Direct synthesis of PMN samples by spray-drying

The processing and characterisation of Pb(Mg_1/3Nb_2/3)O₃ (PMN) materials, obtained either by spray-drying the solution of the precursors or by the conventional “columbite” method, were investigated and the morphological and micro-structural characteristics were compared. The acid solution of ammonium-peroxo-niobium complex, magnesium and lead nitrates was spray-dried and the precursor powder obtained was calcined at different temperatures ranging from 350 to 900 °C. The morphologies and the XRD patterns of the powders were compared. The calcined powders exhibited a pyrochlore phase above 400 °C converting into an almost pure perovskite phase at 800 °C. The powder calcined at 350, 500 and 800 °C were sintered at different temperatures, ranging from 950 to 1150 °C, always resulting in a pure perovskite PMN material. The XRD patterns of as-fired surfaces of samples sintered at 950 and 1050 °C showed an unwanted PbO phase together with the main PMN, nevertheless this secondary phase is not present in the ground surfaces. The high reactivity of sprayed powder is reflected in the formation and densification of pure perovskite PMN material with a faster process as regards the conventional one; in particular samples of about 96% theoretical density were obtained starting from the amorphous powder calcined at low temperature (350 °C) through a reaction sintering process. Furthermore, due to the better flowability of the spray-dried powder, the cold consolidation process is highly improved and no binder addition to powder is necessary.     

Reactions of metal chlorides with hexamethyldisilazane: Novel precursors to aluminum nitride and beyond

Metal nitrides are intensely investigated because they can offer high melting points, excellent corrosion resistance, high hardness, electronic and magnetic properties superior to the corresponding metals/metal oxides. Thus, they are used in diverse applications including refractory materials, semiconductors, electronic devices, and energy storage/conversion systems. Here, we present a simple, novel, scalable and general route to metal nitride precursors by reactions of metal chlorides with hexamethyldisilazane [HMDS, (Me₃Si)₂NH] in tetrahydrofuran or acetonitrile at low temperatures (ambient to 60°C/N₂). Such reactions have received scant attention in the literature. The work reported here focuses primarily on the Al-HMDS precursor produced from the reaction of AlCl₃ with HMDS (mole ratio = 1:3) characterized by matrix-assisted laser desorption/ionization-time of flight, Fourier-transform infrared spectroscopy, thermogravimetric analysis-differential thermal analysis, and multinuclear nuclear magnetic resonance spectroscopy (NMRs) for chemical and structural analyses. The Al-HMDS precursor heated to 1600°C/4 h/N₂ produces aluminum nitride, characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and magic-angle spinning NMR. On heating to 800–1200°C/4 h/N₂, the precursor transforms to an amorphous, oxygen-sensitive powder with very high surface areas (>200 m²/g) indicating nanosized particles, which can be used as additives to polymer matrices to modify their thermal stabilities. Al₂O₃ is also presented in the final product after heating, due to its high susceptibility to oxidation. This approach was extended via proof-of-concept studies to other metal chloride systems, including Zn-HMDS, Cu-HMDS, Fe-HMDS, and Bi-HMDS. The formed precursors are volatile, offering the potential utility as gas-phase deposition precursors for their corresponding metal nitrides.     

Microencapsulation of Radix salvia miltiorrhiza nanoparticles by spray-drying

About 133.5 nm Radix salvia miltiorrhiza nanoparticles were prepared by high speed centrifugal sheering pulverizer and the nanoparticles were characterized by TEM in this study. Microcapsules containing R. salvia miltiorrhiza nanoparticles were produced by spray-drying technique using different proportions of gelatin and sodium salt of carboxymethylcellulose (CMC-Na) as wall materials. The effects of inlet temperature, flow rate, spray-gas flow and the ratio of M_core/M_wall on encapsulation yield (EY) and encapsulation efficiency (EE) were investigated. The EE was determined by reverse high performance liquid chromatography (HPLC); the resulting microcapsules were characterized by FT-IR, SEM, and X-ray diffraction analysis. In addition, in vitro release characters of R. salvia miltiorrhiza raw powder, spray-dried powder and microcapsules were also studied. The results showed that spray-dried microcapsules had a regular spherical shape but the majority presented rough surfaces or invaginations with a diameter of 2-5 μm. R. salvia miltiorrhiza nanoparticles were embedded in the wall system consisting of gelatin and CMC-Na. Higher EE and EY were obtained under the inlet temperature of 80 °C and the ratio of M_core/M_wall of 1/4. In vitro release study showed that R. salvia miltiorrhiza microcapsules could regulate drug release. This study may be helpful to the pharmaceutical application of R. salvia miltiorrhiza.     

