NO2 gas sensing properties of the nitrogen-hyperdoped black silicon (N-Si) modified at different annealing temperatures are studied. Owing to the abundant defects in the material and their changes ...with the annealing, the thermal modification brings a series of novel sensing behaviors and characteristics. Working as the sensitive material in a conductometric gas sensor, the pristine N-Si exhibits an undesirable n- to p-type response transition for higher NO2 concentration, which severely reduces its upper limit of detection (< 5 ppm). However, for the thermally modified N-Si after annealing at higher temperature (≥ 673 K), the abnormal response transition induced by higher concentration disappears. These modified N-Si show consistent p-type response to all tested NO2 concentrations, successfully breaking the detection limit. More interestingly, there is an optimal annealing temperature ~ 873 K, at which the sensor demonstrates outstanding sensing performances, including wide dynamic range spanning 5 orders of magnitude, rapid adsorption and desorption ability, high response and good selectivity, etc. Results indicate that through the thermal modification a novel N-Si gas-sensitive material is obtained. The mechanism for the thermally-induced response type conversion is discussed, in which the activation of acceptor energy levels provided by the complexes associated with substitutional nitrogen are considered.
•Nitrogen-hyperdoped silicon with p-type NO2 response are obtained.•Electrical and sensing properties of thermally modified nitrogen-hyperdoped silicon.•Excellent overall sensing performance at the optimal annealing temperature ~ 873 K.•Discussion for the conduction type conversion, variation in resistance and sensing behaviors.
The risk of possible ignition and burning is one of the greatest disadvantages of using wood as a construction material. An environmentally appropriate method of improving the fire-resistant ...properties of wood is available via thermal treatment. In this study, spruce wood (Picea abies L.) was thermally modified at 160 °C, 180 °C, and 210 °C. The effect of thermal modification on the fire performance of the wood, including weight loss and burn rate, was evaluated. A new testing method was designed to be sufficiently sensitive to monitor fire performance. The results showed that the thermally modified spruce wood had a lower weight loss than untreated wood. The burn rate of wood that was thermally modified at 160 °C was similar to that of untreated wood. Higher thermal treatment temperatures caused a higher burn rate. After the flame was removed, the burning process was rapidly stopped in thermally treated wood.
•Heat treatment of African highland bamboo improved scrimber resistance against basidiomycete monocultures and soft rot (ground contact).•The minimum temperature to improve bamboo scrimber durability ...on industrial scale was 180 °C.•All treatments were classified as slightly durable (DC 4) when measuring stiffness loss, butDC 1 to 3 when looking at mass loss.•For basidiomycete monocultures all samples, treated and control, showed to be very durable (DC 1).•High mass losses due to abiotic factors occurred but reduced with increasing heat treatment temperature.
A novel engineered scrimber was manufactured from heat treated African highland bamboo Yushania alpina (K. Schum.) W.C. Lin on an industrial scale. Scrimber are a group of engineered wood products that consist of long, slender particles resulting from a non-cutting defibration technique. Those are heat treated, impregnated with phenolic resin, highly densified and the product is believed to be resistant to biodegradation by wooddestroying fungi. The highland bamboo scrimber was tested for resistance against basidiomycete monocultures and soft rot in a soil bed test. The soft rot soil bed test caused nearly 20 % mass loss and 61 % stiffness loss for the scrimber made from untreated bamboo. Heat treatment reduced the ML to 5% for the 200 °C variant, whereas stiffness loss was only slightly reduced for heat treated variants. All treatment temperatures led to 50 % fungal stiffness loss. The notably high abiotic mass loss in sterile samples reduced with treatment temperature. The heat treatment did not affect the durability class resulting from the test against basidiomycete monocultures. Although the variability in heat treated samples was slightly lower, all variants achieved durability class 1. The soil bed test against soft rot resulted in durability classes 1, 2, 3 and 4. When based upon stiffness as parameter, the durability class was 4, whereas mass loss led to DC 1 for treatment at 200 °C, DC 2 for 180 and 160 °C and DC 3 for the untreated control, respectively. The development of substrate moisture content over time indicated that fungal growth can possibly be delayed via heat treatment, but not stopped. The minimum target treatment temperature to achieve a notable improvement in mass loss was 180 °C.
•Combined ZnCl2-ultrasound and thermal modification treatment of Moso bamboo was used.•Moso bamboo's dimensional stability and thermal degradation efficiency were improved.•This method increased the ...relative crystallinity of Moso bamboo cellulose.•This method reduced the onset temperature of thermal decomposition.
To save energy and reduce emissions during the thermal modification of Moso bamboo, this study investigated the effect of the combined zinc chloride-ultrasound pretreatment and thermal modification on the physicochemical properties of Moso bamboo.
Samples were pretreated using 5% (w/w) ZnCl2 solution and 40 kHz ultrasonic waves, followed by heat treatment at 160 °C. The samples were characterized by moisture absorption measurements, X-ray diffraction, Fourier-transform infrared spectroscopy, surface wettability measurements, thermogravimetric analysis, and colorimetry.
The results showed that the combined pretreatment method reduced the moisture absorption by 10.15% and increased the relative crystallinity of Moso bamboo cellulose by 4.4%. It also increased the surface contact angle by 25.2%, lowered the onset of thermal decomposition, reduced the temperature required for hemicellulose to reach its maximum thermal degradation rate by 49 °C, and increased the color change (∆E*ab) by 23.60.
