Applications of Colloidal Silica: Past, Present, and Future - Advances

29 Applications of Colloidal Silica: Past,

Downloaded by KUNGLIGA TEKNISKA HOGSKOLAN on October 9, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0234.ch029

Present, and F u t u r e Charles C. Payne Nalco Chemical Company, One Nalco Center, Naperville, IL 60563-1198

Early uses of colloidal silica for catalysis, ceramics, paper and textile applications, strength enhancement in rubber, tobacco treatment, and medicine are discussed. A historical view of the development of applications is highlighted, and future uses are discussed.

Τ

Τ H E N T H O M A S G R A H A M P R E P A R E D S I L I C A C O L L O I D S IN T H E 1860S ( I ,

2),

he couldn't have envisioned its many applications today. The list of applications in Iler's 1979 edition of The Chemistry of Silica (3) is long and varied. Sometimes silica is used to promote adhesion and sometimes to prevent adhesion. These opposing properties from the same material indicate that applications involving silica sols can be quite complex. Bungenburg de Jong (4), in reviewing the origins of colloid science, pointed out that Graham introduced the term ''colloids'' for substances that " i n solution" showed only a very slow diffusion velocity compared with other substances such as sugar and salts. Most of the early literature (5) made no distinction between silicates, polysilicates, and what ultimate ly has come to be known as colloidal silica. Colloidal silica has discrete particles that are generally somewhat spherical and amorphous.

Preparation Procedures E a r l y . Thomas Graham was not the first person to attempt to prepare a colloidal silica. As early as 1747, Pott made a "semisolution of silica", and as early as 1820, a reference is made to the preparation of a sol of "hydrated silica" (6). In 1853, a French researcher named Fremy (7) 0065-2393/94/0234-0581$08.00/0 © 1994 American Chemical Society

In The Colloid Chemistry of Silica; Bergna, H.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.


582

T H E C O L L O I D CHEMISTRY O F SILICA

prepared a dilute colloidal silica from silicon sulfide. By 1864, silica colloids were being prepared by the dialysis of gels and by the hydrolysis of silicate esters (8). A l l products were very dilute. Colloidal silica technology proceeded slowly. The early products were not suitable for most applications because (1) only low silica concentrations were available, (2) the materials were not stable with time, or (3) the products did not have reproducible properties. By 1915, only one patent for preparation of a commercial colloidal silica had been issued (9). Using electrodialysis (Figure 1) to make a product, Schwerin marketed a 2.4% silica sol as a stable material. Schwerin suggested the use of this product for medicinal purposes but did not specify how or where it should be used.

Figure 1. Electrodialysis cell of Schwerin (10). 1941 to 1 9 6 3 . The year 1941 was the turning point toward commercial silica sol production methods. B i r d (10), at Nalco, found that low-molecular-weight silicic acids could be prepared by ion exchange. If a small amount of sodium hydroxide was added to these materials, particles were formed. These materials could then be concentrated with conventional evaporator techniques to about 27.5% silica. Nalco licensed the ionexchange procedure to DuPont, which continued to work on preparation throughout the 1940s. Monsanto (11-14), during the years 1941 to 1951, continued to develop products by peptizing silica gels and thus prepared materials with a broad particle-size distribution, and by 1963 products containing 5 0 % silica were prepared by gel peptization techniques.



29.

PAYNE

Applications of Colloidal Silica

583

The year 1951 is significant for the preparation of colloidal silicas other than by the conventional gel peptization technique. Using Bird's idea of preparing low-molecular-weight silicic acids by ion exchange, Bechtold and Snyder (15), two DuPont scientists under Iler's direction, developed the ingenious method of growing the particles to any given size while concentrating the products to up to 3 5 % silica. This research, coupled with the work by Joseph Rule (16), another DuPont scientist, and his coworkers, determined the parameters needed to keep the products stable at high silica concentrations; thus, the Bechtold and Snyder process became a practical method that turned colloidal silica into a stable product with predictable properties. By 1959, commercial products were available with up to 5 0 % silica concentrations. Rule's work was important in making stable products, but it was also important for using these materials in different applications.

