Net Thermal Effects Research Articles

RETRACTED: Performance of modified montmorillonite clay in mercury adsorption process and thermodynamic studies

The montmorillonite clay sample from amazon region, Para State, Brazil, was used for intercalation process with pyridine (P) and organofunctionalization with 3-aminopropyltriethoxysilane (APS). The montmorillonite-P/APS shows variation of d001 values, by changing d001 from 1.15 to 2.10 nm. The original and modified samples were used for mercury cation adsorption from aqueous solution at room temperature and pH 6.0. The energetic effect caused by mercury cation adsorption was determined though calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant. 2007 Elsevier B.V. All rights reserved.

Preparation of ethylenediamine-anchored cellulose and determination of thermochemical data for the interaction between cations and basic centers at the solid/liquid interface

Cellulose was first modified with thionyl chloride, giving 99% substitution at C6, and then reacted with ethylene-1,2-diamine to produce 6-(2′-aminoethylamino)-6-deoxy-cellulose. From the 8.5% of nitrogen incorporated in the polysaccharide backbone, the amount of ethylene-1,2-diamine anchored per gram of modified cellulose was determined to be 3.03 ± 0.01 mmol. This chemically immobilized surface was characterized by FTIR, TG, 13C NMR, and SEM techniques. The available basic nitrogen centers covalently bonded to the biopolymer skeleton were studied for copper, cobalt, nickel, and zinc adsorption from aqueous solutions and the respective thermal adsorption effects were determined by calorimetric titration. The ability to adsorb cations gave a capacity order of Co 2+ > Cu 2+ > Zn 2+ > Ni 2+ with affinities of 1.91 ± 0.07, 1.32 ± 0.07, 1.31 ± 0.02, and 1.08 ± 0.04 mmol/g, respectively. The net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation and the enthalpy of the interaction was calculated to give the following exothermic values: −20.8 ± 0.05, −11.72 ± 0.03, −7.32 ± 0.01, and −6.27 ± 0.02 kJ/mol for Co 2+, Cu 2+, Zn 2+, and Ni 2+, respectively. With the exception of the entropic value for copper, the other thermodynamic data for these systems are favorable for cation adsorption from aqueous solutions at the solid/liquid interface, suggesting the use of this anchored biopolymer for cation removal from the environment.

Favorable chitosan/cellulose film combinations for copper removal from aqueous solutions

Three well-formed film combinations of chitosan, in the beta form and cellulose acetate biopolymer, having different proportions, have been synthesized and characterized by X-ray diffraction and infrared spectroscopy. The film having a 1.0/0.50 proportion presented 6.87 mmol of nitrogen atoms per gram of synthesized hybrid, with the highest affinity for adsorbing copper from aqueous solutions at 298 ± 1 K. The isotherm obtained in this adsorption showed a saturation plateau that corresponds to 1.92 mmol of copper per gram of hybrid. The energetic effects caused by copper ion interaction were determined through calorimetric titration at the solid–liquid interface in aqueous solution and gave a net thermal effect that enabled the calculation of the exothermic enthalpic values and the equilibrium constant. The complete thermodynamic data showed that the system is favored by exothermic enthalpies, negative Gibbs free energies and positive entropies.

Thermal characteristics of a laboratory electromagnetic launcher

Performance of rail conductors under rapid-fire conditions is limited by the ability to remove the heat generated during each shot. The net thermal effect of each shot is to raise the bulk temperature and induce thermal stresses in the conductors. While the high bulk temperature reduces the strength of the material, the cyclic thermal stress may reduce fatigue cycle life of the components. Various estimates of cooling requirements in rail conductors have been done using one-dimensional and two-dimensional approximations. In this study, we carried out a three-dimensional motion computation of the thermal load experienced by the entire length of a laboratory electromagnetic gun for a single shot firing. The distribution of thermal energy deposited in the rails is compared with the prior solutions. Post-transition energy dissipation and voltage rise due to arcing contact are also characterized.

