Alumina-filled resins

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

Figure 5 shows the effects of filler content on thermal shock resistance at c/R - 0.2 for composites of silicon nitride, silicon carbide, silica, and alumina. The thermal shock resistance of resin filled with silicon nitride increases linearly with the volume fraction. The value of the thermal shock resistance is high, especially at higher volume fraction (Vf > 40%), that is, thermal shock resistance reaches 140 K (Figure 5a). The thermal shock resistance of composite filled with silicon carbide increases rapidly with the increase of filler content, and it reaches 135 K at Vf of 40%, which is similar to the case of silicon nitride (Figure 5b). In the case of silica-filled composites there is also an increase, but above a 30% volume fraction a plateau is reached (Figure 5c). Alumina-filled composites show a decrease in thermal shock resistance with filler content, then an almost constant value starting at Vf = 20% (Figure 5d).

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 ... 

Tang G, Wang Z, Ma Q and Zhao D, Study on improving wear resistance of epoxy resin filled with nanometer alumina . Thermoset Resin 2002 17(1) 4-8 (in Chinese). 

Mineral hydrates, such as alumina trihydrate and magnesium sulfate heptahydrate, are used in highly filled thermoset resins. 

Composite Resins. Many composite restorative resins have incorporated fluoride into the filler particles. One commonly used material, yttrium trifluoride [13709-49-4] is incorporated as a radiopaque filler to aid in radiographic diagnosis, and is also responsible for slow release of fluoride from the composites (280). This same effect is achieved with a barium—alumina—fluoro-siUcate glass filler in composite filling and lining materials. Sodium fluoride [7681-49-4] has also been used in composites by incorporating it into the resin matrix material where it provides long-term low level release (281-283). 

Incorporate the neodymium magnet into the body of the paste of graphite-epoxy composite, 2 mm under the surface of the electrode [1] and continue placing the paste until filling all the cavity. Cure the conducting composite at 40°C during 1 week. Once the resin is hardened, polish the surface first with abrasive paper and then with alumina paper. 

Some inorganic particulate fillers have also been considered as toughening agents for epoxy materials. Glass beads, fly ash, alumina trihydrate, and silica were used early on to improve the toughness of filled epoxy resins. Various studies, however, have demonstrated that the fracture energy of filled epoxies reaches a maximum at a specific filler concentration. 

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. 

Bellstein Handbook Reference) AI3-08678 BRN 0878263 CCRIS 876 DImethoxymethyl-phosphIne oxide Dimethyl methanephosphonate Di-methyl methylphosphonate DMMP EINECS 212-062-3 Fyrol DMMP HSDB 2590 Methyl phosphonic acid, dimethyl ester NCI-C54762 NSC 62240 Phosphonic add, methyl-, dimethyl ester Pyrol dmmp. Flame retardant for applications where high phosphorus content, good solvency, and low viscosity are desired lowers viscosity of epoxy resins and unsaturated polyesters filled with hydrated alumina oxide. Liquid bp = 181 , bp20 = 79.6" d ° = 1.4099 Am = 217 nm (e = 13, EtOH) soluble in H2O, Et20, EtOH LDsO (rat orl) > 5000 mg/kg. Akzo Chemie. 

Styrene (St) (Aldrich, 99%) was used as received and /-butyl aciylate (/BA) (Aldrich, 99%) was passed through a column filled with basic alumina. Tris(2-dimethylaminoethyl)amine (MceTREN, 99 %) and tris(2-pyridylmethyl)amine (TPMA, 99 %) are commercially available from ATRP Solutions Inc (www.atrpsolutions.com). ATHPpare resin (ATRP Solutions Inc.), diethyl 2-bromo-2-methylmalonate (DEBMM) (Aldrich, 98%), copper(ll) bromide (Aldrich, 99%), tin(ll) 2-ethylhexanoate (Sn(EH)2) (Aldrich, 95%), N,N-dimethylformamide (DMF) (Aldrich, 99%), methylene chloride (Fisher Scientific), trifluoroacetic acid (TFA) (Aldrich, 99%) and 2,2 -azo-bis(isobutyronitrile) (AIBN) (Aldrich, 99%) were used as received. Fc203 particles (size < 50 nm) were purchased form Aldrich. 

Alumina Trihydrates Alumina trihydrate is used to improve flame retardancy and reduce smoke emissions of specific resin systems. It is a fine, white filler material which, when added in the proper amount, can improve flame retardancy of halogenated or non-halogenated resin systems. When a properly filled RP is exposed to fire, it decomposes into water and anhydrous alumina. The water cools the RP thus slowing the rate of decomposition or burning. 

The specimen holder of an oxygen index apparatus can be coupled to a balance beam for continuous monitoring of the mass loss of the specimen during the combustion. Such an apparatus was used by Methven for studying polyester resins filled with alumina trihydrate and polyester fabrics finished with flame retardants. 

Alumina trihydrate exerts its considerable flame-retarding effect only at a high proportion, i.e. when incorporated as a filler. For this reason, its application is essentially suitable in conventional filled compounds like polyesters, epoxy resins and PVC cable compounds, etc. " . The oxygen index of a polyester resin is plotted in Figure 5.4 against the proportion of this flame-retardant additive. 

In addition to smoke suppressors, reduced-smoking compounds are also available in a ready-to-process state. For example the Envirez grade of PPG Industries is a styrene-free polyester resin filled with alumina trihydrate. Its smoke production is between 10 and 100 according to ASTM E 84 measured in the Steiner Tunnel (cf. Fig. 3.93, Section 3.2.1), and its value in the NBS chamber (cf. Fig. 4.6, Section 4.1.1.4) is 89, while those of the conventional halogen-containing flame-retarded polyesters are 250 to 1100 (smoke production) and 102 (D value). 

An effective flame-retardant for filled epoxy resins is alumina trihydrate. The burning rate and burning time after ignition, according to ASTM D 635 (cf. Section 3.1.5.2), for a basic epoxy resin and for its filled grade with 60 per cent of alumina trihydrate are plotted against the test temperature in Figure 5.11. 

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