Effect of catalyst preparation on Au/Ce1−xZrxO2 and Au–Cu/Ce1−xZrxO2 for steam reforming of methanol

We tested 3 wt% gold (Au) catalysts on CeO₂–ZrO₂ mixed oxides, prepared by co-precipitation (CP) and the sol–gel (SG) technique, for steam reforming of methanol (SRM). Uniform Ce_1−xZr_xO₂ solid solution was dependent on the Zr/Ce ratio, where the incorporation of Zr⁴⁺ into the Ce⁴⁺ lattice with a ratio of 0.25 resulted in smaller ceria crystallites and better reducibility, and was found to be efficient for SRM activity. The catalytic activity was suppressed when the ratio was ≥0.5, which led to the segregation of Zr from solid solution and sintering of Au nanoparticles. It was found that the CP technique produced better catalysts than SG in this case. For the bimetallic catalysts, the co-operation of Au–Cu supported on Ce_0.75Zr_0.25O₂ (CP) exhibited superior activities with complete methanol conversion and low CO concentration at 350 °C. Furthermore, the size of the alloy particle was strongly dependent on the pH level during preparation.     

Bonded orthotropic strips with cracks

In this paper the elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. It is assumed that the plane contains a series of collinear cracks perpendicular to the interfaces and is loaded in tension away from and perpendicular to the cracks. First the problem of cracks fully imbedded into the homogeneous strips is considered. Then the singular behavior of the stresses for two special crack geometries is studied in some detail. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. An interesting result found from the analysis of the latter which may have an important bearing on a possible delamination fracture initiation at stress-free boundaries in bonded orthotropic materials is that for certain orthotropic material combinations the stress state at the point of intersection of a crack and an interface may be bounded whereas in isotropic materials at this point stresses are always singular. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Finally, some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.

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Résumé Dans ce mémoire, on considère le problème élasto-statique d'un plan non-homogène consistant en deux séries de feuilles orthotropes dissimilaires disposées de manière périodique. On suppose que le plan contient une série de fissures colinéaires perpendiculaires aux interfaces et qu'il est soumis à traction perpendiculairement à ces fissures et suffisamment loin de celles-ci. On considère en premier lieu le problème des fissures complètement noyées dans les bandes homogènes. Le comportement singulier des contraintes dans le cas d'une géométrie de fissures particulières est étudié dans le détail, le premier cas est celui d'une doublure interrompue dont les extrémités de la fissure atteignent l'interface; le second est le cas de fissures traversant les interfaces. Un résultat intéressant qui a été trouvé à partir de l'analyse de ce dernier cas et qui peut revêtir une importante signification sur les possibilités d'amorçage d'une rupture par délamination aux frontières libres de contraintes dans les matériaux orthotropes réunis, est que pour certaines combinaisons de matériaux orthotropes l'état de tension au point d'intersection d'une fissure et d'un interface peut être limité, bien que dans les matériaux isotropes à ce point les contraintes sont toujours singulières. Plusieurs exemples numériques sont examinés en vue de séparer les paramètres primaires du matériau influençant les facteurs d'intensité de contrainte et les puissances de la singularité de contrainte, et en vue de déterminer les tendances relatives à l'influence des paramètres secondaires. Finalement, quelques résultats numériques sont fournis pour les facteurs d'intensité de contrainte relatifs à certaines géométries de fissure de base et pour des combinaisons typiques de matériau.

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This work was supported by NASA-Langley under the Grant NGR-39-007-011 and by the National Science Foundation under the Grant ENG77-19127.     

Physical and Mechanical Properties of PP Composites based on Different Types of Lignocellulosic Fillers

The presents preparation and characterization of different types of lignocellulosic fillers (pine wood sawdust/ walnut shell flour/ black rice husk powder) reinforced polypropylene composites were presented. The effect of MAPP as coupling agent (4wt%) on the physical and mechanical properties was also investigated. Polypropylene composites were prepared at different rates of filler/matrix (wt%) by using extrusion (for melt blending) and hot compression molding process. Maximum values of tensile and flexural strength were obtained as 26.1 and 43.4 MPa, respectively, whereas the elongation at break value was 4.11% at 10% pine wood sawdust reinforced PP. Tensile and flexural modulus of composites reached the maximum values as 3855 and 3633 MPa with the composite of 30% walnut shell flour reinforced PP. Characterization of composites was carried out by using tensile test, flexural test, FT-IR, and SEM.     

