Showing papers on "Calorimeter published in 1977"

The enthalpy of isomerisation of methyl isocyanide

Abstract: A controlled thermal explosion in which methyl isocyanide isomerises quantitatively to methyl cyanide has been studied in a calorimeter at 300 K. The enthalpy of isomerisation ΔH = −23.70 ± 0.14 (2...

Adiabatic calorimeter apparatus and method for measuring the energy change in a chemical reaction

Abstract: A novel adiabatic reaction calorimeter useful for measuring the energy change in a chemical reaction is disclosed. In a specific application, the calorimeter is used to measure the heat energy derived in a chemical reaction. The device includes a reaction vessel which is thermally isolated in the geometric center of a sealed spherical chamber. The chamber, which is filled with a gas atmosphere, is defined within a box structure fabricated of a ceramic foam or plastic foam. An auxiliary vessel is positioned in the chamber adjacent to the reaction vessel and is connected to the reaction vessel by a transfer conduit. In a typical operation, prior to initiating the reaction, one reactant is contained in the reaction vessel and another reactant in the auxiliary vessel. The vessels and the gas atmosphere are heated to a predetermined temperature by electrical power units, with regulation by a temperature control unit. When a desired temperature is reached the reactant in the auxiliary vessel is released into the reaction vessel to initiate the reaction. During the reaction the reaction mixture is continuously stirred in the reaction vessel and the gas atmosphere is circulated in a symmetrical pattern within the chamber. The actual change in temperature which the reaction vessel undergoes during the reaction, together with an electrical calibration of the vessel enables measurement of the energy change.

Calorimetric study of the glassy state. XIII. Thermodynamic properties of normal and deuterated orthoboric acid crystals.

Abstract: Thermal properties of normal and deuterated orthoboric acids were studied through the measurements of heat capacity in the temperature range from 13 to 370 K by using an adiabatic calorimeter and differential thermal analysis curves above room temperature. For both crystals, the heat capacity anomaly was found around 290 K in the heat capacity values dependent upon the thermal history of the specimen; i.e., the endothermic or exothermic enthalpy relaxation was observed in this temperature range. This behavior is of characteristic to the glass transition and is considered to be ascribed to the freezing-in phenomenon of the motion of rearrangement of the protons in hydrogen bondings. The enthalpy relaxation curves were analyzed with the exponential law and the characteristic time constant toward the equilibrium state was longer for enthalpy-excessive side than for enthalpy-deficient side. The glass transition temperature at which the endothermic relaxation time becomes 1 ks is 296.6 K for normal orthoboric ...

Calorimetric determination of the heat capacity changes associated with the conformational transitions of polyriboadenylic acid and polyribouridylic acid

Abstract: The heat capacities of the single-stranded and double-stranded forms of polyadenylic acid, polyuridylic acid, and poly(uridylic and adenylic acid) were determined with a drop heat capacity calorimeter In addition, the temperature dependence of the apparent partial heat capacity (ϕCp) was measured with a newly developed differential scanning calorimeter The calculated ΔCp at 28°C for the transition poly(A)·poly(A) ⇄ 2 poly(A) was found to be 165 ± 24 cal/Kmol-base pair, compared with a value of 140 ± 28 for the transition poly(A)·poly(U) ⇄ poly(A) + poly(U) The temperature dependence of ϕCp of single-stranded poly(U) was consistent with the conclusion that it is totally unstacked at temperatures above 15°C The temperature dependence of ϕCp of single-stranded poly(A) was used to determine the base-stacking parameters for poly(A) The experimental results are consistent with a stacking enthalpy change of −85 ± 01 kcal/mol bases and a cooperativity parameter σ of 057 ± 003 for the stacking of adenine bases These results demonstrate that the heat capacity of single-stranded polynucleotides is greater than that of the double-stranded forms This increased heat capacity is mainly the result of the temperature dependence of the base-stacking interactions in the single-stranded form

Differential thermal analysis cell

Abstract: A heat flow type differential calorimeter uses a planar thermoelectric disc as its major heat flow path for transferring heat to the sample and reference capsules. To improve the reproducibility of the calorimeter, two small discs of a thermoelectric material capable of forming a thermocouple with the thermoelectric disc are attached thereto in face-to-face relationship. Next a thermocouple pair made of the same material as the small disc and a third material, capable of forming a thermocouple with the disc, is attached to the center of each of the small discs. This converts the usual point contact temperature sensor to a large surface area temperature sensor and hence improves the reproducibility of the thermal analyzer.

