Method of Transforming Silico-fluorides and Borofluorides into Corresponding Fluorides or Fluorine Compounds.
Year: 1897

page_text: Date of Application, 14th Sept., 1897-Accepted, 27th Nov., 1897
Method of Transforming Silico-fluorides and Borofluorides into
Corresponding Fluorides or Fluorine Compounds.
I, JULIUS REICH of Czerningasse 3, Vienna II, Austria, Chemist, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
This invention consists of a method for preparing out of silico-fluorides and boro-
fluorides the corresponding fluorides, which may be used as such, or for the
ation of other products.
prepar-
Up to the present no method was known for transforming silico-fluorides and
also borofluorides into the corresponding fluorine compounds with ease and com-
pleteness particularly on the large scale suitable for manufacturing purposes.
If, for instance, an alkaline silicofluoride is ignited, in order to drive out the
silicon fluoride, so as to subsequently obtain the remaining alkaline fluoride (this
method has already been proposed and tried several times), a part of the silicon
fluoride readily separates in the form of a gas; and for this purpose a compara-
tively low temperature suffices. But in order to completely separate all the silicon
fluoride present in combination, long continued and very strong ignition is
necessary, and then the remaining substance will always contain some silic
fluoride (quoted from Lunge, Handbook of Soda Manufacture, 3rd volume, latest
edition, "Theoretical and practical treatise and the manufacture of Sulphuric Acid
and alkali with the collateral branches").
It may further be observed that the complete removal of the silicon fluoride, in
order to obtain a fluoride for further use and application, is not practicable as a
manufacturing process; for at the high temperature necessary, the vessels and
furnaces are strongly attacked not only by the silicon fluoride evolved, but also,
and to a much more considerable extent, by the alkaline fluoride which fuses at
that high temperature. No material is available, that would resist these influences
for even a short time. A further point is, that in consequence of 'this strong
action on the material of the containing vessels (in which the fusion takes place)
the fluoride produced would be very impure and of much reduced value.
Attempts which have been made to produce, by a wet process, the corresponding
fluorides from the silico-fluorides, have also resulted in failure. If, for instance,
an alkaline silico-fluoride is boiled with a solution of caustic alkali or milk of
lime, a reaction does certainly take place, but with difficulty and not completely.
In the first place, alkaline silico-fluoride (and also most of the other silico-fluor-
ides) is difficultly soluble, which makes a double decomposition with other sub-
stances much more difficult. In the second place the reaction is impeded still
further by the silicic acid which is separated at the time in the gelatinous form;
hence, the boiling solution becomes very viscous and thick, which materially
impedes the boiling process and makes it impossible except at a prohibitive cost
to wash out from the very voluminous precipitates, the soluble products formed.
All the above disadvantages occur, to a less or greater extent, not only in the

page_text: case of silico-fluorides but also in that of borofluorides. This invention now pro-
poses to do away with these disadvantages, not only in the case of silico-fluorides
but also in that of borofluorides, and everything that has been stated and will be
stated later on in this specification about the former equally applies to the latter.
Now as the preparation of fluorides, from the corresponding silico-fluorides and
borofluorides by the methods described, is either impossible on a manufacturing
scale, or impracticable on account of prohibitive cost, in my invention (based on
numerous experiments) the desired reaction is produced by heating the silico-
fluoride or borofluoride, which is to be treated, with an oxide of one of the metals
of the alkaline earths, (for instance, calcium oxide, barium oxide, strontium exide,
magnesium oxide,). As an example, to shew how the invention is worked out,
I will describe the treatment of alkaline silico-fluoride.
The experiments made shew that if a mixture of an alkaline silico-fluoride with
an alkaline earth (for instance, lime,) be heated to a low red heat, no silicon
fluoride is evolved, but a mass is left from which all the alkaline fluoride can be
extracted by washing with water. If for instance an alkaline silico-fluoride
(ASF), (where A represents an alkaline metal) is well mixed with lime in the
proportion of, say, one molecule of the former to three molecules of the latter, and
gently heated in a crucible or reverberatory furnace to a low red heat, suddenly, as
soon as any part of the mixture reaches that temperature, a sudden intense ignition
takes place there. This spreads rapidly through the mass even if mo further
external heat be supplied, so that the whole of it, which till then was only black
hot, becomes of a bright red heat. The reaction takes place so vigorously that it
looks as if the whole mass being consumed like glowing tinder.
This appear-
ance is particularly noticeable if, as soon as it commences, all external supply of
heat is cut off; the undisturbed progress of the phenomenon in question may them
be readily observed.
The circumstance that the reaction, if once started can supply its own heat, is
in these cases of importance from the manufacturing point of view, since it makes
it possible to carry out the whole chemical process by supplying heat only till the
reaction commences.
If heat were supplied after the reaction had commenced, the whole mass would
be fused by the raised temperature, whereby the sides of the crucibles and furnaces
(as already mentioned above) would be attacked and the mass itself would suffer
from the addition of a considerable amount of impurity. In order to prevent
this in practice, it is advisable to employ a larger propertion of the metallic oxide
than the molecular proportion given above, in order to prevent the mass from
fusing together; or to add an indifferent body, as diluent, to prevent the mass
from fusing together, for instance difficultly fusible powdered minerals, such as
felspar,. fluorides of the metals of the alkaline earths, etc etc. The ignited mass
may in any case contain, in order to prevent it from cakeing too much, a difficultly
fusible body, such as a silicate, an aluminate, etc., or a metallic oxide which resists
heat and is insoluble in water, such as zinc oxide, ferric oxide, etc.
The reaction takes place without any evolution of gas, as no silicon fluoride is
separated; the opposite is the case with an alkaline silico-fluoride when ignited
by itself. This non-production of silicon fluoride is of importance, as the produc-
tion or escape of this gas (which is difficult to condense) would be very objection-
able from the manufacturing point of view, and at the same time it would
necessarily lead to considerable losses, (not to be avoided) of the materials used
for regenerating hydrogen silico-fluoride.
When the reaction has been completed, the mass, which affer ignition is some-
what caked together, is powdered and treated with water. A strongly alkaline,
pure lye is obtained; in it there is no dissolved alkaline earth (in this case no
dissolved lime) to be found, but all the alkali contained in the alkaline silico
fluoride is dissolved in it in the form of alkaline fluoride.
This alkaline fluoride may be transformed, for instance by lime, into caustic