Crack-reduced alumina/aluminum titanate composites additive manufactured by laser powder bed fusion of black TiO2−x doped alumina granules

Laser powder bed fusion is an emerging industrial technology, especially for metal and polymer applications. However, its implementation for oxide ceramics remains challenging due to low thermal shock resistance, weak densification and low light absorptance in the visible or near-infrared range. In this work, a solution to increase the powder absorptance and to reduce cracking during laser processing of alumina parts is given. This is achieved by the use of a homogeneously dispersed and reduced titanium oxide additive (TiO_2?x) within spray-dried alumina granules leading to formation of aluminum titanate with improved thermal shock behavior during powder bed fusion. The impact of different reduction temperatures on powder bed density, flowability, light absorption and grain growth of these granules is evaluated. Crack-reduced parts with a density of 96.5%, a compressive strength of 346.6 MPa and a Young's modulus of 90.2 GPa could be manufactured using powders containing 50 mol% (43.4 vol%) TiO_2?x.     

Novel bismuth ferrite nanopowder prepared by polyethylene glycol-assisted two-step solid-state reaction: Synthesis and magneto-optical properties

In this study, a bismuth ferrite (BiFeO₃) nanopowder was synthesized by combining Bi(NO₃)₃·5H₂O, Fe(NO₃)₃·9H₂O, and NaOH raw materials in the presence of polyethylene glycol (PEG) with varying polymerization degrees (i.e. PEG200, PEG400, PEG600, and PEG10000). The synthesis process was carried out by room-temperature solid-state reaction followed by subsequent secondary solid-state reaction at 550 °C. The results suggested a significant influence of PEG polymerization degree on the morphology and size of the as-synthesized products. The grain size decreased after the introduction of PEG but increased with the polymerization degree. The vibrating-sample magnetometry data revealed PEG400 and PEG600 with obvious room-temperature ferromagnetism properties. In UV–Vis spectroscopy, the absorption edge exhibited a blue shift as the polymerization degree of PEG rose. In sum, BiFeO₃ nanopowder possessed room-temperature ferromagnetism, thereby suitable photocatalyst for wastewater treatment and environmental purification with convenient recycling and substantial economic value.     

Granule performance of zirconia/alumina composite powders spray-dried using polyvinyl pyrrolidone binder

Polyvinyl pyrrolidone (PVP) was used as a binder in spray-drying a slurry containing zirconia/alumina composite powder and its influence on granulation and granule deformability was compared with those of polyvinyl alcohol (PVA) and polyethylene glycol–hydroxyethyl cellulose cobinder (PEG–HEC). Although the most spherical solid granules were obtained from the slurry containing PEG–HEC, the granules containing PVP were the most deformable during compaction. It was apparent that a high-viscosity organic additive mixture added to the slurry resulted in highly spherical solid granules, and a low T_g of the mixture led to a high deformability. The flexural strengths of composites prepared from granules containing PVP, PEG–HEC, and PVA were 634, 578, and 468 MPa, respectively, which corresponds to the ascending order of T_g of the binders mixed with plasticizers.     

