Crystal growth of diamond from a phosphorus solvent under high pressure–high temperature conditions

Crystal growth of diamond in a phosphorus solvent was studied on a seed of natural octahedral diamond at high pressures and high temperatures of 6.2–6.5 GPa and 1600–1700°C for 5–23 h. Although new growth layers of diamond up to 30 μm in thickness were observed on {111} faces of a seed, growth almost stopped within the first 5 h caused by the following occurrence of spontaneous nucleation. The growth layer was usually gray or bluish gray in color and the surface became undulated with dense triangular growth hillocks and growth steps of 〈110〉 directions. On the grown surface were observed two other characteristic features: one is a circular depression with various size particularly observed in the beginning of the growth and the other is a peculiar growth step with the direction indexed as 〈321〉.     

Diffusion coefficient of carbon in Fe–Ni alloy during synthesis of diamond under high temperature and high pressure

Synthetic diamond particles were prepared under high temperature and high pressure using arrayed seeds. A dense Fe–Ni alloy shell covered each diamond seed during synthesis; the growth of diamond particles was controlled by the diffusion of carbon through the metallic shell. The diffusion coefficient of carbon through Fe–Ni melt at 1600 K and 5.5 GPa is about 5×10^?6 cm²/s, with an activation energy for diffusion of 336 kJ/mol.     

Strain-induced strengthening in superconducting β-Mo2C through high pressure and high temperature

High-strain-induced microstructural refinement and dislocations are critical for the strengthening of metallic materials; however, this is difficult to achieve in ceramic materials due to their unique bonding characteristics and electronic structure. Here, a series of β-Mo₂C bulk ceramics are consolidated by the high pressure and high temperature (HPHT) strategy. Our results demonstrate that high strain-induced grain plastic deformation at high pressure produces a lamellar sub-grain structure with high-density dislocations, and that the dislocations at the lath-like grain boundaries eventually evolve into low-angle grain boundaries. The mechanical properties, superconducting behavior, and onset of oxidation of the specimens are investigated. It is found that superconductivity and hardness arise from the high density of states at the Fermi level, while the high intrinsic hardness is attributed to the strong hybridization between Mo-4d orbitals and C-2p orbitals. Furthermore, strain-induced defect structure (dislocations and low-angle grain boundaries) mainly mainly enhances the intrinsic structure of β-Mo₂C.     

Progress in the catalyst for ethylene/α-olefin copolymerization at high temperature

Ethylene/α-olefin copolymers are one of the most widely-used polyolefin materials. With the continuous improvement of polyolefin catalysts, high-performance polyolefin materials were synthesized by adjusting the chain microstructure, changing the comonomer type and comonomer insertion amount, among which the ethylene/α-olefin random copolymer elastomer (POE) and olefin block copolymer elastomer (OBC) are the most famous and well accepted by the market. The excellent properties of POE and OBC first depend on their polymer chain microstructure. The chain microstructure of polyolefins is fundamentally determined by the catalysts, polymerization conditions, comonomer feed policies, and reaction engineering. High-performance ethylene/α-olefin copolymer elastomers are currently prepared by high-temperature solution polymerization process, which needs to be carried out at a temperature above the melting point of the polymer and is beneficial to speed up the polymerization reaction rate and control the polyolefin chain microstructure. However, the high-temperature solution polymerization process launched more stringent requirements for the olefin coordination polymerization catalyst. Systematic reports on catalysts for high-temperature solution copolymerization of ethylene and α-olefins are lacking. In this review, we screened some catalysts suitable for the controllable copolymerization and high-temperature solution copolymerization of ethylene/α-olefin based on the catalyst's heat resistance, copolymerization activity, comonomer insertion ability, molecular weight, and distribution of the copolymer, including traditional Z–N catalysts, metallocene catalysts, and post-metallocene catalysts. And the future development of catalysts for high-temperature solution copolymerization of olefins, catalysts for precise control of polyolefin chain microstructures, and catalysts for olefin copolymerization with polar monomers at high temperature are envisaged.     