The influence of chitosans with defined degrees of acetylation on the thermodynamic data for copper coordination

The interaction of copper with three different chitosans having degrees of deacetylation of 77.5, 81.5, and 86.1%, named C, A, and F, respectively, was followed by the batch method at 298 ± 1 K and the values obtained were fitted to a modified Langmuir equation. These interactions were also obtained by calorimetric titration. Experimentally, 50.0 mg of each chitosan was suspended in doubly distilled water at 298.15 ± 0.02 K under mechanical turbine stirring. The titration was performed by adding increments of 10 μl of a 0.10 mol dm 3 Cu(NO 3) 2 aqueous solution and the calorimetric isotherms obtained were adjusted to a modified Langmuir equation. From the net thermal effects K and Δ H values were calculated, also permitting the acquisition of other thermodynamic data for the chitosan–copper interaction at the solid/liquid interface. The exothermic enthalpic values of − 45.65 ± 1.97 , − 49.91 ± 1.57 , and − 48.64 ± 0.82 kJ mol −1 , for chitosans C, A, and F, respectively, reflect the degree of deacetylation. The spontaneity of the systems is shown by the negative Δ G values, − 36.1 ± 0.2 , 36.8 ± 0.1 , and − 38.1 ± 0.3 kJ mol −1 for the same sequence of chitosans. The negative entropic values, −34, −44, and −35 J mol −1 K −1, are in agreement with an ordering of solvent as the complexation occurred. The intensity of the thermal effects and the thermodynamic data obtained from the copper/chitosan interactions can be associated with the ability of these biopolymers to extract copper from aqueous solutions.

Some thermodynamic data of the energetics of the interaction cation-piperazine immobilized on silica gel

The interactions involving piperazine-functionalized silica with Cu(II), Fe(III), Cr(III), and Mo(III) chlorides in ethanolic solution were investigated by adsorption using batchwise process and determined by a calorimetric titration technique. The net thermal effects were calculated after subtracting the respective thermal effect of dilution for all systems. The sequence of the maximum retention capacity was 0.56, 0.54, 0.26, and 0.24 mmol g −1 for Cr(III), Cu(II), Mo(III), and Fe(III), respectively. The amount of piperazine anchored on surface of silica was 0.54 mmol g −1 . The enthalpy of these processes gave the following values: −12.90±0.08, −67.83±0.09, −199.08±0.09, and 67±1.5 kJ mol −1 following the same sequence of these mentioned metals, at 25.003±0.003 °C. The Gibbs free energy values are in agreement with favorable processes.

Thermodynamics Data of Interaction of Copper Nitrate with Native and Modified Chrysotile Fibers in Aqueous Solution

The interactions involving chrysotile (CRIO) and propylamine (CRI1), and propyethylenediamine (CRI2) chrysotiles with copper nitrate in aqueous solution were followed through a calorimetric titration technique. The net thermal effects were calculated after subtracting the respective thermal effect of dilution for all systems. The degree of adsorption gave the order CRI0 < CRI1 < CRI2. The mechanism of reaction for copper/chrysotile interaction is due to the ion exchange between the H+ of the external hydroxyl groups of the inorganic matrix, which is covered by the presence of 0.26 mmol g−1 of basic sites on fibers. On the other hand, the interactions on modified chrysotile can be associated to complex formation with the free pendant amine groups. The enthalpy of these processes gave the following values: −4.25±0.27, 19.47±0.60, and −26.55±0.16 kJ mol−1 for CRI0, CRI1, and CRI2 systems, respectively. The different behavior of propylamine chrysotile indicated that the hydration effect is more pronounced than complex formation. The free Gibbs energy values are in agreement with favorable processes. The high entropic values for CRI1 and CRI0 indicated that the adsorption occurs by entropic reasons, while on CRI2 the enthalpic contribution is more pronounced.

Toxic effect caused on microflora of soil by pesticide picloram application.