Synthesis of spherical LiMn2O4 cathode material by dynamic sintering of spray-dried precursors

Spherical LiMn₂O₄ particles were successfully synthesized by dynamically sintering spherical precursor powders, which were prepared by a slurry spray-drying method. The effect of the sintering process on the morphology of LiMn₂O₄ was studied. It was found that a one-step static sintering process combined with a spray-drying method could not be adopted to prepare spherical products. A two-step sintering procedure consisting of completely decomposing sprayed precursors at low temperature and further sintering at elevated temperature facilitated spherical particle formation. The dynamic sintering program enhanced the effect of the two-step sintering process in the formation of spherical LiMn₂O₄ powders. The LiMn₂O₄ powders prepared by the dynamic sintering process, after initially decomposing the spherical spray-dried precursor at 180 °C for 5 h and then sintering it at 700 °C for 8 h, were spherical and pure spinel. The as-prepared spherical material had a high tap density (ca. 1.6 g/cm³). Its specific capacity was about 117 mAh/g between 3.0 and 4.2 V at a rate of 0.2 C. The retention of capacity for this product was about 95% over 50 cycles. The rate capability test indicated that the retention of the discharge capacity at 4C rate was still 95.5% of its 0.2 rate capacity. All the results showed that the spherical LiMn₂O₄ product made by the dynamic sintering process had a good performance for lithium ion batteries. This novel method combining a dynamic sintering system and a spray-drying process is an effective synthesis method for the spherical cathode material in lithium ion batteries.     

Impacts of desugarization and drying methods on physicochemical and functional properties of duck albumen powder

Desugarization of duck albumen using glucose oxidase/catalase was optimized before drying. Optimum condition for desugarization using response surface methodology was as follows: glucose oxidase 31.24 units and catalase 781 units/mL albumen and incubation time of 6.55?h at 30?°C. Foaming capacity (FC) and foam stability (FS) were enhanced, while the solubility decreased after desugarization. This coincided with the increase in surface hydrophobicity (p?<?0.05). Higher trypsin inhibitory activity was found in freeze-dried albumen powder than spray-dried counterpart. Trypsin inhibitory activity was continuously decreased as the inlet temperature for spray-drying increased (p?<?0.05). Desugarization could increase FC and FS, but slightly decreased solubility of powders. No marked differences in protein patterns were observed in all the powders, regardless of desugarization and drying methods. L* of albumen powder decreased but ΔE, a*-, b*-values and browning index increased as spray-drying temperatures increased (p?<?0.05). Therefore, prior desugarization could lower browning and increased foaming property of duck albumen, particularly when spray-dried with inlet temperature of 160?°C.     

Electrical transport and magnetic properties of Mn3O4-La0.7Ca0.3MnO3 ceramic composites prepared by a one-step spray-drying technique

La_0.7Ca_0.3MnO₃/Mn₃O₄ composites can be synthesized in one step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized powders. Another advantage of this composite system is that a long sintering step can be used without leading to significant modification of the manganite composition. The percolation threshold is reached at ∼20 vol% of manganite phase. The 77 K low field magnetoresistance is enhanced to ∼11% at 0.15 T when the composition is close to the percolation threshold.     

Spray-drying of ceramics for plasma-spray coating

The spray-drying process of ceramics which are candidate materials for thermal barrier coatings (TBCs), i.e. 3YSZ+0, 2, 4, 6 wt.% Al₂O₃, is discussed in this paper. The two most important properties of spray-dried powders to determine the coating quality are density and particle size. Polyethyleneimine (PEI) acts as both an organic binder and a dispersant giving low viscosity in the suspension. The optimised suspension composition is: ⩾ 33.6 vol.% powder+1.8 wt.% PEI+ethanol, and operational parameters of the spray-dryer: drying temperature 175°C, feeding rate 55 cm³/min, feeding pressure 1.013×10⁴ Pa.     

Morphology and crystallinity of KNbO3-based nano powder fabricated by sol–gel process

Lead-free KNbO₃ (KN) powder was fabricated by sol–gel process from metal alkoxides. KN precursor solutions were prepared by different preparation conditions such as the order of reflux process for alkoxides and the kinds of solvent. KN powders were sintered at 900 °C with a heating rate of 10 °C/min. Single phase KN powder was obtained using precursor solution prepared by reflux at 120 °C. We considered that the crystallinity of KN powder was affected by the dimer in Nb-pentaethoxide of the starting chemicals. On the other hand, grain shape of the KN powder also depended on the existence of secondary phase K₄Nb₆O₁₇, and the grain size of the fine powder fabricated from precursor solution prepared by reflux at 80 °C using 2-methoxethanol and ethanol solvents was estimated to be about 500 nm and 1 μm, respectively.     

