Amine and Ammonium Silicate Solutions Helmut H. Weldes Philadelphia Quartz Co. Research Laboratories, Primos, Pa. 19018 The preparation a n d properties of stable aqueous amine a n d ammonium silicate solutions by simple ion exchange methods are described. The mole ratio range of amine silicates i s between 2 a n d 10 SiO?/amine, a n d of the ammonium silicates between 2 and
6 SiO>/(NH4)20. These solutions are stable for long periods of time a t moderate concentrations.
CRYSTALLINE
quaternary ammonium silicates have been known for some time (Merrill and Spencer, 1951) and water-soluble alkali metal-quaternary ammonium double silicates have been described (Weldes, 1970). Simple amine and ammonium silicates have not been known before. This study shows that stable amine and ammonium silicate solutions can be prepared by treating a mixture of a water-soluble amine or ammonia and an alkali metal silicate solution with properly pretreated cation exchange resins (Weldes, 1967; Weldes and Derolf, 1967). A number of attempts to prepare ammonium silicate solutions are described in the literature, but none have formed ammonium silicate solutions of low alkali metal ion content and small average particle size. Efforts to prepare ammonium silicates directly have failed. Ammonium hydroxide is not a strong enough base to dissolve silica gel even under conditions of elevated temperature and pressure. Silica sols stabilized with ammonia have been known for some time. Usually the sol has been prepared by a well known process and then stabilized by addition of ammonia as an alkaline stabilizing agent (Deribere, 1942; Kuhn, 1953). I n other cases, silica gel has been peptized by treating the gel under various conditions with ammonium hydroxide (Griessbach, 1933; Schwarz, 1916). This method also leads to stabilized sols and not to ammonium silicates. Such stabilized sols have also been prepared by treating a sodium silicate solution with an ion exchange resin in the ammonia form (Vorhees, 1949; Wolter, 1954). In these cases substantial amounts of alkali metal ions are left in the system and stabilized sols are obtained. Experimental
Materials. The alkali metal silicates used were commercial products produced by the Philadelphia Quartz Co. They had the following composition: S 35 sodium silicate, weight ratio 3.75 S i 0 2 / N a e 0 ,6.75% NazO, 25.3% SiO?, 67.9"~ H 2 0 ; N sodium silicate, weight ratio 3.22 SiOe/ NazO,8.90% N a 2 0 ,28.7% Si02,62.4% H 2 0 ; and D sodium silicate, weight ratio 2.0 Si02/Na20, 14.7% N a 2 0 , 29.4% SiO?,55.8% water. Commercial grade water-soluble amines used included monoethanolamine from the Eastman Kodak Co., diethanolamine and morpholine from the Union Carbide Chemi-
cals Co., triethanolamine from the Fisher Scientific Co., and diethylamine from the Fisher Scientific Co. The cation exchange resin found most useful for this exchange reaction was Amberlite IR-124, a highly crosslinked nuclear sulfonic acid type cation exchange resin produced by Rohm & Haas Co. The sodium form has an exchange capacity of 2.1 meq per ml of wet resin. The standard commercial ammonia solutions used had an ammonia content of 29%. Reagent grade ammonium sulfate was used to load the resin in the hydrogen form with ammonium ions. Ludox SM and HS are alkali metal-stabilized silica sols of E. I. du Pont de Nemours & Co.; Ludox SM has a concentration of 1 5 5 SiO], weight ratio of 150 S i 0 2 / N a z 0 ,average particle size about 7 to 8 mp; Ludox HS has a concentration of 3 0 7 SiO?, weight ratio of 95 S i 0 2 / N a 2 0average , particle size 15 mp. Analytical Procedures. Sodium was determined by a standard flame photometric method using a Beckman DU spectrophotometer with a flame attachment. Total titratable alkali was determined by titration with standard acid using a mixed indicator of methyl orange and xylene cyanole. The ammonia or amine content was obtained as the difference between total titratable alkali and the sodium value determined with the flame photometer. Silica was determined by the usual gravimetric or volumetric methods. Conditioning