Composition for producing phosphine gas

A metal phosphide composition is disclosed for generating a mixture of phosphine and diluent gas(es), presented ready for use in a hydrolysis process or apparatus in the form of a free-flowing particulate metal phosphide material composed of loose particles of said metal phosphide essentially free of metal phosphide dust, essentially free of hydrolysis retarding agents and essentially free of hydrophobic substances in the form of coatings or hydrophobizing additives. In use the hydrolyzable metal phosphide, preferably magnesium phosphide, is released directly into liquid water under an atmosphere of gas inert to phosphine. The generated mixture of phosphine and inert carrier gas, e.g. CO.sub.2, can be used as such or is diluted into a gas mixing chamber with air to a concentration below the ignitability limit before being used in fumigation. The composition is manufactured by reacting a finely divided metal, selected from the group consisting of aluminum, calcium and magnesium with yellow phosphorus in an inert gas atmosphere and in the presence of a catalyst. Throughout the reaction batch and throughout the process, once reacting has commenced, a temperature is maintained within the range of 350.degree. C. to 550.degree. C. The metal phosphide is withdrawn as a particulate free-flowing material and is packaged ready for use in phosphine generation in such free-flowing condition, essentially free of dust, essentially free of hydrolysis retarding agents and essentially free of hydrophobizing substance in the form of coating or hydrophobizing additives, in a gastight container.

FIELD OF THE INVENTION 
The present invention relates to a metal phosphide composition for the 
production of phosphine by hydrolysis, comprising solid particles of metal 
phosphide selected from the group consisting of magnesium phosphide, 
aluminium phosphide and calcium phosphide and mixtures of these, more 
particularly presented in a form ready for use in a process and in a 
phosphine generator for generating a mixture of phosphine and diluent gas 
or gases, wherein such a hydrolysable metal phosphide is contacted with 
liquid water in a generating space, whereby the metal phosphide is 
hydrolysed to release phosphine which is withdrawn from the generating 
space and, where applicable, diluted from the time of its generation to 
its reaching its locality of use with a diluent gas to a composition which 
is non-ignitable under the conditions of use. The invention also relates 
to the use of the metal phosphide composition in such process and/or 
generator. 
CROSS-REFERENCE TO RELATED APPLICATION 
Such a process and generator form the subject of our copending applications 
Ser. No. 08/659,911, of even date, entitled "Process and apparatus for 
producing phosphine-containing gas". 
BACKGROUND OF THE INVENTION 
Phosphine gas is a highly toxic and flammable gas used in large quantities 
in pest control, and in particular for the fumigation of agricultural bulk 
commodities, such as grain and grain products. Phosphine gas generation is 
also subject to some peculiarities giving rise to special problems which 
do not apply to the generation by hydrolysis of other gases, e.g. the 
well-known generation of acetylene gas by hydrolysis of calcium carbide as 
disclosed e.g. in British patent specifications 472 970 (Haworth), 776,070 
(Union Carbide) and 291,997 (Haworth). 
In the case of phosphine gas generation there has always been the problem 
that prior art hydrolysable technical grade metal phosphides contained 
impurities which on hydrolysis liberated autoignitable phosphine 
homologues, phosphine derivatives, organophosphines, diphosphines or 
polyphosphines. This circumstance has created a strong prejudice in the 
art against what the present application proposes in what follows. 
Traditionally compositions containing hydrolysable metal phosphides, in 
particular aluminium, magnesium and calcium phosphides have been used for 
this purpose, applied either in sachets or other dispenser devices or as 
moulded bodies (pellets or tablets). 
In either case, the traditional compositions have always been compounded 
with various additives to a) reduce the reactivity of the metal phosphide 
when exposed to water in vapour or liquid form and b) to depress their 
tendency to autoignite. (Rauscher et al U.S. Pat. No. 3,132,067, Friemel 
et al U.S. Pat. No. 3,372,088, Friemel et al U.S. Pat. Nos. 4,421,742 and 
4,725,418, Kapp U.S. Pat. No. 4,347,241). In spite of these expedients, 
these prior art products remained dangerous substances, involving fire and 
explosion hazards which had never been fully overcome if the products are 
handled inexpertly and stringent safety precautions are neglected. The 
degree of safety also depends on the experience of the manufacturer and 
quality control. The traditional manner of using these products in bulk 
commodity fumigation is to introduce the compositions into the storage 
means (e.g. silos, shipholds) as such. In the case of pellets or tablets, 
these are usually introduced into the bulk commodity itself. This practice 
is nowadays criticised because of the resultant contamination of the bulk 
commodities with the residues of the decomposed tablets or pellets. 
If prior art compositions are apportioned in sachets, bag-blankets, 
bag-chains or similar dispensers, the purpose is to divide the composition 
into small individual portions in order to reduce the hazards of large 
local accumulations of gas and heat build up and at the same time prevent 
direct contact of the compositions with the commodities. These devices 
must, after completion of the fumigation, be retrieved from the storage or 
like facility where the fumigation has taken place. This is often 
difficult and cumbersome. The spent devices must then be disposed of, a 
matter which nowadays may cause problems. 
All these and other prior art fumigation means and their traditional 
methods of application suffer from the drawback that once the devices have 
been introduced into the silo or other storage space and once the 
fumigation has commenced, there is usually very little that can be done to 
influence or even monitor the further progress of the fumigation. In 
particular, if the composition should accidentally be deposited in a wet 
spot inside a grain store, this will neither be noticed in time, nor can 
the resultant dangerous situation be corrected. A fumigation of this type 
once commenced, can normally neither be stopped nor (usually) be 
decelerated or accelerated. 
To overcome these shortcomings to some extent new processes have been 
developed wherein tablets and pellets or the aforesaid sachets, 
bag-blankets, bag chains or similar dispensers are distributed e.g. on the 
surface of the bulk commodity and to then apply recirculation of the gas 
content of the silo, storage space or shiphold; see U.S. Pat. Nos. 
4,200,657 (Cook), 4,651,463 and 4,756,117 (Friemel) and 4,853,241 and 
4,729,298 (Dornemann). 
In those cases contamination, if any, is more localised and the spent 
dispensers are more readily retrieved, although these are still 
inaccessible whilst the process is in progress. The aforesaid climatic and 
humidity limitations still usually apply. The time taken for achieving a 
scheduled concentration of phosphine throughout the storage space still 
depends on the rate at which the metal phosphide composition is hydrolysed 
under prevailing circumstances. If the applied circulation is too slow or 
ceases, e.g. due to a power failure, undesirable concentrations of 
phosphine may accumulate. 
It has been recognised that it would be highly advantageous if it were 
possible to transfer the generation of phosphine gas to a locality outside 
the fumigation space whereafter the gas could then be fed into the 
commodity or storage facility in a controlled manner. However, because of 
the conceived and real risks inherent in phosphine gas and 
phosphine-releasing compositions, very little real progress has been made 
in this regard. 
Thus the use of bottled PH.sub.3, produced by one or other undisclosed 
industrial process, has been proposed in U.S. Pat. No. 4,889,708. Again, 
in order to prevent autoignition once the gas is released into air and the 
mixture of air and gas is used as a fumigant, it was considered necessary 
to bottle the PH.sub.3 highly diluted with an inert carrier gas such as 
CO.sub.2 or N.sub.2. According to U.S. Pat. No. 4,889,708, the PH.sub.3 
concentration in the bottled gas is to be 1.8 to 3% by weight. The storage 
and transport of this highly diluted phosphine gas involves considerable 
logistics problems, besides being very expensive. It also involves the 
grave risk that in the event of an accident on site, in transport or in 
storage or in the event of leaking bottles, e.g. due to defective or not 
properly closed valves, a gas cloud, albeit not readily flammable, is 
formed which is highly toxic and which, because it is heavier than air, 
can accumulate in low-lying areas or in cellars or the like. 
