Vacuum heat treatment of LiAlO2 densified silicon nitride ceramics

The aim of the present work has been to produce high-dense Si₃N₄ ceramics by a cheaper pressureless sintering method and then to attain vacuum heat treatment to remove residual grain boundary glass in gaseous form. LiAlO₂ was used as a sintering additive rather than using Li₂O, since its grain boundary glass is not stable above 1200 °C. LiAlO₂ was synthesised from 42% Li₂CO₃ and 58% Al₂O₃ powder mix reacting together at 1450 °C for 3 h in a muffle furnace. X-ray analysis showed that 95% LiAlO₂ was obtained. LiAlO₂ was milled and added to silicon nitride powder as a sintering additive. Hot-pressing and pressureless sintering of LiAlO₂ containing Si₃N₄ compacts were carried out at temperatures between 1450–1750 °C. The sintered samples were vacuum heat-treated at elevated temperatures under high vacuum to remove intergranular glass and to increase refractoriness of Si₃N₄ ceramics. Scanning electron microscope images and weight loss results showed that Li in grain boundary glass (Li–Al–Si–O–N) was successfully volatilised, and oxidation resistance of the sintered samples was increased.     

Deposition of Sm2O3 doped CeO2 thin films from Ce(DPM)4 and Sm(DPM)3 (DPM=2,2,6,6-tetramethyl-3,5-heptanedionato) by aerosol-assisted metal–organic chemical vapor deposition

Samarium-doped ceria (SDC) thin films were prepared from Sm(DPM)₃ (DPM = 2,2,6,6-tetramethyl-3,5-heptanedionato) and Ce(DPM)₄ using the aerosol-assisted metal–organic chemical vapor deposition method. -Al₂O₃ and NiO-YSZ (YSZ = Y₂O₃-stabilized ZrO₂) disks were chosen as substrates in order to investigate the difference in the growth process on the two substrates. Single cubic structure could be obtained on either -Al₂O₃ or NiO-YSZ substrates at deposition temperatures above 450 °C; the similar structure between YSZ and SDC results in matching growth compared with the deposition on -Al₂O₃ substrate. A typical columnar structure could be obtained at 650 °C on -Al₂O₃ substrate and a more uniform surface was produced on NiO-YSZ substrate at 500 °C. The composition of SDC film deposited at 450 °C is close to that of precursor solution (Sm : Ce = 1 : 4), higher or lower deposition temperature will both lead to sharp deviation from this elemental ratio. The different thermal properties of Sm(DPM)₃ and Ce(DPM)₄ may be the key reason for the variation in composition with the increase of deposition temperature.     

Microstructural and piezoelectric properties of low temperature sintering PMN-PZT ceramics with the amount of Li2CO3 addition

PMN-PZT ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, and their micro structural, dielectric and piezoelectric properties were investigated. The sintering aids were proved to lower the sintering temperature of doped PMN-PZT ceramics due to the effect of LiBiO₂ liquid phase. Optimal values for multilayer piezoelectric transformer application, such as electromechanical coupling factor (k_p) of 0.50, mechanical quality factor (Q_m) of 2264, and dielectric constant (K) of 1216, and curie temperature (T_c) of 317 °C were found at 0.1 wt.% Li₂CO₃ added ceramics sintered at 940 °C.     

In situ co-precipitation synthesis and photoluminescence of YxGd1−xVO4:Tm microcrystalline phosphors by hybrid precursors

Y_xGd_1−xVO₄:Tm³⁺ (5 mol%) phosphors were prepared by in situ co-precipitation technology with the different content ratio of Y/Gd (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, respectively). During the process, rare earth coordination polymers with o-hydroxylbenzoate were used as precursors, composing with polyethylene glycol (PEG) as dispersing media. After heat-treatment of the resulting multicomponent hybrid precursors at 900 °C, the samples were obtained. SEM indicated the particles present good crystalline state, whose crystalline grain sizes were about 0.2–2 μm. Under the excitation of 257 nm, all the materials show the characteristic emission of Tm³⁺ which is the strong blue emission centered at 475 nm originating from ¹G₄ → ³H₆ of Tm³⁺. Besides this, concentration quenching appears in the system of YVO₄:Tm³⁺ and GdVO₄:Tm³⁺. And when x reaches 0.5, the system of Y_xGd_1−xVO₄:Tm³⁺ shows the strongest blue emission.     