Thermal Performance of Multilayer Insulation Applied to Small Cryogenic Tankage

Abstract: Thermal conductivity measurements of multilayer insulations have been made by various experimenters using guarded flat-plate calorimetric techniques[1]. The validity of using flat-plate calorimeter values for design and selection of multilayer insulations to be used on typical cryogenic tankage is questionable. The effective insulation conductivity observed for most tank wraps is greater than the measured flat-plate value due to effects of corner compression, degradation at penetrations, and application technique. This paper discusses and compares a number of tank calorimeter results with values based on flat-plate calorimeter data. Conductivity results are also presented at various pressure levels along with equations for predicting these pressure effects.

Caloric equivalents of some plant and animal material : The importance of acid corrections and comparison of precision between the Gentry-Wiegert micro and the Parr semi-micro bomb calorimeters.

Abstract: Orthogonal regression equations of caloric density on the time of collection are given for several materials of ecological interest. Ninety five percent of replicate samples were within ±1% of the mean cal g-1 using a Parr adiabatic semi-micro bomb calorimeter, while agreement was 2.8% using the Gentry-Wiegert bomb calorimeter. Weight specific acid corrections for low ash content biotic material decrease with increasing sample weight. The acid correction is more important using the Parr calorimeter (equal to 20–30% of the technique variation) than with the Gentry-Wiegert bomb (equal to 10–20% of the technique variation).

Partial molal heat capacities and volumes of electrolytes in nonaqueous solvents and ion–solvent interactions

Abstract: A flow heat capacity calorimeter and a flow vibrating tube densimeter have been used to measure the apparent molal heat capacities and volumes of several alkali metal and tetra-alkylammonium halides in anhydrous N,N-dimethylformamide (DMF), and the standard state partial molal heat capacities and volumes, text-decoration:overlineC0p2 and text-decoration:overlineV02, have been evaluated. A comparison of the data with similar data in water and methanol show that text-decoration:overlineC0p2 for electrolytes in the three solvents behaves quite differently. The alkali metal halides generally exhibit negative heat capacities in water and methanol and positive heat capacities in DMF at 25°C. The temperature dependence of text-decoration:overlineV02 in the three solvents is similar to that of text-decoration:overlineC0p2. Both text-decoration:overlineC0p2 and text-decoration:overlineV02 have been divided into ionic contributions and the values discussed in terms of ion-solvent interactions.

Construction of a 3He Calorimeter and Heat Capacity Measurement of the 1965 Calorimetry Conference Copper Standard between 0.4 and 20 K

Abstract: Construction of an isoperibol-type calorimeter with a 3He cryostat is described. A system of charcoal-adsorption-pump is adopted. A Ge-thermometer used in the heat capacity measurements is calibrated in the temperature range from 0.4 to 1.5 K against the magnetic susceptibility of chromium potassium alum. The precision and the accuracy of the calorimeter is ascertained by the heat capacity measurement of the 1965 Calorimetry Conference Copper Standard (T-8.6) in the temperature range from 0.420 to 19.46 K. The deviation of the experimental points from the “copper reference equation” is within the experimental error of ±2.5% between 0.4 and 0.9 K, ±1.5% between 0.9 and 1.5 K, ±1.2% between 1.5 and 4 K, and ±0.6% between 4 and 20 K. The highest deviation of absolute value of the present heat capacity data of copper is 1.86% smaller than the “selected values (Furukawa et al.)” around 6 K. This difference may be primarily attributable to the NBS-65 temperature scale adopted in the present experiment.

