Kinetics and mechanism of three stages of thermal transformation of kaolinite to metakaolinite

Ptáček, Petr; Frajkorová, Františka; Šoukal, František; Opravil, Tomáš

doi:10.1016/j.powtec.2014.05.047

Cited by 99 publications

(41 citation statements)

References 49 publications

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“…7. The DSC curves exhibited four main regions: i) region 1 (T<200 °C): all samples showed an endothermic peak attributed to elimination of adsorbed and absorbed water [34]; the peak position and intensity increased with increasing additive concentration; this may be due to the presence of high percentage of absorbed water in additives and/or the high pH values (8-9) of additives which improved the kaolin dehydration; ii) region 2 (T=200-820 °C): an endothermic peak centered at 558 °C was assigned to dehydroxylation process of kaolin leading to the transformation of kaolinite to metakaolinite (Al 2 O 3 .2SiO 2 ) and the loss of structural hydroxyl groups; the proposed dehydroxylation mechanism consists of the division of hydroxyl groups into H + and O 2-ions; the H + ions form water molecules with OH -groups while the O 2-ions are bonded to the newly created metakaolinite lattice [35]; it was noticed that the peak position and intensity decreased with the increase of additive concentration; this can be explained by the decrease of kaolin amount in the samples; a new endothermic peak was detected around 780 °C in S30, S50 and S70 samples which may be assigned to the decomposition reactions of carbonate (Eqs. C and E) [14]; iii) region 3 (T=820-1100 °C): the exothermic peak at about 995 °C with a formation enthalpy, ΔH, of -64.24 J/g observed for S0 was related to the transformation of metakaolinite to mullite phase [36]; with the increase of additive concentration, both the peak position and intensity decreased progressively indicating that the mineral formation proportion decreased in all samples; iv) region 4 (T=1100-1500 °C): for the sample S0, an exothermic peak was observed at 1295 °C with a stored enthalpy of about ΔH= -21.30 J/g; this may be due to the crystallization of cristobalite [37]; S10 exhibited two exothermic peaks, the first at 1136 °C corresponding to the formation of albite phase (ΔH= -7.29 J/g) and the second at 1325 °C corresponding to anorthite phase formation (ΔH= -19.24 J/g); sample S30 exhibited two small exothermic peaks at 1194 °C attributed to the albite crystal formation (ΔH= -4.14 J/g) and at 1376 °C (ΔH= -2.81 J/g) corresponding to the anorthite formation; for the sample S50, a small exothermic peak was observed at around 1218 °C which was due to the formation of albite Bulk density (g/cm 3 ) [38]; the same phenomena were observed for the sample S70; the first exothermic peak at 1113 °C corresponded to the formation of albite (ΔH= -4.4 J/g); the endothermic peaks showed the melt points of eutectic 2CaO.SiO 2 -5CaO.…”

Section: [Figura 4: Difratogramas De Raios X Das Cerâmicas Preparadasmentioning

confidence: 99%

Elaboration and characterization of mullite-anorthite-albite porous ceramics prepared from Algerian kaolin

2018

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Mullite-anorthite-albite porous ceramic materials were successfully prepared by a solid-state reaction between kaolin clay and two different additives (CaCO 3 and Na 2 CO 3 ). The starting raw material was characterized by X-ray fluorescence, X-ray diffraction (XRD) and dynamic light scattering techniques. The effect of CaCO 3 and Na 2 CO 3 concentration (10 to 70 wt%) on structure, morphology and thermal properties of the obtained ceramics was investigated by XRD, scanning electron microscopy and differential scanning calorimetry (DSC) techniques. The XRD patterns showed that mullite (3Al 2 O 3 .2SiO 2 ), anorthite (CaO.Al 2 O 3 .2SiO 2 ) and albite (Na 2 O.Al 2 O 3 .6SiO 2 ) were the main crystalline phases present in the materials. The morphology investigation revealed the porous texture of obtained ceramics characterized by the presence of sponge-like structure mainly due to the additive decomposition at high temperatures. The DSC results confirm the presence of four temperature regions related to the kaolin thermal transformations and the formation of minerals. The temperature and enthalpy of mineral formation are additive concentration dependent. As a result, the optimal content of additives which allowed the coexistence of the three phases, a spongelike morphology, and high porosity without cracks corresponded to 15 wt% CaCO 3 , 15 wt% Na 2 CO 3 , and 70 wt% kaolin.

