Journal of Advanced Processes in Materials Engineering
Year:2020 | Volume:14 | Issue:2|Papers Count:7

ZrB2– SiC– ZrC nanocomposite was fabricated by spark plasma sintering using ZrB2– SiC– ZrC synthesized powder by MA-SPS route. In the present research, sintering mechanism was investigated by displacement-temperature-time (DTT), displacement rate vs. temperature and displacement rate vs. time diagrams which were obtained during spark plasma sintering cycles. Sintering process of the composite was completed after 17 min at temperature of 1750° C. By using X-ray powder diffraction (XRD) pattern and Rietveld method, the mean crystallites sizes of about 77, 62 and 56 nm were calculated for ZrB2, SiC and ZrC phases, respectively. The physical and mechanical properties of sintered composite such as: density, tensile strength, Vickers hardness and fracture toughness were% 99/3, 563 MPa, 18 GPa and 4. 9 MPa. m1/2, respectively. Finally scanning electron microscopy (SEM) images show three different phases well distributed all over the sample. It is clear that ZrB2, SiC and ZrC phases are well connected and have good continuity.

Boron carbide is highly regarded because of many properties such as high hardness, high Young’ s modulus, low density and etc. However, application of B4C is rather limited due to difficulties in densification and low fracture toughness. In this research, uniaxial press at constant pressure of 140 MPa was applied to fabrication of boron carbide porous preforms. B4C powder with size of 43. 27 μ m, activated carbon with the amount of 5, 10, 15 Wt. % and phenolic resin powder as a binder and porosity-causing agent with the amount of 9 Wt. %, were used as raw materials. Infiltration operation with molten silicon had performed in vacuum furnace in temperature 1600 ° C. β-SiC phase produced from silicon and carbon that caused the strength properties of specimens during infiltration process. Residual silicon was decreased from 35%. vol to 18 vol. % with increasing activated carbon contents, on the contrary, secondary silicon carbide had increasing continuously from 10%. vol to 2 vol. %. Decreasing in residual silicon and increasing in β-SiC phase determined by Image analysis software.

In this research, the kinetics of carbothermic reduction of molybdenite in the presence of magnesium oxide was studied. Powder samples with a stoichiometric ratio (molybdenite: magnesium oxide: Graphite 1: 2: 2) prepared under simultaneous thermal analysis (STA), with three heating rates of 10, 15 and 20 degrees per minute, respectively. A series of experiments were performed under isothermal argon atmosphere, to determine the intermediate phases formed during the process. The results showed that the process temperature range was 900 º C to 1400 º C and with the formation of intermediate phases of molybdenum oxide (MoO2) and magnesium molybdate (MgMoO4) goes. Kinetic investigations were done with the free model methods such as Friedman, Ozawa and Kissinger as well as model fitting method Coats-Redfern. The results of all methods were in good agreement with each other and suggested that the mechanism of the reaction was chemical control and activation energy was about 425 KJ/mol.

When using Magnesia-Carbon refractories in slag line (1600 ° C) oxidation produces porosity and corrosion. In this research, micro silica is added to produce in situ nano forsterite and act as a binding between MgO grains. This increases Brazilian (strength resistant to crack growth) and lowers chemical potential of silica between brick-slag and decreases diffusion of slag. 3% silicon (anti-oxidant), 1-10% micro silica and in 2nd series of samples ferrosilicon was added. XRD showed increase of forsterite formation with ferrosilicon. Physical and mechanical properties after tempering at 250 ° C and sintering at 1600 ° C were studied. Strength and crack resistance improved. Modified Scherer Equation measured crystals of forsterite as 32 nm. Ratio of Slopes Method calculated 10, 14 and 24% forsterite respectively at 3, 5 and 10% micro silica addition.

