Hydrothermal Crystallization of Zirconia and Zirconia Solid Solutions

Zirconia as well as yttria-zirconia and calcia-zirconia solid-solution powders were crystallized under hydrothermal conditions from (co)precipitated hydroxides. The morphology of the powder particles is strongly dependent on the crystallization conditions. The powders crystallized in a water solution of Na, K, and Li hydroxides show elongated particles of much larger sizes than those which result from the process carried out in pure water or a water solution of Na, K, or Li chlorides. The shapes of the latter particles are isometric. The growth mechanism of the elongated particles is suggested.     

Kinetics of nucleation and crystallization in poly(butylene succinate) nanocomposites

Differential fast scanning calorimetry (DFSC) was employed on poly(butylene succinate) nanocomposites containing silver nanoparticles and multi-walled carbon nanotubes (MWCNT), in order to identify the temperature range of heterogeneous nucleation caused by both nanofillers. The fast scanning rates also allow investigating self-nucleation by recrystallization experiments approaching the crystallization temperature from low temperatures. The recrystallization behavior of PBSu and its nanocomposites is distinct from all other polymers studied so far as only the previously crystallized part of the material is able to recrystallize, independently on the available large number of nuclei. Since full melting of small crystals at low temperatures is observed this highlights the importance of ordered structures remaining in the polymer melt. On cooling from the melt the neat polymer did not crystallize at rates higher than 70 K/s, while the nanocomposites needed rates of 500 K/s and 300 K/s for silver and MWCNT, respectively. Below 280 K the crystallization kinetics of the matrix was almost the same with the nanocomposite samples. The nucleation mechanism changes at 280 K from heterogeneous to homogeneous. The study further confirms that below the glass transition nucleation and crystallization appears only after approaching the enthalpy value of the extrapolated supercooled liquid by enthalpy relaxation.     

Development of crystallographic texture in chemical solution deposited lead zirconate titanate seed layers

Direct seeding of {001} textured lead zirconate titanate (PZT) on platinized silicon substrates was achieved by chemical solution deposition. The processing space for {001} PZT texturing was explored, under fixed PZT pyrolysis and crystallization conditions, by varying the lead content in solution, dopant species, and PZT layer thicknesses for deposition on platinized Si substrates with different platinum grain sizes. Strong {001} texture was achieved on fine‐grained (25 nm) platinum deposited at room temperature and dense, large‐grained platinum (80 nm) deposited at elevated temperature. Increases in lead content of solutions (from lead excesses of 10 at.% to 16 at.%) reduced surface pyrochlore coverage, with no substantial influence on orientation or grain size. Seed layer texturing was found to be insensitive to doping (Mn and Nb) on room temperature platinum, although niobium doping increased pyrochlore coverage. Conversely, on platinum deposited at high temperature, manganese doping reduced the perovskite nucleation, producing a rosette microstructure. Undoped seed layers from 30 to 70 nm thick were found to be strongly {001} textured while thicker layers were {111} textured and thinner layers were poorly crystallized.     

273 K及323 K条件下NaCl–NaBr–CH3OH三元体系相平衡 研究及其应用

为了对苦卤结晶析出的Na(Cl,Br)固溶体中氯化钠组分和溴化钠组分进行分离,测定了NaCl–NaBr–CH3OH三元体系在273及323 K温度时的溶解度数据,根据测得的液相点和湿渣相点确定了对应的固相点,由此绘制出了两个温度下的相图。结果显示,273及323 K温度下该三元体系的相图特征相似,均只有一个共饱点、两条饱和溶解度曲线,对应的固相结晶区有三个：NaCl纯盐结晶区、NaCl和Na(Cl,Br)固溶体共结晶区、Na(Cl,Br)固溶体结晶区。NaBr在无水甲醇中溶解度的增大导致NaCl溶解度大幅减小,说明NaBr对NaCl产生了较强的盐析效应,273 K时两种溶质在甲醇中的溶解度均比323 K时的溶解度大。依据273和323 K的NaCl–NaBr–CH3OH体系相图及298 K的NaCl–NaBr–H2O体系相图设计了分离Na(Cl,Br)固溶体中氯化钠和溴化钠的工艺。     

Influence of the method of mixing on homogeneity and crystallization kinetics of blends of linear and branched polyethylene

