Microcombustion Calorimetry Research Articles

Microcombustion calorimetry as a tool for screening flame retardancy in epoxy

AbstractThrough the use of microcombustion calorimetry several polymer nanocomposite, flame retardant (FR), and polymer nanocomposite + FR systems were screened for flammability performance. The use of this technique allowed for the creation of small batch (less than 50 g) epoxy formulations as compared to 400–500 g needed for cone calorimeter testing of epoxy + fiberglass panels. The results from the microcombustion calorimeter screening suggested that the system with the best flammability performance was a combination of organophosphonate and zinc borate, and not one of the polymer nanocomposite systems. This best candidate was then scaled up and fabricated into a fiberglass‐reinforced composite which was further tested by a cone calorimeter. This paper shows some of the correlations between the microcombustion and cone calorimeter results for this single sample, provides some reasons for why the polymer nanocomposite samples did not provide the best results in flammability reduction, and suggests some caveats when using microcombustion calorimetry as the only screening tool for flammability. Copyright © 2008 John Wiley & Sons, Ltd.

Enthalpies of combustion and formation of α- d-glucoheptono-1,4-lactone and α,β-glucooctanoic-1,4-lactone

The standard molar energies of combustion, Δ c U m ∘ ( cr, 298.15 K ) , of α- d-glucoheptono-1,4-lactone (GH) and α,β-glucooctanoic-1,4-lactone (GO) were obtained by micro-combustion calorimetry. The obtained values are −(2924.6 ± 2.3) kJ · mol −1 and −(3459.5 ± 2.5) kJ · mol −1, respectively. From combustion energies, the standard molar enthalpies of formation in crystalline phase, Δ f H m ∘ ( cr, 298.15 K ) , for GH and GO were determined as −(1546.2 ± 2.5) kJ · mol −1 and −(1690.6 ± 2.7) kJ · mol −1, respectively. Also it was found that when the hydroxyl group number increases in the aldonolactones their standard molar enthalpies of formation increase too.

Energetics of the Thermal Dimerization of Acenaphthylene to Heptacyclene

The energetics of the thermal dimerization of acenaphthylene to give Z- or E-heptacyclene was investigated. The standard molar enthalpy of the formation of monoclinic Z- and E-heptacyclene isomers at 298.15 K was determined as Delta(f)H(m)o (E-C24H16, cr) = 269.3 +/- 5.6 kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, cr) = 317.7 +/- 5.6 kJ x mol(-1), respectively, by microcombustion calorimetry. The corresponding enthalpies of sublimation, Delta(sub)H(m)o (E-C24H16) = (149.0 +/- 3.1) kJ x mol(-1) and Delta(sub)H(m)o (Z-C24H16) = (128.5 +/- 2.3) kJ x mol(-1) were also obtained by Knudsen effusion and Calvet-drop microcalorimetry methods, leading to Delta(f)H(m)o (E-C24H16, g) = (418.3 +/- 6.4) kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, g) = (446.2 +/- 6.1) kJ x mol(-1), respectively. These results, in conjunction with the reported enthalpies of formation of solid and gaseous acenaphthylene, and the entropies of acenaphthylene and both hepatcyclene isomers obtained by the B3LYP/6-31G(d,p) method led to the conclusion that at 298.15 K the thermal dimerization of acenaphthylene is considerably exothermic and exergonic in the solid and gaseous states (although more favorable when the E isomer is the product), suggesting that the nonobservation of the reaction under these conditions is of kinetic nature. A full determination of the molecular and crystal structure of the E dimer by X-ray diffraction is reported for the first time. Finally, molecular dynamics computer simulations on acenaphthylene and the heptacyclene solids were carried out and the results discussed in light of the corresponding structural and Delta(sub)H(m)o data experimentally obtained.

Enthalpies of combustion and formation of fullerenes by micro-combustion calorimetry in a Calvet calorimeter

A set of micro-combustion bombs has been adapted to a Setaram C80 Calvet calorimeter. The calorimetric constant of the micro-bomb in the measurement fluxmeter was determined by combustions with benzoic acid NIST 39 j, giving an uncertainty of less than 0.03% for calibration. The experimental methodology of applying this micro-combustion device to the measurement of the energy of combustion of graphite, C 60 and C 70 is described. Accuracy of better than 0.08% is obtained in some cases.

