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An efficient fractionation of three main components of corn cob and a good delignification effect were reported with formic acid (88%) pretreatment at 80 °C for 3 h. The pretreated substrate demonstrated a poor enzymatic digestibility with a mere 9.1% hydrolysis yield. Subsequently, various post-treatment processes after pretreatment were conducted and the mechanisms behind the effect on the hydrolysis were investigated. During pretreatment, formic acid adsorption occurred, which resulted in a significant inhibiting effect for the hydrolysis of the pretreated substrate. Mild post-treatment quickly removed the easily desorbed formic acid in the solid and cellulose accessibility was found to be increased greatly along with the decrease of formic content. After hot water and alkaline salt post-treatment, the hydrolysis yield increased to 81.2% and 98.5%, respectively. Meanwhile, the formic acid content of the substrate decreased by 15.9% and 61.4%. The restarted hydrolysis performance indicated that the factor associated with the nature of substrate, such as formic acid content, cellulose accessibility, and the existence of ester bonds, should be responsible for the enzymatic digestibility of the substrate. Herein, the proposed two-step pretreatment with formic acid (88%) followed by alkaline salt solution at room temperature demonstrates a remarkable effect on the conversion of lignocellulose material and has high feasibility for industrial application since it is mild to environment and requires low energy.

The passivation behaviour of passive films on the surface of reinforcing steels exposed to alkaline solutions was investigated. Two types of reinforcing steels (low-carbon steel and low-alloy steel...

The effect of carbonation on the chloride resistance of low-carbon steel and two Cr-bearing alloy steels in simulated concrete pore solutions was investigated. The chloride threshold values of steels were determined on the basis of corrosion potential (Ecorr) and polarization resistance (Rp). Moreover, the chloride-induced corrosion behavior of steels was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry, cathodic potentiodynamic polarization, and scanning electron microscopy/energy dispersive X-ray spectroscopy measurements. Alloy steels have higher chloride resistance than low-carbon steel in carbonated and non-carbonated concrete pore solutions. The chloride resistance of alloy steels improves with increasing Cr content. In addition, the chloride resistance of all steels is negatively affected by the carbonation of concrete pore solution, especially for alloy steel with high Cr content in the presence of high chloride content.

The enzymatic digestibility of softwood is hindered for its highly recalcitrant nature to enzymatic attack. In this study, the effects of dilute sulfuric acid pretreatment (DSAP), acidic sodium chlorite pretreatment (SCP), and their combined pretreatments (DSA-SCP and SC-DSAP) on Chinese fir sawdust were investigated, respectively. Results demonstrated that lignin was the most important obstacle, and digestibility increased linearly with lignin removal yield. Furthermore, the results revealed that the order of sequential pretreatment significantly affected the delignification, and hemicellulose should be removed first. Compared to SC-DSAP, DSA-SCP involving the hemicellulose-removal-first strategy exhibited higher delignification efficiency. DSA-SCP caused lignin removal of 92.3% and the enzymatic hydrolysis was high of 97.9%. Finally, a regression model with high reliability was established to quickly evaluate pretreatment process. In summary, this study highlighted the importance of delignification for saccharification of softwood and unveiled the effect of hemicellulose on delignification.

The influence of mill scale and steel type on the passivation capability and impressed current-induced accelerated corrosion behavior of reinforcing steels in concrete was studied using ele...

A Cr-bearing low-alloy (LA) reinforcing steel with two different surface conditions (polished surface and as-received ribbed surface) was investigated using various electrochemical measurem...

In this Letter, we theoretically propose and experimentally demonstrate a three-dimensional soundproof acoustic cage structure, hereby denoted as an acoustic metacage. The metacage is composed of six acoustic metamaterial slabs with open holes and hidden bypass space coiling tunnels connected to the holes. Band structure analysis reveals a novel physical mechanism to open a low-frequency broad partial band gap via the band folding in other directions, which can also be interpreted by an effective medium with indefinite effective mass density and negative effective modulus. Transmission loss in simulations and in the acoustic impedance tube are administered. Strikingly, we prove that the soundproofing effect of the metacage is robust against the airflow perturbation induced by a fan. Our work paves a road for low-frequency airborne soundproof structures in the presence of ventilation.

We report the first realization of a three-dimensional (3D) acoustic double-zero-index medium (DZIM) made of a cubic lattice of metal rods. While the past decade has seen several realizations of 2D DZIM, achieving such a medium in 3D has remained an elusive challenge. Here, we show how a fourfold degenerate point with conical dispersion can be induced at the Brillouin zone center, such that the material becomes a 3D DZIM with the effective mass density and compressibility simultaneously acquiring near-zero values. To demonstrate the functionalities of this new medium, we have fabricated an acoustic waveguide of 3D DZIM in form of a ``periscope'' with two 90\ifmmode^\circ\else\textdegree\fi{} turns and observed tunneling of a normally incident planar wave through the waveguide yielding undistorted planar wave front at the waveguide exit. Our findings establish a practical route to realize 3D DZIM as an effective acoustic ``void space'' that offers unprecedented control over acoustic wave propagation.