In recent years, cryogenic-treatment is considered in order to improve of wear and hardness resistance of tool steels. Cryo-treatment is performed on steel before and after of tempering and quenching treatment, respectively. In this research, the effect of deep cryogenic treatment is investigated on the GOS9HF-steel. In this regard, the quenched-tempered and quenched-Cryo-treated samples are prepared after tempering treatment for 2hrs. then, impact of Cryo-treatment on value of retained austenite, fine carbide precipitations are evaluated by XRD, SEM and the amount of hardness, strength and wear resistance are measured by micro-hardness, tensile and wear tests. The wear test is conducted by pin-on-disc method. The results indicated that the amount of hardness and properties of wear and tensile in the Cryo-treated sample were rather than the quenched-tempered samples at all of tempering temperatures (i. e. from 150 to 650˚ C). Additionally, with increase of tempering temperature, the amount of hardness, wear behavior and tensile property are decreased in both of Cryo-treated and quenched-tempered samples. This can be attributed to the softening of microstructure and the growing of grain sizes. Moreover, it was obvious that improving of Cryo-treated samples are related to the removing of retained austenite, precipitation of fine carbides and more appropriate distribution of these carbides. It is cleared that the Cryo-treatment causes to decrease of value of retained austenite from 12% to below of 1% at quenched-tempered and Cryo-treated samples, respectively. Finally, Cryo-treatment causes to increase of volume fracture of carbides to 52%.

Nano-sized manganese (III) acetylacetonate (Mn(acac)3) was coated on the surface of ammonium perchlorate (AP) by sol-gel method, for reducing thermal decomposition temperature of AP. Analysis of thermal gravimetry (TG) results showed that manganese (III) acetylacetonate nano-coating has been converted to manganese spinel before the thermal decomposition of ammonium perchlorate and this nano-sized manganese spinel had a good catalytic effect on the thermal decomposition of ammonium perchlorate. In this paper, X-ray diffraction pattern (XRD) and scanning electron microscopic images (SEM) were used to prove the formation of nano-coating on the surface of ammonium perchlorate and identification nanocomposites, respectively. As well as, the catalytic effect of nano-sized manganese spinel resulted from manganese (III) acetylacetonate studied by the differential scanning calorimetry (DSC) and Thermogravimetric analysis (TG) on the thermal decomposition of ammonium perchlorate and thermal decomposition of nano composite Mn(acac)3/AP showed that decomposition peaks of ammonium perchlorate decreased from 422 º C to 318 º C and from 317 º C to 279 º C, respectively. According to the reduction effect of the nano-sized coating on the decomposition peaks of AP, it has been revealed that nano-coating has a significant effect on the thermal decomposition of ammonium perchlorate and eventually improved the performance of solid propellants.

In this research, barium hexaferrite samples with BaZn0. 6Zr0. 3X0. 3Fe10. 8O19 (X=Ti, Ce, Sn) composition were synthesized via mechanical activation method and were evaluated by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), vibrating sample magnetometer (VSM) and Vector network analysis (VNA). X-ray diffraction results confirmed the present of barium hexaferrite as a dominant phase with small amount of hematite as a non-magnetic phase in the sample compound. Lattice parameters a and c was increased due to the difference between ionic radius of guest and host ions and the largest increases was related to the sample that containing cerium ion. The FE-SEM results confirmed the average particles size of about 450 nm and 250 nm for samples without and with dopant respectively. According to M-H curves the value of saturation magnetization (Ms) and coercive force (Hc) was reduced in all cases and significant changes were observed in magnetic properties of barium hexaferrite with the effect of substitution of Fe ions. According to the results maximum magnetic saturation (33. 1 emu/g) and minimum coercivity force (8. 14 Oe) were related to samples with composition of BaZn0. 6Zr0. 3Ti0. 3Fe10. 8O19 and BaZn0. 6Zr0. 3Sn0. 3Fe10. 8O19 respectively. According to the results of microwave absorption in the frequency range of 8-12. 4 GHz the maximum absorption was related to the sample with the composition of BaZn0. 6Zr0. 3Sn0. 3Fe10. 8O19 at the frequency of 11. 1 GHz was-16. 3 dB.