Applications T o 1 9 3 3 . Griessbach (17) in 1933 summarized the various methods for preparing and using colloidal silicas up to that time. The methods of preparation of sols included dialysis, electrodialysis, gel peptization, and hydrolysis of the silicate esters or silicon tetrachloride. Silica sols were used in numerous applications at that time. Silica sols were a primary binder in the synthesis of catalysts used in the production of sulfuric acid or the dehydration of alcohols. In ceramics, they were used in glazes and other coatings. Cements and such materials as plaster of Paris could be coated with colloidal silica to improve their resistance to water and acidic substances. Colloidal silica was incorporated into paper and sprayed onto textiles or wood to either strengthen or protect the substrate. It was added to metal solutions such as silver or gold to improve stability so that these materials could be used in medicines. Silica in combination with surfaceactive agents also showed tendencies to emulsify, especially when the sol became destabilized and the viscosity of the system increased. Rubber latex emulsions were coagulated with colloidal silica to strengthen the final rubber product. A novel use for its time was the addition of colloidal silica to tobacco to help with the fermentation process and to aid in the adsorption of nicotine. Apparently, the fact that silica adsorbed and retained water helped to keep the tobacco fresh. The use of silica sols in medicine appears to be an area of great speculation in 1933. Colloidal silica was claimed to be useful for treating subcutaneous wounds, tuberculosis, and many circulation problems such as hardening of the arteries. Griessbach (17) also suggested the immobilization of such enzymes as those involved in the conversion of amylopectin into simple starches.



584


Many of these applications are practiced today. Other applications exist only for specialized situations. For example, silica sols are a desirable source of silica for catalyst substrates. For catalyst preparations, however, colloidal silica is generally used only for specialized applications. Griessbach (17) showed that five companies produced silica sols in 1933. Most products were very dilute, and only one could be considered concentrated. The most concentrated sol available at that time was a product called Kieselsol I.G. (made by I.G. Farbenindustries), which contained 10% silica and was stabilized with ammonium hydroxide. The characteristics of most of the sols were undetermined. Moreover, the difficulty of making a reproducible product that would perform i n a predictable manner for specific uses was technically impossible at that time. This difficulty, most likely, was the major reason that colloidal silica applications did not increase rapidly. Her (18) pointed out that colloidal silica was not accepted for wide commercial use until methods were discovered for producing sols with high concentrations that would not gel or settle with time. The first steps to achieving that goal occurred in 1941 (discussed i n the preceding section on preparation procedures). 1933 to 1955. Iler's 1955 edition of Colloidal Chemistry of Silica and Silicates (5) devotes seven pages to the uses of silica sols at that time. The areas of use included floor waxes, textiles, organic polymers, water treatment, and miscellaneous areas such as in cements and as a binder for luminescent materials used i n television picture tubes. Two areas of major interest i n 1955 were paper antiskid and investment castings. Wilson (19) used colloidal silica to increase the friction between paper surfaces. In this application (Figure 2), the silica sol is typically diluted to 1-7% as silica solids and then applied to multiwall bags, corrugated boxes, and linerboards. Various methods of applying the silica sol were used. Typical applicators were sprays, segmented applicator rollers, knife blades, full roll coaters, sponges, and brushes. Testing to ensure that the colloidal silica has been applied correctly consisted of determining either static or dynamic coefficients of friction with a slide angle tester (Figure 3). The coefficient of friction is defined as the numerical value for the tangent of the angle needed to start sliding (static) or the value needed to maintain sliding (kinetic). Collins (20) used colloidal silica as a binder for investment casting applications. Investment casting techniques are useful for the production of aircraft parts, various industrial castings, dental and jewelry parts, and sporting equipment such as golf club irons and propellers for outboard motors. In a typical procedure, colloidal silica is mixed with a refractory grain such as quartz or alumina, with or without a gelling agent, formed into a ceramic mold, dried, and fired. Other investment castings with expendable patterns included ceramic shell molds; precoats for solid



29.

