A sample-saving method for heat capacity measurements on powders using relaxation calorimetry.
A sample-saving method for heat capacity measurements on powders using relaxation calorimetry.
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DOI：
10.1016/j.cryogenics.2011.04.011
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发表时间：
2011-08
期刊：
影响因子：
2.1
通讯作者：
Benisek A
中科院分区：
文献类型：
--
作者：
Dachs E;Benisek A
提出了一种测量粉末低温热容的方法。该方法基于PPMS和DSC测量的组合。它允许对粉末进行熵测定，精度优于1%。测量过程中，样品未与Apiezon N润滑脂混合。这对于只有少量可用的样本很有用。本文介绍了一种利用量子设计物理性能测量系统（PPMS）测定镁粉样品低温热容的实验方法。将粉末作为约1 mm厚的压缩层包含在Al盘中。与其他方法相比，样品不与Apiezon N润滑脂混合。因此，它没有被污染，可以用于进一步的研究。这对于只有少量可用的样品是必要的。为了证明该方法，研究了各种样品，所有绝缘的性质，包括苯甲酸，蓝宝石和不同的硅酸盐矿物。测量结果表明，在30-50 K温度范围内，本方法的Cp精度优于1%，在30-50 K温度范围内，Cp精度为±3-5%，最高可达±10%。实验过程是基于三个独立的PPMS和三个独立的差示扫描量热法（DSC）测量。DSC Cp数据用于通过因子略微调整PPMS Cp数据。这样做是因为用DSC装置测量的热容在环境温度附近比PPMS值更准确（± 0.6%），并且是可能的，因为PPMS热容与参考值的偏差在约50 K和300 K之间几乎恒定。所得的标准熵同意与公布的参考值在0.21%的硅酸盐，0.34%的硅酸盐，和0.9%的粉末状苯甲酸。因此，该方法允许熵测定粉末的精度优于1%。与其他实验技术相比，我们的方法的优点是样品粉末不受油脂污染，并且热容值在高温下分散较小。
► A method for low-temperature heat capacity measurements on powders is presented. ► The method is based on combined PPMS and DSC measurements. ► It allows entropy determinations on powders with an accuracy of better than 1%. ► The sample is not mixed with Apiezon N grease during measurement. ► This is useful for samples that are only available in tiny amounts. An experimental method is described for determining the low-temperature heat capacity (Cp) of mg-sized powder samples using the Quantum Design “Physical Properties Measurement System” (PPMS). The powder is contained in an Al pan as an ∼1 mm thick compressed layer. The sample is not mixed with Apiezon N grease, as compared to other methods. Thus, it is not contaminated and can be used for further study. This is necessary for samples that are only available in tiny amounts. To demonstrate the method various samples, all insulating in nature, were studied including benzoic acid, sapphire and different silicate minerals. The measurements show that the method has an accuracy in Cp to better than 1% at T above 30–50 K and ±3–5% up to ±10% below. The experimental procedure is based on three independent PPMS and three independent differential scanning calorimetry (DSC) measurements. The DSC Cp data are used to slightly adjust the PPMS Cp data by a factor . This is done because heat capacities measured with a DSC device are more accurate around ambient T (⩽0.6%) than PPMS values and is possible because the deviation of PPMS heat capacities from reference values is nearly constant between about 50 K and 300 K. The resulting standard entropies agree with published reference values within 0.21% for the silicates, by 0.34% for corundum, and by 0.9% for powdered benzoic acid. The method thus allows entropy determinations on powders with an accuracy of better than 1%. The advantage of our method compared to other experimental techniques is that the sample powder is not contaminated with grease and that heat capacity values show less scatter at high temperatures.