Microstructure and luminescence properties of the high pressure high temperature sintered AlN–TiN ceramics

Composite ceramics of titanium nitride grains incorporated in an aluminium nitride matrix have been synthesized by high pressure high temperature treatment of a mechanical mixture of AlN–TiN (3 mol % TiN) powders. The microstructure of the samples analysed by means of electron beam microanalysis and Raman spectroscopy shows that the formation of cubic AlN in the composite begins near titanium nitride grains. The areas of mixed chemical composition, which can be assigned to the formation of the solid solutions Al_1?xTi_xN, have been observed at the phase interfaces. The luminescence properties of AlN–TiN ceramics have been considered focusing on the choice of high pressure and high temperature treatment conditions. Three main components at 2.0 eV, 2.4 eV and 3.1 eV are revealed in the cathodoluminescence spectra analysed quantitatively. The observed emission originates from the radiative transitions with participation of valence band states, oxygen-vacancy centres (V_Al–O_N), nitrogen vacancies V_N, and shallow donors which form a complex system of energy levels in the bandgap of the wurtzite-type AlN.     

In situ synthesis of PcBN composites from Sialon–TiN–TiB2 binder and cBN under high temperature and pressure

Polycrystalline cubic boron nitride (PcBN) composites were synthesized in situ with TiB₂, TiN, and Sialon as binders under ultrahigh temperature (1550°C) and high pressure (5.5 GPa). X-ray diffractometry, universal testing machine, field emission scanning electron microscopy, and transmission electron microscopy were used to study the effect of Sialon content (0%, 20%, 40%, 60%, and 80% by mass of binder) on the phase composition, microstructure, and mechanical properties of PcBN composites. The results show that the main phases in the system are lamellar TiN, needle-rodlike TiB₂, and irregular long-rodlike Sialon. Some TiB₂ grows along the (1 0 −1 0) face, and Sialon grows along the (0 0 0 1) face. The density and mechanical properties of the sintered product are significantly improved due to the formation of Sialon. When the content of Sialon is 60%, the binder is uniformly distributed, the cBN interface is well bonded, and the density is the highest. At this time, the strength reaches the maximum 34.57 GPa, the fracture toughness is 6.82 MPa m^1/2, and the flexural strength reaches the maximum 870.79 MPa. On the whole, cBN composites have excellent prospects for future applications in cutting inserts due to their excellent mechanical properties.     

Living and block polymerization of α-olefins using a Ni(II)-α-diimine catalyst containing OSiPh2Bu groups

A new siloxy-substituted α-diimine compound and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsiloxy-2,6-dimethylphenyl)imino]acenaphthene}dibromonickel (6), were successfully synthesized and the molecular structure of 6 characterized by X-ray crystallography. The precatalyst 6 activated by methylaluminoxane (MAO) or diethylaluminum chloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (e.g. 2.2×10⁷ and 1.8×10⁷ g polymer (mol Ni.h.bar)⁻¹, respectively) and led to a branched polyethylene (ca. 35-55 branches/1000 C). The catalyst system 6/methylaluminoxane (MAO) catalyzes, at −11 °C, living polymerization of propylene, to a polypropylene showing a syndiotactic-rich microstructure (P_r=0.74). 1-Hexene was also successfully polymerized via a living process, both at −11 and +16 °C. The ¹³C NMR spectra of the poly(1-hexene)s obtained at room temperature show a microstructure almost exclusively composed by n-butyl and methyl branches, the latter being present in a much higher number. Diblock polypropylene-block-poly(1-hexene) and triblock poly(1-hexene)-block-poly(propylene-ran-1-hexene)-block-poly(1-hexene) copolymers have also been synthesized and characterized by GPC/SEC, DSC and NMR.     

On‐line addition of catalyst in high‐temperature reactors: high selectivity to olefins

By adding solutions containing catalyst salts to hot monolith catalysts during partial oxidation processes, the salt decomposes instantly and is deposited selectively near the front face. We have used this technique to deposit extremely small amounts of Pt on α-Al₂O₃ monoliths during ethane oxidation to olefins. We find that on this catalyst with H₂ addition, the selectivity to ethylene rises from ∼ to over 80% at an ethane conversion of ∼60% and at complete O₂ conversion. We also examine the addition of promoters including Sn, which gives improved performance compared to the Pt catalyst alone. This appears to be a general effect that could be useful in preparing catalysts with different loadings and distributions in high‐temperature processes. It can also be used for rapid and accurate diagnosis of catalysts and additives and to modify catalysts on‐line in situations where deactivation or catalyst loss occurs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acetone conversion to isobutene in high selectivity using zeolite β catalyst

The catalytic activity of the proton forms of zeolite and ZSM-5 are compared for the conversion of acetone. Zeolite demonstrates markedly enhanced selectivity to isobutene and selectivities of >80% can be achieved for conversions up to 65%. In contrast high selectivities to isobutene with ZSM-5 can be attained only at very low conversions (5%).     

