Qiuyun Wang

Cluster formulae for alloy phases

Composition formulae for alloy phases are developed using first-neighbour coordination polyhedra plus their connections. The resultant cluster formulae [cluster](glue atom) x , similar to molecular formulae for chemicals, contain key structural and composition information on the alloy phases. As examples, Al–Ni–Zr alloy phases are analysed with the objective of revealing cluster formula properties such as the principal cluster, the cluster phase and the definition of complex alloy phases.

24 electron cluster formulas as the ‘molecular’ units of ideal metallic glasses

It is known that ideal metallic glasses fully complying with the Hume-Rothery stabilization mechanism can be expressed by a universal cluster formula of the form [cluster](glue atom)1 or 3. In the present work, it is shown, after a re-examination of the cluster-resonance model, that the number of electrons per unit cluster formula, e/u, is universally 24. The cluster formulas are then the atomic as well as the electronic structural units, mimicking the ‘molecular’ formulas for chemical substances. The origin of different electron number per atom ratios e/a is related to the total number of atoms Z in unit cluster formula, e/a = 24/Z. The 24 electron formulas are well confirmed in typical binary and ternary bulk metallic glasses.

Synthesis of Bottlebrush Polystyrenes with Uniform, Alternating, and Gradient Distributions of Brushes Via Living Anionic Polymerization and Hydrosilylation

By combining living anionic polymerization and hydrosilylation, densely grafted bottlebrush polymers with controlled spacing of branch points are prepared. Dimethyl(4-vinylphenyl)silane and dimethyl(4-(1-phenylvinyl)phenyl)silane are anionically (co)polymerized to synthesize uniform, alternating, and gradient in-chain silyl-hydride (Si-H) functionalized backbones. The spacing of branch points is controlled effectively by regulating the distribution of Si-H groups along the backbones. Three backbones with a similar number of Si-H groups but variable distributions are used to synthesize corresponding bottlebrush polymers via hydrosilylation between the backbones and chain-end vinyl functionalized polystyrene. The uniformly grafted bottlebrush exhibits the highest hydrodynamic radius (Rh ) of 5.6 nm and the lowest Tg of 79 °C which may be attributed to its compact grafted structure. This methodology exhibits high efficiency and convenience for the construction of bottlebrushes with controlled distribution of brushes.

Synthesis of sequence-determined bottlebrush polymers based on sequence determination in living anionic copolymerization of styrene and dimethyl(4-(1-phenylvinyl)phenyl)silane

Sequence-determined bottlebrush polymers in which the branches are distributed with determined sequential arrangements are precisely, efficiently and conveniently synthesized. Living anionic polymerization and hydrosilylation were used to synthesize the backbones, branches and bottlebrushes. Sequence-determined backbones, which include perfectly alternating and gradient structures, were obtained by controlling the monomer feed ratios during the living anionic copolymerization of styrene and dimethyl(4-(1-phenylvinyl)phenyl)silane (DPE-SiH). In addition, the sequential arrangements of branch points in gradient copolymers, i.e., SiH groups, were precisely determined using the timing-sample method under high-vacuum conditions. Then, the branches were conveniently grafted onto the backbones with a corresponding distribution of SiH groups via efficient hydrosilylation. The overall efficiency of the coupling reaction was greater than 91%. The solution properties of the synthesized bottlebrush polymers were investigated, and the results indicated that the sequence of branches may exert an influence on the branching factor (g′) and the hydrodynamic radius (Rh).

Monomer sequence determination in the living anionic copolymerization of styrene and asymmetric bi-functionalized 1,1-diphenylethylene derivatives

Due to their distinct steric hindrance, 1,1-diphenylethylene (DPE) and its derivatives cannot homopolymerize via living anionic polymerization and thus are advantageous for investigating the sequence structure of the corresponding copolymers. The substitution of functional groups on the benzene rings of DPE derivatives can be used to adjust the reactivity ratios for the copolymerization of styrene and the DPE derivatives. Two types of DPE derivatives, DPE-SiH/OMe and DPE-SiH/NMe2, were designed and prepared in this work. An electron withdrawing substituent and an electron donating substituent are simultaneously present at the para positions of the two phenyl rings of DPE. These derivatives were copolymerized with styrene under Schlenk conditions via living anionic polymerization. The statistical in-chain functionalized copolymers were prepared, and the corresponding average reactivity ratios were 1.42 for DPE-SiH/OMe and 1.79 for DPE-SiH/NMe2. Additionally, a time sampling strategy under high vacuum conditions was used during the copolymerization of the two systems (styrene with DPE-SiH/OMe and styrene with DPE-SiH/NMe2) with [MS]0/[MD]0 = 4. The propagation rate constants and statistical sequence structures were analyzed by 1H NMR spectroscopy, SEC and MALDI-TOF MS, and the average sequential arrangements of the corresponding copolymers were determined. The critical conditions for preparing copolymers with alternating structures were determined and implemented, and the monomer unit ratios were both nearly 1:1.

