Volume 32, Issue 1

A modified sol-gel synthesis route has been used to prepare the fine homogeneous powder of Sr 2 CuO 3 ceramic using strontium nitrate, copper nitrate, diethylene glycol monobutyl ether and citric acid. XRD patterns showed that the temperature of forming Sr 2 CuO 3 is about 900°C and single phase of Sr 2 CuO 3 with high purity obtains at 950°C. Influence of concentration of citric acid on the structure of prepared materials was investigated by SEM images.

By means of creep curves measurement and microstructure observation, an investigation has been made into the influence of the element Re on creep behaviors of single crystal nickel-base superalloy at intermediate temperature. Results show that, after fully heat treated, microstructure of the alloy consists of the cubic γ ′ phase embedded coherent in the γ matrix. Comparing with Re-free superalloy, 4.5% Re alloy displays a better creep resistance and longer creep rupture life in the ranges of the applied stresses and temperatures. After crept for 425 h up to fracture at 760 °C/800 MPa, the γ ′ phase in the alloy keeps still the regular cubical configuration, which is attributed to the effect of the element Re decreasing the diffusing rate of other elements during creep. The deformation features of the alloy during creep are that the dislocations move in the γ matrix channels and shear into the γ ′ phase, the 〈110〉 super-dislocation shearing into the γ ′ phase may be decomposed to form the configuration of (1/3)〈112〉 super-Shockleys partials plus the stacking fault, which may hinder dislocations movement and restrain the cross-slipping of dislocations. This is thought to be the main reason of the alloy having a better creep resistance. In the latter stage of creep, the crack is firstly initiated in the interface of γ ′/ γ phases and propagated along the interface vertical to the stress axis up to the occurrence of the creep fracture, which is thought to be the fracture mechanism of the alloy during creep.

In the steelmaking process, various solid oxides such as lime and dolomite are used as flux. It is well known that the dissolution rate of these oxides into the molten slag has an important role to increase the reaction rate between the steel and slag. Although CaO effectively removes phosphorus from iron, undissolved CaO remains in the slag. The dissolution rate of solid oxides has been previously measured using a sintered rod that was immersed and rotated in the molten slag. However, because this sintered rod was dense, it was difficult to estimate the dissolution rate of the solid oxides used in the actual operations. In this study, the dissolution rate of various limes into the slag was evaluated by measuring the compositional changes in the slag after the addition of these oxides into the molten slag. In an experiment, slag was melted in an iron crucible and Ar gas was injected from the bottom of the crucible. An iron rod was used for stirring. Various limes were added to the molten slag and the slag was sampled at each interval. The slag samples were analyzed using XRF after 1:10-dilution with glass beads followed by fine grinding. A sintered rod of lime made from reagent powder of CaO was used as a dense oxide and the metallurgical lime, used in industrial operation, was used as a porous oxide after preheating at 1273 K. The dissolution rate of metallurgical lime was also measured. Three types of slag were used to evaluate the effect of reaction layer between the lime and molten slag on the dissolution rate of CaO–FeO–SiO 2 , B 2 O 3 -CaO-FeO, and Al 2 O 3 -CaO-FeO slag. The CaO–FeO–SiO 2 slag caused the formation of a dense reaction layer of 2CaO–SiO 2 around the lime. It was found that the influence of porosity of lime on the dissolution rate was not so strong when the reaction layer formed. On the other hand, when the reaction layer did not form, the dissolution rate of the porous lime was higher than that of the dense lime because of the penetration effect of slag into the lime. The dissolution rate of metallurgical lime was fast compared with dense and porous limes due to the gas formation internally.

This study gives the Raman frequencies calculated as functions of temperature and pressure for the lattice modes in the solid β phase and close to the melting line (β-fluid transition). The experimental volume data from the literature is used to calculate the Raman frequencies for the molecular nitrogen system. Some observed Raman frequencies are also used as the initial data to perform our calculations given here. It is shown that our values predict the observed Raman frequencies of the lattice modes studied in the β phase and also on the solid β-fluid melting curve. This initiates the applicability of the method given here to calculate the frequency from the volume data in various phases of molecular solids such as solid nitrogen.

The article presents a new technology of thermal barrier coating deposition called Plasma Spray – Physical Vapour Deposition (PS-PVD). The key feature of the process is the option of evaporating ceramic powder, which enables the deposition of a columnar ceramic coating. The essential properties of the PS-PVD process have been outlined, as well as recent literature references. In addition, the influence of a set of process conditions on the properties of the deposited coatings has been described. The new plasma-spraying PS-PVD method is a promising technology for the deposition of modern thermal barrier coatings on aircraft engine turbine blades.

Vacuum glazing is a new building material with excellent energy conservation and sound insulation properties. Usually, the edge sealing layer between two sheets of glass substrates is prepared by spraying the seal glass paste and then sintering. In the present research, a more effective preparation method is reported. The edge sealing layer is prepared with a glass paste by screen printing and then sintering. The glass paste for the preparation of edge sealing layer of vacuum glazing was composed of low melting glass powder, ZrW 2 O 8 powder with negative coefficient of thermal expansion and ethyl cellulose terpineol solution. The rheological, thixotropy and the screen printing behaviors of the typical paste were characterized and discussed. To get a thicker as-printed layer, the paste has high solid content and little thixotropy. The typical paste behaves a typical rheological behavior of pseudoplastic fluid. The test result of the shear strength of the sealing layer indicated that the sealing is reliable.