U.S. Pat. No. 5,098,664 discloses a recent attempt to overcome the 
prejudice existing in the art against the generation of phosphine gas in 
an external generator apparatus, wherein relatively large concentrated 
batches of metal phosphide are hydrolysed by the passage therethrough of 
controlled amounts of water vapour dispersed in humid air, the air serving 
as a carrier gas. This proposal still suffers from certain potential 
shortcomings. That disclosure teaches interrupting the hydrolysis in the 
event of operational failures by displacing the humid air in the generator 
space by an inert fluid, (liquid or gas). The recirculation type of 
process has similarly been improved in accordance with European patent 
application 9 114 856.8 (Degesch GmbH; published after the priority date 
of the present application) in that the hydrolysis of the solid metal 
phosphide compositions takes place outside the space containing the 
commodities to be fumigated in a hydrolysis chamber through which the 
circulatory gas flow is passed. Again, in the event of problems 
necessitating the interruption of gas generation, inert gas is admitted 
into the hydrolysis chamber to displace the humid air. In both the 
aforesaid cases there can be a considerable delay before humidity which 
has already partly reacted with the metal phosphide is fully consumed so 
that no further generation of phosphine takes place. This prolonged 
delayed release of phosphine can be explained by the following reactions. 
Normally the following reaction predominates when magnesium phosphide is 
exposed to humidity: 
EQU Mg.sub.3 P.sub.2 +6H.sub.2 O.fwdarw.3 Mg(OH).sub.2 +2PH.sub.3 
However, if the admission of humidity is interrupted, the already formed 
magnesium hydroxide continues to react with not yet hydrolysed magnesium 
phosphide as follows: 
EQU 3 Mg(OH).sub.2 +Mg.sub.3 P.sub.2 .fwdarw.2PH.sub.3 +6 MgO 
This latter reaction, because of the solid nature of the reactants, is slow 
and continues over a prolonged period. The above phenomenon also applies 
to other metal phosphides, e.g. aluminium phosphide. 
Complete control of all aspects of the aforesaid generator and process is 
nevertheless feasible but is complex and expensive. 
A number of more recent similar proposals are disclosed in PCT application 
WO 91/19671. Some embodiments again involve reaction of metal phosphide 
compositions with water vapour, and these embodiments are subject to the 
abovementioned problems. In most embodiments the phosphine is released 
into air, and the risk of ignitable mixtures of phosphine and air being 
formed cannot be excluded. 
In some other embodiments prior art tablets (as described further above) 
are dropped periodically one by one at a controlled rate into a water bath 
inside a generating space. The compositions, being in the form of 
compressed bodies, namely tablets, are specially compounded to reduce 
their reactivity. These tablets take a relatively long time to decompose 
when dropped into water, even if the water is heated, as proposed in this 
prior art. Accordingly this prior art process and apparatus suffers from 
the drawback that the gas generation is relatively slow and can only be 
accelerated by increasing the rate of feeding tablets into the water. This 
in turn means that the amount of metal phosphide submerged in the water 
bath at any one time is relatively large, and accordingly, if it becomes 
necessary to stop the gas generation because of some operational failure, 
it will take a long time before the gas generation stops, and large 
volumes of phosphine gas are generated during that period which have to be 
disposed of in some way or another. In most embodiments the phosphine is 
released into air and the risk of ignitable mixtures of phosphine and air 
being formed cannot be excluded. In addition, the gases released by such 
prior art composition, when dropped into water have a greater or lesser 
tendency to autoignite. 
Moreover the prior art compositions used in that process release paraffin 
wax or other hydrophobic and other additives into the water bath. The 
hydrophobic contaminants in particular float on the water surface and 
interfere with the smooth progress of the process by forming emulsions and 
entrapping metal phosphide particles and generally contaminate the water 
in the apparatus and the apparatus itself, causing a disposal and cleaning 
problem. These problems also arise from the proposals in PCT application 
WO 93 25075 wherein an extrudable paste of the metal phosphide and a 
water-immiscible, grease-like substance is squeezed into water in a 
generator space. 
Accordingly there existed a need for a process and apparatus of the type 
set out in the aforegoing which does not suffer from the aforesaid 
disadvantages or wherein these disadvantages are substantially mitigated. 
In particular there existed a need for a process and apparatus permitting 
the safe production of phosphine-containing gases in an environmentally 
friendly manner, with a minimum of disposal problems of potentially 
harmful metal phosphide residues and/or oily or greasy contaminants. Such 
process and apparatus should also be easily controllable in the case of 
operational failures, e.g. electrical power failures, and may indeed in 
certain embodiments be operable independently or substantially 
independently of any external electrical power supply. Such process and 
apparatus form the subject of our aforesaid copending application. 
In order to make the aforegoing feasible, there also exists a need for a 
metal phosphide composition suitable for carrying out the process and 
which will deliver a phosphine gas having no or no appreciable tendency to 
autoignite. 
The aforesaid prior art compositions suffered from the disadvantage that 
the phosphine gas released therefrom on hydrolysis has a greater or lesser 
tendency to autoignite. This problem has been linked to the hitherto 
unavoidable presence in the metal phosphide of contaminants which on 
hydrolysis liberate autoignitable phosphine homologues, phosphine 
derivatives, organophosphines, diphosphine or polyphosphines. Because the 
presence of these contaminants was considered unavoidable, the 
incorporation of the additives in accordance with the above cited prior 
art was considered unavoidable. In addition, the aforesaid forms of 
presentation as pressed bodies or in dispensers such as sachets were 
intended to slow down greatly the hydrolysis reaction, to avoid heat 
build-up and build-up of ignitable or explosive gas accumulations and 
concentrations. 
U.S. Pat. Nos. 4,331,642 and 4,412,979 to Horn et al and UK patent 
application 2097775 by Degesch GmbH disclose a process purported to result 
in the formation of magnesium phosphide free of such contaminants by the 
reaction of magnesium and yellow phosphorus at a temperature between 
300.degree. and 600.degree. C. In spite of these claims, it was considered 
necessary to compound this magnesium phosphide with large amounts of 
additives and resinous binder in the form of so-called "plates" as 
described in German patent 2002655. 
This material has, in the past, invariably been phlegmatised immediately 
after its formation by impregnation and coating with a hydrophobic 
substance, preferably hard paraffin in amounts of about 1 to 4%, 
preferably 2 to 3.5%, before any further handling or before storage prior 
to use in the manufacture of compositions for pest control purposes, such 
as the aforesaid "plates". For the aforesaid reasons the pure metal 
phosphide, such as the highly reactive magnesium phosphide, in its 
unphlegmatised form was never as such in the past made available to 
public. 
Although these plates have been very successful commercially and play an 
important role in the art, they have to be handled with the same great 
care as other conventional metal phosphide preparations, inter alia 
because of the risk of autoignition on contact with liquid water, for 
hitherto unknown reasons. 
