Note: Descriptions are shown in the official language in which they were submitted.
~ ~ ~ HOE 84/H 030
The present invention relates to stabilized and desensi-
tized pulverulent flowable red phosphorus consisting substan-
tially of particles with a size of at most 2 mm, and to 3
process for making it.
As is known, red phosphorus is obtained by subjecting
yellow phosphorus to a thermal conversion reaction so as to
obtain the stabler red modification. After termination of the
reaction, the crude red phosphorus containing about 0.5 to
1.5 mass % yellow phosphorus is a compact mass. It is ground
under inert gas and freed from yellow phosphorus by boiling
it with a dilute sodium hydroxide solution (cf. Ullmanns
Enzyclopadie der technischen Chemie, 3rd edition, vol. 13,
1962, Phosphorus, pages 517/518, published by Verlag Urban
und Schwarzenberg, Munchen/8erlin). More recently however the
conversion is effected in a rotating reactor and the red phos-
phorus is obtained as a pulverulent mass. An aqueous suspen-
sion of red phosphorus is taken from the reactor (cf.
European Specification 00 15 384), heated with steam in a
stirring vessel and freed from about 0.1 mass % residual
yellow phosphorus by admixing it portionwise with sodium hy-
droxide solution.
Red phosphorus is used for pyrotechnical purposes, for
making striking surfaces for matches, and also as an agent
imparting flame-retardant properties to plastics materials,
e.g. polyamides or polyurethanes. In all of these fields of
application, the use of readily flammable red phosphorus
has been a problem. More especially, the formation of dust
unavoidable heretofore during the processing of red phos-
phorus has been very hazardous as even an electrostatic
disruptive spark may already initiate a dust explosion pro-
lX~Z~';7~
pagating at a high velocity. This risk is the greater thsgreater the fineness of ground red phosphorus. Finely pul-
verized red phosphorus is however required to be used, e.g.
for imparting flame-retardant properties to plastics mate-
rials.
In a moist atmosphere however, the surface of red phos-
phorus undergoes a chemical reaction during which various
acids of phosphorus of oxidation stages +l to ~5 and hydro-
gen phosphide are formed by oxidation and disproportionation
reactions.
It is therefore highly desirable to avoid these risks
by providing stabilized and desensitized red phosphorus.
The term "stabilization" as used herein denotes an
operation during which the red phosphorus is given an improved
protection against atmospheric influences and which contri-
butes to reducing the formation of oxo-acids of phosphorus
and hydrogen phosphide during storage or processing.
The term "desensitization" as used herein denotes an
operation reducing the tendency of red phosphorus to form
dust, lessening the potential risk of a dust explosion, and
increasing safety during processing.
It has already been suggested that red phosphorus should
be stabilized by means of aluminum hydroxide (cf. Gmelins
Handbuch der anorganischen Chemie, 8th edition, 1964, volume
Phosphorus, part 8, page 83, published by Verlag Chemie,
Weinheim/Bergstrasse, Federal Republic of Germany). By the
subsequent addition of 10 % solutions of sodium hydrogen car-
bonate and aluminum sulfate heated to 55 - 60C, the aluminum
hydroxide is precipitated in the phosphorus particles. Next,
the aqueous suspension is filtered and the filter residue is
257fi
dried. This proces~ is beset with the disadvantage that un-
desirably large quantities of aluminum hydroxide are required
to be used in order to produce a satisfactory stabilizing
effect. In other words, the phosphorus becomes contaminatad
to an unacceptable extent considering the widespread uses
it finds in the most various fields.
A process permitting pulverulent red phosphorus ~o be
protected against the action of air and moisture has already
been disclosed in German Specification 11 85 591, wherein
red phosphorus is intimately blended with finely divided
paraffin and/or wax, the resulting blend is heated to a tem-
perature slightly above the melting point of paraffin and/or
wax and cooled.
Another process for stabilizing red phosphorus (US-PS
15 23 59 243) provides for the red phosphorus to be suspended
in an aqueous 0.04 N solution of sodium aluminate, for air
to be passed through the suspension over a period of 10
hours at 85 to 90C, for the whole to be filtered, washed
with hot water and dried under vacuum.
Apart from aluminum hydroxide, zinc or magnesium hy-
droxide can be used for stabilizing red phosphorus (cf.
US-PS 26 35 953).
