Formation and thermal stability of Cu-Zr-Al-Er bulk metallic glasses with high glass-forming ability

The formation and thermal stabilities of Cu_46.25Zr_46.25-xAl_7.5Er_x, (x=0 to 8) bulk metallic glasses (BMGs) were investigated. The addition of a small amount of Er (2at%) for replacing Zr effectively improves the glass-forming ability of Cu_46.25Zr_46.25Al_7.5 alloy, and the glassy rod with a diameter of at least 12 mm can be formed. The glass transition temperature (T_g), temperature interval of supercooled liquid region ΔT_x (= T_x − T_g, and reduced glass transition temperature T_rg (=T_g/T₁) of Cu_46.25Zr_44.25Al_7.5Er₂ glassy alloy are 699 K, 62 K and 0.607, respectively.     

Glass formation of ternary Sm-based Sm-Al-Co bulk metallic glasses

Ternary Sm-based Sm-Al-Co alloys at specific compositions designed using an e/a- and cluster-related criteria exhibit high glass forming abilities and form bulk glassy rods of 3 mm in diameter by a copper mold suction-casting method. Four composi- tions of bulk metallic glasses (BMGs) are Sm50Al25Co25, Sm52Al24Co24, Sm54Al23Co23 and Sm56Al22Co22, which all satisfy a constant conduction electron concentration of 1.5. Among them, the BMG exhibiting the largest reduced glass transition temperature (Trg) is Sm50Al25Co25, which reaches 0.648. The glass transition temperature Tg and the onset crystallization temperature Tx of this alloy are respectively 579 and 640 K at a heating rate of 20 K/min.     

Preparation of Plate Fe60 Co8 Zr10 Mo5 W2 B15 Bulk Amorphous Alloy and Its Fracture Toughness

With processes of arc melting, inductive melting and copper mold suction casting, a plate Febased bulk amorphous alloy Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a thickness of 1 mm was prepared. The surfaces and fractures of the cast bulk amorphous alloy were aglean and with typical metallic luster. The glass transition temperature (T_g), supercooled liquid region (δT_x) and reduced glass transition temperature (T_g) of prepared Fe-based amorphous alloy are 884 K, 63 K, and 0.611 respectively. The fracture toughness of the cast bulk amorphous alloy is at the level of 1.6 MPa·m^1/2. Funded by the Key Project of National Natural Science Foundation of China (No. 50431030) and the Natural Science Foundation of Jiangsu Province (No. BK2001053)     

Critical serrated flow features during nanoindentation in La-based bulk metallic glasses

La_57.6Al_17.5(Cu, Ni)_24.9 and La₆₄Al₁₄(Cu, Ni)₂₂ bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La_57.6Al_17.5(Cu, Ni)_24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La₆₄A1₁₄ (Cu, Ni)₂₂ BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.     

Crystallization kinetics of calcium aluminate glasses studied by non-isothermal techniques

The crystallization kinetics of 38.0CaO-38.0Al₂O₃-10.5BaO-6.5MgO-6.0Y₂O₃-1.0(Na₂O+K₂O) (wt%) glass was studied by differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques. The results showed that DSC curves of calcium aluminate glass have a single glass transition temperature followed by one crystallization peak for the heating rates β = 5 K/min and two crystallization temperatures T _p1 and T _p2 for β ≥ 10 K/min. The activation energies of crystallization obtained from the Gao-Wang model of the first exothermal peak and the second exothermal peak of calcium aluminate glass are 340 and 662 kJ/mol, respectively. The Avrami exponents of the both crystallization peaks are approximately 2, indicating the twodimensional crystalline growth during its transformation from amorphous to crystalline. Ca₁₂Al₁₄O₃₃, Ca₃Al₂O₆ and unknown crystalline phases firstly appear when calcium aluminate glass is heat-treated. With the extending of heat-treatment duration, BaAl₂O₄ phase comes out.     

