Mechanical properties of silicon carbide—in situ zirconium carbonitride composites

SiC–Zr₂CN composites were fabricated by conventional hot pressing from β-SiC and ZrN powders with 2 vol% equimolar Y₂O₃–Sc₂O₃ as a sintering additive. The effects of the ZrN addition on the room-temperature (RT) mechanical properties and high-temperature flexural strength of the SiC–Zr₂CN composites were investigated. The fracture toughness gradually increased from 4.2 ± 0.3 MPa·m^1/2 for monolithic SiC to 6.3 ± 0.2 MPa·m^1/2 for a SiC–20 vol% ZrN composite, whereas the RT flexural strength (546 ± 32 MPa for the monolithic SiC) reached its maximum of 644 ± 87 MPa for the SiC–10 vol% ZrN composite. The monolithic SiC had improved strength at 1200°C, whereas the SiC–Zr₂CN composites could not retain their RT strengths at 1200°C. The typical flexural strength values of the SiC–0, 10, and 20 vol% ZrN composites at 1200°C were 650 ± 53, 448 ± 31, and 386 ± 19 MPa, whereas their RT strength values were 546 ± 32, 644 ± 87, and 528 ± 117 MPa, respectively.     

Dimerization of 1‐butene via zirconium‐based Ziegler–Natta catalyst

A zirconium‐based Ziegler–Natta catalytic system has been tested in the dimerization of 1‐butene. It was found that the concentration of Et₂AlCl, Ph₃P and PhONa as well as the reaction temperature had great influences on the activity and selectivity of the catalyst. Under the optimum reaction conditions, the conversion of 1‐butene is 91.9%, and the selectivity of dimers is 76.7%. Basic ligands such as Ph₃P and PhONa can inhibit isomerization of 1‐butene to 2‐butene effectively. In addition, the metal hydride mechanism was also suggested and some indirect evidence was obtained in favor of this mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

A simple strategy to synthesize and characterization of zirconium modified PCs/γ–Al_2O_3

Crystalline phase is the key factor for catalyst activity. The zirconium modified PCs/γ-Al_2O_3 samples were prepared through a simple step incipient-wetness impregnation method. The raw materials and samples were characterized by thermogravimetric-differential analysis(TG-DTA), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), temperature-programmed desorption of ammonia and carbon dioxide(NH_3-and CO_2-TPD). The effects of calcination temperature and zirconium content on structure, chemical transformation,and acidity-basicity were investigated. Calcination temperature exhibited the major effect on the crystalline phase of samples. The new phase of Al0.1Zr_(0.9)O_(1.95) was exhibited which was above 650 ℃. In addition, zirconium content was influenced by the acidic and basic properties of the surface. The acidity and basicity of the Zr PCs/γ-Al_2O_3 sample increased with the increasing of zirconium content.     

Application of zirconium (IV) acetylacetonate to the copolymerization of glycolide with ɛ-caprolactone and lactide

Summary A study on the copolymerization of glycolide with lactide and glycolide with ɛ-caprolactone was performed in the presence of zirconium (IV) acetylacetonate at moderate temperatures (100° and 150°C). Zirconium acetylacetonate appeared to be an efficient initiator of copolymerization. The obtained polymers were characterized by high molecular weights. Considerable influence of transesterification on the polymer chain microstructure was found. Received: 13 October 1998/Revised version: 4 January 1999/Accepted: 4 January 1999     

Entrap-immobilization of invertase on composite gel fiber of cellulose acetate and zirconium alkoxide by sol–gel process

We prepared a composite gel fiber by the gel formation of cellulose acetate and zirconium tetra-n-butoxide. Gel fiber is stable in common solvents, phosphate solution, and electrolyte solution. Invertase was entrap-immobilized on the gel fiber. The immobilization was easily performed under the mild conditions. The apparent Michaelis constant (K_m) and maximum reaction velocity (V_max) were estimated from Eadie–Hofstee plot for immobilized invertase. The K_m of immobilized invertase was larger than that of native invertase, while the opposite tendency was observed for the V_max. The activity for the immobilized invertase became higher with increasing fiber diameter. It indicates that the hydrolysis of sucrose occurs in the neighborhood of the fiber surface. The thermal stability of the immobilized invertase was higher than those of its native counterpart. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2084–2088, 2001     

Dodecylbenzenesulfonic acid micelles assisted in situ preparation and enhanced thermoelectric performance of semiconducting polyaniline–zirconium oxide nanocomposites

Herein, we report in situ preparation of dodecylbenzenesulfonic acid (DBSA) micelles assisted polyaniline (Pani)/zirconium oxide (ZrO₂) nanocomposites (Pani/ZrO₂) by using K₂S₂O₈ as an oxidizing agent. Thus prepared nanocomposites were characterized by SEM, FTIR, XRD and UV–vis spectrophotometry. DBSA acted as dopant/surfactant, and the incorporation of ZrO₂ nanoparticles improved the stability, electrical and thermal properties of nanocomposites. From the results of UV–vis absorbance it was observed that Pani/ZrO₂ nanocomposite was more stabilized under UV light than Pani. DC electrical conductivity retention was studied by isothermal and cyclic ageing techniques and was observed to be better than Pani under ambient environmental conditions.     