Bifunctional Catalyst Control of Alkene Isomerization

The ability to control the formation and chemistry of alkenes is of central importance to organic synthesis in both industry and academia. Progress in using catalysts with bifunctional (heteroaryl)phosphines to control positional and/or geometric selectivity in alkene isomerization and related chemistry is summarized.     

Comparison of abrasive wear behavior of ductile iron with different dual matrix structures

Abrasive wear behavior of ductile irons with different dual matrix structures has been investigated. In order to obtain ductile irons with different dual matrix structures an unalloyed ductile iron specimens were austenitized in the two-phase region (α + γ) at various temperature (795 °C and 815 °C) and then rapidly transferred to a salt bath held at the 365 °C for austempering for 30, 90 and 120 min. Some specimens were quenched from same intercritical austenitizing temperatures and tempered at 550 °C for 60 and 300 min. Some specimens were also conventionally austempered and/or quenched from 900 °C for comparison. Experimental results showed that, the tensile strength increased and ductility decreased with increasing martensite volume fraction in the specimen with martensite dual matrix structure. By increasing the tempering time, the yield and UTS decreased and ductility increased. In addition, the specimens with ausferrite dual matrix structures exhibited much greater ductility than conventionally austempered ones. The tensile strength increased while ductility decreased with increasing ausferrite volume fraction. Furthermore in all austenitized specimens, the abrasive weight loss of austempered specimens (A series) was lower than those of quenched specimens (Q series) irrespective of all loads due to increased AFVFs and total elongation. It was shown that wear loss of both tested materials in abrasive wear was proportional to the applied load. However, there was a decreasing trend in the weight loss of the A795 with dual matrix structure austempered for 30 and 90 min with increasing load. The reason was because of the fact that the specimen surface was work hardened with cutting efficiency of the abrasive reduced through clogging, and attrition jointly leading to less weight loss. Moreover, increasing the austempering time caused more ductile ausferritic structure to displace hard martensite. In all austempered samples, the abrasive weight loss increased with increasing the austempering time. As for the case of Q samples, the abrasive weight loss increased more or less linearly with load since an increase in the applied load might increase the contact stress. Among the Q samples, the highest weight loss was obtained for the Q795-300, Q815-300 sample because of lower martensite volume fraction, but the lowest weight loss was observed for the Q900 sample due to the highest martensite volume fraction. For Q900 samples, the amount of fracture of the abrasives was found to be increase with the harder specimen, and it may have contributed somewhat to the increased wear.Furthermore, microchips were dominant wear mechanism by cutting mode for higher ductile materials while micro-ploughing was predominant wear for harder materials, but wear also occurred by combinations of ploughing and embedding particles into the surface for Q samples. Cross-section examination by SEM through the wear surfaces revealed that a more smoother surface was observed for the A795 sample than that of the Q795 sample. However, a more rougher surface was observed for the A900-120 sample than that of the Q900 sample.     

Prediction of surface roughness in abrasive waterjet machining of particle reinforced MMCs using genetic expression programming

Machining of particle-reinforced metal matrix composites has been considerably difficult due to the extremely abrasive nature of the reinforcements that causes rapid tool wear and high machining cost. Abrasive water jet (AWJ) machining has proven to be a viable technique to machine such materials compared to conventional machining processes. The present study is focused on the surface roughness of AWJ cut surfaces and genetic expression programming (GEP) was proposed to predict surface roughness in AWJ machining of 7075 Al alloy composites reinforced with Al₂O₃ particles. In the development predictive models, characteristics of materials such as size and weight fraction of reinforcement particles, and depth of cut were considered as model variables. The training and testing data sets were obtained from the well-established machining test results. The weight fraction of particle, size of particle, and depth of cut were used as independent input variables, while arithmetic mean of surface roughness, maximum roughness of profile height, and mean spacing of profile irregularity as dependent output variables. Different models for the output variables were predicted on the basis of training data set using GEP and accuracy of the best model was proved with testing data set. The test results showed that output variables increased with increasing input variables. The predicted results were compared with experimental results and found to be in good agreement with the experimentally observed ones.     