PAYNE


585

Air Compressor

Figure 2. Spray unit for paper antiskid application.

molds; backups for solid molds, "tamp and pack" methods, and solid molds with no precoats. Colloidal silica was used i n general foundry applications such as gunning mixes, ceramic mold facings for core boxes and the like, mold washes, and semi-permanent molds with renewable facings. It was also used in the production of wallboard (Figure 4). 1955 to 1962. In 1962, Monsanto (21) reviewed the patent literature and listed the promising applications for colloidal silica at that time. They grouped the areas of application into the categories cellulosics, ceramics, electricity, floor waxes, flotation, insulating coatings, refractory molds, paints, photography, printing, paper, rubber, textiles, and miscellaneous; "miscellaneous" tends to involve some type of coating or inorganic-organic composition. A n area of interest at that time was the incorporation of colloidal silica into emulsion systems. Typical emulsions included floor waxes or rubber latices. Conventional wax compositions ordinarily included certain extenders or modifiers in the wax dispersions. These may comprise wax-soluble or water-dispersible resins (natural or synthetic). These formulations can produce coatings with a pleasing appearance; however, many lack slip resistance. The incorporation of colloidal silica into the formulation produces coatings that prevent slipping.



586


to to CO

to .g. S-

to

6UD •S

«ri

ε

SUD &



To Dryer Section

Figure 4. Typical flow diagram of wallboard production.

liner Board


oo

01

to

ζΟ


588


Her (22, 23) described typical formulations with Carnuba wax, which is dispersed in water containing colloidal silica, a fatty acid like oleic acid, triethanolamine, and potassium hydroxide. This composition can then be applied, for example, as a thin coating to linoleum floor. The product forms a lustrous coating without rubbing while providing a slip resistance. Mixtures of rubber latices or elastomer foams were modified with colloidal silica to give improved properties. Typical processes involved drying, gelling, or coagulating the colloidal silica within the elastomer system. Silica sols were used with phenolic, formaldehyde-based, melamine, polyester, acrylic, vinyl or styrène polymer-copolymer, polyamide, and styrene-butadiene rubber systems to provide strength to films and coatings. A typical rubber formulation, for example, that demonstrates the surface area properties of silica sol can be seen in the Talalay process for making foam rubber (24); the elastomer foam is in a latex form, to which is added an accelerator, an antioxidant, a vulcanizing agent, and carbon black. The mixture is then foamed, either mechanically or chemically, gelled, vulcanized to make the rubber, washed, and dried. The dried material is then postdipped in colloidal silica to reinforce the walls and prevent the crumbling effect seen on poorly made foam rubber pillows and so forth. Originally, a 20-nm silica sol was used. If a colloidal silica with a smaller particle size is used, the corresponding higher surface area allows less silica to be used in the system; thus the cost of the whole process is reduced. 1962 to 1 9 7 9 . When Iler's book, The Chemistry of Silica, came out in 1979 (3), the section on the applications for colloidal silica had increased to 21 pages, compared to seven pages in the 1955 book (5). The increase in the number of applications was largely due to the efforts of Her. As technical manager of DuPont's colloidal silica area, Her enlisted the help of some excellent researchers whose job it was to develop new application areas. As a result, numerous application patents were issued during this time period. The areas of application were many and varied during the period of 1962 to 1979. They can broadly be subdivided into binding and nonbinding systems. For example, silica sols are used as a binder for thermal insulation (Figure 5) or for catalyst manufacture and as a polishing agent for silicon wafers in a nonbinding application. Stiles, McClellan, and Sowards (25-28) showed that colloidal silica is a good source of raw material for making the base catalyst. Silica sols have the advantage of a uniform distribution and known particle size. Thus, the catalyst manufacturer can predict the pore size and volume of the final product. Colloidal silicas also offer the advantage of low levels of sodium (compared to sodium silicate), a known catalyst poison, and therefore require less washing and processing to remove the unwanted cation. In



To Drain

To Drain

Whitewater Tank

Figure 5. Vacuum forming process for preparing thermal insulation.

