S I LI C O N E S THERE’S MORE TO IT THAN YOU THINK. HDK ® – PYROGENIC SILICA

CREATING TOMORROW’S SOLUTIONS

HDK ®

WHETHER TOP PERFORMANCE, INTEGRATED SOLUTIONS OR GLOBAL SERVICE – WE MEET YOUR INDIVIDUAL REQUIREMENTS

Contents Competence and Performance Perfect Properties HDK® Applications Production Processes Chemical Structure Individual Viscosity Reinforcement Where It’s Needed Optimum Flow Properties A Survey of Product Data Physicochemical Properties of HDK® Grades Applications and Effects Customized Packaging WACKER at a Glance

You want to gain a competitive lead by maximizing product capabilities and at the same time make your production processes as efficient as possible? Then HDK® is the right choice for you. This pyrogenic silica boosts performance in every respect. Whether in the form of corrosion-protection coatings or high-resolution printed images – many different products make a lasting impression with exceptional performance levels. The secret behind this variety of excellent properties is HDK®.

WACKER started producing pyrogenic silica over thirty years ago and has continued to develop it ever since. HDK® is now a performance enhancer that will allow you to optimize a whole range of product properties. HDK® gives you perfect control over thickening, thixotropic and flow properties, and makes for optimum performance in thermal insulation, reinforcement and chemical-mechanical planarization. In applications for an extremely wide range of industries, from foods and cosmetics, pharmaceuticals, through paints and surface coatings, composites, adhesives and sealants, elastomers and toners, to paper coatings.

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All this is backed up by 40 years’ experience in silicon chemistry, a complete product range, uniformly high quality standards and comprehensive individualized service. WACKER has also prepared for continual market growth by expanding its Nünchritz site for the development of silicon-based products and boosting silica production capacities. With three production sites, we are now one of the world leaders in the manufacture of pyrogenic silica. You can count on continuity of supplies from us, and rest assured that we will stay one step ahead of market needs.

A Partner with Initiative In WACKER SILICONES, you have a globally active technological leader, and an innovation partner at your side. We understand your needs precisely, and develop integrated solutions that reinforce your competitiveness and open up future markets for you.

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HDK ® ADDS PERFECTION TO YOUR PRODUCT PROPERTIES

WACKER SILICONES has developed a wide range of HDK® grades for customizing product properties to specific applications. Fascinatingly Versatile Even though HDK® pyrogenic silica is an established and highly successful product, WACKER SILICONES continues to push forward with its R&D. There are always new potential solutions that can further boost product performance and quality. The extensive selection of available hydrophilic and hydrophobic HDK® grades and HDK® dispersions offer a highly versatile and comprehensive solution to a wide range of needs.

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The key uses of HDK® are as rheology control and reinforcing agents, thickeners and flow enhancers. The table opposite shows what effects amorphous silica has in various fields of application. Our HDK® brochures on individual applications will tell you about the benefits for specific application areas and the special advantages for your product. You can order them directly from WACKER SILICONES. Or visit us on the internet at: www.wacker.com/hdk Impressive Expertise WACKER SILICONES offers system solutions. That means that in addition to our applications-oriented products, we also offer customer-oriented service through our technical centers and sales subsidiaries. We have a local presence worldwide.

Our services include • Technical support by experts • Laboratory support to optimize your products and formulations • Joint R&D projects • Tailored pyrogenic fumed silicas with customized properties • Information material, product data sheets and up-to-date publications

Applications of HDK® Field of Application Unsaturated polyester PVC Printing inks Paints and coatings Adhesives and sealants Insulating gels Accumulators CMP Natural and synthetic rubber Silicone elastomers Grouting compounds Toners and developers Cosmetics, pharmaceuticals, animal feed and foods Bulk materials Paper coating Textile impregnation

Effect of HDK® Thickening, thixotropic agent, antisedimentation Thickening, thixotropic agent, antisedimentation, anti-adhesive agent, flow improver, improvement of dielectric properties Thickening, thixotropic agent, antisedimentation, regulation of water content, improved brilliance and contrast Thickening, thixotropic agent, antisedimentation, in powder coating systems, additional optimization of flow and electrostatic application properties Thickening, thixotropic agent, antisedimentation, processing auxiliary, adhesion improver Thickening, thixotropic agent, water repellency Thickening, thixotropic agent Mechanical planarization Reinforcement Reinforcement, increase of dielectric properties Reinforcement, thixotropic agent Free-flow agents, external charge control for positive and negative systems, self-cleaning Thickening, thixotropic agent, antisedimentation, free-flow agents, carriers for actives, tableting aids Free-flow agents, processing auxiliaries, flow enhancers Adsorptive binding of the liquid ink, fixing of the ink colorant or pigments Stabilization