The present paper aims to investigate the passivation capability and accelerated chloride-induced corrosion behaviour of a novel alloy steel (00Cr10MoV) and a conventional low-carbon steel (20MnSiV) in ordinary Portland cement (OPC) and alkali-activated slag (AAS) mortars. Both steels were embedded in mortars with intact mill scale. Compared with OPC mortar, AAS mortar resulted in the formation of less protective passive film for both 20MnSiV and 00Cr10MoV steels after passivation due to the presence of reducing sulphides. Despite this, the initial negative effect of AAS mortar on 20MnSiV steel can be well compensated by its denser interfacial microstructure after the occurrence of active corrosion induced by chlorides. As for 00Cr10MoV steel in AAS mortar, however, this compensating effect was less pronounced. Moreover, unexpected low passivation capability and corrosion resistance can be confirmed for 00Cr10MoV steel in both OPC and AAS mortars due to the presence of defective and Cr-depleted mill scale.

The distribution of corrosion products at the steel-concrete interface and the pattern of corrosion-induced cracks were characterized using X-ray computed tomography (X-CT) and environmental scanning electron microscopy (ESEM). A novel low-alloy reinforcing steel (LA steel) and the conventional low-carbon reinforcing steel (LC steel) embedded in concrete were subjected to impressed current accelerated corrosion. The results of Raman spectroscopy showed that non-protective lepidocrocite (γ-FeOOH) was the main corrosion products for LC steel, while stable and protective maghemite (γ-Fe2O3) and less crystallized feroxyhite (δ-FeOOH) and ferrihydrite (5Fe2O3·9H2O) were identified in the Cr-enriched inner rust layer of LA steel.

This study investigated the corrosion performance of reinforcing steels in concrete exposed to flowing 3.5 wt% NaCl solution for 4 years. Two kinds of steels were selected: low-carbon (LC) steel and low-alloy (LA) steel with alloying element Cr. Both steels were prepared with two surface conditions: as-received one (with mill scale) and pickled one (removal of the mill scale). The microstructure of the steel-concrete interface was observed to investigate the effect of steel type and surface condition on the corrosion pattern. The results reveal that the corrosion resistance and the corrosion pattern of steels were largely influenced by the feature of the mill scale.

Prior to natural carbonation, a protective passive film could be formed naturally on reinforcing steel when exposure to alkaline concrete environment. To evaluate the modification of passive films caused by carbonation on a corrosion-resistant steel containing Cr and Mo in alkaline concrete pore solution, the passivation capability and passive film composition were investigated in moderate carbonation (pH = 11) and severe carbonation (pH = 9) conditions using various electrochemical measurements (OCP, LPR, EIS, M − S and CV) and X-ray photoelectron spectroscopy (XPS). The results revealed that carbonation with various contents of carbonate/bicarbonate ions could exert different effects on naturally passivated corrosion-resistant steel by modification of the chemical composition of passive films, thus providing new insights into the field application of corrosion-resistant steels in carbonated concrete.

The influence of red mud (RM) on electrochemical behaviour, chemical composition, surface morphology and thickness of passive films naturally formed on low-carbon steel and 2304 stainless steel in alkaline concrete pore solutions was investigated using electrochemical measurements, XPS, AFM and SEM/EDS. Furthermore, chloride-induced pitting corrosion of passivated steels was characterized with and without RM. Results show that RM was detrimental to the passivity of steels by forming defective passive films with reduced thickness. Despite the formation of a less protective passive film on low-carbon steel, beneficial role of RM was highlighted in preventing chloride-induced depassivation and corrosion propagation.

In this study, the passivation and chloride-induced corrosion behavior of a novel duplex alloy steel (00Cr10MoV) and low-carbon (LC) steel in ordinary Portland cement (OPC) extract solution and alkali-activated slag (AAS) extract solution were evaluated by electrochemical measurements and corrosion morphology observation. Seawater corrosion-resistant 00Cr10MoV steel with the addition of alloying elements Cr and Mo was designed to be used in concrete structures exposed to the tidal zone. The results show that 00Cr10MoV steel exhibits significantly higher corrosion resistance than LC steel in OPC extract with chlorides due to the formation of a more protective passive film. However, the high corrosion resistance of 00Cr10MoV steel is less pronounced in AAS extract with chlorides. Accordingly, this duplex alloy steel is not recommended to be utilized in combination with AAS materials in marine environments.

In this study, two types of reinforcing steels (conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions (ordinary Portland cement (OPC) extract and alkali-activated slag (AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various NaCl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.

