scholarly journals Size Effects of the Crystallite of ZSM-5 Zeolites on the Direct Catalytic Conversion of L-Lactic Acid to L, L-Lactide

Crystals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 781
Author(s):  
Qintong Huang ◽  
Rui Li ◽  
Guangying Fu ◽  
Jiuxing Jiang
Keyword(s):  
Lactic Acid ◽  
Size Effect ◽  
Ball Milling ◽  
Size Effects ◽  
Proton Nuclear Magnetic Resonance ◽  
Reaction Products ◽  
Diffusion Controlled ◽  
Crystallite Sizes ◽  
Surface Poisoning ◽  
Chiral Gas Chromatography

ZSM-5 zeolites are commonly used as a heterogeneous catalyst for reactions. Four ZSM-5 catalysts (with various crystallite sizes and a similar ratio of Si/Al) and their ball-milling/surface-poisoning derivates were used to convert L-lactic acid to L, L-lactide. The reaction products were analyzed by three independent analytical methods (i.e., Proton nuclear magnetic resonance (1H NMR), high-pressure liquid chromatography (HPLC), and chiral gas chromatography (GC)) for determining the L, L-lactide yield and L-lactic acid conversion. A clear size effect, i.e., smaller catalysts providing better performance, was observed. Further ball-milling/surface-poisoning experiments suggested that the size effect of the ZSM-5 catalysts originated from the diffusion-controlled nature of the reaction under the investigated conditions.

Particle size effects in the selective hydrogenation of cinnamaldehyde over supported palladium catalysts

RSC Advances ◽  
2016 ◽  
Vol 6 (79) ◽  
pp. 75541-75551 ◽  
Author(s):  
Feng Jiang ◽  
Jian Cai ◽  
Bing Liu ◽  
Yuebing Xu ◽  
Xiaohao Liu
Keyword(s):  
Particle Size ◽  
Size Effect ◽  
Selective Hydrogenation ◽  
Size Effects ◽  
Palladium Catalysts ◽  
Particle Size Effect ◽  
Particle Size Effects ◽  
Supported Palladium Catalysts ◽  
Supported Palladium ◽  
Palladium Particles

Palladium particles of different sizes obtained directly and indirectly by various methods were studied to clarify the particle size effect in the selective hydrogenation of cinnamaldehyde (CAL).

Modeling of Size Effects on the Flow Stress of Type 304 Stainless Steel and Application in Coining Process

2007 ◽  
Author(s):  
Gap-Yong Kim ◽  
Muammer Koc ◽  
Jun Ni
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Flow Stress ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
304 Stainless Steel ◽  
Length Scales ◽  
Type 304 ◽  
Type 304 Stainless Steel

Application of microforming in various research areas has received much attention due to the increased demand for miniature metallic parts that require mass production. For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/meso-scale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the “feature/specimen size” effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with experiments obtained from previous research and showed a very good agreement. The model was also applied to forming of micro-features by coining. A flow stress model for Type 304 stainless steel taking into consideration the effect of the grain and feature size was developed and implemented into a finite element simulation tool for an accurate numerical analysis. The scaling model offered a simple way to model the size effect down to length scales of a couple of grains and extended the use of continuum plasticity theories to micro/meso-length scales.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

scholarly journals Mechanocatalytic Production of Lactic Acid from Glucose by Ball Milling

Catalysts ◽  
2017 ◽  
Vol 7 (6) ◽  
pp. 170 ◽  
Author(s):  
Luyang Li ◽  
Lulu Yan ◽  
Feng Shen ◽  
Mo Qiu ◽  
Xinhua Qi
Keyword(s):  
Lactic Acid ◽  
Ball Milling

scholarly journals Ringwoodite rim around olivine core in shock-induced melt-vein of GRV 022321 chondrite: Transformation kinetics of olivine to ringwoodite

2021 ◽  
Author(s):  
Zhidong Xie ◽  
Thomas G. Sharp ◽  
Shuhao Zuo ◽  
Xiaochun Li
Keyword(s):  
Electron Microscopy ◽  
Raman Spectroscopy ◽  
Natural Occurrence ◽  
Controlled Growth ◽  
Rock Fragments ◽  
Nano Crystalline ◽  
Diffusion Controlled ◽  
State Diffusion ◽  
Crystallite Sizes ◽  
Electron Imaging

