Thermo-mechanical Properties of Al/Si Incorporated Low Carbon Al2O3-C Slide Plate Materials

Low carbon Al₂O₃ - C refractory materials were prepared by Al/Si metal incorporated,in-situ formed non-oxides method using corundum,Al powder,Si powder and flake graphite as starting materials.High temperature strength,stress - strain relationship and thermal shock resistance of these composites were investigated. The results show that these composites possess improved high temperature strength and good thermal shock resistance. When Al addition increases from 0 to 8 mass%, correspondingly,Si addition decreases from 8 mass%to 0,hot modulus of rupture at 1 400℃increases significantly from 10.4 MPa to 32.4 MPa;the maximum strain under 6.5 MPa stress at 1 400℃decreases from 215μm to 90μm;residual strength ratio after 3 thermal shock cycles（1100℃,air quenching） decreases from 80%to 65%.This may be attributed to in-situ formation of nonoxides because Al and Si react with C,CO and N₂ to form Al₄C₃,AlN and SiC creating strengthening and toughening effects.     

Tetralin hydrogenation catalyzed by Mo2C/Al2O3 and WC/Al2O3 in the presence of H2S

Supported molybdenum and tungsten carbides were synthesized by temperature-programmed reactions. These materials were characterized by XRD, EDS analysis, HRTEM and CO chemisorption. Hydrogenation of tetralin was carried out at a total pressure of 4 MPa (3.06 MPa of H₂), at 573 K, without or with sulfur (200 ppm of sulfur as DMDS). The resulting activities were compared with those of MoS₂/Al₂O₃ and Pt (1% (w/w) metal loading) supported on Al₂O₃ or SiO₂. In the absence of sulfur, WC/Al₂O₃ showed an initial activity similar to that of Pt/SiO₂, higher than that of MoS₂/Al₂O₃ but lower than that of Pt/Al₂O₃. In the presence of H₂S, WC/Al₂O₃ showed a steady-state activity similar to that of Pt/Al₂O₃ (which suffered a marked deactivation). Post-reaction characterization did not show any sulfur poisoning of the supported carbides. Therefore the supported carbides are sulfur-tolerant and promising catalysts for the hydrogenation of aromatics in diesel fuels in the presence of small amounts of S-containing compounds.     

Design and construct CeO2-ZrO2-Al2O3 materials with controlled structures via co-precipitation method by using different precipitants

To design and construct CeO₂-ZrO₂-Al₂O₃(CZA) materials with controlled structure via co-precipitation method, the NH₃·H₂O and (NH₄)₂CO₃ were worked as precipitants, respectively. And the influence of the precipitants on nucleation, growth and thermal behavior of the CZA materials were investigated. Results of H₂-TPR, XRD, XPS, UV–Vis, TEM and HAADF-TEM elemental mapping show that using NH₃·H₂O as precipitant facilities to form homogeneous CeO₂-ZrO₂(CZ) solid solution with better solid solubility but the resulting CZA materials sinters severely due to the “mechanical-like” mixing mode between Ce, Zr and Al. On the contrary, the CZA materials precipitated by (NH₄)₂CO₃ shows a better textural and structural stability due to the uniform distribution of Ce, Zr and Al. However, the H₂ consumption of CZA precipitated by (NH₄)₂CO₃ is limited by the inferior Ce and Zr solid solubility due to stronger interactions among the components. It is also found that the surface and subsurface reduction of CZA materials are controlled by specific surface area and crystal size, while the bulk reduction of CZA materials correlates with solid solubility of Ce and Zr, crystal size and surface Ce/Zr ratio simultaneously.     

Improved thermal shock performance of Al2O3-C refractories due to nanoscaled additives

Carbon bonded alumina refractories with approximately 30 wt.-% residual carbon after coking are widely used as functional components such as submerged entry nozzles, monobloc stoppers and ladle shrouds in steel casting operations. Compositions with less residual carbon after coking based on nanoscaled magnesium aluminate spinel (MgAl₂O₄), alumina nanosheets (α-Al₂O₃) and carbon nanotubes (CNTs) either as single additives or combinations have been investigated according to their physical, mechanical and thermo-mechanical properties. The combination of nanoscaled powders based on carbon nanotubes and alumina nanosheets lead to superior thermal shock performance with approximately 30% less residual carbon in comparison to commercial available material compositions.     

