Thermally stimulated current analysis

Figure 16 Thermally stimulated current analysis of a freeze-dried drug. Lower curve polarisation current. Upper curve depolarisation current. Heating rate 7°C min for both experiments...

Current Measurcoient (Thermally Stimulated Current Analysis) electric field TSCA... 

Cambridge University Press, Cambridge. A related technique, that of thermally stimulated current analysis is described by Ibar IP (1993) Fundamentals of Thermal Stimulated Current and Relaxation Map Analysis. SLP Press, New Canaan. 

In terms of modulated thermal analysis techniques , TMDSC clearly dominates the group. However, there is limited literature on temperature modulated thermogravimetic analysis (TMTGA) and temperature modulated thermomechanical analysis (TMTMA). Modulation principles have been applied to some less common thermal analysis techniques such as DMA and thermally stimulated current analysis and these developments will be briefly addressed here. It appears that the major development in thermal analysis in the next decade will be in the temperature modulated domain. 

Finally, temperature modulated thermally stimulated current analysis has been applied to study dielectric materials via the separation of reversible pyroelectric effects from nonreversing thermally stimulated discharges. 

Thermally stimulated current analysis (TSCA) is another member of the TEA group of techniques. In TSCA, the sample is subjected to a constant electric field and the current that flows through the sample is measured as a function of temperature. The mode of operation usually involves heating the sample to a high temperature under the applied field followed by quenching to a low temperature. This process aligns dipoles within the sample. The polarization field is then switched off and the sample is reheated and the current flow resulting from the relaxation of the induced dipoles back to the disordered state is monitored. 

Thermally Stimulated Current Analysis of Thick PMMA Films... 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

Thermally stimulated creep (TSCr) method, 21 742-743 Thermally stimulated current spectrometry (TSC), 21 743 Thermal mass meters, 20 681 Thermal mechanical analysis (TMA), of polyester fibers, 20 21 Thermal motion, in silicon-based semiconductors, 22 237-238 Thermal noise, silicon-based semiconductors and, 22 237 Thermal oxidation, 10 77-78, 79 in VOC control, 20 683-685 Thermal oxidation rates, silicon, 22 490 Thermal oxidizers... 

Fig. 4 (a) and (b) explain the principle. This is the thermally stimulated current to be used for the analysis of the trap depth and its population. In so far as the film has no experience of being heated above 110°C, the same film assembly could be used repeatedly many times with satisfactory reproducible results. 

On the methods of analysis of the thermally stimulated current and the values of the trap depth in poly-N-vinyl-carbazole... 

Some recent thermally stimulated current (TSC) data obtained by Martin and Bois (1978) are shown in Fig. 8. Here the maximum occurs at 264°K, giving Ei0 0.61 eV,forcrBj 10-1S cm2. Evidently, a was not varied in this experiment. Note that the dark current begins to increase rapidly near room temperature in these data. Here our analysis must break down since capture... 

The book opens with the first three chapters devoted to differential scanning calorimetry (DSC), the most commonly used thermal method. These chapters cover the principles, optimal use, and pharmaceutical applications of the method. Subsequent chapters explore modulated temperature DSC, thermogravimetric analysis, thermal microscopy, microcalorimetry, high sensitivity DSC, dynamic mechanical analysis, and thermally stimulated current, all of which have attracted great interest within the pharmaceutical field. Each chapter includes theoretical background, measurement optimization, and pharmaceutical applications. 

Thermally Stimulated Current (TSC). This relatively straightforward method has been used for years as a method of thermal analysis comparable in some aspects to Thermal Mechanical Analysis (TMA). For example, TSC is able to detect many of the same transitions as seen by the mechanical methods. The advantages of TSC include its extremely high sensitivity and its low... 

Electrical Properties Dielectric Thermal Analysis Thermally Stimulated Current DEA TSC Dielectric Constant/ Dielectric Loss measured Current... 

Yoshida, F. Maeta, S. "Proposal of Asymptotic Estimation v Method Evaluating Escape Frequency Factor from a Partial Thermally Stimulated Current Curve Directly", Trans. Inst. Electr. Eng. Jpn., Vol.lll-A, No.4, pp.323-331, (1991) [in Japanese] Yoshida, F., Tanaka, M. Maeta, S. "Proposal of Asymptotic Estimation I Method with High Sensitivity to Thermally Stimulated Current Curve and its Application to New Analysis",Trans. Inst. Electr. Eng. Jpn., Vol.lll-A, No.2, pp.104-110, (1991) [in Japanese]... 

Solomat Instrumentation X TSC/RMA Spectrometer Thermally Stimulated Current Depolarization/ Relaxation Map Analysis... 

In response to criticism from members of the electronics industry that thermal analysis methods are often incompatible with the rapid pace of corporate research development, new sections have been introduced on thermally stimulated current spectroscopy, thermal conductivity, optothermal transient emission radiometry and micro-thermal analysis (/ TA). 

Technical Analysis Description 3.1 Thermally Stimulated Current (TSC)... 

Relaxation-map analysis (RMA) n. A technique used on the results of a series of thermally stimulated current experiments in which the TSC data are transformed into relaxation times and plotted versus reciprocal absolute temperature to estimate enthalpy and entropy of activation for the molecular relaxations. 

Another TL application is the analysis of the electronics states in materials, which are defined by both material and technology of its production. For example, for PS different contact methods to define the electronics states in metal/PS stmctures have been aheady applied thermally stimulated depolarization currents (TSDC) and thermally stimulated current (TSC) (Ciurea et al. 1998 Anastasiadis and Triantis 2000 Brodovoy et al. 2002), optical charging spectroscopy (OCS) (Ciurea et al. 2000), and deep-level transient spectroscopy (DLTS) (Pincik et al. 1999 Tretyak et al. 2003). The mentioned methods determine the parameters of traps related with both PS material and metal/PS interface and often differ from results obtained from TL experiments. Two advantages of the TL method are that it is contactless and it can reveal the energy distribution of both bulk and/or surface states. The obvious drawback of TL is that it can only be applied to luminescent materials. 

Although the above approaches may all be amenable to detection of crystallization in finished products, they can also be used to characterize the HME (i.e., prior to downstream processing). Further, many other techniques are often applied exclusively to the HME intermediate. For instance, optical microscopy offers excellent detectability of crystalline material in transparent extrudates. Dielectric analysis (DBA Alie et al. 2004 Bhugra et al. 2007, 2008) and thermally stimulated current IR spectroscopy (Shah et al. 2006 Rumondor and Taylor 2010), atomic force microscopy (ATM Lauer et al. 2013 Marsac et al. 2012 Price and Young 2004), and calorimetric methods have also been used to detect crystallization from an amorphous matrix (Baird and Taylor 2012 Pikal and Dellerman 1989 Avella et al. 1991). 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

Aspects of common DEA techniques are presented in the following paragraphs, with emphasis on the instrumentation that is likely to be used in a typical thermal analysis laboratory examples are Novocontrol Spectrometers (BDS), TA Instruments (DEA 2970, although the production of this instrument has been discontinued), and Polymer Laboratories (DETA, this instrument is not available any more either). Dielectrometers (Micromet Instruments, now owned by Netzsch), used for in-process cure monitoring of thermosets, operate on similar principles. Features of the sensitive thermally stimulated current technique, and its comparison to DEA, are also discussed. 

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