A cost-effective, scalable and versatile method of preparing nano-ink without hazardous chemical precursors is a prerequisite for widespread adoption of printed electronics. Precursor-free synthesis by spark discharge is promising for this purpose. The synthesis of platinum nanoparticles (PtNPs) using a spark discharge under Ar, N2, and air has been investigated to prepare highly conductive nano-ink. The size, chemical composition, and mass production rate of PtNPs significantly depended on the carrier gas. Pure metallic PtNPs with sizes of 5.5 ± 1.8 and 7.1 ± 2.4 nm were formed under Ar and N2, respectively. PtNPs with sizes of 18.2 ± 9.0 nm produced using air consisted of amorphous oxide PtO and metallic Pt. The mass production rates of PtNPs were 53 ± 6, 366 ± 59, and 490 ± 36 mg/h using a spark discharge under Ar, N2, and air, respectively. It was found that the energy dissipated in the spark gap is not a significant parameter that determines the mass production rate. Stable Pt nano-ink (25 wt.%) was prepared only on the basis of PtNPs synthesized under air. Narrow (about 30 μm) and conductive Pt lines were formed by the aerosol jet printing with prepared nano-ink. The resistivity of the Pt lines sintered at 750 °C was (1.2 ± 0.1)·10−7 Ω·m, which is about 1.1 times higher than that of bulk Pt.

We have applied spark ablation technology for producing nanoparticles from platinum ingots (purity of 99.97 wt. %) as a feed material by using air as a carrier gas. A maximum production rate of about 400 mg/h was achieved with an energy per pulse of 0.5 J and a pulse repetition rate of 250 Hz. The synthesized nanomaterial, composed of an amorphous platinum oxide PtO (83 wt. %) and a crystalline metallic platinum (17 wt. %), was used for formulating functional colloidal ink. Annealing of the deposited ink at 750 °C resulted in the formation of a polycrystalline material comprising 99.7 wt. % of platinum. To demonstrate the possibility of application of the formulated ink in printed electronics, we have patterned conductive lines and microheaters on alumina substrates and 20 μm thick low-temperature co-fired ceramic (LTCC) membranes with the use of aerosol jet printing technology. The power consumption of microheaters fabricated on LTCC membranes was found to be about 140 mW at a temperature of the hot part of 500 °C, thus allowing one to consider these structures as promising micro-hotplates for metal oxide semiconductor (MOS) gas sensors. The catalytic activity of the synthesized nanoparticles was demonstrated by measuring the resistance transients of the non-sintered microheaters upon exposure to 2500 ppm of hydrogen.

The paper represents the investigations of dimensional and structural properties of nanoparticles produced by pulsed-periodic spark discharge by simultaneous electrical erosion of germanium and tin electrodes in inert atmosphere. Two alloys of GeSn nanoparticles with different mass fractions of tin were obtained by altering the polarity of the electrodes. The nanoparticles’ sizes from 4 to 45 nm were observed. It was shown that the samples consist of core-shell nanoparticles agglomerates, where both β-tin crystals and cubic germanium ones presence as a core; the shell is a mixed germanium tin oxide. Furthermore, a shift of a maximum of Raman peak by 3.5 cm−1 to lower wave numbers with an increase in relative fraction of tin was detected.

Results of an experimental study of the physicomechanical properties of refractory materials for the lining of aluminum electrolyzers are reported. INSTRUMENTATION AND TEST METHODOLOGIESIK-4 and TÉP test complexes and a tensile testing machine equipped with an electric furnace for heating specimens were used in the study of physicomechanical properties of hearth blocks and mixes, refractory and heat-insulating materials for the lining of electrolyzers.IK-4 test complex (Fig. 1), equipped with automatic control and computer-assisted data processing facilities, is used for determining the so-called sodium expansion, thermal linear expansion coefficient (TLEC), for measuring thermal expansion, compression, shrinkage, elastic modulus, and compressive strength of refractory lining materials.Sodium expansion. Test unit 1 in the IK-4 test complex is used to determine the linear sodium expansion of the hearth and wall blocks during electrolysis (Rapoport test). The components of the test unit are: an electric furnace for heating the test specimen and electrolyte; a mechanism for lifting and letting down the furnace; a loading device to apply a constant pressure (from 1 to 10 MPa) to the specimen; conductors to carry current to the specimen and crucible. To prevent oxidation of the material of specimen and crucible, the electrolysis is carried out under argon.The sodium expansion test for the carbon-graphite lining includes the following operations:-preparing cylindrical specimens of diameter 30 mm and length 100 mm;-preparing an electrolyte with a cryolite ratio of 3 ± 0.05 and composition (wt.%): Na 3 AlF 6 , 86.0 (658 g); CaF 2 , 5.0 (38 g); Al 2 O 3 , 9.0 (69 g); -drying the specimen, crucible, and alundum disk at 100°C for 3 h;-placing a graphite crucible with the specimen and electrolyte in an electric furnace;-applying a load of 1 MPa to the specimen; -heating to 980 ± 10°C and holding until a steadystate regime is attained; -performing electrolysis for 2 h at a current density of 0.7 A/cm 2 , with the measured data stored in a computer and graphically displayed on the screen; -plotting the sodium expansion diagrams. Temperature expansion. Test unit 3 of the IK-4 test complex serves to measure the expansion of the "green" hearth mix (on heating from room temperature to 950°C) and the TLEC of lining materials. It is composed of an electric furnace, a heat insulator, a quartz retort, a quartz measuring rod, a displacement sensor, and a fume hood.Methodology for measuring the temperature expansion of the lining involved the following operation:-preparing cylindrical specimens of diameter and length 50 mm;-placing a retort with the specimen and measuring rod in the furnace;-heating the hearth mix specimen to 950°C at a rate of 200°C/h and holding time of 2 h; to measure TLEC, the heating rate is 200°C/h up to 520°C (when needed, to 950°C) and holding time 2 h; -processing data on a computer and displaying results. Elastic modulus and compressive strength. Test specimens of diameter 40 mm and length 50 mm are prepared. ...