High temperature neutron diffraction study of the Al2O3–Y2O3 system

The phase diagram of the Al₂O₃–Y₂O₃ system has been investigated with five different compositions by XRD and in situ high temperature neutron diffractometry. High purity YAG, YAP and YAM compounds have been produced successfully through a melt extraction technique. High temperature neutron diffraction has made it possible to follow, in real time, the reactions involved in this system, especially to determine the temperature range of each reaction, which would have been impossible to determine by other means. A good agreement between the experimental results and the phase diagram of the Al₂O₃–Y₂O₃ system has been observed.     

Sulphur trap materials based on mesoporous Al2O3

Different sulphur trap materials based on mesoporous Al₂O₃ supports modified with the storage component Ca or Ba and the oxidation components Pt or Cu or Mn were prepared and the SO₂ uptake behaviour examined in the temperature range 50–600 °C. A comparison between the different oxidation components shows that the presence of Pt is not a necessary precondition for attaining a good storage behaviour under these test conditions. Mn is the most suitable oxidation component.

Tests performed over four temperature cycles show that the removal efficiency for SO₂ gradually decreases over the course of temperature cycles. Moreover, a progressive diminution of the SO₂ uptake is observed especially in the lower temperature range during the temperature cycles. A further modification with Na prevents this drawback. Especially a distinct improvement is observed with the Ca-containing material. It stored 22 wt.% sulphate during the four temperature cycles. This material is regarded as being most suitable for application as sulphur trap material.     

Influence of glass phase on Al2O3 fiber-reinforced Al2O3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al₂O₃ fibers (33 wt%) and Al₂O₃ (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al₂O₃ fibers into Al₂O₃ particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Fabrication and characterization of spray dried Al2O3-ZrO2-Y2O3 powders treated by calcining and plasma

In this paper, the Al₂O₃-20 wt.%ZrO₂ (8 wt.%Y₂O₃) feedstocks were fabricated and treated by spray drying, calcination, and plasma treatment technology. The morphology of feedstocks was characterized by scanning electron microscope (SEM). The phase structure and grain size were analyzed by X-Ray diffraction (XRD). The flowability and density were measured by Hall Flowmeter and density instrument, respectively. The sphericity and flowability of feedstocks treated by plasma flame increased greatly compared with that of the feedstocks without plasma treatment, and the particle surfaces were very smooth. The optimum flowability was obtained when the critical plasma spray parameter (CPSP) was 363. The compactness also increased greatly with the increment of CPSP, and the maximum value of compactness was got with CPSP of 325. Calcination can make the grain grow and plasma treatment can lead to the decrement of grain size. The phase structure of Al₂O₃ did not change, which was α-Al₂O₃ in the composites. The phase structure of ZrO₂ (8 wt.%Y₂O₃) changed from t-phase to c-phase which was affected greatly by plasma treatment.     

Characterization and tribological investigation of sol-gel Al2O3 and doped Al2O3 films

Thin films of Al₂O₃ and doped Al₂O₃ were prepared on a glass substrate by dip coating process from specially formulated ethanol sols. The morphologies of the unworn and worn surfaces of the films were observed with atomic force microscope (AFM) and scanning electron microscope (SEM). The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of obtained thin films sliding against Si₃N₄ ball were evaluated and compared with glass slide on a one-way reciprocating friction tester. XPS results confirm that the target films were obtained successfully. The doped elements distribute in the film evenly and exist in different kinds of forms, such as oxide and silicate. AFM results show that the addition of the doped elements changes the structure of the Al₂O₃ films, i.e., a rougher and smoother surface is obtained. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, the doped films exhibit better tribological properties due to the improved toughness. Sever brittle fracture is avoided in the doped films. The wear of glass is characteristic of brittle fracture and severe abrasion. The wear of Al₂O₃ is characteristic of brittle fracture and delamination. And the wear of doped Al₂O₃ is characteristic of micro-fracture, deformation and slight abrasive wear. The introduction of ZnO is recommended to improve the tribological property of Al₂O₃ film.     

