Whether a compound will thermoparticulate, that is, decompose to produce particles detectable by an ion chamber monitor or a condensation nuclei monitor and, if so, at what temperature, is predicted by determining the decomposition products of the compound, eliminating the compound if none of its decomposition products are greater than 25 .ANG., and using the temperature at which the decomposition products greater than 25 .ANG. have a vapor pressure of 10 millimeters as an estimate of the temperature at which the compound will decompose to produce products detectable by the monitor. Also disclosed are compounds which have been found to thermoparticulate at low temperatures.

BACKGROUND OF THE INVENTION 
Electrical apparatus, such as motors and turbine generators, occasionally 
overheat due to shorts or other malfunctions. The longer the overheating 
continues the more damage is done to the apparatus. If the malfunction is 
detected immediately it may mean only a quick repair, but if the 
overheating continues, the entire machine may be damaged. Large rotating 
electrical apparatus is usually cooled with a hydrogen gas stream. The 
organic compounds in the apparatus are first to be affected by the 
overheating and may decompose to form particles which enter the gas 
stream. Monitors then detect particles in the gas stream and sound a 
warning or shut down the apparatus when too many particles are detected. 
Special coatings may be applied to the apparatus which decompose and form 
detectable particles at lower temperatures than the usual organic 
compounds found in the apparatus. See U.S. Pat. Nos. 4,142,416; 4,108,001; 
4,130,009; 4,102,809; 3,973,439; 4,102,193; 4,056,005; 3,973,438; 
4,046,733; 4,046,512, 3,972,225; 4,056,006; 4,106,745; 3,957,014; 
3,995,489; 3,797,353; 4,046,943; 3,973,438; and 3,995,417. The 
thermoparticulating compounds disclosed in these patents produce 
detectable signals at temperatures below 200.degree. C., which is about 
the maximum temperature tolerable in turbine generators before serious 
damage is done to the generator. 
Until now efforts to identify compounds which thermoparticulated at 
temperatures below 200.degree. C. has proceeded by trial and error. At 
first it was thought that there might be a correlation between the 
thermoparticulating temperature and the melting point of the compound but 
after observations on over 500 organic compounds were made, it was 
discovered that there was no correlation between the melting point of a 
compound and its thermoparticulation temperature. Also, no correlation was 
discovered between the thermoparticulation temperature and the 
decomposition temperature of the organic compounds. And finally, there did 
not appear to be any correlation between the structure of the compounds 
and the thermoparticulation temperature. 
SUMMARY OF THE INVENTION 
We have discovered a method of predicting whether or not a compound will 
thermoparticulate and if so at what temperature. By means of the method of 
this invention one can tell from the properties of a compound and its 
decomposition products whether or not it will thermoparticulate and, if 
so, one can estimate the thermoparticulation temperature. Thus it is no 
longer necessary to test hundreds of compounds in the hopes of finding a 
few which all thermoparticulate. Rather, one can examine published data in 
chemical handbooks and thereby eliminate much unnecessary laboratory work. 
Using the method of prediction of this invention we have discovered many 
compounds which thermoparticulate at low temperatures. 
DESCRIPTION OF THE PRIOR ART 
The patents listed in the Background of the Invention are the best known 
prior art. 
DESCRIPTION OF THE INVENTION 
In order to determine whether or not a compound will thermoparticulate, 
that is, decompose to produce particles detected by an ion chamber monitor 
or a condensation nuclei monitor, and if so, at what temperature it will 
thermoparticulate, it is first necessary to determine the probable 
decomposition products of the compounds, because if the decomposition 
products are not larger than 25.ANG. they are not detectable by the ion 
chamber monitor. The decomposition products of some compounds are better 
known and described in the literature. If the decomposition products are 
not described in the literature they can be determined by identifying the 
activation energy of the different bonds in the compound so that one can 
tell which bonds will break first and, therefore, what the resulting 
products will be. If the degradation products are less than 25.ANG. but 
are capable of hydrogen bonding with themselves, they can form products 
which are greater than 25.ANG. and which will be detectable by the ion 
chamber monitor. Any compound which is not capable of forming at least one 
decomposition product greater than 25.ANG. is eliminated from 
consideration. 