Fiber Slurry

Wire Screen

LFyU

Vacuum Forming Mold


To Vacuum


590


addition, colloidal silicas, because they are liquid, can be mixed with metal salts such as bismuth and molybdenum and spray-dried. Uniform dispersion of the silica with the expensive "active" metals gives a highly desirable catalyst with no " h o t " spots. Consequently, high yields of expected products result. Such catalysts can be used in the conversion of propylene and ammonia to acrylonitrile (29, 30). One application area between 1962 and 1979 that has an impact on today's problems is the manufacture of wallboard. Wallboard was prepared by sandwiching a gypsum mixture between heavy papers. A typical core consists of gypsum, starch, potash, a pulp slurry, an asphalt or rosin-size emulsion, and gauging water (i.e., a colloidal silica plus polymer binder system). The mixture is blended together and placed between liners made on linerboard machines. One way this application can be used to solve today's problems was presented early in 1990 by A i r Products and Chemicals Inc. A power plant in Indiana was going to use a high-sulfur coal to generate its electricity. The acidic gas emissions, which consist of sulfur dioxide, was scrubbed with a limestone plus water mixture. The resulting calcium sulfite is oxidized to form calcium sulfate, which is then washed, centrifuged, rinsed, and dried. The final product is gypsum that contains less than 10% water. Because the average modern house is estimated to use 8000 square feet of wallboard, the process solves the gas emission problem while producing a low-cost construction material. Colloidal silicas can also be used as a fine polishing abrasive for silicon wafers. Typical operations (31, 32) involve feeding a dilute silica " s l u r r y " (i.e., silica sol) that has been adjusted with a caustic agent onto a revolving polishing wheel containing a polishing pad. The silicon wafer is fixed to a polishing head and placed in contact with the polishing pad. As the system rotates, the high p H and the abrasive property of the colloidal silica removes silicon from the surface of the wafer. The resulting wafer has a mirrorlike surface onto which an electrical circuit can be placed. Other applications of this time period can be found in Iler's discussion and references (3). 1979 to P r e s e n t . The literature from 1979 to the present shows that the major application areas for colloidal silica involve coatings and "inorganic-organic compositions." Most of these compositions use the silica sol in a binder application. Japanese research far exceeds that of all other countries. Coatings is a diversified application area involving a substrate and some type of surface covering. The type of substrate material to be coated can be plastics such as polycarbonate or polypropylene, metals, silicone rubber, ceramic- or refractory-like materials, fabrics like nylon and rayon, photographic films, paper materials, walls (painted or not), eyeglass lenses,



29.

PAYNE


591

inorganic fibers such as fiberglass, stone for buildings, investment casting molds, leather or leather substitutes, and concrete surfaces. Typical coating materials tend to be polymeric in nature, although some applica tion areas use the colloidal silica without organic polymers. For example, Nippon Steel Corporation (33) disclosed the use of a colloidal silica in combination with phosphates and chromic oxide or chromate to make a nondirectional magnetic film for steel sheets. Toshiba Silicone Company, L t d . (34), on the other hand, uses a silane-colloidal silica mixture to coat glass lenses. Inorganic-organic composition uses are similar to coatings uses except that no substrate is involved. A variety of mixtures can be used in which the colloidal silica is added to impart strength. A n example of this type of system was disclosed by Asahi Glass Company, L t d . (35); colloidal silica was added to isophorone diisocyanate and a pentaerythritol triacetate-tetraacetate mixture to produce a material for a polycarbonate plate. Colloidal silica continues to be used i n the conventional application areas such as catalysis, paper antiskid, refractory insulation, and photogra phy. Its use, however, is dwarfed by that of coatings and inorganic-organic compositions. T h e F u t u r e . Two types of silica sol products are needed in the 1990s: specialty products and organosols. Specialty products are used i n high-technology areas. Price is generally unimportant if they work. Typical examples of specialty products are monodisperse sols [i.e., one particle size, low sodium, and low metal (aluminum, iron, etc.) concentrations, and no aggregation]. Monodisperse silica sols are important in the previously mentioned Talalay process for making foam rubber pillows. If a 4-nm silica sol is normally used, then a substitution of a 3.5-nm particle at the same silica dosage would theoretically increase the strength of the rubber by 14.3%. If, however, the particle size is changed from 4.5 to 5.0 nm, the strength of the rubber would decrease by 11 to 20% at the same silica dosage. Under these conditions, the crumbling effect of the foam rubber would return. The second application area of interest is organosols. Organosols involve the use of nonaqueous systems, for example, in making magnetic colloids and recording media, high^technology ceramic composites, and catalyst supports (36). The high solid loadings, the lack of aggregation, and the improved uniformity of the colloid and the final product can only be obtained from colloidal systems. Silica organosols are dispersions of silica colloids in an organic solvent. Silica organosols can be used as a lowtemperature binder (37), as an adhesion promoter (Schmidt, Κ. E., personal communication), or as a silica source for magnesia refractories. For example, magnesia refractories use silica as a binder to make hightemperature materials through the formation of a magnesium silicate