Waste shell stacking with odor and toxicity is a serious hazard to our living environment. To make effective use of the natural resources, the shell powder was applied as a filler of outdoor thermal insulation coatings. Sodium stearate (SS) was used to modify the properties of shell powder to reduce its agglomeration and to increase its compatibility with the emulsion. The oil absorption rate and the spectrum reflectance of the shell powder show that the optimized content of SS as a modifier is 1.5wt%. The total spectrum reflectance of the coating made with the shell powder that is modified at this optimum SS content is 9.33% higher than that without any modification. At the optimum SS content of 1.5wt%, the thermal insulation of the coatings is improved by 1.0°C for the cement mortar board and 1.6°C for the steel plate, respectively. The scouring resistance of the coating with the 1.5wt% SS-modified shell powder is three times that of the coating without modification.

In this study, the corrosion behavior of reinforcing steels in concrete under simultaneous flexural load and chlorides attack was studied by means of linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP) measurements. The influence of different stress ratios and exposure zones in marine environments on uniform corrosion resistance and pitting corrosion resistance of steels was analyzed. Moreover, different corrosion patterns were observed for the top part and bottom part of steels according to the casting direction. It was proposed that the tensile stress effect and the possible steel-concrete interfacial defects are mainly responsible for this difference.

To remove the rust on rebars and passivate the fresh surfaces, electrodes reversing electrolytic plasma processing (EPP) was proposed and conducted in a 10 wt.% Na2CO3 aqueous solution. The morphology and the composition of the surface were investigated by SEM and XPS. Experimental results show that the rust on the surface was removed effectively by cathode EPP, and a passive film containing Cr2O3 was achieved by the succeeding anode EPP treatment, by a simple operation of reversing the bias. The corrosion resistance was evaluated in a 3.5 wt.% NaCl aqueous solution using an electrochemical workstation. In comparison, the corrosion resistance was improved by the succeeding anode EPP treatment, which is evidenced by a positive shift of the open-circuit potential, an increase in the electrochemical impedance representing the inner layer by 76.8% and the decrease in the corrosion current density by 49.6%. This is an effective and environment-friendly technique to clean and passivate rebars and similar steel materials.

In many industrial applications, large-sized SiC components are increasingly desired through a conventional and pressureless brazing method. In present study, Ni-Si-Ti powder mixtures containing 0~10 wt.% Ti were used to braze SiC ceramics. Differential thermal analysis (DTA) and wetting tests were carried out to determine the appropriate joining temperature to be at 1450 °C. Microstructure, phase constituents, and mechanical strength of the prepared SiC joints were characterized. For a brazing composition without Ti addition, the interlayer primarily consists of NiSi and Ni3Si2 phases. With the addition of Ti, Ni49Ti14Si37 phase is newly formed within the interlayer besides the Ni-Si compounds. The bending strengths of SiC joints locate in 66~75 MPa as brazed at present conditions and the specimens generally fracture from the interface between alloy interlayer and SiC substrate.

The different corrosion behaviors of top part and bottom part of horizontal steel (with respect to casting direction) in mortars after exposure to 3.5% NaCl solution were investigated. The results of electrochemical impedance spectroscopy (EIS), X-ray computed tomography (X-CT) confirm non-destructively that the formation of loose and porous defects at the bottom steel-mortar interface results in low corrosion resistance of adjacent steel, whereas few distinct defects can be found at the top steel-mortar interface. It is confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) analysis that the defects at the steel-mortar interface play a dual negative role on the corrosion resistance of steel: the passive films gradually lose their stability due to the depletion of the protective Ca(OH) 2 layer in the defects, and chlorides are prone to accumulate in the defects which further attack the passive films of steel.

Ti 2 SnC powders are expected to find promising applications such as in electrical contacts while an efficient synthesis process has not been established yet. Highly phase-pure Ti 2 SnC powder was synthesized with Ti/Sn/C (molar ratio 2:1:1) powder mixture as starting materials by a pressureless synthesis process. Four primary morphologies of the synthesized Ti 2 SnC were found, namely near-spherical, flower-like, bowknot-like and triangular. The phase composition and microstructure of the materials in different morphologies were analyzed and discussed. The reaction route and formation mechanism of Ti 2 SnC was revealed according to the results of differential scanning calorimetry, X-ray diffraction and scanning electron microscopy.

Electrochemical impedance spectroscopy, cyclic potentiodynamic polarization measurements, and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy were used to investigate the influence of mill scale and rust layer on the passivation capability and chloride-induced corrosion behaviors of conventional low-carbon (LC) steel and low-alloy (LA) steel in simulated concrete pore solution. The results show that mill scale exerts different influences on the corrosion resistance of both steels at various electrochemical stages. We propose that the high long-term corrosion resistance of LA steel is mainly achieved through the synergistic effect of a gradually formed compact, adherent and well-distributed Cr-enriched inner rust layer and the physical barrier protection effect of mill scale.

