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首页> 外文期刊>Physics and chemistry of minerals >Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non?isothermal/isothermal thermogravimetric analysis and high?temperature X?ray powder diffraction study
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Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non?isothermal/isothermal thermogravimetric analysis and high?temperature X?ray powder diffraction study

机译：温石棉与水镁石脱羟基反应的动力学：非等温/等温热重分析与高温X射线粉末衍射研究的结合

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The dehydroxylation reactions of chrysotile Mg_3Si_2O_5(OH)_4 and brucite Mg(OH)_2 were studied under inert nitrogen atmosphere using isothermal and non-isothermal approaches. The brucite decomposition was additionally studied under CO_2 in order to check the influence of a competing dehydroxylation/carbonation/decarbonisation reaction on the reaction kinetics. Isothermal experiments were conducted using in situ high-temperature X-ray powder diffraction, whereas non-isothermal experiments were performed by thermogravimetric analyses. All data were treated by model-free, isoconversional approaches (‘time to a given fraction’ and Friedman method) to avoid the influence of kinetic misinterpretation caused by model-fitting techniques. All examined reactions are characterised by a dynamic, non-constant reaction-progress-resolved (‘α’- resolved) course of the apparent activation energy E_a and indicate, therefore, multi-step reaction scenarios in case of the three studied reactions. The dehydroxylation kinetics of chrysotile can be subdivided into three different stages characterised by a steadily increasing Ea (α ≤ 15 %, 240–300 kJ/mol), before coming down and forming a plateau(15 % ≤ α ≤ 60 %, 300–260 kJ/mol). The reaction ends with an increasing Ea (α ≥ 60 %, 260–290 kJ/mol). The dehydroxylation of brucite under nitrogen shows a less dynamic, but generally decreasing trend in Ea versus α (160–110 kJ/mol). In contrast to that, the decomposition of brucite under CO_2 delivers a dynamic course with a much higher apparent Ea characterised by an initial stage of around 290 kJ/mol. Afterwards, the apparent Ea comes down to around 250 kJ/mol at α ~ 65 % before rising up to around 400 kJ/mol. The delivered kinetic data have been investigated by the z(α) master plot and generalised time master plot methods in order to discriminate the reaction mechanism. Resulting data verify the multi-step reaction scenarios (reactions governed by more than one rate-determining step) already visible in E_a versus α plots.
机译：利用等温和非等温方法研究了在惰性氮气气氛下温石棉Mg_3Si_2O_5（OH）_4与水镁石Mg（OH）_2的脱羟基反应。为了检查竞争的脱羟基/碳酸化/脱碳反应对反应动力学的影响，还另外对水镁石在CO_2下的分解进行了研究。使用原位高温X射线粉末衍射进行等温实验，而通过热重分析进行非等温实验。所有数据均采用无模型的等转换方法（“给定分数的时间”和Friedman方法）进行处理，以避免因模型拟合技术引起的动力学错误解释的影响。所有检查的反应的特征在于表观活化能E_a的动态，非恒定的反应进行分辨（“α”分辨）过程，因此，在研究了这三种反应的情况下，可以指示多步反应方案。温石棉的脱羟基动力学可分为三个不同的阶段，其特征在于Ea稳定增加（α≤15％，240–300 kJ / mol），然后下降并形成平稳状态（15％≤α≤60％，300–300）。 260 kJ / mol）。反应以增加的Ea结束（α≥60％，260–290 kJ / mol）。在氮气氛下水镁石的脱羟基反应动力学较弱，但Ea相对于α（160-110 kJ / mol）总体呈下降趋势。与此相反，在CO_2下水镁石的分解提供了一个动态过程，其表观Ea值高得多，其初始阶段约为290 kJ / mol。之后，表观Ea在α〜65％时降至约250 kJ / mol，然后升高至约400 kJ / mol。传递的动力学数据已通过z（α）主图和广义时间主图方法进行了研究，以区分反应机理。所得数据验证了在E_a对α图中已经可见的多步反应场景（反应由多个速率确定步骤决定）。

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