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THE EFFECTIVENESS OF HDK ® IS A RESULT OF THE PRODUCTION PROCESS

Reactor

Air

Molecules

SiO2

SiO2

SiO2

SiO2

Protoparticles

Primary particles

Aggregates

Agglomerates

>1,500 °C SiCl 4+ 2H2 + O2

SiO2 + 4HCl

HDK pyrogenic silica Formation in a flame ®

WACKER has been producing pyrogenic silica for the world market since 1968, and has continually optimized its production processes ever since. HDK® is produced in multiple sites by an integrated, efficient and environmentally compatible process that saves energy and raw materials.

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Hydrophilic HDK® with a Large Surface Area The production parameters are responsible for the excellent properties of hydrophilic, pure and odorless HDK®. Pyrogenic silica and hydrogen chloride are formed by hydrolysis at over 1,000 °C. This is performed by introducing volatile chlorosilanes into an oxyhydrogen flame, producing high-viscosity SiO2 primary particles about 5 – 30 nanometers (10–9 m) in size. These particles have a smooth surface that is not microporous. In the flame, the primary particles fuse together permanently to form large units, or aggregates (100 – 1,000 nm in size). That is to say, individual primary particles only exist in the reaction zone itself. On cooling, the aggregates mechanically entangle to form agglomerates, known as tertiary structures. They are about 1 – 250 micrometers (10-6 m) in size and the inhalable fraction is less than 1%.

HDK® agglomerates have a special feature: they are open-structured and therefore mesoporous. They also have a very high BET specific surface area because of the small diameters of the primary particles that are fused together in the aggregates, and the large accessible surface areas of the aggregates and agglomerates. This large surface area-to-mass ratio causes intense inter-particular interactions, which are the result of attractive dispersion and dipolar forces. And that is precisely the reason for the outstanding rheological effect of HDK®. Important Note: The terms primary particles, aggregates and agglomerates are taken from DIN 53206 part 1 (08/72). Aggregates are defined as primary particles that have amalgamated to form a planar or angular structure; these aggregates cannot be further disintegrated. Agglomerates are defined as collections of primary particles that have fused to form a face-to-face sintered structure.

Hydrophobic HDK® with Modified Surface Hydrophobic HDK® is available in a wide range of grades to meet different requirements. The hydrophobic agents are applied with a gas phase to distribute them uniformly on the silica particle surfaces. Controlled quantitative chemical addition of the modifiers to the silica surfaces is achieved by means of hydrolysis-resistant Si-O-Si bonds. The degree of modification is ensured by precise monitoring of process parameters, such as volume flow rate, temperature and residence time. Uniform product quality is ensured by almost real-time process analysis, such as carbon-content determination.

Typical modifiers include: • Organochlorosilanes, such as dimethyldichlorosilane • Polydimethylsiloxanes • Hexamethyldisilazane • Long-chain alkylsilanes, such as octylsilanes High-Stability Aqueous Dispersions HDK® dispersions are highly stable against, for example, sedimentation and gelling. This is the result of efficient colloidal stabilization combined with high shear forces during dispersion of the silica.

The colloidal stability of the dispersions is ensured by electrostatic stabilization and steric stabilization if appropriate. During dispersion, high shearing energy is introduced by means of high-speed shearing units, such as rotor-stator systems. To ensure product quality, the progress of dispersion is checked continually by various analytical methods, including particle size determination by photon correlation spectroscopy, laser diffraction or zeta potential measurements.

Production of hydrophobic HDK®

Si

OH +

Si

∆T

Si Si

O

–XH X X = Hal, O-Alk, OH, O2/2SiR2 7

TOP PERFORMANCE HAS A SPECIAL CHEMISTRY

Hydrophilic HDK®

Hydrophilic HDK®

Amorphous SiO2

OH Si O O O O O Si O O Si O O O Si O

5 – 50 nm

OH Si O O O Si O O Si O O O O Si O OH O

OH OH Si O O O O O Si O O Si O O O Si O

OH

Reactive isolated silanol groups Large surface area 50 – 400 m2/g No micropores

Chemical Structure HDK® is made up of SiO4/2 tetrahedrons. These tetrahedrons are joined together by siloxane bridges (Si-O-Si bonds). About every second Si atom on the surface of HDK® bears a hydroxyl group and thus forms a silanol group (≡Si-OH).

H atom

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C atom

O atom

Si atom

Hydrophilic Property HDK® receives its outstanding hydrophilic properties from the Si-OH groups and the polar Si-O-Si backbone. The silanol groups (Si-OH) act as reactive centers and form hydrogen bonds to other polar substances. Hydrophilic HDK® has ca. 2 silanol groups per 1 nm2.