The influence of mixing method—solution and melt mixing—on the homogeneity and crystallization kinetics of a series of blends of single‐site materials of linear polyethylene and ethyl‐branched polyethylene was studied by differential scanning calorimetry. Data obtained for heats of melting and crystallization, melting and crystallization peak temperatures, and melting and crystallization temperature profiles were essentially the same for the samples obtained by the two mixing methods. The results obtained can be interpreted as indicating that melt mixing is capable of producing homogeneous melts of these relatively low molar mass polymers, given that solution mixing is considered to give perfectly homogeneous blends. The heat associated with the high temperature melting peak after crystallization at 125°C of the blend samples, obtained by the two preparation methods, was higher than that of the linear polyethylene included in the blends, suggesting that a part of the branched polyethylene crystallized at 125°C. The unblended branched polyethylene showed no crystallization at 125°C. Samples obtained by powder mixing showed independent crystallization and melting of the linear and branched polyethylene components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1730–1736, 2004     

Fast preparation of porous anatase material via CuO-mediated glass crystallization and acid-leaching

As an attempt to facilitate the mass production of porous anatase catalysts in industry, in this work, frits with molar ratios of MgO:TiO₂:P₂O₅ = 20:32:24 and an extra addition of CuO (0, 8, 16, and 24 mol%) were first prepared by melt water-quenching method. The frits were further heat- and acid-treated, forming porous anatase consisting of nanosheets. The study showed that the CuO-containing samples had increasing crystallization of anatase and even the crystallization of CuO nano-rods. The easy dissolution of CuO nano-rods and the abundant grain boundaries in the heat-treated samples provided path for the acid-leaching and greatly accelerated the selective dissolution of the crystallized samples, reducing the acid-leaching time from 48 h for the CuO-free sample to 3 h for the sample containing 24 mol% CuO to form a similar porous structure. The preformed anatase acted as nucleus to induce the in situ growth of anatase nanosheets. As a result, CuO greatly fastened the formation of porous anatase, making the industrial production of porous anatase possible.     

Synthesis of submicron zeolite LTA particles from natural clinoptilolite and industrial grade chemicals using one stage procedure

A powdered natural clinoptilolite-rich tuff (100 mesh) from Semnan region of Iran was successfully converted to higher value-added synthetic zeolite A (submicron particles of ~ 200–300 nm) in a single stage procedure under a hydrothermal condition. Effect of different parameters such as crystallization temperature, sodium hydroxide concentration, solid/liquid ratio (the mass of clinoptilolite; g; to the volume of sodium hydroxide solution; ml) and crystallization duration on the final product were investigated. The formation of zeolite A was ascertained by X-ray powder diffraction, X-ray florescence (chemical analysis), and scanning electron microscopy techniques. The results were revealed that reaction temperature of 353 K, sodium hydroxide concentration of 2 M, crystallization time of 4 h, and solid to liquid ratio of 1/18 were optimized condition for this conversion.     

Enhanced crystallization of poly(lactide) stereocomplex by xylan propionate

The effect of xylan propionate (XylPr) as a novel biomass‐derived nucleating agent on the poly(lactide) sterecomplex was investigated. Addition of XylPr to an enantiomeric blend of poly(l ‐lactide) (PLLA) and poly(d ‐lactide) (PDLA) was performed in either the solution state or molten state. The solution blend of PLLA/PDLA with XylPr was prepared by mixing equal volumes of 1 wt% XylPr/PLLA and 1 wt% XylPr/PDLA solutions in chloroform and precipitating in methanol. The solution blend with XylPr showed shorter half‐time crystallization than the solution blend without XylPr in isothermal crystallization between 80 and 140 °C, although homocrystallization occurred. Enhanced stereocomplex crystallization in the solution blend with XylPr was observed at 180 °C, where no crystallization occurred in the solution blend without XylPr. Addition of XylPr to PLLA/PDLA blend in the molten state was performed at 240 °C. Thereafter, the melt blend of PLLA/PDLA with or without XylPr was either quenched in iced water or isothermally crystallized directly from the melt. Isothermal crystallization of the melt‐quenched blend with XylPr gave a similar result to the solution blend with XylPr. In contrast, the melt‐crystallized blend with XylPr formed only stereocomplex crystals after crystallization above 140 °C. Furthermore, the melt‐crystallized blend with XylPr showed a higher crystallinity index and melting temperature than the melt‐crystallized blend without XylPr. This shows that XylPr promotes stereocomplex crystallization only when the blend of PLLA/PDLA with XylPr is directly crystallized from the molten state just after blending. © 2016 Society of Chemical Industry     

A comparison of crystallization behavior for melt and cold crystallized poly (l-Lactide) using rapid scanning rate calorimetry

