Sustainable synthesis and manufacturing of silver powder-based metal clay for zero-waste technology applications

In this work, information on the metal clay technique is presented. Silver clays with different metal powder content were produced, and their selected properties were examined. The research part was divided into two parts. In the first part, silver powder was produced by solid state hydrogen reduction. The average particle size of the resulting silver powder falls within the range of 0.5 to 4.5 jm. Next, seven silver clays with different powder to binder ratios were made. Then, samples for testing were prepared from the commercially available silver clay. In the second part, tests of the samples were carried out. The susceptibility of clays to shaping, density, hardness and roughness were examined. A sample with 1% methylcellulose showed a roughness of less than 1 jm. The shrinkage value ranged from more than 30% to less than 5% for the highest and lowest methylcellulose clays, respectively. Tensile strength ranged from 90 to 100 MPa for samples with lower methylcellulose content in the clay and from 30 to 80 MPa for samples with higher methylcellulose content. The highest electrical conductivity was achieved for samples with the lowest content of methylcellulose, reaching almost 80% of the conductivity of bulk silver. The microstructure of the powders and the produced samples were tested. Recycling reactions of reactants have been postulated, to obtain sustainable production by-design. A holistic sustainability assessment is quantified using circular and green metrics as well as life cycle assessment. A material circularity indicator (MCI) of 0.50 and an E-factor of 0.29 were determined, generating environmentally relatively harmless water (84%) and green gases such as O2 and H2 (7%) as waste/by-products. The cost of producing 1 kg of silver powder utilizing the closed-loop technology presented in this paper amounts to euro1103.45.