Hydrophobic HDK®

Hydrophobic HDK®

Amorphous SiO2 Me

5 – 50 nm

O

Me Me

Si O

Me

O

O Si Si O O O O O O O Si O Si O Si Me O O

Me Si Me

O

Me

Me O Si Me Si O O O O O Me Si O O Si Si O Me O O O Si O

O

Si

Me Si O O O O O O Me Si O O Si Si O Me O O O Si

O

O

Si Me

Me

O

Si Me

Me

Large surface area 50 – 400 m2/g No micropores

Hydrophobic Properties If the Si-OH groups are allowed to react with organosilicon compounds, hydrophobic properties are imparted to HDK®. Hydrophobic HDK® has ca. 1 silanol group Si-OH per 1 nm2. Highly hydrophobic HDK® has ca. 0.5 Si-OH groups per 1 nm2. The hydrophobic treatment reduces or eliminates the moisture absorption of the silica. Other basic properties of the pyrogenic amorphous silica are not changed.

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Intensity [cps]

50

40

35

30

25

20 15 2 theta [degrees]

Toxicological Properties If used as recommended, HDK® is not known to have any harmful effects on humans. HDK® does not irritate the skin. Degreasing of the skin may occur after prolonged contact. Unlike crystalline silica, there are no indications of HDK® causing silicosis.

X-ray diffraction diagram of amorphous HDK®

Intensity [cps]

Electron diffraction diagram of amorphous HDK®

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In animal experiments there are no indications of reproductive effects. Amorphous silica such as pyrogenic silica, precipitated silica and silica gel is not carcinogenic (Group 3 “not classifiable as to its carcinogenicity to humans,” IARC Monograph Vol. 68, 1997.

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Electron diffraction pattern of crystalline quartz

Amorphism HDK® is a completely amorphous product. This is proved by the absence of a sharp X-ray diffraction pattern and a characteristic electron diffraction diagram for amorphous structures. The HDK® X-ray diffraction diagram, unlike that of crystalline quartz, shows a broad, unresolved diffraction structure. This is typical of amorphous structures. The electron diffraction diagram of HDK® has a diffuse scattering pattern. In a reference measurement with crystalline quartz, distinct, well-resolved scattering signals can be seen.

45

40

35

30

25

20 15 2 theta [degrees]

Further information on toxicology is given in the appropriate material safety data sheets.

X-ray diffraction pattern of crystalline quartz

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Viscosity ␩

HDK ® PRECISELY ADJUSTS VISCOSITY AS REQUIRED

Shear rate ␥ⴢ

Flow curve of a system filled with HDK®

Precise Thickening and Thixotropic Properties The shear-thinning or thixotropic effect of HDK® offers you perfect control over the flow properties of liquid systems. The system thus has precisely the viscosity required for the particular application. In shear-thinning systems, the viscosity is reduced by shearing loads. The shearthinning liquid can also have a yield point, and therefore, in a stationary state, form a viscoelastic solid (gel structure). The shear-thinning of non-Newtonian liquids is generally a reversible process. If, when the shear force is removed, the system returns to its original viscosity after a time delay, the behavior is called thixotropic.

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Efficient Increase of Viscosity If HDK® is dispersed in a liquid, a threedimensional network can form as a result of forces of attraction between the HDK® aggregates. This network, together with the immobilized liquid within the silica aggregates, causes a strong viscosity increase. Since HDK® has a particularly high structure, it is very efficient and even small quantities are enough to provide a high viscosity. The forces of attraction in hydrophilic HDK® consist mainly of van der Waals forces such as dispersion or dipolar attractions. If it is allowed to physically adsorb oligomeric or polymeric substances, such as binders, it can provide further effects, such as polymer bridging or steric stabilization. In the case of hydrophobic HDK®, overlapping silylated surfaces result in additional hydrophobic interactions and forces of adhesion.

Effective Reduction of Viscosity Liquids containing HDK® as an additive undergo a reduction in viscosity when subjected to shear forces, such as stirring, spraying or spreading. Shear forces break down the three-dimensional silica network. The silica aggregates can move with respect to one another and the immobilized liquid volume becomes smaller. The stronger the shear force, the stronger is the viscosity-reducing effect. If necessary, the viscosity can even be reduced to a minimum plateau value. Once shearing stops, the liquid regains its original viscosity. The time it takes for this structural relaxation to occur depends on the type and amount of the silica used and the physicochemical properties of the liquid, for example the viscosity or polarity of the pure liquid.

