1,721,061 research outputs found
Effects of grain size on the reactivity of limestone temper in a kaolinitic clay
No full textCarbonates in clay based ceramics produces higher sintering at lower firing temperatures, but may cause lime spalling, affecting the physical and mechanical behaviour of the ceramic body. The present study investigated the mineralogical and microstructural changes that occur in a kaolinitic clay tempered with different contents of limestone sand with two skewed grain size distributions, after firing. The firing temperatures were set at 500, 750 and 1000 °C. The mineralogy of the fired bodies was analyzed by XRPD and quantitative phase analysis was performed using Rietveld method. SEM-EDS analyses were carried out to investigate the changes in microstructures and the clay/limestone reactivity. The use of sand-sized limestone temper and short firing times induced the formation of non-stoichiometric phases at the clay/limestone boundary, ruled by the lateral variation of CaO activity. The structure and composition of the spinel-type phase (e.g. γ-Al2O3), as typical firing product of kaolinite clays, were investigated. Different Ca-silicates and -aluminosilicates (gehlenite, rankinite and larnite) in ceramics fired at 1000 °C are found according to the limestone grain size. Lime spalling already occurs in ceramics fired at 750 °C; it is triggered by coarse calcined grains (σspalling > σmatrix failure) and then fractures propagates through finer calcined limestone grains
Isolation of bacteria with potential plant promoting traits and optimization of growth conditions
Full text linkThis research aimed at investigating the isolation and identification of bacterial strains with biological nitrogen-fixing
capability and phosphate, potassium, and zinc solubilization activities from a durum wheat field under two different tillage practices including 10 years of conventional tillage (CT) and no-tillage (NT) practices. Attempts were also extended to
estimate their relative abundances in the soil as well as to develop accurate mathematical models in determining the effect of different temperatures, NaCl concentrations and pH on the growth, and activity of selected isolates. Twelve effective bacterial strains, including Pseudomonas, Acinetobacter, and Comamonas genera, were identified with a great potential to solubilize the insoluble forms of phosphate (from 11.1 to 115.5 mg l−1 at pH 8), potassium (from 32.2 to 35.6 mg l−1 at pH 7), and zinc (from 1.11 to 389.90 mg l−1 at pH 9) as well as to fx N2 gas (from 19.9 to 25.2 mg l−1). To our knowledge, this is the frst report of the ability of Comamonas testosteroni and Acinetobacter pittii to fix nitrogen and to solubilize insoluble potassium compound, respectively. Three families, Moraxellaceae, Pseudomonadaceae, and Comamonadaceae, showed a higher percentage of abundance in the NT samples as compared to the CT, but only significant difference was observed in the relative abundance of Pseudomonadaceae (P<0.01). These strains could be definitely recommended as inoculants to promote plant growth in the wide ranges of pH, salinity levels (with maximum growth and complete inhibition of growth from 0.67–0.92% to 3.5–9.3% NaCl, respectively), and temperatures (2.1–45.1 °C)
"Molino Mastricarro", la miniera delle meraviglie
No full textNel vecchio sito a ovest di Catanzaro,
lungo il corso del torrente Fiumarella,
i ricercatori del Dipartimento
di Biologia, Ecologia e Scienze della Terra dell’Unical
hanno scoperto la Linarite e la Connellite,
due minerali rari appartenenti alla classe dei solfati
Il ritrovamento, in collaborazione con l’università di Bari,
segue quello della wulfenite e conferma
l’importanza e le potenzialità attrattive della zon
Strength of kaolinite-based ceramics: Comparison between limestone- and quartz-tempered bodies
No full textThe addition of temper was a common practice in the fabrication of traditional ceramics. The present work shows the effects of limestone or quartz added as temper to a kaolinitic clay, on the strength of the ceramic body. With this purpose ceramic tests were prepared adding the 5, 15 and 25% of each temper to a kaolinitic clay. Unimodal skewed grain size distributions (GSDs) for temper were used instead on single grain sizes used in previous experimental works. Furthermore, samples were fired at 500, 750 and 1000 °C in order to analyse the effect of firing temperature on ceramic strength. A correlation between the strength and the porosity, the mineralogy and the microstructure of the samples is presented. Results shows that while temper improves the strength of 500 °C- and 750 °C-fired bodies, it worsens that of samples fired at 1000 °C. Moreover, while at 500 and 1000 °C limestone-tempered materials are less strong than quartz-tempered ones, at 750 °C the opposite occurs. For quartz-tempered bodies fired up to 750 °C, no difference in strength changing the temper GSD is observed, while in other cases the coarser the temper, the less strong the ceramic
The effect of temper on the thermal conductivity of traditional ceramics: Nature, percentage and granulometry
No full textTraditional ceramics were commonly produced using a mixture of clay and temper materials, which were added in different percentage according to the craftsman purposes. The present study aims to examine up to which extent some technological parameters (nature, granulometry and percentage of the temper and firing temperature) affect the thermal conductivity of traditional ceramics. With this purpose a kaolinitic clay was tempered either with quartz or limestone belonging to two different granulometric distributions in percentage of 5%, 15% and 25%, and fired at 500, 750 and 1000 C. Moreover the dependence on firing temperature was studied. Thermal conductivity was measured with a modified Lee's disks apparatus in a temperature range from 120 to 370 C. It was found that quartz-tempered ceramics are more conductive than the fired non-tempered clay, while limestone-tempered sample are less conductive. Mineralogical and microstructural data are also provided and the influence of the α-β quartz-phase transition on the thermal conductivity of ceramics is discussed. © 2014 Elsevier B.V
The effect of mineralogy, microstructure and firing temperature on the effective thermal conductivity of traditional hot processing ceramics
No full textThe present work analyses the effect of mineralogy, microstructure and firing temperature on the effective thermal conductivity of traditional hot processing ceramics. Samples prepared with two quartz-rich kaolinitic clays (BAR1 and BAR2), a fine kaolinitic clay (ARG) and a glaucophane-rich clay (SIF), were fired in the range between 950 and 1350 °C. The effective thermal conductivity is principally affected by the porosity of the body. Mullite further improves the thermal conductivity of BAR1 and BAR2 ceramics, while in ARG samples cristobalite is correlated with the increase in thermal conductivity. In SIF ceramics, the higher densification and the formation of spinel, pyroxene and hematite results in a higher conductivity compared to the other samples. The amorphous phase improves the ceramics’ thermal conductivity since it seals voids between particles. In samples in which quartz exceeds 50 wt%, the ceramics’ thermal conductivity decreases because of fissures and detachment zones formed after the α-β quartz phase transition. Finally, functional conclusions are drawn on traditional cooking pot and Medieval glass crucibles
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Development and Application of X-rays in Metal Analysis of Soil and Plants
Full text linkNo abstract: Special Issue Editorial articl
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