The toxic effect of the herbicide picloram on the microbial population of a typical Brazilian red Latosol soil was studied in a series of microcalorimetric experiments. The activity of the soil was stimulated by the addition of 6.0 mg of glucose and 6.0 mg of ammonium sulfate, under 34.8% controlled moisture, to a 1.50 mg soil sample, at 298.15 +/- 0.02 K. The net thermal effect due to the addition of the picloram to the soil was determined by interpreting the power-time curves, which were recorded on the microcalorimeter. The total thermal effect evolved by the microorganisms was affected by the increasing doses of herbicide, and varied from 0 to 10.00 micrograms g-1. An increase in picloram exposure caused a decrease of the original thermal effect, reaching a null value above 20.89 micrograms of herbicide per gram of soil. The decreases of the thermal effect evolved by microorganisms and the increase of the lag phase period are associated with the death of the microbial population. The effects caused by picloram application in this typical Brazilian soil resulted in a strong effect on the soil microbial communities.

DSC study on the influence of meat source, salt and fat levels, and processing parameters on batters pressurisation

Hydrostatic high-pressure/temperature treatments were conducted at low (10 °C) and high temperatures (60, 70, and 80°C) on different types of meat batters. Pressure-induced effects on proteins were intensified by sodium chloride molarity at low and high temperatures. Treatments at 10°C under pressurisation yielded net thermal destabilisation effects on meat proteins pertaining either to muscle or batter systems. Heating at usual cooking temperature of 70°C under pressure yielded net stabilising effects on meat batter proteins. Overheating at 80°C was needed for entire protein denaturation. Pork and chicken meats were very similar in behaviour but chicken batters exhibited relatively higher thermal- and pressure-induced protein denaturation. Both kinds of physical destabilisation/stabilisation of proteins by pressure-induced effects increased with pressure level.

Mercaptopropyl magnesium phyllosilicate — thermodynamic data on the interaction with divalent cations in aqueous solution

Magnesium phyllosilicate (SILMgSH) was obtained by the sol–gel process involving the reaction of magnesium cation and mercaptotrialkoxysilane in aqueous basic solution at 298 K. The inorganic–organic hybrid was characterized by elemental analysis to give a presence of 4.88 mmol g −1 of organic chains, and X-ray diffraction (XRD) patterns gave basal peaks associated with an interlayer distance of 1300 pm. The interactions between the terminal thiol groups of the organic chains of a silylating agent attached to magnesium phyllosilicate and the divalent cations copper, nickel, cobalt and zinc in aqueous solution were followed through calorimetric titrations. After subtracting the thermal effect of dilution, the net thermal effects were adjusted to a modified Langmuir equation, and the enthalpy of the interaction calculated to give the following exothermic values: −47.06±1.00, −27.63±0.50, −21.92±0.50 and −14.66±0.52 kJ mol −1, for copper, nickel, cobalt and zinc cations, respectively. The distinct behavior of the copper cation involves the formation of a more organized compound. Gibbs free energy values changes are negative. With the exception of copper, all reactions were entropically favoured and the final products of adsorption presented an increased crystallinity clearly detected by XRD.

Some features of crystalline α-titanium hydrogenphosphate, modified sodium and n-butylammonium forms and thermodynamics of ionic exchange with K + and Ca 2+

Crystalline α-titanium phosphate (TPH) was modified to sodium (TPNa) and n-butylammonium-intercalated (TPBA) forms. These materials were characterized and then used as exchangers with potassium and calcium in aqueous medium by the batch method at 298.2 ± 0.2 K. Thermodynamic determinations for all ion-exchange processes were performed by calorimetrically titrating suspensions of each exchanger in water (2.0 cm 3) with an aqueous cation solution in a heat-flow microcalorimeter at 298.15 ± 0.02 K. The enthalpy of the ion exchange with the general exchanger TPY can be represented as: nTPY aq+M n+ aq=(TP) n M aq+ nY + aq; Δ r h, where Y = H, Na, BA and M = K +, Ca 2+. In all cases, the net thermal effects were calculated after subtracting the respective thermal effect of dilution. The enthalpy of the exchange process for potassium gave the following exothermic values for all matrices: −0.54 ± 0.01, −2.67 ± 0.05 and −4.97 ± 0.04 kJ mol −1 for TPH, TPNa, TPBA, respectively. These values contrast with those obtained for calcium, which are endothermic for the same sequence of ionic exchangers: 5.82 ± 0.24, 3.74 ± 0.05 and 0.74 ± 0.02 kJ mol −1, respectively. The Gibbs free energy values indicated that the processes are spontaneous. During the ionic exchange process, the water hydration sphere of the cation promoted deorganization by increasing the molecules of solvent in the media, entropically favoring the system.

