Platinum black sinters for heat exchangers at very low temperatures

We have investigated a series of Pt black sinters for use as heat exchanger s to cool liquid or solid helium to temperatures below 1 mK. They had thick nesses between 60 and 80 mu m and specific surface areas up to 39.7 m(2)/g and 304 m(2)/cm(3). The sintering was on highly polished Cu surfaces of 12. 7 x 15.2 mm(2), a geometry close to one we plan to use in neutron scatterin g experiments from solid He-3. The electrical resistivity of one broken pie ce of sinter was about 60 mu Omega cm which should be sufficient to give go od thermal contact internally. Since the sinters were bonded very well to t he copper surface, good thermal contact between the helium and the bulk met al is expected even at very low temperatures. (C) 1999 Elsevier Science Ltd . All rights reserved.