Quantitative texture analysis (QTA) and SEM were used to characterize microstructural characteristics. Flexural strength, Young modulus and fracture toughness are closely related to size and organization degree of the mullite network. In general, mullite length favors the increase of strength and fracture toughness. But a high organization degree of the mullite network favors the occurrence of interconnected crystals and increases mechanical properties.