Aluminum-filled epoxy resins

We will be talking about the casting process using molding plaster of pahs as the molding medium. Another easting material that we will be discussing is aluminum filled epoxy resin. Both are thermoset materials. 

These resin cement systems require only moderate capital investment, yet can yield dramatic results. For example, the many thousands of cracks in the Los Angeles City Hall produced by the 1971 earthquake were repaired by the use of 20 thousand gallons of an aluminum and ceramic filled epoxy resin mortar.— Likewise, wood whose cracks have been sealed by polyurethane mortars is suitable for continuous lathe cutting for veneer manufacture. 

Of course you should be warned that a plaster mold will not last as long as one made from epoxy resin. Plaster tends to be brittle around the edges of the mold cavity. And chunks can easily chip away when removing finished parts. You will be lucky if you get more than 1 or 2 shots out of a plaster mold, but the cost of the plaster is so minimal tliat it is really the only way to learn how to produce molds using the casting method. Save the aluminum filled epoxy for those molds you plan to use a lot. 

A few examples of thermosetting materials are epoxies often used for mold making and tools. In fact, we will be discussing the use of aluminum filled epoxy to make molds later in the book. Melamine, (Dishes are often made of melamine). Phenol resins are commonly used in higher temperature and strength applications such as home appliance handles and parts. Other uses for phenol resins would be distributor caps, coil tops, phone housings and tool housings to name a few. 

The interaction between these films and bulk epoxy resin was assessed by immersing an aluminum mirror coated with an air-dried primer film in a Petri dish filled with the epoxy resin, heating the dish in an oven at 100°C for 1 h, allowing the dish to cool overnight, and then extracting any unreacted material from the surface of the mirror by MEK extraction. Figure 6A is the reflection spectrum of a relatively thick film (ca. 3 / n) of neat DGEBA resin (cast onto polished aluminum from a 3% solution in toluene), and Fig. 6B shows the RAIR spectrum obtained from the mirror that was primed, heated in resin, and extracted. The... 

Major results. Figure 14.7 shows that the resistivity of aluminum-filled PMMA changes abruptly. Smaller volumes of filler contribute a little to resistivity but, after certain threshold value of filler concentration, further additions have little contribution. A similar relationship was obtained for nickel powder the only difference is in the final value of resistivity, which was lower for nickel due to its higher conductivity. The same conclusions can be obtained from conductivity deteiminations of epoxy resins filled with copper and nickel. Figure 14.8 shows the effect of temperature on the electric conductivity of butyl rubber filled with different grades of carbon black. In both cases, conductivity decreases with temperature, but lamp black is substantially more sensitive to temperature changes. Even more pronounced changes with temperature were detected for the dielectric loss factor and dissipation factor for mineral filled epoxy." ... 

Molds can range from hardwood for short runs to filled and unfilled high temperature polyester (TS) and epoxy resins, cast solid urethane, sprayed metal, cast aluminum, cast porous aluminum, and machined steels. The... 

Aluminum powders have been added to acetals and nylons to produce conductive moldings suitable for plating. Epoxy resin formulations that are highly filled with aluminum have been used to cast tools and guides and for producing metal cements and coatings. 

Figure 106. Flame-sprayed aluminum oxide coating on steel, with contrast enhanced by Pt/02, BF. The sample was impregnated with epoxy resin before sectioning and then mounted in epoxy resin. The gap at the boundary between the ceramic and the metal (see arrows) is filled with resin, which indicates that this defect was already present before sectioning. The impregnated cavities are dark, the aluminum oxide is gray, and the steel substrate is bright.