Abstract Here we report the natural occurrence of the ringwoodite rims around olivine cores in shock-induced melt veins of the Antarctic chondrite GRV 022321. Electron microprobe analysis (EMPA), Raman spectroscopy, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used to examine the sample to better elucidate the mechanisms of transformation of the olivine to ringwoodite and Fe-Mg partitioning in olivine under the shock. The GRV 022321 is an L6 chondrite with a network of black veins enclosing abundant olivine host-rock fragments. Some of the enclosed fragments ranging from 5 µm to 100 µm in size have bright rims up to 20 µm wide, and a dark core under reflected light and backscatter electron imaging. Raman spectroscopy reveals that rims are made of ringwoodite, and cores are predominantly olivine. EMPA data show the ringwoodites in rims are richer in Fe (Fa46) than the olivine cores (Fa10-Fa23). The olivine cores have variable contrast in BSE images with the heterogeneities in fayalite content (Fa10 to Fa23) and a branching network of low-Fa olivine. FIB-TEM observations reveal that the ringwoodite rims are polycrystalline with crystallite sizes from 200 nm to 800 nm, while the olivine cores are also polycrystalline, but with smaller crystallites from 100 nm to 200 nm. Based on observation, we conclude that the original Fa23 olivine transformed to Fa10 olivine and Fa46 ringwoodite by a solid-state diffusion-controlled growth mechanism during shock, and the branching network of low-Fa olivine acted as long-range(up to 10µm)high-diffusion pathways for grain-boundary Fe-Mg interdiffusion through highly deformed nano-crystalline olivine to accommodate the diffusion-controlled growth of ringwoodite.

scholarly journals Size Effect in Fracture of Sandwich Structure Components: Foam and Laminate

2001 ◽  
Author(s):  
Zdeněk P. Bažant ◽  
Yong Zhou ◽  
Drahomír Novák ◽  
Isaac M. Daniel
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Sandwich Structure ◽  
Maximum Load ◽  
Material Strength ◽  
Large Structures ◽  
Nominal Strength ◽  
Sandwich Plates And Shells ◽  
Extensive Test ◽  
Plates And Shells

Abstract In the design of sandwich plates and shells for very large structures, such as ships in the range of 100 m length, it is very important to take the size effect on the nominal strength into account, and do so in a realistic, physically justified, manner. Before the size effect is addressed for a sandwich structure, it must be understood for its components — the foam core and the laminate skins. In the current practice, the size effects are automatically attributed to the randomness of material strength, as described by the Weibull theory. The purpose of this paper is to show that in both the foam and the laminate there are deterministic size effects, which are generally more pronounced. They are caused by stress redistribution and energy release due to the growth of large fractures or large cracking zones prior to attaining the maximum load. This deterministic size effect is verified and calibrated by new tests of notched specimens of rigid close-cell vinyl foam. A combined deterministic-probabilistic theory of size effect of the laminates is proposed and verified by extensive test data.

Biophysical properties of electrospun chitosan-grafted poly(lactic acid) nanofibrous scaffolds loaded with chondroitin sulfate and silver nanoparticles

2021 ◽  
pp. 088532822110464
Author(s):  
Alexandre F Júnior ◽  
Charlene A Ribeiro ◽  
Maria E Leyva ◽  
Paulo S Marques ◽  
Carlos R J Soares ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Lactic Acid ◽  
Proton Nuclear Magnetic Resonance ◽  
Poly Lactic Acid ◽  
Fibroblast Cells ◽  
Biophysical Properties ◽  
Electrospinning Technique ◽  
Average Pore ◽  
H Nmr ◽  
Substitution Degree

