CHEMICALS
Aluminum Stabilizes Colloidal Silica Stability through pH range of 2 to 10 comes from aluminum substitution on silica sphere surfaces With its alumina-modified silica sol now in production, Du Pont is eying the 22 million pound-a-year market for colloidal silicas, hopes to capture a bigger share of that market with its new product. The silica's main selling point is its stability over a wide range -from pH 2 through pH 10. Du Pont partially substitutes aluminum for silicon on the the surface of silica spheres. The resulting permanent charge increases the usable range of the colloidal silicas. Conventional sols, at practical concentrations, are
not stable in the pH range from 4 to 7. Known as Ludox AM (for alumina modified) the material is now being offered for sale at 18.75 cents per pound, in bulk, for 30% silica content material. It is being made at Du Pont's East Chicago, Ind., plant and is being sold as a liquid dispersion in 55-gal. drums, tank cars or trucks. Like other currently available liquid dispersions of silica, this colloidal silica will freeze at 32° F. and so must be moved in heated trucks and stored in heated places.
STABLE SOL Du Pont's Ludox AM is stable at pH 5.5 and pours easily, whereas unmodified silica aquasol gels at this pH. Both have about 3 0 % solids
How It's Made. Ludox AM is made by passing sodium silicate (water glass) through an ion exchange column (cationic and anionic resins) to remove the sodium. This yields silicic acid. What follows next is not known for certain, but it's postulated that silicic acid combines with a silicate ion, while in the column, to form a dimer. The dimer, through a condensation step that removes water, yields disilicic acid, which has a siloxane center. The disilicic acid polymerizes to a spherical shape upon the addition of silicic acid. The internal structure of the sphere is that of siloxane, but the surface is hydroxylated. It is here that the liquid-dispersed colloidal silicas differ from the solid colloidal silicas that are only slightly hydroxylated. The polymer spheres have a density of about 2.1 grams per c c , the same as that of amorphoifs silica, which, in effect, they are. The spheres also exhibit the same thermal expansion rates as amorphous silica. In the modified product, aluminum replaces some of the silicon atoms in the outer surface of the spheres. In Ludox AM there is roughly 0.2% aluminum as A120 in the sol. The sphere's permanently negative charge comes from charged hydroxyi groups adsorbed on the sphere's surface. This minimum charge remains on the sphere regardless of solution pH. As pH increases, hydroxyi ion increases in the solution and the charge on the spheres becomes greater. This charge is sufficiently high, even at its minimum, to keep the spheres from colliding. Thus colloidal suspensions of such modified spheres have extremely long gelation times. The charge is sufficiently high, also, to counteract the catalytic effect of the hydroxyi ions, which would induce the agglomeration of the hydroxylated silica spheres—in essence siloxane formation. Unlike conventional colloidal silica sols, Ludox AM is little affected by sodium chloride or divalent or trivalent salts. Therefore, it's not necessary to buffer pH or adjust salt concentration to maintain this colloidal silica in a liquid dispersion. Colloidal silicas find a wide variety of uses, such as increasing the coefficient of friction of floor polishes, textiles, metals, and paper bags and cartons. They serve as binders for inorganic fibers, ceramics, and papers. OCT. 2, 1961 C&EN
69
How MOD-EPOX® liquefies viscous epoxy resins and "liquidates" some of the cost
PERFORMANCE: Reactive MOD-EPOX reduces epoxy resin vis cosity as much as 75 %, combines chemically in the curing to become part of the resin. This means you can use more filler, yet have faster flow, less entrapped air, fewer rejected finished parts. And final properties are actually improved: FLEXURAL
STRENGTH O F 4-PLY GLASS L A M I N A T E S ( A S T M D638)
FORMULATION:
Control
MOD-EPOX liquid e p o x y resin diethylenetriamine m a g n e s i u m o x i d e (fluffy) FLEXURAL
FIBER-EPOXY
STRENGTH:
original k e t o n e — 4 0 hrs. @, r o o m t e m p . w a t e r — 4 0 hrs. @ 100°C. 1 0 % c a u s t i c — 2 7 hrs. @ 1 0 0 ° C
with MOD-EPOX 25 100 8 0.25
100 12 psi
psi
42,400 42,400 29,400 8,500
48,400 47,700 37,600 9,200
Epoxy resins modified with MOD-EPOX for better flow and lower cost show better dimensional stability — lower power factor — equivalent hardness — and higher adhesive strength {shear bond strength of a standard epoxy adhesive increases more than 50%, steel-to-steel). ECONOMY: NOW . . . MOD-EPOX at 36^/lb.* costs less than any grade or brand of epoxy resin, 50-75% less than most other modifiers . . . AND reduces the curing-agent requirements to about % of usual amounts. FACTS: Technical Bulletin PL-313 gives complete performance data—including specific details on how MOD-EPOX can help you make: •
e a s y - h a n d l i n g electronic potting c o m p o u n d s .
•
l o w - c o s t a u t o - b o d y - s o l d e r formulations.
•
h i g h - s t r e n g t h casting a n d encapsulating c o m p o u n d s .
•
tenacious adhesives for metals a n d glass.
*T/L and C/L, F. Ο. Β. Monsanto, Illinois
Monsanto
MONSANTO CHEMICAL COMPANY Organic Chemicals Division Plasticizer Council, Dept. 4 4 1 1 - X St. Louis 6 6 , Missouri
Please rush my copy of Technical Bulletin PL -313. Name Company
Monsanto Plasticizer Council... for plasticizer guidance that pays !
