Mechanical properties of metal-coated cenospheres
Waldemar Pichór, Krzysztof Mars, Elżbieta Godlewska, Ryszard Mania
Quarterly No. 2, 2010 pages 149-153
DOI:
keywords: cenospheres, magnetron sputtering, metallic layers, electroless metallization
abstract The paper presents selected mechanical properties of cenospheres modified with metallic layers. Copper was deposited either by electroless (chemical) method using palladium catalyst or by magnetron sputtering. Nickel was deposited by magnetron sputtering only. Magnetron was supplied by Dora Power System (DPS) which generated sinusoidal pulses with a frequency of 80 kHz. This is why the applied technique can be referred to as Pulsed Magnetron Sputtering. Targets (cathodes) were made of suitable metals, i.e. copper or nickel. The magnetron sputtering process was conducted under an argon pressure of about 0,4 Pa and current intensity not exceeding 0.5 A. A specially designed vibrating support enabled rotation of cenospheres during the deposition. The pressureless deposition of copper was conducted at a temperature of 20oC in three steps. The first one, lasting about 1 hour, consisted in sensitization of the microsphere surface with tin (II) ions in an aqueous soluteon composed of 5 g/L SnCl2 and 30 ml/L HCl. In the second step, the earlier adsorbed tin ions were replaced by metallic palladium (Pdo) in a solution composed of 0.5 g/L PdCl2 and 5 ml/L HCl. The third step, lasting about 6 min, comprised direct deposition of metallic copper from a solution composed of 5 g/L NaOH, 30 g/L NaKC4H4O6, 12 g/L CuSO4.5H2O and 20 mL/L HCHO. Morphological observations and analysis of chemical composition by scanning electron microscopy and energy dispersive X-ray spectroscopy indicated that the magnetron-sputtered nickel and copper layers were homogeneous and compact. The crystallites forming a columnar structure had submicrometric sizes. Electroless copper layers were characterized by random orientation of crystallites. The experimental load-deformation curves were used to determine compressive strength and crushing strength. It has been found that metallic layers, not exceeding 2 μm in thickness, brought about strengthening of the cenospheres. Cracking of the cenospheres was not accompanied by exfoliation of the metallic layers, which suggested good adherence. The effect of increased compressive strength appears particularly important for the envisaged application of cenospheres modified with metallic layers as components of composites.