Experimental and numerical study of granular medium-rough wall interface friction

Wall roughness plays a crucial role in granular medium - rough wall interface friction. In this study, an experimental device has been designed to study the influence of boundary conditions, more specifically wall roughness, on the behavior of sheared granular medium. The study is based on use of an analog model, and consists of simulating roughness by means of notches and grains in the medium by monodisperse beads and on use of a numerical model based on the discrete element method. The test protocol entails displacing at fixed speed notched rods under confined granular medium. Movement of the beads layer near the rods as well as friction of the beads against the rods are both studied herein. Results indicate that the parameter controlling friction at the granular medium - rough wall interface is primarily the depth of beads embedment in surface asperities. The objective of the associated numerical modeling is to supplement the experimental results.     

Regeneration of a solid waste from an edible oil refinery

This work presents a valorization of a solid waste originating from an edible oil refinery called spent bleaching earth (SBE). The SBE material is first impregnated with an ammonium chloride solution (3 M), then treated directly in furnace at 400 °C during an hour followed by a washing in the cold by HCl 1 M. To elucidate the changes in its crystalline structure, induced by the regeneration method, the obtained material (RSBE) is characterized by several physicochemical methods (X-ray diffraction, FTIR, thermal analysis, BET and SEM). The characterization results show that the heat treatment in furnace and the chemical treatment (decomposition of NH₄Cl) don’t affect the structure of montmorillonite of regenerated material (RSBE). The study of porous texture by the nitrogen adsorption technique at −196 °C shows that the specific surface area S_BET and the pore volume increased in the RSBE material compared to those of virgin bleaching earth VBE (unused) and their values are respectively of 145.68 against 115.5 m² g⁻¹ and of 0.287 against 0.234 cm³ g⁻¹. Calculations by the adsorption equations using BJH method, applied to both materials, show that the treatment generate an increase in the micropores in the RSBE material. We belonged the values of the micropores area of S_mic = 41.98 cm² g⁻¹ and of V_mic = 0.074 cm³ g⁻¹ for the volume.     

Influence of the application method of release agents on thickness of mould oils

The parameters likely to influence the appearance of the concrete facings are in particular the casting process of the concrete in the formwork, characteristics of the wall and the nature of the release agent. This study looks at the influence of the thickness of vegetable or mineral-based oils on the aesthetic quality of facings. The thickness of the oil films has been measured with a variant of the PIXE method specially developed for this study. Moreover, to create the conditions of a concrete poured into a formwork, a tribometer for fluid material developed in our laboratory was used. With the help of these devices, the thickness of the oil film before and after the pouring of a concrete in a metallic mould was studied. The vegetable oil film has a good resistance with the concrete friction and a film from 1 to 2 μm is enough to obtain a high quality facing.     

Role of demoulding agents during self-compacting concrete casting in formwork

The use of “super-plasticisers” to obtain concretes that are highly workable, easy to place in formwork and require no vibration has spread throughout Europe in the last few years. The placing process for fresh so-called Self-Compacting Concrete (SCC) is linked to the friction that occurs at the concrete/wall interface. A rectilinear movement tribometer has been developed. Tests performed with certain modifications of the interface conditions show that friction is governed by the characteristics (viscosity, tensioactivity, etc.) on the demoulding agents used. The interface appears to undergo two types of phenomena.

-shear stress in the thick lubricating layer, which entails low shear stresses.

-granular behaviour. The shear stress is higher in the second case.