Synthesis of La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 using a polymeric method

Nanocrystalline La_0.9Sr_0.1Al_0.85Mg_0.1Co_0.05O_2.875 (LSAMC) powders were synthesized via a polymeric method using poly(vinyl alcohol) (PVA). The effect of PVA content on the synthesized powders was studied. When the ratio of positively charged valences (Mⁿ⁺) to hydroxyl groups (OH) is 1.5:1, crystalline LaAlO₃ could be obtained at such a low calcination temperature as 700 °C. While at 900 °C the ratio is of less importance, since pure LaAlO₃ perovskite could be formed for all powders after calcination at 900 °C. Thermal analysis (TG/DTA) was utilized to characterize the thermal decomposition behaviour of precursor powders. The chemical structure of the calcined powder was studied by Fourier transform infrared (FTIR) spectroscopy. The powder morphology and microstructure were examined by SEM. Dense pellets with well-developed submicron microstructures could be formed after sintering at 1450 °C for 5 h. Compared with the solid-state reaction method, the sintering temperature is substantially lower for powder prepared by the PVA method. This is due to the ultrafine and highly reactive powder produced.     

Submicro-sized LiMn2O4 prepared by a sol–gel, spray-drying method

Submicro-sized LiMn₂O₄ powders were produced by a sol–gel, spray-drying method in which a brown gel precursor was prepared via the reaction of LiOH alkaline solution with 1 M Mn(CH₃COO)₂. The gel precursor was then transferred into a dry precursor powder via a spray-dry process. After heating treatment the spinel LiMn₂O₄ powder was obtained. The composition and the crystal size of the samples were strongly affected by the spray speed in the drying process and the heating temperature. The structure and the morphology of LiMn₂O₄ powder were investigated by DTA, TGA, IR, XRD and SEM methods. It was discovered that submicro-sized LiMn₂O₄ powder could be formed under the conditions of rotating spray speed of 15 000 rpm and syntheses temperature of 700 °C. The electrochemical properties of LiMn₂O₄ samples in 1 M LiPF₆, EC:DMC = 1:1 solution were tested by measuring the voltammograms and charge–discharge curves. The submicro-sized LiMn₂O₄ sample made at 700 °C has a capacity of 128 mAh g^–1 and good cycle stability for Li⁺ intercalation reaction. This method may be applied to the industrial-scale production of superfine LiMn₂O₄ powder for use in lithium ion batteries.     

Synthesis of hollow spherical WO3 powder by spray solution combustion and its photocatalytic properties

Hollow spherical WO₃ powder was prepared from mixed solution of ammonium metatungstate, glycine and ammonium nitrate by spray solution combustion synthesis (SSCS) method. The effects of fuel ratio, temperature, precursor solution concentration on the structure and morphology of as-prepared powder, and the SSCS mechanism have been discussed in detail. When precursor solution concentration is 0.10 mol/L, in which the fuel ratio is 2, and reaction temperature set to be 800 °C, the spherical WO₃ powder with smooth surface and a median diameter of 24.02 μm can be obtained, which consists of particles with a diameter of about 30 nm, and the specific surface area is 13.5 m²/g. Moreover, the as-synthesized WO₃ powder is applied to degrade RhB solution in visible light to evaluate its catalytic performance by PLS-SXE300/300UV. Only 10 mg powder can degrade 70.1% RhB solution within 2 h.     