A high-speed humidity sensor based on a nanostructured chiral sculptured thin film (CSTF) was fabricated and tested. The sensing principle is based on the shift of the central wavelength of the circular Bragg regime of the CSTF caused by adsorption and desorption of water vapor in the void regions of the CSTF. Spectral changes due to varying relative-humidity (RH) levels in the ambient environment were measured by a spectrometer. The CSTF sensor exhibited excellent reversibility and reproducibility from 40% to 100% RH. Moreover, the adsorption time of the sensor was measured to be as low as ∼140 ms, making it promising for many high-speed humidity-sensing applications.

This study focuses on the corrosion inhibition of molybdate on low-carbon (LC) steel and 10% Cr steel with high chloride contamination after the natural formation of passive films in alkaline concrete pore solution with various concentrations of molybdate. Chloride-induced corrosion could be inhibited for LC steel with molybdate, which is more pronounced with increasing concentration of molybdate and prolonged immersion time. However, detrimental impact is highlighted for molybdate on the corrosion resistance of 10% Cr steel. According to the formation and breakdown of passive films, the beneficial and detrimental impacts of molybdate on the corrosion resistance of steels are discussed.

The long-term corrosion resistance of reinforcing steel embedded in alkali-activated slag (AAS) mortar and ordinary Portland cement (OPC) mortar, when subjected to aggressive marine environments (chloride exposure and atmospheric exposure) for 54 months, was evaluated by electrochemical impedance spectroscopy. Corrosion morphology at the steel-mortar interface, composition of steel corrosion products and microstructure of mortar substrate were also investigated for AAS mortar in different aggressive environments. After long-term atmospheric exposure, AAS mortar provided unexpectedly lower corrosion resistance for steel compared with that for chloride exposure, which can be further evidenced by interfacial morphology and composition of steel corrosion products.

The influence of molybdate on the spontaneous passivation of the low-carbon steel and a novel 10% Cr steel in saturated Ca(OH)2 solution was investigated in this study. The results show that molybdate promotes spontaneous passivation of low-carbon steel at the early exposure time and its passivation capability can be further enhanced with increasing concentration of molybdate. Unexpectedly, when adding excessive concentration of molybdate, the detrimental effect on passivation is highlighted for 10% Cr steel after 10 days of passivation. According to these findings, the passivation mechanism of molybdate for steels in alkaline solution is proposed.

Corrosion inhibition of MoO42− for AA6061 aluminium alloy in simulated concrete pore solutions was investigated. Electrochemical methods were adopted to assess corrosion behaviour of AA6061 and surface characterizations were employed to obtain composition and morphology of oxide layers. Results show that low concentration (6 mM) of MoO42− cannot inhibit corrosion, while MoO42− of 10–30 mM effectively inhibits corrosion, which obeys Langmuir adsorption isotherm. MoO42− acts as an anodic inhibitor. 10 mM MoO42− exhibits an optimum corrosion inhibition efficiency. A uniform oxide layer consisting of Al-Ca-Mo(V)-O(H) complexes forms in moderate concentration of MoO42− (10 mM). Inhomogeneous oxide layer consisting of Al-Mg-Si-O(H) and Al-Ca-Mo(VI)-O(H) complexes forms in high concentration of MoO42− (30 mM).

The mechanism for spontaneous tin (Sn) whisker growth has been elusive for nearly 70 years. This study is to understand this phenomenon based on a new substrate system rather than traditional ones (Sn and its alloys). On ball-milled Ti/Sn/C samples, spontaneous growth of Sn whiskers different from general ones was observed. Ti2SnC grains were found to form during ball milling process, and the Sn atom planes of such Ti2SnC grains served as nucleation sites for Sn whiskers formation. The findings and the new mechanism proposed herein might renovate the research of spontaneous growth of metal whiskers, and are of significance to uncovering the phenomenon which resisted interpretation.

The corrosion performance of a fine-grained (FG) rebar designed for high-speed railway construction was investigated and compared with that of a conventional low-carbon (LC) rebar. Electrochemical measurements and microstructure characterisation were conducted on two investigated rebars in mortars with and without pre-mixed chlorides. The results indicate that FG rebar exhibits improved passive film compared to LC rebar in the absence of pre-mixed chlorides. However, after 24 wetting–drying cycles in 3.5 wt.% NaCl solution, the corrosion resistance of FG rebar is slightly lower than that of LC rebar, both with and without pre-mixed chlorides. It is proposed that the higher grain boundary density with more dispersive detrimental manganese sulphide (MnS) inclusions may be primarily responsible for the low corrosion resistance of FG rebar in chloride-containing environments.