Isothermal decomposition of urea nitrate

Decomposition of urea nitrate in an initially evacuated system gave sigmoidal pressure vs. time curves. The experimental kinetic data fit the growing nuclei model with a measured enthalpy of activation of 142 -b 12.5 kJ/mole as compared to 115 -[-11.3 k J/mole obtained thermogravimetrically. This higher value of AH~; is explained on the basis of two factors: 1) the inhibitory effect of the product gases and 2) self heating, whose extent increased AHr by about 12.5 k J/mole.

Section: Resultssupporting

confidence: 91%

Section: )supporting

confidence: 66%

Section: Resultsmentioning

confidence: 99%

“…3 CO(NH2) 2 " HNO~ --* 6 H20 + 3 N20 + CO2 + CN 9 NH 9 CONH2 (Cyanourea) (1) while others have reported [4] 4 CO(NH2)2 " HNO3 --* N20 + 2 CO2 + 2 CO(NH2) 2 + 3 NH4NO 3…”

mentioning

confidence: 98%

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Measurement of reaction kinetics by a pressure rise method

Borham

Olson

1980

“…Results of thermogravimetric analysis, obtained under isothermal [1 ] and nonisothermal [2,3] conditions in the course of a reaction, may be used for kinetic research of the processes of thermal decomposition of solid components.…”

mentioning

confidence: 99%

Kinetics of aluminium hydroxide dehydration

Živković

Dobovišek

1977

Non-isothermal thermogravimetric analysis was used for determination of the kinetics of aluminium hydroxide dehydration in an air atmosphere and for processing of the experimental results by the method due to Chatterjee.Aluminium hydroxide dehydration proceeds according to the following mechanism: AI(OH)3 --~ A1OOH + H20 2 A1OOH ~ A120 3 + H20 Both reactions proceed in the diffusion region, the first up to 526 K and the second up to 700 K, and the corresponding activation energy values are 15.7 and 0.2 kJ/mole, respectively.By continuous increase of temperature over 526 K in the first, and over 700 K in the second case, the rates of these reactions become limited by the rate of crystallochemical transformation and the activation energy values are 116.9 and 91.9 kJ/mole, respectively.Results of thermogravimetric analysis, obtained under isothermal [1 ] and nonisothermal [2,3] conditions in the course of a reaction, may be used for kinetic research of the processes of thermal decomposition of solid components.In recent, non-isothermal methods of research the kinetics of thermal decompositions of solid components have found wider and wider application because of the particular advantages they have over the methods of research under isothermal conditions.The advantages of the determination of reaction kinetics via continuous temperature increase lie in the facts that a significantly smaller number of experimental data is required than for isothermal methods of research and that process kinetics may be studied fully over the complete temperature range in a continuous way. At the same time, this resolves the difficulty always present in isothermal research, at the beginning of the process when the cold sample is put into the heated furnace, during which process, de-facto, there are non-isothermal conditions, so that the beginning of the reaction cannot be taken into account in such research.The process of aluminum hydroxide dehydration was studied by Drobot and Hozanov [4] under isothermal conditions, using high-temperature infra-red spectroscopy for determination of the level of reaction flow with time, which is not applicable for research of this type.

Vacuum sublimation kinetics of urea nitrate

Borham

Olson

1980

Urea nitrate completely sublimes in a continuously pumped vacuum at a rate dependent upon the extent of the surface area. The fraction sublimed (c0 vs. time (t) curve is sigmoidal in shape with an inflection point fluctuating between 5.3 and 8.1 ~ weight loss in the temperature range 56 to 97 ~ .The experimental data fit the grain burning model 1 --(1 --/3) 1/3--k~(t--to) /3 = ct --/3o,/3 = 0 at inflection point where ks is a sublimation rate constant, and the constants/3o and t o are the respective values of a and t at the inflection point. This equation yielded an activation enthalpy of sublimation of 79 q-5.4 kJ/mole. Sublimation of urea nitrate was measured using a thermogravimetric method in the temperature range 56 to 97 ~ under a continuously pumped vacuum. Four rather conclusive evidences support the conclusion that the weight loss was exclusively due to sublimation allowing a kinetic treatment of vacuum sublimation of urea nitrate. Firstly, 100 ~o weight loss was posssible. Secondly, the study was well below the lowest possible decomposition temperature of about 105 ~ Thirdly, a 30 mg sample was placed in a 4 mm I.D. by 20 cm long sample tube and evacuated continuously with about one-third of the tube being inserted in boiling water (94 ~ ) and the urea nitrate disappeared from the bottom of the sample cell and condensed on the walls of the upper part of the sample cell which were at room temperature. The sublimate was about 95 ~ of the initial sample weight and on the basis of X-ray and infrared measurements it was found to be urea nitrate. Fourthly, an 8 nag sample was heated at 66 ~ under continuous vacuum in the thermogravimetric system [1] and the residues after 8 ~ and 69~ weight toss were respectively analyzed by infrared spectroscopy. The infrared patterns of both of these residues were the same and matched exactly that of the original urea nitrate showing that no decomposition had occurred. ExperimentalTechnique. A thermogravimetric system utilizing a Cahn R. G. electrobalance with a sensitivity of 0.05 #g was used to monitor the fractional weight loss-time curve. The system was pumped continuously with a mechanical vacuum pump.* Currently with Anaconda Copper Co., Box 27007, Tucson, AZ, 85726.