As epoxy and silicone rubber are completely immiscible, the addition of a compatibilizer is necessary to obtain a satisfactory dispersion of the rubber in the resin. The main objective of Kasemura and coworkers [216] was to find an appropriate surface-active agent to reduce the interfacial tension between the resin and the rubber, in order to compatibilize the two components. These authors achieved adequate compatibility in the epoxy resin with the use of a polyester-modified silicone oil to disperse an RTV (room temperature vulcanizing) silicone rubber or silicone diamine. The results showed that the impact fracture energy of the resin was increased by the addition of the RTV silicone rubber, up to two times that of the unmodified resin, whereas the addition of silicone diamine had almost no effect, possibly because the molecular weight was too low. Moreover, T-peel strengths of aluminum plates bonded by epoxy resin filled with RTV silicone rubber and with silicone diamine effectively increased with the silicone content, showing a maximum at 10-20 pph. By scanning electron microscopy, many particles of silicone rubber, 1-20 xm, were observed across the whole of the fracture surface. 

Iwo-component adhesives that are used for household applications differ quite strongly as to their properties. For instance, there are epoxy resin adhesives that are very well suited for bonding glass, china, ceramics and metals. They set ss-clear, are dishwasher-safe, and therefore exceptionally well suited for repairing dishes or similar household articles. Usually, the two components resin (epoxy) and hardener (amine or mercaptan) are filled in aluminum tubes or plastic double syringes and are mixed before application according to the directions for use. Other two-component adhesives are based on meffiacrylate and contain a powder hardener (dibenzqyl peroxide in gypsum). These adhesives bond materials such as stone, plastics, ceramics, and metal ... 

An air-permeable plate can be an epoxy resin filled with aluminum grit. The advantage of this material is that no bore holes have to be drilled. The disadvantage is the low stiffness and the relatively bad thermal conductivity. 

Other filled resin systems that require a coupling agent include highly filled sand cores with ftiran urea-formaldehyde and urethane resins in the foundry industry highly filled polymer concrete where polyester and epoxy binders are used to bond aggregate and cultured marble, cultured onyx, and cultured granite, where a highly filled thermoset resin is used to bond and aluminum trihydrate. 

Table 2 lists thermal conductivity values for several metals as well as for beryllium oxide, aluminum oxide, and several filled and unfilled resins. Fig. 2 shows the thermal conductivity for an epoxy resin as a function of volume fraction of heat-conductive filler. 

The best current 100% solids epoxy adhesives contain about 70% aluminum oxide by weight and give thermal conductivities in the range of 0.8-1 in the English units shown in Table 2. For convenience, a conversion chart is included in Table 2 to permit conversion to any other set of units. The k values for the best alumina-filled epoxies are 10-12 times greater than for unfilled epoxy resins, but are still much lower than for pure metals or solders. Nevertheless, heat flow is adequate for bonding most components. For example, an adhesive with a thermal conductivity of 0.91 and a bond thickness of 3 mils would be able to transfer about 20 W/cm of surface area, with a AT only about 10 C above the heat sink temperatures ... 

In the following sections, some work is presented in which the properties of nano- and microparticle filled composites were determined under variation of the filler contents. These materials were made on the basis of standard epoxy resins cured by amine hardeners. The nanofillers were aluminum oxide (AljOj, 13 nm), titanium dioxide (Ti02, 300 nm and 20 nm) and also calcium silicate (CaS103,5-10 /xm) microparticles. All these fillers are commercially available as powders. The composites were prepared by mechanical mixing using a Dissolver mixing device, as shown in Figure 3. 

K would cause a AT of almost 100 °C. For at least two decades, alumina and crystaUine silica have been used to boost the thermal conductivity of epoxy resins. When highly conductive fillers such as boron nitride, aluminum niliide, and diamond powders become commercially available, these materials have been incorporated in adhesive compositions. The expected target was the attainment of kg values of at least 10 W m K if not better. Such high values have been claimed for diamond-filled adhesives but they remain currently questionable with regard to the experimental results. summarized in the graph of Fig. 12.18. 

A comparison of critical temperature differences of resins filled with several ceramic particulates is shown in Figure 4. The volume fraction of all these composites is 34.2%. The critical temperature difference of epoxy filled with hard particulates was classified into three groups on the basis of thermal shock resistance. Composites filled with a strong particulate, such as silicon nitride or silicon carbide, showed high thermal shock resistance. Some improvement in thermal shock resistance was recognized for silica-filled composites. Composites filled with alumina or aluminum nitride showed almost comparable or lower resistance compared with the neat resin. 

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