Thermal stability and glass-forming ability of Y-Ce-Co-Al bulk metallic glasses

The thermal stability and glass-forming ability of Y_56-xCe_xCo₂₀Al₂₄ (x=15, 20, 25, 28, 38, 41, 44) bulk metallic glasses with a diameter of 5 mm were investigated by differential scanning calorimetry and X-ray diffraction. The results show that the thermal stability of the alloys decreases with the addition of Ce. It has the best glass-forming ability when x=25, whose calculated values can reach about 30 mm in diameter. The effect of Ce element could be explained on the view of Miedema's theory and electronegativity difference of amorphous alloys.     

Spontaneous Magnetic Transitions and Corresponding Magnetoelastic Properties of Intermetallic Compounds <Emphasis Type="Italic">R</Emphasis>Mn<Subscript>2</Subscript>Ge<Subscript>2</Subscript> (<Emphasis Type="Italic">R</Emphasis>=Gd,Tb and Dy)

The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn₂Ge₂ (R=Gd, Tb and Dy) were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature T_N (T_N=368, 423 and 443 K for GdMn₂Ge₂, TbMn₂Ge₂ and DyMn₂Ge₂, respectively) and the first-order antiferromagnetic - ferrimagnetic transition at temperature T_t (T_t=96, 80 and 40 K for GdMn₂Ge₂, TbMn₂Ge₂ and DyMn₂Ge₂, respectively) as the temperature decreases. The temperature dependence of the lattice constant a(T) displays a negative magnetoelastic anomaly at the second-order transition point T_N and, at the first-order transition T_t, a increases abruptly for GdMn₂Ge₂ and TbMn₂Ge₂, Δa/a about 10^-3. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at T_t is explained by the Kittel mode of exchange inversion.     

Effects of rare earth oxides on viscosity,thermal expansion,and structure of alkali-free boro-aluminosilicate glass

Effects of rare earth oxides(Y_2O_3,La_2O_3,and Er_2O_3) on the viscosity,thermal expansion,and structure of alkali-free boro-aluminosilicate glasses were investigated by the rotating crucible viscometer,dilatometry and FT-IR absorption spectra.The results showed that the melting temperature of alkali-free boroaluminosilicate glasses decreased from 1 697.55 to 1 662.59,1 674.37 and 1 640.87 ℃ with the introduction of 1 mol%La_2O_3,Y_2O_3 and Er_2O_3,respectively.However,the glass transition temperature T_g,dilatometric softening temperature T_d and coefficient of thermal expansion of alkali-free boro-aluminosilicate glasses increased when adding the rare-earth oxides.At high temperatures,incorporating rare earth oxides into glass resulted in the peak at about 1 085 cm~(-1) towards lower wavenumber and the absorption band in the region of850-1 260 cm~(-1) broader,which indicated that rare earths acted as network modifiers and increased the numbers of non-bridging oxygen in the glass melts.However,the rare earths had an opposite effect and accumulated the glass structure at low temperatures near T_g.     

Microstructure and microwave dielectric properties of lead borosilicate glass ceramics with Al2O3

The effects of Al₂O₃ addition on both the sintering behavior and microwave dielectric properties of PbO-B₂O₃-SiO₂ glass ceramics were investigated by Fourier transform infrared spectroscope (FTIR), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase of Al₂O₃ content the bands assigned to [SiO₄] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature T _g and softening temperature T _f of PbO-B₂O₃-SiO₂ glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al₂O₃ content, but the dielectric loss is worsened. By contrast, the 3% (mass fraction) Al₂O₃-doped glass ceramics sintered at 725 °C have better properties of density ρ=2.72 g/cm³, dielectric constant ɛ _r =6.78, dielectric loss tan δ=2.6×10⁻³ (measured at 9.8 GHz), which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.     

