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Aluminum hydroxide is an effective defluoridation adsorbent; however, the poor defluoridation performance limits its wide application. In this work, amorphous and crystalline AlOOH adsorbents are synthesized through hydrolysis of Al salts, and their defluoridation performances are evaluated in terms of adsorption capacity and rate, sensitivity to pH value, and water quality after defluoridation. The defluoridation performance of AlOOH is closely related to the hydrolysis pH value, but hardly to the type of Al salts. The adsorbent can remove >95% fluoride in the first 2 min and reach adsorption equilibrium within 2 h, and the maximum defluoridation capacity is 41.9 mg/g. Furthermore, the adsorbent exhibits an excellent defluoridation efficiency at a wide pH range of 4.5–10.5. After fluoride removal, the adsorbents prepared at pH values of 6 and 7 exhibit low residual Al concentration. The Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm that the fluoride removal mechanism is the ligand exchange between fluoride and hydroxyl groups. The excellent defluoridation capacity and low residual Al demonstrate that AlOOH is a potential adsorbent for fluoride separation from water.

In this work, for the first time, high-activity filtrates were prepared by the reaction of aluminum (Al) powder with hydrogen peroxide (H2O2) in acidic solution and then filtration, which were used to degrade various organic pollutants such as phenol, methyl orange, and bisphenol A. It was found that the filtrates can effectively degrade and mineralize various organic pollutants and have a high efficiency comparable to their parent Al + acid + H2O2 suspensions. The filtrates can keep their high activity for several weeks under ambient conditions, and the activity depends on their initial pH value. At a pH value of ∼3.5, the reaction activity of filtrates is the best. Electron spin resonance spectroscopy (ESR) analyses indicated that there is a large quantity of stable hydroxyl radicals (OH•) existing in the filtrates, which are responsible for the removal of organic pollutants. Furthermore, the related factors are discussed.

In this work, pristine aluminum (Al) powder was soaked in deionized water for a time period and then it was dried and heat-treated at 400 °C such that a layer of fine Al2O3 grains covered the Al particle surfaces, forming oxide modified Al powder (OM-Al). It was found that OM-Al greatly enhanced the efficiency in removing methyl orange (M-orange) and methyl blue (M-blue) in aqueous solution. The time to completely degrade M-orange and M-blue by OM-Al is about one third of that by pristine Al powder, and decreases with increasing dosage of OM-Al. The enhancement in dye removal rate by oxide modification is much better than that with ultrasonic assistance, especially for M-blue. LC/MS spectrum analyses revealed that large dye molecules are broken into small biodegradable organic molecules after reaction with OM-Al. It is deduced that the promotion of fine Al2O3 on the hydration process of Al surface passive oxide film is the main mechanism responsible for the enhancement of dye removal by OM-Al. Furthermore, OM-Al has a good recyclability and 80% of M-orange and M-blue can be removed even when it was reused for up to three cycles. These results indicate that oxide modification is an effective way to activate Al for the removal of organic dyes.

Excessive intake of fluoride can lead to a series of fluorosis-based diseases, and how to remove the excess fluoride from water is an urgent issue worldwide. Among various defluoridation methods, adsorption is a well-studied and widely used technology due to its simple design, convenient operation and low cost. In this review, we comprehensively summarized and evaluated different kinds of defluoridation adsorbents developed in the last decade, including adsorbents derived from natural minerals, industrial wastes and biomass, metal oxide and hydroxide adsorbents, and carbon-based adsorbents. The preparation methods of adsorbents and the strategies to enhance their defluoridation performance are highlighted. It is found that regulating and controlling the crystalline phases, microstructures and active sites and incorporating other materials to form composites are effective methods to enhance the defluoridation performances of adsorbents. The water quality after defluoridation and related influencing factors are discussed in detail. Moreover, the fluoride removal mechanisms of different adsorbents are outlined and analyzed. Based on the review, the advantages and disadvantages of different adsorbents, as well as the prospects and challenges are also discussed.

