Sample pans

The types of pans available can be divided into three general types general, hermetic, and high-pressure. 

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Ngo et al. [24] have shown that the thermal decomposition of ionic liquids, measured by TGA, varies depending on the sample pans used. Increased stabilization of up to 50 °C was obtained in some cases on changing from aluminium to alumina sample pans. 

DSC Calorimetry was done in a Perkin-Elmer DSC II at a scan rate of 20°C/min. The scale used is 2mcal/sec. full scale. Sample weight was 12" 20 mg. with an empty sample pan as reference. 

We use differential scanning calorimetry - which we invariably shorten to DSC - to analyze the thermal properties of polymer samples as a function of temperature. We encapsulate a small sample of polymer, typically weighing a few milligrams, in an aluminum pan that we place on top of a small heater within an insulated cell. We place an empty sample pan atop the heater of an identical reference cell. The temperature of the two cells is ramped at a precise rate and the difference in heat required to maintain the two cells at the same temperature is recorded. A computer provides the results as a thermogram, in which heat flow is plotted as a function of temperature, a schematic example of which is shown in Fig. 7.13. 

Differential photocalorimetry (DPC) is included here since the instrument used is essentially an adaptation of DSC instrumentation. The photocalorimeter comprises a DSC instrument with a UV/visible source mounted on top, such that light of appropriate wavelength or wavelength region from the source is focused onto the measuring head (both reference and sample pans). The most frequent use of DPC is in the study of polymer cure reactions, but it may also be used to follow such as UV degradation. 

Thermal decomposition was performed using a SDT Q-600 simultaneous DSC-TGA instrument (TA Instruments). The samples (mass app. 10 mg) were heated in a standard alumina 90 il sample pan. All experiments were carried out under air with a flow rate of 0.1 dm3/min. Non-isothermal measurements were conducted at heating rates of 3, 6, 9, 12, and 16 K/min. Five experiments were done at each heating rate. 

When heated, many solids evolve a gas. For example, most carbonates lose carbon dioxide when heated. Because there is a mass loss, it is possible to determine the extent of the reaction by following the mass of the sample. The technique of thermogravimetric analysis involves heating the sample in a pan surrounded by a furnace. The sample pan is suspended from a microbalance so its mass can be monitored continuously as the temperature is raised (usually as a linear function of time). A recorder provides a graph showing the mass as a function of temperature. From the mass loss, it is often possible to establish the stoichiometry of the reaction. Because the extent of the reaction can be followed, kinetic analysis of the data can be performed. Because mass is the property measured, TGA is useful for... 

It is most essential in TG design that the temperature readout pertain to that of the sample, and not to that of the furnace. To achieve this end, the thermocouple or resistance thermometer is normally mounted as close to the sample pan as possible, in direct contact if this can be achieved. 

Sensitive balance with the sample pan inside a furnace whose temperature can be accurately controlled and programmed for change. Facilities for... 

Glass transition temperatures of the uv-hardened films were measured with a Perkin Elmer Model DSC-4 differential scanning calorimeter (DSC) that was calibrated with an indium standard. The films were scraped from silicon substrates and placed in DSC sample pans. Temperature scans were run from -40 to 100-200 °C at a rate of 20 ° C/min and the temperature at the midpoint of the transition was assigned to Tg. 

A top-loading balance is an electronic balance with the sample pan on the top. It is not enclosed, which means that it is capable of measuring only to the nearest hundredth of a gram. See Figure 3.3. 

Prior to conducting the sorption experiment, the coal extract (200 mg) was first placed in a Wig-L-Bug capsule and ground for 1 minute under nitrogen. This grinding effectively reduces the extract to a fine powder, which is then used for the sorption experiment. Approximately 50-70 mg of the extract was then placed on the sample pan and the hangdown tube was replaced. The sample was maintained at 30.00 0.02 C by means of a constant temperature bath which surrounded the hangdown tube. 

A solution of 3.36 w% initiator in TEGDA was used for DSC, TMS and DMTA measurements. DSC sample weights were about 1 mg, corresponding to a thickness of about 60 fim when aluminum lids of standard sample pans are used. 

Next the time to reach the maximum signal and the relative peak area were determined as a function of the duration of the shutter opening (Figure 6). Relative peak area is almost constant after 1 s, whereas the time to reach the maximum amplitude becomes constant beyond 6 s. These findings are consistent with the presence of barriers to heat transfer in the DSC itself and between sample pan and the thermistor, which delay the transfer of the heat rather than changing the total amount of heat detected. 

DSC can also be used to determine starch retrogradation. After heating potato starch (30% (w/w)) to 180°C, samples are cooled to 5°C. Once the temperature reaches 5°C, the sample is immediately removed from the DSC and stored at low temperature. After a certain number of days, the sample pan is placed into the sample holder of the DSC, and heated from 5 to 180°C at 10°C /min. The instrument is calibrated using indium and an empty pan as a reference. The enthalpy (AH) of phase transitions is measured from the endotherm of DSC thermograms based on the mass of dry solid. Transition temperatures such as onset, peak, and completion temperature are also measured. 

Use forceps to handle the sample pan and lid. Obtain the tare weight of a sample pan and lid (the type that can be hermetically sealed is not required). (Note Select pans with flat undistorted bottoms so that good contact with the cell platforms is assured.)... 

Record the mass of the sample pan and lid to five significant figures. 

Add about 10 mg of polyamide or calibration standard to the sample pan and lid and weigh again. A powdered sample provides better thermal contact. 

Remove the polymer sample pan and lid carefully from the balance using forceps. (Note Skin moisture and oils will be left on the sample pan and lid if they are picked up by fingers. This extra mass will effect the DSC experiment.)... 

Differential scanning calorimetry is primarily used to determine changes in proteins as a function of temperature. The instrument used is a thermal analysis system, for example a Mettler DSC model 821e. The instrument coupled with a computer can quickly provide a thermal analysis of the protein solution and a control solution (no protein). The instrument contains two pans with separate heaters underneath each pan, one for the protein solution and one for the control solution that contains no protein. Each pan is heated at a predetermined equal rate. The pan with the protein will take more heat to keep the temperature of this pan increasing at the same rate of the control pan. The DSC instrument determines the amount of heat (energy) the sample pan heater has to put out to keep the rates equal. The computer graphs the temperature as a function of the difference in heat output from both pans. Through a series of equations, the heat capacity (Cp) can be determined (Freire 1995). 

Glass transition temperatures of the polymers were measured with a Rigaku Denki Calorimeter, Model 8001 SL/C, at a heating rate of 10°C/min using an aluminum sample pan with lid. 

We have observed such a transition in intact membranes of M. laidlawii which occurs at the same temperature as in the membrane lipids dispersed in water (77). Figure 11 shows representative endothermic transitions of membranes and lipids in water. Membranes were prepared for calorimetry by sedimenting at high speed, then 90-100 mg. of packed pellet were sealed in a stainless steel sample pan. The material was neither dried nor frozen before examination. Total membrane lipids were extracted with chloroform-methanol 2 1 v/v then dried and suspended in water. Lipids from the membranes of cells grown in the usual tryptose medium without added fatty acids are shown in a, while b and c are scans of intact membranes from the same cells. In b the membrane preparation had not been previously exposed to temperatures above 27 °C. The smaller transition at higher temperature probably arises from... 

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