In German Specification DE-OS 28 13 151, it has finally
been suggested that red phosphorus should be stabilized
using a blend of aluminum hydroxide and lead hydroxide.
These known processes do not permit red phosphorus to
be satlsfactorily stabilized to oxidation with a minimum
of stabilizer. In fact, the oxidation stabilizers described
heretofore present an unsatisfactory thermal stability,
water being split off at elevated temperatures. ~lith respect
' -
lZP~2~'i7Çi
to plastics which are to be processed on an extruder and have
red phosphorus as a flame-proofing agent incorporated there-
in, which in turn contains an oxidation stabilizer, it is
generally accepted that the oxidation stabilizer should pre-
sent thermal stability in the absence of any tendency to split
off water or to undergo decomposition, even at temperatures
above 300C.
This is a disadvantageous effect which has also been
encountered in the stabilization process described in German
Offenlegungsschrift 2,622,296. In that process, the stabiliz-
ing effect is achieved by precipitating small amounts or
metal salts of various acid orthophosphoric acid esters onto
the surface of the red phosphorus.
The orthophosphoric acid metal salts suggested for us~
as stabilizers in German Offenlegungsschrift 2 631 532, pro--
- duce material which has an inadequate stability to oxidation
for a variety of uses.
The metal salts of phosphoric acids and phosphonic acids
(cf. German Offenlegungsschrilt 2 647 093 and German ûffen-
legungsschrift 2 632 296 respectively) admittedly produce
good thermal stability and oxidation stability, but they are
relatively expensive products and have to be used in propor-
tions as high as 3 - 5 mass %.
As described in German Patent Specification 2 655 739
and German Offenlegungsschrift 2 705 042 it is possible for
the stability to oxidation of red phosphorus to be effectively
improved by applying a thin layer of a melamine/formaldehyde
resin to the surface of the red phosphorus particles. Ho~ever,
these stabilizers prove unsatisfactory inasmuch as the staoiliz-
ing effect is largely lost if the stabilized phosphorus is
.~
stored under tropical conditions, that is to say at 50C
and 100 % relative atmospheric moisture, such as are simulated
in the modified Indian Standard Test (IS 2012 - 1961).
German Patent Specification 2 625 674 discloses an agent
which permits the use of red phosphorus in plastics, without
hydrogen phosphide being liberated as a result of the process-
ing temperature of the plastic and of the presence of small
amounts of water or moisture in the plastic to be processed.
The agent comprises epoxide resins, which encapsulate the phos-
phorus particles, the resins being used in proportions of 5 -
50 mass %.
Finally, German Specification DE-PS 29 45 118 discloses
stabilized, pulverulent red phosphorus, consisting of phos-
phorus particles having a particle size of at most about 2 mm,
and an oxidation stabilizer encapsulating the phosphorus
particles in the form of a thin layer.
The process for making such stabilized pulverulent red
phosphorus comprises admixing an aqueous suspension of red
phosphorus with a water-soluble aluminum salt and also with an
aqueous or alcoholic solution or dispersion of an epoxide resin
and a hardener, estabilishing a pH-value within the range 5 to
9 and stirring the mixture over a period of 1 to 3 hours at
20 to 90C for precipitating the aluminum hydroxide and
simultaneously hardening the epoxide resin, filtering the
whole and drying the stabilized phosphorus at elevated tempe-
rature.
German Specification DE-AS 22 49 638 describes a process
for desensitizing red phosphorus with the aid of an organic
or organo-silicon compound which is liquid, inactive with
respect to red phosphorus and has a minor vapor pressure at
\ ~ Zfit~7f~
room temperature and atmospheric pressure. The desensitizer
is used in a quantity within a preferred range of 4 to 10
mass %. This relatively high proportion of desensitizer
naturally affects the uses red phosphorus is put to, In addi-
tion, this prior process for applying the desensitizer byintimately blending the components is beset with considerable
technical disadvantages. In a preferred variant of this prior
process, red phosphorus is blended with a solution of the
desensitizer in an inert solvent having a boiling point of at
most 60C, and the solvent is subsequently removed by evapo-
ration. Deficiencies reside in that the formation of dust
which may entail a dust explosion cannot reliably be prevented
during processing and in that a desensitizer solution is used
which makes it necessary for the solvent to be completely
removed subsequently.