Effect of Li doping on the superconducting properties of single domain GdBCO bulks fabricated by the top-seeded infiltration and growth process

Single domain GdBCO bulk superconductors have been fabricated by the top-seeded infiltration and growth process (Gd+011 TSIG) with solid phase compositions of (1-x)(Gd₂O₃+1.2BaCuO₂)+xLi₂CO₃, (x=0, 0.04, 0.08, 0.10, 0.12, 0.16 wt%). The effect of Li₂CO₃ doping on the growth morphology, microstructure, levitation force, trapped field and critical temperature (T_c) of single domain GdBCO bulks have also been investigated based on these samples. The results show that the single-domain GdBCO bulks can be fabricated when x is in the range of 0–0.16 wt%. The size and distribution of Gd211 particles are not influenced by the Li₂CO₃ doping in the samples. The T_c of the samples decrease from 92.5 K (x=0 wt%) to 89.5 K (x=0.16 wt%) when x increases. The decreasing trend of T_c was caused by the substitution of Li⁺ on Cu²⁺ site in the GdBCO crystal. Both of the levitation forces and trapped fields of the samples increase first and then decrease with the increase of x; both of the largest levitation force of 38.5 N（77 K，0.5 T） and the largest trapped field of 0.31 T（77 K，0.5 T） are obtained in the sample when x=0.10 wt%. These results show that appropriate Li doping is an effective way to enhance the flux pinning force and the other physical properties of GdBCO bulk superconductors fabricated by the Gd+011 TSIG method.     

Evaluation of crushing strength of spray-dried MgAl2O4 granule beds

The crushing strengths of four different experimental magnesium aluminate spinel (MgAl₂O₄) granule beds were monitored with the axial die pressing test after heat treatments. Precursor, magnesium hydroxide (Mg(OH)₂) and magnesium oxide (MgO) as Mg precursor and aluminium oxide hydroxide Al(O)OH and α-Al₂O₃ as Al precursor, were used for experimental granules, which were manufactured via a dispersion manufacturing and spray-drying process. After spray-drying, granules were heat treated in air at 1000, 1100, 1200, 1300 and 1400 °C. In order to understand the potential effect of precursor, phase structure, morphology, particle size distribution and density of granules on crushing strength behaviour, scanning X-ray diffraction (XRD) was used together with electron microscopy (SEM) and laser diffraction (LDPA) for characterisation. All precursor mixtures formed spherical granules during the spray-drying process and pure spinel phase structure during heat treatment. The crushing strength test results indicated that the Al precursor clearly affected the crushing strength behaviour of experimental granule beds. The highest strength was observed for granule beds with Al(O)OH) as Al and Mg(OH)₂ as Mg precursor.     

Selective laser reaction synthesis of SiC,Si3N4 and HfC/SiC composites for additive manufacturing

Selective laser reaction sintering techniques (SLRS) techniques were investigated for the production of near net-shape non-oxide ceramics including SiC, Si₃N₄, and HfC/SiC composites that might be compatible with prevailing powder bed fusion additive manufacturing processes. Reaction bonded layers of covalent ceramics were produced using in-situ reactions that occur during selective laser processing and layer formation. During SLRS, precursor materials composed of metal and/or metal oxide powders were fashioned into powder beds for conversion to non-oxide ceramic layers. Laser-processing was used to initiate simultaneous chemical conversion and local interparticle bonding of precursor particles in 100 vol% CH₄ or NH₃ gases. Several factors related to the reaction synthesis process—precursor chemistry, gas-solid and gas-liquid synthesis mechanisms, precursor vapor pressures—were investigated in relation to resulting microstructures and non-oxide yields. Results indicated that the volumetric changes which occurred during in-situ conversion of single component precursors negatively impacted the surface layer microstructure. To circumvent the internal stresses and cracking that accompanied the conversion of Si or Hf (that expands upon conversion) or SiO_x (that contracts during conversion), optimized ratios of the precursor constituents were used to produce near isovolumetric conversion to the product phase. Phase characterization indicated that precipitation of SiC from the Si/SiO₂ melt formed continuous, crack-free, and dense layers of 93.7 wt% SiC that were approximately 35 µm thick_, while sintered HfC/SiC composites (84.2 wt% yield) were produced from the laser-processing of Hf/SiO₂ in CH₄. By contrast, the SLRS of Si/SiO_x precursor materials used to produce Si₃N₄ resulted in whisker formation and materials vaporization due to the high temperatures required for conversion. The results demonstrate that under appropriate processing conditions and precursor selection, the formation of near net-shape SiC and SiC composites might be achieved through single-step AM-compatible techniques.     