Hydrogen generation via Al‐water reaction promoted by special catalysts has great potential, which can provide hydrogen source for portable fuel cells. In this work, we use wet chemical reduction method to prepare a high‐activity Fe/AlOOH composite with better stability and demonstrate its usage as a catalyst for Al‐water reaction. It is found that Fe/AlOOH composite not only significantly promotes the Al‐water reaction but also shortens the induction time. The catalytic activity of Fe/AlOOH directly correlated with its active area, which, in turn, is closely related to the AlOOH:Fe molar ratio. In addition, increasing the weight content of Fe/AlOOH, reaction temperature, and the Al:water ratio improve the hydrogen generation performance of Al‐water reaction. Mechanism analyses show that water dissociation on AlOOH surface and galvanic microinteractions between Fe and Al promotes the hydration of surface passivating oxide film of Al particle, which improves the Al‐water reaction dynamics. The present work provides a new way to produce hydrogen from Al‐water reaction for portable devices.

Al-water reaction promoted by catalysts is a promising hydrogen generation technology. In this work, a high-activity M-B/γ-Al2O3 (M = Co, Ni) catalyst is prepared by wet chemical reduction method. It is found that M-B/γ-Al2O3 catalyst significantly promotes the Al-water reaction and decreases the induction time. When the molar ratio of γ-Al2O3 to Co-M in Co–B/γ-Al2O3 catalyst is 1:1, the induction time is only 0.43 h. The catalytic activity of M-B/γ-Al2O3 is proportional to its active area. SEM analyses show that M-B particles are dispersed on γ-Al2O3 surface, which reduces the agglomeration of M-B and increases the active surface of M-B/γ-Al2O3, leading to a high catalytic activity. A possible mechanism is proposed, which shows that the dissociation of water molecules on γ-Al2O3 surface and the microgalvanic interaction between M-B and Al can promote the hydration process of passive oxide film on Al particle surface, speeding up the Al-water reaction.

Arc discharge method with Fe catalyst was used to prepare single-wall carbon nanotubes (SWCNTs) and there are an amount of iron nanoparticles formed tightly on SWCNTs. Nanometer iron oxide anchored to SWCNT composite (AO-Fe-SWCNTs) was obtained in situ by oxidizing the above as-grown SWCNTs (As-Fe-SWCNTs) in air at 375 °C. AO-Fe-SWCNTs exhibited an excellent performance of adsorption, Fenton and photo-Fenton degradation of methyl blue (MB) and methyl orange (MO) in aqueous solutions. Adsorption of MB and MO by AO-Fe-SWCNTs could reach equilibrium within 10 min and its maximum adsorption capacity for MB and MO was up to 256.69 mg g−1 and 93.58 mg g−1, respectively. MB could almost be decomposed within 10 min depending on their concentration using AO-Fe-SWCNTs as catalyst under the assistance of H2O2. UV–Vis light irradiation further speeded up the above Fenton reaction and the degradation of MB and MO in solutions. It was revealed that the small sizes of iron oxides (several nanometers) and their good dispersion on SWCNTs are the main reason responsible for the good property of AO-Fe-SWCNTs. Furthermore, iron oxides-SWCNTs heterojunctions probably improve electron-hole separation during irradiation and promote the generation of hydroxyl radicals. The present study indicates that AO-Fe-SWCNTs with firm web structure are a promising material for adsorption and degradation of organic dyes.

Single-wall carbon nanotubes (SWCNTs) were prepared by arc discharge evaporation of a carbon electrode containing Fe catalyst so that there are an amount of iron nanoparticles attached tightly on SWCNTs. The iron oxide nanoparticle coated SWCNT composite was prepared in situ by oxidizing the above as-grown SWCNTs in air at 350°C, which was used as an adsorbent for As5+ removal from water. It was found that the maximum As5+ adsorption capacity of the composite was 42.30 mg g−1 at pH 8 and 49.65 mg g−1 at pH 4, respectively. The kinetics data were best fitted with a pseudo-second order, thus suggesting chemical adsorption on the surface and pores of iron oxide nanoparticles. The adsorption isotherm obtained at pH 8 was best fitted to the Freundlich model, therefore a non-ideal adsorption on heterogeneous surfaces for As5+ ions on iron oxide nanoparticles was proposed. The firm web structure with high adsorption capacity makes the composite a promising adsorbent for arsenic removal in contaminated water.

