X-RAY DIFFRACTION AND ADSORPTION ISOTHERM STUDIES OF THE CALCIUM MONTMORILLONITE-WATER SYSTEM

Highway Research Record Pub Date : 1900-01-01 DOI:10.31274/RTD-180813-2894

D. Senich, T. Demirel, R. Handy

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引用次数: 3

Abstract

ADSORPTION ISOTHERM AND X-RAY DIFFRACTION TECHNIQUES WERE USED TO STUDY THE ADSORPTION OF WATER ON A HOMOIONIC CALCIUM MONTMORILLONITE AT 25 C. THE BASAL D SPACINGS OF THE PRIMARY AND SECONDARY REFLECTIONS, THEIR INTENSITIES AND LINE BREADTH VARIATIONS WERE DETERMINED IN A SPECIALLY CONSTRUCTED X-RAY ADSORPTION CHAMBER. THE FIRST-ORDER BASAL SPACING WAS FOUND TO CHANGE IN A CONTINUOUS BUT NONUNIFORM MANNER. THE INTENSITY OF SECONDARY REFLECTIONS WAS EXPLAINED ON THE BASIS OF LAYER ELECTRON DENSITY DISTRIBUTION. A COMPARISON OF THE LINE BREADTH, INTENSITY AND ADSORPTION DATA INDICATES AN ICE-LIKE CONFIGURATION OF INTERLAYER ABSORBED WATER IN THE P/P SUB O RANGE ABOVE 0.95. PROLONGED X-RADIATION CAUSED A DISCOLORATION OF SAMPLES ATTRIBUTED TO RADIATION-INDUCED COLOR CENTERS. TWO SUCCESSIVE ADSORPTION AND DESORPTION ISOTHERMS OF WATER VAPOR ON A MONTMORILLONITE POWDER COMPRESSED AT 25 KG/CM SQ. WERE DETERMINED USING AN ELECTROBALANCE AND AN AUTOMATIC RECORDING DEVICE. THE ISOTHERMS EXHIBITED A HYSTERESIS BUT WERE COMPLETELY REVERSIBLE IN THE RELATIVE VAPOR PRESSURE RANGE FROM ZERO TO 0.20. THE RATE OF ADSORPTION WAS GREATER THAN RATE OF DESORPTION. THE LANGMUIR MONOMOLECULAR MODEL FOR THE ADSORPTION PROCESS AND THE BET /BRUNAUER, EMMETT, TELLER/ MULTI-MOLECULAR MODEL WERE COMPARED, AND THE LATTER WAS FOUND TO FIT THE ADSORPTION DATA MORE CLOSELY. THE BET EQUATION WAS FOUND TO BE APPLICABLE IN THE RELATIVE PRESSURE RANGE FROM P/P SUB O EQUAL TO 0.11 TO P/P SUB O EQUAL TO 0.27. THE SPECIFIC SURFACE AND HEAT OF ADSORPTION OF THE FIRST MONOLAYER WERE CALCULATED FROM THE BET PARAMETERS. THE ADSORPTION ISOTHERMS WERE USED TO CALCULATE THE FREE ENERGY CHANGES ON ADSORPTION. THE FREE ENERGY CHANGES ON SUCCESSIVE ADSORPTION CYCLES COMPARED FAVORABLY WITH LOOSE POWDER DATA, INDICATING THAT COMPRESSION HAD LITTLE EFFECT ON THE MAGNITUDE OF THE FREE ENERGY CHANGE. THE FREE ENERGY CHANGES WERE DIVIDED INTO TWO COMPONTNES: ONE FOR ADSORPTION ON INTERNAL SURFACES AND ONE FOR ADSORPTION ON EXTERNAL SURFACES. USING THE DATA, EXPANSION ENERGIES AND SWELLING PRESSURES EXERTED BY CALCIUM MONTMORILLONITE WERE CALCULATED . /AUTHOR/

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钙蒙脱石-水体系的x射线衍射和吸附等温线研究

采用等温线和x射线衍射技术研究了25℃时同离子钙蒙脱土对水的吸附，在特制的x射线吸附室中测定了主反射和二次反射的基本间隔、强度和线宽变化。发现一阶基间距以连续但不均匀的方式变化。根据层电子密度分布解释了二次反射的强度。谱线宽度、谱线强度和吸附数据的对比表明，在p / p < 0 > 0.95范围内，层间吸附水呈冰状结构。长时间的x射线辐射导致样品变色，这是由于辐射引起的色心。压缩为25kg / cm2的蒙脱土粉末上水蒸气的连续两次吸附和解吸等温线。用电子天平和自动记录装置测定。在相对蒸汽压0 ~ 0.20范围内，等温线表现出迟滞性，但完全可逆。吸附速率大于解吸速率。将Langmuir单分子吸附模型与bet / brunauer、emmett、teller /多分子吸附模型进行了比较，发现后者更符合吸附数据。在p / p / p = 0.11至p / p = 0.27的相对压力范围内，发现bet方程是适用的。根据这些参数计算了第一层膜的比表面积和吸附热。利用吸附等温线计算吸附过程中自由能的变化。在连续的吸附循环中，自由能的变化与松散粉末的数据相比要好，这表明压缩对自由能变化的大小影响很小。自由能变化分为内表面吸附和外表面吸附两部分。利用这些数据，计算了钙蒙脱土的膨胀能和膨胀压力。/作者/

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Highway Research Record

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