SUMMARY OF THE INVENTION 
The present invention now provides a metal phosphide composition as set out 
in the Field of the Invention, comprising the feature that it is presented 
in a form ready for use in a hydrolysis process performed in a generator 
and is in the form of a free-flowing particulate metal phosphide material 
composed of loose particles of said metal phosphide essentially free of 
metal phosphide dust, essentially free of hydrolysis retarding agents and 
essentially free of hydrophobic substances in the form of coatings or 
hydrophobising additives. 
The present invention had to overcome several serious prejudices existing 
in the art, based on problems real or conceived. The invention, when used 
as herein disclosed, can provide a number of safety features which each, 
taken alone constitute a great improvement over the prior art and which 
are preferably used in combination. 
Thus, it has now surprisingly been found possible to provide a metal 
phosphide composition for the production of phosphine by hydrolysis, 
comprising solid particles of metal phosphide selected from the group 
consisting of aluminium phosphide, calcium phosphide and magnesium 
phosphide and mixtures of these, free of impurities, which on hydrolysis 
liberate autoignitable phosphine homologues, phosphine derivatives, 
organophosphines, diphosphine or polyphosphines, in the form of a 
free-flowing powder essentially free of metal phosphide dust, essentially 
free of hydrolysis retarding agents and essentially free of hydrophobic 
substance in the form of coatings or additives, which surprisingly can be 
used to produce phosphine gas safely by exposure to liquid water in the 
manner described further below. 
Because of the nature of the novel metal phosphide composition being used 
in the preferred process, the phosphine formed is free of autoigniting 
contaminants, and the gas mixture formed was found to have no tendency to 
autoignite, even when released into air in such amounts that the 
concentration of the phosphine in air exceeds the ignition limit as known 
for, mixtures of air and phosphine. Moreover, because in the preferred 
process a carrier gas is selected which is inert to the phosphine and 
preferably non-flammable, the gas mixture as such is quite safe. 
Preferably the particles contain more than 90%, preferably not less than 
95% by weight pure metal phosphide. 
The composition may include a substance enhancing the free-flowing 
characteristics, which, however, should not be hydrophobic, at least not 
to any material extent. Preferably, the substance enhancing free-flowing 
characteristics is graphite dust in an amount of from about 0.1% by weight 
upwards, preferably up to 0.5% by weight. 
The preferred metal phosphide is essentially magnesium phosphide, more 
particularly produced from magnesium and yellow phosphorus at a 
temperature of from 350.degree. to 550.degree. C., throughout the reaction 
batch and more specifically in the manufacture of which care is taken that 
the temperature nowhere exceeds from 450.degree. to 550.degree. C. 
Surprisingly it was found that if these conditions are meticulously 
observed in a manufacturing process otherwise substantially as described 
in U.S. Pat. Nos. 4,331,642 and 4,412,979 and UK patent application 
2097775 and contamination with the additives conventionally used in prior 
art manufactures of metal phosphide compositions, in particular the usual 
hydrophobic substances, is avoided, there is obtained a metal phosphide 
essentially free of contaminants which on hydrolysis create an 
autoignition hazard. This is particularly so if, in the case of magnesium 
phosphide, the reaction mixture at the end of the main reaction is 
subjected to tempering treatment at 530.degree.-550.degree. C., preferably 
substantially at 550.degree. C. (i.e. just below the melting point of the 
phosphide) of 20 minutes to 3 hours, preferably about 1 hour in order for 
any unreacted phosphorus to become wholly reacted. When following the 
procedures described in UK patent application 2097775 without the 
aforesaid tempering treatment, traces of unreacted phosphorus are still 
likely to be present in the final product. 
In this context it is pointed out that the prior art metal phosphide, e.g. 
as produced in accordance with the aforesaid references, is always, in 
normal conventional manufacture, impregnated with a hydrophobic substance, 
usually about 3.5% molten paraffin wax, immediately after leaving the 
reactor and whilst still hot, in order to reduce the reactivity of the 
metal phosphide and render it safer to handle, or so it was believed. 
On the basis of prior art knowledge there exists no ready explanation why 
the metal phosphide composition according to the invention and prepared in 
the absence of prior art hydrophobic coating substances should be even 
safer for purposes of the present invention than the prior art products 
impregnated with paraffin wax. 
However, in the light of the new, quite unexpected findings, it appears 
conceivable that contaminants which on hydrolysis give rise to 
autoignitable phosphorus compounds may be formed during the impregnation 
by some unknown reaction between the hot metal phosphide and the 
hydrophobic substance. 
The preferred composition is composed of particles of which more than 90% 
by weight are in the particle size range of from 0.1 to 2.5 mm, preferably 
elongate particles having a length of about 0.8-1.4 mm and a thickness in 
the range of 0.1-0.3, say 0.2 mm. More particularly the manufacture is so 
controlled that the particles are composed of magnesium phosphide granules 
as directly formed in the magnesium phosphide production process, i.e. 
from magnesium particles having substantially the same particle 
dimensions. This offers the advantage that no milling is necessary which, 
apart from the costs and wear and tear involved, would give rise to 
undesirable dust formation. 
The composition is preferably sealed in a gastight dispenser container and 
preferably the gastight container contains an atmosphere of carrier gas 
inert to the metal phosphide. More particularly the container has a 
connection locality designed to be connected to a phosphine generator and 
said connection locality includes a region which, when opened, and after 
having been connected, releases the composition into the generator. 
Preferably the interior of the container tapers towards the said region in 
a funnel-like manner. 
The fact that the metal phosphide, in contrast to all prior art metal 
phosphide compositions, in particular pest control compositions, does not 
have to contain the usual additives, helps to avoid the introduction of 
moisture into the container which conventionally gives rise to undesirable 
phosphine release during storage. Accordingly the compositions according 
to the invention have excellent storage characteristics. 
As taught in our aforesaid copending application, the metal phosphide 
composition may be used in a process, wherein the metal phosphide is 
released into liquid water in a free-flowing particulate form, composed of 
loose metal phosphide particles, essentially free of metal phosphide dust 
and of hydrolysis retarding agents and essentially free of hydrophobic 
substance in the form of coatings or hydrophobising additives, and, in the 
event that dilution commences already in the generating space, under an 
atmosphere comprising a carrier gas inert to the phosphine, forming at 
least part of the diluent gas. 
Preferably dilution commences already in the generating space and the 
carrier gas inert to the phosphine is also inert to the metal phosphide 
and the metal phosphide is maintained in an atmosphere of said carrier gas 
before entering the water. 
An advantageous feature is that the particulate metal phosphide released 
into the water, because of its small particle size, high reactivity and 
the absence of reaction retarding additives, in particular an absence of 
hydrophobic coatings, sinks in the water, becomes wholly submerged and 
hydrolyses almost immediately, and in any event in less than 3 minutes, 
preferably less than 1 minute. Indeed, using magnesium phosphide, the 
hydrolysis is normally complete within a few seconds. 
If the particles are relatively large or have a relatively moderate 
reactivity as in the case of aluminium phosphide the rate of hydrolysis is 
preferably accelerated by acidifying the water, e.g. with 5% HCl or 
rendering it alkaline. This may be preferred to heating the water as 
disclosed in the aforesaid PCT application WO 91/19671. In fact, cooling 
and/or recirculation of the water may sometimes be resorted to, to prevent 
undesirable rises in temperature. The reason is that at high temperature 
the water evaporates more rapidly, sometimes resulting in an undesirable 
moisture content of the generated gas mixture. In such cases, the 
temperature of the water is preferably maintained at below 60.degree. C. 