The aim of this work was to study the biophysical properties of the chitosan-grafted poly(lactic acid) (CH-g-PLA) nanofibers loaded with silver nanoparticles (AgNPs) and chondroitin-4-sulfate (C4S). The electrospun CH-g-PLA:AgNP:C4S nanofibers were manufactured using the electrospinning technique. The microstructure of the CH-g-PLA:AgNP:C4S nanofibers was investigated by proton nuclear magnetic resonance (1H-NMR), scanning electron microscopy (SEM), UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), and Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR and 1H-NMR confirm the CH grafting successfully by PLA with a substitution degree of 33.4%. The SEM measurement results indicated apparently smooth nanofibers having a diameter range of 340 ± 18 nm with porosity of 89 ± 3.08% and an average pore area of 0.27 μm2. UV-Vis and XRD suggest that silver nanoparticles with the size distribution of 30 nm were successfully incorporated into the electrospun nanofibers. The water contact angle of 12.8 ± 2.7° reveals the hydrophilic nature of the CH-g-PLA:AgNP:C4S nanofibers has been improved by C4S. The electrospun CH-g-PLA:AgNP:C4S nanofibers are found to release ions Ag+ at a concentration level capable of rendering an antimicrobial efficacy. Gram-positive bacteria ( S.aureus) were more sensitive to CH-g-PLA:AgNP:C4S than Gram-negative bacteria ( E. coli). The electrospun CH-g-PLA:AgNP:C4S nanofibers exhibited no cytotoxicity to the L-929 fibroblast cells, suggesting cytocompatibility. Fluorescence microscopy demonstrated that C4S promotes the adhesion and proliferation of fibroblast cells onto electrospun CH-g-PLA:AgNP:C4S nanofibers.

scholarly journals Size Effects in Ruthenium-Based Thick-Film Resistors: Rutile vs. Pyrochlore-Based Resistors

1991 ◽  
Vol 14 (3) ◽  
pp. 163-173 ◽  
Author(s):  
M. Prudenziati ◽  
F. Sirotti ◽  
M. Sacchi ◽  
B. Morten ◽  
A. Tombesi ◽  
...  
Keyword(s):  
Size Effect ◽  
Thick Film ◽  
Sheet Resistance ◽  
Firing Temperature ◽  
Size Effects ◽  
Conductive Phase ◽  
Lower Sheet ◽  
Lower Sheet Resistance

The size effect, namely the change of sheet resistance, Rsas a function of resistor length, has been investigated in layers whose conductive phase evolves from Pb-rich (Ru-deficient pyrochlores) to Pb2Ru2O6.5and finally to RuO2by increasing the firing temperature. It is found that Bi diffusion from the terminations is responsible for lower sheet resistance values in shorter resistors whatever the conductive phase is. On the contrary, Ag diffusion is responsible for lower sheet resistance values in shorter resistors only in the case of ruthenate conductive grains while the reverse is observed in RuO2-based layers. Size effect can be suppressed with Pt/Au-based terminations provided that no Bi is contained and with Au-metallorganic-based contact provided that the peak firing temperature is not too high.

Review of Research Progress on Size Effect in Micro-Forming

2016 ◽  
Vol 717 ◽  
pp. 118-121 ◽  
Author(s):  
T.T. Qiu ◽  
Ying Ke Hou ◽  
H.L. Cao
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Test Methods ◽  
Research Progress ◽  
Test Apparatus ◽  
Micro Forming ◽  
High Productivity ◽  
Material Usage ◽  
Deformation Behaviors ◽  
Micro Level

Microforming process is a promising approach to manufacture microparts for its high productivity, high material usage and good part properties. However, when the part size is scaled down from macro to micro level, the deformation behaviors of materials change and the size effects occur. This makes it difficult to use microforming process in industry. In the last decade, many studies have been conducted with different test methods and materials. In this paper, the main test apparatus and the methods used to study the size effect and the significant results are reported.

Experimental Investigation of Size Effects of FCC Polycrystal by Shear Banding

1999 ◽  
Vol 121 (2) ◽  
pp. 156-161
Author(s):  
Osamu Watanabe ◽  
Takayuki Kurata
Keyword(s):  
Size Effect ◽  
Cross Section ◽  
Size Effects ◽  
Rectangular Cross Section ◽  
Pure Aluminum ◽  
Shear Banding ◽  
Compressive Loading ◽  
Thickness Effect ◽  
Internal Mechanism ◽  
Meso Scale

Several plasticity phenomena display a size effect where the smaller the size is the stronger its response. This effect relates to the plastic gradients, appearing in plastically inhomogeneous material. The present paper describes results of an experimental meso-scale study using the specimens having rectangular cross section made of FCC polycrystal of pure Aluminum and OFHC Copper under the tensile or compressive loading. Experimental measurements are carried out to investigate thickness effect and grain size effect in connection with size effect, and the internal mechanism of plastic flow in the specimens is also discussed.

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