Controlled Heating Rate Research Articles

Characterization of Polymers by Direct Pyrolysis/Chemical Ionization Mass Spectrometry

Abstract The characterization of polymers by pyrolysis directly in the ion source of a double focusing magnetic sector mass spectrometer, operating in the chemical ionization mode, is described. Pyrolysis is achieved by two different probe techniques. A low temperature, slow heating rate direct insertion probe (DIP) is used at 400°C, and a specifically constructed high temperature, fast heating rate, high temperature pyrolysis (HTP) probe is used at 1000°C. This probe is capable of achieving pyrolysis temperatures of 1200°C at controlled heating rates up to 20,000°C/s. The mass spectrometric analysis of the pyrolysis products was achieved under chemical ionization (CI) conditions utilizing methane, isobutane, and ammonia as reagent gases. Under CI conditions the molecular ions formed in the mass spectrometer show little tendency to fragment. The CI mass pyrograms are very simple, with each peak in the spectra ascribable to a particular component in the pyrolysis product mixture. The results of the two probe pyrolysis techniques are compared and the utility of each technique for the characterization of polymers is demonstrated using the vinyl polymers polymethyl methacrylate, polyvinyl chloride, and polystyrene.

Captive sample reactor for kinetic studies of coal pyrolysis and hydropyrolysis on short time scales

An apparatus has been designed for kinetic studies of coal devolatilization under closely controlled heating rates, temperatures, and pressures. The reactor system employs a wire-mesh pyrolysis furnace driven by an electronically-controlled power supply to ensure uniform heating rates and precise crossover to a variable length isothermal period; a rapid quenching scheme permits resolution of kinetic processes in 0.1 s intervals, extending the sensitivity of kinetic measurements from the initial stage of pyrolysis through to completion of primary devolatilization. Time-resolved kinetic studies on a bituminous coal in vacuo (13 Pa) and under helium (0.22 MPa) illustrate the operation of the reactor.

Gravimetric determination of carbon in uranium carbide

The results of the determination of combined carbon and free carbon in uranium carbide in oxygen by a differential temperature technique suggest the pre-mature oxidation of the free carbon due to the local heating of the sample caused by the exothermic decomposition of the carbide. However, it was found possible to overcome this difficulty employing air as supporting gas at controlled heating rates.

Processing and Composition Control of Weak-Acid-Resin-Derived Fuel Microspheres

The current recycle fissile fuel for steam cycle high-temperature gas-cooled reactors in the U.S. is derived from weak acid ion-exchange resin microspheres loaded with uranyl ions. This material offers great versatility in the control of chemical and physical properties through careful process control. Processing the upgraded loaded resin begins with thermal decomposition or carbonization, which yields finely dispersed UO2 in a porous carbon matrix. This step requires a controlled heating rate from 350 to 450°C (623 to 723 K), and is complete by ∼900°C (1173 K). If carbide or mixed-oxide/carbide fuel is desired, carbothermic reduction, or conversion, is done at 1500 to 1750°C (1773 to 2023 K). This step reduces the UO2 to UC2 to optimize irradiation performance.Physical properties after carbonization correlate with the observed thermogravimetric behavior. The mercury density, volume decrease, weight loss, bulk density, carbon content, and particle size depend strongly on the particular heating rate employed through the 350 to 450°C (623 to 723 K) region.The conversion process generally follows the anticipated thermodynamic behavior for removal of carbon monoxide based on its partial pressure. The particular phases present after conversion can be manipulated by controlling the conversion temperature or by additions of hydrogen or carbon monoxide to the fluidizing gas.

Study on a dynamic adiabatic calorimeter. II. Adiabatic scanning calorimeter and some applications

An adiabatic scanning calorimeter has been made with a controlled heating rate. The sample used was relatively small (3-10g), but the accuracy of the calorimeter was found to be within 2% in temperatures ranging from room temperature to 1000K. It is shown that the temperature distribution in the sample vessel produced in the continuous heating type calorimeter is proportional to the heating rate and inversely proportional to the thermal diffusivity in the sample vessel. An estimate of, and the correction for, the error due to the temperature distribution in the sample vessel has been made. The dehydration reaction of CuSO45H2O was studied, and very sharp, separate, endothermic peaks of the dehydration reaction were obtained.

A temperature-controlled cryostat for optical, electrical and glow curve measurements between 77 and 800 K

A cryostat is described in which a sample may be rapidly cooled or linearly heated at various rates to any final temperature in the range 77-800 K. The controlled heating rate ranges from 3 to 50 K min-1 with linearity to better than 1%. The final temperature may be stabilized to better than 0.1 K, for long periods of time. This cryostat may be used for electrical, optical glow curve measurements.