More preferably the temperature of the water is regulated to from 
3.degree. to 40.degree. C. 
On the other hand, if moisture in the gas is not objectionable, heating 
and/or a build-up of reaction heat may be resorted to in order to 
accelerate the hydrolysis. Indeed, because the hydrolysis takes place 
under an inert atmosphere, it was found to be quite safe to allow the 
water temperature to rise to near the boiling temperature, preferably to 
up to about 75%. 
Preferably the water is also agitated with the carrier gas. 
The process is preferably carried out with the above-described embodiment 
of the metal phosphide composition which is sealed in a gastight dispenser 
container. In that case, preferably, the metal phosphide powder of the 
composition after having been discharged from the container is entrained 
in the carrier gas and thus entrained is carried into the generator space 
and there enters into the water. For example, the contents of the 
dispenser container are introduced into the water in from 30 minutes to 30 
hours. 
The process is preferably carried out with a specially designed generator 
apparatus according to the invention described in our copending 
application. 
It is an important advantage of the invention that the nature of the 
carrier gas as well as the ratio of phosphine to carrier gas can be 
selected within wide limits to suit a desired purpose. In practice, a 
convenient upper limit has been about 75% v/v phosphine gas. 
Particularly if the gas mixture is to be used for fumigation purposes and 
depending on the conditions of the fumigation process the metal phosphide 
composition may, for example, be introduced into the water at a rate 
adapted to the rate of admission of carrier gas and the rate of withdrawal 
of the mixture to produce said mixture in a ratio of from about 40:60 to 
3:95 by volume of phosphine : carrier gas. Preferably said ratio is from 
30:60 to 5:93, more particularly from 17:82 to 10:90, e.g. 13:87. For some 
purposes a ratio of not more than 8:92 is preferred, because such mixture 
will no longer support a flame in an ordinary air atmosphere. 
In such uses as in fumigation the carrier gas is preferably non-flammable. 
Preferably the carrier gas inert to phosphine is selected from the group 
consisting of CO.sub.2, argon, helium, nitrogen, ammonia, methylbromide, 
freon and halon gases and mixtures of two or more of these. For fumigation 
purposes nitrogen or CO.sub.2, particularly the latter, are particularly 
preferred, inter alia because CO.sub.2 synergistically enhances the 
effectiveness of PH.sub.3 as a fumigant. Moreover, being weakly acidic, 
CO.sub.2 in the process according to the invention offers the further 
advantage that it accelerates the hydrolysis of the metal phosphide. 
For purposes where the gas mixture is to be heavier than air, optional 
carrier gases heavier than air may be used. Where flammability is not an 
obstacle, such carrier gases may, for example, include hydrocarbon gases 
heavier than air such as propane and butane and their isomers. For special 
purposes a gas lighter than air such as helium, methane or hydrogen may be 
employed, although in the latter two cases special precautions against 
fire and explosion hazards need to be taken, so that helium is generally 
preferred. 
The phosphine produced in accordance with the invention may be so pure that 
it can be used for semiconductor doping. In that case the preferred 
carrier gas is argon. 
In certain circumstances it may be necessary to limit the phosphine 
concentration so as not to exceed 2.4% v/v, which was found to be the 
limit up to which phosphine cannot be ignited in air under conditions 
considerably more stringent than those to be expected in practice. 
According to preferred embodiments of the process, great savings of inert 
gas may be achieved and risks of operating with high concentrations of 
phosphine gas may be further reduced, in that the mixture of phosphine gas 
and carrier gas inert to phosphine, withdrawn from the generator space, is 
mixed with air in a ratio of phosphine to air below the ignition limit of 
phosphine in a mixing space isolated from the environment and upstream of 
a feed duct for the mixture. 
As a further safety feature, the mixing space is preferably temperature 
monitored, so that the admission of phosphine gas to the mixing space may 
be interrupted, preferably automatically in the event of a predetermined 
temperature limit being exceeded. 
In the preferred process, water from the generator space is withdrawn and 
forwarded into an aerating space and air is bubbled through the water in 
the aerating space and from there is forwarded into the mixing space and 
mixed there with the phosphine gas and, where applicable, the mixture of 
phosphine gas and carrier gas inert to phosphine to form said 
non-ignitable mixture. 
Preferably the air is withdrawn from a closed fumigation space wherein 
fumigation is to take place and the non-ignitable mixture is fed into the 
fumigation space. 
In arriving at these embodiments the inventors had to overcome great prior 
art prejudices arising from the fire hazards perceived to arise from high 
concentrations of phosphine gas. However, surprisingly, when testing these 
embodiments under extreme conditions which could not realistically occur 
in practice, even when producing phosphine concentrations in CO.sub.2 in 
the generating space as high as 300 000 ppm, feeding such phosphine 
mixture into the mixing chamber and then reducing the admission of air to 
the mixing chamber so much that the ignition limit for phosphine was 
greatly exceeded (a situation which, as will be described further below, 
is normally prevented by a number of safety features), and then 
artificially igniting the gas mixture in the feed duct, leading to the 
fumigation space, the flame on reaching the mixing space was rapidly 
extinguished, when the thermal monitoring means caused a shut-off of the 
phosphine supply. In a more extreme test, involving prolonged failure of 
the temperature monitoring means as well, the fire in the mixing chamber 
continued without doing any harm, because the feed duct made of plastics 
melted off, thereby interrupting the communication between the mixing 
chamber and the fumigating space. 
The gas mixture may be introduced into a fumigating space containing a 
commodity to be fumigated with phosphine, where the phosphine is diluted 
by the atmosphere in that space to suitable concentration levels. In a 
preferred fumigation process the gas in the fumigating space, including 
the mixture is recirculated. More particularly the commodity is a bulk 
commodity and the gas recirculation is performed through the bulk 
commodity. 
Preferably the bulk commodity is a heaped particulate agricultural or 
forestry commodity. 
More particularly the bulk commodity is a commodity selected from the group 
consisting of grain, beans, peas, lentils, oil seeds, soya beans, nuts, 
coffee beans, tea, any of the aforegoing in comminuted, granulated, 
pelleted or flaked form, milling products of agricultural commodities, 
particulate or pelleted animal feeds, wood in a particulate form, animal 
or fish meal, bone meal, bark in a particulate form, cotton, cotton lint, 
dried fruit, dehydrated vegetables, spices, sago, farinaceous products and 
confectionery. 
The gas mixture may also be employed in the so-called SIROFLOW process, 
developed by the CSIRO in Australia. (R. G. Winks, "The Effect of 
Phosphine on Resistant Insects", GASGA Seminar on Fumigation Technology, 
Tropical Development and Research Institute, Storage Department, Slough 
18-21 Mar., 1986 and R. G. Winks "Flow-Trough Phosphine Fumigation--A New 
Technique", Stored Grain Protection Conference, 1983 Section 5.1; WO 
91/00017 (CSIRO)). 
This invention has also been found to be very useful for space fumigation, 
e.g. of storage sheds, but in particular of grain mills and factories e.g. 
for the manufacture of farinaceous products, e.g. noodles and other kinds 
of pasta. In such cases the mixture of phosphine and carrier gas, which 
preferably consists of inert gas, e.g. CO.sub.2 used in carrying out the 
hydrolysis with liquid water diluted with air to attain a phosphine 
concentration not exceeding 2.4% v/v, a concentration of about 18000 ppm 
(parts per million) being preferred, is introduced from the generator into 
the space and distributed there by piping, preferably including an 
appropriate number and configuration of branch pipes leading to various 
parts, and where applicable different levels of the space(s) to be 
fumigated. 