of Cation Exchange Resin with Amines. The Amberlite IR-124 resin obtained in the sodium form is converted to the hydrogen form by treatment with an excess of 2N HC1, followed by washing with distilled water until the effluent is free of chloride ions. This resin in the hydrogen form is then loaded to a certain degree with the water-soluble amine from which the particular amine silicate is to be prepared. This pretreatment is done batchwise by gently agitating overnight a mixture of the resin in the hydrogen form and the desired amine hydrochloride solution. The desired degree of amine loading on the resin is controlled by the amine hydrochloride concentration in the treating solution. The resin is then filtered off and washed with distilled water until the filtrate is free of chloride ions. Conversion of Cation Exchange Resin to Ammonia Form. A 100% ammonia-loaded Amberlite IR-124 cation exchange resin is prepared by treating 500 ml of the Ind. Eng. Chem. Prod. Res. Develop., Vol. 9 , No. 2, 1970 249
resin in the hydrogen form with a solution of 280 grams of ammonium sulfate in 500 grams of water. A 50% ammonia-loaded resin is prepared by treating 500 ml of the resin in the hydrogen form with a solution of 70 grams of ammonium sulfate in 500 grams of water. The conversion is carried out batchwise, not in an ion exchange column, by gently agitating the mixture of resin and treating solution for 1 hour. The treated resin is then filtered off on a Buchner funnel and washed free of sulfate ions with distilled water. Amine Silicate Solutions. A generally applicable preparation procedure was developed. Sodium silicate is diluted with water to a predetermined value. Water-soluble amine is added to this diluted silicate solution in an amount to correspond to the final ratio of silica to amine desired in the product. The concentrations are chosen so that the Si02 concentration in the sodium silicate-water-soluble amine admixture is not more than about 10% by weight. When the amount of Si02 exceeds that concentration, the admixtures of amine and sodium silicate solution become too viscous and cannot be mixed properly with the cation exchange resin. The amine-sodium silicate mixture is treated batchwise with the cation exchange resin which had previously been loaded, as described above, with the same amine to a predetermined value. This amine loading is necessary to prevent loss of amine from the solution while removing the alkali metal ions. The degree of amine loading on the resin depends on the relative amounts of amine and silica in the starting solution. When there is a high ratio of silica in solution with respect to amine, there is neckssarily relatively less amine, and resin with a lower loading of amine will suffice. However, when the ratio of silica is low with reference to the amine, the amine content is relatively high and the protective loading of amine on the exchange resin must be increased. The amount of alkali metal ions removed by the loaded resin is a function of time and relative concentrations and has to be adjusted for each amine and for each ratio of silica to amine desired in the end product. At the end of the exchange period, the resin is simply filtered off and the amine silicate solution concentrated in vacuo to the desired concentration. A number of different amine silicate solutions were prepared by this method from mono-, di-, and triethanolamine, morpholine, and diethylamine. The procedure is illustrated by using triethanolamine silicate preparation as an example. A starting mixture was made by adding a solution of 157.5 grams of triethanolamine in 700 grams of water to a vigorously agitated solution of 500 grams of S 35 sodium silicate in 752.5 grams of water. The mixture showed neither floc nor coacervate formation and contained 6.05 SiO,, 1.60% NazO, and 7.475 triethanolamine. To this solution was quickly added 1825 ml of Amberlite IR-124 exchange resin in the hydrogen form, which had been loaded to 75% of its exchange capacity with triethanolamine. The slurry was gently agitated for 6 minutes and then the resin was quickly filtered off on a Buchner funnel. The clear amine silicate solution contained 6.36% triethanolamine, 5.797 Si02,0.07% N a 2 0 , and had a mole ratio of 2.25 SiOr/triethanolamine, 85.5 SiOr/Na20. The ratio limits of amine silicate solutions prepared from sodium silicate-amine mixtures by ion exchange removal of the sodium ion were established in the mole ratio range of 2.0 to about 10 Si02/amine. Amine silicates 250