592


called Fosterite. If a silica sol in water is used, the magnesia grain reacts to form magnesium hydroxide. The reaction with silica then proceeds by a different phase diagram. The firing temperature must be raised to almost 2000 °F (1100 °C) before the cold crush strength increases with increasing firing temperature. When an organosol is used, the cold crush strength increases with increasing firing temperature immediately, as expected. Currently, there are now greater demands on those industries in which colloidal silica has been used in the past to develop higher quality products. Thus, a cement to which colloidal silica was added to improve its strength properties years ago must now be UV-resistant and also have better than 9 0 % reflectivity (38). One application of current interest is in the area of papermaking (39-43). Colloidal silica is mixed with starch and slurried paper fibers. It is then formed into paper on the wire of a paper machine. The addition of the silica sol to the system gives improved dewatering of the flocced slurry as well as a high retention of the paper fines and fillers. The result is lower heating costs for drying the paper and better mat formation. Considerable savings can be realized for the papermaker using this system. Greater retention properties mean that more recycled, and therefore cheaper, paper can be added to the paper furnish (formula) without sacrificing strength, because recycled paper contains more fines, and paper strength depends on fiber-fiber interactions.

Conclusions Where will future applications come from? One source is universities, and a second is extension of existing applications. Some applications of colloidal silica originating in universities include the following: • grinding aid for pharmaceutical formulations (Modena University, Modena, Italy, 1988) (44) • stabilizing agent for organic compounds subject to temperature-humidity degradation conditions (Hamburg University, Hamburg, Germany, 1989) (45) • mixtures (silica sol + montmorillonite clay) to give pillared clays with super galleries (Michigan State University, East Lansing, M I , 1988) (46) • catalytic agent for hydrolysis of silane-coupling agents (Nihon University, Tokyo, Japan, 1988 (47) Silica applications are, indeed, a global endeavor. Extending ideas of other applications involves the technique known as an "association of ideas." For example, in U.S. Patent 4,637,867 (48),



29.

PAYNE


593

colloidal silica is used as a dispersing agent (and probably a crystal modifier) for preparing fine crystal particles of maleic anhydride. This same idea can be used for making crumb rubbers in elastomer systems (49) into fine-grain emulsions i n photographic systems (50). One might argue that silica sols can easily be used as a dispersing agent, but that this kind of argument does not apply to other systems. The use of colloidal silica as a frictionizing agent, however, shows that the technique works for other systems. Historically, silica sols have been used in paper antiskid applications, floor waxes, hot pressing railroad engine drive wheels, and polishing applications. One Japanese researcher used the frictionizing properties of silica for improving nonwoven fiber black board erasers. Extending this same idea, why not use silica sols for cleaning cloths and floor mops or for rubber or nonrubber pencil erasers? Historically, colloidal silica has been tried i n many applications. In many cases, the reason that it is not used is not that it didn't work, but the cost of the products is more than the customer wants to pay for improvements. Colloidal silica has been used in the making of opals, in the balancing of large-diameter industrial saws, as an anticaking agent for explosives, and as a frictionizing agent for baseball bats to improve the hitting performance of minor league players. Colloidal silica will continue to be a versatile product with an applicability limited only by the imagination of the researcher.

References 1. Graham, T . J. Chem. Soc. 1862, 15, 216. 2. Graham, T . J. Chem. Soc. 1864, 17, 318. 3. Iler, R. The Chemistry of Silica; Wiley-Interscience: N e w York, 1979; pp 415-438. 4. Bungenburg de Jong, H. G. In Colloid Science;H.R.Kruyt, E d . ; Elsevier: N e w York, 1949; V o l . Π, pp 1-5.

5. Iler, R. The Colloidal Chemistry of Silica and Silicates; Cornell University Press: N e w York, 1955; p 87. 6. Hauser, E . A . Silicic Science; V a n Nostrand: Princeton, N J , 1955; p 54.