The high temperature–high pressure sintering of diamond–Cu–Si–B composite

Such elements like Si, B and Cu have been utilized as components of binder aiming at acquiring high adhesion of the binder with the diamond grains, thermal stability of the composite and, relatively low fusion temperature of the binder. The present work has as its main objective the study of the interaction between components during sintering of polycrystalline diamonds with addition of binders under high pressures, in the range from 5.0 to 6.0 GPa and high temperatures, in the range from 1473 to 1773 K with process time between 15 and 30 s. After sintering the compacts were subjected to investigations concerning the influence of the mixture composition and of the process parameters on the density and wear resistance of the compacts. The method of factorial planning was utilized in order to obtain model which describes influence of sintering parameters on the properties of compacts.     

Synthesis and characterization of ethylene-propylene copolymer and polyethylene using α-diimine nickel catalysts

The dilute solution properties of polymeric quaternary ammonium betaines derived from poly(N-vinylimidazole) PNVI and containing either a methylene (B1), ethylene (B2), or propylene (B3) betaine group, respectively, were analyzed. A PNVI blank was also tested. The weight-average molecular weight $ {{\overline{M}}_{\text{w}}} $ , second virial coefficient A ₂, radius of gyration R _g, and hydrodynamic radius R _h of unfractionated probes were determined by MALLS (multiangle laser light scattering) and WALLS (wide-angle laser light scattering) measurements. All of these parameters varied with the type of solvent: pure water, an aqueous solution of 0.5?M NaCl, or an alcohol. These solution properties were useful for predicting the interactions of the polycarboxybetaines (acting as antimicrobial agents) with the components of the bacterial cell wall. Some of the polycarboxybetaines exhibited antimicrobial activities, as shown by the Kirby?CBauer diffusion method. A concentration of about 20?mg?mL^?1 for B1 or B3 in an aqueous solution of 0.5?M NaCl is sufficient to inhibit the growth of Escherichia coli.     

Polymerization of ethylene using a nickel α-diimine complex covalently supported on SiO2–MgCl2 bisupport

Bisupported catalyst for ethylene polymerization was prepared by mixing alcohol solution of MgCl₂ with pretreated SiO₂ in heptane, and further treating with bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino) acenaphtheneNiBr₂ (abbreviated as NiLBr₂) solution. The bisupported catalyst could be used to polymerize ethylene with high activity using alkylaluminum halides as inexpensive cocatalysts. According to high-temperature GPC, the weight-average molecular weights of the polymers obtained ranged from 2.15 × 10⁵ to 9.27 × 10⁵, with molecular weight distributions of 3.12–4.23. By adjusting the polymerization temperatures, the products with good morphologies could be obtained. The resultant polyethylenes were confirmed by ¹³C-NMR to contain significant amounts not only of methyl but also of ethyl, propyl, butyl, amyl, and longer side chains (longer than six carbons).     

Microstructure and thermoelectric properties of α-and γ-Al2O3 doped ZnO under high pressure

Using high pressure and high temperature (HPHT) technology to improve the thermoelectric properties of oxides is a feasible solution. To further understand the micro-physical mechanism improving the thermoelectric performance of ZnO in a higher pressure environment, the effects of α and γ lattice structure Al₂O₃ (α-Al₂O₃, γ-Al₂O₃) on doped ZnO were systematically studied. ZnO samples with different Al doping ratios (α-x, γ-x; x = 0.02, 0.04, 0.06, 0.08) were prepared by HPHT. Test results show that the high pressure and high temperature synthesis method effectively improves the solid solubility of α-Al₂O₃ and γ-Al₂O₃ in ZnO, among which γ-Al₂O₃ is more easily dissolved into the zinc oxide crystal lattice. Under the same doping ratio, the electronic conductivity of the sample synthesized with γ-Al₂O₃ is higher than that of the sample synthesized with α-Al₂O₃. In addition, the ZnAl₂O₄ phase precipitated out of the sample with increased Al doping. Although the ZnAl₂O₄ phase decreases the electrical properties of the sample, a small amount of ZnAl₂O₄ is uniformly dispersed in the ZnO sample, which can inhibit the growth of crystal grains, and assist grain refinement. The optimized high pressure sintering temperature was 1123 K, and the zT value of γ-0.04 was 0.17 at 973 K.     