Standard enthalpies of formation of phenanthrene and naphthacene

Standard enthalpies of combustion of phenanthrene and naphthacene were determined to be −(7048.7 ± 0.9)kJ · mol−1and −(9005.1 ± 1.8)kJ · mol−1, respectively, by means of high-precision micro-combustion calorimetry. The former result agrees very well with that reported by Steele et al.(AIChE Symposium Series 279,1990 , 86, 138–154). The latter confirms theoretical predictions. By using standard enthalpies of sublimation from the literature, the standard molar enthalpies of formation of phenanthrene and naphthacene in the gas phase were derived to be (201.7 ± 2.9)kJ · mol−1and (331.6 ± 4.4)kJ · mol−1, respectively. The enthalpy of the rearrangement reaction from anthracene to phenanthrene was evaluated to be −(28.4 ± 4.1)kJ · mol−1.

Enthalpy of formation of benzo[k]fluoranthene

The standard molar enthalpy of formation of benzo[ k ]fluoranthene, (CAS number 207-08-9) in the crystalline state, at T= 298.15 K, was determined as ΔfHmo(C 20H 12, cr ) = (172.4 ± 4.3)kJ · mol−1, by micro-combustion calorimetry. Vapour pressure against temperature measurements recorded using the Knudsen effusion method led to ΔcrgHmo(C 20H 12) = (124.2 ± 4.7)kJ · mol−1, at T= 298.15 K and hence ΔfHmo(C 20H 12, g ) = (296.6 ± 6.4)kJ · mol−1, at T= 298.15 K. The results reported in this work show that, in terms of the homodesmotic stabilization enthalpy criteria, benzo[ k ]fluoranthene is an aromatic compound, in agreement with the evidence from 1H-NMR spectroscopy, and the prediction by Craig’s rules.

Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH2.76O3.89 (Adams' catalyst) and dehydrated oxide PtO2.52 at T=298.15 K were determined to be -519.6±1.0 and -101.3 ±5.2 kJ mol-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO2 was estimated to be -80 kJ mol-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric.

The design, construction and testing of a microcombustion calorimetersuitable for organic compounds containing C, H and O

To obtain reliable standard energies of combustion with smallamounts of C, H, O compounds, a new microcombustion calorimetry system hasbeen set up. The design, construction, calibration and measurement experimentsare described. The system includes a commercial combustion bomb with aninternal volume of 22 cm3. Samples of around 80 mg are suitable ifone wants to retain the same levels of accuracy and reproducibility as thosein macrocombustion experiments. Calibration of the calorimeter was performedusing benzoic acid. ε(calorimeter) = 2083.74±0.48JK-1 was obtained. Combustion measurements using m-methoxybenzoic acidwere made in order to verify the chemistry of the combustion process involvedin the corresponding analysis of results and the accuracy of the measurementof combustion energy. The uncertainty of the results shows that the instrumentdescribed and the experimental procedure used for the determination ofenthalpies of formation of compounds containing C, H and O provide a highreliability.

Micro-combustion calorimetry of coronene

The standard massic energy of combustion of coronene was determined to be −(37.616 ± 0.012)kJ · g−1by means of micro-combustion calorimetry. The standard molar enthalpies of formation of coronene in the crystalline and gaseous phases were found to be (146.5 ± 4.8)kJ · mol−1and (302.0 ± 8.0)kJ · mol−1, respectively. The values obtained were very consistent with the literature values. This suggests that the new micro-combustion calorimetric technique is viable for polycyclic aromatic hydrocarbons.

Utilisation du microcalorimetre CRMT en calorimetrie de combustion

From several series of expriments using, successively, benzoic, salicylic and succinic acids, the authors study the possibility of using the CRMT calorimeter for combustion calorimetry. Based on experimental results, the discussion emphasizes possible errors in microcombustion calorimetry in general, and more particularly in the case of using a CRMT calorimeter. Means of avoiding such errors are proposed.