For carrying out the process the invention according to the copending 
application provides a phosphine generator which comprises a phosphine 
generating chamber containing liquid water, optionally and preferably an 
inlet connected or adapted to be connected to a supply of a gas inert to 
phosphine and for introducing an atmosphere of said gas into the phosphine 
generating chamber, an inlet for admitting a hydrolysable metal phosphide 
composition into the water in the generating chamber, a gas outlet adapted 
to discharge the phosphine and, where applicable, a mixture of the 
phosphine and gas inert thereto from the generating chamber and feed means 
adapted for feeding the metal phosphide through the inlet at a controlled 
rate, characterized in that the feed means is adapted to feed said metal 
phosphide in a free-flowing particulate form, composed of loose metal 
phosphide particles. This generator is designed to use the free-flowing 
metal phosphide composition according to the invention. 
The invention also provides a process for the manufacture of a metal 
phosphide composition according to the invention which comprises reacting 
a finely divided metal, selected from the group consisting of aluminium, 
calcium and magnesium with yellow phosphorus in an inert gas atmosphere 
and in the presence of a catalyst, selected from the group consisting of 
chlorine, bromine, iodine, compounds of any of the aforegoing with one of 
phosphorus, sulphur, hydrogen, zinc, ammonium and the aforesaid metals and 
of water at a temperature between 300.degree. and 600.degree. C., 
characterized in that throughout the reaction batch and throughout the 
process, once reacting has commenced, said temperature is maintained 
within the range of 350.degree. C. to 550.degree. C., that the metal 
phosphide is withdrawn as a particulate free-flowing material and is 
packaged ready for use in phosphine generation in such free-flowing 
condition, essentially free of dust, essentially free of hydrolysis 
retarding agents and essentially free of hydrophobising substance in the 
form of coating or hydrophobising additives, in a gastight container. 
Preferably the metal is magnesium. 
Preferably, in the manufacture, said temperature is nowhere outside the 
range of 450.degree. to 550.degree. C. 
Also preferably the metal is employed with a particle size of from 0.1 to 
2.5 mm and the particulate metal phosphide produced has essentially the 
same particle size. 
In the preferred process, after substantial completion of the reaction, the 
reaction product is maintained just below its melting point of about 
550.degree. C., for a period of 20 minutes to 3 hours and residual traces 
of unreacted phosphorus are removed. 
Also preferably, before packaging as aforesaid, the particulate metal 
phosphide is mixed with about 0.1 to 0.5% by weight of graphite or other 
suitable non-hydrophobic substance enhancing the free-flowing 
characteristics. 
The above process is a modification and an improvement of the process in 
accordance with U.S. Pat. Nos. 4,331,642, 4,412,979 and GB 2062602. 
Because of the nature of the metal phosphide composition, pollution and 
waste disposal is non-problematic. The metal phosphide, being 
substantially additive-free, decomposes substantially entirely, leaving 
behind only a harmless metal hydroxide residue which by the CO.sub.2 is 
converted into carbonate in the form of an environmentally harmless 
sludge, which can be drawn off from time to time.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION 
The following is to be read against the background of the more general 
description of the invention further above. 
Example of magnesium phosphide manufacture 
Magnesium phosphide for use in the process and apparatus was produced by 
the method in accordance with U.S. Pat. Nos. 4,331,642, and 4,412,979, GB 
application 2062602 and GB application 2097775 at a temperature between 
450.degree. and 550.degree. C., great care being taken that nowhere in the 
reactor a temperature of 550.degree. C. was exceeded. Extremely pure 
magnesium powder having a particle size ranging from 0.1 to 2 mm was 
employed as the starting material and the resulting magnesium phosphide 
formed in the reactor in the form of a granulate having the same particle 
size. This granulate, after having been discharged from the reactor, was 
maintained at 550.degree. C. for a further 1 hour to cause residual traces 
of unconverted phosphorus to be converted as well. In contrast to the 
prior art procedure the resultant granulate was not impregnated with 
paraffin wax or with any other hydrophobic substance. No additives were 
incorporated in this very pure magnesium phosphide powder except for an 
admixture of 0.3% graphite powder to improve the free-flowing properties. 
Testing of the magnesium phosphide so produced revealed none of the usual 
contaminants which give rise to autoigniting phosphorus compounds in the 
phosphine gas when the powder is subjected to hydrolysis. 
The metal phosphide composition is then filled into and sealed in a 
container as described with reference to FIG. 2 of the drawings. 
Aluminium phosphide and calcium phosphide are produced in substantially 
analogous manner. 
Examples of use of the composition 
Referring now to FIG. 1 of the drawings, the apparatus may be considered as 
comprising basically two parts. On the lefthand side, generally denoted as 
1 there is provided an apparatus 1 for feeding at a controlled rate a 
free-flowing particulate material, namely in the present instance the 
free-flowing metal phosphide material. On the righthand side there is 
shown the gas generator vessel proper generally denoted as 2. 
Dealing now first with the apparatus for feeding the metal phosphide, this 
includes a gastight closed supply vessel 3, the bottom 4 of which is 
funnel-shaped, terminating in an apex 5 and which contains a bed of 
particulate material. The top 6 of the supply vessel includes a feed inlet 
7, closable in a gastight manner. 
Inside the supply vessel, starting from close to the apex 5 and rising 
vertically near the centre line of the vessel, a riser tube 8 is provided, 
its lower end near the apex 5 being open at its inlet region through 
apertures 9 to the supply vessel and facing a venturi nozzle 10 which is 
vertically upwardly directed into the riser tube 8 and forms the end of a 
propellant gas supply tube 11 passing through the apex 5 and leading to a 
propellant gas supply, not shown, for example a carbon dioxide bottle. In 
use the inlet region is immersed in the bed of particulate material. 
Shortly underneath the top 6 of the supply vessel the riser tube has a bend 
12, leading by way of a duct 13 through the side wall of the supply vessel 
outside the latter. The duct 13 can be opened or closed by a valve or gate 
which in the present example is a ball valve 14 having an operating lever 
15. The lever 15 is biased to the closed position by, for example, a 
spring 16. A pressure actuated device diagrammatically shown as 17, 
connected to the feed duct for the carrier gas (CO.sub.2) 11 by a 
connection which is not shown, holds the valve 14 open for as long as the 
carrier gas pressure in duct 11 prevails, against the bias of spring 16. 
However, once the pressure is turned off or seizes due to the gas bottle 
being empty, the spring 16 will automatically return the valve 14 to its 
closed position, thereby sealing off the supply vessel 1 from the 
continuation of the duct 13. 
It will be understood that the valve means 14, 15, 16, 17 may be replaced 
by an electromagnetic valve device. 
On the upwardly facing side of the bend 12, at the beginning of the bend, 
in the outer periphery thereof, and in axial alignment with the riser tube 
8, an upwardly directed aperture 18 is provided. Aperture 18 may be of 
fixed size but is preferably adjustable by means of an adjustment gate 19, 
operable by an adjustment screw 20 passing through the top 6 of the supply 
vessel. Aperture 18 enters the gas space of the supply vessel, i.e. above 
the level of the bed of particulate material. 
