A novel, simple, quick, and economic method has been developed to etch samples for characterizing the structural aspects of carbonized pitch alone and in baked anodes. Hot air is used to etch the ...polished carbonized pitch surface for creating its topography; followed by the characterization of the structure using scanning electron microscope. Hot air preferentially etches the carbonized pitch, which make the differentiation of carbonized pitch from the calcined coke particles possible in baked anode. After etching, lamellar parallel cracks are created and fine granular mosaics are observed on the surfaces of carbonized pitch. The structural composition in baked anode differs visibly from the pure carbonized pitch baked under the same conditions. This may be due to the effect of fine coke particles in anode on the formation of structure during baking. The etching technique permits the determination of the internal structure of carbonized pitch and its interface with coke in anode.
The outer environment, especially UV portion of solar radiation and water (in the form of moisture or rain) has an adverse effect on the surface appearance of heat-treated wood. Exposure to UV ...triggers the chain scission reactions which change the intrinsic properties of heat-treated wood and discoloration of wood surface. Repeated temperature and humidity variations cause swelling and shrinking of wood surface, which consequently create cracks and fissures exposing wood's sub superficial layers to atmospheric agents. Therefore, wood industries move towards the development of coatings in order to protect the heat-treated wood while retaining wood's natural look. Water based acrylic polyurethane coatings are highly efficient, non toxic and durable coatings with upgraded film properties. In this study, an attempt is made to improve the performance of these coatings by incorporating natural antioxidant (bark extract) and inorganic UV absorbers (nano and micro titania and nano zinc oxide) into the coatings. The main objectives of this study are to investigate the wetting and penetration characteristic of these new coatings on the wood surface and to study coating thickness variation with weathering time. The Sessile-drop method and fluorescence microscope are used for this investigation. The wettability of different coatings applied to heat-treated jack pine early wood and late wood is compared. The results show that there is a significant difference between the contact angle of early wood and late wood for acrylic polyurethane coating containing titania micro particles. The contact angle between water and coated wood surface reveals that the degree of orientation of the coating materials increases as the weathering time increases. The penetration characteristics of all the four coatings are found to be very poor. In addition, the relationship between the coating thickness and the UV exposure time is studied for four water based acrylic polyurethane coatings with different additives. It is found that the coating thickness decreases with increasing weathering time and a tissue deformation beneath the coating surface takes place during weathering.
Wood is a porous, anisotropic and hygroscopic material. The heat treatment of wood at high temperature improves dimensional stability and increases durability and resistance to biological degradation ...like fungi attack. The improved characteristics of heat-treated wood offer many potential and attractive opportunities to the wood product industry. Furthermore, the quality of treated wood depends on several parameters that must be monitored and controlled.
In the present paper, a three-dimensional modeling of thermal treatment of wood at high temperature is presented. This model is based on the coupling of the energy and mass conservation equations for wood with the average Reynold Navier–Stokes equations as well as the energy and concentration equations for the fluid field. Some parametrical investigations have been done using the coupled system in order to optimize the process design. First, the quality of heat-treated wood was improved by moisture injection in the fluid flow during the heat treatment process. Then, the quality highly depends on the physicochemical properties like thermal conductivity and moisture diffusivity. These two parameters should preferably be parameterized within the modeling, more particularly the mass diffusion coefficient, to improve the realism of the modeling.
Heat-treated wood is a value-added product but its exposure to various environmental factors leads to discoloration of wood surface due to the photochemical reactions. Discoloration has become an ...important economic problem for wood industries since product specifications are now more demanding. In addition, stricter environmental legislations necessitate the development of environmentally friendly transparent coatings with minimal use of chemicals which balances aesthetic and protection. In this study, the acrylic polyurethane coating was improved with the addition of natural antioxidant (bark extract) and lignin stabilizer alone or in combination to enhance the resistance of this coating to different weathering factors. An accelerated aging test was conducted with the aim of comparing the acrylic polyurethane coatings containing different additives with the commercially available pigmented solvent borne coating used by industry and organic UV absorbers. The modifications in chemical structure of coatings were characterized by ATR–FT-IR analysis. The color change data showed that the coating containing bark extract was the most effective and performed better than the industrial coating. However, the visual assessment showed that the coating containing bark extract and lignin stabilizer had the best performance. FT-IR analyses suggested that the chain scission reaction took place throughout the weathering but its effect was not significant for any of the coatings.