Solubilities of CO2 in some glycol ethers under high pressure by experimental determination and correlation☆

The binary vapor–liquid equilibrium data of CO_2 in diethylene glycol(monomethyl,monoethyl,monobutyl,dimethyl,diethyl,dibutyl)ether were determined from 288.15 to 318.15 K at pressure up to 6 MPa based on the constant-volume method.It was found by contrast that the ether group in solvents can promote the CO_2 absorption,but the hydroxyl group will inhibit the CO_2 absorption.Furthermore,the solubilities of CO_2 showed an upward trend with the increasing molecular lengths of absorbents.The experimental data were also correlated with a modified Patel–Teja equation of state(PT EOS)combined with the traditional van der Waals one-fluid mixing rules and the results showed a satisfactory agreement between the model and the experimental data.     

Catalysis and high pressure – a useful liaison?!

The influence of high pressure (1–10 kbar) in solution on transition metal and in particular on palladium catalyzed reactions is examined both under the aspect of reactivity as well as selectivity. Although the field of research described here is rather young, some general conclusion on the scope and limitation of high pressure for catalysis can be drawn. This revised version was published online in June 2006 with corrections to the Cover Date.     

Polymerization temperature effects on the properties of l-lactide and ε-caprolactone copolymers

Summary The large difference in reactivity of L-lactide and -caprolactone in ring opening polymerization with stannous octoate, leads to the formation of copolymers with blocky structures. By varying the polymerization temperature, copolymers with different average sequence lengths and molecular weights can be synthesized. It is shown that the average monomer sequence length has a large effect on the thermal and mechanical properties of these copolymers.     

β-SiAlON–BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

Infiltration-mediated SHS of β-S_i6–z Al _z O _z N_8–z –BN composites was explored upon variation in applied nitrogen pressure, amount of combustible and low-melting components in green mixture, sample size, and BN content of resultant composites. Synthesized ceramic composites of different density and BN content were characterized by their strength parameters, tribological behavior, and thermal shock resistance.     

Polymerization of propylene catalyzed by α-diimine nickel complexes/methylaluminoxane: catalytic behavior and polymer properties

α-Diimine nickel dibromide complexes of dibromo[N,N’-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) (A) and dibromo[N,N’-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) (B) were synthesized under controlled conditions. The catalysts A, B and mixed of 1:1 weight ratio of them (C) were activated by methylaluminoxane and were used for propylene polymerization in a semi-batch reactor. In study of the catalytic systems behavior, activities, glass transition temperature (T _g) and viscosity average molecular weight (M _v) values related to the catalyst C were between those related to the catalysts A and B under same conditions. The highest and the lowest molecular weights of the obtained polymers were produced by the catalysts B and A which were about 80,000 and 70,000 (g/mol) under same conditions, respectively. The T _g of polypropylenes produced by the catalysts was about ?34 °C. The resulting polymers had similar behavior with ethylene-propylene copolymer which it could be due to formation of ethylene-type units in the polymer chain.     

Piezoelectric properties and temperature stabilities of Mn- and Cu-modified BiFeO3–BaTiO3 high temperature ceramics

The structures, microstructures, electrical properties and the thermal stability have been investigated for the MnO₂-doped (1 ? x)BF–xBT system and the MnO₂ and CuO-doped (1 ? x)BF–xBT system, where x ranges from 0.25 to 0.35. The XRD analysis shows that the two systems have a single perovskite phase, and the MnO₂ and CuO-doped (1 ? x)BF–xBT system has a morphotropic phase boundary (MPB) with the coexistence of rhombohedral and pseudo-cubic phases in the system about x = 0.325. The addition of small amount of CuO was quite effective to lower the sintering temperature. The diffusive phase transition characteristics were observed in the MnO₂-doped (1 ? x)BF–xBT system and a normal ferroelectric phase transition characteristics were observed in the MnO₂ and CuO doped (1 ? x)BF–xBT system. Compared with the MnO₂ doped (1 ? x)BF–xBT system, the ?_m, Curie temperature (T_c), depoling temperature (T_d), and piezoelectrical properties were improved evidently with the MnO₂ and CuO doping.