No abstract

No abstract

No abstract

Immersion tin is widely used as a lead free surface finish in the printed circuit board technology. Tin prevents the underlying copper from corrosion and preserves its solderability during a long storage and lead-free assembly processes. Investigated immersion tin coatings were deposited on copper foil from thiourea-type baths with hydrochloric acid addition (SnHCl coatings) or methanesulfonic acid addition (SnMSA coatings). Obtained coatings were investigated in the as deposited state and after aging (4 h at 155 8C, in air). The scanning electron microscopy studies revealed differences in structure of tin samples deposited from different baths. Results of polarization and impedance investigations indicated that as deposited SnHCl coatings had better corrosion resistance in 0.5 M NaCl solution than SnMSA coatings. The aging resulted in the improvement of the corrosion resistance of thinner coatings (0.2 and 0.5 mm thick SnHCl and 0.3 mm thick SnMSA), which were thoroughly converted into Sn-Cu intermetallic (IMC) phases. In contrary, thicker coatings exhibited some worsening of the corrosion resistance upon aging. The solderability of all as-deposited tin coatings was acceptable, but decreased after aging, especially for thinner coatings, showing the through conversion into Sn-Cu IMC phases.

No abstract

In this work, the results of studies on the preparation of carbon fibres (Tenax HTA40) for composites with an aluminium alloy matrix are presented. In the first step of preparation, the epoxy sizing was removed to assure adhesion of the Ni-P coating as a barrier to prevent the formation of brittle Al4C3. Removal of the sizing also decreases the risk of gas formation underneath the metal coatings in contact with the liquid metal matrix. Methods of sizing removal included annealing in air (300-600°C) and dissolving in solvents (acetone, toluene) and in inorganic solutions (HNO3, H2O2, NaOH), followed by SnCl2/PdCl2 activation are described. It was found that the chemical removal of epoxy sizing from carbon fibres is not an appropriate method for further studies on the electroless metallisation of carbon fibres. The thermal treatments in air atmosphere seem to be more useful for removing epoxy sizing. The result of the present studies was the optimisation of the temperature of the annealing of carbon fibres as 400-500oC. The morphology of the carbon fibre surface before and after sizing removal was characterised using SEM and in terms of the mass loss. A glycine-buffered electroless bath was used for the Ni-P coating of the fibre with a wide range of deposition rates and alloy compositions (2-12 wt% P). An advantage of electroless plating is that the process is carried out without electrical current. The coating is deposited as the result of the controlled reduction, which is catalysed by the metal being deposited. Two different pH values of metallisation baths were selected (pH=4.5 and pH=8.5). The time of Ni-P deposition ranged from 5 to 30 minutes. The process parameters were optimised for Ni-P coatings on 1D carbon fibres and 2D/3D woven fabrics. It was found that the process developed can be used for 2D and 3D woven fabrics.

No abstract

No abstract