Calorimetric study of maltitol: correlation between fragility and thermodynamic properties

The heat capacity of maltitol was measured with an adiabatic calorimeter. The crystalline form was measured from 100 to 425 K (T_m=420 K), the glass form from 249 K to T_g (around 311 K) and the liquid form from T_g to 400 K. The heat of melting is 55.068 kJ mol⁻¹. The calorimetric glass transition occurs at about T_g=311 K with a sudden jump of the heat capacity ΔC_p(T_g) of about 243.6 J mol⁻¹ K⁻¹. The excess entropy between the under-cooled liquid and the crystal was calculated from the heat capacity data and was used to estimate the Kauzmann temperature T_K, which was found to be 50 K below T_g. ΔC_p(T_g) and T_K values for maltitol were compared with those of other compounds such as sugars, polyols and hydrogen-bonded liquids. It was found that the glass former maltitol is a ‘fragile’ liquid from the thermodynamic point of view.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

Shear viscosity of inorganic glasses and polymers

The viscosity of metaphosphate glasses and polystyrene was measured in the shear deformation mode above and below the glass transition temperature T_g. The temperature dependence of the viscosity above T_g was well expressed by the Vogel–Tammann–Fulcher formula, while two relaxations of thermal activation type appeared below T_g. The overall temperature dependence in both materials was very similar with each other. The relaxation at the lower temperature was found to be sensitive to the internal state of the materials.     

Glass-forming ability and magnetic properties of mechanically solid-state reacted Co100−xTix alloy powders

A high-energy ball milling technique using the mechanical alloying method has been employed for fabrication of glassy Co_100−xTi_x (25≤x≤67) alloy powders at room temperature. The fabricated glassy alloys in the Co-rich (33≥x) side exhibit good soft magnetic properties. The binary glassy alloys for which the glass transition temperatures (T_g) have rather high temperatures (above 800 K), show large supercooled liquid regions before crystallization (ΔT_x larger than 50 K). The reduced glass transition temperature (ratio between T_g and liquidus temperatures, T_l (T_g/T_l)) was found to be larger than 0.56. We have also performed post-annealing experiments on the mechanically deformed Co/Ti multilayered composite powders. The results show that annealing of the powders at 710 K leads to the formation of a glassy phase (thermally enhanced glass formation reaction), of which the heat of formation was measured directly. The similarity in the crystallization and magnetization behaviors between the two classes of as-annealed and as-mechanically alloyed glassy powders implies the formation of the same glass state.     

Pressure effect on the structural relaxation and glass transition in metallic glasses

Two different enthalpy recovery methods were applied to investigate the effects of pressure on structural relaxation and glass transition temperature (T_g) in two metallic glasses (Pd₄₀Ni₁₀Cu₃₀P₂₀ and Zr₆₅Al_7.5Cu_27.5). The pressure-induced enhancement of T_g (dT_g/dP) was derived to be 6 K/GPa in Pd₄₀Ni₁₀Cu₃₀P₂₀ glass, while an increment of 50 K/5 GPa was observed in Zr₆₅Al_7.5Cu_27.5 glass. Activation (formation and migration) volumes of the flow defect were used to interpret the pressure dependence of the structural relaxation and T_g in terms of the free volume model. According to the measured results, the activation volume of relaxation was derived to be 16.7 ų for Pd₄₀Ni₁₀Cu₃₀P₂₀, which is much smaller than that of the polymers.     

Microformability of optical glasses for precision molding

We investigated macroscopic and microscopic deformation of optical glasses K-PSK100 and K-PG375 for precision molding. The materials are characterized by a low glass transition temperature T_g; T_g is 663 K for PSK100 and 616 K for PG375. The materials exhibit Newtonian viscous flow above T_g. We studied the temperature dependence of the normal viscosity and evaluated the microformability by the geometrical transferability of a V-grooved die shape to the material. The dies were made of (1 0 0)Si and the width of the V-groove W_g was 0.1–2.0 μm. After die-forming, we measured the transferred shape of the material with AFM and analyzed the curvature r of the tip of the deformed specimen and the formed and filled area to the V-groove R_f. As a result, we found that the materials exhibit superior microformability due to the homogeneity on a nanometer scale and will be applied to micro- or nano-forming and thus contribute to mass production of micro/nano-devices.     

Structure relaxation and crystallization of Al83Ni10Ce7 metallic glass

Structure relaxation and crystallization of Al₈₃Ni₁₀Ce₇ metallic glass were studied by different scanning calorimetry (DSC) and X-ray diffraction (XRD). According to the DSC scan, it is interesting to find that the second exothermic peak changes with pre-annealing temperatures (below glass transition temperature), suggesting a change in the amorphous structure upon relaxation. Continuous heating crystallization and isothermal crystallization exhibit different crystallization mechanism of the present alloy. fcc-Al and a metastable phase precipitate simultaneously in the first stage crystallization during continuous heating; however, only a metastable phase precipitates during isothermal annealing below glass transition temperature (T_g).     

