Heat conduction effects during the calorimetric determination of absorbed dose to water in radiotherapy beams

A transportable water calorimeter for the determination of the quantity of absorbed dose to water in radiotherapy beams has been developed at the PTB and is presented in detail in this investigation. Heat conduction effects occurring in the calorimeter are studied for different lateral sizes of high-energy photon beams, for different depth dose distributions of electron beams and for a scanned-beam irradiation with a heavy ion beam. The corresponding correction factors are calculated and arguments are given under which conditions these can adequately be applied.     

Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.     

室温离子液体EMIES的标准生成焓

在(298.15 ±0.01) K下用转动弹热量计测定了离子液体硫酸乙酯-1-甲基-3-乙基咪唑(EMIES)及合成它的原料1-甲基咪唑的恒容燃烧热,通过计算得到它们的标准燃烧焓 分别为(－2671±2) 和(－286.3±0.5) kJ·mol－1;标准生成焓 分别为(－3060±3) kJ·mol－1和(－2145±4) kJ·mol－1.结合文献上硫酸二乙酯的标准生成焓数据,得到了合成离子液体EMIES的反应热(－102.3±1.0) kJ·mol－1,与合成实验中观察到的强烈放热现象是一致的.根据离子液体EMIES的热容数据,计算了不同温度下EMIES的标准生成焓.     

Modulated differential scanning calorimetry in the glass transition region

Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate) (PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be used to match model and experiment.On leave from Toray Industries, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy, under contract number DE-AC05-96OR22464. Support for instrumentation came from TA Instruments, Inc. Research support was also given by ICI Paints, and Toray Industries, Inc.     

Determination of the enthalpy of fusion of K3TaF8 and K3TaOF6

The areas of the fusion and crystallization peaks of K₃TaF₈ and K₃TaOF₆ have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K₃TaF₈ at temperature of fusion 1039 K: Δ_fusH_m(K₃TaF₈; 1039 K) = (52 ± 2) kJ mol⁻¹ and of K₃TaOF₆ at temperature of fusion 1055 K: Δ_fusH_m(K₃TaOF₆; 1055 K) = (62 ± 3) kJ mol⁻¹ have been determined.     

Calorimetric study of the immersion heats of lead(II) and chromium(VI) from aqueous solutions of Colombian coffee husk

Summary This work shows the result of the study of the Pb(II) and Cr(VI) ions adsorption by means of a Calvet type calorimeter of heat conduction that can operate at 150şC. The calorimeter was electrically calibrated to establish its sensitivity and reproducibility, obtaining K=12.95±0.05 W V^-1 and chemically it was examined with tris-(hydroxymethyl)-aminomethane (THAM)-HCl system, obtaining ΔH= -30.91±0.03 kJ mol^-1. The activated carbon sample obtained from coffee husk and the calorimetric results obtained were related to other techniques used to perform this type of studies.     

Differential 3ω calorimeter

We have developed a new dynamic calorimeter using the differential 3ω detection method. The differential 3ω calorimeter is capable of measuring dynamic heat capacity of liquid samples. The new calorimeter consists of a Wheatstone bridge made of two identical heater/sensors, and is based on the sensitive null detection method. The balancing is done automatically at all frequencies and is independent of temperature; once a sample is placed on one heater/sensor, a third harmonic signal is produced due to the difference in the two arms of the bridge. The differential 3ω calorimeter provides enhancements over traditional dynamic methods in dynamic range (up to 30 kHz), resolution, and ease of operation.     

Study on properties of flame‐retardant cyanate esters modified with DOPO and triazine compounds

Ternary flame‐retardant modified cyanate ester blends (CEPG and CEPA) are formed by combining triazine compounds (TGIC or TAIC) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide with cyanate ester resin. The curing behaviors, thermal and mechanical properties, and the flame‐retardant properties are investigated. The results show that the CEPG and CEPA blends result in lower curing temperatures and glass transition temperatures than those of neat CE. Both of CEPG and CEPA blends significantly improve the flame‐retardant properties of CE resins, and UL‐94V‐0 rate is achieved for CEPG‐1.0 and CEPA‐0.5. The dielectric constant and loss of CEPA blends are lower than those of CEPG blend with the same phosphors content, and both of them are lower than those of neat CE. Therefore, the ternary flame‐retardant modified cyanate ester blends provide 2 ways for composites of producing printed circuit board with high flame‐retardant property and low dielectric constant and loss.     

Photopolymerization studies of alkyl and aryl ester derivatives of ethyl α-hydroxymethylacrylate

Several new benzoate ester derivatives of ethyl α-hydroxymethylacrylate were synthesized using phase transfer catalysis and found to display unexpectedly rapid photopolymerization; i.e., from 2 to 8 times faster than MMA. New derivatives described here include the 4-fluoro-, 4-trifluoromethyl-, 4-methyl-, 2-hydroxy-, 4-nitro-, 4-methoxy-, 4-cyano-, and 3,4,5-trimethoxybenzoate esters along with the parent benzoate ester. Relative reactivities of these monomers in photopolymerizations were compared with those of the nonaromatic formate, acetate, hexanoate, and stearate derivatives. Reactivities of the nonaromatic ester derivatives increased with the length of the side chain while for the more reactive aromatic esters, rates increased in the order 4-methyl-, 4-fluoro- and benzoate < 4-trifluoromethyl- and 2-hydroxy- < 4-cyano- < 4-methoxy- < 3,4,5-trimethoxybenzoate. T_gs of the benzoate polymers ranged from 125°C for the 4-fluoro to 163°C for the 4-cyanobenzoate while those of the alkyl ester derivatives ranged from 15 to 78°C. Number average molecular weights of photoinitiated polymers (ca 10,000–20,000) were lower than those found for bulk and solution polymers (20,000—708,000) consistent with higher radical concentrations from photoinitiation. These materials greatly expand the number of candidates available for rapid photocure in thin film and coating applications, especially because their physical properties are those of linear rather than highly crosslinked structures formed from multifunctional systems. © 1996 John Wiley & Sons, Inc.     

Development and application of chip calorimeter as an X-ray detector

Radiotherapy for cancer patients requires accurate measurement of the absorbed dose of radiation in a treatment planning step. Various types of radiation detectors are currently utilized for dose measurement. Among them, calorimeters are known to be the most precise detector for measuring absorbed dose, but their on-site application is limited by the large size of the equipment. We developed a miniaturized chip calorimeter for application as a radiation detector. The calorimetric radiation detector was built using micro/nano fabrication techniques, and consists of an SU-8 photoresist absorber and high-sensitivity vanadium oxide (VO_x) thermistors. The thermistors had a temperature resolution of 135 μK, and the calorimeter showed a thermal conductance of 11 μW/K. The detector was irradiated with various X-ray dose rates from a linear accelerator, and the absorbed dose to SU-8 was measured. The detector responses showed high linearity with dose rates, demonstrating the feasibility of the radiation detector for practical uses.