US2230629A - Manufacture of semipyrophoric compounds - Google Patents

Description

Patented Feb. 4, 1941 MANUFACTURE OF SEMIPYROPHORIC COMPOUNDS Alfred Schmid, Berlin-Dahlem, Germany, asignor to Oswald Fidel Wyss, Berlin, Germany No Drawing. Application August 11, 1937, Serial No. 158,594. In Germany August 25, 1936 Claims.

This invention relates to a process for the manufacture of semipyrophoric compounds and -to compositions containing these compounds.

The semipyrophoric condition of metals is well- 5 known as are also processes for obtaining metals in this condition. As distinguished therefrom, the present invention is concerned essentially with the production of metal compounds, for example lower oxides, in a semipyrophoric condition. It is possible by means of the invention to obtain the compounds in any intermediate stage, 'as desired, between the ordinary condition and the pyrophoric condition, all of which intermediate conditions are comprised under the term semipyrophoric. It is also possible to produce metal compounds which ignite at a desired temperature.

The semipyrophoric condition of metal compounds may be defined as being similar to the semipyrophoric condition of metals, that is to say it includes those forms of the compounds of which the ignition temperature lies between that of the normal substance and that of the pyrophoric substance. This temperature difierence may be from about 50 to 300 C.

The causes of the pyrophoric condition are not exactly known and can not be ascertained from the literature on the subject. .Similarly the causes of the semipyrophoric condition of a metals and'metal compounds cannot be exactly explained, although it may be assumed that the semipyrophoric condition dependsin part upon the size of the particles of, the substance in question and is also a consequence of adsorption phenomena .which result in chemical changes taking place at least at the surface. The semipyrophoric compounds which are manufactured in accordance with the invention are, for example, semipyrophoric metallic sub-oxidies, such as FeO. In view of what is known about semipyrophoric metals it is surprising that it is also 1 possible to manufacture semipyrophoric metal compounds and that these may'even be oxides. In view of the low heat tone of oxides such a i ready oxidation would not be expected at low temperatures.

The semipyrophoric compounds can be manufactured, in accordance with the invention, by

the decomposition, for example by means of hea of metal compounds, for example by decomposi- 'tion'of ferrous oxalate into ferrous oxide. Since these metal compounds can also be obtained in a pyrophoric form as well as in a semipyrophoric form, the conditions under which the reaction is carried out in accordance with the invention must be such, as regards pressure, temperature etc., that neither the normal nor the pyrophoric form is produced. In this case, according to the conditions of the reaction a part of the starting material can be simultaneously obtained in the 5 form of semipyrophoric metal, so that mixtures of semipyrophoric metal compounds" in a low stage of oxidation together with semipyrophoric metals can be produced. .The properties of both substances are however so similar that separa- 10 tion is only possible with difficulty. This resemblance between the properties of semipyrophoric metals and those of semipyrophoric metal compounds enables the latter metal compounds to be used for the same purposes as the semipyrol6 phoric metals and also for other-purposes. For

, many purposes however, the low heat tone when semipyrophorlc metal compounds are burned as compared with semipyrophoric metals'isa decided advantage, since this property can be em- 20 ployed for retarding the combustion process and for regulating the heat produced.

In the investigation of semipyrophoric substances and in the development of processes for their manufacture considerable difliculties were as encountered in connection with the apparatus to be used. The reproduction of the same substance v with exactly the same properties depends not only on the canditions of the reaction, such as pressure, temperature, and time, under which neither the pyrophoric nor the normal form is produced, being kept constant, but also on the quantities which are being worked with and on the form of the apparatus as a whole. A numberof contradictory statements which are to be 35 found in the literature rega;dlng the semipyrophoric state can be entirely explained as being due to the use of diflerenttypes of apparatus to which insuflicient attention was paid by the authors of the statements in question. 40

The great advantage of using semipyrophoric compounds as initial igniting substances, or as combustible materials instead of the known substances such as carbon, sulphur, phosphorus which have previously been used for similar purposes is that the semipyrophoric compounds burn without giving off noxious, poisonous or nauseating gases. In the various processes by which metal compounds are decomposed, it may be assumed, in general, that the pyrophoric condition has to be passed through before the semipyrophoric condition is arrived at. Owing to this it is possible to develop a number of variants of the same process. One process in accordance with the invention consists in obtaining the a metal compound to be decomposed by maintaining definite conditions during the course of the reaction without interrupting the process of manufacture. Another: possible process is to isolate the pyrophoric body and to subject it sep-' arately to further treatment. In this case the reaction proceeds in two stages, namely:

1. The decomposition of the metal compound to form'a pyrophoric substance, and I v 2. The conversion of the pyrophoric substance into the semipyrophoric condition.