Display omitted
High hygroscopicity is an important factor that influences the durability and service life of wood structures. Joint modification of tung oil impregnation and thermal modification (OTM) has been ...acknowledged as an effective technique to reduce wood hygroscopicity and preserve mechanical properties. However, the contribution of this approach to the effect of wood cell wall properties at the microscopic level remains unclear. In this study, the surface morphology, micromechanical properties, and dynamic moisture absorption of OTM-modified wood cell walls were characterized. The results of morphological observation clearly demonstrated and quantified the spatial distribution of tung oil within wood pores, including porous capillary structures and wood cell walls. It is also observed that an interpenetrating polymer network was formed between tung oil and the cell wall components. The cell wall roughness of all thermally modified samples increased as the temperature rose, while the oven-dried density and equilibrium moisture content decreased. Notably, the immersion of tung oil in cell wall structures significantly alters the surface morphology of cell wall, transitioning from ellipsoidal protrusions in the control group to spiky protrusions with rounded tips in the OTM samples. Moreover, 210 ℃ was identified as a critical turning point for Young’s modulus and hygroscopicity in cell wall of thermally modified wood. Below 210 ℃, Young’s modulus showed an upward trend as the temperature increased, while a precipitous drop occurred in air thermally modified (TM) samples at 210 ℃. However, due to the impregnation of tung oil, the effect of thermal modification on Young’s modulus of wood was attenuated, especially at high temperatures. The OTM wood (7.87 ± 0.79 GPa) at 210 ℃ showed a larger Young’s modulus compared to TM wood (3.03 ± 0.42 GPa), corresponding to an increase of 159.7%. Additionally, TM samples at 210 ℃ also showed increased water absorption, water absorption rate, and reduced hygroscopic hysteresis in comparison to the control group. Conversely, the moisture content of OTM samples continued to reduce at 210 °C. In conclusion, the formation of a polymer network between wood components and tung oil could further reduce the hygroscopicity of thermally modified wood while maintaining the micromechanical properties of the cell walls.
Display omitted
•OTM helps reduce wood hygroscopicity and maintain micromechanical properties.•Interpenetrating polymer network formed between tung oil and wood cell wall components.•Tung oil helps remodel the surface morphology of wood cell walls and reduce their roughness.•WTNs enhance the Young’s modulus of the S2 layer within wood cell walls.•WTNs reduce hydroxyl accessibility and available water space of wood cell walls.
Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and ...chemical changes in spruce (
Picea abies
L.) and oak wood (
Quercus robur
F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the
L
*
a
*
b
* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-
O
-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.
To quantify the possible impact of different wood protection techniques on the aquatic environment, we applied a tiered Integrated Testing Strategy (ITS) on leachates obtained from untreated (UTW) ...Norway spruce (Picea abies), specimens treated with a copper-ethanolamine-based preservative solution, complying with the Use Class 3 (UC3), and specimens thermally modified (TM). Different maturation times in water were tested to verify whether toxicant leaching is time-dependent. Tier I tests, addressing acute effects on Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna, evidenced that TM toxicity was comparable or even lower than in UTW. Conversely, UC3 significantly affected all species compared to UTW, also after 30 days of maturation in water, and was not considered an environmentally acceptable wood preservation solution. Tier II (effects on early-life stages of Lymnea auricularia) and III (chronic effects on D. magna and L. auricularia) performed on UTW and TM confirmed the latter as an environmentally acceptable treatment, with increasing maturation times resulting in decreased adverse effects. The ITS allowed for rapid and reliable identification of potentially harmful effects due to preservation treatments, addressed the choice for a less impacting solution, and can be effective for manufacturers in identifying more environmentally friendly solutions while developing their products.
Display omitted
•Toxicity of untreated and treated wood was assessed using an Integrated Testing Strategy (ITS).•Copper(II)octanoate vacuum-pressure impregnation is acutely toxic to freshwater species.•Thermal modification was the less toxic wood treatment for freshwater species.•Copper and Cu-complexes are identified as main contaminants of concern in leachates.•The ITS is a versatile tool and can be applied to different wood and treatments.
The development of non-biocidal and environmentally friendly systems to protect wood against biological decay has become a high priority in recent years. In the present study the impact of an ...innovative modification procedure, combining two environmentally friendly modification methods: thermal modification and mineralisation, using an aqueous solution of calcium acetoacetate as a precursor, on the fungal durability of wood was evaluated. European beechwood (Fagus sylvatica) and Norway sprucewood (Picea abies) were selected as model wood species. Wood samples were treated using either a single or combination of both methods and exposed to four different fungi: Gloeophyllum trabeum, Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus. The effect of the different modifications on moisture content, dynamic vapour sorption, contact angle and pH value was also evaluated. Overall, the highest durability against Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus was achieved through thermal modification in both wood species, while the combination of mineralisation and thermal modification has a synergistic effect against degradation by Gloeophyllum trabeum. In the case of beechwood the mass loss decreased from 41% for native to 6% for combined modified samples. We proved that the effectiveness of different treatment against fungal decay of wood were in strong dependence of their moisture content, dynamic vapour sorption, contact angle and pH values. The role of fungi on the morphology of the wood and on crystal structure of formed carbonate was investigated using SEM-EDS analysis.
Display omitted
•Presented ecological modification of wood can be an alternative to biocides.•A significant improvement in the fungal durability of wood was achieved.•Thermal modification and mineralisation work synergistic against wood decay fungi.•The reasons for a synergistic effect of combining methods were proposed.•The mass loss decreased from 41% for native to 6% for combined modified beechwood.
PDF