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 2, 1970
with mole ratios below 2.0 SiOn/amine, especially 1 SiO2/ amine, are unstable and gelled or formed coacervates. Any alkali metal silicate solution in the mole ratio range of alkali metal oxide to SiOz between 1 to 1 to 1 to 4 may be used in this procedure. High ratio sodium silicates with a mole ratio of SiOz/NazO of 3.22 or 3.75 work best because their relatively low NanO content requires a minimum amount of ion exchange capacity to remove the alkali metal ions. The dilute amine silicate solutions, preferably prepared at a 6% Si02 concentration, sometimes gel shortly after preparation and removal of the ion exchange resin but redissolve on standing a t room temperature for some time. These dilute silicate solutions are stable for several years when stored at room temperature in closed containers. They cannot be concentrated to above 10% silica concentration without further treatment. If they are concentrated above lo%, they gel or coacervate because of the small average particle size of the silica micelles in these solutions. The light-scattering patterns of amine silicate solutions were determined and compared with those of a silica sol of known average particle size (Ludox SM, a silica sol with a known particle size of 7 to 8 mp) and mixtures of this sol with the same amines as in the amine silicates. The light-scattering data were determined as a function of concentration between 1 and 5% SiO, on a Lumetron colorimeter (Model 402-E) with the 90' light-scattering accessory. Ludox SM at 1.25% Si02 concentration was used as a standard at a scale setting of 100 using a mercury vapor lamp and monochromatic light of 365 mp. Figure 1 shows a plot of the instrument readings as a function of the silica concentration for a triethanolamine silicate with a mole ratio of 4.23 Si02/triethanolamine, Ludox SM, and a Ludox SM-triethanolamine mixture of the same mole ratio as that of the triethanolamine silicate. Comparison of the scattering curves shows that the triethanolamine silicate has a much smaller average particle size than the Ludox SM or the Ludox SM-triethanolamine mixture. The average particle size of the triethanolamine silicate can be estimated to be less than 5 mp. Similar relationships have been found for all the other amine silicates prepared by this procedure. These conclusions were verified by average molecular weight determinations on a triethanolamine silicate of mole ratio 4.29 SiOr/triethanolamine from light scattered at 90" using a Brice-Phoenix light-scattering photometer (Model DM-2000). Light source was a mercury vapor lamp; monochromatic light a t 436 mp was used. Solutions ranging from 1 to 6 grams of SiO? per 100 ml were held in a semioctagonal cell having a light path of 40 mm. Dissymmetry of scatter was determined by making measurements at 45" and 135" angles, and appropriate corrections were made assuming that the particles were spherical. For comparison, the average molecular weights of Ludox SM silica sol and a mixture of this sol with triethanolamine of the same mole ratio as that of the triethanolamine silicate were determined. Average particle diameters were calculated from the relationship M = 690.d3, assuming a density of 2.2 for amorphous silica. The average molecular weights and average particle diameters obtained by this method are shown in Table 1.
I t is possible to produce very stable, more concentrated amine silicate solutions by heat-treating the dilute amine
280 0,
c
e
t
a 500
240-
.'
P-.
c 0
a
E
16, hrs.
2
e
L
200-
-c M
a L e In
8 0)
$100-
E 160-
>
I
m
-5
u
C
3
5 120 >
-
50-
d
c m
.-L
2 *
80-
0
u
-
v)
c
40-
I
I
?