It has been found that the temperature at which the decomposition products 
have a vapor pressure of 10 mm is a very good estimate of the 
thermoparticulation temperature of the compound. Thus, once the 
decomposition products larger than 25.ANG. have been identified one can 
refer to published data to determine at what temperature they have a vapor 
pressure of 10 mm and thereby estimate the thermoparticulation temperature 
of the initial compound. This procedure will be further illustrated in the 
examples to follow. 
The compounds which thermoparticulate at low temperatures which have been 
discovered using the method of this invention are typically incorporated 
in a resinous composition for application to the generator and other types 
of apparatus. A composition is prepared of the thermoparticulating 
compound in a solution of a resinous carrier. The thermoparticulating 
compound may be dispersed if it is insoluble in the solvent or it may be 
in solution if it is soluble in the solvent. Dispersions are preferred as 
they produce a stronger signal than do solutions. A particle size of the 
dispersed thermoparticulating compound of about 25 to about 1,000 microns 
is suitable. 
An acceptable composition is a resinous carrier, about 20 to about 250 phr 
(parts by weight per hundred parts of resinous carrier) of 
thermoparticulating compound, and about 25 to about 75% (by weight based 
on the resinous carrier) of a solvent for the resinous carrier. If the 
amount of thermoparticulating compound is less than about 20 phr the 
quantity of particles given off during decomposition may be too low to be 
detected by presently existing detectors. However, the construction of 
more sensitive detectors would permit a lower amout of thermoparticulating 
compound. If the amount of thermoparticulating compound exceeds about 250 
phr the composition is thick, difficult to apply, and does not bond well. 
The preferred amount of thermoparticulating compound, which usually gives 
the best results, is about 40 to about 60 phr. If the amount of solvent is 
less than about 25% the composition is generally too viscous to apply 
easily and if the amount is greater than about 75% the composition is 
unnecessarily dilute and the coating may be too thin to produce an 
adequate number of particles during decomposition, at least while the 
malfunction is highly localized. Best results are usually obtained with 
about 45 to 55% solvent. The composition also contains about 0.1 to about 
3 phr of a drier for the resinous carrier when it is an epoxy resin or 
similar resin to promote its room temperature cure. Lead naphthenate or 
cobalt naphthenate is preferred although stannous octoate, zinc stearate, 
etc., could also be used. Resins such as polyesters may also require the 
presence of an organic peroxide as is known in the art. Mixtures of 
various resins, solvents, or driers are contemplated. 
The composition may be prepared by simply mixing the ingredients but it is 
preferable to mix the drier, resinous carrier, and solvent first and add 
the thermoparticulating compound later to prevent the inclusion of the 
drier in the thermoparticulating compound and thereby obtain a more 
homogeneous dispersion of the thermoparticulating compound. 
The thermoparticulating compounds of the invention may be described by ten 
general formulae. The first group of compounds have the general formula 
M.sup.+ (R).sub.4 X.sup.-, where M is nitrogen, phosphorus, arsenic, or 
antimony, each R is independently selected from hydrogen, alkyl C.sub.20, 
aryl, alkaryl C.sub.20, aralkyl C.sub.20, heterocyclic with nitrogen, 
oxygen or sulfur, or substituted aromatic with nitro or halide 
substituents, and X is chloride, bromide, iodide, carboxylic C.sub.20, 
dimethyl phosphate, or hydroxide. Preferred compounds which have been 
found to give strong signals at low temperatures include tetrabutyl 
phosphonium acetate, tetrabutyl phosphonium chloride, triphenylmethyl 
phosphonium iodide, methyltrioctyl phosphonium dimethyl phosphate, 
tetrabutyl arsonium chloride, tetraphenyl arsonium iodide, tetrabutyl 
stibonium chloride, tetraphenyl stibonium iodide, triphenyl methyl 
stibonium bromide, triethylmethyl ammonium chloride, triethylmethyl 
ammonium iodide, and triethyl, n-propyl ammonium iodide. M is preferable 
nitrogen or phosphorus as those compounds are readily available. R is 
preferably alkyl to C.sub.8 or benzyl as those compounds give stronger 
signals. X is preferably chlorine, iodide, or acetate as those compounds 
give stronger signals. 