Levels of thermal stability in some glassy alloys of the Ge–Sb–Se system by differential scanning calorimetry

The thermal stability and crystallization of alloys in the Ge–Sb–Se system were studied by differential scanning calorimetry (DSC). A comparison of various simple quantitative methods to assess the level of stability of the glassy materials in the above-mentioned system is presented. All of these methods are based on characteristic temperatures, obtained by heating of the samples in non-isothermal regime, such as the glass transition temperature, T_g, the temperature at which crystallization begins, T_in, the temperature corresponding to the maximum crystallization rate, T_p, or the melting temperature, T_m. In this work, a parameter K_r(T) is added to the stability criteria. The thermal stability of some ternary compounds of Ge_xSb_0.23−ySe_0.77−x+y type has been evaluated experimentally and correlated with the activation energies of crystallization by this kinetic criterion and compared with those evaluated by other criteria.     

Boron content dependence of crystallization, glass forming ability and magnetic properties in amorphous Fe-Zr-B-Nb alloys

The glass forming ability (GFA) was investigated in Fe_91−xZr₅B_xNb₄ alloys with B contents of 0–36 at.%. The GFA changes with B content, and fully amorphous alloys were prepared by melt spinning for B contents between 5 and 30 at.%. The amorphous alloys crystallize with a primary crystallization mode in the low B content range of 5≤x≤20 at.%, but in the eutectic mode in the high B content range of 20<x<30 at.%. A single new metastable Fe-Zr-B-Nb cubic phase with a lattice constant of 1.0704 nm, a saturation magnetization of 137 emu/g and a coercivity of 7.3 Oe at room temperature is formed when crystallizing in a polymorphous mode at x=30 at.%. The glass transition temperature (T_g), crystallization temperature (T_x), Curie temperature (T_c) and saturation magnetizations (M_s) of the amorphous alloys increase with increasing B content, but the coercivity (H_c) decreases. As the B content exceeds 20 at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but also the concentration dependence of the T_c and M_s changes. It is concluded that the amorphous alloys have better GFA, thermal stability and soft magnetic properties for the high B contents of 25–30 at.% than for the low B contents of 5–20 at.%.     

Effects of Annealing Below Glass Transition Temperature on the Wettability and Corrosion Performance of Fe-based Amorphous Coatings

This study investigated the effect of annealing below glass transition temperature (T_g) on the microstructural characteristics, mechanical property, wettability, and electrochemical performance of activated combustion-high velocity air fuel (AC-HVAF)-sprayed Fe-Cr-Mo-W-C-B-Y amorphous coatings (ACs). Results showed that Fe-based ACs with a thickness of ~ 300 μm exhibited a fully amorphous structure with low oxidization. Originating from the reduced free volume, sub-T_g annealing increased the thermal stability, hardness, and surface hydrophobicity of Fe-based ACs. The enhanced corrosion resistance of sub-T_g annealed ACs in 3.5 wt% NaCl solution was attributed to the increased surface hydrophobicity and passivation capability. This finding elucidates the correlation between sub-T_g annealing and the properties of Fe-based ACs, which promotes ameliorating ACs with superior performance.     

Thermal stability and mechanical properties of Gd-Co-A1 bulk glass alloys

The glass forming ability of Gd-Co-A1 ternary alloy systems with a composition ranging from 50% to 70% （molar fraction） for Gd and from 5% to 40% （molar fraction） for AI were investigated by copper mold casting and Gd60Co25Al15 bulk glass alloy cylinders with the maximum diameter of 5 mm were obtained. The reduced glass transformation temperature （TG/Tm） and the distance of supercooling region ATx are 0.616 and 45 K, respectively for this Gd-Co-A1 alloy. The compressive fracture strength （σf） and elastic modulus （E） of Gd-Co-A1 glassy alloys are 1 170-1 380 MPa and 59-70 GPa, respectively. The Gd-AI-Co bulk glassy alloys with high glass forming ability and good mechanical properties are promising for the future development as a new type function materials.     