Bromate, a toxic by-product of bromide-containing drinking water after disinfecting with ozone, has attracted much attention in the past two decades. Traditional methods to activate zero-valent metals for reducing bromate are to eliminate their surface oxide layer by acid washing. In this work, for the first time, zero-valent Al (ZVAl) was surface treated by the following procedures including soaking, soaking and freeze-drying, soaking and heat-treating, and γ-Al2O3 covering Al particle surfaces (GCAP). It was found that all of above surface treated ZVAls have an obvious high efficiency for bromate reduction relative to pristine ZVAl. The bromate reduction rate is GCAP > soaking Al > freeze-drying Al > soaking and heat-treating Al > pristine Al, and using GCAP just 30 min is taken to completely reduce bromate to bromide in neutral solution. Mechanism analyses revealed that Al surface treating or covered by fine γ-Al2O3 phase can promote the hydration and breakage of Al surface passive oxide layer, resulting in a fast contact of inner Al with outside ions, leading to a high reduction rate of bromate in neutral solution. XPS analyses indicated that there are no bromate or bromide ions adsorbed on Al particle surfaces, implying that there is a high direct donating efficiency of electrons from inner Al to bromate ions in solution. Furthermore, GCAP has a good reusability and >90% bromate can be reduced even it was reused up to 4 cycles.

Al powder was stored in saturated water vapor, oxygen, nitrogen and drying air separately for a time period of up to ∼six months, the degradation behavior of Al activity was characterized by the reaction of Al with water. It was found that water vapor decreased the induction time for the beginning of Al–water reaction and reduced the total hydrogen generation per unit weight of Al, while oxygen increased the induction time and retarded the Al–water reaction. In contrast, the effect of nitrogen and drying air on Al activity was weak. The mechanism analyses indicated that water vapor promoted the hydration of the Al surface passive oxide film and sped up the reaction of Al with water, while oxygen thickened the passive oxide film of the Al surface and prolonged its hydration process. These results imply that water vapor rather than oxygen is responsible for the degradation of Al activity during storage in the atmospheric environment.

The kinetics of the Al–water reaction promoted by an ultrasonically prepared Al(OH)3 suspension is investigated. It is found that the induction time for the beginning of the Al–water reaction decreases and the reaction rate increases with increasing suspension concentration, volume, and temperature, because the Al–water reaction is exothermic. When the weight ratio of Al to water increases to 1:15, there is almost no induction time, and more than 80% of Al in the Al(OH)3 suspension is consumed within 40 min, which is comparable to the behavior of Al in NaOH solution. A collision model based on Brownian motion is proposed to analyze the reaction process, which shows that the contact between Al and Al(OH)3 particles and the reaction heat are two key factors that control the reaction progress.

Zero-valent aluminum has attracted considerable attention in degradation of organic contaminants and reduction of heavy metal ions due to its very low redox potential (E0(Al3+/Al0) = −1.662 V). Usually there is a passive oxide film on Al surface, inhibiting its electron transfer and leading to low reaction efficiency. In this work, metal Al surface was modified by loose fine Al2O3 (SM-Al) using a procedure of soaking Al powder in water for a time period and then heat-treating in vacuum. It was found that surface modification remarkably enhanced the reaction efficiency of zero-valent Al in reduction of Cr(VI) to Cr(III) ions in aqueous solution. The longer the soaking time of Al powder in water is, the higher the efficiency in removing Cr(VI) is. The effects of Al particle size and dosage, initial Cr(VI) concentration and reaction temperature on Cr(VI) removal were investigated as well. XPS analyses revealed that the decrease in thickness of Al surface passive oxide films and the promotion of surface covered loose Al2O3 phases on hydration of passive oxide films are two main reasons responsible for the rapid removal of Cr(VI) by SM-Al. Meanwhile, SM-Al exhibited an excellent recyclability and the reused SM-Al has a very fast reaction rate relative to as-prepared SM-Al, 80% of Cr(VI) can be removed even it was reused up to five cycles. The present study provides a new route to activate Al in removal of contaminants in aqueous solution.

