Monitoring of the Variation in Pore Sizes of Woven Geotextiles with Uniaxial Tensile Strain

Characteristic pore-opening size O95 or O90 has been widely used in the filter design of woven geotextiles. These manufactured products have different pore size proportions of large pore diameters, medium pore diameters, and small pore diameters, respectively. Therefore, uncertainties still exist regarding the prediction of geotextile pore diameter variations under the uniaxial tensile strain. This paper investigates the variations in five characteristic pore-opening sizes O95, O80, O50, O30, and O10, with uniaxial tensile strain by using the image analysis method. The large pore diameters, medium pore diameters, and small pore diameters show different variation behaviors as the uniaxial tensile strain increases. Fifteen specific pores are selected and then their pore diameter variations are monitored under each tensile strain of 1%. The colorful pore size distribution diagram is a visual way to identify the variation of pores arranged in the tension direction (warp direction) and the direction perpendicular to tensile loads (weft direction). The various pore diameters are proved to agree well with the bell-shaped Gaussian distribution. The results exhibit an accurate prediction of the variation in large pore sizes, medium pore sizes, and small pore sizes, respectively, for all tested woven geotextiles with uniaxial tensile strain.

DEVELOPMENT OF LOW-MELTING GLASSCERAMIC BONDS FOR HIGH RESOURCE DIAMOND-ABRASIVE TOOLS

Research is aimed at creating high-resource diamond-abrasive tools with a large-pore structure of the working layer, the use of which reduces the occurrence of grinding defects when processing materials sensitive to overheating. The formation of an open structure of the working layer ensures effective chip removal, which excludes a decrease in the сutting ability of the tool due to contamination with grinding sludge and creates favorable conditions for intensifying the processing of materials when using high-speed cutting modes. As part of the research, low-melting glass-ceramic binders for diamond-abrasive tools have been developed, which make it possible to increase the tool service life due to the prevention of diamond grains premature destruction and the creation of a large-pore open structure of the working layer. Using a set of calculated data about the main characteristics of glass compositions by factor planning means, the dependences «composition - properties» were determined and the area of optimal compositions of glass-ceramic bonds was established, which ensure sintering of a diamond-containing composite at a temperature of 550–650 °C. The efficiency of the use of alumino-silicate microspheres of technogenic origin as a structure-forming filler providing the formation of a large-pore structure is shown. The features of the chemical and phase composition of the technogenic spheres recovered from the fly ash of the Krivoy Rog TPP have been determined. It has been established that when the diamond-bearing layer of the tool is sintered in the shell of the ash spheres, crystalline new formations with high hardness (hercynite, mullite, maghemite, spinel) are formed. Using ash spheres and developed low-melting binders, which include up to 30 mass. % of glass waste, the laboratory samples of diamond-containing composites with open porosity of 45-50% were made. Studies of their microstructure and morphological features made it possible to determine the pore size (130-200 μm) and establish that during grinding, partial destruction of ash spheres occurs with the formation of additional cutting elements, which increases the tool cutting ability. The research results indicate the advisability of using the proposed approach for selection of the diamond-ceramic composite components and the modes of heat treatment of the diamond-bearing layer when creating a tool. This approach will significantly expand the possibilities of manufacturing large-pore diamond-abrasive tools with a high service life at minimal material costs and will improve the processing of parts made of difficult-to-machine materials.

Kinetic Analysis for the Catalytic Pyrolysis of Polypropylene over Low Cost Mineral Catalysts

A kinetic analysis of non-catalytic pyrolysis (NCP) and catalytic pyrolysis (CP) of polypropylene (PP) with different catalysts was performed using thermogravimetric analysis (TGA) and kinetic models. Three kinds of low-cost natural catalysts were used to maximize the cost-effectiveness of the process: natural zeolite (NZ), bentonite, olivine, and a mesoporous catalyst, Al-MCM-41. The decomposition temperature of PP and apparent activation energy (Ea) were obtained from the TGA results at multiple heating rates, and a model-free kinetic analysis was performed using the Flynn–Wall–Ozawa model. TGA indicated that the maximum decomposition temperature (Tmax) of the PP was shifted from 464 °C to 347 °C with Al-MCM-41 and 348 °C with bentonite, largely due to their strong acidity and large pore size. Although olivine had a large pore size, the Tmax of PP was only shifted to 456 °C, because of its low acidity. The differential TG (DTG) curve of PP over NZ revealed a two-step mechanism. The Tmax of the first peak on the DTG curve of PP with NZ was 376 °C due to the high acidity of NZ. On the other hand, that of the second peak was higher (474 °C) than the non-catalytic reaction. The Ea values at each conversion were also decreased when using the catalysts, except olivine. At <0.5 conversion, the Ea obtained from the CP of PP with NZ was lower than that with the other catalysts: Al-MCM-41, bentonite, and olivine, in that order. The Ea for the CP of PP with NZ increased more rapidly, to 193 kJ/mol at 0.9 conversion, than the other catalysts.

Structured large-pore foams improve thermal performance of LiMIT-style liquid lithium PFC

As magnetically confined fusion devices improve, the conditions at the walls become increasingly intense. Plasma facing components (PFCs) must withstand these extreme heat and particle loads without damage or degradation. Liquid lithium PFCs are known to be quite resilient, and the presence of lithium also serves to improve plasma properties. The Liquid Metal Infused Trench (LiMIT) concept is an open surface liquid lithium PFC design that has been tested extensively at the University of Illinois and in fusion devices around the world. LiMIT utilizes thermoelectric magnetohydrodynamics (TEMHD) to passively drive liquid lithium flow. This work demonstrates an extension of the LiMIT trench geometry to 3 dimensions. Additively manufactured large pore metallic foams maintain TEMHD drive while drastically improving heat flux handling and resistance to lithium dryout, a phenomenon where locally high TEMHD forces depresses the lithium level and exposes underlying solid structure. COMSOL Multiphysics modeling of the system yields insight into the forces at play in dryout development, and shows the 3-D structures can eliminate dryout. Low heat proof-of-concept experimental testing of the system matches computational results, and high heat flux electron beam tests more than double the proven operational range of a LiMIT-style PFC, to 6.8 MW/m2, with no indications of dryout or impending damage.