Differential Thermal Analysis Instrument Research Articles

Three new energetic coordination polymers based on nitrogen-rich heterocyclic ligand for thermal catalysis of ammonium perchlorate

Three new one-dimensional energetic coordination polymers (ECPs) were prepared by solvothermal method and liquid diffusion method, namely, [Mn(BODDTO)(H2O)4]n (1), [Zn(BODDTO)(H2O)4]n (2) and [Pb(BODDTO)(H2O)4]n (3) (H2BODDTO ​= ​5,5'-([3,3′-bi(1,2,4-oxadiazole)]-5,5′-diyl)bis(1H-tetrazol-1-ol)). Compounds 1 and 2 possess the same crystal structures, crystallizing in the triclinic space group P-1 with a calculated density of 1.970 ​g ​cm−3 for 1 and 2.047 ​g ​cm−3 for 2. Meanwhile, Compound 3 pertains to the P212121 space group of the orthorhombic crystal system with a density of 2.618 ​g ​cm−3. The thermal behaviors were studied by employing a Thermogravimetry instrument, the results show that the compounds have good thermal stability with the decomposition temperatures above 520 ​K. The studies of mechanical sensitivity and detonation performance reveal that these complexes are both safe and have high energy. Furthermore, the ability to catalyze the thermal decomposition of ammonium perchlorate (AP) by compounds 1–3 was studied through a differential thermal analysis instrument. The high-temperature decomposition peak temperature of AP is reduced by 94.8 ​K at most and the activation energy is also decreased. It is disclosed that three compounds can be potentially used as high-energy AP catalysts.

An assessment of barium and strontium carbonates as temperature and enthalpy standards

A study of the thermal behavior of both barium and strontium carbonates was performed in dynamic argon atmosphere over a wide range of temperatures. Both barium and strontium carbonates are white crystalline powders at room temperature. These compounds undergo reversible polymorphic transitions from the orthorhombic to hexagonal crystal forms when heated to temperatures above 800 °C. On further heating, the barium carbonate undergoes an additional polymorphic transition where the hexagonal form transforms to a face-centered cubic form near 976 °C. On continued heating, this cubic form of barium carbonate decomposes to barium oxide liberating carbon dioxide gas. Strontium carbonate, on the other hand, tends to be thermally less stable than barium carbonate. It is reported to lose mass over a broad range of temperatures beginning below the observed polymorphic transition (Charsley et al. in J Therm Anal Calorim 40:1415–1422, 1993). Our studies, using both differential thermal analysis (DTA) and thermogravimetric analysis techniques, attempt to answer questions of uncertainty of the reported temperatures of transition, as well as heats of transition, for these industrially important compounds. As a result of these findings, recommendations are given for the use of these compounds as reference standards for calibration of DTA instruments.

Analysis of Solidification of High Manganese Steels Using Improved Differential Thermal Analysis Method

High manganese steels can damage the differential thermal analysis (DTA) instrument due to the manganese evaporation during high temperature experiments. After analyzing the relationship between residual oxygen and manganese evaporation, tantalum metal was employed to modify the crucible of DTA, and zirconium getter together with strict gas purification measures were applied to control the volatilization of manganese. By these modifications, problems of thermocouple damage and DTA instrument contamination were successfully resolved. Cobalt samples were adopted to calibrate the accuracy of DTA instruments under the same trial condition of high manganese steel samples, and the detection error was confirmed to be less than 1 °C. Liquidus and solidus temperatures of high Mn steels were measured by improved DTA method. It was found that the liquidus temperatures of samples tested by experiments increased linearly with the heating rates. To eliminate the effects of the heating rate, equilibrium liquidus temperature was determined by fitting the liquidus temperatures at different heating rates, and referred as real liquidus temperature. No clear relationship between solidus temperatures and heating rates was found, and the solidus temperature was finally set as the average value of several experimental data.

Design, construction and calibration of a portable multi sample DTA setup

Calorimetric techniques have become essential tools for the characterization of materials such as ceramics, polymers, metals, drugs, foodstuffs as a function of their thermal properties. The knowledge of these thermal properties (melting temperature, crystallization, glass transition, denaturation or decomposition temperature) plays a role of great importance in the selection of the material and its manufacturing conditions. Despite the importance of thermal characterization there are no simple and accessible alternatives to commercial instruments, whose main limitations are their high costs and the fragility of their constitutive parts during operation. In this work we present the design and construction of a portable, robust and low cost differential thermal analysis instrument which allows for the simultaneous analysis of three samples and it is suitable when corrosive substances are intended to be thermally characterized. This device represents an alternative to commercial devices, with applications in research and development of materials in various types of industries and apt for academic training.

Preparation of CuInSe 2 thin films by paste coating

Precursor pastes were obtained by milling Cu-In alloys and Se powders. CuInSe 2 thin films were successfully prepared by precursor layers, which were coated using these pastes, and were annealed in a H 2 atmosphere. The pastes were tested by laser particle diameter analyzer, simultaneous thermogravimetric and differential thermal analysis instruments (TG-DTA), and X-ray diffractometry (XRD). Selenized films were characterized by XRD, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results indicate that chalcopyrite CuInSe 2 is formed at 180°C and the crystallinity of this phase is improved as the temperature rises. All the CuInSe 2 thin films, which were annealed at various temperatures, exhibit the preferred orientation along the (112) plane. The compression of precursor layers before selenization step is one of the most essential factors for the preparation of perfect CuInSe 2 thin films.