Preparation and characterization of low-melting glasses used as binder for protective coating of steel slab

The low-melting phosphate glass was prepared for production of glass binders for protective coating of steel slab. Effects of different O/P ratios on glass structures and properties were analyzed. Differential thermal analysis (DTA) and infrared spectroscopy (IR) techniques were applied for low-melting glass binder. It was found that the glass transition temperature(T _g) was about 300 °C and softening temperature(T _f) was about 480 °C. The choice of O/P ratio was very important to the glass transition and softening temperatures. When more P=O bonds existed in the glass networks, P-O-P bond angle was deformed with decreasing of the ratio of O/P. The coatings could adhere to the substrates instantaneously at 800 °C when the content of binder exceeded 3wt%. The optimal content of glass binder was 5wt%.     

Properties of Aluminosilicate Glasses Prepared by Red Mud with Various [Al<Subscript>2</Subscript>O<Subscript>3</Subscript>]/[CaO] Mass Ratios

By introducing other oxide materials (SiO₂, Al₂O₃, CaO) into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe₂O₃-5.7CaO-18.2Al₂O₃-50SiO₂-5.9Na₂O-3TiO₂ system glasses, [Al₂O₃]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al₂O₃ when [Al₂O₃]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al₂O₃]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite (γ-Fe₂O₃) will increase which provides the possibility for production of black glass-ceramic further.     

A cluster line approach to finding new Fe-B-Y-Nb-Zr bulk metallic glasses

The glass forming ability of the [(Fe_12/13Y_1/13)_100-xB_x]₉₆Nb₂Zr₂ (x=9–26) system was investigated using a series of cluster lines. Three types of clusters, an icosahedron (Fe₁₂Y), a capped Archimedes anti-prism (Fe₈B₃) and a capped trigonal prism (Fe₉B), as well as a binary eutectic (Fe₈₃B₁₇) were considered. Bulk glassy alloy rods of 3 mm in diameter were synthesized using a copper mold suction-casting method. The glass transition temperature was observed for all samples in the boron range of 15.9at%-25.7at%, with the alloy at 15.9at% of boron having the best thermal properties. The ferrous-based bulk metallic glasses (BMG) obtained have high reduced glass transition temperatures with the maximum reaching 0.63 and large supercooled liquid regions with the maximum reaching 111 K. Magnetic testing revealed a large value of coercive force and remanent magnetization, being 11 kA/m and 0.1 T, respectively.     

Multiple steady states in rapid solidification and the glass transition

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Effect of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> on structure and properties of calcium aluminate glasses

The effect of Ga₂O₃ on the structure and properties of calcium aluminate glasses fabricated by vacuum melting process was investigated by Raman spectrum, differential scanning calorimeter (DSC), and infrared spectrum methods. The results show that calcium aluminate glass network only consists of [AlO₄] tetrahedral units. With the gradual addition of Ga₂O₃, the quantity of [GaO₄] tetrahedral units increases. Substitution of Ga₂O₃ for Al₂O₃ results in a decrease in T _g T _x, and T _p, and an increase in the thermal stable index ΔT. Similarly, the absorption band around 3.0 μm obviously reduces and the transparency in 4.0-6.0 μm rapidly increases with increasing Ga₂O₃ content. However, the chemical stability of calcium aluminate glasses decreases if Ga₂O₃ is introduced due to the increasing of [GaO₄] units in the glass network.     

Thermodynamic assessment of solar-aided carbon dioxide conversion into fuels via Tin oxides

The conversion of CO_2 to liquid hydrocarbon fuels using solar energy is gaining attraction as a means to deal with climate change and energy depletion,and assessment for related thermochemical cycles has attracted great interests in recent years.Here,we perform the thermodynamical analysis on solar-aided CO_2 conversion reactions based on Tin oxides.The equilibrium compositions,production purity and CO_2 conversion are obtained.Also,the variations of conversion efficiency with respect to temperature,normal beam solar insolation,mean flux concentration ratio,initial CO_2 to SnO ratio and heat recuperation percentage are revealed.Our results indicate the initial CO_2 to SnO ratio,χ_(ini),has an evident impact on conversion efficiency andχ_(ini)=0.5,T=700 K andχ_(ini)=1,T=950 K,are favourable for solid C and gaseous CO production,respectively.The calculated maximum cycle efficiency with direct work production is 0.340 at T=950 K andχ_(ini)=1,demonstrating the high conversion efficiency of the proposed system.     