The magnitude of the acidity of the oxyluciferin in water in the ground and excited state is investigated, and it is found for the first time using computational approach that the enol group of the phenol-enol species is the most acidic in the ground state, but the deprotonation of the phenol of the phenol-keto form is the most favored in the excited state. The relative order of the acidity among the hydroxyl groups in the oxyluciferin is attributed to the sequence of the O-H bond lengths in the enol and phenol group of the phenol-enol form, and the phenol group of the phenol-keto species. The mechanism of determining the dominant emissive species in the excited state is proposed, and the dependence of emission light colors on the photoexcitation energy is elucidated by the high relative concentration of six chemical forms in the ground state and the absorption efficiency.

Previous works indicated that aluminum hydroxide could act as catalyst to assist the hydrolysis reaction of Al, but the catalytic activity of commercial aluminum hydroxide was very poor. In the present research, an AlOOH catalyst with high activity and excellent stability is synthesized using hydrothermal method, and the catalytic effect of this AlOOH catalyst on Al hydrolysis is researched systematically. The results show that AlOOH not only significantly shortens the induction time but also accelerates Al hydrolysis, and the catalytic activity of AlOOH depends on its preparation conditions. The SEM and XRD analyses reveal that the hydrothermal temperature and hydrothermal time have great influence on the crystallinity and grain size of AlOOH, which in turn impact the catalytic activity of AlOOH. The AlOOH catalyst prepared at the hydrothermal temperature of 165 °C for 24 h has the best activity, and it shortens the induction time from 5.00 h to 0.58 h. This work provides a novel and feasible way to generate hydrogen for portable devices.

Fe-based metal-organic framework MIL-88A microrods were synthesized by hydrothermal method, which were used to adsorb As(V) in water for the first time. The experimental results indicated that MIL-88A has a very fast adsorption rate towards arsenic in water. The kinetic and isothermal data for arsenic removal were better fitted to the pseudo-second-order kinetic model and Langmuir model, respectively, implying a chemical and monolayer adsorption for As(V) on MIL-88A microrods. Two rate-controlling processes during adsorption were revealed by the intraparticle diffusion model. The maximum adsorption capacity of MIL-88A reached 145 mg g−1, higher than those of Fe-based MIL adsorbents reported previously, which probably originates from its unique microstructure with abundant OH− groups and an unusual large swelling towards water. These show that Fe-based MIL-88A is a good candidate for arsenic removal.

Here we report the electrochemical performance and long-term stability of La 0.8 Sr 0.2 CoO 3−δ (LSC), La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF) and SmBa 0.5 Sr 0.5 Co 2.0 O 5+δ (SBSC) infiltrated (ZrO 2 ) 0.89 (Sc 2 O 3 ) 0.1 (CeO 2 ) 0.01 (SSZ) cathodes at low temperatures. At 700 °C, the initial polarization resistance of the infiltrated cathodes increased in following order: SBSC-SSZ (0.054 Ω cm 2 ) 2 ) 2 ). After the heat treatment at 620 °C (820–1400 h), the degradation rate of the polarization resistance of LSC-SSZ, LSCF-SSZ and SBSC-SSZ cathode was 179%, 53.9% and 93.1% kh −1 , respectively, while that of the ohmic resistance was 10.6%, 8.86% and 40.9% kh −1 , respectively. X-ray diffraction (XRD) and scanning electron microscope (SEM) observation showed that the degradation was mainly caused by the morphological change of the infiltrated particles while the solid reactions between the infiltrated materials and SSZ backbones were not observed.

Previous works showed that oxide-modified Al powder could react with water and generate hydrogen under ambient condition. The activation mechanism was believed to be the weakening of passive oxide film on Al particle surface due to all its constituents transforming into loose γ-Al 2 O 3 phase during the heat-treatment. In this work, a model experiment was performed, in which pure Al powder and the mixture of Al + γ-Al 2 O 3 powders were heat-treated in vacuum from room temperature to 600 °C. It was found that the induction time for the reaction of heat-treated pure Al powder with water decreased obviously when the heat-treating temperature was above 200 °C. However, the reaction induction time of the mixture of Al + γ-Al 2 O 3 powders was always considerably shorter than that of pure Al powder even if no heat-treatment was done. This implies that the catalytic effect of external oxides on the hydration of passive oxide film on Al particle surface plays a dominant role in promoting the Al-water reaction and hydrogen-generation. This clarification is also helpful in understanding the corrosion behavior of metal Al in different environment.