The second group of compounds has the general formula M'(C.sub.x H.sub.y 
O.sub.z).sub.n where M' is copper, chromium, iron, cobalt, nickel, lead, 
titanium, zinc, zirconium, sodium, or potassium, x is 6, 7, or 9, y is 7, 
9, or 11, z is 2, 3, or 4, and n is 1 to 3. M' is preferably copper, iron, 
cobalt, nickel, or lead as these compounds are less thermally stable and 
gives stronger signals at low temperatures. X is preferably 6, y is 
preferably 9, z is preferably 3, and n is preferably 2 or 3, especially 3, 
as these compounds give stronger signals. Examples of suitable compounds 
include copper ethyl acetoacetate, chromium ethyl acetoacetate, iron 
(ferric) ethyl acetoacetate, copper diethyl malonate, zinc diethyl 
malonate, chromium diethyl malonate, copper formyl acetophenone, and 
chromium formyl acetophenone. 
The third group of compounds has the general formula M"R'.sub.m A.sub.n 
where M" is tin, antimony, tiitanium, boron, phosphorus, or chromium, R' 
is R, halide, or oxygen, A is amine, amide, catechol, or pyrogallol, and m 
is 1 to 5. Preferably M" is tin, boron, or chromium and A is a primary 
amine up to C.sub.4, a primary amide up to C.sub.4, or catechol as these 
compounds give stronger signals. Examples of suitable compounds include 
triphenyltin chloride-morpholine, triphenyltin chloride-n-propylamine, 
diphenyltin dichloride-morpholine, diphenyltin 
dichloride-benzyldimethylamine, boron trifluoride-monoethylamine, antimony 
pentafluoride-triethylamine, antimony pentachloride-pyridine, and titanium 
tetrachloride-morpholine. 
The fourth group of compounds are amine-picric acid molecular complexes 
having the general formula 
##STR1## 
where A' is A, anthracene, naphthalene, phenanthrene, or corononene. 
Examples of suitable compounds include n-butylamine picrate, triethylamine 
picrate, m-phenylene diamine picrate, 1-methylimidazole picrate. 
The fifth group of compounds are extra-coordinate siliconate salts having 
the general formula 
##STR2## 
where p is 1 or 2. For these compounds R is preferably hydrogen or alkyl 
C.sub.4 as these compounds give stronger signals. Examples of suitable 
compounds include benzyl dimethyl ammonium bis (0-phenylene dioxy) phenyl 
siliconate, triethylammonium bis (0-phenylene dioxy) phenyl siliconate, 
and triethanolamine bis (0-phenylene dioxy) phenyl siliconate. 
The sixth group of compounds are glyoximes having the general formula 
##STR3## 
where R'" is R or 
##STR4## 
Preferably R'" is 
##STR5## 
and also R is preferably hydrogen as these compounds are more readily 
available. 
The seventh group of compounds are sulfamic acids having the general 
formula 
##STR6## 
The preferred compound under this general formula is cyclohexene. 
The eight group of compounds are thiosemicarbazides having the general 
formula 
##STR7## 
Preferably at least one of the R groups is hydrogen as this leads to 
hydrogen bonding in the decomposition products. 
The ninth group of compounds are nitronaphthols having the general formula 
##STR8## 
where q is 1 to 4 and r is 1 to 7. An example is 2,4-Dinitro-1-naphthol. 
The tenth group of compounds are anthranols having the general formula 
##STR9## 
where s is 1 to 6 and t is 1 to 9. 
In all of the above general formulae the same definitions of the various 
groups are applicable to all formulae. 
