Properties of bio-based gum Arabic/clay aerogels

Lightweight bio-based aerogels from sustainable gum Arabic (GA) and sodium montmorillonite (Na+-MMT) clay were prepared by means of a simple freeze-drying process. GA/clay aerogels showed high porosity (87.9%–94.9%) of mainly open type and the mechanical properties were improved by the clay. When 40% of clay was added to pure GA, the specific modulus and the absorbed energy of resultant aerogels increased by 1.6 and 4.2 times respectively. On the other hand, the exponent value for modulus in the power-law model for cellular materials increased from 1.95 to 3.28 due to the more anisotropic structures induced by the presence of the clay. In terms of thermal stability and flame retardancy, clay content played a dominant role. With 50% of clay loading, the initial decomposition temperature increased by nearly 16 °C and the peak of heat release rate was 3-fold reduced.Peer ReviewedPostprint (author's final draft

Timescales of carbon turnover in soils with mixed crystalline mineralogies

Organic matter–mineral associations stabilize much of the carbon (C) stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in young soil. However, in soils with few SRO minerals and a predominance of crystalline aluminosilicate or Fe (and Al) oxyhydroxide, C turnover should be governed by chemisorption with those minerals. Here, we correlate mineral composition from soils containing small amounts of SRO minerals with mean turnover time (TT) of C estimated from radiocarbon (¹⁴C) in bulk soil, free light fraction and mineral-associated organic matter. We varied the mineral amount and composition by sampling ancient soils formed on different lithologies in arid to subhumid climates in Kruger National Park (KNP), South Africa. Mineral contents in bulk soils were assessed using chemical extractions to quantify Fe oxyhydroxides and SRO minerals. Because of our interest in the role of silicate clay mineralogy, particularly smectite (2 : 1) and kaolinite (1 : 1), we separately quantified the mineralogy of the clay-sized fraction using X-ray diffraction (XRD) and measured ¹⁴C on the same fraction. <br><br> Density separation demonstrated that mineral associated C accounted for 40–70 % of bulk soil organic C in A and B1 horizons for granite, nephelinite and arid-zone gabbro soils, and &gt; 80 % in other soils. Organic matter strongly associated with the isolated clay-sized fraction represented only 9–47 % of the bulk soil C. The mean TT of C strongly associated with the clay-sized fraction increased with the amount of smectite (2 : 1 clays); in samples with &gt; 40 % smectite it averaged 1020 ± 460 years. The C not strongly associated with clay-sized minerals, including a combination of low-density C, the C associated with minerals of sizes between 2 µm and 2 cm (including Fe oxyhydroxides as coatings), and C removed from clay-sized material by 2 % hydrogen peroxide had TTs averaging 190 ± 190 years in surface horizons. Summed over the bulk soil profile, we found that smectite content correlated with the mean TT of bulk soil C across varied lithologies. The SRO mineral content in KNP soils was generally very low, except for the soils developed on gabbros under more humid climate that also had very high Fe and C contents with a surprisingly short, mean C TTs. In younger landscapes, SRO minerals are metastable and sequester C for long timescales. We hypothesize that in the KNP, SRO minerals represent a transient stage of mineral evolution and therefore lock up C for a shorter time. <br><br> Overall, we found crystalline Fe-oxyhydroxides (determined as the difference between Fe in dithionate citrate and oxalate extractions) to be the strongest predictor for soil C content, while the mean TT of soil C was best predicted from the amount of smectite, which was also related to more easily measured bulk properties such as cation exchange capacity or pH. Combined with previous research on C turnover times in 2 : 1 vs. 1 : 1 clays, our results hold promise for predicting C inventory and persistence based on intrinsic timescales of specific carbon–mineral interactions

Geology of the Brixton Deverill - East Knoyle district (Wiltshire), 1:10000 sheets ST83NE (Brixton Deverill) and ST83SE (East Knoyle) : part of 1:50000 sheet 297 (Wincanton)

The Brixton Deverill-East Knoyle d i s t r i c t lies at the western endof Salisbury Plain and encompasses the north-western part of the Vale of Wardour. The central part of the d i s t r i c t forms part of a dissected plateau developed on Upper Chalk (Figure 1); this reaches a maximum height of 238 m south-east of Brixton Deverill. In the north-west, there are prominent escarpments capped by the Lewes Chalk on either side of the Wylye valley. In the south, the Mere Fault and associated monoclinal structure play an important part in shaping the landscape. In the west, the chalk rises steeply on the north side of the fault from the clay vale to the south. Between West Knoyle and East Knoyle, the steeply dipping Upper Greensand and Chalk strata give rise to strongly featured ground. The principal drainage in the northern part of the d i s t r i c t is northwards by the River Wylye, the only permanent river on the chalk outcrop and its tributaries. In the south-central area, drainage is eastwards by a series of valleys that coalesce just west of Hindon and ultimately join the River Nadder at Tisbury. In the south, on the clay vale, drainage is southwestwards by tributaries of the River Lodden, and south-eastwards by tributaries of the River Nadder. The lowest point in the d i s t r i c t , c.96 m OD, lies in the southern tract. Soils developed on the Upper Greensand and most of the Chalk are light and w e l l drained. However, s o i l s on the West Melbury Chalk, together with some on the clay-with-flint deposits and Kimmeridge Clay are much heavier and poorly drained. Agriculture is a mixture of arable and pasture, with the latter dominant on the Kimmeridge Clay Vale. There are few woods, with deciduous woods confined mostly to the clay vale and the relatively newly planted coniferous plantations on the Chalk and Upper Greensand. Agriculture is the only industry in the area