I
2
I
3
4
I
5
I
I
6
% Si02 I
2
3
4
5
6
Ye Si02 Figure 1. Light scattering as a function of Si02 concentration of triethanolamine silicate (O), Ludox SM silica sol (0) average particle size 7 mp, and Ludox SM plus triethanolamine (A) Mole ratio of SiOz/triethanolamine in both cases 4.23
silicates without evaporation before they are concentrated. For example, a 3.1 mole ratio triethanolamine silicate freshly prepared at 5.8'C Si01 was heated in a closed container at 95" C for several hours. After this treatment, the solution could be concentrated to over 20% SiO? content and remained stable for more than 6 months on storage a t room temperature in a closed container. This solution had a viscosity of 1.68 poises at 25"C, a specific gravity of 1.173 a t 20°C, and a pH of 10.25 a t 25°C. A triethanolamine silicate solution with a mole ratio of 9.0 SiOz/triethanolamine was heated in a closed vessel at 125"C for several hours and then concentrated in vacuo to a silica content of 30.0%. A stable solution was obtained which had a viscosity of 8.7 poises a t 25°C. Heat treatment without evaporation of the amine silicate solutions increases the average particle size of the silica in these silicates. For example, Figure 2 compares the light-scattering data for a triethanolamine silicate with a mole ratio of 9.0 SiOr/triethanolamine as obtained directly from the ion exchange process and after heat treatment for several hours at 125"C in a closed container and that of Ludox SM with an average particle size of 7 to 8 mp and Ludox HS with an average particle size of 15 mp. Heating periods of less than 5 hours increase
Table I. Comparison of Triethanolamine Silicate Solution with Silica Sol
Triethanolamine silicate Ludox SM silica sol Ludox SM + triethanolamine
Av. Molecular Weight
Av. Particle Diameter, Mp
52,000 310,000 1,710,000
4.2 7.7 13.5
Figure 2. Light scattering of triethanolamine silicate (V), mole ratio 9.0 SiOz/triethanolamine, as a function of S i 0 2 concentration and time of heating at 125°C in a closed vessel Compared with light scattering v s . Si02 concentrotion for Ludox SM silica sol (average particle size 7 mF) and Ludox HS silica sol (average particle size 15 mF)
the particle size of the amine silicate t o only a small degree. After heating for 7 hours an average particle size of close to 7 mp is obtained and the average particle size does not increase very much over this value on heating for up to 16 hours. Amine silicates prepared from different water-soluble amines behaved very similarly and showed the same properties as the triethanolamine silicates. Ammonium Silicate Solutions. Ammonium silicate solutions can also be prepared by a simple ion exchange method. An aqueous ammonium hydroxide solution is added to a dilute sodium silicate solution a t room temperature with vigorous agitation to give a double silicate solution of an alkali metal and ammonium ions with the final silica concentration in the range of 6 to 1 2 % . The ammonium hydroxide is usually added to just below the point of instability (coacervation), and more particularly the amount is chosen so that the mole ratio of S O L / (NH,)*O is within the range of about 2 to about 6. If the amount of ammonia is increased beyond this range, the volatility of the ammonia in both the initial double silicate solution and the final ammonium silicate product increases and the actual loss of ammonia as well as the odor becomes a problem. The sodium-ammonium double silicate solution is treated with a specially prepared cation exchange