A Versatile Oven with Very Little Thermal Inertia For kinetic studies of gas phase reactions a hatch reactor can often he used. Generally, in this case, the vessel is placed in an electric oven having a great thermal inertia which gives good temperature regulation. However, in order t o study a very fast reaction, it is necessarv to use an aoen reactor which allows short time maces. Thus. in these cases, the thermal inertia of the oven must be as small as possible, and the electronic regulator must have very short response time. T h e simplest oven we can imagine is composed of an insulated resistant wire coil, without interspace, wound round the reactor. Generally this kind of coil is made of the resistant wire itself, insulated by a steel (or Ineonel) protecting sheath. To decrease heterogeneous effects in homogeneous chemical kinetics, kinetieists avoid using metallic reactors and prefer vessels in borosilieated glass or quartz. Thus, the great difficulty is to coil the insulated, resistant wire around the reactor, when the latter is spherical, because of the steel sheath rigidity.
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A brass hemisphere and a spherical open reactor with its two heating semi-spheres. one of them slightly pulled
each winding keeps its shape. Let us note that in &der to fix windings together one could silver-solder them, thus ohtaining a rigid semi-sphere; however, this operation requires too much heat and the insulating sheath is damaged. Thus, after cooling, both the coiled hemispheres are set round the reactor and fired on it by awire-netting made of "fireproof' metal (for example: Ni-Cr or Ni-AI).
a n electric power of 2 KW. The contact between the insulated wire and the reactor surface is very goad; and, to obtain a constant wall temperature, it suffices to set a fine insulated thermocouple (less than 0.5 mm diameter) into this narrow space and have it control an electronic temperature regulator. Heat insulation is obtained by packing the reactor with quartz-wool. In this manner we have made ovens for reactors from 30 to 150 mm diameter. Of course such an oven can be used far other studies than chemical kinetics whenever one needs a heating medium with a very little thermal inertia. P. Azay
P.M. M a r q u a i r e P. Pamrnier G. Seaeehi E.R.A.no 136 CNRS ENSIC-1 rue. Grandville 54042 Nancy Cedex, France
Volume 58
Number 5
May 1981
441
