The evaluation of geopolymer properties prepared by alkali activation of black coal ashes with high content of loss on ignition

The utilization of fly ashes in Slovakia is lower than in other countries and dumping of fly ashes prevails. The dumping changeschemical and phase composition of fly ashes and so it decreases possibilities for their utilization. Fly ashes are mainly used in buildingindustry, where the content of loss on ignition (LOI) is limited due to standards. Black coal fly ashes produced in Slovakia have a highcontent of loss on ignition – more than 20 % - so they straight utilization in building industry is not possible. The current possibility fortheir utilization is in geopolymer synthesis. Products with 28-day compression strength of 35.7 MPa and 180-day compression strengthof 55.0 MPa were obtained by alkali activation of fly ashes with 23.25 % LOI with 8 wt% Na2O and their next hardening in temperatureof 80 °C during 6 hours. Products have a great frost-resistance and aggressive environments resistance (NaCl a H2SO4 solutions)

The influence of solutions of NaOH and plasticizers on the wettability of PVC and PET plastics

Flotation of plastics becomes a very prospective method of their separation as a reflection of the industrial quality of purity requirements. The problem is however that most of the plastics have relatively similar hydrophobic surfaces preventing them to be selectively sorted by the flotation method. That is why various ways have been proposed in order to stimulate the wetting of the plastics´ surfaces selectively (gamma flotation, selective adsorption of wettting substances or depressants, physical treatment, and chemical treatment). Unfortunately, the application of traditional use of depressants is questionable since there are different or even contrast theoretical explanations of their adsorption mechanism on the plastics´ surfaces. In this article, a brief theoretical overview is presented summarizing the possible mechanisms of the selective adsorption of organic depressants from the standpoint of modern surface thermodynamics approaches. On the other hand, the method of chemical treatment of the plastics´ surfaces known as the selective hydrophobic modification is better studied and so understood. Therefore, the influence of NaOH solutions as well as of two plasticizers (diisodecyl phtalate and diethylen glycol dibenzoate) on the surface wettability of PVC and PET plastics has been studied experimentally

Evaluation of the aggregation stability of colloidal silica in the presence of CTAB. Part 1: Kinetic parameters of coagulation

The coagulation rate of colloidal silica (synthetic SiO2) spheres in aqueous solution of hexadecyltrimety-amonium bromide (CTAB) was investigated at the concentration scale of 10-5 - 5×10-4 M and pH of 4.7 8.1. The computer-controlled spectrophotometer was used to detect absorbance of the colloidal system as a function of time. From the absorbance-vs.-time dependence, the coagulation rate constant, stability ratio and critical concentration of coagulation (c.c.c.) have been determined by using a linearization and approximation method. Both methods provided c.c.c. values of the initially hydrophilic silica spheres to be ca. 2×10-4 M CTAB (pH 6.8), suggesting an adsorption-induced hydrophobization of their surface by CTAB cations. A slight influence of pH was also observed, probably related to the ionization degree of the CTAB cations

Study on Mechanical Properties of Heap Deposited Fly Ash Based Geopolymers with Different Alkaline Activator Properties

Geopolymers can improve environmental protection and are therefore considered a 21st-century material that requires special attention. The main objective of this study was to examine the utilization of fly ash deposited on a heap as a potential raw material for the geopolymerization process. In this work, flexural and compressive strengths, as well as water absorption of geopolymers, were evaluated based on alkaline activator properties. Na2O content, SiO2/Na2O molar ratio and fly ash-to-water ratio were key observed factors. Mechanical strengths tests were conducted after 7, 28, 90, 180, and 360 days. The research findings showed that geopolymer cured at appropriate conditions and with a suitable alkaline activator can reach a compressive strength of more than 55 MPa. The presented study highlighted the possibility of the efficient use of fly ash to produce useful materials, i.e., geopolymers, which contribute to environmentally friendly solutions. This approach is fully in line with the principles of sustainable development

Community structure of insect herbivores is driven by conservatism, escalation and divergence of defensive traits in Ficus

Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant‐herbivore arms race. We studied the defences and caterpillars associated with 21 sympatric New Guinean figs. Herbivore generalists were concentrated on hosts with low protease and oxidative activity. The distribution of specialists correlated with phylogeny, protease and trichomes. Additionally, highly specialised Asota moths used alkaloid rich plants. The evolution of proteases was conserved, alkaloid diversity has escalated across the studied species, oxidative activity has escalated within one clade, and trichomes have diverged across the phylogeny. Herbivore specificity correlated with their response to host defences: escalating traits largely affected generalists and divergent traits specialists; but the effect of escalating traits on extreme specialists was positive. In turn, the evolution of defences in Ficus can be driven towards both escalation and divergence in individual traits, in combination providing protection against a broad spectrum of herbivores.</div

Species swarms and their caterpillar colonisers: phylogeny and polyphenols determine host plant specificity in New Guinean Lepidoptera.

The majority of multi-cellular terrestrial life is found in tropical forests and is either an invertebrate or a plant: for decades ecologists have sought to understand why. As global change erodes the list of extant species on our planet quantifying what species remain, along with their origins and ecology, contributes to our ability to preserve ecosystem functioning and resilience. Here we study three feeding guilds of caterpillars (Lepidoptera) and seek to understand the drivers of their diet breadth across four diverse tropical plant genera in Papua New Guinea. Host specificity is central to biodiversity estimates and the resilience of ecological networks. Specifically, we calculate distance-based host specificity in relation to plant phylogenetic relationships alongside chemical and mechanical traits of leaves. In terms of chemical defenses, we focus on the major polyphenol groups, a compound class shared across many plant species. We refine our data exploration using food webs and ordinations to pick out specific traits of relevance to insect host specificity. Our results showed that the degree of specialization for caterpillars took the following order: phylogenetic>polyphenol>mechanical, such that insect specificity was explained best by host phylogeny and polyphenol chemistry in our study system. Leaf mining insects had higher host specificity than those feeding externally. Of the traits studied hexahydroxydiphenoyl derivatives, galloyl derivatives, trichome density, quinic acid derivatives, myricetins and successional index explained the most variation in overall insect community structure. Our findings build on earlier studies of New Guinean rainforest communities and add a mechanistic explanation to previous findings that host genera are functional islands for insect herbivores. Further, we demonstrate that different plant genera combine different defensive traits that appear to drive associated insect diversity. Our approach integrates trait data and phylogeny to explore dimensions of specialization and we welcome metabolomic studies that will provide more detailed explanations for insect-herbivore host use. Finally, chemical diversity is directly linked to organismal diversity and by studying a range of insect herbivore guilds we make a connection between feeding ecology and specialization that will help to predict species interactions and, potentially, the persistence of ecological networks