Could readily silanized silica particles substitute silica coating and silanization in conditioning zirconium dioxide for resin adhesion?

This study investigated the effect of particle types with different morphology and surface properties on the wettability and adhesion of resin cement to zirconia. Zirconia specimens (5 × 5 × 1 mm³) were wet polished. Specimens were randomly assigned to one of the following protocols (N = 36, n = 9 per group): Group CON: Control, no surface conditioning; Group AL: Chairside air-abrasion with aluminium trioxide (50 μm Al₂O₃) + silane; Group SIL: Chairside air-abrasion with alumina particles coated with silica (SIL) (30 μm SiO2, SilJet) + air-drying + silane; Group 4: Chairside air-abrasion with readily silanized silica particles (SILP) (30 μm SiO_2, SilJet Plus). Adhesive resin was applied and resin cement (Variolink II, Ivoclar) was bonded using polyethylene moulds and photo-polymerized and aged (thermocycling, 6.000 cycles, 5–55 °C). Shear bond test was performed using Universal Testing Machine (1 mm/min). Pretest failures were considered 0 MPa. Contact angle measurements were performed (n = 2/group, sessile drop with water). Data (MPa) were analyzed (ANOVA, Tukey’s (α = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (0), values were calculated. Contact angle measurements were in descending order as follows: SIL (74°)^c < CON (60°)^c < AL (51°)^b < SILP (40°)^a. Bond strength (MPa) with SIL (17.2 ± 4)^a and SILP (17.3 ± 1.9)^a demonstrated no significant difference (p > 0.05), being higher than AL (8.4 ± 1.5)^b and CON (0)^c (p < 0.05). Failure types were exclusively adhesive in all groups. Weibull distribution presented the highest shape (0) for SILP (10.8). SILP presented better wettability than AL. SILP provided similar bond strength to SIL. Readily silanized silica particles may substitute for conventional silica coating and silanization.     

Tensile strength of a water-setting (hydration-hardening) zirconium dioxide based concrete in the 300–2300 k range

Conclusions During primary heating of the modified zirconium dioxide-based water-setting concrete (TsGBM), after attaining the desired temperature level, _tns increases up to approximately 1h if the temperature is below 2000 K (due to sintering of the finely dispersed barium aluminate separated during the decomposition of the crystallohydrates and due to the transformation of the concrete into a two-phase ceramic) and up to approximately 5 h if the temperature exceeds 2000 K (owing to sintering of the particles of the electromelted zirconium dioxide filler) and, thereafter, it remains constant:the level of the stationary strength of TsGBM decreases monotonically with increasing temperature from 3.5 N/mm² (under normal conditions) up to 0.25 N/mm² (at a temperature exceeding 2100 K) and corresponds to the strength of a granular and porous zirconium dioxide ceramic;up to 1200 K, the stationary strength of the concrete is determined by the quantity and the crystallohydrates of barium aluminate and their bond strength; up to 2100 K, it is determined by the degree of sintering and the intrinsic strength of barium aluminate; and above 2100 K, it owes to the formation and the strength of the zirconium dioxide-zirconium dioxide type bonds.Translated from Ogneupory, No. 5, pp. 4–8, May, 1991.The authors gratefully acknowledge the help rendered by T. A. Melekhin and T. A. Evdokimov in carrying out specimen preparation and Yu. I. Chubarov in the operation of the testing unit.     

One-step ethylene separation from ternary C2 hydrocarbon mixture with a robust zirconium metal–organic framework

One-step separation of high-purity ethylene(C₂H₄) from C₂ hydrocarbon mixture is critical but challenging because of the very similar molecular sizes and physical properties of C₂H₄,ethane(C₂H₆),and acetylene(C₂H₂).Herein,we report a robust zirconium metal–organic framework(MOF) Zr–TCA(H₃TCA=4,4’,4’’-tricarboxytriphenylamine) with suitable pore size(0.6 nm×0.7 nm) and pore environment fo...     

Study of the local environment around zirconium ions in polycrystalline α-alumina in relation with kinetics of grain growth and solute drag

The aim of the present work, made up of two parts, consists in studying the behaviour of the local environment of the doping zirconium, in the polycrystalline α-alumina related to the material microstructure. At first, the kinetics of grain growth has been studied, and local chemical analyses on thin foils at grain boundaries using the energy dispersive X-ray spectroscopy (EDXS) technique, were performed. In the second part, we shall consider the evolution of the local order around the doping element, related to the microstucture, by X-ray absorption spectroscopy (XAS) measurements. This study was performed on doped α-polycrystalline alumina (0.03 wt% ZrO₂) samples. According to the experimental results, we can show a great interaction between the zirconium and the grain boundaries of the alumina: during the grain growth, grain boundaries drag most of the doping element in solid solution. A transition in the environmental configuration around the doping in grain boundaries is observed, when the segregation ratio of the zirconium in grain boundaries reaches the value of about (4±2)×10³. In these conditions, a change in the local order is observed, around the segregated zirconium. This change varies from a statistical disorder to an ordered state, and can be described as an assembly of nanocrystalline metastable, tetragonal zirconia particles. This transition of the environmental configuration in grain boundaries is correlated to the increase of the grain growth velocity, according to the kinetics studies.     