Agents and processes which would permit commercially
available red phosphorus to be satisfactorily stabilized and
desensitized without affecting either the product or process
have not been described heretofore.
- 20 We have now unexpectedly found that all the adverse
effects referred to hereinabove can be obviated using the
agent and process of this invention for stabilizing and
desensitizing red phosphorus.
The present invention relates more particularly to
stabilized and desensitized pulverulent flowable red phos-
phorus consisting substantially of particles with a size of
at most 2 mm, which is characterized in that
a) the phosphorus particles are encapsulated in a thin layer
formed of an oxidation stabilizer and desensitizer;
b) the oxidation stabilizer consists of aluminum hydroxide
l~R25~fi
and a hardened epoxide resin;
c) the oxidation stabilizer is used in a total proportion of
0.1 to 5 mass %, based on the quantity of red phosphorus;
d) the aluminum hydroxide is used in a proportion of 0.01 to
3 mass % and the epoxide is used in a proportion of 0.09
to 4.99 mass %, the percentages being in each case based
on the quantity of red phosphorus;
e~ the desensitizer is a water-emulsifiable organic compound
which is liquid, inactive with respect to red phosphorus
and has a minor vapor pressure at room temperature and
atmospheric pressure;
f) the desensitizer is used in a total proportion of 0.05
to less than 2 mass %, based on the quantity of red phos-
phorus.
The present invention also relates to a process for making
` stabilized and desensitized pulverulent flowable red phosphorus,
which comprises: preparing red phosphorus from yellow phosphorus
and freeing an aqueous suspension of pulverulent red phosphorus
from residual fractions of yellow phosphorus by treating the
suspension with a sodium hydroxide solution; stabilizing the
red phosphorus in said aqueous suspension with aluminum hy-
droxide and a hardened epoxide resin and desensitizing it in
said aqueous suspension by means of a water-emulsifiable organic
liquid being liquid,inactive with respect to phosphorus, and
having a minor vapor pressure at room temperature and at
atmospheric pressure; filtering the suspension and drying it.
The present invention is the first to disclose a techni-
cally progressive process wherein the steps of purifying,
stabilizing and desensitizing red phosphorus are effected in
the aqueous phosphorus suspension originating from production
12~25~7~
and under circumstances even in one and the same pot from
- which the red phosphorus is ultimately removed by filtration.
More particularly, the process of this invention comprisas:
a) freeing an aqueous suspension of red phosphorus with a
particle size of at most 2 mm from residual fractions of
yellow phosphorus by boiling it in known manner ~lith
sodium hydroxide solution while stirring;
b) stabilizing, in a subsequent processing stage, the red
phosphorus in the aqueous suspension so freed from yellow
phosphorus by admixing the suspension with a water-soluble
aluminum salt; establishing a pH-value of 5 to 9 and add-
ing an aqueous or alcoholic solution, emulsion or disper-
sion of an epoxide resin and hardener so as to have 5 to
0.1 mass parts oxidation stabilizer per 95 to 99.9 mass
parts red phosphorus, the aluminum hydroxide fraction be-
ing present in a proportion of 0.01 to 3 mass % and the
epoxide fraction being present in a proportion of 0.09 to
4.99 mass ~0, the percentages being in each case based on
the quantity of red phosphorus; and stirring the blend
over a period of 1 to 3 hours at 20 to 90C for precipi-
tating the aluminum hydroxide and simultaneously harden-
ing the epoxide resin;
c) admixing, in a subsequent desensitizing stage, the aqueous
suspension of stabilized red phosphorus with an aqueous
emulsion of the organic desensitizer being liquid, in-
active with respect to red phosphorus and having a minor
vapor pressure at room temperature and at atmospheric
pressure so as to have less than 2 to O.û5 mass parts
organic desensitizer per more than 98 to 99.95 mass parts
stabilized red phosphorus, establishing at least once a
lZ~257fi
pH-value between 5 and 9, and stirring the mixture ov~r
a period of 0.5 to 3 hours at 20 to 90~C, and
d) filtering and drying at elevated tem?erature the red phos-
phorus encapsulatzd in a thin layer of oxidation stabilizer
and desensitizer.