The system CaOAl2O3Fe2O3 with added fluoride flux

Effects of fluoride fluxes, especially CaSiF₆·2H₂O upon phase equilibria in the system CaOAl₂O₃Fe₂O₃ are described, presenting liquidus data, new phase field boundaries and invariant points and solid solution areas. The primary phase field for C_12?xA₇·CaF₂ is increased substantially in size, and liquidus or invariant temperatures are depressed by amounts ranging from 20 to 80°C.     

Effect of surface-modified Al2O3 on the thermomechanical properties of polybutylene succinate/Al2O3 composites

This study investigates the effect of the incorporation of alumina particles on the thermomechanical properties of polybutylene succinate (PBS)/Al₂O₃ composites. The alumina surface was modified with the carboxylic groups of maleic acid through simple acid-base and in situ polymerization reactions. Scanning electron microscope (SEM) results revealed the introduction of maleic acid treated alumina significantly affect the morphology of the PBS/Al₂O₃ composites as compared to the neat PBS. The thermal conductivity of the composite (0.411?W?m^?1 K^?1) was more than twice that of neat PBS. The composite containing polymerization-modified alumina showed a 50% increase in storage modulus compared with that of neat PBS. In addition, universal testing machine (UTM) and differential scanning calorimetry (DSC) measurements indicated an increase in the tensile strength and degree of crystallinity after the incorporation of modified alumina in the PBS/Al₂O₃ composite.     

Comparison of catalytic activity and selectivity of Pd/(OSC + Al2O3) and (Pd + OSC)/Al2O3 catalysts

The effect of the Pd addition method into the fresh Pd/(OSC + Al₂O₃) and (Pd + OSC)/Al₂O₃ catalysts (OSC material = Ce_xZr_1−xO₂ mixed oxides) was investigated in this study. The CO + NO and CO + NO + O₂ model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al₂O₃) catalyst than for the fresh (Pd + OSC)/Al₂O₃ catalyst during the CO + NO + O₂ reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al₂O₃) catalyst was higher than that of the (Pd + OSC)/Al₂O₃ catalyst.     

Effect of Al2O3 on mechanical properties of Ti3SiC2/Al2O3 composite

The effect of Al₂O₃ on mechanical properties of Ti₃SiC₂/Al₂O₃ composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti₃SiC₂/Al₂O₃ composite can reach 10.28 GPa, 50% higher than that of pure Ti₃SiC₂. However, slight decrease in the other mechanical properties was observed with Al₂O₃ addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al₂O₃ in the composite.     

Fe/Al_2O_3催化剂催化氧化兰炭废水

采用浸渍法制备Fe/Al_2O_3催化剂,采用BET、XRD和穆斯堡尔谱等进行结构和性能表征。以自制Fe/Al_2O_3为催化剂,应用催化湿式过氧化氢氧化技术处理COD为6 742 mg·L-1的兰炭废水,通过建立正交实验确定最佳实验条件,结果表明,在p H=4、过氧化氢添加量9.6 m L、反应时间150 min和反应温度80℃条件下,兰炭废水COD去除率达66.30%。对催化氧化后的废水进行GC-MS分析,确定最终氧化产物主要为乙酸。表明自制Fe/Al_2O_3催化剂具有优良的催化效果,并使大分子难降解有机污染物分解为易生化的小分子污染物,甚至被完全分解矿化。     

Preparation of in situ grown silicon carbide whiskers onto graphite for application in Al2O3-C refractories

C-SiC composite powders were prepared by salt-assisted synthesis from Si powders, graphite, and a molten salt medium (NaCl and NaF) with the molar ratio of Si/C =?1/2 at 1300?°C for 3?h. After the C-SiC composite powders part and complete replacement of the graphite, the mechanical properties, oxidation resistance and slag-corrosion resistance of the Al₂O₃-C materials were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), as well as with dedicated equipment. The results indicated that SiC whiskers, with lengths of 10–50?nm, formed on the surface of the flake graphite, and the activation energy of oxidation of the C-SiC composite powder increased by 45.72?kJ?mol^?1 as compared to that of flake graphite. Furthermore, the decarburization area and slag erosion area of the Al₂O₃-C material decreased after 3?wt% of C-SiC composite powder was substituted for the flake graphite. Meanwhile, the cold modulus of rupture was maintained when 3?wt% of C-SiC composite powder was added. This improved both the oxidation and slag resistance of the Al₂O₃-C materials.     