A unique rapid scanning rate differential scanning calorimeter is used to examine the differences in melt and cold crystallized poly (l-Lactide) (PLLA), a biodegradable semi-crystalline polymer. After isothermal melt and cold crystallization at various temperatures, both melt and cold crystallized PLLA are characterized by similar melting temperatures (T_m) and exhibit multiple melting behavior on heating at 500 °C/min. However, cold crystallization results in a higher degree of crystallinity (w_c) compared to melt crystallization. While the overall amorphous fraction is higher for melt crystallization, the mobile amorphous fraction (w_a) is found to be higher for cold crystallization. The rigid amorphous fraction (w_raf) in PLLA is determined to be higher for melt crystallization than for cold crystallization at almost all temperatures. The higher values of w_raf also appear to result in higher values of the glass transition temperature (T_g) for melt crystallized samples due to a reduction in mobility of amorphous phase. These dramatic differences depending on whether the material is brought to the crystallization temperature from the melt or the glassy state, could have profound implications for processing and optimizing the properties of PLLA.     

Catalyzed synthesis of rhombohedral boron nitride in sodium chloride molten salt

Although a variety of methodologies/techniques have been used to prepare h-BN powders with different sizes and purities, only a few methods are reported to synthesize r-BN. In this work, highly crystalline r-BN with a purity of 94 wt% was successfully synthesized in sodium chloride molten salt using Na₂B₄O₇ and Mg powders as starting materials at 1000 °C in nitrogen atmosphere. The sodium (Na) produced by the reaction of Mg and Na₂B₄O₇ has a positive effect on the formation r-BN in the molten salt. The effect of Na as a crystallization promoter to produce crystallized r-BN was demonstrated by heating a mixture of t-BN and Na at 800–1200 °C. The formation, dissolution and evaporation of Na in the melt was discussed. The influence of synthesis temperature on the phase composition and morphology of the final products in the melt was also investigated. The possible formation mechanism of r-BN is proposed.     

Effect of crystallization temperature on the synthesis of ETS-4 and ETS-10 titanosilicates

The effect of temperature on the crystallization and purity of (Na,K)-ETS-4 and (Na,K)-ETS-10 from gels with an optimized composition was examined. Microporous titano silicates (Na,K)-ETS-4 and (Na,K)-ETS-10 were obtained by hydrothermal synthesis from gels of molar composition 5x.Na₂O: 3KF: TiO₂: 6.4x.HCl: 7.45SiO₂: 197.5 H₂O where x = 2.0 for ETS-4 and x = 1.0 for ETS-10 in absence of seeds and organic template agents. The kinetics of crystallization at 160, 180 and 200 °C, respectively, by comparing gel crystallinity (%) at different times, the induction times and the apparent activation energies for nucleation and crystallization were studied. The induction time (linked to the formation of the first nuclei) suggests that the nucleation is more difficult in the case of ETS-10 and the crystal growth rates are similar at higher temperatures (>180 °C). The apparent activation energies are smaller for the (Na,K)-ETS-4 (a stable structure) crystallization than of (Na,K)-ETS-10 (a metastable structure). The characterization of these microporous materials was carried out by XRD, SEM and TGA-DSC techniques.     

Hydrothermal synthesis of nickel ferrite powders,their properties and sintering

NiFe₂O₄ powders were synthesized by co-precipitation with ammonia solution using aqueous solution of NiCl₂ and FeCl₃ followed by hydrothermal treatment of the precipitate. It was found that crystallization in water led to nanometric in size and isometric in shape crystallites, whereas crystallization in sodium hydroxide solution results in particles of well defined walls. Generally, particles crystallized in water were smaller and their particle size distribution was narrower than those crystallized in NaOH solution. Behaviour of the powders under dry compaction and sintering strongly depended on the powder morphology. The powder crystallized in NaOH solution gave compacts of higher density and sintered density of this powder was also higher than that of the powder processed in water.     

Crystallization behavior of poly(β-propiolactone)-block-polyethylene copolymers with varying polyethylene crystallinities

The crystallization behavior of poly(β-propiolactone)-block-polyethylene (PPL-b-PE) copolymers with high PE crystallinities χ_PE (>0.30) has been examined using time-resolved synchrotron small-angle X-ray scattering and Fourier transform infrared spectroscopy, where the PE block crystallized first and subsequently the PPL block crystallized on quenching from a strongly segregated melt. The crystallization of PE blocks destroyed the lamellar microdomain structure (LMS) existing in the melt to form the crystalline lamellar morphology (CLM), and then PPL blocks crystallized within CLM. This morphology formation was compared to our previous results for the crystallization of PPL-b-PE copolymers with low χ_PE (0.12 < χ_PE < 0.26), where the crystallizability of PE blocks was not sufficiently large to destroy LMS. As a result, PE blocks crystallized promptly within LMS to reinforce and stabilize it against the subsequent crystallization of PPL blocks, yielding the confined crystallization of both blocks within LMS. We summarize these results including the case of χ_PE = 0, and propose three mechanisms of morphology formation occurring in PPL-b-PE copolymers according to χ_PE (i.e., high, low, or zero).     