Formation and soft magnetic properties of Co (-Fe)-Si-B-Nb bulk metallic glasses in relation to clusters

Bulk metallic glass formations in Co-based alloy systems are investigated with the guidance of our cluster line approach and minor-alloying principle. Basic ternary alloy compositions in Co-B-Si system are first determined by cluster lines defined by linking special binary clusters to third elements. Then these basic ternary alloys are further minor-alloyed with 4-5 at. % Nb and bulk metallic glasses of 3 mm in diameter are formed in (Co8B3-Si)-Nb, Co8B3 being dense-packed cluster. The bulk metallic glasses are expressed approximately with a unified simple composition formula: (Co8B3)1(Si,Nb)1. Finally a quantity of Fe substitution for Co further improves the glass-forming abilities and these Co-Fe-based quinary bulk metallic glasses have good soft magnetic properties with high saturation magnetization Is, up to 0.98T, and low coercive force Hc, below 6 A/m.

Preparation of functionalized precursor of SiC ceramic via hydrosilylation polymerization of 1,1-diphenylethylene derivatives

Polycarbosilanes were prepared via hydrosilylation polymerization of functional 1,1-diphenylethylene (DPE) derivatives (dimethyl-[4-(1-phenylvinyl)phenyl]silane (DPE-SiH) and 1-(4-methyloxyphenyl)-1′-(4-dimethylsilanephenyl) ethylene (DPE-SiH/OMe)). Both DPE-SiH and DPE-SiH/OMe were synthesized as monomers and then utilized to prepare corresponding oligomers with Si–C bonds and phenyl rings in their backbones. The DPs were calculated to be 5.9 and 6.3, respectively, while the β-additions were 88.8 and 88.0%. The Td5 of DPE-SiH and DPE-SiH/OMe oligomers were 270 and 345 °C, respectively, and their weight residue was approximately 20% even heated at a temperature near 1200 °C in nitrogen. The compact tiny pores distributed on cross section of the resultant SiC ceramics were observed with the scanning electron microscopy. The thermal analyses verified that the oligomers of DPE-SiH and DPE-SiH/OMe possessed favorable thermal stabilities and could be taken as the proper PCSs precursor for preparation of SiC ceramic materials.

A cluster line approach for composition rules of quasicrystals and bulk metallic glasses

This paper analyzes the structure and composition characteristics of ternary quasicrystals and bulk metalic glasses from the viewpoint of atomic clusters. It is pointed out that quasicrystals and bulk metallic glasses satisfy a cluster line rule. The cluster line refers to a straight composition line linking a specific cluster to the third element in a ternary alloy phase diagram. A ternary quasicrystal or bulk metallic glass composition is located at the intersection point of two cluster lines. Ternary quasicrystal and bulk metallic glass compositions can be the expressed with a cluster-plus-glue-atom model which can predict new ternary bulk metallic glasses.

Cluster-based bulk metallic glass formation in Fe-Si-B-Nb alloy systems

Bulk metallic glass formations have been explored in Fe-B-Si-Nb alloy system using the so-called atomic cluster line approach in combination with minor alloying guideline. The atomic cluster line refers to a straight line linking binary cluster to the third element in a ternary system. The basic ternary compositions in Fe-B-Si system are determined by the inetersection points of two cluster lines, namely Fe-B cluster to Si and Fe-Si cluster to B, and then further alloyed with 3-5 at. % Nb for enhancing glass forming abilities. BMG rods with a diameter of 3 mm are formed under the case of minor Nb alloying the basic intersecting compositions of Fe8B3-Si with Fe12Si-B and Fe8B2-Si with Fe9Si-B. The BMGs also exhibit high Vickers hardness (Hv) of 1130-1164 and high Youngs modulous (E) of 170-180 GPa

Formation of Cu-Zr-M ternary bulk metallic glasses based on atomic clusters

Ternary Cu-Zr-M (M= Al, Ti and Ag) bulk metallic glasses are investigated using a cluster line approach. New bulk metallic glass rods with compositions lying along the cluster line Cu5Zr6-M were fabricated by copper mould suction, where binary cluster Cu5Zr6 is an Archimedean octahedral antiprism, M being about 4~13.2 at.% for Al, 8.3 at.% for Ti and 9 at.% for Ag. The relevant mechanism was discussed in the light of the cluster-plus-glue-atom model.