Insertion/extraction reactions of lithium with LiV2O4

Lithium has been inserted into, and extracted from, the spinel Li_1.0V₂O₄ both electrochemically and chemically. Electrochemical and structural data show that in the system Li_1+xV₂O₄, for 0 < x ≤ 0.5, Li⁺ ions are inserted into the interstitial octahedral sites of the A_tet[B₂]_octX₄ spinel structure. At x ≈ 0.5, Li⁺ ions in the tetrahedral A-sites are displaced into the remaining octahedral sites to yield, at x = 1, a rocksalt phase Li₂V₂O₄; the [B₂]X₄ framework is unperturbed by the lithiation process. This framework also remains intact when Li⁺ ions are removed from Li_1.0V₂O₄ to a composition Li_0.67V₂O₄. Further extraction of lithium from the structure is accompanied by migration of some vanadium ions from the B-sites to the interstitial octahedral sites of the spinel structure. This process reduces the crystal symmetry from cubic to trigonal symmetry. In Li_0.27V₂O₄ the structure resembles that of Li_0.22VO₂, obtained by delithiation of layered LiVO₂, in which the vanadium cations are distributed in a 2:1 ratio between alternate cubic-close-packed oxygen layers; in the LiV₂O₄ spinel this ratio is 3:1.     

Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi₂Ti₂O₇ ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi₂Ti₂O₇ phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ at 850–1150 °C. The single phase of Bi₂Ti₂O₇ reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm⁻² and coercive field is 24 kV cm⁻¹. Thus, the Bi₂Ti₂O₇ did not exhibit ferroelectricity, but the mixed phase of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ did.     

Structural and electrochemical characterization of LiMn2−δVδOy spinels

The spinel phase compounds with the composition of LiMn_2−δV_δO_y were prepared by solid reaction of the mixture of LiNO₃·H₂O, MnCO₃ and NH₄VO₃ powders. Evolution of the crystalline phases of the samples versus the vanadium content was analyzed using X-ray diffraction (XRD) technique, EPR and FT-IR spectroscopes. Cubic spinel is the predominant phase in the powders under heat treatment at 550 °C for 5 h. The valence state of manganese ion changed from +4 to +3 with vanadium substitution for charge compensation. The vanadium substitution of manganese leads the decline in capacity and cyclic behavior of the powders. The electrochemical behaviors relating to the variation of structure corresponding to the vanadium substitution were discussed.     

Atomic-layer doping in Si by alternately supplied PH3 and SiH4

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH₃ and SiH₄ was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH₃ exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH₄ exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH₃ at 300–450°C and SiH₄ at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of 10²¹ cm⁻³ are formed. The resistivity of the film is as low as 2.4×10⁻⁴ Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.     

Preparation of cobalt oxide nanoparticles and cobalt powders by solvothermal process and their characterization

Co₃O₄ nanoparticles and cobalt (fcc-Co) powders were successfully synthesized by solvothermal process from a single precursor. The reaction of Co(Ac)₂ with sodium dodecylbenzenesulfonate (SDBS) shows evident-dependent temperature effect. At 180 °C, Co(Ac)₂ reacts with SDBS to produce precursor CoCO₃ plate structures, which are assembled by small nanoparticles. At the temperature of 250 °C, the precursor CoCO₃ can be gradually decomposed to form Co₃O₄ nanoparticles with diameter of ca. 70 nm. While, at 250 °C, the reaction of Co(Ac)₂ with SDBS also produce precursor CoCO₃ nanoparticles/plates, but the CoCO₃ nanoparticles/plates would only decompose to give metal Co. In this process, SDBS acts as not only a surfactant but also a reagent. Magnetic measurements reveal that the as-prepared Co₃O₄ nanoparticles exhibit weak ferromagnetic properties and Co powders show ferromagnetic properties. In addition, a possible formation mechanism was elaborately discussed.     