Different Al(OH)3 powders were used as adsorbents for fluoride removal from water. The results showed that the defluoridation performance of ultrasonically prepared Al(OH)3 (UAH) is much better than that of commercially available Al(OH)3 and is comparable to that of activated alumina, because the ultrasonic waves effectively break the agglomerates in the suspension so that the UAH particles are fine and have a beneficial phase constituent. Furthermore, the residual aluminum concentration in aqueous solution after defluoridation by Al(OH)3 was found to be one order of magnitude lower than that obtained with activated alumina which is below the World Health Organization (WHO) guideline for aluminum (0.2 mg L−1) in drinking water. The defluoridation dynamics and mechanism for UAH are discussed in detail.

The Tb1−xYxMn2Ge2 series (x = 0, 0.1, 0.2) compounds are found to exhibit two magnetic phase transitions with decreasing temperature: from the paramagnetic state to the antiferromagnetic interlayer state at TNinter and from an antiferromagnetic interlayer structure to a collinear ferrimagnetic interlayer structure at TCinter. Compared with the slight change of TNinter (409 K, 410 K and 417 K for x = 0, 0.1 and 0.2 respectively), the replacement of Y for Tb leads to a significant decrease in TCinter from 97.5 K for x = 0 to 74.6 K for x = 0.2. The variation in TCinter can be ascribed to the combination of two effects: (1) chemical pressure and (2) magnetic dilution effect by Y substitution for Tb. Besides, a strong anisotropic magnet-volume effect has been detected around TCinter in all compounds with Δa/a = 0.125%, 0.124% and 0.130% for x = 0, 0.1 and 0.2, respectively while no obvious effect is detected along the c-axis. The maximum magnetic entropy change were found to be −ΔSmax = 9.1 J kg−1 K−1, 11.9 J kg−1 K−1 and 6.3 J kg−1 K−1 with a field change from 0 T to 5 T for x = 0, 0.1, 0.2 respectively.

A high-activity Al(OH) 3 suspension is prepared by the reaction of Al with water using an ultrasonic procedure. The above Al(OH) 3 suspension could considerably promote the Al-water reaction and hydrogen-generation under ambient condition. This Al(OH) 3 suspension has a good stability in air and its activity increases with decreasing the particle sizes of Al powder to prepare it. The mechanism analyses reveal that the Al(OH) 3 particles in ultrasonically prepared Al(OH) 3 suspensions are very fine, which could effectively dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces, speeding up the Al-water reaction. As the present Al(OH) 3 suspension is chemically neutral and there is no special treatment for Al powder, the present method provides a viable way to generate hydrogen for portable application.

The effect of initial gas pressure on Al–water reaction was investigated systematically. It was found that there is a non-monotonic relationship between the initial pressure and the induction time for the beginning of Al–water reaction. The induction time decreases with decreasing the initial pressure at the first stage from atmospheric pressure, then reaches a minimum, and finally increases with further decreasing the initial pressure. The mechanism analyses revealed that the special vacuum pressure corresponding to the minimum induction time is close to the saturated vapor pressure, below which probably there are some vapor bubbles passing or adsorbing on Al particle surfaces due to boiling, retarding the hydration process of Al surface oxide film and increasing the reaction induction time. The present results imply that a suitable initial gas pressure should be chosen for Al–water reaction to generate hydrogen.