As can be seen in FIG. 1a, as an alternative to apertures 9 in FIG. 1 at 
the lower end of the riser tube 8, that lower end terminates with a gap 9' 
between itself and the apex 5. The venturi nozzle 10 is formed by a screw 
threaded insert screwed into the bottom spigot 5' to which the gas supply 
tube 11 is connected. The gas supply tube 11 is represented by a gas hose 
connector nipple 11' entering sideways into the tubular member 11" welded 
at one end in axial alignment to the bottom spigot 5'. The opposite end 
terminates in a sliding seal 201 through which passes a needle valve 
needle 202, the tip 203 of which, in the closed position, as shown in the 
drawing, passes through and closes the venturi nozzle 10. This serves 
three purposes: to clear the nozzle of any blockages, to prevent solid 
particles from entering the nozzle and the tubular member 11" and closing 
the nozzle 10 in a substantially gastight manner even if gas pressure were 
to be admitted through the nipple 11'. The far end of the needle 202 is 
pivotally connected, diagrammatically shown at 204, to an operating lever 
205, pivotally supported at 206 and having an operating handle 207. 
Movement of the handle in the direction of arrow 208 causes the withdrawal 
of the needle tip from the nozzle 10 and opening of the needle valve. 
Optionally the manual lever may be replaced by a pneumatically or 
electromagnetically operating mechanism which may optionally be programmed 
to operate automatically. 
As a powder feeding apparatus the apparatus 1 operates as follows: 
An amount of free-flowing particulate material, a powder or granulate, is 
charged into the supply vessel 3 through the inlet 7. The inlet is 
appropriately closed in sealing relationship after the powder has been 
introduced, for example up to a level 21. The carrier gas supply is then 
opened to admit gas pressure to the carrier gas duct 11 and the device 17 
which causes the valve 14 to open. Gas now enters from the gas feed duct 
11 through the nozzle 10 and into the riser tube 18 as indicated by the 
arrows. The venturi effect of the nozzle 10 causes particulate material to 
be drawn into the riser tube 8 through the apertures 9 to be entrained in 
the riser tube and carried upwards. If the aperture 18 were to be 
completely closed, all the entrained particulate material would be carried 
through the bend and through the duct 13. However, depending on the amount 
by which the aperture is opened by the operation of the slide gate 19 a 
portion of the particulate material will be flung by its momentum in the 
axial direction of the riser tube through the aperture 18 and from there 
will drop back into the supply vessel 3. By adjustment of the gate 19 the 
ratio of particulate material proceeding through the duct 13 and that 
which is returned to the supply vessel can be adjusted at will resulting 
in a very accurate setting up of a desired feed rate for the particulate 
material through the duct 13, without necessarily changing the feed rate 
of the gas. 
As soon as the supply of pressure to the carrier gas feed duct 11 is 
discontinued either voluntarily or by the gas supply running empty, the 
pressure drop will cause the device 17 to discontinue its push against the 
lever 15 of the ball valve 14 and the bias of the spring 16 will 
automatically cause the ball valve 14 to close. The effect of this is that 
the contents of the supply vessel 3 are completely sealed off from the 
outside. If, for example, the particulate material is a metal phosphide 
powder or granulate, e.g. magnesium phosphide, no humidity can enter the 
vessel 3 from the outside and the magnesium phosphide remains completely 
protected against atmospheric hydrolysis. 
If the apparatus is equipped with a needle valve 10, 202, as shown in FIG. 
1a, that needle valve is normally kept closed when the feeder device 1 is 
not in operation. The needle valve is opened prior to the admission of gas 
pressure to the gas supply duct 11. If the carrier gas is inert to the 
particulate material and the particulate material is to be kept under an 
inert atmosphere, the needle valve is opened prior to introducing the 
particulate material in order to flush the supply vessel 3 with inert gas 
admitted through the gas supply duct 11. 
Dealing now with the righthand side of FIG. 1 the generator vessel 2 
comprises a closed vessel 22 wherein a supply of water 23 is maintained up 
to a level 24 by supplying water through water supply spigot 25 up to the 
level 24 which is dictated by the water overflow device 26 which includes 
a drainage tube 27 leading from near the bottom of the vessel 22 to a pipe 
bend 28 leading horizontally outside through the side wall of the vessel 
22 at a level which determines the water level 24 and leading into a 
downwardly directed drainpipe 29. In order to prevent the device from 
acting as a siphon and causing drainage of the vessel down to the bottom 
end of the drainpipe 29, an upwardly directed vent pipe 30 is provided on 
the pipe bend 28. 
On the lefthand side of the vessel 22 a vertical powder feed pipe 31, 
connected to the duct 13, enters through the top of the vessel 22 for 
admitting powder advanced by the feed apparatus into the vessel 22. 
An upwardly directed extension of the pipe provides a cleaning aperture 32, 
which is normally closed by means not shown. On the righthand side of the 
top of the vessel 22 as shown in the drawing, a gas outlet pipe 33 passes 
from the top of the vessel 22 through a droplet separator 34 into an 
outlet duct 35 through which the gas mixture generated in the generator is 
forwarded to wherever the gas is required, e.g. a silo, the contents of 
which are to be fumigated. 
A pipe nipple 36 on the droplet separator 34 serves for the withdrawal of 
gas samples for analysis. 
A further pipe nipple 37 on the righthand side of the top of the vessel 22 
leads to a pressure monitoring device (not shown). 
The gas space 38, 39 above the water surface 24 in the top part of the 
vessel 22 is subdivided into two chambers 38 and 39 by a vertical 
partition 40 extending from the top of the vessel down to the water 
surface and physically separates the entry for the metal phosphide powder 
supplied by ducts 31, 13 from the exit region for the generated gas 
through the duct 33. In the bottom of the vessel 22 underneath the chamber 
38, that is to say the region where the metal phosphide is introduced, an 
inlet duct 41 for carrier gas, preferably CO.sub.2 is provided, through 
which gas is bubbled into and through the water 23 for purposes of 
agitation. Also in the bottom of the vessel 22, at its lowest point, a 
valve controlled water and sludge drainage spigot 42 is provided. 
The apparatus functions as follows. Before the start of phosphine 
generation CO.sub.2 is bubbled through the duct 41 to displace any air 
from the apparatus. Once this has happened feeding of particulate metal 
phosphide material, preferably very pure magnesium phosphide may commence 
from the feed device 1 through the duct 13, 31 into chamber 38 from where 
the magnesium phosphide particles drop into the water 23 and are almost 
instantly hydrolysed. Agitation by the continued admission of CO.sub.2 
through duct 41 continues and further CO.sub.2 is admitted to the vessel 
22 through the duct 31 together with the magnesium phosphide powder. The 
resultant mixture of phosphine generated in the vessel and carbon dioxide 
admitted through ducts 31, 41 is so regulated that a desired ratio of 
phosphine to carbon dioxide accumulates in chamber 39 and is discharged 
through the outlet means 33, 34, 35. Because the hydrolysis of metal 
phosphides is highly exothermal, the temperature of the water 23 is kept 
below a predetermined level, e.g. 45.degree. C. by the continued admission 
of cool water through the water inlet 25, causing the overflow of 
displaced warm water and sludge resulting from the hydrolysis of the 
magnesium phosphide to be drained off through the overflow 27, 28, 29. 
This water and sludge, composed initially of magnesium hydroxide which 
then, due to reaction with the carbon dioxide bubbling through the water, 
is largely or wholly converted into magnesium carbonate, represents no 
environmental or disposal problem. Also, because of the low solubility of 
phosphine in water, the amount of phosphine lost with the water 
overflowing at 26 through system 27, 28, 29 is low. 