70
C&EN
OCT. 2, 1 9 6 1
Street City
Zone - -
State
Fluorosilicones Go into Commercial Production Dow Corning adds fluids, greases, and compounds to its line of fluorosilicone products Confident that it can stimulate a modest but profitable demand for fluorosilicone fluids and greases, Dow7 Corning has begun commercial pro duction of these products. This moves' the company a step further in the fluorosilicone line. It has been pro ducing fluorosilicone rubber, under the brand name Silastic LS, since 1956. During this time, General Electric has been concentrating on nitrile sili cones aimed at the same general markets as fluorosilicones (C&EN, May 29, page 46). GE feels that lower production cost is in the nitriles' favor. Union Carbide also favors the nitrile approach. Dow Corning, on the other hand, feels the fluoro com pounds give better performance, thus balance their higher cost. The basic difference between Dow Coining's fluorosilicones and conven tional dimethyl silicones is that di methyl silicones have the methyl groups attached to the siloxane poly mer, whereas the fluorosilicones have fluoroalkyl groups substituted for some of the methyl groups. These fluoro silicones are found to have extremely good solvent resistance and lubricity, operate over a wide temperature range. Dow Coming's first commercially available fluorosilicone fluid, FS 1265 fluid, is insoluble in most petroleum oils, fuels, water, and other solvents (except ketones). It can be used as a lubricating fluid under extreme tem peratures and pressures. It's also used as a defoamer in nonaqueous systems. Dow Corning is also producing valve lubricants for applications in volving extremes of heat or cold. The grease-like materials, FS 1280 and FS 1281, are composed of a fluorosilicone fluid, thickened with finely divided silica filler. These compounds are extremely re sistant to most oxidizing agents, and they are expected to find use as seal ing materials and as lubricants for lowspeed bearings. The greases, Dow Coming's FS 1290 and FS 1291, are a fluorosilicone fluid thickened with a lithium soap. They are intended for use in bearings of all types, when good lubricity over a wide temperature range is needed.
NEW CHEMICALS Lithium hypochlorite is available in pilot plant quantities from Lithium Corp. of America, New York, N.Y. The product, which is stable, readily soluble, and calcium free, is used as a dry bleach in laundries. C1
Polymeric plasticizer for use with polyvinyl acetate has been introduced by the Harchem Division of Wallace & Tiernan, Inc., Belleville, N.J. Called Harflex 340, the plasticizer is for use with polyvinyl acetate, and imparts wet tack, specific adhesion, and per manency to polyvinyl acetate adhesives, the company says. The plasti cizer has FDA approval for food use,
and other suggested applications are for carpet backing compounds, bind ers for nonwoven fabrics, laminating adhesives, and barrier coatings. C2
I
Further useful information on keyed Chemical items mentioned is readily available . . .
Use handy coupon on page 72
Readers' Information Service Use this handy self-mailer to obtain further information or literature. Simply mark the items desired, fill out the information requested, clip the coupon, fold, staple, and mail. (Please fill out coupon completely.)
Company: Street: Zone
State
Your Title: Your Function (Check One): Corporate Management Technical Management Product Research Product Design & Development Process Research
6Π 7Π 8Π 9Π 10 Π
I
Oak Ridge National Laboratory offers more than 300 radioactive and stable isotope products. RADIOISOTOPES Processed Solutions — 90 processed ra dioisotopes may be obtained, including many carrier-free and high specific activ ity products. Now Available-Scandium-46 at $150 a curie; sulfite-free 1-131 at $2 per m c ; technetium (as element or ammonium pertechnetate) $100 a gram; calcium-47, with less than 5% Ca-45, $200 per m c ; 1-125 in research quantities.
Name:
1Π 2Π 3Π 4Π 5Π
for Your Development Work
Zinc chloride solution is now available from Pears all Chemical Corp., Phillipsburg, N.J. It is being shipped in rubber-lined tank cars or trucks, or in 55-gal. polyethylene-lined drums. It is supplied in both 53° and 72° Baume solutions. C 3
October 2, 1961
City
ISOTOPES
Process Design & Development Production—Processing Purchasing Analysis—Testing Consulting
STABLE ISOTOPES More than 200 stable isotopes available from 50 elements Chemical processing and target fabrication services also of fered. . . . Ultra-high iso topic purity in a number of isotopes. For information or literature, write t o : Isotopes Division, Oak Ridge National Laboratory, P . O. Box X , Oak Ridge, Tennessee.
CLIP COUPON—Fold along this line—fasten (staple, tape, glue) MAIL
Your Industry:
1• 2• 3• 4• 5Π 6• 7• 8D 9• 10 •
Construction Food & Kindred Products Textile Mill Products Paper & Allied Products Printing, Publishing, etc. Chemicals & Allied Products Plastics; Synthetic Resins Drugs Soap, Detergents, Cosmetics Paints, Varnishes, etc.
11 •
Petroleum Réf., Asphalts, Lubricants 12 Π Rubber; Plastic Products 13 • Leather & Leather Products 14 • Stone, Clay, & Glass Products 15 • Primary Metal Industries 16 • Fabricated Metal Products 17 • Machinery & Equipment 18 • Transportation Equipment 19 • Instruments 20 Π Education
ISOTOPES
OAK RIDGE N A T I O N A L LABORATORY Operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION
OCT. 2, 1961 C&EN
71