The Al–water reaction has attracted considerable attention in the past few years, because it is an economically viable way to supply hydrogen for portable and kW-grade fuel cells. The water type is found to have a significant impact on Al–water reaction. In this work, the effect of trace species in water on Al–water reaction is investigated systematically. It is found that the trace organic acids originated from the decay of botanies and animals in nature and trace F − ions, rather than other cations and anions, play a key role in the reaction dynamics of Al with water. The mechanism analyses reveal that the organic acids and F − ions form complexes with aluminol groups on Al particle surfaces to impede the hydration process of Al surface oxide film and retard the reaction of Al with water. The present results imply that a suitable water should be chosen for the Al–water reaction to generate hydrogen. At the same time, the organic acids and trace F − ions could be used as the agents to prevent undesirable Al–water reaction.

SUMMARY Hydrogen generation by the reaction of pure Al powder in water with the addition of Al(OH)3, γ-Al2O3, α-Al2O3, or TiO2 at mild temperatures was investigated. It was found that the reaction of Al with water is promoted and the reaction induction time decreases greatly by the above hydroxide and oxides. X-ray diffraction analyses revealed that the hydroxide and oxide phases have no any change during the Al–water reaction, indicating that they are just as catalysts to assist the reaction of Al with water. A possible mechanism was proposed, which shows that hydroxide and oxides could dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces. Copyright © 2013 John Wiley & Sons, Ltd.

Hydrogen-generation by the reaction of pure Al powder with deionized water under ambient condition was investigated systematically. The results showed that both nano- and micro-sized Al powders could react with water and generate hydrogen under ambient pressure at mild temperature. The nanometer Al powder almost completely reacted with water at 20 °C, most of micrometer Al powders could react with water at a temperature of >40 °C, implying that small-sized Al powder could directly be able to generate hydrogen without any activation or modification. A shrinking core model was used to analyze the reaction progress, indicating that the Al-water reaction was controlled by the surface chemical mechanism at the initial stage, and then by the H2O molecule diffusion in the byproduct layer afterwards. The activation energy was calculated, which increased from 64.2 kJ/mol to 88.7 kJ/mol with increasing the Al particle sizes from 98.38 nm to 24.94 μm. X-ray analyses revealed that the reaction byproducts are bayerite, boehmite or a mixture of them, depending on the reaction temperature. The reaction dynamics mechanisms are discussed.

Four different-sized pure Al powders were used to react with distilled water at 55°C in a low vacuum, and their effect on the reaction dynamics and hydrogen-generation rate was investigated. It was found that the Al particle sizes not only affect the hydrogen-generation rate but also affect the induction time for the beginning of the reaction. The induction time strongly depends on the Al particle sizes, which obviously increased with the Al particle sizes. The hydrogen-generation rate increased with the decreasing Al particle sizes, because the small-sized Al powder has a high surface area. Mechanism analyses revealed that the long induction time for the large Al particles probably originates from a long time for their H diffusion to reach a saturation concentration in the bulk Al metal. The reaction rate of Al with water could be qualitatively explained by a shrinking core model.

TiO2 films were prepared by infiltrating a titanium (IV) butoxide solution to the porous structures of glass and rutile TiO2, respectively, then dried and calcined at a moderate temperature of 550°C. Well-characterized porous nanometer TiO2 films were formed. Nanometer TiO2 film on glass matrix has an anatase phase, while that on rutile TiO2 has a rutile phase. These indicate that the phase formation of nanometer TiO2 could be tailored by the different matrices.

Unlike traditional batteries, small fuel cells have a high energy density and can work uninterruptedly, being better energy suppliers for portable devices. Such devices require an economically viable fuel. Recent findings showed that metal Al particle surfaces could be modified by fine ceramic oxide grains through a ceramic processing procedure, and the modified Al powder could continuously react with pure water and generate hydrogen under ambient conditions. The reaction of Al with water produces as much as 3.7–4.8 wt% hydrogen, and the reaction byproducts are chemically neutral. Metal Al is cheap and hydrogen generation from the reaction between surface-modified Al particles and water is a simple process. These features make this new process a cost-efficient way of generating hydrogen for small fuel cells in comparison with other portable hydrogen-generation materials and technologies. In this paper, the state of the art of portable hydrogen-generation materials is surveyed, and the ceramic oxide-modified Al–hydrogen technology and its potential are highlighted.