If water is scarce, the overflowing water and sludge may be drained into a 
clarifying vessel, from where water, after the sludge has largely settled 
out, may be returned through a cooling system back to the water feed 
spigot 25. 
Referring now to FIG. 2 of the drawings, there is shown a metal phosphide 
composition according to the invention 50 in an atmosphere 51 of the 
carrier gas CO.sub.2 sealed in a gastight dispenser container in the form 
of an aluminium flask 52 of a size sufficiently large to hold a 
standardised quantity of the free-flowing magnesium phosphide composition 
50. For example there may be provided different sizes of flasks holding, 
for example amounts of 1 kg, 2 kg and 5 kg respectively of the metal 
phosphide composition. The mouth of the flask is sealed with a gastight 
seal of aluminium foil 53 which is protected by a screw cap 54 screwed 
onto the threaded neck 55 of the flask. 
It will be seen that the side walls of the flask 52 taper towards the neck 
55 in a configuration which forms a funnel when the flask is positioned 
upside down. 
Referring now to FIG. 3 of the drawings, the screw threaded neck 55 of the 
flask 52 matches the internal thread and size of the inlet spigot 7 in the 
top 6 of the supply vessel 3 of the apparatus shown in FIG. 1. In FIG. 3 
the flask 52 is shown screwed tightly into the spigot 7 at a stage when 
the seal 53 is still intact. Inside the supply vessel there is mounted a 
seal perforating device, by the operation of which the seal 53 may be cut 
open. It includes a bush 56 in which is slidably mounted a plunger 57 
carrying at its far end, upwardly directed and facing the seal 53, a punch 
bit 58 having sharp edges 59 similar to the punch bits of an office paper 
punch. In its retracted position of rest, the shoulder 60 rests on the 
upper edge of the bush 56, being biased into that position by a spring 61 
between the lower edge of the bush 56 and a flange 62 near the bottom end 
of the plunger 57. Between the flange 62 and a second flange 63 slightly 
lower down, the plunger 57 is engaged by the prongs of a fork-shaped end 
64 of a lever arm 65 mounted irrotationally on a horizontal shaft 66 
passing through the side wall of the supply vessel 3 in pivotal and 
sealing relationship, provided by a bush 67. On the outside of the supply 
vessel 3 a second lever arm 68, terminating in a handle 69 is 
irrotationally mounted on the shaft 66. Operation of the lever 68, 69 in 
the direction of the arrow 70 causes upward swinging of the lever arm 65 
in the direction of arrow 71 thereby moving the plunger 57 with its 
plunger bit 58 upwardly against the bias of the spring 61 causing the 
sharp edge 59 to punch a neat hole through the seal 53 as closely as 
possible to the inner periphery of the neck 55. Subsequent withdrawal of 
the plunger from the hole cut into the seal frees the mouth of the flask 
52 and the free-flowing powder 50 then runs into the supply vessel 3. In 
this manner the contents of the flask 52 are transferred into the supply 
vessel 3 without any atmospheric humidity having an opportunity to enter 
into contact with the metal phosphide powder 50, the supply vessel 3 
having previously been flushed out with carbon dioxide. The dimensions and 
design are so chosen that the punched out disk cannot interfere with the 
operation of the apparatus, e.g. by blocking the apertures 9. The 
apparatus is now ready for use. Once the contents of the flask 52 have 
been consumed, and if more metal phosphide is needed, the flask 52 may be 
screwed off, and a further flask may be screwed in place with a slight 
positive carbon dioxide pressure prevailing in the supply vessel so that 
no moisture can enter from the atmosphere. The seal is then again punched 
open. 
If the phosphine gas which is extremely pure is to be used for 
semi-conductor doping, argon can be used as a carrier gas instead of 
CO.sub.2. 
Referring now to FIG. 4 of the drawings (from which the feeder device', 
identical to that of FIG. 1, has been omitted in order to avoid 
overcrowding of the drawing), the reference numbers are used as in FIG. 1 
to indicate substantially identical integers. These will not be described 
all over again. 
The main difference resides in that the gas outlet pipe 33 leading from the 
gas space 39 above the water level 24 of the hydrolysis chamber 22 and the 
droplet separation chamber containing water disentrainment means 34 (any 
suitable packing for that purpose) is adjoined by and communicates with a 
gas mixing chamber 100 through a duct 35'. The mixing chamber is likewise 
packed with a water disentrainment packing 34'. The water collected in the 
packing 34 drains back into the water bath 23 through a draining pipe 101 
extending well below the water level 24. 
Any water collected in the mixing chamber 100, drains into a cavity 26' 
extending from the mixing chamber to near the bottom of the hydrolysis 
chamber 22 and separating in conjunction with an overflow weir 102 the 
water bath 23 from the water 103 in the aerating chamber 104. The overflow 
weir 102 extends up to the water level 24 and divides the cavity 26' into 
water inflow cavity 27' and outflow cavity 29' which communicate above the 
overflow weir 102 through the overflow and venting chamber 30' (28'). 
At the bottom of the aerating chamber 104 an air distributor and bubbling 
device 105 is provided, connected to a source of air formed by an air duct 
106, an air blower 107 and an air suction duct 108 connected to a 
fumigation space (109). An air space 110 above the water 103 in the 
aerating chamber discharges thereabove through a discharge duct 111 into a 
disentrainment chamber 112, containing a droplet separator packing 34" and 
communicating with the gas mixing chamber 100 through an air passage 113. 
The mixing chamber has a gas mixture outlet 35" connected by a feed duct 
114 to the fumigation space (109) not shown as such. 
The aerating vessel 104 on its side opposite the overflow weir 102 and 
associated walls 27' and 29' is bordered by a similar overflow structure. 
This is formed by a wall 115 extending from the top of air chamber 110 
down to near the bottom 116 of the aerating chamber, an overflow weir 117 
and an overflow passage 118 leading into an outlet chamber 119 and outlet 
duct 120. The top of the outlet chamber 119 forms an air space 121 with a 
vent duct 122. 
The bottom of the hydrolysis chamber 22 slopes towards a drainage spigot 42 
connected to a drainage pump 123. Likewise the bottom of the aerating 
chamber 104 slopes towards a draining spigot 124 connected to a drainage 
pump 125. The outlet duct 120 is connected to a drainage pump 126. 
It should be understood that a single pump combined with an appropriate set 
of valves could be used instead of three separate pumps 123, 124 and 126. 
However, the combination of these pumps lends itself to particularly easy 
automatic pre-programmed operation. 128 represents a feed tank for 
cleaning fluid (HCl) which is introduced at the end of a generating cycle 
(or after 10 kg of magnesium phosphide have been consumed). Its contents 
are discharged through a hose 129 into the generator chamber 22 to assist 
the cleaning water to wash out solid precipitates of magnesium carbonate. 
130 is a pressure equalisation hose. 
It should be understood that the air blower 107 can also be employed to 
apply recirculation of the mixture of phosphine and air and/or other 
diluent gas (e.g. CO.sub.2) through a heaped bulk commodity (e.g. a 
particulate agricultural or forestry commodity) contained in the 
fumigating space (e.g. a silo or shiphold), e.g. in the manner known from 
the above-cited prior art. 
Finally, reference must be made to the important safety feature of a 
thermal switch 127 in the mixing chamber connected to switch off the 
supply of metal phosphide to the hydrolysis chamber from the feed device 
(1) and thereby, within seconds interrupting the supply of further 
phosphine in the event of an excessive temperature (more than 100.degree. 