Phyllosilicate-like structure anchored silylating agents: calorimetric data on divalent cation–aminated centre interactions in the lamellar cavity

Nanocomposites with phyllosilicate-like structure containing silylating agents have been synthesized by using metal ions to aid the formation of the inorganic matrix, giving a structure similar to that of talc. Two distinct silicates were prepared by treating magnesium chloride with 3-aminopropyltrimethoxysilane or 6-amino-4-azahexyltrimethoxysilane, catalysed by sodium hydroxide, to give SILMg1 and SILMg2, with lamellar distances of 1731 and 2053 pm, respectively. Adsorption isotherms were obtained by suspending the solid with M(NO3)2 solutions (M = Cu, Zn, Ni or Co), which gave the number of moles adsorbed as 7.70 ± 0.050, 6.10 ± 0.04 and 3.81 ± 0.01, 2.20 ± 0.01 mmol g–1 for SILMg1 and SILMg2 with Cu2+ and Zn2+, respectively. These data obtained from a batch method were adjusted to the Langmuir model. The adsorption process was also followed by microcalorimetry, by suspending the mass of material in 2.0 cm3 of water and titrating with aqueous solutions of the cations. From these values, the respective thermal effects of dilution were subtracted to give the net thermal effects, which enabled the determination of ΔH and K values and from them ΔG and ΔS values. The exothermic enthalpic values for Cu2+, Zn2+, Ni2+ and Co2+ were –8.62 ± 0.56, –8.20 ± 0.48, –3.78 ± 0.03 and 8.86 ± 0.81 for SILMg1 and –8.40 ± 0.50, –9.29 ± 0.55, –20.12 ± 0.67 and –61.55 ± 0.06 for SILMg2. The entropic values varied from 27 to 143 J K–1 mol–1. The exothermic values for all free energies indicated that the cations are favourably bonded to the pendant groups disposed in the lamellar cavities.

Crystalline α-titanium(IV) hydrogenphosphate and its sodium- and n-butylammonium-intercalated forms: ion exchange and thermochemistry

Crystalline α-titanium(IV) hydrogenphosphate and its sodium- and n-butylammonium-intercalated forms were used as exchangers with MX 2 (M = Zn or Cu; X = Cl, NO 3 or MeCO 2 ) in aqueous medium at 298.2 ± 0.2 K. An enhancement of the exchange capacity was observed for α-Ti(HPO 4 ) 2 and its sodium form when acetate was used as the counter ion for both zinc and copper cation solutions. Thermodynamic determinations for all ion-exchange processes were performed by titrating calorimetrically a suspension of a given exchanger in water (2.0 cm 3 ) with an aqueous cation solution in a heat-flow microcalorimeter at 298.15 ± 0.01 K. In all cases the net thermal effects were calculated after subtracting the corresponding dilution thermal effects. With the exception of exothermic ion-exchange processes involving CuCl 2 with the α-Ti(HPO 4 ) 2 and sodium forms, and Zn(NO 3 ) 2 with α-Ti(HPO 4 ) 2 , which gave -2.40 ± 0.12, -1.01 ± 0.01 and -12.26 ± 0.15 kJ mol -1 , respectively, all other exchange processes were endothermic in nature with low enthalpy values, varying from 0.010 ± 0.001 to 8.59 ± 0.14 kJ mol -1 for the Zn(NO 3 ) 2 and Zn(O 2 CMe) 2 systems, with the sodium form. The number of moles exchanged did not correlate with the corresponding enthalpies. However, the thermodynamic data are in agreement with the occurrence of a spontaneous and entropically favourable ion-exchange process for all systems considered.