resin in a batchwise operation. The resin is loaded with ammonia to lO0Yc of its exchange capacity, to prevent undue loss of ammonium ions from the solution while removing the alkali metal ions. Resins with a loading lower than 100% will remove ammonium ions along with the alkali metal ion from the double silicate solution. The optimum contact time of the ammonia-loaded resin with the double silicate solution was found to be 6 minutes. After this treatment time, the resin and ammonium silicate solution are separated by filtration. lnd. Eng. Chem. Prod. Res. Develop., Vol. 9,No. 2 , 1970 251
The advantage of treating a sodium-ammonium double silicate solution with ammonia-loaded cation exchange resin over the use of a pure sodium silicate as a starting material can be shown very simply. For example, 250 grams of S 35 sodium silicate was diluted with 805 grams of distilled water without the addition of ammonia. This solution contained 1.60% Na?O, 6.00% SiO2, and had a mole ratio of 3.87 Si02/Na20. Portions of this dilute sodium silicate solution (20 grams) were treated batchwise for 6 minutes with 15, 20, and 25 ml of the 100% ammonialoaded resin. The compositions of the resulting solutions are shown in Table 11. A double silicate solution was prepared a t the same final Si02 and NalO concentrations as the above diluted sodium silicate solution by mixing 250 grams of S 35 sodium silicate with 500 grams of water and then adding to this with vigorous agitation a solution of 29.9 grams of 2970 aqueous ammonia in 275.1 grams of water. A slightly hazy, stable solution was obtained containing 1.60% N a 2 0 , 1.25% ( N H a ) 2 0 ,6.00% SiOl, mole ratios of 3.87 SiO?/NaeO, 4.16 S i 0 2 / ( N H 4 ) 2 0and , 0.93 ( N H 4 ) ? 0 / Na20. This solution (20-gram portions) was also treated batchwise for 6 minutes with 15, 20, and 25 ml of the 100% ammonia-loaded cation exchange resin. After filtration, ammonium silicate solutions of the composition shown in Table 111 were obtained. Comparison of these two series shows that ammonium silicates of very much improved ratios are obtained when the ammonium-alkali metal double silicate solution is treated with the 100% ammonia-loaded cation exchange resin as compared to a pure sodium silicate starting solution. The data in Table I11 show that the ammonium ion content of the silicate solution is not changed by this treatment, indicating that a stoichiometric exchange between sodium ions from solution and ammonium ions from the resin takes place under these conditions. Much lower ratio ammonium silicate solutions were prepared from a mixture of 250 grams of S 35 sodium silicate diluted with 500 grams of water and a solution of 59.8 grams of 29% aqueous ammonia in 245.2 grams of water. The slightly hazy, stable solution contained 1.60% N a 2 0 , 2.51% ( N H 4 ) ? 06.00% , S O z , with mole ratios of 2.07 S O z / ( N H 4 ) 2 0 , 3.87 SiOe/Na20, and 1.87 ( N H 4 ) ? 0 / X a 2 0 .
Table It. Ammonia Resin Treatment of Pure Sodium Silicate Solution Amt. of Resin, MI
(NH4)nO
...
...
15 20 25
7.44 8.42 9.22
SiOz/ No20
(NH4)z0/ No20
NozO,
Yo
YO
3.87 25.7 26.9 32.6
... 3.60 3.19 3.53
1.60 0.24 0.23 0.19
0.69 0.61 0.59
("4)?0,
...
SiOz, YO
6.00 5.97 5.97 5.97
Table Ill. Ammonia Resin Treatment of Double Silicate Solutions Amt. of Resin, MI
... 15 20 25
252
Table IV. l o w Ratio Ammonium Silicate Solutions Amt. of Resin, MI
... 15 20 25 30
35 40 50
Mole Ratios SiOz/ ("4)zO
2.07 2.35 2.45 2.55 2.64 2.86 3.12 3.58
SiOz/ No20
3.87 32.2 41.6 89.4 100.5 67.0 75.4 117.6
(NHI)PO/ NazO