C.) in the mixing chamber indicating fire or fire risk. 
Referring now also to FIG. 5, there is shown diagrammatically the apparatus 
in accordance with FIG. 4 and its control means within the confines of a 
cabinet, diagrammatically indicated by the outlines 200. The apparatus is 
connected on the inlet side to a carbon dioxide bottle 210. Likewise, 
water feed pipe 25 is connected to an outside source of fresh water, not 
shown. The space to be fumigated is diagrammatically shown by block-shaped 
outlines 109. The waste water outlet 120 leads to a drain or collecting 
vessel outside the apparatus. The cabinet has an electronic mode control 
panel 300 with four control buttons, a start button 301, a pause button 
302, a restart button 303 and a washing mode button 304, each one adjoined 
by a pilot light 310 to indicate the particular operating mode which has 
been set. A general on/off switch is diagrammatically indicated as 311. 
Further, there is diagrammatically indicated a manual and visual flow 
control panel 400 on which is mounted the control lever 207 in accordance 
with FIG. 1a and which includes manual flow regulating valves 401, 405 and 
409 each associated with a visual flow indicator 402, 406 and 410 
respectively. The functions of these will be explained in what follows. 
The CO.sub.2 bottle 210 is connected by a gas hose 211 to a manifold 212, 
one arm of which leads into the CO.sub.2 inlet duct 41, leading into the 
gas bubbling device at the bottom of the generator chamber 23. This duct 
includes the manual control valve 401 and the visual flow indicator 402 on 
the panel 400, an electronic flow monitor 403 and an electronically 
controlled regulator valve 404. 
The other branch of the manifold 212 leads into the propellant gas duct 11 
of the pneumatic feed device 1. Duct 11 includes the manual regulator 
valve 405 and visual flow indicator 406 of panel 400, an electronic flow 
monitor 407 and an electronically controlled regulator valve 408. 
The fresh water inlet 25 feeding water into the generator chamber 23 
includes a manual flow control valve 409 and visual flow rate indicator 
410 on panel 400 and an electronic flow monitor 411 and electronically 
controlled regulator flow valve 412. It furthermore optionally includes a 
fresh water temperature gauge 414, which serves for information only and 
has no control function. 
Likewise, the wall temperature gauge 413 in the top part 38 of the 
generator vessel is purely for information purposes as is the water 
temperature gauge 415 inside the water bath of the generator chamber 23. 
On the other hand, the water level monitor 416 in the generator chamber is 
connected to the automatic electronic control means of the apparatus for 
automatic corrective action in the event of the water level 24 deviating 
from normal. 
The flow rate of air in the air duct 106, leading into the aerating chamber 
103 of the generator, drawn through duct 108 from the fumigation space 109 
by the blower 107 is automatically electronically monitored by the gas 
flow rate monitor 417. A further electronic gas flow rate monitor 418 is 
provided in the duct 33 leading from the generator gas space 39 into the 
water disentrainment chamber preceding the mixing chamber 100. 
Apart from the few manual control means mentioned further above, the 
apparatus is programmed to operate fully automatically and the operator 
need only press the appropriate button on the panel 300. First the start 
button 301 is operated. This causes the water, CO.sub.2 and air feeds and 
water pump 126 to be switched on. If the electronic monitoring means 
indicate that all four critical parameters are in order, the apparatus 
runs for about seven minutes as a pre-preparationary period, until the 
correct water level 24 has been attained. If in this respect any 
operational fault is detected, the apparatus is switched automatically to 
"pause" mode and an alarm is sounded. If everything is in order, the 
electronically controlled valves for CO.sub.2 and magnesium phosphide are 
opened in the course of a period of about thirty seconds. After one 
further minute the feed control valves for CO.sub.2 in the duct 11 of the 
metal phosphide feed device 1 are operated and metal phosphide is now 
propelled at the desired controlled rate through the riser tube 8, duct 13 
and valve 14 into the gas chamber 38 of generator vessel 23 and drops into 
the water, whereby the generation of phosphine gas commences. 
The process can be interrupted at will by pressing the "pause" button 302, 
to be restarted if desired by pressing the "restart" button 303. 
After a preprogrammed dosage period has expired, the CO.sub.2 valves and 
the electronically controlled valves for CO.sub.2 and metal phosphide are 
automatically closed and the washing phase commences. For the washing 
phase the vessel 128 at a preprogrammed stage receives an appropriate 
volume of hydrochloric acid which is admitted to the generator space 24 
where it mixes with washing water which is withdrawn by pump 123 and 
forwarded into the aerating chamber 103 from where in turn it is forwarded 
by pump 125 into the outlet chamber 119, 121 from where it is finally 
withdrawn by pump 126 and discharged through duct 120. 
The washing programme can also be started at will by pressing the "washing" 
button 304. 
The complete programme is diagrammatically illustrated in the diagram of 
FIG. 6. In that diagram the horizontally shaded transverse columns 
represent monitoring and the cross-hatched transverse columns represent 
material feeding periods. 
The vertical columns represent the following: 
A: starting up period 
B: metal phosphide feeding 
C: washing 
D: final rinsing 
The sub-headings of the vertical columns (t) represent the times in minutes 
for the various product phases (where x is variable). 
On the left hand side of the diagram the headings for the transverse 
columns have the following meaning: 
I: CO.sub.2 admission through duct 41 
II: CO.sub.2 admission through duct 11 
III: fresh water admission through duct 25 
IV: air circulation through duct 106 106 
V: admission of hydrochloric acid (HCl) 
VI: pump 126 
VII: pumps 123 and 125 
VIII: maintenance of water level 24 
IX: temperature monitoring at 127 (max 100.degree. C.) 
After numerous tests it was concluded that the apparatus can be operated 
conveniently and safely with CO.sub.2 and metal phosphide (MeP) flow rates 
being adjusted to result in a ratio of phosphine to CO.sub.2 of 59:41 v/v. 
In fact, no problems were experienced with a ratio as high as 75:25 v/v. 
In the mixing chamber 100 dilution with air was carried out to a 
concentration of 18000 ppm PH.sub.3. The tests were performed with 
magnesium phosphide of 95% w/w purity produced as described in the 
Example. 
Aluminium phosphide can be used if the temperature of the water bath is 
preferably at least 60% and if 5% HCl is added. 
The above apparatus was found to offer considerable advantages over the 
prior art. 
Because of the free-flowing nature of the metal phosphide it is possible to 
feed the metal phosphide accurately at the desired rate and in a form 
wherein it is hydrolysed and releases phosphine almost immediately. The 
feed means is completely isolated from moisture and before the metal 
phosphide enters the phosphine generating chamber it is maintained in a 
completely inert, moisture-free environment. The moment the propellant gas 
supply is interrupted--intentionally or otherwise--the feeding of metal 
phosphide composition is interrupted and the metal phosphide inside the 
feed device is isolated from the generating space. Because of the small 
amount of metal phosphide present in the water at any one time and the 
very rapid hydrolysis thereof, the generation of phosphine ceases almost 
immediately. The relatively small amount of phosphine still formed is 
present in the form of a safe mixture with the inert carrier gas, which, 
because of the small amount, can either be vented off, or better still, 
can be fed to wherever it is to be used, e.g. into the fumigation space. 
In that case this phosphine is not lost due to the interruption. 
The claims which follow and the priority document are part of the present 
disclosure.