Further preferred and optional features of the present
process provide:
a) for the aqueous suspension to contain up to 75 mass % red
phosphorus;
b) for the red phosphorus to consist substantially of particles
having a size of from 0.0001 mm to 0.5 mm;
c) for the epoxide used in the stabilizing stage to be a
liquid epoxide r.esin which has a very low or mean viscosity,
is 100 % reactive, and hardenable with a hardener soluble
or emulsifiable in water;
d) for the epoxide resin used in the stabilizing stage to be
an unmodified, liquid,100 % reactive reaction product of
epichlorhydrin and bisphenol A (2,2-bis(4-hydroxyphenyl)-
propane) hardenable with a hardener soluble or emulsifiable
in water;
e) for the epoxide resin used in the stabilizing stage to be
an aqueous epoxide/phenol resin-dispersion;
f) for the epoxide resin used in the stabilizing stage to be
a water-emulsifiable, 100 % reac~ive epoxide resin ester
hardenable with a hardener soluble or emulsifiable in
water;
g) for the hardener used in the stabilizing stage to be a
water-soluble, internally modified polyamine or a water-
emulsifiable polyamino-amide;
h) for the epoxide resin used in the stabili2ing stage to be
lZf;~ fi
hardened in aqueous phase at a temperature of 20 - 9~5
and at a pH within the range 5 to 9;
i) for the aqueous emulsion used in the desensitizing stags
to contain up to 25 mass % of the organic compound serv-
ing as the desensitizer;
k) for the aqueous suspension/emulsion-mixture in the dssen-
sitizing stage to consist of 98.2 to 99.95 mass parts
stabilized red phosphorus and 1.8 and 0.05 mass parts
organic desensitizer;0 1) for a pH of 6 to 8 to be established in the desensitizing
stage and for the mixture to be stirred for 1 hour at a
temperature of 60C;
m) for the organic compound serving as the desensitizar to
be di-2-ethylhexylphtalate; and
n) for the filtered product to be dried at 80 to 120C.
The red phosphorus stabilized and desensitized in accor-
dance with this invention and the process for making it com-
pare favorably with the prior art products and processes. The
stabilizing agent has thermal stability and is highly active.
In fact, very minor proportions of it have to be added to red
phosphorus to obtain a product having a stability satisfactory
for a variety of uses. On the other hand, it is possible to
achieve the desensitization targeted with the use of very
minor quantities of desensitizing agent.
The product obtained in accordance with this invention
is readily flowable and substantially non-dusting. The forma-
tion of dust is considerably reduced so that the red phosphorus
so modified can be used in the fields described hereinabove,
without difficulties.
The following Examples illustrate the invention which
~2P.ZS7~i
is naturally not limited thereto.
Example 1
3 l PHOSPHORUS RED-suspension ~"hich had a liter weight of
1200 q was taken from the converslon reactor and given into a
5 1 beaker glass. After having been allowed to deposit over a
period of about 3 hours, 1.5 1 supernatant clear liquid ~,las
siphoned off. A PHOSPHORUS RED-suspension which had a liter
weight of 1360 9 was obtained. It was found to contain 0.14 %
yellow phosphorus.
Next, a pH of 12 was established by addition of sodium
hydroxide solution of 25 % strength. The suspension was heated
to 90C while stirring and maintained at that temperature over
a period of 1 hour. Hydrogen phosphide obtained by-dispropor-
tionation, was expelled by injecting nitrogen. Once again, the
content of yellow phosphorus was determined; it was less than
0.005 %.
After cooling to about 60C, the suspension was admixed
dropwise while stirring with a solution of 25 9 aluminum sul-
fate (Al2(S04)3 . 18 H20) in 250 ml water. Next, a pH of 5 was
established by addition of sulfuric acid of 5 % strength. After
this had been done, an aqueous/methanolic emulsion of 5 9 of a
liquid, unmodified epoxide resin (BECKOPOX EP 140, this is a
registered Trade Mark of HOECHST AKTIENGESELLSCHAFT, Frankfurt/
Main, Federal Republic of Germany) which had an epoxide equiva-
lent weight of about 190, a dynamic viscosity of 9000 - 12,000
mPa.s (at 25C) and a density of 1.16 g/ml (at 25C) and 5 q
of a modified aliphatic polyamine (BECKOPOX - special hardener
EH 623, this is a registered Trade Mark of HOECHST AKTIENGE-
SELLSCHAFT, Frankfurt/Main, Federal Republic of Germany)
dissolved in water which hacl a H-active equivalent weight of
~2~..r;7fi
200, a dynamic viscosity of 10 000 - 14 000 (at 25C) and a
density of 1.10 g/ml (at 25C) in water/methanol (1:1) "ere
added dropwlse. The suspension was stirred for 2 hours at 60C,
a pH of 7 was established by addition of sodium hydroxide solu-
tion of 5 % strength and the whole was stirred for a further
1 hcur at 60C. Next, 25 ml o~ a di-2-ethylhexylph~ala'ce-
(DOP)-emulsion of 20% strangth was added. The suspension was
stirred for 1 hour at 60C and filtered. The filter residue
was water washed and dried at 100C in a stream of nitrogen.