BaCO 3 nanoparticles with different morphologies including needle-like, rod-like, bird's nest-like and flower-like have been successfully synthesized by the microwave homogeneous precipitation method using BaCl 2 ·2H 2 O, NaOH and (NH 2 ) 2 CO as raw materials with the help of different guide reagents, such as citric acid (CA), sodium triphosphate (STPP) and ethylene diamine tetraacetic acid (EDTA). Their phases and morphologies were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The characterization results show that different guide reagents have little effect on the phase structure and composition of products while they play significant roles in determining the morphology of products. All the synthesized BaCO 3 nanoparticles have typical orthorhombic structures that are well-crystallized.

Six new heat resistant and optically active poly(amide-imide)s 5a–f were prepared by the direct polycondensation reaction of N,N′-(4,4′-pyromellitoyl)-bis-L-phenyl acetic acid 3 with various different diamines 4a–f in a medium consisting of triphenyl phosphite, N-methyl-2-pyrrolidone, pyridine and calcium chloride. These polymers were obtained in high yields and had inherent viscosities between 0.35–0.50 dL/g. The resulting polymers were characterized by viscosity measurements, thermal gravimetric analysis (TGA and DTG), differential scanning calorimeter (DSC), solubility test, specific rotation, FT-IR and 1 H NMR spectroscopy. N,N′-(4,4′-pyromellitoyl)-bis-L-phenyl acetic acid 3 was prepared by an one-stop reaction of pyromellitic anhydride 1 with L-phenyl acetic acid 3 in acetic acid solution in quantitative yield.

In materials refining processes such as steelmaking process, bath-entry of agents such as CaCO 3 attracts career gas around their entire surface so that the dispersion in the bath can be inhibited. To shed light on the still vague instant phenomenon, this study employs a water model experiment and carries out the visualization. Therefore, this study visually demonstrates the growth and rupture of air cavity due to water entry of horizontal superhydrophobic circular cylinders with the aid of a high-speed camera. Here, we show that the water entry of the horizontal hydrophobic cylinder forms a film of cavity behind the cylinder whereas a hydrophilic cylinder forms a cavity from both ends of the cylinder. In a high Froude number entry, once the cavity film ruptured on both sides of it, the contact lines of the cavity film abruptly move along the surface of the cylinder. In a low Froude number entry, the influence of weak fluid inertia force makes several ruptures on the cavity film which grow individually and split off the cavity. Of a particular interest is the fact that the multi-rupture regime appeals for the spanwise three-dimensionality on the cavity film against the previous studies within two-dimensional treatment. Furthermore, this report finds the trend for some range of Fr that the nondimensionalized closure depth of the cavity film z c with diameter of the cylinder obeys z c / d  ∼ Fr 1/3 in the range 4.7 ≤ Fr ≤ 40 although it depends on Fr in the water-entry problem of a hydrophobic sphere.

Ti-45Al-7Nb alloys are produced by liquid-metal-cooling (LMC) directional solidification (DS) furnace with different temperature gradients (G) at a range of 40–80 K/cm. The growth directions of primary β phases and the deflection angles relative to the 〈100〉 β direction were investigated. The solidification pathway of alloy is: Liq. → Liq. + β → β → β + α → α + γ → lamella (α 2  + γ) + B2. Primary dendrite arm spacing λ reduced from 611.4 µm to 508.7 µm when G increased from 40 K cm −1 to 80 K cm −1 . Grains with lamellar orientation aligned at the angles of 12–15° and 55° to growth direction were favored for various G. The orientations of the γ lamellas in steady-state regions were identified by the electron backscattered diffraction analysis (EBSD). The results indicated that the growth directions of primary bcc-β dendrites were 〈211〉 β and 〈110〉 β at 40 K/cm, 〈210〉 β and 〈211〉 β at 50 K/cm and 〈211〉 β at 80 K/cm, the deflection angle of 〈211〉 β relative to 〈100〉 β direction is 35.3°.

The paraelectric-ferroelectric transition in NaNO 2 is studied using the Levanyuk-Sannikov and the mean field models which we have developed here. From both models, the temperature dependence of the spontaneous polarization is derived and is fitted to the experimental data from the literature. Our results show that both mean field models are adequate to describe the observed behaviour of the spontaneous polarization close to the paraelectric-ferroelectric transition in NaNO 2 . The two models are compared in regard to the transition mechanism in this crystal.

The oxidation of Fe-36Ni invar alloy in 5%O 2 -15%CO 2 -80%N 2 atmosphere at 1200 °C for 4 h and the cause of rolling cracks have been investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Gleeble thermal simulation machine. The result showed that the scales consisted of the external scale and the subscale. The external scale had stratified structures of Fe 2 O 3 /Fe 3 O 4  + NiO/Fe 3 O 4  + FeO + NiO from outside to inside. The subscale had a typical substructure of the intra-granular subscale and the inter-granular subscale. Oxidation particles of (Fe 3 O 4  + FeO) were isolated in FeNi 3 matrix in the intra-granular subscale zone. The grain boundary was the preferential short-circuit diffusion paths of the diffusing O and was first to be oxidized. The inter-granular subscale led to the subscale and was the origin of rolling cracks. The protective heating measure was put forward to prevent rolling cracks.

The effect of temperature and alloy content on the strength and plasticity of austenitic stainless steel was investigated in this paper. A series of expressions for quantitative calculation via computer were obtained according to the experimental data and are shown as ; ; ; ; . The obtained results were reliable and can be applied to the design and calculation of the high-temperature strength and plasticity of austenitic stainless steel.