Showing papers by "Nanjing Tech University published in 2002"

YSZ‐SrCo0.4Fe0.6O3‐δ membranes for the partial oxidation of methane to syngas

Abstract: The perovskite-related yttria-stabilized zirconia promoted SrCo0.4Fe0.6O3-δ (SCFZ) oxides were used to construct membrane reactors for the partial oxidation of methane to syngas (POM). The oxygen permeability study of the SCFZ membrane in the air/helium gradient showed that the apparent activation energy was about 69±5 kJ/mol at 1,023∼1,223 K, and the oxygen flux was controlled by the bulk diffusion and surface exchange rate. In a cofeed reactor packed with SCFZ pellets and a blank SCFZ membrane reactor without any catalyst packing, the SCFZ oxides showed low catalytic activity for POM in the fixed-bed reactor and no POM catalytic activity in the membrane reactor. An SCFZ membrane reactor with NiO/Al2O3 catalyst was continuously running for over 220 h under constant operational conditions. While about 64% of methane was converted with 100% CO selectivity after reaching the steady state, the oxygen flux was about 10 times the value of the air/helium gradient, in the reactor packed with the catalyst. The oxygen flux of SCFZ membranes in the reducing atmosphere could be limited by the surface reaction rate at the reaction side.

Catalytic behavior of alumina-promoted sulfated zirconia supported on mesoporous silica in butane isomerization

Abstract: Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by “direct impregnation” of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO2 loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.

A blended cement containing blast furnace slag and phosphorous slag

Abstract: Blended cement containing blast furnace slag (BFS) and phosphorous slag (PS) is a new kind of cement. The total content of blended materials could increase if two additives were used. Using the same admixtures, the properties of the blended cement with 70% additives could reach the standard of 525-grade slag cement according to GB. The strength of cement with 80% additives could reach the standard of 425-grade slag cement. The tests of strength, pore structure, hydration products, inhibiting alkali-aggregate reaction, resistance to sulfate corrosion of BFS-PSC were performed.

Oxygen Transport Properties and Stability of Mixed-Conducting ZrO2-Promoted SrCo0.4Fe0.6O3-δ Oxides

Abstract: The oxygen nonstoichiometry, transport properties, and structure stability of ZrO2-promoted SrCo0.4Fe0.6O3-δ (SCFZ) were investigated. The nonstoichiometry of SCFZ increased with increasing temperatures and decreasing oxygen partial pressures. The results of X-ray diffraction and oxygen desorption experiments showed that the addition of ZrO2 in SrCo0.4Fe0.6O3-δ (SCF) stabilized the phase structure under low oxygen partial pressure. The chemical diffusion coefficient of oxygen in SCFZ in a temperature range of 928−1178 K was obtained using the weight relaxation technique. A simple transport equation correlating oxygen flux to the oxygen diffusion coefficient was deduced. Model calculations, based on the transport equation in conjunction with data of oxygen permeation and oxygen nonstoichiometry, were performed. The rates of oxygen permeation fluxes measured at various temperatures and time showed that the long-term operation stability of the SCF membrane with the addition of ZrO2 was greatly improved. The ...

Optimal policies for a database system with two backup schemes

Abstract: . This paper considers two backup schemes for a databasesystem: a database is updated at a nonhomogeneous Poisson processand an amount of updated les accumulates additively. To ensure thesafety of data, full backups are performed at time NT or when thetotal updated les have exceeded a threshold level K , and betweenthem, cumulative backups as one of incremental backups are made atperiodic times iT ( i =1 ; 2 ; ;N− 1). Using the theory of cumulativeprocesses, the expected cost is obtained, and an optimal number N of cumulative backup and an optimal level K of updated les whichminimize it are analytically discussed. It is shown as examples thatoptimal number and level are numerically computed when two costs ofbackup schemes are given. Keywords. Database, full backup, cumulative backup, cumulativeprocess, expected cost. 1. Introduction A database in a computer system is frequently updated by adding or deletingdata les, andisstoredinfloppydisksorothersecondarymedia. Evenhighreliablecomputers might sometimes break down eventually by severalerrorsdue to noises,human errors and hardware faults. It would be possible to replace hardware and

Thermal conductivities of PTFE composites with random distributed graphite particles

Abstract: A two-dimensional finite element model for PTFE composite with random distributed circular graphite particles was developed to study its effective thermal conductivity. The experiments on thermal conductivities of these composites were conducted. Results from experiments and finite element analysis (FEA) were compared which show that non-uniform distribution lead to low thermal conductivity and there is a saturated conductivity ratio of the inclusion to the matrix at a certain volume fraction. The saturated ratio rises with the increasing of volume percentage.