The di-2-ethylhexylphtalate-(DOP)-emulsion was prepared
in the following manner:
0.75 9 suitable emulsifier (e.g. ARKOPAL N O 90, this is
a registered Trade Mark of HOECHST AKTIENGESELLSCHAFT, Frank-
furt/Main, Federal Republic of Germany) was stirred into 100 9
di-2-ethylhexylphtalate (e.g. GENOMOLL 100, this is a registered
Trade Mark of HOECHST AKTIENGESELLSCHAFT, Frankfurt/Main,
Federal Republic of Germany) and 400 ml water was added ~Jhile
the whole was intensively stirred.
The red phosphorus was analyzed and found to contain 0.51
% aluminum hydroxide and 0.58 % epoxide resin as stabilizers
and 0.44 % DOP as desensitizer.
The test results obtained with red phosphorus so stabilized
and desensitized are indicated in Tables 1 to 4 hereinafter.
Example 2
The procedure was as in Example 1, but 50 9 aluminum sul-
fate and 10 9 BECKOPOX EP 140 and 10 9 BECKOPû~ special
hardener EH 623 were used. The product was analyzed and the
following results were obtained:
0.96 % Al(OH)3
1.09 % epoxide resin
12
lZF'~ZS76
0.46 % DOP
The test results obtained with red phosphorus so stabilized
and desensitized are indicated in Tables 1 to 4 hereinafter.
Example 3
The procedure was as in Exar:lple 1, but the BECKOPOX special
hardener EH 623 was replaced by the following resin/hardener-
combination:
6,5 9 BECKOPOX EP 140
3.5 9 BECKOPOX special hardener EH 655
(this is a solvent-free polyamidoamine
which has a H-active equivalent ~"eight o
100, a dynamic viscosity of 1000 - 2000
mPa.s (at 25C) and a density of 0.95 g/ml
(at 25C).
The product was analyzed and the following results were
obtained:
0,58 % Al(OH)3
0.64 % epoxide resin
0.42 % DOP
The test results obtained with red phosphorus so stabilized
and desensitized are indicated in Tables 1 to 4 hereinafter.
Example 4
The procedure was as in Example 3, but 50 9 aluminum sul-
fate, 13 9 BECKOPOX EP 140 and 7 9 BECKOPOX special hardener
EH 655 were used.
The product was analyzed and the following results were
obtained:
1.04 % Al(OH)3
1.19 % epoxide resin
0.45 % OOP
13
~z~Z~fi
The test results obtained with red phosphorus so sta~i-
lized and desensitized are indicated in Tables 1 - 4 herein-
after.
The values and test results referred to in the Examples
and Tables were determined by the following procedures going
beyond analytic routine methods.
Determining DOP-content
50 9 specimens (prepared as described in Examples 1 to 4)
were placed in a measuring flask, admixed up to the 500 ml
mark with methanol, and the whole was stirred over a period
of 10 tG 15 minutes using a magnetic stirrer. Next, ths whole
was filtered using a plaited filter 32 cm in diameter, and the
filtrate was collected in a dry glass vessel. The commonly
turbid filtrate was admixed with 10 - 20 drops of a solution
of 10 9 concentrated hydrochloric acid in 100 ml methanol and,
after the whole had been t'noroughly mixed, filtered off using
double plaited filters 32 cm wide, and collected in a dry 250
ml measuring flask. The clear slightly yellowish filtrate was
introduced into a weighed 500 ml distilling flask having 2-3
boiling stones placed therein. After the bulk of the methanol
had been distilled off, the distilling flask was placed in an
electrically heatsd drying cabinet and heated at 120C until
constant weight. The flask was allowed to cool, and the
quantity of di-2-ethylhexylphtalate was determined gravimetri-
cally.
