MODIFICATION OF MINERAL RAW MATERIAL BY RADIATION PRE-TREATMENT BEFORE PROCESSING: FEATURES AND PROSPECTS

The earlier case-studies of rebellious lead-zinc ore with grain size of -3 mm at the Chinakal Institute of Mining and Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences provided data on improvement of disintegration selectivity and improved dissociation of useful minerals owing to preliminary treatment by a stream of electrons. The goal of this research is the integrated analysis of the change in the strength of core samples of some rocks, such as limestone, hornfels and granite, after their modification by radiation by a stream of high-energy electrons. It is found that the increase in the absorbed radiation dose results in the change in the strength and deformation properties: ultimate compression strength, modulus of deformation and elasticity modulus. In case of limestone, the ultimate uniaxial compression without radiation treatment is 49.11 MPa and drops to 35.24 MPa at the absorbed dose of 15 kGy. In case of granite, the absorption dose of 10 kGy decreases the ultimate compression strength from 68.33 to 35.08 MPa. The energy input in fracture and crushing is estimated on the equipment designed for uniaxial loading of cores at the Chinakal Institute of Mining. The energy input in fracture and crushing make 78.6 and 7004.2 J/kg for initial granite and 30.6 and 4708.8 J/kg for granite modified by radiation. The size of particle after crushing of treated cores reduces from 10.98 to 8.76 mm. The novelty of this study is the found effect of the range coverage in weakening of minerals with grain sizes to 30-50 mm, including cylindrical granite cores with diameters of 30 mm and lengths of 60 mm (equivalent spherical diameter is 43.2 mm) due to the shock waves generated in minerals during deceleration of electrons in the stream. This effect can be utilized to reduce the energy consumption of the pre-treatment technology and to minimize mineral losses in subsequent processing.

Development of Lightweight Magnesium/Glass Micro Balloon Syntactic Foams Using Microwave Approach with Superior Thermal and Mechanical Properties

Magnesium matrix syntactic foams (MgMSFs) are emerging lightweight materials with unique capabilities to exhibit remarkable thermal, acoustic, and mechanical properties. In the current study, lightweight glass micro balloon (GMB)-reinforced Mg syntactic foams were synthesized via the powder metallurgy technique using hybrid microwave sintering. The processing employed in the study yielded MgMSFs with refined grain sizes, no secondary phases, and reasonably uniform distributions of hollow reinforcement particles. The developed MgMSFs exhibited densities 8, 16, and 26% lower than that of the pure Mg. The coefficient of thermal expansion reduced (up to 20%) while the ignition resistance improved (up to 20 °C) with the amount of GMB in the magnesium matrix. The MgMSFs also exhibited a progressive increase in hardness with the amount of GMB. Although the MgMSFs showed a decrease in the yield strength with the addition of GMB hollow particles, the ultimate compression strength, fracture strain, and energy absorption capabilities increased noticeably. The best ultimate compression strength at 321 MPa, which was ~26% higher than that of the pure Mg, was displayed by the Mg-5GMB composite, while the Mg-20GMB composite showed the best fracture strain and energy absorption capability, which were higher by ~39 and 65%, respectively, when compared to pure Mg. The specific strength of all composites remained superior to that of monolithic magnesium. Particular efforts were made in the present study to interrelate the processing, microstructural features, and properties of MgMSFs.

Assessing the Physical-Mechanical Characteristics of Hydroxyapatite-Titanium Oxide Biocomposites Produced by the Polymeric Wax Addition Method

The aim of the present study is to assess the physical-mechanical properties of hydroxyapatite-titanium oxide composites used in porous scaffolds produced by the polymeric wax addition method. Mixtures composed of 50%-50%wt. (sample A), 60%-40%wt. (sample B), and 70%-30%wt. (sample C) of hydroxyapatite-titanium oxide were prepared. Subsequently, 70%vol. of each sample was combined with 30%vol. polyethylene wax. Forty-five (45) specimens per composition (12 mm diameter and 10 mm height) were prepared through uniaxial pressing. The specimens were subjected to calcination at 500°C (1°C/min) and left to rest for 1 h for polymeric wax elimination. Next, they were sintered at 1250°C, 1300°C, and 1350°C for 2 h. Physical-mechanical assays were conducted to assess apparent porosity, water absorption, specific gravity, firing linear retraction, and ultimate compression strength. As temperature increased, firing linear retraction, specific gravity, and ultimate compression strength increased in all samples, whereas water absorption and apparent porosity decreased. Sample A presented the highest densification and ultimate compression strength rates at 1350°C. Overall, the physical-mechanical characteristics of these composites made them suitable to be used as biocomposites.

Highly-refractory spinel-bonded aluminapericlase-carbonaceous ceramic materials

The slag-resistant highly-refractory alumina-periclase carbonaceous ceramic materials were synthesized out of the Kazogneupor's electro-cast corundum, Zinel'bulaksk's (Uzbekistan) talc, and enriched graphite concentrate (Uzbekistan). The crystal structure of the materials is formed of corundum and spinel. The refractoriness of the ceramic samples is higher than 1800 °C, the density is 2520‒2880 kg/m3, the water absorption is 6,75‒11.71 %, open porosity is 16‒21 %, and the ultimate compression strength is 100‒120 MPa.Ill. 3. Ref. 9. Tab. 2.

Influence of Sintering on the Structure and Properties of Ceramics from Silica Nanopowders

In this paper the ceramics obtained from various silica powders investigated. Two different methods for ceramics receiving (with consecutive pressing and sintering, and the method of hot-pressing (spark plasma sintering)) were tested. For ceramics obtained by different methods the microhardness, ultimate compression strength and grain size were compared. At a classical method of powders sintering the microhardness and durability growth is observed at reduction of the initial particles size though the observed size of grains in ceramics is approximately identical for all types of powders. It is received that vitrification of samples of ceramics created by the SPS method, happens at much smaller temperature (1100°C), than the corresponding temperature at consecutive operations of pressing and sintering (1550°C). Values of microhardness of the ceramics received by two various methods, were similar (~ 2 GPa). Ultimate compression strength value (0,25 GPa) for the samples received by a method of spark plasma sintering, only slightly exceeds the value of ultimate compression strength for the samples created in the traditional way (0,23 GPa). If at consecutive operations of pressing and sintering the ceramics with a micron size of grain turns out, at the SPS method the grains of received ceramics have the size about 300 nm. It speaks about prospects of nanopowders sintering by the method of spark plasma sintering at which nanostructural parameters of powder in the consolidated material remain

Experimental study on the Crack Initial Stress and the Crack Damage Stress of Red Sandstone Under Different Strain Rate Conditions

In order to investigate the progressive failure process of brittle rock, the mechanical properties of red sandstone from southeast Shandong province were systemic studied. The stress-strain curves and failure modes of samples under different strain rates were recorded as original data. Based on these data, the axial stiffness, the volume strain, the crack volume strain, and so on were deduced for further analysis. The crack initial stress and the crack damage stress were identified by Moving Point Regression Technique and stiffness curves. The influence of strain rate on the micro-cracking process and the ultimate compression strength of red sandstone were then studied. The results show that: as the strain rate increases, the ultimate compression strength first decreases and then increases as the strain rate increases, and the ratio of crack initial stress/ultimate compression strength and crack damage stress/ultimate compression strength decreases.