The resinous carrier used in the composition performs a function of bonding 
the thermoparticulating compounds to the apparatus since the coating of 
the thermoparticulating compounds by themselves does not adhere well. The 
resinous carrier should be compatible with the other resins used in the 
apparatus and therefore it is usually advantageous to use these same 
resins used elsewhere. The resinous carrier is curable at 60.degree. C. 
and is preferably air dryable since it cannot be easily cured in place 
with heat. Also, it should be stable, after curing, for several years at 
60.degree. C. The resin must be substantially unreactive with the 
thermoparticulating compound for otherwise suitable thermoparticulation 
will not occur. The thermoparticulating compound and the resin form a 
mixture and the thermoparticulating compound does not catalyze the cure of 
the resin. Epoxy resins are preferred as they are usually used elsewhere 
in the apparatus. Polyester resins, silicon rubber, polystyrene, etc. 
could also be used. The solvent for the resinous carrier depends on the 
particular resinous carrier used. Toluene, xylene, benzene, methylethyl 
ketone, ethyl alcohol, diethyl ether, acetone, cellosolve, etc. or other 
common solvents may be used. Toluene is preferred as it is inexpensive and 
dissolves most resins. 
The composition is applied to portions of the electrical apparatus which 
are exposed to the gas stream. The coating does not function as insulation 
and is usually applied on top of insulation, but it can also be applied to 
conductors. The application may be made by brushing, spraying, dipping, 
grease gun, troweling, or other techniques. A suitable coating thickness 
(after drying) is about 1/16 to about 178 inch. The dispersed particles 
of thermoparticulating compound should not be covered with excessive 
resinous carrier as that may prevent the decomposition products from 
escaping into the gas stream. After evaporation of the solvent and room 
temperature cure of the resinous carrier, if necessary, the apparatus is 
ready to be operated. The monitor can be an ion chamber monitor, where the 
presence of particles lowers the current flowing across a sample of the 
gas stream, or a condensation nuclei monitor, where the presence of 
particles condenses water vapor obscuring a light beam. When 
thermoparticulation occurs and the monitor sounds an alarm a sample of the 
gas stream can be collected and analyzed. Since different 
thermoparticulating compounds can be used in different areas of the 
apparatus and their thermoparticulation products are different, analysis 
of the sample can pinpoint the location of the overheating.

The following examples further illustrate this invention. 
EXAMPLE 1 
Compositions were prepared as follows using various thermoparticulating 
compounds: 
______________________________________ 
Parts by Weight 
______________________________________ 
Thermoparticulating compound 
100 
Epoxy resin, 50% solids in toluene, 
100 
made from 200 pbw (parts by weight) 
linseed fatty acids, 200 pbw styrene, 
and 300 pbw diglycidyl ether of 
Bisphenol A, sold by Westinghouse 
Electric Corporation as "B-276" 
Varnish (See Example I of U.S. Pat. 
No. 2,909,497 for detailed description) 
6% solution in low boiling hydro- 
1.0 
carbons of cobalt naphthenate 
24% solution in low boiling hydro- 
0.25 
carbons of lead naphthenate 
______________________________________ 
The cobalt and lead naphthenate solutions were added to the epoxy resin 
prior to the addition of the thermoparticulating compound. 
Samples were prepared by brushing the above composition onto 3 inch by 1 
inch aluminum sheets 1/16 to 1/4 inch thick. The samples were dried 
overnight at 60.degree. C. to form coatings 1/4 inch thick, then placed in 
a forced-air oven at 60.degree. C. for various periods to determine if 
they were stable and would function after aging. 
The samples were placed one at a time in a stainless steel boat within a 1 
inch o.d. stainless steel tube. Hydrogen was passed over the samples at a 
flow rate of 6-1/min. A phase-controlled temperature regulator and 
programmer controlled the temperature in the boat and the temperature in 
the boat was measured by mounting a hot junction chromel-alumel 
thermocouple within a small hole in the boat. The output of the 
thermocouple and the detector were monitored on a two-pen potentiostatic 
recorder. At 60.degree. C./min. heating rate was maintained in each 
experiment after the insertion of the sample in the boat. The "alarm" 
temperature at which considerable thermoparticulation occurred was taken 
from the chart; this corresponded to a 50% decrease in the initial ion 
current of the Generator Condition Monitor (usually 0.8 to 0.4 mA). 
The following table gives the compounds tested, the diameter of the largest 
decomposition product formed, the temperature at which the vapor pressure 
of the decomposition products is 10 mm, and the actual thermoparticulating 
temperature. 
______________________________________ 
The Fatty Acid Family and 
Their Approximate Molecular Dimensions 
Thermo- 
"Diame- particu- 
ter" of Temp. at which 
lating 
Mole- Vapor Pres. = 
Temp. 
