Thermal Analysis UserCom 47

In recent decades, chalcogenide glasses have been the subject of intense interest because of their unique physical properties such as high infrared transparency, strong light sensitivity, and high refractive index. The glasses are used for optical fibers, lenses, sensors and phase change storage systems, as well as for data storage media (RW-CD / DVD / Blu-Ray). The applications are based on reversible amorphous crystalline phase changes. Phase transitions like this exhibited by Se1-xTex alloys were investigated using ultrafast differential scanning calorimetry (Flash DSC).

Introduction

Currently, Flash EEPROMs are used to store information, for example in smart phones, laptops and USB sticks. A disadvantage of Flash EEPROMs is their limited lifetime due to the maximum number of about 10⁶ writing cycles.

Many more writing cycles can be achieved with phase change materials (PCMs). This makes use of the properties of the different phases (e.g. amorphous and crystalline).

In this respect, chalconide glasses are an interesting class of materials in which the classical glass-forming elements silicon and oxygen are replaced by germanium and arsenic, and by sulfur, selenium and tellurium in the heavier chalconides.

In chalcogenide PCMs, the change from the amorphous to the crystalline phase (Figure 1) can occur reversibly up to 1011 times [1].

The different phases are switched by pulses of a defined length and intensity. If high energy pulses are used, the sample is strongly heated and the crystals melt.

In these glasses, the critical cooling rate (at which no crystallization occurs) is so low that no crystals form on rapid cooling after the pulse. The material remains amorphous.

Crystalline phases occur when “low energy pulses" and longer pulse widths are used. The material heats up to the crystallization temperature and the amorphous phase changes to a crystalline phase. As indicated in Figure 1, the phase transition takes place in a spatially restricted region in order to achieve a sufficiently large data density. The phase transitions are very fast and can be simulated using ultrafast DSC.

A SeTe alloy was chosen as a model substance to study the phase transition and to investigate the following aspects:

(i) reversible phase switching through melt-quenching to an amorphous phase and recrystallization on heating,

(ii) precise control of the thermal history of the material,

(iii) the repetition of measurements using the same sample.

The aim of the research work was to gain an insight into the phase transition kinetics of this material. The measurements were performed using a METTLER TOLEDO Flash DSC 1. Detailed information on our work can be found in [2] and [3].

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References

[1] A. Sebastian, M. Le Gallo, and D. Krebs, “Crystal growth within a phase change memory cell,” Nat. Commun. (2014), 5: 4314.
[2] P. A. Vermeulen, J. Momand, and B. J. Kooi, “Reversible amorphouscrystalline phase changes in a wide range of Se1-xTex alloys studied using ultrafast differential scanning calorimetry,” J. Chem. Phys. (2014), 141, 024502.
[3] B. Chen, J. Momand, P.A. Vermeulen, and B.J. Kooi "Crystallization Kinetics of Supercooled Liquid Ge–Sb Based on Ultrafast Calorimetry", Cryst. Growth Des. (2016), 16, 242–248
[4] G. Ghosh, R. C. Sharma, D. T. Li, and Y. a. Chang, “The Se-Te (Selenium-Tellurium) system,” J. Phase Equilibria (1994), 15: 213–224.
[5] H. E. Kissinger, “Reaction Kinetics in differential Thermal Analysis,” Anal. Chem. (1957), 29: 1702–1706.

Dimethylformamide is a high boiling point liquid that is used as a solvent for organic compounds, for chemical reactions and in the production of polymer fibers, films or coatings. It has a harmful vapor and is irritating to the skin, eyes and respiratory system. In this article, we show how low concentrations of DMF can be determined by TGA-GC/MS.

Introduction

Dimethylformamide (DMF) is a solvent that is miscible with water and with most organic liquids. It is used as a solvent in the manufacture of textile fibers (acrylic fibers) or coatings. Its vapor is harmful and irritates the skin, eyes and respiratory system. The question is what concentrations of DMF can be detected in products and quantified.

In this article, we show how this can be done using a powder coating as an example.

Experimental details

The measurements were performed using a TGA/DSC 3+ coupled to an SRA Instruments IST16 storage interface and an Agilent (7890 GC with 5975C MSD) GC/MS.

A trial experiment was carried out using a TGA/DSC 3+ coupled to a Pfeiffer Thermostar MS GSD 320. The measurements were performed with sample masses of about 100 mg in 150-μL aluminum oxide crucibles and a nitrogen flow rate of 60 mL/min.