A 3D oxalate-bridged [CuIIFeII] coordination polymer as molecular precursor for CuFe2O4 spinel—photocatalytic features

A 3D heterometallic oxalate-bridged coordination polymer [Cu^IIFe^II₂(H₂O)(terpy)(C₂O₄)₃]_n (terpy = 2,2′:6′,2″-terpyridine) ( 1 ) was investigated both as photocatalyst for the organic dye removal and as a single-source precursor for the preparation of the copper ferrite (CuFe₂O₄) nanocrystals by thermal processing. The dual functionality of 1 was supported by the degradation of aqueous solutions of rhodamine B (RhB) and methylene blue (MB) solutions under visible (Vis) and ultraviolet (UV) light irradiation, powder X-ray diffraction data collection at room temperature, and the optical and scanning electron microscopy analyses. A close inspection of the X-ray diffraction patterns unveiled qualitative and quantitative information on the phase composition obtained after the single-source molecular precursor route to spinel oxide. By optimizing the temperature levels and setting the controlled heating rate at 6 h of holding time, the phase composition of thermal processing of 1 was evaluated—thermal treatment of 1 at 950°C for 6 h and a heating/cooling rate of 10°C min⁻¹ resulted in the formation of solely tetragonal spinel phase of CuFe₂O₄, whereas the formation of both tetragonal and cubic CuFe₂O₄ phases was observed at 950°C by the heating rate of 30°C min⁻¹. To obtain the high-temperature cubic CuFe₂O₄ oxide, compound 1 was heated and then quenched at 925°C, which led to the formation of the cubic spinel ferrite as the main crystalline oxide phase. Moreover, the photocatalytic properties of the t-CuFe₂O₄ spinel were investigated under the same conditions as for 1 . The optical bandgap energies were estimated from UV–Vis absorption spectra for both metal oxide and precursor powder.     

Alkali-activated waste ceramics: Importance of precursor particle size distribution

The waste ceramics belongs to wide range of aluminosilicate materials which can be alkaline-activated to geopolymer cement – possible “green” alternative to conventional Portland cement. The studied ceramic material is generated during the size adjustment of ceramic building blocks by means of grinding. It means that most of the material is very fine, but it contains also some larger shards. This ceramic powder was used as geopolymer precursor “as received” and after removal of particles retained on 1, 0.5 and 0.125 mm sieves. These four types of precursor were activated by sodium silicate (SiO₂/Na₂O = 1) solution. The prepared mortars were tested for strength, basic physical properties, transport parameters and characterized by help of XRD and thermal analysis. It was found that the best mechanical performance provided the precursor after removal of particles retained on 0.5 mm sieve thanks to the highest geopolymerization rate. The presence of coarser particles in precursor gave rise to porosity, what consequently influenced transport parameter of geopolymers towards the lower thermal conductivity and faster moisture transport.     

Fat encapsulation in spray-dried food powders

The surface composition of spray-dried sodium caseinate/lactose emulsions having different oil phases were estimated using electron spectroscopy for chemical analysis (ESCA), and the particle structure was studied using scanning electron microscopy (SEM) both before and after storage under humid conditions. After spray-drying, powders in which the oil phases consisting of fats with intermediate melting points, such as hardened coconut oil and butter fat, had the highest surface coverage of fat, approximately 34%. The powder with soybean oil as the oil phase had a surface coverage of fat of approximately 15%. The high-melting hardened rapeseed oil was almost completely encapsulated after spray-drying. After storage in a humid atmosphere, fat was released onto all the powder surfaces (surface fat after storage, between 50–65%) except for those with hardened rapeseed oil in which the fat remained encapsulated. These observations are consistent with the powder structure observed by SEM. The surface composition estimated by ESCA for spray-dried sodium caseinate/lactose-containing emulsions with different amounts of soybean oil and a constant lactose/sodium caseinate ratio showed an almost completely encapsulated oil-phase after drying. Storage of these powders in a humid atmosphere leads to a release of fat onto the powder surface even if the soybean oil content is low (1% of the dry weight). Powders made from soybean oil emulsions with sodium caseinate alone exhibit a much lower degree of encapsulation than in the system where lactose is present.