Effect of heating rate on gas emissions and properties of fired clay bricks and fired clay bricks incorporated with cigarette butts

In general, the firing process of clay bricks generates a range of gas emissions into the atmosphere. At high concentrations, these volatile emissions can be a serious source of environmental pollutions. The main purpose of this study was to evaluate the effect of different heating rates on gas emissions and properties during the firing of clay bricks and clay bricks incorporated with cigarette butts (CBs). In this investigation, four different heating rates were used: 0.7 °C min−1−1, 2 °C min−1, 5 °C min−1 and 10 °C min. The samples were fired in solid form from room temperature to 1050 °C. During the firing cycles, carbon monoxide, carbon dioxide, nitrogen oxides,hydrogen cyanide and chlorine emissions were measured at different heating rates. All bricks were also tested for their physical and mechanical properties including dry density, compressive strength, tensile strength, water absorption and initial rate of absorption. Results show that gas emissions were reduced significantly with higher heating rates (10 °C min) followed by 5 °C min−1−1 and 2 °C min for both types of brick samples. Higher heating rates also decrease the compressive strength and tensile strength value but demonstrate an insignificant effect on the water absorption properties respectively. In conclusion, a higher heating rate is preferable in terms of decreasing gas emissions and it is also able to produce adequate physical and mechanical properties especially for the CB brick

Enriched Reedy categories

We define the notion of an enriched Reedy category and show that if A is a C-Reedy category for some symmetric monoidal model category C and M is a C-model category, the category of C-functors and C-natural transformations from A to M is again a model category.This research was partially conducted during the period the author was employed by the Clay Mathematics Institute as a Liftoff Fellow

Influence of alkali resistant (AR) glass in porcelain clay for vitrified clay pipes

The aimed of the present work is to produce porcelain clay reinforced with Alkali Resistant (AR) glass for vitrified clay pipes at minimum sintering temperature. In this study, AR fiberglass as a reinforcement was milled into an average particle size of 90 μm and mixed with porcelain in different weight percentage at 3 wt%, 6 wt%, 9 wt%, and 12 wt%. The sample was prepared by using powder compaction and then fired for 2 hours at 900°C, 1000°C 1100°C and 1200°C. Based on the chemical analysis, it was found that SiO2, Al2O3, Na2O and K2O is the significant element to produce the material. Result of thermal analysis shows that sintering start occurs at 900°C to 1300°C. The result of volume shrinkage, apparent porosity, water absorption, bulk density and flexural strength were recorded for each samples. Scanning electron microscope (SEM) was used to observe the microstructural morphology of samples. It was found that the addition of AR glass can dramatically lowering the apparent porosity as well as water absorption and increase the value of volume shrinkage, bulk density and flexural strength with the rising of sintering temperature. It can be seen that the volume shrinkage is satisfy the typical ceramic shrinkage where is quarter than original dimension which is 31.75%. Based on the result, the favorable properties of porcelain clay sintering were obtained at sintering temperature of 1100°C with addition of 3 wt% AR glass. Thus, the suitable value of apparent porosity, water absorption and density obtained was 0.41%, 6.27% and 2.29g/cm3 respectively. Meanwhile, the maximum value for flexural strength gained was 76.40MPa. Based on the microstructure image, it can be seen that the reduction of porosity and increasing of glassy phase was corresponded to the addition of AR glass and rising of sintering temperature. In conclusion, the objective of this study were achieve to satisfied the value of vitrified clay pipes standard based on EN 295

Carbon storage and DNA absorption in allophanic soils and paleosols

Andisols and andic paleosols dominated by the nanocrystalline mineral allophane sequester large amounts of carbon (C), attributable mainly to its chemical bonding with charged hydroxyl groups on the surface of allophane together with its physical protection in nanopores within and between allophane nanoaggregates. C near-edge X-ray absorption fine structure (NEXAFS) spectra for a New Zealand Andisol (Tirau series) showed that the organic matter (OM) mainly comprises quinonic, aromatic, aliphatic, and carboxylic C. In different buried horizons from several other Andisols, C contents varied but the C species were similar, attributable to pedogenic processes operating during developmental upbuilding, downward leaching, or both. The presence of OM in natural allophanic soils weakened the adsorption of DNA on clay; an adsorption isotherm experiment involving humic acid (HA) showed that HA-free synthetic allophane adsorbed seven times more DNA than HA-rich synthetic allophane. Phosphorus X-ray absorption near-edge structure (XANES) spectra for salmonsperm DNA and DNA-clay complexes indicated that DNA was bound to the allophane clay through the phosphate group, but it is not clear if DNA was chemically bound to the surface of the allophane or to OM, or both. We plan more experiments to investigate interactions among DNA, allophane (natural and synthetic), and OM. Because DNA shows a high affinity to allophane, we are studying the potential to reconstruct late Quaternary palaeoenvironments by attempting to extract and characterise ancient DNA from allophanic paleosol