page_text: alkali. The caustic alkali may also be obtained by using the necessary excess of
lime added to the mixture before ignition; the solution obtained will then contain
caustic alkali, and no alkaline fluoride
If the solution of alkaline fluoride obtained from the ignited mass is to be
transformed into a caustic lye, or a carbonate one by boiling with milk of lime, etc,
then calcium fluoride is separated which may be used by itself for the reproduc-
tion of hydrogen silico-fluoride or of alkaline silico-fluoride; or together with the
other residue.
If, as already mentioned above, the caustic alkali, or the alkali carbonate, is to
be obtained directly in the ignition process from the alkaline fluoride formed in
it, this is done as already mentioned, by increasing the amount of alkaline earth
(oxide of a metal of an alkaline earth, or material producing it): thus for instanco
by using an excess of quicklime, or of a mixture of calcium carbonate and carbon.
In that case, which however necessitates the supply of external heat to be consider-
ably increased, the alkaline fluoride is first formed in the process of the reaction
during ignition and this, by a secondary reaction is transformed into caustic alkali
or alkaline carbonate, which may then be extracted by water.
It is self-evident that mixtures can be used which contain oxides of alkaline
earth metals or mixtures of silico-fluorides or boro-fluorides with the given
alkaline earths or mixtures of them, for the purposes of the reaction.
It may here he remarked, that according to the experiments made, the oxides
only (specially of the alkaline earth metals) give the above described reaction
which is strongly exothermic, and are therefore specially suited for the practical
carrying out of the process in question. But a saving of oxides may be effected if,
in the mixture of silico-fluoride and oxide, a part of the oxide is replaced by
material which contains such oxides either singly or collectively, or else is capable
of forming the oxides at the temperature employed. Such is, for instance, calcic
carbonate, calcic carbonate with carbon and nitrates also aluminates of the
alkaline earths or carbides.
The heat of the reaction produced by the alkaline earth present is then utilised
so that, for instance, added carbonate of an alkaline earth is transformed by it
into oxide.
It is evident, on the other hand, that economy of oxide necessitates a consider-
ably greater supply of external heat in order to complete the reaction, as the heat
produced in the reaction is used up for the decomposition (in the instance given,
of a carbonate of, an alkaline earth) of material; and fresh heat must be supplied
to the freshly formed oxide in order to enable it to itself take part in the reaction.
The described compounds such as the carbonates, nitrates, and other oxy-salts
of the alkaline earths, as they do not react by themselves, much less exothermi-
cally, can consequently generally be used only together with oxides of the metals
of the alkaline earths, as described. It is better practically to replace, by them,
excess of oxide, which serves to prevent fusion, or to transform the alkaline
fluoride formed into caustic alkali; in that case the excess of heat formed during
the reaction is practically employed to advantage.
The addition of carbon to the mixture in all cases has an advantageous effect
on the commencement of the reaction it is specially recommended when a part of
the oxide of the alkaline earth metal is substituted by one of the proposed alkaline
earth compounds, so as to assist in the reduction of the latter to oxide, (for instance,
to remove the carbonic acid from a carbonate).
In certain cases the progress of the reaction may be accelerated by the addition
of alumina or silica to the mixture so that the appearance of incandescence by
which the reaction is accompanied and its progress shewn will be perceptibly
quicker than when this is not done. The effect produced by the above mentioned
addition may be explained as a contact-action" of the alumina or silica and by
the quality possessed by these materials as heat transporters in the mixture
which communicate and distribute the heat among the mixed substances.

page_text: .
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1. A method of transforming silico-fluorides, and also borofluorides into the
corresponding fluorides, which can be further transformed into oxides or oxysalts,
by igniting the compounds in question with oxides of the metals of the alkaline
earths; the reaction may be assisted by the addition of carbon in certain cases also
alumina and silica, substantially as described.
2. In the method described in Claim 1, economising oxide by partially substutut-
ing for it compounds and salts of the alkaline earths (to be used together with
oxide) or substances containing or producing such materials, substantially as
described.
3. In the methods described in Claims 1 and 2, the use of such an excess of oxide
or an oxy-salt of an alkaline earth, that the fluoride formed as the first product is
at once decomposed into oxide or oxy-salt, substantially as described.
Dated unis Fourteenth day of September 1897.
For the Applicant,
GEDGE & FEENY,
60, Queen Victoria Street, London, Chartered Patent Agents.