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In the processing of thermoplastics, the water content of the granules used is of major importance for the quality of the final product. This article shows how the water content of granulates can be determined by Karl Fischer titration, TGA, and TGA-Micro GC/MS.

Introduction

Thermoplastics (polyethylene, polyamides, etc.) are supplied by the manufacturers as granules to plastics processing plants. Processing of the granules to products takes place afterward in extruders (semi-finished products such as plates, tubes, etc.) or in injection molding machines.

In both processes, the granules are melted and then extruded under pressure through suitable nozzles as semifinished products or injected under pressure into a mold (injection molding). This enables plastic components to be produced in practically any form desired. An important parameter in the extrusion of the granules is their water content: even a water content of less than 0.1% can adversely affect the quality of the final product (bubble formation, surface defects, etc.).

In this article, we show how the water content in polymer granules can be determined by Karl Fischer titration and TGA. The purpose is also to determine the optimum extraction temperature at which any water present can be removed in the shortest possible time by means of a flow of gas without the material decomposing. An ABS granule (ABS: acrylonitrile- butadiene-styrene) was investigated as an example.

Experimental details

The determination of the water content by titration was performed using a volumetric Karl Fischer titrator (METTLER TOLEDO V30S) together with a METTLER TOLEDO InMotion KF Pro autosampler. The method consists of heating a sample with an unknown water content at a constant heating rate in a constant flow of dry gas (typically between 80 and 150 mL/min).

Any gaseous products released from the sample (e.g. water, solvents, possibly decomposition products, etc.) are transferred by the dry gas (usually nitrogen or synthetic air) into the titration cell where they are titrated. Here, one should be aware of the fact that in a Karl Fischer (KF) titration not only water but also other substances can be detected if they react with the KF reagents.

In the case of granules, this can in particular be decomposition products. To make sure that only water originating from the sample is measured, the measured titration curve can be corrected with a so-called blank curve. This curve is measured by heating an empty sample vial using the same measurement program.

Any water content detected is due to possible transmission of air through of the tubing and residual moisture in the sample vial.

In our example, 1.78 g ABS was weighed into a 10-mL sample vial and heated at 2 K/min from 40 to 280 °C in a flow of 100 mL/min nitrogen.

The TGA measurements were carried out using a METTLER TOLEDO TGA/DSC 3+ coupled to a Micro GC/MS. In addition, a DSC measurement was performed using a DSC 3+. The measurements were conducted out at a heating rate of 2 K/min and a flow rate of 50 mL/min nitrogen. The sample mass for the TGA-Micro GC/ MS measurement was 446.076 mg.

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Data integrity is a major issue within the pharmaceutical industry due to regulatory inspections discovering problems from poor data management practices to falsification of records. The regulatory background will be discussed in this article followed by system architecture issues and ways to prevent regulatory citations. The principles described here are also relevant to laboratories working to similar regulations and quality standards in medical devices, food, environmental but also research.

What’s all the fuss about data integrity?

The hottest topic now in Good Manufacturing Practice (GMP) regulated laboratories in the pharmaceutical industry and associated support organizations is data integrity. Although this discussion is focused on regulated laboratories, data integrity also has a wider impact.

Virtually all academic research facilities have introduced code of ethics for scientists to prevent scientific fraud to protect their reputations and that of the parent institution.

Environmental laboratories have requirements in laboratory standards specifically to ensure the involvement of senior management to write data integrity policies and procedures with training to ensure staff know how to behave and record data correctly.

However, in this article we will focus on GMP regulated laboratories working in or for the pharmaceutical industry but the principles described here can be used for all industries and laboratories with high quality standards or similar regulations.

Data integrity is however, an issue even in research laboratories with the data falsification scandal such as the 2002 Jan Schön case that resulted in over 20 scientific papers being withdrawn from journals such as Science and Nature [1].

Regulations and warning letters

GMP laboratories work can work to one or more of the following regulations e.g.

• US Current Good Manufacturing Practice for Finished Pharmaceutical Products (21 CFR 211) [2]
  
• EU GMP Parts 1 and 2 for Medicinal Products and Active Pharmaceutical Ingredients respectively [3, 4]
  
• US Electronic Records; Electronic Signatures final rule (21 CFR 11) [5]
  
• EU GMP Annex 11 for Computerized Systems [6]
  

The first two regulations are applicable to all analytical work. The last two regulations are only involved when a computerized system is used.

As this article is for thermal analysis we will consider a thermal analysis instrument with a computerized system for control, data acquisition and processing of data.

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