Otomar Špalek

Kinetics of the decomposition of hydrogen peroxide in alkaline solutions

Hydrogen peroxide decomposition in 1–5 mol dm–3 KOH and 1–2 mol dm–3 NaOH solutions is a first-order reaction with respect to undissociated hydrogen peroxide. The decomposition is catalysed by compounds of heavy metals (Fe, Cu) present as trace impurities in these solutions and is first order with respect to them. The hydroxyl ion concentration exerts a significant effect on the decomposition rate, which has been explained by its influence on the activity of catalysing species having colloidal character, which are probably the active sites for the decomposition.

Preliminary experimental results on chemical generation of atomic iodine for a COIL

A chemical method of atomic iodine generation with a potential application in chemical oxygen-iodine laser (COIL) was investigated experimentally. The process consists in a fast reaction of gaseous hydrogen iodide with chlorine atoms produced in reaction of gaseous chlorine dioxide with nitrogen oxide. In conditions characteristic for a subsonic mixing region of COIL, atomic iodine was produced with a yield of 20-50 %. This is in a fair agreement with results ofmathematical modeling ofthis complex reaction system.

Atomic iodine generation via F atoms for COIL

Chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) was investigated experimentally. This all-gas process includes atomic fluorine as an intermediate species. In the two-step reaction mechanism, F atoms are produced in reaction of molecular fluorine with NO and react further with hydrogen iodide to iodine atoms. The efficiency of this process was studied in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The maximum concentration of atomic iodine was obtained at approximately equimolar ratio of reacting gases (F2, NO and HI), which agrees with the stoichiometry of the production reactions. A shortage of any of the reacting gases limits the rate of atomic iodine formation. A considerable excess of F2 against NO at a simultaneous deficit of HI had a most detrimental effect on atomic iodine production. Sufficiently high concentrations of atomic iodine (5 to 8 x 1015 cm-3) can be achieved by this method even at pressure 4 - 9 kPa that enable to inject the gas with iodine atoms into the singlet oxygen flow upstream the nozzle throat in the chemical oxygen-iodine laser.

Chemical oxygen-iodine laser with atomic iodine generated via Cl or F atoms

Two alternative chemical methods of atomic iodine generation for a chemical oxygen-iodine laser (COIL) were studied. These methods are based on fast reactions of gaseous hydrogen iodide with chemically produced chlorine and fluorine atoms. Both processes were studied first in small-scale reactors. A yield of atomic iodine in the Cl system and nitrogen (non-reactive) atmosphere exceeded 80%, while in the F system it was only up to 27% related to F2 or 50% related to HI. The process of atomic iodine generation via Cl atoms was employed in operation of the supersonic COIL. A laser power of 430 W at 40 mmol Cl2/s, and the small signal gain up to 0.4%/cm were attained. The proposed methods promise an increase in laser power, easier control of laser operation, and simpler iodine management in comparison with the conventional source of atomic iodine using I2. The experimental results obtained so far with this experimental arrangement did not proved yet increasing COIL chemical efficiency because some process quenching a part of singlet oxygen was indicated. Therefore a modified experimental set-up has been designed and prepared for further investigation.

Research on advanced chemical and discharge oxygen-iodine lasers

Generation of singlet oxygen and atomic iodine for operation of the chemical or discharge oxygen-iodine laser (COIL/DOIL) is described, employing novel methods and device configurations proposed in our laboratory. A centrifugal spray generator of singlet oxygen was developed, based on the conventional reaction between chlorine and basic hydrogen peroxide. Recent results of theoretical and experimental investigation of the generator parameters are presented. A new conception of the discharge generator of singlet oxygen was initiated, based on a combined DC arc jet and RF discharge techniques. Principle of the generator currently developed and constructed is described. A new device configuration was designed for the alternative method of atomic iodine generation using a radiofrequency discharge decomposition of iodine compounds like CH3I or CF3I. Some recent experimental results of this research are also presented.

Spray generator of singlet oxygen with a centrifugal separation of liquid

A new spray-type generator of singlet oxygen, O2(1Δ), with a following centrifugal separation of depleted liquid was studied. This generator was developed to fulfill following requirements suitable for an advanced Chemical Oxygen- Iodine Laser (COIL): (i) a high-pressure operation, (ii) a single pass of reaction liquid, (iii) an efficient disengagement of gas/liquid mixture, and (iv) a scalability for airborne and mobile application. The generator design takes advantage of very high g/l interfacial surface area of a fine spray produced by a two-phase nozzle and a very fast liquid separation by applying a high centrifugal force.

Study of COIL active medium with atomic iodine generated via fluorine atoms

A generation of atomic iodine via F atoms with their immediate injection to the supersonic COIL nozzle has been studied. Very high concentrations of I atoms were obtained in the laser cavity in the absence of O2(1Δg). Low values of small signal gain measured in the O2(1Δg) flow did not correspond to high efficiency of I generation. This was ascribed to O2(1Δg) quenching by DO2· radical.

Contribution to development of chemical and discharge oxygen-iodine lasers

A chemical centrifugal spray generator of singlet oxygen, chemical methods of atomic iodine generation, and discharge generation of atomic iodine for chemical and/or discharge oxygen iodine lasers (COIL and/or DOIL) are the topics investigated currently in the Institute of Physics AS in Prague. Some main results of this research are presented on a background of the general COIL technology.

Advanced spray generator of singlet oxygen

A spray type singlet oxygen generator (SOG) for chemical oxygen-iodine laser (COIL) was studied. Mathematical modeling has shown that a high O2(1&Dgr;) yield can be attained with BHP (basic hydrogen peroxide) spray in the Cl2-He atmosphere. It was found experimentally that O2(1&Dgr;) was produced with a ≥50% yield at a total pressure up to 50 kPa (375 Torr). A rotating separator was developed that can segregate even very small droplets (≥0.5 &mgr;m) from O2(1&Dgr;) flow.

Generation of atomic iodine for a COIL via atomic fluorine at higher pressure

New results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. Atomic fluorine was produced at first step by the reaction of molecular fluorine with nitrogen oxide. At second step atomic fluorine reacted with hydrogen iodide producing atomic iodine. It follows from obtained results that two experimental arrangements may be used in COIL. First, atomic F generated in a separate reactor may be injected into singlet oxygen stream with a subsequent HI injection. Second, atomic I may be produced in a separate reactor and then injected into a singlet oxygen stream. It was found that yield of the atomic iodine in the second arrangement may be higher, but a higher loss of I atoms at I atoms injection is anticipated due to wall recombination. The processes of I atoms and F atoms injection will be investigated in a near future.