NozO,
(NHa)20,
Yo
Y O
SiOz, YO
1.87 13.3 17.0 35.0 38.1 23.4 24.1 32.9
1.60 0.20 0.15 0.07 0.06 0.09 0.08 0.05
2.51 2.23 2.14 2.06 1.92 1.77 1.62 1.38
6.00 6.00 6.00 5.83 5.83 5.83 5.83 5.70
Table V. Ammonium Silicate Solutions Prepared from 2 Ratio Sodium Silicate
Mole Ratios
Son/
Batchwise 6-minute treatment of 20-gram portions of this double silicate solution with increasing amounts of a 100% ammonia-loaded Amberlite IR-124 cation exchange resin yielded ammonium silicate solutions of compositions as shown in Table IV. Table IV shows that optimum conditions for the preparation of ammonium silicate solutions with a mole ratio of 2.6 Si02/(NH4)20containing less than 0.170NazO are a 6-minute batchwise treatment a t room temperature of 20 grams of a starting solution containing 1.60% N a 2 0 , 1.65% NH3, and 6.00% Si02 with 30 ml of 100% ammonialoaded Amberlite IR-124 cation exchange resin. The resulting ammonium silicate solution contains 0.06% N a 2 0 , 1.92% ("4)20, 5.83% SiO2, with mole ratios of 2.64 SiOd ( N H 4 ) 2 0and 100.5 Si02iNazO. Lower ratio sodium silicates may also be used as starting materials for the preparation of ammonium silicate solutions. Table V shows that the addition of ammonia to sodium silicate solutions containing a relatively high proportion of sodium ions (2.0 weight ratio Si02/Na20) before treatment with the ammonia-loaded resin helps maintain the concentration of Si02 and increases the proportion of ammonia to N a 2 0 in the final product. I t is evident, however, that a high ratio sodium silicate is a better starting material for ammonium silicate preparation because much less sodium has to be removed; thus, high ratio sodium silicate solutions give ammonium silicates of considerably lower inorganic alkali content. More concentrated sodium-ammonium silicate solutions can be treated with ammonia-loaded resins in the same way, but the sodium removal is not as complete with
Mole Ratios SiO2,
Amt. of Resin, MI
("I)PO/ N0z0
Non0, %
(NHa)zO,
SiOz,
O h
Y O
...
... 3.66 4.20 5.55 5.95
2.0 15.8 21.4 21.2 21.8
...
20 30 40 50
4.3 5.0 3.8 4.6
3.0 0.38 0.28 0.27 0.21
0 1.38 1.18 0.87 0.81
6.0 5.82 5.82 5.56 5.56
...
4.16 2.41 2.85 2.98 3.44
2.05 17.5 24.5 23.8 30.6
0.48 7.3 8.6 8.0 8.9
3.0 0.35 0.25 0.24 0.19
1.25 2.13 1.81 1.64 1.42
6.0 5.93 5.93 5.63 5.63
2.07 2.06 2.34 2.12 2.60
2.0 19.9 25.7 26.0 30.0
0.99 9.7 10.8 12.1 11.5
3.0 0.30 0.24 0.22 0.19
2.52 2.51 2.20 2.26 1.85
6.0 5.97 5.97 5.53 5.53
20 30 40 50
SiOn/ (NHa)20
SO?/ NazO
(NH~)IO Nan0
NanO,
(NHa)zO,
Yo
YO
Y O
...
4.16 3.64 3.64 3.88
3.87 25.3 34.1 36.3
0.93 6.94 9.37 9.36
1.60 0.23 0.17 0.16
1.25 1.34 1.34 1.25
6.00 5.62 5.62 5.62
25 30 40 50
Ind. Eng. Chern. Prod. Res. Develop., Vol. 9, No. 2, 1970
Mole Rotios SiOa/ SiOn/ ( N H P ) ~ ~NozO
these more concentrated solutions and not as pure ammonium silicate solutions are obtained as when starting solutions of 6% SiO, are applied. Comparison of the results in Tables IV and VI illustrates this point. The ammonium silicate solutions are slightly hazy, stable solutions. They smell strongly of ammonia and have to be kept in closed containers to prevent loss of ammonia. They are not stable on heating in open vessels or in vacuo because of the volatility of the ammonia. I t is, therefore, difficult to concentrate them without loss of ammonia, and they are generally used a t the concentration at which they are obtained from the resin treatment. Ammonium silicate solutions with silicate concentrations from 6 to 1 2 c ~and mole ratios of 2 to 6 S i 0 , / ( N H 3 ) r 0 are