A constant-flow calorimeter for the measurement of acoustic power at megahertz frequencies

Abstract: The calorimeter absorbs, in a flow of castor oil, a fraction of the acoustic power output of an ultrasound transducer. It has been used to measure powere of between 1 mW and 10 W at frequencies from 1-5 to 3 MHz. Examples are given of results obtained for an ultrasound therapy unit and an ultrasonic pulse--echo scanner. Sources of inaccuracy are defined. It appears that constant-flow calorimetry offers a potentially very sensitive method for the absolute measurement of acoustic power.

Evaluating the inequivalence and a computational simplification for the NBS laser energy standards.

Abstract: A model with two time constants is used to estimate the inequivalence in response between a laser energy pulse and an electrical energy pulse put into a calorimeter of the C series type The results are as follows: the calorimeter labeled C41 showed a 015% inequivalence and the calorimeter labeled C46 showed none We also find that the complicated model currently used to get the corrected temperature rise of a measurement can be replaced by a simpler four-data-point method with no significant loss in accuracy This simplification means we can substitute a microprocessor for a large computer to get the corrected temperature rise in an electrical calibration or laser energy measurement

A sensitive adiabatic calorimeter for measurement of low-temperature specific heats

Abstract: An adiabatic calorimeter has been designed and constructed which allows measurements of the absolute value of specific heat to be made on small quantities of material in the temperature range 20-300K. The exchange of heat between the calorimeter and its environment has been eliminated with the aid of three screens which were automatically controlled to have the same temperature as the calorimeter. The elimination of heat loss allowed the temperature of the calorimeter to be measured after a stabilization period had followed the heating of the calorimeter. The experimental results are shown to be reproducible and to reflect the sensitivity of the method.

Temperature dependence of specific heat of perfluoromethylcyclohexane/carbon tetrachloride mixtures of critical composition near the critical solution temperature

Abstract: Measurements of the temperature dependence of specific heat of a perfluoromethylcyclohexane/ carbon tetrachloride mixture of critical composition near the critical solution temperature Tc are reported. The experiments are carried out in an isothermal heat flow calorimeter in a temperature range of 4×10−3 K? (T‐Tc) ?10.921 K. The experimental results are discussed in terms of current concepts of critical phenomena.

Precision titration mini-calorimeter

Abstract: The design and test of a small volume calorimeter of high precision and simple design is described. The calorimeter operates with solution sample volumes in the range of 3 to 5 ml. The results of experiments on the entropy changes for two standard reactions: (1) reaction of tris(hydroxymethyl)aminomethane with hydrochloric acid and (2) reaction between mercury(II) and bromide ions are reported to confirm the accuracy and overall performance of the calorimeter. (BLM)

Differential calorimeter for measurement of absorbed energy in laser‐produced plasmas

Abstract: Accurate estimates of the amount of optical energy absorbed by a target are an important diagnostic of laser‐induced fusion experiments. Measurements of the total energy blown off of a target in the form of charged particles is one method of evaluating the percentage of optical absorption. We have developed a special calorimetric device that is suitable for the measurements of the total flux of both charged particles and x rays. These devices provide high sensitivity to ions and x rays while maintaining good discrimination against scattered light.

Circulated‐liquid calorimeter for the detection of high‐power and high‐energy pulsed laser signals

Abstract: The design, construction, calibration, and testing of a circulated‐liquid volume absorption calorimeter are described. The device is designed to operate at input irradiance/energy combinations at which surface absorption calorimeters are damaged. It has been tested with pulsed laser signals at the several‐hundred‐joule input level at two widely separated wavelengths and should function well at the multikilojoule level.

Water bath temperature control and temperature measurement devices for calorimetry

Abstract: A low-cost water bath temperature control device, and an apparatus designed to monitor temperature variation from a null point both inside a precision calorimeter and in the surrounding bath, are described. Bath control to better than +or-0.002K in the 280-350K region can be achieved. Temperature variations in ranges between +or-2K and +or-0.02K can be measured to better than 5*10-2K and 5*10-4K respectively.