Well-Dispersed Gallium-Promoted Sulfated Zirconia on Mesoporous MCM-41 Silica

Abstract: Gallium-promoted sulfated zirconia (SZ) was confined inside pure-silica MCM-41 (abbreviated as SZGa/MCM-41), where the latter served as a host material. It was prepared by direct dispersion of metal sulfate in the as-synthesized MCM-41 materials, followed by thermal decomposition. The SZGa/MCM-41 catalysts were characterized by XRD, N2 adsorption, HRTEM, DRIFT, NH3-TPD, and TPR. The experimental results showed that the ordered porous host structure was still maintained in the catalyst. SZ was in meta-stable tetragonal phase and highly dispersed on the interior surface of MCM-41 even at a high loading of 50 wt%. Additionally, a small fraction of SZ nanoparticles on the external surface of MCM-41 was obtained. The catalytic activity of SZGa/MCM-41 was examined in n-butane isomerization. In comparison to SZ/MCM-41 without promoter, the catalytic activities of the Ga-promoted catalysts were greatly improved. The reason proposed for the higher activity of the Ga-promoted catalysts was that Ga enhances the oxidizing ability of the catalysts.

Liquid−Liquid Equilibria for 1-Propanol (or 2-Propanol)−Water Systems Containing Potassium Fluoride

Abstract: Liquid−liquid equilibrium (LLE) data for 1-propanol (or 2-propanol)−water−potassium fluoride systems were measured at various temperatures. The salting out efficiency of potassium fluoride was also investigated. It was shown that potassium fluoride has a greater salting out effect on 1-proppanol than on 2-propanol. These data are correlated with the modified Setschnow model, and the results correspond rather well.

Measurement of Local Creep Deformation in Cross-Weld Specimen by Optical Fiber Marking and Remote Monitoring

Abstract: Creep deformation localization is a common occurrence generally found in high temperature components, typically at weldments and geometrical discontinuities. The deformation in a small region cannot be measured by a conventional displacement gage. A new technique for measuring long-term local creep deformation was developed. It uses quartz optical fiber marking, remote monitoring, and image processing. Long-term measurements of the creep deformations of base metal, weld metal, and heat-affected zone in cross-weld specimens were performed at high temperature, which verify the new technique. Strain distributions and evolutions in the weldments are obtained.

Superelastic deformation of a TiNi shape memory alloy subjected to various cyclic loadings

Abstract: Superelasticity is one of the important mechanical properties of shape memory alloys (SMAs). In the present paper, the superelastic deformation behaviour of a TiNi SMA under various loading conditions with different experimental temperatures and strain rates was investigated. The characteristics of transformation stress during cyclic deformation were analysed. The relationship between the residual stress and strain accumulated during cyclic loading is expressed by a straight line. After mechanical training with cyclic deformation, two-way deformation appears on account of R-phase transformation. The starting and finishing conditions of the transformation become unclear after cyclic deformation at high temperature.

An investigation of submicrostructural evolution of freshly precipitated ZrO2 in digestion for ultrafine sulfated ZrO2 catalysts by SAXS technique.

Abstract: Coupled with XRD, BET, and TEM, the small-angle X-ray scattering (SAXS) technique has been effectively used to probe and characterize the submicrostructure of freshly precipitated hydrous zirconia and its evolution during digestion. It has been found that fresh hydrous zirconia particles possess an average diameter of about 5 nm and rather rough surfaces describable in terms of fractal concepts. The digestion of zirconia precipitates at 100 degrees C with their mother liquors may remarkably smooth the particles' rough surface and provoke fractal aggregation of the particles but make little change in average particle dimensions. A local dissolution-reprecipitation mechanism is regarded as a basic process to accompany particle surface smoothing, particle aggregation, and coarsening at the neck areas between joint particles, which may greatly strengthen the particle networks and enhance their resistance to crumbling while calcinated at high temperatures. On the basis of the submicrostructural features unraveled by SAXS, a coherent and significant physical picture has been raised out to demonstrate and interpret the relationship underlying the submicrostructure, the surface area variation, and the heating behavior of hydrous zirconia precipitates.

An object-oriented inference model and its knowledge representation

Abstract: Knowledge representation is one of the kernel problems in research of expert system. Production rule and procedure knowledge play an important role in the development of expert system. This paper analyzed and designed an inference model (RBIM) based on production system in object oriented programming language, which can combine representation of predication and procedure. On the basis of object oriented knowledge representation, the model supports proposition object, predication object and procedure object as basic element of production rule. RBIM provides a good interface on knowledge representation.