stable for many months. Ammonium silicate solutions are much more compatible with water-miscible organic solvents than sodium silicate solutions of the same ratio and the same silica concentration (Table VII). The pH values of ammonium silicate solutions are about one pH unit lower than those of sodium silicate solutions of comparable ratio and concentration (Table V I I I ) . The relative particle sizes of ammonium silicate solutions compared with those of commercial alkali metal-stabilized silica sols and mixtures of such sols with ammonia were estimated by plotting particle size us. light-scattering value for silica sols of known average particle size a t a concentration of 1% SOL. The light-scattering data were determined on a Lumetron colorimeter with the 90" light-scattering accessory using Ludox SM a t 1.255 Si02 as a standard at a scale setting of 100, a mercury lamp as the light source, and monochromatic light of 365 mp. The lightscattering values a t 15 SiO, concentration of ammonium silicate and mixtures of Ludox SM and HS silica sols with ammonia a t the same mole ratio of 2.61 S O 2 /( N H 4 ) 2 0 were located on the extrapolated curve for these sols (Figure 3). The extrapolated particle size for the ammonium silicate is about 1 to 3 mp, much smaller Table VI. Ammonium Silicate Solution from Concentrated Sodium Silicate Amt. of Resin, MI
... 25 30 40 45
Mole Rotios SiOz/ (NHI)IO
SiO% Na?O
2.07 2.56 2.55 2.82 2.94
3.87 34.0 39.0 53.3 68.4
(NHI)IO/ No10
1.87 13.3 15.3 18.9 23.2
Na,O, %
(NH4)20, O h
SiO?, %
2.67 0.30 0.24 0.18 0.14
4.18 3.33 3.16 2.86 2.74
10.0 9.86 9.28 9.28 9.28
Table VII. Compatibility of Aqueous Ammonium Silicate and Sodium Silicate Solutions with Water-Miscible Organic Solvents Maximum Amount of Solvent in Stable Mixture, Weight Yo 150-
PrOH
MeLC0
Dioxan
THF
43
31
39
32
33
14
11
12
15
13
MeOH EtOH
Ammonium silicate (2.46 SiOL/ (NH,)>O;5.7'c SiO,) Sodium silicate (2.48 Si02/ Na>O; 5.7&c SiOJ
19
Table VIII. pH of Ammonium and Sodium Silicate Solutions of Identical Mole Ratio [2.2 SiOn/NanO or ("4) 201 pH at 25°C
Yo SiO?
Concentration,
Ammonium silicate
Sodium silicate
10.78 10.78 10.70 10.60 10.52 10.40
11.80 11.80 11.78 11.74 11.65 11.48
5.22 5.0 4.0 3.0 2.0 1.0 I
I
1
\
,'xLudox
I
Ludox HS + Ammonia
SM
/
/ I /
/
dxAmmoniurn
Silicate
I
I
I
I
I
I
5
IO
15
20
25
30
mp
Figure 3. Particle size of ammonium silicate solution, silica sols, and mixtures of silica sols and ammonia
than that of Ludox SM, which has an average particle size of 7 mp. Figure 3 also shows that the particle size of silica sols increases when they are mixed with ammonia to give the same ratio as that of the ammonium silicate solution. Acknowledgment
The author thanks M. R . Derolf for his help with the experimental and analytical work and N. R. Horikawa and R. W. Spencer for determining the light-scattering data. literature Cited
Deribere, M., Chem. Ind. (Paris) 47 (5), 538 (1942). Griesbach, R., Chem. Ztg. 57,253, 274 (1933). Kuhn, H., J . Praht. Chem. 59, 1 (1953). Merrill, R . C., Spencer, R . W., J . Phys. Colloid Chem. 55,187 (1951). Schwarz,, R., Ber. 49, 2358 (1916). Voorhees, Vanderveer, U.S. Patent 2,457,971 (Jan. 4, 1949). Weldes, H . H., IND.ENG.CHEM.PROD. RES. DEVELOP. 9, 243 (1970). Weldes, H. H., U.S. Patent 3,326,910 (June 20, 1967). Weldes, H . H., Derolf, M. R . , U S . Patent 3,346,334 (Oct. 10, 1967). Wolter, J. F., U.S. Patent 2,671,056 (March 2, 1954). RECEIVED for review September 4,1969 ACCEPTED February 24,1970 Ind. Eng. Chern. Prod. Res. Develop., Vol. 9, No. 2, 1970
253