Structural, optical and electrical characterization of spray-deposited TiO2 thin films

Titanium oxide (TiO₂) thin films were deposited onto glass substrates by means of spray pyrolysis method using methanolic titanyl acetyl acetonate as precursor solution. The thin films were deposited at three different temperatures namely 350, 400 and 450 °C. As-deposited thin films were amorphous having 100–300 nm thickness. The thin films were subsequently annealed at 500 °C in air for 2 h. Structural, optical and electrical properties of TiO₂ thin films have been studied. Polycrystalline thin films with rutile crystal structure, as evidenced from X-ray diffraction pattern, were obtained with major reflexion along (1 1 0). Surface morphology and growth stages based on atomic force microscopy measurements are discussed. Electrical properties have been studied by means of electrical resistivity and thermoelectric power measurements. Optical study shows that TiO₂ possesses direct optical transition with band gap of 3.4 eV.     

Carburization performance of Incoloy 800HT in CH4/H2 gas mixtures

Carburization performance of Incoloy 800HT has been studied after cyclic and isothermal exposures to CH₄/H₂ carburizing gas mixtures at high temperatures for 500 h. At 800 °C in 2% CH₄/H₂, Incoloy 800HT suffered external oxidation and carburization, the external continuous layer of reaction products consists primarily of Cr₇C₃, Mn_1.5Cr_1.5O₄, and FeCr₂O₄ with Fe(Cr, Al)₂O₄ as a minor phase. At 1100 °C in 10% CH₄/H₂, external carburization did not occur likely due to high carbon dissolution in the alloy substrate at this temperature. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior, while above this temperature reducing carburizing behavior should occur. The experimental results approximately agree with the thermodynamic analysis. Metal dusting was not observed under highly carburizing conditions (a_C>1). The size and morphology of Cr-rich phases (or Cr-carbides) are both temperature- and time-dependent, while the external continuity is more temperature-dependent rather than time-dependent.     

Formation of nanocrystalline structure of Ti–6Al–4V alloy by cyclic hydrogenation–dehydrogenation treatment

Ti–6Al–4V (Ti64) sheet specimens were cathodically hydrogenated in sulfuric acid solution at ambient conditions. The hydrogenated specimens were then sent to go through the designed thermohydrogen processing (THP) twice to obtain a nano-sized grain structure. The average grain size of resulted microstructure was found to be 10–20 nm obtained by TEM. Qualitative and quantitative analyses performed by employing X-ray diffractometry (XRD) and elemental analysis (EA) showed that the addition of As₂O₃ as hydrogenation promoter in electrolyte significantly increased the hydrogen uptake. The high concentration of hydrogen arising from promoter action is the key factor in grain refinement. The optimal processing parameter found for grain-refining Ti64 was: (1) electrolytic hydrogenation at 100 mA cm⁻² for 3 h in 1 N H₂SO_4(aq) by adding 0.1 g L⁻¹ As₂O₃; (2) β transformation carried out at 850 °C for 1 h in air furnace, followed by a furnace cooling to 590 °C and held for 6 h; (3) oxide film removed and then dehydrogenated at 650 °C and 1.0 × 10⁻⁶ Torr for 10 h; (4) repeated the same processes once more.     

Effect of β-spodumene on the phase development in an alumina/aluminium-titanate system

The effect of β-spodumene additions on the in situ phase formation and abundances in an Al₂O₃–Al₂TiO₅ system in the temperature range 1000–1400 °C has been studied by neutron diffraction and differential thermal analysis. Results show that β-spodumene began to decompose by phase separation and partial melting at 1290 °C, followed by complete melting at 1330 °C. Formation of Al₂TiO₅ was observed to occur at 1310 °C and its abundance increased with temperature. The addition of β-spodumene as a sintering aid did not cause its reaction with alumina or rutile to form additional phases. Addition of β-spodumene in excess of 5 wt% resulted in pronounced vitrification, which partly recrystallised when cooled to room temperature. The temperatures of Al₂TiO₅ formation and melting of β-spodumene are consistent with the results of differential thermal analysis.     