ZrO 2 ceramics usually have nonuniform microstructures due to the agglomeration of fine ZrO 2 powders. In this paper, the thermal conductivity of porous ZrO 2 ceramics with different microstructures was investigated by the laser-flash method. It was found that the thermal conductivity of porous ZrO 2 ceramics with uniform microstructure was clearly lower than that of ceramics with nonuniform microstructure. Scanning electron microscopy observations showed that porous ceramics with nonuniform microstructures have wider pore and grain size distributions, relative to those with uniform microstructures. Theoretical analyses were done to model the thermal conductivity of porous ceramics using an effective medium approach. These analyses revealed that matrix grain size distribution has a significant impact on the thermal conductivity of porous ceramics, while the effect of pore size distribution is negligible.

Previous experiments showed that γ-Al2O3-modified Al powder could continuously react with water and generate hydrogen at room temperature under atmospheric pressure. In this work, a possible physicochemical mechanism is proposed. It reveals that a passive oxide film on Al particle surfaces is hydrated in water. OH− ions are the main mobile species in the hydrated oxide film. When the hydrated front meets the metal Al surface, OH− ions react with Al and release H2. Because of the limited H-soluble capacity in small Al particles and the low permeability of the hydrated oxide film toward H+ species, H2 molecules accumulate and form small H2 gas bubbles at the Al:Al2O3 interface. When the reaction equilibrium pressure in H2 bubbles exceeds a critical gas pressure that the hydrated oxide film can sustain, the film on the Al particle surfaces breaks and the reaction of Al with water continues. As the surface oxide layer on modified Al particles has a lower tensile strength, the critical gas pressure in H2 bubbles is lower so that under an ambient condition, the reaction of modified Al particles with water is continuous. The proposed mechanism was further confirmed by a new experiment showing that the as-received Al powder could continuously react with water at temperatures above 40°C and under low vacuum, because the vacuum makes the critical gas pressure in H2 bubbles decrease as well.

A unidirectional porous glass structure coated with a nanometer TiO2 thin film on pore walls was successfully fabricated by a two-step process. Firstly, a water-based slurry of sheet glass was frozen while controlling the growth direction of ice crystals, and then sublimation of the ice under vacuum formed the green body. The green body was subsequently sintered to produce porous glass with unidirectional pores. Secondly, the sintered porous glass was infiltrated by a titanium (IV) butoxide solution, and then dried and calcined at a moderate temperature to generate a nanometer TiO2 film on pore walls. The present porous glass with nanometer TiO2 has more total surface area than the TiO2 film on glass plates, which is believed to be more effective in the phtotocatalysis application for air or water purification.

The firefly chromophore, oxyluciferin, is in the pocket of the firefly luciferase and is surrounded by the side-chains of some amino acid residues. The charged residues produce the local electrostatic field (LEF) around the oxyluciferin. The emitted wavelengths and intensities of the oxyluciferin and its heterocyclic analogs under the LEF are examined. The common overlapping volumes of the HOMO and LUMO explain why the oscillator strengths vary under the LEF. Three average Ex change rates of the first excited energy are introduced to measure what luciferins are more sensitive to the LEF. The first excited energies and intensities in two enzymatic-like microenvironments are simulated via the LEF. The oscillator strengths and the net electric charges of the O6' and the O4 are applied to explain the experimental bioluminescent intensities.

Porous Al2O3/Al catalyst supports were fabricated using a mixture of Al(OH)3 and Al powders, followed by pressureless sintering at a temperature of 600 °C in vacuum. Different pressures were used to prepare green compacts. High compaction pressure led to a high surface area and good mechanical and electrical properties for the sintered specimens. However, when the Al content in the sintered specimen exceeded a definite value, high compaction pressure decreased the surface area abruptly. Scanning electron microscopy observations revealed that agglomeration in the starting mixture has a significant effect on the microstructure of the sintered specimens. High compaction pressure greatly eliminated the agglomerates and led to a uniform microstructure for the sintered specimens. However, when the Al content in the starting mixture was too high, Al particles in the compacts prepared by the high pressure were largely sintered due to the high compact density so that most of the pores were closed. The present study indicates that a suitable compaction pressure is critical to obtaining superior Al2O3/Al supports.