Differential scanning calorimetry studies on coal. 1. Pyrolysis in an inert atmosphere

Results of thermal changes involved during the pyrolysis of twelve US coals of various ranks in a helium atmosphere at 5.6 MPa (gauge) and temperatures up to 580 °C are reported. Thermal effects during pyrolysis of coals ranging in rank from anthracite to HVC bituminous are endothermic in nature over the temperature range investigated. Exothermic heats are observed only in the case of sub-bituminous and lignitic coals. The net thermal effects, that is the resultant of endothermic and exothermic heats, go from endothermic to exothermic with increase in carbon content, a transition occurring around 66% carbon and another in the reverse direction at about 75% carbon. A maximum in exothermicity occurs around 71% carbon and in endothermicity at about 81% carbon. Results have been compared with published DTA data on coals. The fallacy in the interpretation of published DTA thermograms of coals, where weight changes accompany thermal effects, is discussed.

The heat of shortening during the plateau of tetanic contraction and at the end of relaxation.

1. The net thermal effect of shortening on the heat production of the sartorius muscle of Rana temporaria has been studied at 0 degrees C in tetanic contractions of either 1.2 or 2.0 sec analysed up to the end of relaxation.2. Three types of contractions have been compared: isometric at the standard length (l(o)); isometric at a shorter length (l(o) minus 4.27 mm); and rapid shortening at constant velocity between those two lengths during the plateau of tetanic activity, the work being collected by an ergometer of the Levin-Wyman type. After the end of the shortening, stimulation was continued long enough to allow a complete recovery of tension before relaxation started.3. In those conditions, shortening heat appears clearly by comparison with the isometric contractions, and most of its effect persists up to the end of relaxation. However, a reduction of the net thermal effect, of the order of 15-25%, is observed during relaxation.4. The net supplement of heat is the same whether the shortening occurs in the beginning (0.4 sec) or towards the end (1.2 sec) of the contraction period; the reduction of the effect during relaxation is more important in the pelvic part than in the tibial part of the muscle.5. This small reduction of the thermal effect of the shortening is fully accounted for by the fact that the tension redeveloped after the end of the movement remains always below the tension developed in a tetanus at the same final length, but isometric from the start.6. As the greater part of the net thermal effect of the shortening persists at the end of relaxation, shortening heat cannot be part of a cyclic process reversed during relaxation; it must derive from some chemical source of energy.

Vacuum differential thermal analysis of coal

Samples of 25-30 mgs of various coals and their constituents were analyzed by vacuum differential thermal analysis using a heating rate of 20 degrees C per minute. Exothermic and endothermic peaks obtained by this technique provide graphic representations of the net thermal effects from the physical and chemical changes that take place during carbonization. Replicate analyses show that both peak temperature and the area under a peak can be reproduced readily.Thermograms of vitrains selected from a number of coals of widely different rank show an increase in peak temperature with increasing rank. Similar correlation is obtained between peak temperatures and fixed carbon values using vitrains from coals of the bituminous A group.A study of samples of known petrographic composition reveals that neither exinite nor opaque matter exerts any evident control on the peak temperature. Peak temperatures of average samples of coal from different intervals in a column sample show no correlation with the percentages of fixed carbon. The peak temperatures are relatively constant for average samples taken from a given column sample, but the fixed carbon values show considerable spread. It is concluded that the fixed carbon of a vitrain provides a better index of rank than the fixed carbon of an average sample.Further conclusions are that thermographic analysis is a useful method for the detection of cellulose in lignites and that the chemical fraction of the coal extractable with pyridine gives rise to the peaks. The suggestion is made that future investigators should consider the possibilities of relating the thermographic curves to the coking properties of coal.

The energetics of relaxation in a muscle twitch

When a muscle relaxes under a load heat is produced which is equivalent, or nearly equiva­lent, to the mechanical energy which disappears. The appearance of this heat is simultaneous with the disappearance of the mechanical energy. When a muscle is without load, or under zero tension, during the interval normally occupied by relaxation, there is no measureable heat after shortening is complete. This is true whatever the initial load, or the work done. If chemical changes occur during relaxation their net thermal effect is negligibly small. The heat produced in an isometric contraction is of a very complex nature, involving internal shortening, the transfer of work from one part to another and the dissipation of mechanical energy as heat. The nature of relaxation is discussed, and an analogy described with the process of ʻcold­ drawing’ of a crystalline long-chain polymer.