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Abstract  

Dynamic and controlled rate thermal analysis (CRTA) has been used to characterise alunites of formula [M(Al)3(SO4)2(OH)6] where M+ is the cations K+, Na+ or NH4 +. Thermal decomposition occurs in a series of steps: (a) dehydration, (b) well-defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration and dehydroxylation.

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Abstract  

Anionic surfactant and silane modified layered double hydroxides (LDHs) were synthesized through an in situ coprecipitation method. The structure and morphology were characterized by XRD and TEM techniques, and their thermal decomposition processes were investigated using infrared emission spectroscopy (IES) combined with thermogravimetry (TG). The surfactant modified LDHs (H-DS) shows three diffractions located at 1–7° (2θ), while there is only one broad reflection for silane grafted LDHs (H–Si) in this region. The morphologies of the H-DS and H–Si show fibrous exfoliated layers and curved sheets, respectively. The IES spectra and TG curves indicate that alkyl chain combustion and dehydroxylation are overlapped with each other during heating from 373 to 723 K in H-DS and to 873 K in H–Si. Sulfate anion transformation process occurs at 473 K in H-DS and 523 K in H–Si. The derivant of sulfate can exist even above 1073 K. After further decomposition, the metal oxides and the new type of Si–O compounds are formed beginning at around 923 K in silane modified sample.

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Abstract  

Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic ammonium jarosite. Five mass loss steps are observed at 120, 260, 389, 510 and 541°C. Mass spectrometry through evolved gases confirms these steps as loss of water, dehydroxylation, loss of ammonia and loss of sulphate in two steps. Changes in the molecular structure of the ammonium jarosite were followed by infrared emission spectroscopy (IES). This technique allows the infrared spectrum at the elevated temperatures to be obtained. IES confirms the dehydroxylation to have taken place by 300°C and the ammonia loss by 450°C. Loss of the sulphate is observed by changes in band position and intensity after 500°C.

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Abstract

Hydrocalumite (CaAl-Cl-LDH) has the similar structure to layered double hydroxide (LDH). The effects of Na-dodecylsulfate (SDS) on the structure, morphology, and thermal property of CaAl-Cl-LDH have been investigated. Through ion exchange, CaAl-Cl-LDH had been modified with SDS at two concentrations: 0.005 mol L−1 and 0.2 mol L−1. Two different adsorption behaviors were observed through Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns. When the SDS concentration was 0.005 mol L−1, surface anion exchange was the major process. When the SDS concentration was 0.2 mol L−1, anion exchange intercalation occurs, with the interlayer distance expanded to 3.25 nm, and the particle morphology from regular hexagons to irregular platelets. The thermal analysis (TG–DTA) showed that dehydration and dehydroxylation occur at a lower temperature when hydrocalumite was intercalated with dodecylsulfate. All these observations revealed that the property of CaAl-Cl-LDH has been changed by SDS modification.

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Journal of Thermal Analysis and Calorimetry
Authors: Yuri Park, Godwin A. Ayoko, Janos Kristof, Erzsébet Horváth, and Ray L. Frost

Abstract

In this study, mono- and di-alkyl cationic surfactants were used to prepare organoclays through ion exchange and the prepared organoclays were characterised by X-ray diffraction (XRD) and thermogravimetric analysis (TG). Larger basal spacings were observed in the interlayer of the organoclays intercalated with DDDMA than organoclays intercalated with DDTMA. The DTG curves identify the thermal stability of organoclays intercalated with two different types of surfactants (DDTMA and DDDMA) and the different arrangements of the surfactant molecules intercalated in the montmorillonite. Both organoclays intercalated with organic surfactant molecules proved to be thermally stable at high temperature. This study provides an understanding of the structure and properties of organoclays, which will enhance the potential applications of organoclays in environmental remediation.

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Journal of Thermal Analysis and Calorimetry
Authors: Yuri Park, Godwin A. Ayoko, Janos Kristof, Erzsébet Horváth, and Ray L. Frost

Abstract

High resolution thermogravimetric analysis (TG) has attracted much attention in the synthesis of organoclays and its applications. In this study, organoclays were synthesised through ion exchange of a single cationic surfactant for sodium ions, and characterised by methods including X-ray diffraction (XRD) and TG. The changes of surface properties in montmorillonite (MMT) and organoclays intercalated with surfactant were determined using XRD through the changes in the basal spacing. The TG was applied in this study to investigate more information of the configuration and structural changes in the organoclays with thermal decomposition. There are four different decompositions steps in differential thermogravimetric curves. The obtained TG steps are relevant to the arrangement of the surfactant molecules intercalated in MMT and the thermal analysis indicates the thermal stability of surfactant modified clays. This investigation provides new insights into the properties of organoclays and is important in the synthesis and processing of organoclays for environmental applications.

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Abstract

The thermal behavior and decomposition of kaolinite–potassium acetate intercalation complex was investigated through a combination of thermogravimetric analysis and infrared emission spectroscopy. Three main changes were observed at 48, 280, 323, and 460 °C which were attributed to (a) the loss of adsorbed water, (b) loss of the water coordinated to acetate ion in the layer of kaolinite, (c) loss of potassium acetate in the complex, and (d) water through dehydroxylation. It is proposed that the potassium acetate intercalation complex is stability except heating at above 300 °C. The infrared emission spectra clearly show the decomposition and dehydroxylation of the kaolinite intercalation complex when the temperature is raised. The dehydration of the intercalation complex is followed by the loss of intensity of the stretching vibration bands at region 3600–3200 cm−1. Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm−1. Dehydration is completed by 400 °C and partial dehydroxylation by 650 °C. The inner hydroxyl group remained until around 700 °C.

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Abstract

The removal of the sulfate anion from water using synthetic hydrotalcite (Mg/Al LDH) was investigated using powder X-ray diffraction (XRD) and thermogravimetric analysis (TG). Synthetic hydrotalcite Mg6Al2(OH)16(CO3)·4H2O was prepared by the co-precipitation method from aluminum and magnesium chloride salts. The synthetic hydrotalcite was thermally activated to a maximum temperature of 380 °C. Samples of thermally activated hydrotalcite where then treated with aliquots of 1000 ppm sulfate solution. The resulting products where dried and characterized by XRD and TG. Powder XRD revealed that hydrotalcite had been successfully prepared and that the product obtained after treatment with sulfate solution also conformed well to the reference pattern of hydrotalcite. The d(003) spacing of all samples was found to be within the acceptable region for a LDH structure. TG revealed all products underwent a similar decomposition to that of hydrotalcite. It was possible to propose a reasonable mechanism for the thermal decomposition of a sulfate containing Mg/Al LDH. The similarities in the results may indicate that the reformed hydrotalcite may contain carbonate anion as well as sulfate. Further investigation is required to confirm this.

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