The thermal behavior of kaolinite intercalation complexes-A review

The kaolinite intercalation and its application in polymer-based functional composites have attracted great interest, both in industry and in academia fields, since they frequently exhibit remarkable improvements in materials properties compared with the virgin polymer or conventional micro and macro-composites. Also of significant interest regarding the kaolinite intercalation complex is its thermal behavior and decomposition. This is because heating treatment of intercalated kaolinite is necessary for its further application, especially in the field of plastic and rubber industry. Although intercalation of kaolinite is an old and ongoing research topic, there is a limited knowledge available on kaolinite intercalation with different reagents, the mechanism of intercalation complex formation as well as on thermal behavior and phase transition. This review attempts to summarize the most recent achievements in the thermal behavior study of kaolinite intercalation complexes obtained with the most common reagents including potassium acetate, formamide, dimethyl sulfoxide, hydrazine and urea. At the end of this paper, the further work on kaolinite intercalation complex was also proposed.

The thermal behavior of kaolinite intercalation complexes : a review

The thermally induced transformation of kaolinite to metakaolin is simulated using molecular dynamics through a step-wise dehydroxylation approach. The simulation shows that the removal of structural water through dehydroxylation produces a distortion or buckling effect in the 1 : 1 Al–Si layers, which is due to the migration of the aluminium into vacant sites provided by the inter-layer spacing. The structural change is characterized by a loss of crystallinity and a concomitant change in aluminium coordination from octahedral to tetrahedral, with this study confirming the presence of 5-fold aluminium within the metakaolin structure. The degree and probability of Al migration are proportional to the amount of local disorder within the structure, which is governed by the degree of local hydroxyl group loss. This results in the formation of aluminium clusters within the layers. This study proposes that instead of a uniform structure, metakaolin exhibits regions of differing aluminium concentrations, which can have major effects in the reaction chemistry at those sites.

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Dehydroxylation of Kaolinite to Metakaolin - A Molecular Dynamics Study

The kinetic analysis of the thermal decomposition of kaolinite by DTG technique

Effect of the rate of calcination of kaolin on the properties of metakaolin-based geopolymers

Isothermal kinetic analysis of the thermal decomposition of kaolinite: The thermogravimetric study

The non-isothermal kinetic analysis of the thermal decomposition of kaolinite by thermogravimetric analysis

The study investigates the properties of alkali-activated binders with waste glass (WG) under hydrothermal treatment. WG was dosed in 0-30 wt.% and was used as a substitute for raw materials. Solid precursors were mixed with sodium water glass. The prepared specimens were cured in ambient conditions (20°C and RH 98%) and hydrothermal conditions (105°C and 150°C). The effect of glass and hydrothermal treatment on physical and mechanical properties after 2, 7, 28, 56, 90 and 180 days was monitored. Prepared hybrid zeolite-geopolymer materials were characterised by X-ray diffraction analysis, SEM, and MIP. It was confirmed that replacing raw materials with glass up to 20 wt.% did not deteriorate long-term properties under ambient conditions. The positive effect of hydrothermal curing was manifested, especially at a temperature of 150°C, when 20 wt.% glass was used.

Use the waste glass for the synthesis of geopolymer-zeolite composites


Purpose
The purpose of this study is to verify how the carbon doping of the WC-Co cemented carbide (CC) affected their structure before their processing by hot isostatic pressing (HIP) technology.


Design/methodology/approach
The samples for this experiment were fabricated by selective laser melting technology (SLM) using a YAG fiber laser with a power of P = 40 W and a scanning speed of 83 mm/s. The subsequent carbon doping process was performed in a chamber furnace at 900 0 C for 1, 4 and 12 h. The HIP was performed at 1,390°C and pressures of 40 MPa, 80 MPa and 120 MPa. The changes induced in the structures were evaluated using X-ray diffraction and various microscopic methods.


Findings
X-ray diffraction analysis showed that the structure of the samples after SLM consisted of WC, W2C, Co4W2C and Co phases. As a result of the increase in the carbon content in the structure of the samples, the transition carbide W2C and structural phase Co4W2C decayed. Their decay was manifested by the coarsening of the minor alpha phase (WC), which occurred both during the carburizing process and during the subsequent processing using HIP. In the samples in which the structure was carburized prior to HIP, only the structural phases WC and Co were observed in most cases.


Originality/value
The results confirm that it is possible to increase the homogeneity of the CC structure and thus its applicability in practice by additional carburization of the sample structure with subsequent processing by HIP technology.


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The structure and the properties of WC-Co samples produced by SLM technology and carbon-doped prior to HIP processing

The interfacial transition zone is one of the weakest areas in concrete. Microcracks and new phases often form in this zone, affecting the resulting concrete’s mechanical properties. In this research, concrete in which Portland cement was partially replaced by powdered limestone and/or metakaolin was cured for 1 and 28 days and then mechanical properties were tested. The interfacial transition zone was studied by scanning electron microscopy and selected phases were analyzed by electron microprobe. The addition of a small amount of limestone or metakaolin increases the strength of the concrete. The strength significantly decreases with a content of 10% or more supplementary cementitious materials (SCMs) in concrete. The microcrack’s thickness at the binder-aggregate interface reaches up to 0.8 μm. In concretes with limestone, rhombohedral calcite crystals up to 0.5 μm in size accumulate in the interfacial zone. This accumulation can significantly reduce the strength of the concrete when the amount of limestone is high. Zeolites with a composition corresponding to Mg-mazzite are formed at the interface of cement paste, quartz and albite, partially replaced by sericite.

Dana Kubátová

Papers

Isothermal kinetic analysis of the thermal decomposition of kaolinite: The thermogravimetric study

The non-isothermal kinetic analysis of the thermal decomposition of kaolinite by thermogravimetric analysis

Use the waste glass for the synthesis of geopolymer-zeolite composites

The structure and the properties of WC-Co samples produced by SLM technology and carbon-doped prior to HIP processing

Study of interfacial transition zone in concrete with SCMs