Physico-chemical characteristics of chemically activated cement containing boron

The use of colemanite ore waste (CW) containing boron as a cement replacement material increases the long-term strength of the concrete. Despite this benefit, the use of CW is limited due to the low-early strength of the CW concrete. The study reported below intended to eliminate this problem. The experimental part comprises two stages: in the first stage the possibility of using CW instead of natural gypsum has been investigated through several tests. In the second stage, a number of chemical activators, namely, sulphonated melamine formaldehyde (SMF) condensates, sulphonated naphthalene formaldehyde (SNF) condensates, _Na2SO4${\mathrm{Na}}_2{\mathrm{SO}}_4$, and calcium chloride were used. The results showed that replacement of natural gypsum by CW results in an acceptable initial and final setting time of cement and increases the compressive strength of the mortar at long term. The addition of chemical activators into the system accelerated pozzolanic reaction and considerably increased early strength of the mortars. The results also indicate that chemical activators not only alter the rate of cement paste hydration, but the microstructure of mortar as well.     

Characterization of chemically sprayed CdO films on borate and phosphate glass substrates produced by melt-quenching technique

The properties of substrates used to deposit thin films are an important parameter in thin film production. Instead of using a commercial substrate, in this work, borate and phosphate glasses have been obtained by classic melt-quenching technique to be used as substrates for CdO films. Also, a microscope glass substrate has been used to compare the coating properties by other glass substrates. All films have been produced by Ultrasonic Spray Pyrolysis technique. The substrate temperature has been selected as 275 ± 5 °C. Thicknesses and some optical parameters such as refractive index and extinction coefficient have been determined by spectroscopic ellipsometry. Absorbance and transmittance spectra have been taken by UV/VIS spectrophotometer. Four-probe method has been used to determine the electrical resistivity values of the films. XRD investigations have shown that type of the substrate dramatically affects the characteristics of CdO films. CdO film deposited on phosphate glass substrate has the best structural quality. Atomic Force Microscope has been used to investigate the surface properties and roughness values of the films.     

Experimental dynamic analysis on naturally curved honeycomb sandwich beams with different damage patterns

In this study, dynamic analysis of naturally curved honeycomb sandwich beam including two surface cracks and an impact region at the facing skin is presented. Laminates of facing skin and backing skin are known as carbon fiber‐plain weave composite laminates with 1.6 mm in thickness. In the first part, in order to determine mechanical properties of both the skin with no‐crack/crack(s) and the honeycomb core of the composite beam, static tensile tests are conducted with respect to straingage measurement technique. In the second part, drop weight impact tests and vibration tests are performed to present the free vibration characteristics of the clamped‐clamped honeycomb sandwich beam including cracks and an impact‐damaged region. Corresponding to damage patterns of the sandwich beam, experimental dynamic analyses consist of six steps: (1) Vibration analysis with no‐crack and no‐impact region, (2) Vibration analysis with no‐crack and an impact region, (3) Vibration analysis with a surface crack and no‐impact region, (4) Vibration analysis with a surface crack and an impact region, (5) Vibration analysis with two surface cracks and no‐impact region, (6) Vibration analysis with two surface cracks and an impact region. For these purposes, an impact hammer with a force transducer is used to excite the undamaged or damaged naturally curved honeycomb sandwich beam through the selected points. After the excitation, the responses are obtained by an accelerometer. Resonant frequencies for the modal responses of the naturally curved honeycomb sandwich beam with different damage patterns are discussed.