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The contamination of soils by polycyclic aromatic hydrocarbons (PAHs) is a widespread environmental problem and the remediation of PAHs from these areas has been a major concern. The effectiveness of many in situ bioremediation systems may be constrained by low contaminant bioavailability due to limited aqueous solubility or a large magnitude of sorption. The objective of this research was to evaluate the effect of methyl-ß-cyclodextrin (MCD) on bioaugmentation by Paracoccus sp. strain HPD-2 of an aged PAH-contaminated soil. When 10% (W/W) MCD amendment was combined with bioaugmentation by the PAH-degrading bacterium Paracoccus sp. strain HPD-2, the percentage degradation of total PAHs was significantly enhanced up to 34.8%. Higher counts of culturable PAH-degrading bacteria and higher soil dehydrogenase and soil polyphenol oxidase activities were observed in 10% (W/W) MCD-assisted bioaugmentation soil. This MCD-assisted bioaugmentation strategy showed significant increases (p < 0.05) in the average well color development (AWCD) obtained by the BIOLOG Eco plate assay, Shannon-Weaver index (H) and Simpson index (k) compared with the controls, implying that this strategy at least partially restored the microbiological functioning of the PAH-contaminated soil. The results suggest that MCD-aided bioaugmentation by Paracoccus sp. strain HPD-2 may be a promising practical bioremediation strategy for aged PAH-contaminated soils. [ABSTRACT FROM AUTHOR]

Abstract: The dense ceramic part was prepared firstly using silazane with filler. The composition, structure and ceramic yield of silazane were characterized by elemental analysis, nuclear magnetic resonance (NMR), IR and thermogravimetric analysis (TGA). The ceramic yield was 63wt% upon pyrolysis at 1000°C under N2 atmosphere. The fabrication of ceramic part involved cross-linking of the silazane with metallic fillers (Ti particles) followed by a polymer-to-ceramic transformation step. Near net shape manufacturing of polymer derived ceramics could be achieved. The strength of ceramic parts could achieve 450±15MPa and scanning electron microscopy (SEM) observation showed that there was very low porosity on the fracture surface of pyrolysed body. [Copyright &y& Elsevier]

Alumina/titanium silicon carbide (Al2O3–Ti3SiC2) composites and its functionally graded materials (FGMs) were fabricated by a powder metallurgy processes and their microstructure and properties were investigated, respectively. The experimental results showed that the Vickers hardness of composites decreased with increasing Ti3SiC2 content while the fracture toughness and strength exhibited the opposite trend. Minimum Vickers hardness (4 GPa), maximum strength (598 MPa) and maximum toughness (11.24 MPa m1/2) were reached in the pure Ti3SiC2 material. Strength and hardness of FGMs were evaluated. Observation using an scanning electron microscope (SEM) indicated that the presence of Ti3SiC2 of FGMs inhibited the growth of alumina grains through a pinning mechanism. The study shows that the combination of the layered Ti3SiC2 structure and the fine alumina grains can result in a Al2O3–Ti3SiC2 composites possessing a high toughness and low Vickers hardness without a sacrifice in the strength. [Copyright &y& Elsevier]

Abstract: Si3N4–TiN composite powders were obtained by in situ pyrolysis of polytitanosilazane. Dense Si3N4–TiN composites were prepared by hot-pressing at 1800°C under 20MPa for 2h without sintering additive. Crystallization of amorphous PTSZ powders occurred between 1400 and 1500°C with major phases, α-Si3N4, β-Si3N4, and small amount of phase TiN. Mechanical properties and microstructure of Si3N4–TiN composites were characterized. The results showed that the mechanical strength was 620MPa, the fracture toughness was 7.8MPam1/2 and the Vickers hardness was 8.5GPa. SEM analysis indicated that Si3N4–TiN composite possessed excellent fracture toughness because TiN grains produced by in situ pyrolysis were well dispersed in Si3N4 matrix. [Copyright &y& Elsevier]

