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The geopolymerization reaction is a chemical process involving the dissolution of amorphous, semi-crystalline and crystalline phases following alkaline or acid attack at ambient or at low temperature (T˂100 °C). Together with precondensed entities of the used activator solution the dissolved parts form a geopolymer network which glues together all remaining unreacted parts as ingredients of the artificial stone. The fate of the mineralogical phases present in the precursors used in the synthesis of alkaline and acid geopolymers is reviewed in this article. The different starting materials used in the synthesis of geopolymers and the different techniques used to modify the reactivity of these materials are reported. The mineralogical evolution of the amorphous, semi-crystalline and crystalline phases after activation at ambient and at low temperatures (T < 100 °C) is also reported. This study shows that for the mineralogical investigation of raw material, precursors and geopolymers, XRD is the most widely used analytical method. The most commonly used method to confirm the participation of crystalline phases in geopolymerization is the comparison of the diffractograms of the raw material to those of the products. It also indicates that, in addition to the amorphous aluminosilicate phases, certain semi-crystalline, and crystalline phases participate in this geopolymerization dynamic either by undergoing total or partial dissolution to form an inorganic macromolecule with an amorphous structure of the zeolitic type and other new minerals. The composition of the phases formed depends on the base material. Increasing the synthesis temperature promotes the dissolution of phases, the formation of geopolymer networks, and in some cases, the formation of new phases such as sodalities, zeolite A and zeolite P. Little work has been done to quantify the mineralogical phases before and after precursor activation, making it impossible to assess dissolution, the degree of geopolymerization, and mineral formation. The exact structure of the phases formed is often questionable, as most of the papers do not mention their reference structure number. There is also a lack of quantification of the amorphous phase resulting from the hardening of the activating solution and the evaluation of the fraction of the amorphous phase contained in the precursor remains unreacted. The mineralogical investigation must also extend to the quantification of phases using Rietveld refinement with internal standards to correlate these with the physical and mechanical properties of geopolymer products. Additional mineralogical study techniques, such as thin sections, should be used in future work for in-depth mineralogical investigation of geopolymers. [ABSTRACT FROM AUTHOR]

The article presents the research results for the synthesis of inorganic sorbents based on manganese oxide compounds. It shows the results of the lithium sorption from brines with the use of synthesized sorbents. The effect of temperature, the molar ratio of Li/Mn, and the duration for obtaining a lithium-manganese precursor and its acid treatment was studied. The sorption characteristics of the synthesized sorbents were studied. The effect of the ratio of the sorbent mass to the brine volume and the duration of the process on the sorption of lithium from brine were studied. In this case, the sorbent recovery of lithium was ~86%. A kinetic model of the lithium sorption from brine on a synthesized sorbent was determined. The kinetics of the lithium sorption was described by a pseudo-second-order model, which implies limiting the speed of the process due to a chemical reaction. [ABSTRACT FROM AUTHOR]

LaAlO3 was synthesized using microcrystalline LaOCl and amorphous Al2O3 precursors. The precursors were derived with single inorganic materials through spray pyrolysis. The precursors and derived oxide powders were characterized by differential thermal analysis, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. LaAlO3 was found to crystallize directly from microcrystalline LaOCl and amorphous Al2O3 precursors at 1073 K for 2 h in air, and the LaAlO3 product purity is more than 99.9%. [ABSTRACT FROM AUTHOR]

Aza-amino acid precursors with an aromatic side chain were synthesized using hydrazine alkylation. This synthetic pathway avoided use of hydrogen gas and expensive hydrogenation catalysts. For the optimization of this alkylation reaction various solvents and different reaction conditions were used. Aza-phenylalanine, aza-tyrosine, and aza-tryptophan precursors with different N- and side-chain protecting groups were synthesized starting from N-protected hydrazines. [ABSTRACT FROM AUTHOR]

Abstract: In this work multiphase Nb(C,N)/Nb5Si3 ceramic composites containing niobium silicide, nitride and carbide phases were designed by using the polymer derived ceramic (PDC) route to avoid the complicated shaping of refractory metal compounds. Starting from polycarbosilazane (PCSZ) precursor powder and metallic niobium as reactive filler green compacts were manufactured by uniaxial warm pressing and stabilized by subsequent crosslinking. Due to the reactivity of both the Nb and the rearrangements within the forming amorphous SiCN phase a porous ceramic material is generated via solid-state reaction during thermal treatment. Depending on the amount of PCSZ as well as on the pyrolysis conditions the particles within this network reveal a core/rim structure containing submicron-sized Nb2CN, NbC as well as coarse-grained Nb2N phases in the core and Nb5Si3 or alternatively metastable Nb5Si4C phase at the particle surface. [Copyright &y& Elsevier]

ZrC was synthesized by pyrolysis of a novel polymeric precursor, which was prepared from the reaction of zirconium tetrachloride with acetylacetone, methanol and 1,4-butanediol. The pyrolysis behavior and structural evolution of the precursor, the microstructure and composition of the synthesized ZrC particle were fully investigated. The results showed that the precursor could completely transform into ZrC after heat treatment in argon at temperatures above 1400°C. However, the initial formation temperature of ZrC was as low as 1200°C whereas ZrO2 as an intermediate product was also produced from the precursor at 1000°C, and the mixture was finally transformed into pure ZrC at elevated temperatures. The obtained ZrC particles exhibited face-centered cubic lattice structures with the size ranging from 50 to 100nm. [ABSTRACT FROM AUTHOR]

Abstract: Thermolysis of magnesium zinc bis(citrato) ferrate pentahydrate, MgZn2[Fe(C6H5O7)2]25H2O, has been investigated from ambient to 600°C employing various physico-chemical techniques viz. TG–DTG–DSC, IR, XRD and Mössbauer spectroscopy for the characterization of intermediates and final thermolysis products. Dehydration of the precursor completes at 140°C followed by abrupt exothermic decomposition to yield α-Fe2O3, ZnO and MgO as intermediate oxide phases. Finally solid state reaction between oxides results in the formation of spinel ferrite Mg0.3Zn0.7Fe2O4 as the final thermolysis product at a temperature (350°C) much lower than for the ammonium substituted citrate precursor (540°C) and conventional ceramic method (1350°C). Monodispersed and nanosized nature of ferrite with average particle diameter of 35nm is confirmed by transmission electron microscopy (TEM). The Mössbauer spectrum of the final thermolysis product displays a doublet owing to the presence of superparamagnetism (SPM) at room temperature. SPM in multi-domain particles is attributed to weakening of A–B exchange interactions, resulting in lowering of anisotropic energy which facilitates onset of SPM at room temperature. Thermolysis pattern has been compared with pure magnesium ferricitrate and ammonium substituted ferricitrate. [Copyright &y& Elsevier]