The effect of Hf substitution for Zr on glass forming ability and magnetic property of FeCoZrMoBAlY bulk metallic glasses

Bulk metallic glasses (BMGs) Fe₆₁Co₆Zr_8−xHf_xMo₇B₁₅Al₁Y₂ (x = 0–8) have been produced by copper mold casting technique using industrial raw materials. The effect of substitution of Hf for Zr on the glass forming ability (GFA) and the magnetic property has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). It was found that the substitution of an appropriate amount of Hf for Zr can improve the GFA of the base alloy Fe₆₁Co₆Zr₈Mo₇B₁₅Al₁Y₂, as demonstrated by the increase in reduced glass transition temperature T_rg (=T_g/T_l) and GFA parameters of γ (=T_x/T_g + T_l) and δ (=T_x/T_l − T_g). The Fe₆₁Co₆Zr₅Hf₃Mo₇B₁₅Al₁Y₂ alloy exhibits the highest GFA with the largest T_rg (0.612) and δ (1.633), and can cast a fully amorphous rod in 3 mm diameter. The substitution of Hf for Zr also enhances the magnetic properties, as verified by the increase in saturation magnetization (M_s) in the alloy of Fe₆₁Co₆Zr₃Hf₅Mo₇B₁₅Al₁Y₂, whose M_s is approximately 1.5 times higher than that of the base alloy (x = 0) at room temperature. Finally, the effect of the substitution of Hf for Zr on glass forming ability and magnetic properties is discussed.     

Thermal and structural properties of KPO3·Ln(PO3)3 glasses (Ln=rare earth ion)

Glass transition temperatures T_g and Raman spectra of KPO₃·Ln(PO₃)₃ (Ln=rare earth ion) glasses were measured for all rare earth members (except Pm). From the series behavior of the T_g and Raman data, it is concluded that the coordination number around rare earth ions changes, probably from nine to eight, in the middle of the rare earth series.     

Effect of Si addition on the glass-forming ability of a NiTiZrAlCu alloy

The effect of Si addition on the glass-forming ability (GFA) of a NiTiZrAlCu alloy was investigated by using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The maximum diameter of glassy rods increased from 0.5 mm for the Ni₄₂Ti₂₀Zr₂₅Al₈Cu₅ alloy (the base alloy) to 2.5 mm for the Ni₄₂Ti₂₀Zr_21.5Al₈Cu₅Si_3.5 alloy and to 3 mm for the Ni₄₂Ti₁₉Zr_22.5Al₈Cu₅Si_3.5 alloy, when prepared by using the copper mould casting. The GFA of the alloys can be assessed by the reduced glass transition temperature T_rg(=T_g/T_l) and a newly proposed parameter, δ(=T_x/T_l − T_g). An addition of a proper amount of Si and a minor substitution of Ti with Zr can enhance the GFA of the base alloy by suppressing the formation of primary Ni(TiZr) and (TiZr)(CuAl)₂ phases and inducing the composition close to eutectic.     

A new biodegradable copolyester poly(butylene succinate-co-ethylene succinate-co-ethylene terephthalate)

To obtain a biodegradable polymer material with satisfactory thermal properties, higher elongation and modulus of elasticity, a new copolyester, poly(butylene succinate-co-ethylene succinate-co-ethylene terephthalate) (PBEST), was synthesized via direct polycondensation from three prepolymers of butylenes succinate, ethylene succinate and ethylene terephthalate (ET). The resulting copolyesters, PBEST, were characterized by ¹H-NMR, DSC, TG and WAXRD, and their melting temperature (T_m), melting heat of fusion (ΔH_m), glass-transition temperature (T_g), and thermal decomposition temperature (T_d) (1.5 wt%) were obtained. Compared to poly(butylene succinate-co-ethylene succinate) (PBES), PBEST has improved thermal properties such as higher T_m and T_d due to the incorporation of poly(ethylene terephthalate) unit into the main chains of copolyesters, but very low crystallization speeds. The degradation test of copolyesters in a compost condition shows that the degradability of PBEST is as a function of content of ET.     

Theory of dislocation tunneling through a pinning point

We have calculated the transition rate for a string unpinning from a point barrier, using a truncated parabolic potential. In this approximation, it was shown that the result for this N-dimensional system has the one-dimensional form R=ν_effexp (−ΔU/kT_eff), where ν_eff is an effective frequency, ΔU the barrier height, T_eff the effective temperature. There is a crossover temperature T* separating the high temperature classical behavior from the low temperature quantum rate and given by T*=ω_eff/2k. The effective temperature is given by the actual temperature above T*, while below it, is given by the ground state energy, calculated using the effective frequency. The important point is that if one knows the transition rate at high T, then the crossover temperature and the low T transition rate may be calculated. The effective frequency has been calculated for dislocations in the classical regime: ν_eff0.26 (U₀/Gb³) ν_D, where U₀ is the binding energy with a pinning atom, G the shear modulus, b the Burgers vector, and ν_D is the Debye frequency. The predicted crossover temperature of a few tenths Kelvin for an Al crystal is in good agreement with our recent experimental results.     