Name Formula cule*, .ANG. 
10 mm (.degree.C.)** 
(.degree.C.) 
______________________________________ 
Caprylic Acid 
C.sub.8 H.sub.16 O.sub.2 
20 
Nonanoic Acid 
C.sub.9 H.sub.18 O.sub.2 
22 
Decanoic Acid 
C.sub.10 H.sub.20 O.sub.2 
25 
Hendecanoic 
C.sub.11 H.sub.22 O.sub.2 
28 149 156 
Acid 
Lauric Acid 
C.sub.12 H.sub.24 O.sub.2 
30 166 168 
Tridecanoic 
C.sub.13 H.sub.26 O.sub.2 
33 181 184 
Acid 
Myristic Acid 
C.sub.14 H.sub.28 O.sub.2 
35 190 191 
Pentadecanoic 
C.sub.15 H.sub.30 O.sub.2 
38 
Acid 
Palmitic Acid 
C.sub.16 H.sub.32 O.sub.2 
206 210 
Stearic Acid 
C.sub.18 H.sub.36 O.sub.2 
225 229 
______________________________________ 
*A. I. Kitaigorodskii, "Organic Chemical Crystallography", Consultants 
Bureau Publishers, New York, 1961. 
**Handbook of Chemistry and Physics, 49th Edition, The Chemical Rubber 
Co., Cleveland, Ohio, 1968, Section D120 to D135. 
As the above table shows, no signals were obtained for caprylic acid, 
nonanoic acid, or decanoic acid indicating that the diameter of the 
decomposition products must be greater than 25.ANG.. It was also 
discovered that there was an excellent correspondence between the 
temperature at which the vapor pressure of the decomposition products is 
10 mm and the actual thermoparticulation temperature. 
EXAMPLE 2 
Example 1 was repeated using other types of compounds. The following table 
gives the temperature at which the decomposition products had a vapor 
pressure of 10 mm, and the actual thermoparticulation temperature. 
______________________________________ 
Temperature at 
Thermoparticulation 
10 mm (.degree.C.) 
Temperature (.degree.C.) 
______________________________________ 
Tetracosane 238 232 
Cetyl alcohol 
178 182 
Benzoic anhydride 
198 203 
Phenanthrene 173 177 
Biphenyl 117 121 
2-Naphthoic acid 
203 200 
2-Naphthol 146 145 
______________________________________ 
EXAMPLE 3 
Example 1 was repeated using other types of compounds. The following table 
gives the compounds tested, their predicted thermoparticulation 
temperature and the actual thermoparticulation temperature obtained. 
______________________________________ 
Thermoparticulation 
Temperature, .degree.C. 
Compound Predicted.sup.(1) 
Experimental.sup.(2) 
______________________________________ 
BF.sub.3 : monoethylamine 
100-150 140 
complex 
BF.sub.3 : dimethyl formamide 
100-150 105 
complex 
Glyoxime 150-200 167 
Thiosemicarbazide 
150-200 175 
Cyclohexane Sulfamic 
150-200 168 
Acid 
2,4-Dinitro-1-naphthol 
l50-200 172 
Triethyl, n-propylammonium 
150-200 155 
iodide 
Sulfabenzamide &gt;200 &gt;200 
Sulfadiazine &gt;200 &gt;200 
Zinc Oxalate &gt;200 &gt;200 
Zinc Formate &gt;200 &gt;200 
Zinc Tartrate &gt;200 &gt;200 
Zinc Laurate &gt;200 &gt;200 
Zinc Palmitate &gt;200 &gt;200 
______________________________________ 
.sup.(1) From molecular size, vapor pressure, and activation energy data 
given in: (1) "Handbook of Chemistry and Physics", 49th Edition, The 
Chemical Rubber Co., 1968; (2) "The Chemist's Companion", A. J. Gordon, 
Wiley Interscience, 1972; (3) "The Condensed Chemical Dictionary", A. 
Rose, 7th Edition, Reinhold Co., 1966; (4) "Kinetic Data on Gas Phase 
Reactions"; S. W. Bensen, Nat. Bur. Stand., 1970. 
.sup.(2) Using a Generator Condition Monitor.