7. Fremy, E . Ann. Chem. Phys. 1853 (3), Bd. 38, S 312-344. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Graham, T . Ann. Chem. 1862, Bd 123, S 8 6 0 - 8 6 1 . Schwerin, B . U.S. Patent 1,132,394, 1915. Bird, P. U.S. Patent 2,244,325, 1941. White, J . F . U.S. Patent 2,285,477, 1942. White, J . F . U.S. Patent 2,375,738, 1945. Trail, H . S. U.S. Patent 2,572,578, 1951. Trail, H . S. U.S. Patent 2,573,743, 1951. Bechtold, M F.; Snyder, Ο. Ε. U.S. Patent 2,574,902, 1951. Rule, J. M. U.S. Patent 2,577,485, 1951. Griessbach, R. Chem. Ztg. 1933, 57, N r 26, S 2 5 3 - 2 6 0 , 2 7 4 - 2 7 6 .

18. Iler, R. The Colloidal Chemistry of Silica and Silicates; Cornell University Press: N e w York, 1955; p 89. 19. Wilson, I. V . U.S. Patent 2,643,048, 1953.



594 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50.


Collins, P. F . U.S. Patent 2,380,945, 1945. Monsanto Technical Bulletin 1-237, Monsanto Silicas for Industry, 1962. Iler, R. U.S. Patent 2,597,871, 1947. Iler, R. U.S. Patent 2,726,961, 1955. Talalay, A . et al. U.S. Patent 2,926,390, 1960. McClellan, W . R. U.S. Patent 3,415,886, 1968. Stiles, A . B.; McClellan, W . R. U.S. Patent 3,497,461, 1970. Sowards, D . M . ; Stiles, A . B. U.S. Patent 3,518,206, 1970. M c C l e l l a n W . R.; Stiles, A . B . U.S. Patent 3,678,139, 1972. Callahan, J. L. U.S. Patent 2,974,110, 1961. Callahan, J. L.; Szabo, J. J.; Gertisser, B. U.S. Patent 3,322,847, 1967. Walsh, R. J.; Herzog, A . H . U.S. Patent 3,170,273, 1965. Sears, G . W . U.S. Patent 3,922,393, 1975. Nippon Steel Corp., Japanese Patent 57/192,222, 1982. Toshiba Silicon Company, L t d . Japanese Patent 60/166,355, 1985. Asahi Glass Company, L t d . Japanese Patent 60/137,939, 1985. Smith, T. W . U.S. Patent, 4,252,671, 1979. Bikadi, Z.; Guder, H . European Patent E P 390276, 1989. Page, C. H.; Thanavala, D . N . ; Thombare, C . H . ; Kamat, R. D . ; Bapat, V . S. Indian Patent 163,979, 1988. Batelson, P. G . Canadian Patent 1,154,564, 1983. Andersson, K.; Andersson, K; Sandstrom, A ; Stroem, K.; Basla, P. Nord. Pulp Pap. Res. J. 1986, 1 (2), 2 6 - 3 0 . Johnson, K. A . U.S. Patent 4,643,801, 1987. Sofia, S. C.; Johnson, Κ. Α.; Grill, M . S.; Roop, M. J.; Gotberg, S. R.; Nigrella, A. S.; Hutchinson, L . S. U.S. Patent 4,795,531, 1989. Rushmere, J . D . U.S. Patent 4,798,653, 1989. Forni, F.; C o p p i , G.; Iannuccelli, V.; Vandelli, Μ. Α.; Cameroni, R. Acta Pharm Suec 1988, 25 (3), 173-180. Krahn, F . U . ; Mielck, J . B. Int. J. Pharm. 1989, 53 (1), 2 5 - 3 4 . M o i n i , Α.; Pinnavaia, T. J . Solid State Ionics 1988, 26 (2), 119-123. Nishiyama, N . ; Asakura, T.; Houe, Κ. J. Colloid Interface Sci. 1988, 124 (1), 14-21. Herbst, R. U.S. Patent 4,637,867, 1987. Payne, C . C . , unpublished data. Saleck, W . ; Himmelmann; Huckstadt, H . ; Meyer, R. Belgian Patent 766095, 1971.

RECEIVED for review February 19, 1991. ACCEPTED revised manuscript March 24, 1992.


Applications of Colloidal Silica: Past, Present, and Future - Advances

Recommend Documents