     

Post-exposure processes in Temoporfin-photosensitized cells in vitro: reliance on energy metabolism

The progressive responses to photodynamic treatment (lambda > 590 nm) mediated by Temoporfin have been investigated in vitro on two rodent cell lines: BHK and murine hepatoma MH22 cells. Comparisons are made of two light exposure/post-exposure incubation media: Dulbecco's minimal essential medium (DMEM) and phosphate-buffered saline (DPBS) depleted of energy sources. Enhancement of lipid peroxidation is an early response to Temoporfin photosensitization in either experimental set. It is restored to the initial level by subsequent incubation in DMEM, but not in DPBS. The decrease in MTT specific activity and especially lactate dehydrogenase leakage from the cells are faster in DPBS and continue to proceed during the post-exposure incubation in the both media. The intracellular ATP pool is completely depleted within 3 h of post-exposure incubation in DPBS, but not in DMEM where, in contrast, an initial increase in ATP is observed. Based on these preliminary observations, it is presumed that ATP synthesized by injured mitochondria and activated glycolysis is being used to restore the deteriorated cell functions and/or to allow reactions involved in apoptosis to proceed.     

Designing and perfecting a tribometer for the study of friction of a concentrated clay-water mixture against a metallic surface

Extrusion shaping of tiles and bricks containing clay meets with lots of problems because of friction at the interface wall-paste in the extruder and in the die. These frictions lead to wear of the walls and create defects which alter the materials and its mechanical properties. In this paper a new device (tribometer) is presented allowing the study of friction of paste samples (kaolin+water) pressed against a plate put into translation. The analysis of the results obtained with the tribometer, together with observations made on a model, enables us to understand the mechanisms occurring at the interface paste-steel. It appears that two types of phenomena are present at the interface, depending on the paste composition and the plate surface characteristics:

- The flow of water coming from sample consolidation creating enough pressure to build the normal force.

- The movement of particles governed by the relationship between the particle size and the plate roughness amplitude.

     

Tribological behaviour of self compacting concrete

The use of superplasticizers to obtain concretes that are highly workable, easy to place in formwork and require no vibration has spread throughout Europe in the last few years. The placing process for fresh, so-called self-compacting concrete (SCC) depends on the friction that occurs at the concrete/wall interface.A rectilinear movement tribometer was developed to characterize SCC. The effect of several parameters affecting the concrete/metal plate friction coefficient is examined. These parameters include the roughness of the plate, the sliding velocity against the plate, the pressure or normal stress and the nature of the demoulding agent at the concrete/wall interface. Physical mechanisms are proposed.     

Photocatalytic Reactors Dedicated to the Degradation of Hazardous Organic Pollutants: Kinetics,Mechanistic Aspects,and Design – A Review

In recent years, heterogeneous photocatalysis has emerged as a new effective, powerful, clean, and safe decontamination technology for the treatment of organic pollutants and the transformation of hazardous chemicals into different forms. This review focuses on the recent development of various conventional technologies of reactors designated for the photodegradation of hazardous organic pollutants with their limitations. This phenomenon is strongly influenced by reaction conditions such as temperature of reaction, pH, light intensity and wavelength, pollutant concentration, photocatalyst quantity, relative humidity (RH), and other parameters. The catalyst photoactivity depends on the structural characteristics of the semiconductor, its morphology, and its particles size.

This paper presents the progression of photocatalytic reactors for synthetic dyes degradation with special consideration to the use of supported photocatalyst and nanostructured titanium supported over volcanic ashes, owing to the major advantage of an easy separation of the catalyst when compared to homogenous system, namely suspended catalyst. In addition, special attention was paid to the literature dealing with the promotion of light efficiency by testing various light sources.     

Influence of grain size on the phase transition β2 → ? in Bi4La2O9 material

This paper deals on a study realized in order to elaborate dense ceramic of Bi₄La₂O₉ oxide conductor. A wet method in nitric media, usually favorable to obtain low grain size, did not allow to isolate the stable phases. Material with particle low size has been obtained by attrition treatment after conventional solid state powder synthesis. The decrease of particle size (≅4 times), evidenced by X-ray diffraction and SEM, influences the reversibility of transitions between monoclinic ? and rhombohedral β₂ varieties on powder, as well as ceramics, leading to an improvement of the conductivity level of these ones after a thermal cycle.