Stress [N/mm2]

HDK ® SELECTIVELY IMPROVES PROPERTIES

Fracture

10

With 30 % HDK®

2

Without filler 100

500

Strain [%]

Deformation

Tensile-stress/strain diagram of silicone elastomers with and without HDK®

Tailored Elasticity For processors of natural and synthetic rubber and of silicone elastomers to obtain the best results, their products must have precisely defined mechanical properties, such as tensile strength, elongation at break and tear strength. The required system properties can be obtained with HDK®.

Optimum Reinforcement The outstanding reinforcing properties of HDK® are the result of its huge specific surface area and the numerous points of interaction with the polymer chains in the elastomer network. The specific particle structure of HDK® distributes the mechanical stresses and forces throughout the elastomer network and restricts the entropy space of the polymer chains. This process increases the elastomers’ strength, elongation at break and load bearing capacity. High Sag Resistance In non-polar silicone rubber, HDK® can be used as both a reinforcing thickener and rheological additive. The pronounced thickening effect of hydrophilic HDK® provides the necessary sag resistance, so that low-viscosity systems do not run off vertical surfaces.

Good Processability In silicone elastomers, hydrophilic HDK® provides excellent reinforcement while increasing the viscosity, which may make it difficult to process. Process auxiliaries such as low-molecular plasticizers are used here, which block the interaction between the HDK® particles by adsorption and reduce the viscosity. This provides the system with the required excellent processing properties. Hydrophobic HDK® grades can be used to obtain desired properties, i.e. high tear strengths together with good processability. WACKER SILICONES offers grades with modified structures for this purpose.

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HDK ® ENSURES OPTIMUM FLOW PROPERTIES

Versatile Applications HDK® can optimize the flow properties of different powder-form cohesive solids. And it is economical, since even tiny amounts of HDK® greatly improve the flow properties of such substances. Typical applications include bulk materials and powders for cosmetics, foods, animal feeds, pharmaceutical or fireextinguisher powders. WACKER SILICONES also offers special highly sophisticated HDK® grades for improving the flow and electrical charging properties of toners, developers and powder paints for automotive finishes and industrial coatings.

Free Flow When HDK® is mixed with the solid powder, it is distributed on the surfaces, separating the individual powder particles from one another. This allows the powder to flow freely.

Effective Drying The high specific surface area of hydrophilic HDK®, together with its high surface energy, allows moisture to bind effectively to the surface of hygroscopic powders. This drying effect enhances the powder’s flow properties. Typical applications include finely divided food solids, such as table salt.

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PACKAGED TO CUSTOMERS’ NEEDS

Packaging Units The smallest packaging unit leaving our production is the pallet. Each pallet is shrink-wrapped in PE foil to protect the HDK® in the multilayer valved paper bags within against moisture. This allows the product to be stored for several months in dry conditions. If the shrinking foil is damaged or single bags are removed, care must be taken to protect the remaining bags / individual bags against moisture by either wrapping in plastic or other appropriate measures. The quantity of bags per pallet depends on the HDK® grade and its bulk density. Bags are available in various weights to suit customer demands. The data sheet indicates which form of packaging is used for a particular product.

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Big Bags Special HDK® grades are available in Big Bags. These woven super sacks are delivered on an individual pallet. The Big Bags are also shrink-wrapped in polyethylene film as reliable moisture protection and to ensure stability during transport. Another advantage of this form of container is dust-free HDK® processing. Bulk Vehicles WACKER SILICONES offers delivery in bulk vehicles. Since the full load must be accepted, this form of delivery assumes that the customer has a storage silo big enough to receive the entire delivery.

Supply of HDK® Dispersions All HDK® dispersions are delivered in 200-liter PE drums, or alternatively in road tankers. Handling and Product Safety HDK® is not classified as a hazardous substance as defined by the German chemicals law (Chem G) and the law on the transport of hazardous goods (GG BefG). Further information on toxicology is given in the appropriate material safety data sheets. Detailed information on handling can be found in the product data sheets.

6173e/08.10 supersedes 6173e/10.05

S I LI C O N E S

Wacker Chemie AG Hanns-Seidel-Platz 4 81737 München, Germany [email protected] www.wacker.com/hdk

Wacker Chemical Corporation 3301 Sutton Road Adrian, MI 49221-9397 USA Tel. +1 517 264-8500 Fax +1 517 264-8246 [email protected] www.wacker.com/hdk

Wacker Chemicals Trading (Shanghai) Co. Ltd. 31 F., Bank of China Tower 200 Yin Cheng Road Central Pudong Shanghai 200 120 China Tel. +86 21 6100-3400 Fax +86 21 6100-3500 [email protected] www.wacker-chemicals.com.cn