The electrical properties of BaZrO3 containing 2 to 6 at.% La were investigated. Room-temperature dielectric constants at 1 M c were about 43 and the mean temperature coefficients of K were about -240 ppm per "C. The admixture of La3+ raised the volume resistivity by several orders of magnitude. Values as high as 10" ohm-cm were observed at 500OC. Q values at 1 M c and 500°C ranged between 100 and 400. Wafers 10 mils thick endured 1000-hour life tests at 250' and 35OOC in a field of 60 volts per mil and at 500°C in a field of 30 volts per m.il with good stability. Breakdown strengths as high a s 680 volts per mil were measured for specimens 10 mils thick. The mechanism of conduction was indicated to b e #-type, with La3+ improving resistivity by lowering the hole concentration.
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in the brick lining {15, 30). For example, steel sheet is pickled by a continuous process in tanks 300 feet long handling 25% sulfuric acid at 210°to 220°F. These 300-foot tanks have about 20 expansion joints inserted at regular intervals in the brick lining. INDUSTRIAL APPLICATIONSIt should be helpful to the chemical engineer to list some of the more important applications of corrosion cements in various chemical industries. Brick-lined reactors, storage tanks, absorption towers, fume ducts, fume stacks, floors, sumps, trenches, manholes, and tanks for neutralization of wastes are used throughout the chemical industry in the production of acids, alum, corn products, copper sulfate, dyes, organic chemicals and solvents, fertilizers, insecticides, pigments, plastics, and soaps. Practically all steel mills use brick-lined pickling tanks, stacks, floors, and tanks for neutralization of acid wastes. Food and beverage plants such as breweries, dairies, bakeries, and meat packing plants are using more and more acidproof tile floors joined with furan cement because of stringent sanitary requirements, In pulp and paper mills, digesters, blowoff pits, process tanks, and floors are protected with brick linings joined with resin cements {4-7). The numerous applications of corrosionproof cements in rayon plants are shown in Table I, LITERATURE CITED
Hypereutectic aluminium silicon alloys, e.g. casted AlSi17Cu4Mg, are commonly used in the automotive and aeronautical industries. These alloys consist of hard, abrasive silicon particles in a soft aluminium matrix and thus place high mechanical loads on the tool during machining processes. Polycrystalline Diamond or CVD (chemical vapour deposition) diamond based cutting tools can be used for the high speed machining of these alloys due to their high hardness and wear resistance. Diamond thin film coatings of different film morphologies are commonly applied on cemented carbide tools using Hot Filament CVD. The distinguishing characteristic to other coatings is utmost hardness resulting in high resistance to abrasion, low tendency to adhesion and low friction coefficient. The manufacturing of CVD diamond coated shaft type cutting tools is challenging due to the complex design of the cutting edges and the demanding stress behaviour during tool application. The influencing parameters of substrate type, chemical and mechanical substrate pretreatment as well as diamond film modification on the tool cutting performance are discussed. The manufacturing route of CVD diamond coated thread milling drills is analysed with the use of material and tribological tests. The complex thread manufacturing tools are then applied in the machining of AlSi17Cu4Mg, whereby the tool performance is characterised with respect to their wear behaviour, the process forces and temperatures as well as the workpiece quality.Keywords Machining Á CVD diamond Á Coating Á Wear Á Tool manufacturing Á Thread mill drilling 1 CVD diamond thin films on cutting tools CVD diamond thin films offer the only approach to combine diamond hardness and wear resistance with arbitrary cutting tool geometry. State of the art in diamond tooling is the generation of different diamond thin film systems on cemented carbides distinguished by crystallite size (Fig. 1). CVD diamond coatings are mostly applied on indexable inserts for milling and turning as well as geometrically simple shaft tools. Cemented carbide grades feasible for CVD diamond deposition are limited to a cobalt content of 10 wt% [1][2][3][4].The manufacturing chain of CVD diamond coated cemented carbide tools commences with the identification of a suitable substrate as well as the substrate pre-treatment to remove cobalt from the surface layer and to structure the tungsten carbide with undercuts. This is necessary to prevent a catalytic reaction of cobalt with diamond during film deposition and to provide a mechanical bond between cemented carbide substrate and diamond film. These manufacturing steps are followed by cleaning and diamond seeding measures before CVD diamond deposition is carried out [1].The current state of research of diamond thin film technology on cutting tool substrates comprises diamond film deposition adapted substrate development and treatment, CVD diamond film post-treatment and increased diamond film adhesion by analysing strength and residual stress behaviour. Fine grain cemented ...
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