Co2O3-doping effect on the formation of 3CaO·3Al2O3·CaSO4

The Co₂O₃-doping effect on the formation of 3CaO·3Al₂O₃·CaSO₄ from CaCO₃-Al₂O₃-CaSO₄·2H₂O mixtures was investigated by means of SO₂ emission behavior, chemical analysis, X-ray diffraction, differential thermal analysis and scanning electron microscopy. The experimental results show that Co₂O₃ addition increases the reactivity of the CaCO₃-Al₂O₃-CaSO₄·2H₂O system significantly, by reducing SO₂ emissions in combustion and f-CaO contents in the clinkers, promoting the nucleation and growth of 3CaO· 3Al₂O₃·CaSO₄, and intensifying the formation of 3CaO·3Al₂O₃·CaSO₄. Moreover, Co₂O₃ addition lowers the formation temperature of 3CaO·3Al₂O3·CaSO₄ by 18 °C, and similarly increases the thermal stability of it at a wider temperature range.     

Direct synthesis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-modified Li(Ni<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>)O<Subscript>2</Subscript> cathode materials for lithium ion batteries

To improve the cyclic stability at high temperature and thermal stability, the spherical Al₂O₃-modified Li(Ni_0.5Co_0.2Mn_0.3)O₂ was synthesized by a modified co-precipitation method, and the physical and electrochemical properties were studied. The TEM images showed that Li(Ni_0.5Co_0.2Mn_0.3)O₂ was modified successfully with nano-Al₂O₃. The discharge capacity retention of Al₂O₃-modified Li(Ni_0.5Co_0.2Mn_0.3)O₂ maintained about 99% after 200 cycles at high temperature (55 °C), while that of the bare one was only 86%. Also, unlike bare Li(Ni_0.5Co_0.2Mn_0.3)O₂, the Al₂O₃-modified material cathode exhibited good thermal stability.     

Structural Properties and Energy Analysis of ZrxCu90-xAl10Ternary Metallic Glasses

Classical molecular dynamics(MD) were conducted to study the structure and energy distribution of Zr_xCu_90-xAl₁₀(x=20, 30, 40, 50, 60, 70) ternary alloys. When the Zr composition is 30%, the glass transition temperature reaches the maximum value and the Zr₃₀Cu₆₀Al₁₀ owns high glass forming ability(GFA). Analysis of the short-range structure shows that there are more low-energy Zr-centered polyhedron with high coordination number(CN...     

Tensile and compression properties of Zr-based bulk amorphous alloy at different temperatures

Since the discovery of the Au-Si metallic amorphous alloy ribbon in 1960 by Duwez and co-workers[1] by rapid quenching, rapid developments have been obtained on the preparation of the amorphous alloy with the rapid quenching technique. However, from 1960 to 1989, the amorphous alloy could be only produced into forms of ribbon, flake, wire and powder due to the limitation of the cooling rate (>105 K/s). In the late 1980s, the Inoue group at Tohoku University in Sendai, Japan, investigated th…     

YVO_4基纳米光催化剂制备及其光催化脱汞性能评价

采用水热反应法制备YVO4光催化剂,并通过掺杂C和Sm3+对其进行改性,通过X射线衍射仪(XRD)、扫描电镜(SEM)和比表面积(BET)对其形态、结构、组成和性质进行表征.在紫外光条件下,对YVO4及其改性后的催化剂进行脱除气态元素汞(Hg0)评价,YVO4,YVO4掺碳,YVO4掺Sm3+,YVO4掺Sm3+掺碳催化剂脱汞效率分别为10.5%,9.1%,5.2%,19.6%.其中YVO4∶Sm3+/C效果最好,但也只有19.6%.这可能是紫外光激发了YVO4导带的电子,且电子成功地跃迁到了价带,但由于此反应产生的光生载流子能量较弱,不足以激发自由·OH,只能靠光生载流子直接氧化汞,导致样品不能高效光催化氧化汞.