Mechanically induced crystalline–glassy phase transformations of mechanically alloyed Ta55Zr10Al10Ni10Cu15 multicomponent alloy powders

New multicomponent Ta-based glassy alloy powder was synthesized by mechanical alloying (MA) the elemental powders of Ta₅₅Zr₁₀Ni₁₀Al₁₀Cu₁₅ at room temperature, using a low-energy ball milling technique. During the early stage of milling the agglomerated crystalline powders are mechanically crushed and fresh surfaces are rapidly created. Kneading of such ground powders enhances the atomic diffusion and leads to local alloying. As the MA time increases, the number of vacancies in the Ta lattice (base material) increases so that the atoms of the alloying elements for Zr, Al, Ni and Cu tend to migrate to the open defected lattice of metallic Ta. The number of atoms of the alloying elements that migrate to the bcc lattice of the base material are increasing with increasing MA time and this leads to a monotonic expansion of the Ta lattice. Further milling time (86–130 ks) plays an important role in increasing the rate of diffusion and this leads to an increase in the number of migrated atoms of the alloying elements that pass into the Ta lattice. The a₀ of the yielded solid solution at this stage does not change anymore with increasing MA time and a homogeneous supersaturated bcc-solid solution is obtained after 130 ks of MA time. This solid solution, which is subjected to continuous imperfections, is gradually transformed into a glassy phase upon increasing the MA time. The glassy powders of the final-product (1080 ks) in which its glass transition temperature (T_g) lies at a high temperature (834 K), crystallize through a single sharp exothermic peak at 1004 K (T_x). The total enthalpy change of crystallization (ΔH_x) is −10.32 kJ/mol. The width of the supercooled liquid region before crystallization (ΔT_x) of the synthesized glassy powder shows the largest value (170 K) of any reported metallic glassy system.     

Mechanical Relaxation of a Ti_(36.2)Zr_(30.3)Cu_(8.3)Fe_4Be_(21.2) Bulk Metallic Glass: Experiments and Theoretical Analysis

The dynamic mechanical relaxation behavior of Ti_(36.2)Zr_(30.3)Cu_(8.3)Fe_4Be_(21.2) bulk metallic glass with good glass-forming ability was investigated by mechanical spectroscopy. The mechanical relaxation behavior was analyzed in the framework of quasi-point defects model. The experimental results demonstrate that the atomic mobility of the metallic glass is closely associated with the correlation factor χ. The physical aging below the glass transition temperature T g shows a non-Debye relaxation behavior, which could be well described by stretched Kohlrausch exponential equation. The Kohlrausch exponent β_(aging) reflects the dynamic heterogeneities of the metallic glass. Both concentration of "defects" and atomic mobility decrease caused by the in situ successive heating during the mechanical spectroscopy experiments.     

Characterization of crystallization kinetics of a Ni- (Cr, Fe, Si, B, C, P) based amorphous brazing alloy by non-isothermal differential scanning calorimetry

The thermal stability and crystallization kinetics of a Ni- (Cr, Si, Fe, B, C, P) based amorphous brazing foil have been investigated by non-isothermal differential scanning calorimetry. The glass transition temperature T_g, is found to be 720 ± 2 K. The amorphous alloy showed three distinct, yet considerably overlapping crystallization transformations with peak crystallization temperatures centered around 739, 778 and 853 ± 2 K, respectively. The solidus and liquidus temperatures are estimated to be 1250 and 1300 ± 2 K, respectively. The apparent activation energies for the three crystallization reactions have been determined using model free isoconversional methods. The typical values for the three crystallization reactions are: 334, 433 and 468 kJ mol⁻¹, respectively. The X-ray diffraction of the crystallized foil revealed the presence of following compounds Ni₃B (Ni₄B₃), CrB, B₂Fe₁₅Si₃, CrSi₂, and Ni_4.5Si₂B.     

A mechanical spectroscopy study of the Zr69.5Cu12Ni11Al7.5 alloy

The vibrating reed technique has been used to investigate the Zr_69.5Cu₁₂Ni₁₁Al_7.5 glass forming alloy. The phase transformations of the material, as can be seen through the changes of the resonance frequency of the sample as a function of temperature, have been studied and the results have been compared with TEM and DSC measurements confirming the development, above T_g, of a metastable quasicrystalline state prior to crystallisation. Hydrogen-induced damping peaks were then observed in the different phases of the material with particular attention to the quasicrystalline state, where it seems that the microscopic reorientation mechanism responsible for the internal friction peaks should be similar to the one already known in the amorphous phase (hydrogen jumps between tetrahedral sites). Shortly after crystallisation, three damping peaks were observed, two of which are attributed to relaxation processes (Zener-type or intercrystalline Gorsky effect) taking place in the tetragonal CuZr₂ phase.