Processing of refractory materials using various magnesium sources derived from Zinelbulak talc-magnesite

Magnesia（MgO） is widely used in the production of refractory materials due to its high melting point,high thermal shock,and excellent slag resistance.The properties of refractory materials depend upon magnesia sources and processing parameters.In this work,three different magnesium sources,namely,magnesium hydroxide concentrate,magnesium carbonate concentrate,and intermediate flotation concentrate,were obtained from the Zinelbulak talc-magnesite,Uzbekistan,by causticization-hydration and flotation processes,respectively.A series of refractory materials were prepared on the basis of these magnesium sources,and their effects on physico-mechanical properties and microstructures were investigated as a function of sintering temperature,molding pressure,and the particle size of magnesium sources.The experimental results showed that a refractory material obtained from the magnesium hydroxide concentrate at 1600℃ for 4 h demonstrated favorable parameters due mainly to a higher degree of contact among fine particles.The results obtained from X-ray diffraction and optical microscopy confirmed the presence of periclase and forsterite as the predominant phases in refractory specimens.The prepared refractory materials meet the requirements of the State Standards（Nos.4689-94 and 14832-96） for magnesia and forsterite refractories,respectively.It is,therefore,suggested herein that the use of different magnesium sources derived from the Zinelbulak talc-magnesite will offer the potential to provide economic benefits in the refractory industry.

Characterization and processing of talc-magnesite from the Zinelbulak deposit

The characteristics of talc-magnesite from the Zinelbulak deposit(Uzbekistan) were investigated via X-ray diffraction, differential thermal analysis,infrared spectroscopy and optical microscopy.The mineralogical composition of the Zinelbulak talc-magnesite consists of 52 wt.%talc,43 wt.%carbonates and 5 wt.%of the iron-containing minerals magnetite,siderite and chlorite.Petrographic analysis confirmed the presence of carbonates in two forms:magnesite and breunnerite.Grindability tests revealed that talc and magnesite particles are completely separated after a grinding process carried out for 10～12 min.The distribution of the yield of talc and magnesite,as a function of the particle size,shows an irregular feature in that a comparatively coarser sample(>0.1 mm) is richer in magnesite and poor in talc while a comparatively finer sample(<0.1 mm) has a composition poorer in magnesite.The dressability of the Zinelbulak talc-magnesite was tested using conventional gravity concentration,flotation and electromagnetic separation.Gravity concentration was found to be the most economic initial process for the complete separation of magnesium carbonate and talc.Subsequent flotation and magnetic separation techniques could further increase the yield of high quality magnesite and talc.Refractory samples prepared by heating the separated magnesite at 1600℃for 2 h met the State Standards for refractory materials.

作为核废料载体锆石缺陷结构的能量学研究

用原子模拟技术拟合锆石某些物理性质的实验值获得了锆石平衡结构模型的势能参数。在锆石平衡结构的基础上 ,结构中基本点缺陷及其形成能和结构无序态及其形成能得到了详细研究。锆石中Pu、U和Th与Zr的类质同象替代方式及其类质同象形成热的研究发现 ,组分为Pu75mol%—Zr2 5mol%处存在一不混溶间隔 ,这表明锆石中放射性核素的荷载量应小于5 0mol%

Solid-state single-crystal growth of YAG and Nd: YAG by spark plasma sintering

Recent studies have shown that many challenges encountered in conventional single crystal growth methods, including high production costs, can be overcome by using the solid-state single-crystal growth(SSCG) approach, which has been recognized as a simple and cost-effective alternative for obtaining single crystals. In this work, YAlO(YAG) and Nd-doped YAG(Nd:YAG) single crystals were grown via the SSCG method using spark plasma sintering(SPS). The growth of single crystals was initiated at the surface of(110) YAG single-crystal seeds embedded inside YAG and Nd:YAG powder beds, and this growth continued as the surrounding polycrystalline matrix was converted into a single crystal. The application of external pressure during the SPS process has been found beneficial for reducing the porosity of the grown single crystals. Moreover, high Nddoping levels had a positive effect on the conversion kinetics,with a growth rate of almost 50 μm/h, which increased the driving force for single-crystal growth through the solute drag effect. EDS elemental mapping and line scans confirmed the compositional uniformity of the grown single crystals, while EBSD images verified their crystallization in the(110) direction. The obtained results confirm the strong potential of the SSCG technique coupled with SPS for the growth of undoped and highly doped YAG single crystals with excellent quality.

Phase separation and crystallization of La2O3 doped ZnO-B2O3-SiO2 glass

In order to investigate the effect of the La2O3 on the phase separation and crystallization of ZnO-B2O3-SiO2 glass, after the occurence of the phase separation and crystallization of glasses by heat treatment, the microstructure morphology and distribution of elements in different sample areas were characterized by the scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS);the non-isothermal crystallization kinetics of the glass samples was studied by using a differential scanning calorimeter(DSC) and the precipitated crystals of crystallized glass were determined by the X-ray diffraction(XRD). The results suggest that the phase separation and crystallization of 60ZnO-30 B2O3-10SiO2 glass occur at glass surface, and the incorporation of small amount(<4 mol%) of La2O3 significantly inhibits the glass phase separation and consequently improves the thermal stability of glass.Doping of La2O3 accelerates the glass crystallization at the elevated temperature(660 ℃), making the depth of crystal layer thicker and diffraction intensity in XRD patterns stronger. However, due to the precipitation of several crystals that occur simultaneously when La2O3 doping amount is 4 mol%, crystallization of the 60ZnO-30B2O3-10SiO2 glass is obviously depressed, the crystallization activation energy Ec and the relative crystallinity Xc of the glass reach the maximum and the minimum values, respectively.Although transition from one-dimensional growth of crystals to two-dimensional growth of crystals results from La2O3 addition, the one-dimensional growth of crystals remains dominant in crystallization process. This work can provide some useful information for preparing glass ceramics with nano-crystals precipitated in the glass surface.

Novel transparent MgGa_(2)O_(4) and Ni^(2+)-doped MgGa_(2)O_(4) ceramics

In this study we fabricated, for the first time, magnesium gallate (MgGa_(2)O_(4), a partially inverted spinel) transparent ceramics, both undoped and doped with 1 at% Ni. The specimens were derived from in-house prepared powder, with a crystallite size of ∼10 nm (by wet chemistry) and densified by pulsed electric current sintering (PECS;peak temperature 950 ℃ for 90 min). Densification levels of 99.84% and 99.52% of theoretical density were attained for doped and undoped materials, respectively. Doping with Ni was seen to marginally improve the densification level. Quite transparent specimens were produced: the best showing transmission of ∼89% of the theoretical level (thickness t = 0.85 mm). The absorption spectra revealed that the dopant was accumulated as Ni^(2+) in the octahedral sites of the lattice, as occurs in single-crystal specimens. After excitation at 980 nm, the doped disks exhibited a wide fluorescence band centered at 1264 nm.