Abstract: Titanium silicon carbide (Ti3SiC2) ceramic was synthesized by in-situ reaction of metal titanium and polycarbosilane. Reaction mechanisms which lead to the formation of Ti3SiC2 were suggested on the basis of XRD analysis. The content of Ti3SiC2 reached 93% in products obtained from heating the Ti/polycarbosilane green compact at 1400 °C in Ar. The morphology and compositions of the products were examined by SEM equipped with EDX. The typical laminate structure of Ti3SiC2 particles with 1–4 μm in thickness and 4–15 μm in length was observed. EDX results showed that the atomic ratio of Ti:Si:C of grains is close to 3:1:2, which agrees with Ti3SiC2 composition. [Copyright &y& Elsevier]

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic (As) and cadmium (Cd) in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3-16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid (from 11.3% to 61.7%) made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal(loid)s in the grain of rice grown in soils polluted with both As and Cd. [ABSTRACT FROM AUTHOR]

Abstract: A pot experiment was conducted to examine the roles of indigenous and non-indigenous arbuscular mycorrhizal (AM) fungi in As uptake by maize (Zea mays L.) from original As-polluteded soil, and their effects on As and P fractions in the rhizosphere. The As-polluted soils with three As levels, were collected from As-polluted arable soil near an As mine. Indigenous AM fungi (M2: including Glomus spp., Acaulospora spp.) isolated from these soils were compared with a non-indigenous AM fungus (M1: Glomus caledonium 90036). The plants were harvested after 10 weeks of growth. Mycorrhizal colonization rate, dry weight (DW) and P, As concentrations in plants, as well as As and P fractions, were determined. Compared to the non-mycorrhizal treatment, at the high soil As level, maize inoculated with AM fungi had higher shoot and root DW and P contents, both M1 and M2 inoculations increased As accumulation in root, though M1 reduced shoot As content, and M2 transported more As from roots to shoots. M1 decreased root and shoot As contents at the low and medium soil As levels. Plants mainly took up non-specifically sorbed As at the high soil As level, but As was taken up from hydrous oxides of Fe and Al at the low and medium soil As levels. All results indicate that indigenous consortia M2 could protect their host plants from the toxicity of excessive As through P nutrition by activating P, though non-indigenous M1 could alleviate As toxicity through stabilizing As and P in the soil. [Copyright &y& Elsevier]

Lanthanum phosphate powders were synthesized by direct solid–liquid reaction of lanthanum oxide and phosphoric acid at the La:P ratio of 1:1. Phase-pure and fine grain size LaPO4 powders could be obtained by calcining the as-received powders at the temperature higher than 600 °C. It was demonstrated that the phase type, grain size and morphology of the LaPO4 powders were calcined at various temperatures. We have studied the microstructure of sintered LaPO4 ceramic and Al2O3/LaPO4 composite using the synthesized powders by SEM and TEM analysis. An interesting layered crystal structure and lots of dislocations inside LaPO4 grains and at the interface of Al2O3/LaPO4 composite were observed. Low hardness and multiple dislocations and dislocation networks indicated the layered LaPO4 ceramic could possess excellent machinability. As an example for engineering application, machinable Al2O3/LaPO4 composite with weak bonding was fabricated and characterized. [Copyright &y& Elsevier]

A new design method of machinable ceramic composites was proposed, which applies the graded-structure concept to the design of machinable Si3N4 ceramics. Silicon nitride/hexagonal boron nitride (h-BN) ceramic composites and functionally graded materials were fabricated by hot pressing at 1750 °C for 2 h, varying the alignment of the amount of hexagonal BN using powder layering method. The improved machinability of Si3N4/h-BN composite can be attributed to addition of layered structure hexagonal BN. Hexagonal BN possesses excellent cleavage planes perpendicular to the c-axis. Ease of machining depends on degree of crystal interlocking; hence volume content of h-BN crystals and their aspect ratio affect machinability. The texture of h-BN and β-Si3N4 was observed during hot pressing sintering. Physical and mechanical properties of Si3N4/h-BN with different content of h-BN were investigated, such as bulk density, Vickers''s hardness, flexural strength, and elastic modulus. All of these properties are important for the design of the machinable Si3N4/h-BN FGM (Functionally Graded Materials). [Copyright &y& Elsevier]