Oetermining stability to oxidation
Test 1:
450 ml water and 1 9 pretreated red phosphorus were in-
troduced into a three-necked flask equipped with a gas inlet
tube, thermometer, reflux condenser and magnetic stirrer, the
14
~L2F~Z~
mixture was heated to 80C and 10 1 oxygen per hour was
passed into the mixture, under agitation. The gas mixture
which escaped via the reflux condenser and consisted of
oxygen and hydrogen phosphide which had been produced, to-
gether with acids of phosphorus of various oxidation levels,by disproportionation of the red phosphorus, ~,las led through
two washbottles which were arranged one downstream of the
other1 and which each contained 100 ml of a 2,5 % strength
by weight aqueous mercury(II)chloride solution.
In this method, the hydrogen phosphide reacted ~,lith the
mercury(II)chloride in accordance with the following equa-
tion:
PH3 + 3 HgCl2 ~ P(HgC1)3 + 3 HCl
The amount of oxo-acids of phosphorus coniained in the
aqueous suspension of the red phosphorus, and the hydrochlo-
ric acid contained in the gas washbottles, served as an in-
dex of -the oxidation stability of the red phosphorus. The
contents of phosphorus acids and of hydrochloric acid were
determined titrimetrically. The values calculated therefrom
are shown in Table 1, columns A and B.Column A shows the
amount of PH3 (mg of PH3 per gram of phosphorus per hour)
formed during oxidation of the red phosphorus. The values
in column B are index of the acidity of the aqueous phos-
phorus-containing suspension, resulting from the formation
of phosphorus acids during oxidation of the phosphorus (mg
of KOH per gram of phosphorus per hour).
Test 2:
The oxidation stability was determined on the basis of
Indian Standard "Specification of red phosphorus" (IS 2012 -
1961),
l'
12Pi;~
To this end, 5.0 9 of red phosphorus was ~/eighed out into
a crystallizing dish of 50 mm diameter and the dish ,las
stored in a closed glass vessel for 168 hours at .50C and 100
% relative atmospheric humidity. The hydrogen phcsphide there-
by formed was expelled from the glass vessel by means of astream of air (10 l/h) and caused to react with 2.5 % strength
by weight mercury(II)chloride solution in a gas washbottle,
and the amount of hydrochloric acid thereby formed was deter-
mined titrimetrically.
To determine the content of the various oxo-acids of
phosphorus, the sample of phosphorus was transferred into a
250 ml beaker, 120 ml of water and 40 ml of n-propanol were
added, and the mixture was heated to the boil for 10 minutes
and then filtered. The quantitative analytical determination
of the oxo-acids in the filtrate was then carried out by
titration with 0.1 N NaOH up to the equivalent point for the
2nd titration stage, at pH 9.5.
Determining flowability:
The flowability was determined using a test device accord-
ing to PFRENGLE as described in DIN-specification (DIN stands
for German Industrial Standard) 53 916 (edition August 1974):
Determination of flowability of powders and granules).
Determining formation of dust:
A relative comparison of dust formation was made with
the aid of a Konimeter, type H-S, a product of Messrs Sartorius~
Gottingen, Federal Republic or Germany. This device has been
described by K. Guthmann, in Stahl und Eisen (Steel and Iron),
79, page 1129 (1959).
The prepare for measurement, 1 9 specimen was ~eighed
into a dry 250 ml gasbottle provided with a screw cover and
16
intensively shaken for 2 minutes. The screw sover ~,laa remo~ed
and the phosphorus dust was determined at the interv31s i~di-
cated in Table 4.
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The values determined for the stability to oxidation
(Tables 1 and Z) show very distinctly that the stabilizer
system of this invention compares favorably ~lith the stan-
dard stabilizers, e.g. magnesium hydroxide (commercial
product A).
As can be seen from Table 3, the flowability of red
phosphorus stabilized and desensitized in accordance with
this invention remains practically unchanged, unlike the
flowability of non desensitized red phosphorus (commer-
cial products A and B).
The values determined relative to the formation of
dust (Table ~) indicate that red phosphorus stabilized
and desensitized in accordance with this invention has a
drastically reduced tendency to form dust.