The two stages can also be conducted in such a way that a continuous process results.

The conversion from the pyrophoric to the semipyrophoric state is eflected either by treating the pyrophoric substance with a gas free from oxygen at an elevated temperature and maintaining such conditions during the reaction that the substance loses the p'yrophoric condition but does not attain the normal condition, or by storing the pyrophoric body for a considerable time in an atmosphere which is free from oxygen but to which very diluted oxygen has slow access. A further possibility is to introduce the pyrophoric substance in a hot or cold state into a suitable liquid, for example methyl alcohol, acetone, esters, ketones, aldehydes, ether, etc., which is then evaporated or the suspension itself is subjected to further treatment.

In accordance also with the invention these various possibilities can also be employed for the manufacture of semipyrophoric metals.

The invention will now be explained with the aid of the following examples which explain both the process of manufacture and the manner in which the semipyroph'oric material can be used.

Example 1.For the manufacture of a'semipyrophoric ferrous oxide which-consists mainly of FeO, 1.50 grams of ferrous oxalate are heated at a temperature of 390-410 C. in a glass tube -at the other end, The decomposition of the ferrous oxalate which can be recognised by the change of color from light yellow to greenish black and then to deep blue-black, is complete afterabout five minutes. The heating: is then continued for about 5 to 6 minutes andthe material is allowed to cool down to room temperature. About 0.61 gram of senilpyrophoric ferrous oxide are obtained.

The gases formed during the reaction consist mainly of steam, which originates from the water of crystallisation and ,carbon monoxide.

Example 2.-Pyrophoric iron manufactured by thermal'decomposition. of ferrous oxalate becomes semipyrophoric after being stored for 58V? eral days in an atmosphere of nitrogen.

Example 3.Into a vessel which contains pyrophoric iron oxide in an atmosphere of hydrogen, air is allowed to enter slowly during'the course of several; days untilthe hydrogen has been driven out. The residual powder is semipyro phoric. v

Example 4.A current of nitrogen is allowed to flow for some minutes over freshly prepared pyrophoric iron oxide while it is cooling down, that is to say at a temperature of about 100 to 300 C. when room temperature is reached the 9,230,629 semipyrophoric final product directly from the pyrophoric-iron oxide has become semipyrophoric.

Example 5.Freshly prepared pyrophoric iron is allowed to fall while still hot, ,into acetone, the access of air being excluded. The supernatant acetone is decanted and the remainder of the acetone is allowed to evaporate in the air. Semipyrophoric iron remains behind.

Example 6.--Freshly prepared pyrophoric iron oxide is allowed to fall in a cold condition into acetone, access of air being excluded; the supernatant acetone is decanted and the remainder of the acetone is allowed to evaporate in the air.

Examples of the applications to which. the semipyrophoric substances can bev put the carrier. I

B. Semipyrophoric metal compounds are used for the manufacture of combustible bodies which contain substances which are easily vaporised. Thus, the following combustible composition can be used for the development of iodine vapor. 10 parts of semipyrophoric ferrous oxide are mixed with 1 part of adsorption charcoal in which about 10% of elemental iodine has been adsorbed. The powdery mixture is stirred into a paste with a suitable binding agent, for example collodion solution, and may or may not be applied to a suitable carrier. The dry mass can be ignited by means of a flame. compound with corresponding development of Oxidation of the metalheat then begins at the place at which it was ignited. The reaction proceeds slowly from the point at which ignition was effected and-spreads through the mass, while at the same time, owing to the rise in temperature, the adsorbed iodine is driven 05 from the charcoal.

These examples illustrate only two of a large number of possibilities, and the invention is not restricted to these two examples.

I claim:

1..A' safety igniting composition which comprises a mixture of a binding agent, a. frictionproducing agent and a semipyrophoric iron oxide.

2. A safety igniting composition which'comprises a mixture of a binding agent, a frictionproducing agent,' and semipyrophoricflerroua oxide.

3. A' safety igniting composition which com prises a binding agent, a friction producing agent,

semipyrophoric iron and a semipyrophoric iron consisting of a mixture of a semipyrophoric iron oxide and semipyrophoric iron.

ALFRED SCHMID.