Microstructure and properties of ablative C/ZrC–SiC composites prepared by reactive melt infiltration of zirconium and vapour silicon infiltration

C/ZrC-SiC composites with a density of 3.09 g/cm³ and a porosity of 4.8% were prepared by reactive melt infiltration and vapour silicon infiltration. The flexural strength and modulus were 235 MPa and 18.3 GPa, respectively, and the fracture toughness was 7.0 MPa m^1/2. The formation of SiC and ZrSi₂ during vapour silicon infiltration, at the residual cracks and pores in the C/ZrC, enhanced the interface strength and its mechanical properties. The high flexural strength (223 MPa, c. 95% of the original value) after oxidation at 1600 °C for 10 min indicated the excellent oxidation resistance of the composites after vapour silicon infiltration. The mass loss and linear recession rate of the composites were 0.0071 g/s and 0.0047 mm/s, respectively and a fine ablation morphology was obtained.     

Study of local structure around zirconium ions in grain boundaries of polycrystalline α-alumina by X-ray absorption spectroscopy and chemical analysis of thin foils

The chemical state and local structure around zirconium ions in doped α-polycrystalline alumina (300 wt ppm ZrO₂) was studied by X-ray absorption spectroscopy measurements at the zirconium K edge and by scanning transmission electron microscopy on thin foils. The zirconium segregation in alumina grain boundaries depends on alumina grain size: for a mean grain size of about ∼3·5 μm, the grain boundaries are saturated with zirconium. The zirconium grain boundaries to bulk concentration ratio, calculated from energy dispersive X-ray spectrometry measurement on thin foils is equal to ∼(5±3)×10³. The zirconium located in grain boundaries forms nanocrystalline tetragonal zirconia particles. This allotropic zirconia form is stabilised at room temperature because of the important contribution of the surface free energy. ©     

Bis(cyclopentadienyl)zirconium Dichloride: An Efficient Catalyst for Highly Selective Formation of β-Alkoxy Alcohols Via Ring Opening of 1,2-Epoxides with Alcohols

Bis(cyclopentadienyl)zirconium dichloride catalyzed ring-opening reactions of epoxides derived from styrene, cyclohexene, norbornene and stilbene, in the presence of primary, secondary, tertiary, cyclohexyl, allyl and propargyl alcohols, resulted in the formation of -alkoxy alcohols in good to excellent yields with high regio- and stereoselectivity.     

Polymerization of ethylene to branched poly(ethylene)s using <Emphasis Type="Italic">ansa</Emphasis>-η<Superscript>5</Superscript>-monofluorenyl cyclohexanolato zirconium(IV) complex/methylaluminoxane

ansa-η⁵-Monofluorenyl cyclohexanolato zirconium complex 3 was shown to be active for the polymerization of ethylene when activated with methylaluminoxane (MAO) at 5 bar. Up to a polymerization temperature of 40 °C, 3/MAO resulted in linear poly(ethylene)s with saturated chain ends. However, at polymerization temperatures of 60, 80, and 100 °C, a mixture of branched poly(ethylene)s, linear α-olefins and long chain alkanes was obtained. The poly(ethylene)s produced at 80 and 100 °C exhibited a bimodal molecular weight distribution indicative of multiple active species. Very high molecular weight (M _v > 5 × 10⁵) linear poly(ethylene)s were obtained using 3/MAO at 25 °C.     

Zn<Superscript>2+</Superscript>-exchange kinetics and antimicrobial properties of synthetic zirconium umbite (K<Subscript>2</Subscript>ZrSi<Subscript>3</Subscript>O<Subscript>9</Subscript>·H<Subscript>2</Subscript>O)

Zirconium umbite, K₂ZrSi₃O₉·H₂O, is a microporous framework ion exchanger whose potential as a carrier for Zn²⁺ ions in antimicrobial formulations has not yet been investigated. Accordingly, batch Zn²⁺-exchange kinetics of synthetic zirconium umbite (K-UM) and the subsequent antimicrobial action of the zinc-bearing phase (Zn-UM) against Staphylococcus aureus and Escherichia coli are reported. Nonstoicheiometric over-exchange of Zn²⁺ for K⁺ was observed and attributed to hydrolysis and complexation reactions of Zn²⁺ within the umbite framework. The exchange process, which was described by a simple pseudo-first-order model (k ₁ = 2.69 × 10⁻⁴ min⁻¹, R ² = 0.992), did not achieve equilibrium within 120 h at 25 °C, by which time the uptake of zinc was found to be 1.04 mmol g⁻¹. The minimal bactericidal concentrations of Zn-UM for E. coli and S. aureus were found to be >10 g cm³ and <1.0 g cm³, respectively.