Design guidelines for titania-silica-alumina ceramics with tuned anatase to rutile transformation

Titania-based ceramics with adjustable anatase-rutile fractions were obtained by milling of anatase, quartz and corundum precursors, uniaxial pressing and firing at 1100?°C. The influence of silica and alumina, combined with milling time and compaction pressure, was studied by design of experiments. The L9 orthogonal array with a three-level noise factor was employed. Firing of pure titania at 1100?°C yielded complete anatase to rutile transformation (ART), whereas stabilized samples show that an optimum amount of 9% silica and 33% alumina reduces phase transformation to only about 5?wt% rutile. An extended correlation matrix combined with analysis of variance (ANOVA) was applied to assess the combined effects of quartz, alumina, milling time and uniaxial compressing pressure on relative density, and anatase to rutile transformation. Results show absence of ART after milling, and controlled partial conversion of anatase to rutile after firing. Very good fitting was obtained by multivariate analysis on considering first and second order terms for dependence on silica contents and interactions between silica and each of the remaining factors, including milling time. This empirical dependence could be interpreted on a sound physicochemical basis, allowing the prediction of suitable compositions and processing conditions to obtain rutile-free samples by conventional ceramic processing, and to design ceramic samples with controlled fractions of anatase and rutile.     

金红石与磷灰石浮选分离中硫酸铝的作用研究

研究表明．在FL108作捕收剂条件下，硫酸铝强烈抑制金红石而使磷灰石上浮，采用“FL108＋Al2（SO4）3”的浮选药剂制度，可实现两矿物的分离。通过分析Al3＋和金红石表面Ti4＋、磷灰石表面Ca2＋的水解特性，还阐述了Al2（SO4）3的选择抑制机理。     

TiO2对烧成镁钙砖烧结性能的影响

研究了两种晶型的TiO2(锐钛矿型和金红石型)作为添加剂对烧成镁钙砖烧结性的影响.结果表明,两种晶型的TiO2都能显著促进镁钙砖的烧结,其中以锐钛矿晶型为添加剂的效果好于金红石型的.XRD分析结果表明,TiO2与CaO反应生成了CaTiO3,这是加入TiO2使镁钙砖烧结性变好的主要原因.     

Time-dependent universal conductance fluctuations in IrO2 nanowires

Single-crystalline iridium dioxide nanowires show the time-dependent universal conductance fluctuations (TUCFs) at cryogenic temperatures. The conductance fluctuations persist up to temperature T as high as nearly 10 K. The root-mean-square TUCF magnitudes increase with decreasing T, reaching approximately 0.1 e² / h at 1.7 K. We ascribe these conductance fluctuations to originating from the conduction electrons scattering upon mobile defects (moving scattering centers). Our measured TUCF characteristics are satisfactorily explained in terms of the existing TUCF theory in its three-dimensional form. The extracted electron dephasing length L_φ(1.7 K) ≃90 nm is smaller than the diameter (≈ 180 nm) of our nanowires.     

Formation and crystal growth of needle-like rutile in glass- ceramics

Glass-ceramic, which has negligible dielectric loss, high mechanical strength, excellent drop resistance, low CTE, and low density for lightweight design, is the best option for the back cover of mobile devices in the 5 G era. Herein, the effect of P₂O₅ on the phase separation and crystallization of MgO–Al₂O₃–SiO₂-TiO₂ glass-ceramics is studied. The incorporation of P₂O₅ in the glass structure leads to phase separation, in which the P and Mg-enriched phase was formed in the glass matrix, and promotes the increase of T_g. With the increase of P₂O₅ content, the precipitated crystals change significantly. First, the silicate crystals (Mg₂SiO₄) disappear, whereas the phosphate crystals (LiMgPO₄) emerge when 2 mol% P₂O₅ is introduced. Second, titanate crystal (MgTi₂O₅) can not be observed when 4 mol% P₂O₅ is introduced. The Ti₅O₉ crystals appear simultaneously with LiMgPO₄ crystals and transform to rutile TiO₂ crystals at high temperature. Interestingly, the needle-like rutile TiO₂ crystals, which is 300 nm long and 20 nm wide, have been found in a glass with 4 mol% P₂O₅. The large L/D ratio of needle-like crystals increases the hardness significantly from 6.08 GPa to 7.14 GPa. Similar to other fiber reinforced composites, this needle-like crystals provide a new strategy to improve the mechanical properties of glass ceramics.     