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Section: [Figura 4: Difratogramas De Raios X Das Cerâmicas Preparadasmentioning

confidence: 99%

Elaboration and characterization of mullite-anorthite-albite porous ceramics prepared from Algerian kaolin

2018

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“…8, 12, 14 and 17 then provide the set of important parameters, which can have interesting utilization in many branches of heterogeneous kinetics. For example, it enables to eliminate the constant term from Kissinger Equation [14,15]:…”

Section: J•k à1mentioning

confidence: 99%

“…It was also recognized that the value of B(x) is not affected by the size of crystallites in the sample. Another example could be the dehydroxylation step during the process of thermal decomposition (400-700 C) of kaolinite [15]:…”

Section: J•k à1mentioning

confidence: 99%

Introducing an Approach to Effective Mass of Activated Complex

Ptáček¹,

Opravil²,

Šoukal³

2018

Introducing the Effective Mass of Activated Complex and the Discussion on the Wave Function of This Instanton

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This chapter provides the information about the concept of effective mass and effective velocity of the activated complex and its connection to the transition state theory. Therefore, these parameters are of essential importance for the field of homogenous as well as heterogeneous kinetics. They also prove to be useful for the calculation of many other properties of activated state, such as momentum, energetic density, mass flux, etc., as will be demonstrated on the example of thermal decomposition of calcite and aragonite. Since the activation energy and the momentum of activated state enable to complete the characterization of motion of this instanton (pseudoparticle) alongside the reaction coordinate, these parameters can be then considered as two quantum numbers of activated complex. The quantum numbers of activated state, that is, the activation energy and momentum, also explain the relation of activated complex to Planck energy, length and time, as well as to the Gravitational constant. This idea was also applied to derive the wave function of activated complex pseudoparticle, which is affected by the isotopic composition of the sample and polymorphism as well. Furthermore, the findings introduced in this chapter enable to derive and propose the modified Kissinger equation and experimental solution for the approximation parameter in the Doyle equation of temperature integral.

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“…Kaolinite is the main structure of kaolin mineral. Kaolinite consist of aluminosilicate hidrate compound Al 2 Si 2 O 5 (OH) 4 which consist of Si-O crystal tetrahedral layer (SiO 4 ) connected with alumina crystal octahedral layer (Al (O, OH)6) [1] . During calcination, the main reaction which occured is the breaking off the kaolinite structure.…”

Section: Introductionmentioning

confidence: 99%

“…The heating reaction breaks off -OH chain from the mineral, and collapsing the kaolinite structure, resulting in an amorphous aluminosilicate structure (Al 2 O 3 .2SiO 2 ) known as metakaolinite. Theoritically, there are three stages of thermal transformation of kaolinite to metakaolinite [2][3][4][5]:  When the heating process begin, kaolinite structure will break down and separate the alumina layer and silicate layer and break down the long order structure. This process occured until the heating temperature reach 400 o C, caused by the dehydroxilation of hydroxil structure in the layer which cause the water crystal to evaporate and leave the main structure.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Fabrication of Metakaolin using Pulau Bangka Kaolin

2018

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Geopolymer material is an advanced material that is now being looked for its use as a refractory material, additive for building material, as well as other applications. Geopolymer is produced by polymerizing the precursor used in the process. One of the common precursors being used as geopolymer is metakaolin. The metakaolin was produced by thermal treatment (calcination) of kaolin minerals, which will convert its mineral structure from crystaline into amorphous and make it more reactive. This paper presents the fabrication and characterization of metakaolin using kaolin from Bangka island. The main structure of kaolin used in this study are kaolinite and muscovite according to XRD results obtained. Metakaolin was produced by thermal treatment using three different calcination temperatures ranged from 600 to 700 o C and calcined for 4 hours. Prior to calcination, some specimens will be mechanically milled using planetary ball mill for 15 minutes with the milling speed of 20.00 rad/s and will also be calcined with the same parameter. As a comparison, commercial metakaolin MetaStar also be used to compare it to all metakaolin produced. All metakaolin produced are characterized by XRD and SEM, and STA test will be performed to kaolin to examine its thermal behavior. The STA test performed to both milled and non-milled sample shows that dehydroxylation and reconstruction process occurs at temperature range of 460-520 o C and 520-640 o C for kaolin sample, and at temperature of 426-537 o C and 537-618 o C for milled kaolin sample. XRD pattern obtained shows that almost all metakaolin produced have the relatively similar pattern to each other as well as to MetaStar, with the main peak of quartz (SiO 2 ) at 2= 26.60 o to 26.65 o . The SEM results shows the characteristic layered-laminate plate-like structure of kaolin. Compared to another SEM results obtained, it can be concluded that there are no changes to the visible structure of metakaolin produced with the same kaolin used after calcination.

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Kinetics and mechanism of three stages of thermal transformation of kaolinite to metakaolinite

Cited by 99 publications

References 49 publications

Elaboration and characterization of mullite-anorthite-albite porous ceramics prepared from Algerian kaolin

Elaboration and characterization of mullite-anorthite-albite porous ceramics prepared from Algerian kaolin

Introducing an Approach to Effective Mass of Activated Complex

Characterization and Fabrication of Metakaolin using Pulau Bangka Kaolin

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