Carbon anodes are used in the electrolytic production of aluminum. The quality of anodes is directly related to the production cost, carbon and energy consumption, and environmental emissions. It is ...desired that the anodes have high density, low porosity/cracks, low electrical resistivity as well as low air and CO
2
reactivities. Low resistivity of anodes reduces energy required to produce aluminum during electrolysis. The presence of cracks and pores increases the anode electrical resistivity. Therefore, it is important to know how and when the pores and cracks form during the anode production so that the necessary actions could be taken to prevent their formation. A study was carried out to investigate the effect of different anode production parameters such as anode composition, type of raw material used, time and top-former bellow pressure of vibro-compactor, green anode cooling medium, and heating rate used during baking on the crack formation. The anodes are fabricated at the carbon laboratory of University of Quebec at Chicoutimi (UQAC) and characterized by measuring their properties (density, electrical resistivity, and surface crack density). The anode properties, hence the anode quality, were correlated with the anode production parameters. Also, their tomographic analysis was carried out to visualize and quantify the internal cracks.
Graphical abstract
Heat treatment of wood has attracted a lot of attention both in Europe and recently in North America as an environmentally-friendly wood-protection method. The untreated wood is hydrophilic (high ...affinity for water). During the heat treatment, wood becomes more and more hydrophobic (low affinity for water) with increasing heat treatment temperature. As a result, it becomes more resistant to biological attacks. Furthermore, it becomes dimensionally more stable compared to untreated wood. Its hardness increases. As the wood becomes more hydrophobic, its wettability by water decreases. The effect of heat treatment is different for each species. Studying the wetting characteristics of heat treated wood gives a good indication of the heat treatment effects on certain wood properties which are related to its degree of hydrophobic character. The aim of this work was to study the characteristics of dynamic wetting process for two different heat-treated North American wood species white ash (
Fraxinus americana
) and soft maple (
Acer rubrum
). Contact angle measurements before and after heat treatment showed a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases higher for heat-treated wood than for untreated wood.
The high temperature thermal treatment of wood is an environment-friendly method for wood preservation. This technique has attracted considerable attention in recent years. The GRTB (groupe de ...recherche sur la thermotransformation du bois) at the University of Quebec at Chicoutimi, Canada, has been working on this subject for the past number of years. In this article, the work is presented with a focus on the mathematical modelling of the process.
Three models (model based on Luikov's approach, diffusion model, and multiphase model) have been developed for the high temperature treatment of wood. The predictions of the models are compared with the experimental data. The diffusion model was found to be the most practical approach when the accuracy of the results and the computation times are both taken into account.
▸ Wetting and degradation behavior of PUA with natural antioxidant was studied during this work. ▸ Wetting behavior of coatings was highly dependent on capillary penetration rate. ▸ The lowest ...contact angle was obtained at mid grain size sanded wood surface. ▸ The highest water repellency was exhibited by coating with bark extract and lignin stabilizer. ▸ Color change occurred during accelerated aging was due to the degradation of wood surface layer beneath coating.
Heat-treated wood is value added product which attracted the attention of consumers due its dark brown color which is of interest for decorative purposes. But this dark brown color fades when subjected to outdoor environment turning to grayish white color along with formation of small cracks and checks on the surface. In order to prevent the color change, an effort has been put forward for developing new coatings. The acrylic polyurethane coating with bark extract with or without lignin stabilizer proved to be very effective in protecting the surface of heat-treated jack pine. In this study, the interaction of these coatings with heat-treated jack pine surface was investigated and the results were compared with those of industrially available Laurentide coating. The capillary penetration was found to be the most important phenomenon in wood-coating interaction. The results revealed that capillary penetration rate was highly dependent on different additives used as well as surface tension and viscosity of the coatings. Two different models were used to evaluate volume change of the coating drop with time which is the indication of capillary action during wetting on heat-treated jack pine. Influence of mechanical surface treatment also plays an important role in wetting phenomenon of wood coating irrespective of wood grain direction. Water penetration through coatings is very important for wood discoloration during aging. Therefore, measurement of contact angle between water and coated/heat-treated wood system gave insight to water penetration at different aging times. Furthermore, the degradation at wood-coating interface was studied using a fluorescence microscope which did not reveal any degradation at the interface for coating containing bark extract and coating containing bark extract together with lignin stabilizer. The results of this study give an insight into high performance of acrylic polyurethane containing bark extracts alone or together with lignin stabilizer against color change of heat-treated jack pine.
Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of ...petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several factors, defects (cracks/pores) appear in anodes during the fabrication process, affecting their quality. It is thus essential to control the quality of anodes before their use in the electrolysis cell. Current practice for the quality evaluation (visual inspection, core analysis) gives limited information. As an alternative to this practice, electrical resistivity measurements can be used. Electrical resistivity is one of the key indicators for anode quality and its homogeneity. A simple and non-destructive method has been developed for the specific electrical resistivity measurement of anodes (SERMA) for on-line control of anode quality. Various tests have been carried out at both lab scale and industrial scale. In this study, the electrical resistivity distributions in the lab-scale anodes were measured and compared with those of the tomography analysis. The method is able to detect defective anodes even before the baking process.
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