Fabrication of novel multilayer Al2O3-(m-ZrO2)/t-ZrO2 fibrous ceramics composites

A novel layered microstructure in the Al₂O₃/ZrO₂ composites system was fabricated by the multipass extrusion method. The microstructure consisted with very fine alternate lamina of Al₂O₃-(m-ZrO₂) and t-ZrO₂. The composites were designed in such a way that a small group of 7 cylindrical alternate layers of Al₂O₃-(m-ZrO₂) and t-ZrO₂ made a concentric microgroup around 40 μm in diameter, with a common boundary layer between the adjacent groups. The thickness of both layers was around 2-3 μm. The microstructure was unidirectionally aligned throughout the composites. The composite microstructure was fibrous due to the unidirectional orientation of these microgroups. Detailed microstructure of the fabricated composites was characterized by SEM. The effect of the concentric layered microstructure on mechanical behavior was discussed. Material properties such as density, bending strength, Vickers hardness and fracture toughness were measured and evaluated depending on different sintering temperatures.     

Influence of CdO on the early hydration of 3CaO.Al2O3

The influence of CdO on the hydration of 3CaO.Al₂O₃ at 25 °C was studied by X-ray diffraction, scanning electron microscopy, thermal gravimetry, and calorimetry for hydration times less than one day. The CdO had a small effect on the thermal characteristics of hydration. Slightly less heat was liberated when CdO was added to the 3CaO.Al₂O₃. The presence of CdO increased the formation of the cubic hydrated phase. The cadmium was retained in the matrix as Cd(OH)₂.     

The interaction of spherical Al2O3 particles with molten Al2O3-CaO-FeOx-SiO2 slags

The present paper investigates the rate of chemical dissolution of Al₂O₃ particles in synthetic Al₂O₃-CaO-FeO_x-SiO₂ slags as a function of time under an atmosphere where Fe²⁺ would be the stable state for iron ions dissolved in the slag. Two aspects of the interaction between the Al₂O₃ spheres and slags were studied, namely (i) the speed at which the particle sinks into the slag and (ii) how rapidly the particles dissolve. The objectives are to elucidate interactions between oxide particulate material, either from the refractory wall or from the mineral constituents in the fuel feedstock, with the slag formed at the wall in entrained-slagging gasifiers.The particle settling was found to proceed first rapidly, but subsequently slowing down and this behavior was in qualitative agreement with model predictions based on a balance between gravity-, drag-, capillary-, and added mass forces. The effect of increasing temperature and FeO_x content are investigated and it is shown that both contribute towards increasing the dissolution rate. The rate appears to be governed by a combination of the driving force for dissolution and transport properties in the slag.     

Matrix–filler interactions in polysilazane-derived ceramics with Al2O3 and ZrO2 fillers

Interactions between a poly(vinyl)silazane and Al₂O₃ or Y₂O₃-stabilised ZrO₂ fillers were studied during the fabrication of polysilazane-derived bulk ceramics in order to investigate the influence of oxide fillers on resulting properties. Specimens were produced by coating of the filler powders with the polysilazane, warm-pressing of the resulting composite powders, and pyrolytic conversion in flowing N₂ at various temperatures between 1000 °C and 1400 °C. Significant differences in densification were observed, depending on the filler used. Reactions between the polysilazane-derived matrix and Al₂O₃ or ZrO₂ at temperatures ≥1300 °C resulted in the formation of Si₅AlON₇ or ZrSiO₄, respectively. Reactivity in the polysilazane-derived component was a result of SiO₂ contamination caused primarily by adsorbed species on the filler particle surface. Knowledge of polysilazane/filler interface processes is found to be decisive for the prediction of properties such as shrinkage and porosity, which heavily influence performance of a material.