Microstructure and Its Effect on the Magnetic, Magnetocaloric and Magnetostrictive Properties of Tb55Co30Fe15 Glassy Ribbons

In the present work, the microstructure and its effect on the magnetic, magnetocaloric, and magnetoelastic properties of the Tb55Co30Fe15 melt-spun ribbon were investigated. The ribbon exhibits typical amorphous characteristics in its X-ray diffraction examination and differential scanning calorimetry measurement. However, the magnetic properties of the ribbon indicate that the ribbon is inhomogeneous in the nanoscale, as ascertained by a high-resolution electron microscope. Compared to the Tb55Co45 amorphous alloy, the Tb55Co30Fe15 ribbon shows poor magnetocaloric properties but outstanding magnetostriction. A rather high value of reversible magnetostriction up to 788 ppm under 5 T was obtained. The mechanism for the formation of nanoparticles and its effect on the magnetocaloric and magnetostrictive properties were investigated.

Temperature-induced first-order displacive phase transition of isonicotinamide-4-methoxybenzoic acid co-crystal

Isonicotinamide–4-methoxybenzoic acid co-crystal (1), C6H6N2O·C8H8O3, is formed through slow evaporation from methanol solution and it undergoes a first-order isosymmetry (monoclinicI2/a↔ monoclinicI2/a) structural phase transition atTc= 142.5 (5) K, which has been confirmed by an abrupt jump of crystallographic interaxial angle β from variable-temperature single-crystal XRD and small heat hysteresis (6.25 K) in differential scanning calorimetry measurement. The three-dimensional X-ray crystal structures of (1) at the low-temperature phase (LTP) (100, 140 and 142 K) and the high-temperature phase (HTP) (143, 150, 200, 250 and 300 K) were solved and refined as a simple non-disordered model with finalR[F2> 2σ(F2)] ≃ 0.05. The asymmetric unit of (1) consists of crystallographically independent 4-methoxybenzoic acid (A) and isonicotinamide (B) molecules in both enantiotropic phases. MoleculeAadopts a `near-hydroxyl' conformation in which the hydroxyl and methoxy groups are positioned on the same side. Both `near-hydroxyl' and `near-carbonyl' molecular conformations possess minimum conformational energies with an energy difference of < 0.15 kJ mol−1from a potential energy surface scan. In the crystal, molecules are joined into linearABBAarrays by intermolecular N—H...O and O—H...N hydrogen bonds which were preserved in both phases. However, theseABBAarrays are displaced from planarity upon LTP-to-HTP transition and the changes in inter-array interactions are observed in two-dimensional fingerprint plots of their Hirshfeld surfaces. ThePIXELenergies of each molecular pair in both phases were calculated to investigate the difference in intermolecular interaction energies before and after the displacement ofABBAarrays from planarity, which directly leads to the single-crystal-to-single-crystal phase transition of (1).

Synthesis and properties of (A2+B4)-type hyperbranched polyimides with different terminal groups

To investigate the effect of terminal groups on the properties of hyperbranched polyimides (HBPIs) for potential optical applications, a series of HBPIs bearing different terminal groups have been synthesized through a novel aromatic CF3-containing tetra-amine, 4,4′-di[3,5-di(2-trifluoromethyl-4-aminophenoxy)phenoxy] sulfone, and a long chain dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane, via a two-step polycondensation procedure. The synthesized HBPIs could form flexible and tough polyimide (PI) films, which exhibit good thermal stability with the glass transition temperatures of 191–234°C for differential scanning calorimetry measurement, the 5% weight loss temperatures of 533–610°C, and residual weights of 45.8–58.6% at 800°C under nitrogen atmosphere. The PI films have favorable mechanical properties with tensile strengths of 77–92 MPa, elongation at break of 3.55–7.99%, and initial modulus of 2.05–2.86 GPa. The films also exhibit the good transmittance of higher than 80% at 800 nm. The average refractive indices ( nav) and in-plane/out-of-plane birefringence (Δ n) measured at 632.8 nm are in the range of 1.5539–1.6022 and 0.0065–0.0077, respectively. The good transmittance in the visible region, tunable nav, and low Δ n are very suitable for optical applications.

Development of Microstructure and Properties of Mg-Y-(Nd)-Zn Alloys during Heat and Mechanical Treatment

This work is focused on development of microstructure and properties of Mg-Y-Zn and Mg-Y-Nd-Zn alloys during heat and mechanical treatment. In the as-cast state both alloys exhibit almost equiaxed grains with little larger size in Mg-Y-Zn alloy and grain boundaries decorated by different structures - long period ordered structure (LPSO) was detected in Mg-Y-Zn alloy and eutectics of Mg3Nd type structure in alloy with Nd addition. A high density of stacking faults is evident in both alloys. Both alloys were repeatedly isochronally heat treated from room temperature up to 440 °C. Resistivity and microhardness measurement was performed after each heating step. Stacking faults persist both annealings in both alloys and microhardness development shows no remarkable differences. LPSO in Mg-Y-Zn alloy disappears after the first annealing and was again detected after repeated annealing up to 340 °C. After the whole treatment no grain growth appeared. Differential scanning calorimetry measurement was performed at both repeatedly heated alloys up to 540 °C. There are three exothermic peaks in DSC curves of Mg-Y-Zn alloys that can be ascribed to embedding solute atoms in stacking faults, LPSO development and transformation and coarsening of grain boundary particles. DSC curves of Mg-Y-Nd-Zn alloy exhibit two exothermic peaks that probably correspond to precipitation of basal plates of γ ́and γ phase. Measurement of microhardness was performed after sequential deformation of both alloys in the as-cast state. The alloys were cold rolled in steps of 0,9 % thickness reduction up to cracks formation. Strengthening of both alloys is very similar but formation of cracks in the alloy with Nd addition begins after a lower reduction (about 11 %) compared to Mg-Y-Zn alloy (about 15 %).