Long crack R-curve of a porous Si3N4 with aligned fibrous grains was investigated, using a chevron-notched beam technique. A crack was constrained to propagate normal to the grain alignment. The crack growth resistance of aligned porous Si3N4 was much larger compared with that of dense Si3N4 ceramics. Microstructure observations showed that pullouts of fibrous grains in aligned porous Si3N4 markedly increased during crack propagation relative to those of dense Si3N4, due to the existence of pores. The efficient grain pullouts in porous Si3N4 increased the bridging stress at the crack wake.

Previous experimental results showed that a ceramic/superplastic laminate exhibited multiple cracking in ceramic layers during a three-point bending test. In this work, a model analysis has been developed based on bending theory. It reveals that there are two basic processes that occur after a ceramic layer fractures: one is a relaxation process of the residual stress in the ceramic layer, due to the confinement by the superplastic layers; the other is a shear process of superplastic flow, which originates from the difference in strain rate between the fractured and unbroken ceramic layers. The total stress in an as-fractured ceramic layer is the sum of the residual stress and a shear-accumulated stress, depending on time. When the total stress at a critical distance from the fractured surface exceeds the fracture strength of a ceramic layer, new cracking occurs. There is a critical roller speed below which no multiple cracking occurs, depending on specimen dimensions and material properties. The number of multicracks in one ceramic layer decreases with the progress of the fracture in the laminate, due to the decrease in shear-accumulated stress. The theoretical predications are in good agreement with the experimental results. Moreover, the variations in fracture energy of the laminate due to the multiple cracking are discussed in detail.

A crack-tip blunting mechanism in porous ceramics was identified in this study. The reinforcement by crack tip blunting in porous ceramics was analyzed quantitatively, based on a grain fracture model. The investigation revealed that the crack tip blunting increases the fracture toughness of porous ceramics, depending on pore morphology and grain arrangement. The theoretical predictions were in good agreement with the experimental results.

Effects of trace rare earth impurities on grain boundary bonding in Al 2 O 3 -5 vol.% SiC composites were investigated. It was found that doping of 800 ppm different rare-earth impurities (Y 3+ , Nd 3+ and La 3+ ) led to a fracture-mode change from transgranular in dopant-free composites to intergranular in rare-earth doped composites. The fracture toughness of rare-earth doped composites was higher than that of the composites without dopants, due to an increased crack deflection in doped composites caused by the intergranular fracture. Boundary chemistry analyses showed that rare-earth impurities and Si 4+ ions both segregated at the Al 2 O 3 grain boundaries and resulted in a weak grain boundary bonding.

Direct observation on fatigue crack growth behavior in SiC (SCS-6) fiber-reinforced Ti-15-3 alloy matrix composite subjected to a constant tension–tension loading mode was performed by scanning electron microscope using a single edge-notched specimen in vacuum at room temperature and 550 °C. The fatigue crack growth rate at 550 °C was lower than that at room temperature, and the difference between the fatigue crack growth rates at room temperature and 550 °C increased with increasing fatigue cycles. The crack opening displacement at 550 °C was smaller than that at room temperature when the crack length exceeded a definite value, though the interface friction stress between the fiber and matrix at elevated temperature was much smaller than that at room temperature. The above results were explained qualitatively by a residual stress mechanism at the crack front and the crack closure behavior at crack wake, which could be produced by matrix creep asymmetry in tension and compression at elevated temperature during each fatigue cycle.

Al2O3-5 vol% SiC particle composites doped with 800 ppm rare-earth impurities (Y3+, Nd3+, and La3+) were fabricated by hot-pressing at a temperature of 1550°C. Doping of rare-earth impurities in Al2O3-SiC composites led to a fracture- mode change from transgranular in dopant-free composites to intergranular in rare-earth-doped composites. The fracture mode change obviously increased the crack deflection so that the fracture toughness of rare-earth-doped composites was higher than that of the composites without dopants, especially for the Nd3+- and La3+-doped composites. It was found that the fracture-mode change originated from a weak grain-boundary bonding caused by co-segregation of the rare-earth dopants and Si4+ ions dissolved from the SiC particle surfaces.