Suspension high velocity oxy-fuel spraying of TiO2: A quantitative approach to phase composition

A range of coatings from a water based suspension of anatase has been prepared by suspension high velocity oxy-fuel spraying with the aim to study effects of heat power of the flame on phase composition, microstructure and surface topography. Three most commonly used approaches of quantitative phase analysis have been scrutinized with respect to their applicability and as some of the coatings showed presence of preferred orientation and it was argued that quantitative Rietveld refinement is the most accurate method for phase composition determination. Coatings had a layered duplex anatase/rutile microstructure with fraction of rutile increasing exponentially with heat power. Spraying at the lower heat power led to a lower surface roughness and higher power resulted in surfaces with pronounced humps, which were distributed homogeneously on the surface. The emergence of humps is related to an increase in macroscopic surface area of up to 30% with respect to the flat coating.     

Dye sensitized solar cells based on hydrothermally grown TiO2 nanostars over nanorods

A rutile titanium dioxide nanostar over nanorods is synthesized by a simple and cost-effective hydrothermal deposition method onto conducting glass substrates. In order to study the effect of precursor concentrations on the growth of TiO₂, the amount of Ti precursor is varied from 0.1 mL to 0.5 mL at the interval of 0.1 mL. These TiO₂ thin films are characterized for their morphological, structural, optical and J–V properties using various characterization techniques. SEM images showed the formation of densely packed nanostars over nanorods for 0.3 mL titanium tetraisopropoxide (TTIP). XRD patterns show the formation of polycrystalline TiO₂ with tetragonal crystal structure possessing rutile phase. Further, the TiO₂ thin films are used for dye sensitized solar cells using N3-dye.The films were photoelectrochemically active and can be viewed as a promising application in DSSC with maximum current density of 1.459 mA/cm² with enhanced photovoltage of 696 mV for the sample prepared at 0.3 mL TTIP.     

提高胂酸对金红石浮选性能的研究

摘要通过对金红石矿石浮选研究发现：用苄基胂酸（BAA）：非离子型表面活性剂（F2）：离子型表面活性剂（E4）配比为l：l：002组成复合捕收剂（BF2／E4）浮选原生金红石矿石，结果粗精矿品位为75．41％，回收率68．25％；而单一BAA浮选金红石粗精矿品位为76．24％，回收率66．89％，这两者结果是很相近的。在捕收剂总用量不变条件下，复合BF2／E4中的BAA用量只有单一BAA用量一半，而且F2来源广，价格低，无毒。使用BF2／E4后，不仅提高了浮选作业回收率，而且该作业成本将降低1／3左右，环境污染也相应地减轻了。     

Carbon induced phase transformation in electrospun TiO2/multiwall carbon nanotube nanofibers

Nanofibers of titania and composite nanofibers of titania and multiwall carbon nanotubes were synthesized by electrospinning using a sol-gel process combined with activated carbon nanotubes. The relationships of treatment temperature, carbon nanotube content on the crystal phase, fiber morphology, and electric properties are reported. It is found that the rutile phase becomes more prominent at low heat treatment temperatures with an increase of carbon content in nanofibers, be it for higher amount of carbon due to reducing atmosphere or due to an increase in MWCNT. Atmospheric control and lower heat treatment temperatures enable crystalline nanocomposite fibers of anatase where the level of rutile is below the detection limit of XRD or Raman spectroscopy. This work provides a new path to fabricate electrospun TiO₂/MWCNT nanocomposite nanofibers with limited C-induced rutile phase.     

复合捕收剂浮选金红石的研究

通过浮选试验以及吸附量、表面张力等的测定,研究了复合捕收剂对金红石的捕收性能。添加剂F能大大降低捕收剂B的用量,并与捕收剂B产生缔合作用吸附在矿物表面。