Effect of SnO2 on the photocatalytical properties of TiO2 films

TiO₂/SnO₂ thin films with different tin atomic percentages were successfully prepared on glass substrates by the spray pyrolysis method from an alcoholic solution of TiO[C₅H₇O₂]₂ with different concentrations of SnCl₄. The TiO₂/SnO₂ thin films prepared at 450 °C presented the anatase phase in polycrystalline configuration from %Sn = 0 in the starting solution up to %Sn = 20, at higher tin content the films present an amorphous configuration. The resulting thin films have a homogeneous surface structure with some porosity. The photocatalytical properties of the films were evaluated with the degradation of methylene blue. The products of the degradation reaction were identified by ¹H nuclear magnetic resonance and the film properties were studied by atomic force microscopy, scanning electron microscopy, UV–Vis spectroscopy, and X-ray diffraction.     

Temperature dependence on addition of urea and its related compounds on formation of neodymium condensed phosphates

Urea (CO(NH₂)₂) and its related compounds (biuret: NH(CONH₂)₂ and cyanuric acid: (CONH)₃) were mixed with phosphoric acid (H₃PO₄) and neodymium oxide (Nd₂O₃). The thermal behavior of these dried mixtures was estimated by differential thermal analyses, X-ray diffraction, and Fourier-transform infrared spectroscopy. Furthermore, specific surface area of phosphates was calculated by BET method using nitrogen adsorption. The addition of urea prevented the crystal growth of Monazite-type NdPO₄ in samples at P/Nd = 2 heated at 450 and 550 °C, and promoted the dehydration–condensation reaction of phosphate. Urea was considered to be decomposed at 400–450 °C in these systems. The decomposition of urea was considered to be related to the formation of neodymium dihydrogenphosphate and then this phosphate transformed to neodymium polyphosphate. The ratio of urea and phosphorus had influence on the promotion of the dehydration–condensation reaction. Thermal behavior of sample added with biuret or cyanuric acid was also investigated.     

Recovery of valuable elements from spent Li-batteries

This work examines two recycling processes for spent Li/MnO₂ and Li-ion batteries. The anode, cathode and electrolyte (LiPF₆) were submitted to one of the following procedures: (a) calcination at 500 °C (5 h) followed by solvent extraction to recover lithium salts (fluoride, phosphate) in good yield (90 wt%). The residual solid was treated with H₂SO₄ containing H₂O₂ and on evaporation gave high purity grade cobalt or manganese sulfate; (b) fusion with KHSO₄ (500 °C, 5 h). The resulting aqueous solution was added dropwise to a solution of NaOH, giving cobalt or manganese as impure precipitate. Addition of KF precipitated high purity grade LiF in moderate yield (50 wt%). The final aqueous solution on treatment with calcium sulfate precipitated the corresponding phosphate and fluoride salts.     

Piezoelectric and dielectric properties of PZT–PZN–PMS ceramics prepared by molten salt synthesis method

Piezoelectric powders and ceramics with the composition of Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Mn_1/3Sb_2/3)O₃ (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: _r = 1773; tan δ = 0.0040; T_c = 280 °C; d₃₃ = 455 pC/N; k_p = 0.70; Q_m = 888; E_c = 10.3 kV/cm; and P_r = 28.2 μC/cm², at calcination of 800 °C and sintering of 1120 °C temperature.     