Constructing a High-Sensitivity, Computer-Interfaced, Differential Thermal Analysis Device for Teaching and Research

We report the construction of a homemade differential thermal analysis instrument interfaced with a computer through a data acquisition board and handled with a program written in LabVIEW. This instrument has been used for teaching purposes, in the construction of phase diagrams, and for research purposes, particularly to measure glass transition temperatures because of its demonstrated sensitivity. Constructing this instrument serves as an excellent opportunity to help students understand the basic elements of analytical instrumentation and as a simple way of introducing them to digital data acquisition and computer interfacing, which are important skills for modern chemists.

A digital differential thermal analysis instrument

Differential thermal analysis is usually employed to characterize new materials. The structure of a prototype of a differential thermal analysis instrument, based on a microcontroller is described. The design of the controllers for a constant rate reference temperature variation is discussed. Experimental and simulation results are presented.

Compatibility of mixtures of deoxyribonucleic acid with hydroxypropylcellulose in concentrated aqueous solutions

In order to obtain information about the compatibility between biopolymeric substances and water-soluble polymers, the phase states of mixtures of DNA with hydroxypropylcellulose (HPC) in concentrated aqueous solutions were studied by simultaneous measurement of differential thermal analysis (DTA) and laser transmittance (He-Ne gas laser; λ 0 = 633 nm), and by means of a polarization microscope and a refractometer. From the results obtained, the phase states in mixture I exhibit an isotropic phase. Mixture II exhibits an anisotropic phase with a slight birefringence from the measurement of the refractive index at 298 K, suggesting that an anisotropic phase in this region corresponds to a quasi-liquid crystal similar to that found previously in the concentration range 3.00–5.00 wt.% of DNA solutions. The phase states in mixture III exhibit birefringence from the measurement of refractive index at 298 K, suggesting that these phase states form stable liquid crystals which are essentially different from an already known liquid crystal of HPC or DNA in concentrated solutions. It is suggested that these liquid crystals are formed by the interaction between DNA and HPC. In order to obtain information about the enthalpy change associated with the liquid crystal formation, the phase states of mixtures I, II and III were also studied using a DTA instrument equipped with a laser, under the same experimental conditions as observed with the polarization microscope. From the thermal and optical properties obtained, the degree of formation α of liquid crystal phases of the mixture formed by the interaction between DNA and HPC is estimated, making use of the degree of precipitation accompanying the phase separation of HPC corresponding to the difference in intensity Δ Iof the transmitted laser light before and after the change in the laser with increasing temperature. From the α value, the net heat of fusion of liquid crystal phases of the mixture formed by the interaction of DNA with HPC is estimated to be about 2.4 kJ per mol of nucleotide.

An unusual kaolinite-calcite interaction

In a CO 2 atmosphere, one particular sample of kaolinite from Cornwall, England, when mixed with calcite in the proportions 4:1 or greater gave a very small, sharp endotherm at 840–845°C on curves obtained on three differential thermal analysis instruments of different design. Scanning electron microscopy suggests that this endotherm is associated with surface melting or sintering of the calcite rhombs, but X-ray diffraction and infrared absorption spectrometry reveal that other changes also occur. It is suggested that volatiles evolved from the kaolinite initiate a series of complex reactions.

Finite-element simulation of the differential thermal analysis response to ignition of a pyrotechnic composition

A two-dimensional finite-element code for heat-transfer analysis has been used to simulate the heating, in a typical differential thermal analysis (DTA) instrument, of a sample that undergoes a strongly exothermic reaction, e.g. a pyrotechnic delay composition. The parameters required for the simulation, especially values for thermal resistances at interfaces, have been related to those of real DTA instruments by comparison of simulations with the results of simple calibration experiments.The effects on the DTA response of varying the thermal conductivity of the sample and the possibility of extracting kinetic information from the DTA response are discussed.

Selfignition of powders studied by high pressure differential thermal analysis

The technique of differential thermal analysis was used, in an original way, for studying spontaneous ignition and combustion of powders. The measurements were performed with a high-pressure differential thermal analysis instrument. Selfignition temperatures of powders were determined by analysing the samples under a high pressure of oxygen (25 bar). Self ignition temperature values are given for powders which are of interest in the food industry.

Mathematical treatment of heat flow in differential scanning calorimetry and differential thermal analysis instruments

A general mathematical treatment is given which relates the techniques of classical differential thermal analysis, power-compensated differential scanning calorimetry, and heat-flux differential scanning calorimetry. An idealized system, representative of almost any type of differential thermal instrument, is presented, which, unlike those of previous treatments, incorporates two separate thermal resistances. This modification allows the heat-flux d.s.c. instrument to be considered in a unified analysis with the other techniques. General aspects of the idealized system are presented, and the equations governing heat flow within the system are developed. For each separate technique, the components of the idealized system are identified with the actual components of the physical instrument, and the specific equations which describe the measuring principles of that technique are derived. It is shown that a similar type of thermal resistance governs sample-temperature lag in both the power-compensated and heat-flux d.s.c. cases, and the method of estimating the value of this resistance from the slope of a fusion peak is discussed.