Preparation of a Poly(Lactic Acid)/Montmorillonite Nanocomposite

Poly (L-lactic acid)/organically modified montmorillonite (PLLA/OMMT) nanocomposites were fabricated by a solution intercalation method. OMMT, modified with quaternary alkylammonium ion, was prepared by alkyltrialkoxysilane. The differential scanning calorimetry measurement revealed that the crystallization temperatures of PLLA/OMMT nanocomposites were at around 110 °C regardless of the existence of OMMT or the weight fraction of them. X-ray diffraction patterns suggested that the (001) diffraction was around 2θ = 2.5°. The TEM image showed variously expanded interlayer galleries of OMMT and partially exfoliated silicate layer unit in the matrix. Board-shaped specimens for mechanical property tests were fabricated by compression-molding at 190 °C (including 30 min annealing at 110 °C). The flexural modulus of the nanocomposites increased with increasing content of OMMT. Vickers hardness of the nanocomposites were almost same independent on weight fraction of OMMT.

Characterization of nano-enhanced interconnect materials for fine pitch assembly

Purpose – Multiple fillers are adopted to study the filler influences on electrical and mechanical properties of the conductive adhesives. The performances of the developed nano-enhanced interconnect materials in printing process are also evaluated. The paper aims to discuss these issues. Design/methodology/approach – Micron-sized silver flakes are used as the basic fillers, and submicro- and nano-sized silver spheres and carbon nanotubes (CNTs) are adopted to obtain conductive adhesives with multiple fillers. Differential scanning calorimetry measurement is carried out to characterize the curing behavior of the samples with different fillers, four-probe method is used to obtain the bulk resistivity, shear test is conducted for adhesive strength, and environmental loading test is also involved. Furthermore, printing trials with different patterns have been carried out. Findings – The electrical resistivity of the adhesives with submicro-sized silver spheres does not monotonically change with the increasing sphere proportion, and there exists an optimized value for the ratio of silver flakes to spheres. Samples with relatively small amount of CNT additives show improved electrical properties, while their mechanical strengths tend to decrease. For the printing application, the adhesives with 18.3 volume% filler content behave much better than those with lower filler content of 6 percent. The presence of the nano-particles makes a slight improvement in the printing results. Research limitations/implications – More detailed printing performance and reliability test of the samples need to be carried out in the future. Originality/value – The conductive adhesives as interconnect materials exhibit some improved properties with optimized bimodal or trimodal fillers. The additive of the nano-fillers affects slightly on the printing quality of the bimodal conductive adhesives.

Reversible structural phase transition of pyridinium-4-carboxylic acid perchlorate

Pyridinium-4-carboxylic acid perchlorate (C6H6NO2·ClO4) was synthesized and separated as crystals. Differential scanning calorimetry measurement shows that this compound undergoes a reversible phase transition at about 122 K with a heat hysteresis of 1.8 K. A dielectric anomaly observed at 127 K further confirms the phase transition. The low-temperature (LT;T= 103 K) structure has space groupP21/cand cell parametersa= 17.356 (6),b= 13.241 (3),c= 16.161 (7) Å, β = 138.055 (17)°. The high-temperature (HT;T= 298 K) structure has space groupP21/cand cell parametersa= 5.5046 (11),b= 13.574 (3),c= 11.834 (2) Å, β = 99.35 (3)°, but can be re-described using new axesa′ =a,b′ =b,c′ = −2a+c,V′ =Vto give the cella′ = 5.5046 (11),b′ = 13.574 (3),c′ = 17.424 (3) Å, β′ = 137.92 (3)° and space groupP21/c. The associated coordinate transformation isx′ =x+ 2z,y′ =y,z′ =zand the associated reflection index transformation ish′ =h,k′ =k,l′ =l− 2h. The relationship between the two cells is 3a,b,c(HT) approximatesa,b,c(LT). The crystal comprises one-dimensional hydrogen-bonded chains of the pyridinium-4-carboxylic acid cations and perchlorate anions. A precise analysis of the main packing and structural differences as well as the changes in the intermolecular interactions between the HT phase and the LT phase reveals that the disorder–order transition of the perchlorate anions may be the driving force of the transition, and the hydrogen-bonding effect may contribute to the transition as a secondary parameter.

Parallel nano-Differential Scanning Calorimetry: A New Device for Combinatorial Analysis of Complex nano-Scale Material Systems

ABSTRACTA new device is presented for the combinatorial analysis of complex nano-scale material systems. The parallel nano-differential scanning calorimeter (PnDSC) is a micro-machined array of calorimetric cells. This new approach to combinatorial calorimetry should expedite the analysis of nano-scale material thermal properties. A power compensation differential scanning calorimetry measurement, not yet performed on a device of this type, is described. A NiTi specific heat measurement demonstrates the scanning calorimetry capability of the PnDSC.