Characterization of the thorium phosphate-hydrogenphosphate hydrate (TPHPH) and study of its transformation into the thorium phosphate-diphosphate (β-TPD)

The preparation of thorium phosphate-diphosphate (Th₄(PO₄)₄P₂O₇, TPD) was developed through the precipitation of thorium phosphate-hydrogenphosphate hydrate (Th₂(PO₄)₂(HPO₄)·H₂O, TPHPH) at 150–160 °C in closed PTFE container or in autoclaves. From EPMA analyses and SEM observations, the initial precipitate was single phase and multilayered. The behaviour of TPHPH (orthorhombic system with a = 21.368(2) Å, b = 6.695(1) Å and c = 7.023(1) Å) was followed when heating up to 1250 °C. It was first dehydrated leading to the anhydrous thorium phosphate-hydrogenphosphate (TPHP, orthorhombic system with a = 21.229(2) Å, b = 6.661(1) Å and c = 7.031(1) Å at 220 °C) after heating between 180 and 200 °C. This one turned progressively into the new low-temperature variety of TPD (called -TPD, orthorhombic system with a = 21.206(2) Å, b = 6.657(1) Å and c = 7.057(1) Å at 300 °C) correlatively to the condensation of hydrogenphosphate groups into diphosphate entities. These three phases (TPHPH, TPHP and -TPD) exhibit closely related 2D layered structures, therefore different from the 3D structure of the thorium phosphate-diphosphate (high-temperature variety). This latter compound, now called β-TPD, was obtained by heating -TPD above 950 °C. All the techniques involved in this study (XRD, Raman and IR spectroscopy, ¹H and ³¹P NMR) confirmed the successive chemical reactions proposed.     

Effect of PWVA/Sb2O3 complex inhibitor on the corrosion behavior of carbon steel in 55%LiBr solution

The inhibition performance of PWVA/Sb₂O₃ complex inhibitor on carbon steel was studied in 55%LiBr + 0.07 mol L⁻¹ LiOH solution. Results indicated that the complex inhibitor decreased both anodic and cathodic polarization current density and widened the passive potential region of carbon steel in test solution and can be classified as mixed inhibitor. The complex inhibitor exhibited excellent inhibition performance on carbon steel when the concentrations of PWVA and Sb₂O₃ were 300 and 200 mg L⁻¹, respectively. With the solution temperature increasing from 145 to 240 °C, the corrosion rates of carbon steel increased from 4.71 to 120.66 μm y⁻¹. In solution containing the complex inhibitor, the relationship between relative coverage ratio of inhibitor on carbon steel surface and inhibition efficiency at 145 °C was obtained as the equation μ = 0.94η, it was a direct proportion. This result proved that the complex inhibitor inhibited the corrosion of carbon steel by geometric blocking effect. When solution temperature was 160 °C, the adsorption Gibbs free energy of PWVA and Sb₂O₃ on carbon steel were −49.59 and −44.29 kJ mol⁻¹, respectively. It indicated that the adsorption processes of PWVA and Sb₂O₃ on carbon steel surface were spontaneous processes. As a strong oxidant, PWVA facilitated the compact passive film comprising of FeO, Fe₂O₃ and Fe₃O₄ forming on the surface and itself was reduced to heteropoly blue. Sb₂O₃ adsorbed on carbon steel surface formed an adsorption film. PWVA and Sb₂O₃ behaved synergistic effect. The corrosion resistance performance of carbon steel in 55%LiBr + 0.07 mol L⁻¹ LiOH solution was improved by PWVA/Sb₂O₃ complex inhibitor.     

Effect of hydrogen radical on growth of μc-Si in hetero-structured SiCx alloy films

The changes of the crystallinity of μc-Si phase are studied in samples deposited with hydrogen dilution ratio, H₂/SiH₄, from 9.0 to 19.0 by hot-wire CVD (Cat-CVD). In the samples deposited at filament temperature, T_f, of 1850 °C, the crystalline fraction and the crystallite size of μc-Si phase increased with increasing the H₂/SiH₄. The carbon content, C/(Si+C), was almost constant. In the XRD patterns, the intensity of Si(1 1 1) peak decreased and that of Si(2 2 0) peak increased with increasing the H₂/SiH₄. In the samples deposited at T_f of 2100 °C with H₂/SiH₄ over 11.4, the μc-Si phase was not formed and the C/(Si+C) increased. The growth mechanism of μc-Si in hetero-structured SiC_x alloy films is discussed.