Effects of composition and phase relations on mechanical properties and crystallisation of silicate glasses

Crystallization, mechanical properties and workability are all important for commercialization and optimization of silicate glass compositions. However, the inter-relations of these properties as a function of glass composition have received little investigation. Soda-lime-silica glasses with Na2O-MgO-CaO-Al2O3-SiO2 compositions relevant to commercial glass manufacture were experimentally studied and multiple liquidus temperature and viscosity models were used to complement the experimental results. Liquidus temperatures of the fabricated glasses were measured by the temperature gradient technique, and Rietveld refinements were applied to X-Ray powder diffraction (XRD) data for devitrified glasses, enabling quantitative determination of the crystalline and amorphous fractions and the nature of the crystals. Structural properties were investigated by Raman spectroscopy. Acoustic echography, micro-Vicker’s indentation and single-edge notched bend testing methods were used to measure Young’s moduli, hardness and fracture toughness, respectively. It is shown that it is possible to design lower-melting soda-lime-silica glass compositions without compromising their mechanical and crystallization properties. Unlike Young’s modulus, brittleness is highly responsive to the composition in soda-lime-silica glasses, and notably low brittleness values can be obtained in glasses with compositions in the wollastonite primary phase field: an effect that is more pronounced in the silica primary phase field. The measured bulk crystal fractions of the glasses subjected to devitrification at the lowest possible industrial conditioning temperatures, indicate that soda-lime-silica glass melts can be conditioned close to their liquidus temperatures within the compositional ranges of the primary phase fields of cristobalite, wollastonite or their combinations

Construction of the new Troja Bridge in Prague

Obecnie w Pradze budowana jest północna część obwodnicy miasta. Projekt ten jest znany pod nazwą kompleks tunelowy Blanka, a w jego skład wchodzą liczne budowle tunelowe. Do kompleksu zaliczany jest również nowy most przez Wełtawę, który będzie służył komunikacji tramwajowej, samochodowej oraz pieszej. Po jego ukończeniu możliwa będzie rozbiórka istniejącego mostu tramwajowego, który jest eksploatowany od czasu ostatniej przebudowy mostu Barykadników.The new Troja Bridge in Prague represents a significant original hybrid structure crossing the Vltava River. The network steel arch with the deck made of prestressed concrete forms the main span of the bridge 200.4 m long. The side span made of prestressed concrete is about 40 m long. The construction was started by incremental launching of the bridge deck using temporary supports in the river. After casting of the slab of the bridge, the arch was assembled. The final stage will be the installation and pre-stressing of the hangers. Then, the temporary supports will be removed and the bridge will be completed

Fungal bioremediation of creosote-contaminated soil: A laboratory scale bioremediation study using indigenous soil fungi

The aim of the study is to determine the efficacy of indigenous soil fungi in removing (PAHs) from creosote-contaminated soil with a view to developing a bioremediation strategy for creosote-contaminated soil. Five fungal isolates, Cladosporium, Fusarium, Penicillium, Aspergillus and Pleurotus, were separately inoculated onto sterile barley grains and incubated in the dark. The colonized barley was inoculated onto creosote-contaminated (250 000 mg kg(-1)) soil in 18 duplicate treatments and incubated at 25 degrees C for seventy days. The soil was amended with nutrient supplements to give a C:N:P ratio of 25:5:1 and tilled weekly. Creosote removal was higher (between 78 and 94%) in nutrient supplemented treatments than in the un-supplemented ones (between 65 and 88%). A mixed population of fungi was more effective (94.1% in the nutrient amended treatment) in creosote removal than single populations wit a maximum of 88%. Barley supported better fungal growth and PAH removal. Pleurotus sp. removed the creosote more than the other isolates. Two and three-ring PAHs were more susceptible to removal than the 4- and 5-ring PAHs, which continued to remain in small amounts to the end of the treatment. Reduction of creosote in the present study was higher than was observed in an earlier experiment using a consortium of microorganisms, mainly bacteria, on the same contaminated soil (Atagana, 2003)

Influence of Short Central PEO Segment on Hydrolytic and Enzymatic Degradation of Triblock PCL Copolymers

Hydrolytic, enzymatic degradation and composting under controlled conditions of series of triblock PCL/PEO copolymers, PCEC, with central short PEO block (M (n) 400 g/mol) are presented and compared with homopolymer (PCL). The PCEC copolymers, synthesized via ring-opening polymerization of epsilon-caprolactone, were characterized by H-1 NMR, quantitative C-13 NMR, GPC, DSC and WAXS. The introduction of the PEO central segment ( lt 2 wt%) in PCL chains significantly affected thermal degradation and crystallization behavior, while the hydrophobicity was slightly reduced as confirmed by water absorption and moisture uptake experiments. Hydrolytic degradation studies in phosphate buffer after 8 weeks indicated a small weight loss, while FTIR analysis detected changes in crystallinity indexes and GPC measurements revealed bulk degradation. Enzymatic degradation tested by cell-free extracts containing Pseudomonas aeruginosa PAO1 confirmed high enzyme activity throughout the surface causing morphological changes detected by optical microscopy and AFM analysis. The changes in roughness of polymer films revealed surface erosion mechanism of enzymatic degradation. Copolymer with the highest content of PEO segment and the lowest molecular weight showed better degradation ability compared to PCL and other copolymers. Furthermore, composting of polymer films in a model compost system at 37 A degrees C resulted in significant degradation of the all synthesized block copolymers