Material properties scratch resistance

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

The heat resistance and water resistance of the resins are attractive properties for surface coatings but the poor scratch resistance of the materials has limited applications of straight silicone resins. 

Hardness is closely related to strength, stiffness, scratch resistance, wear resistance, and brittleness. The opposite characteristic, softness, is associated with ductility. There are different kinds of hardness that measure a number of different properties (Fig. 5-5). The usual hardness tests are listed in three categories (a) to measure the resistance of a material to indentation by an indentor some measure indentation with the load applied, some the residual indentation after it is removed, such as tests using Brinell hardness,... 

In principle these compounds offer access to materials with AliCh-SiCL and Al203 2Si02 stoichiometries. The latter stoichiometry is equivalent to the Al[OSi(OBu-t)3 (OBu-t)] precursor. The major drawbacks with these materials are their air and moisture sensitivity, and the cost of the starting materials. Although the idealized stoichiometries of the above ceramics products are not those of crystalline aluminosilicates, amorphous aluminosilicate glasses are often important in optical applications or in scratch-resistant coatings. Furthermore, they may offer potential for CVD-type applications. There still remains considerable need for simple precursors to crystalline aluminosilicates, especially for structural applications. Dense, phase pure crystalline ceramic materials are desired for optimal mechanical properties, e.g. ceramic fibers for composite manufacture. 

Regarding the properties required of the solidified materials in 2D printing, the most important properties are generally related to thin material layers, such as color, adhesion to the substrate, hghtfastness, and scratch resistance, whereas in 3D printing, the most important properties are generally related to the bulk material mechanical and thermomechanical properties, for example tensile and flexural properties, impact resistance, and Glass Transition Temperature (Tg). 

CVD is known to polymerize an order of magnitude more easily (Ref. 143) than the analogous bis-allyl carbonate marketed under the designation CR-39 which is the leading material for casting prescription eyewear since decades. The crosslinked homopolymer of CVD exhibits similar properties but with the advantages of much better scratch resistance and higher hardness and modulus. 

Diamond-like carbon since its inception in 1962 has found applications in some very important areas. These applications include coatings used in scratch-resistant optics, razor blades, prosthesis in medical applications electron emission surfaces in electronics as an insulator material for copper heat sinks in semiconductors such as solar cells and sensors for visible to infrared radiations and as structural materials such as deuterated DLC film used for neutron storage in advanced research instrumentation. As technology matures the unique properties of DLC will find new and important applications. 

Figure 8.41 shows the structure of a novel nanocomposite and how it was formed.This nanocomposite has high scratch resistance. It is currently used for an optical lens coating. Its scratch resistance was increased by factor of 3 in the diamond scratch test when compared with conventional hard coatings and by factor of 2 in lens testing where lenses are rotated in drum of abrasive material. These excellent properties are due to a structure which makes both the filler and the matrix a singular, ordered material. 

A closely related mechanical property which has been used extensively in glass literature is the microhardness. Micro in microhardness only indicates that the hardness measurements have been made on a micron scale. Microhardness actually measures only the scratch resistance of the material and thus a scale of microhardness is a scale of the scratch resistances - harder material can scratch the surface of the softer material. One of the widely used scales is Mohs scale of hardness calibrated with the hardness of the hardest material, namely diamond, marked with a value of 10 and with the hardness of the softest material, namely talc, marked with a value of 1. On this scale most oxide glasses register microhardnesses between 5 and 7. In scientific investigations two other scales are used, namely Knoop s hardness number (KHN) and... 

Several nanoscale multilayered materials have been prepared. Techniques of Rutherford backscatteiing, electron microscopy and microanalysis and other metallurgical tools have been used to investigate wear resistant, scratch resistant, microhardness, and spark erosion properties of these nanoscale multilayered materials. Preliminary results indicate that nanoscale multilayered materials with improved thermomechanical, properties can be synthesized for application in the EM gun system. Application of ion beam technology for the synthesis of gradient materials appears to have great potential for design of new materials with improved properties to be used in fabrication of many armament materials. 

The distinct mechanical characteristics of diamond are based on its lattice stmc-ture and electronic properties. It stands out for the highest hardness ever measured for a natural material, for large moduli of bulk and shearing and for a high scratch-resistance. Dislocations are little mobile in its lattice, and the material features a very high surface energy contributing to the hardness as well. 

Wollastonite is not yet used in commercial WPC materials, but it is currently under investigation to further enhance the properties of WPCs. The mineral is used worldwide in many plastic applications providing improvement in stiffness, impact, scratch resistance, lower thermal coefficient of expansion-contraction, and flame retardancy. The unique morphology of wollastonite and the variety size grades available can provide benefits that are not obtained by other minerals. In a number of cases, wollastonite has successfully replaced talc in plastic applications where further improvements in properties such as greater strength and improved scratch resistance were required. 

The aluminum die-cast deck of a mower tractor has been replaced with PC/PBT alloy incorporating molded-in color, saving 3.6 kg of weight and 25% of cost. The same material finds application in tractor hoods. PC/ABS has also been used on the inlet of a vacuum/chipper. Important properties for these applications can be summarized as resists breakage scratch resistance UV resistance injection moldability... 

Possessing both olefinic and non-olefinic characteristic, Hivalloy products are designed to combine the most desirable properties of PP, such as processability, chemical resistance and low density, with many of desirable features of engineoing resins which cannot be achieved with currently available polyolefins, such as improvements in the material s stiffiiess/impact balance, improved mar and scratch resistance, reduced molding cycle time and improved creep resistance. 

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