Polymorphism of POS. II. kinetics of melt crystallization

Melt crystallization of four polymorphs of POS, α,δ, pseudo-β′ andβ, was examined with pure samples (>99.9%). Induction time, τ, for newly occurring crystals was measured with a polarizing microscope equipped with a temperature-controlled growth cell. Rate of crystallization, 1/τ, was obtained for each polymorph, whose identification was done with x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Two modes of crystallization, melt cooling and melt mediation, were applied. From these experiments, the following conclusions were obtained: (i) The rate of melt-mediated crystallization was always higher than of simple melt cooling; (ii) the pseudo-β′ form was crystallized in a wider range of temperature than the less stable δ form; (iii) the occurrence behavior of the polymorphs differed between simple melt cooling and melt mediation; (iv) the δ form was crystallized only by simple melt cooling in a narrow range of temperature, 25.5°C∼28.3°C. This means that there is a possibility that δ may result from racemic compounds that are crystallized in a specific manner. The experimental results are discussed in comparison to 1,3-dipalmitoyl2-oleoylglycerol (POP), 1,3-distearoyl-2-oleoylglycerol (SOS) and cocoa butter.     

AlCl3·6H2O在盐酸体系中的结晶行为

研究了AlCl₃·6H₂O在盐酸体系中的结晶行为,考察了铁、钙、镁、钾、钠等杂质对AlCl₃·6H₂O结晶行为的影响,并利用聚焦光束反射测量技术（FBRM）和颗粒录影显微镜（PVM）探讨了不同盐酸滴加速度下AlCl₃·6H₂O的结晶粒度分布及形貌。结果表明,AlCl₃·6H₂O的结晶量随着盐酸加入量的增加而增加,当浓盐酸加入量为AlCl₃饱和溶液体积的2.25倍时,25℃时的结晶效率可达到80%。溶液中Fe的存在可促进AlCl₃·6H₂O的结晶,在1.5 mol·kg^-1的AlCl₃溶液中,当铝铁摩尔比低于3：1时,得到的AlCl₃·6H₂O晶体中铁的含量小于0.1%。钾、钙、镁、钠等杂质对AlCl₃·6H₂O的结晶影响不大。盐酸添加速度影响AlCl₃·6H₂O的形貌,快的盐酸添加速度易使晶体发生团聚,颗粒粒径小,盐酸添加速度较慢时,可得到颗粒较大、形貌好的单晶。     

Solubility limit of Si in YAG at 1700 °C in vacuum

Measurement of the solubility limit of Si in yttrium aluminum garnet (YAG-Y₃Al₅O₁₂) is crucial for understanding the mechanisms by which Si influences grain boundary mobility, and the mechanisms by which grain boundaries migrate. In the present work, the solubility limit of Si in YAG at 1700 °C in vacuum (5 × 10⁻⁶ Torr), which are the most common sintering temperature and environment for YAG, was measured for the first time. Measurements were conducted by wavelength dispersive spectroscopy (WDS), using polished YAG specimens with 3700 ppm Si (0.8 wt% SiO₂). Si content to ensure saturation with Si. The accuracy of the WDS result was confirmed by using a series of doped specimens and by comparing to inductively coupled plasma mass spectrometry ICP-MS results. The results indicate that the solubility limit of Si in YAG at 1700 °C (5 × 10⁻⁶ Torr), is 980 ± 60 ppm. The measured Si solubility was found to significantly depend on the cooling rate, where for furnace cooled specimens the measured Si solubility was 650 ± 60 ppm. A second phase in triple junction was repeatedly observed when higher content of Si was used, confirming this work results.     

Melt crystallization of syndiotactic polypropylene in nanolayer confinement impacting structure

Layer multiplying coextrusion technique was used to fabricate films with hundreds of alternating layers of a crystallizable polymer, syndiotactic polypropylene (sPP), and an amorphous polymer, polycarbonate (PC). Atomic force microscopy and wide-angle X-ray scattering revealed the absence of any oriented crystal morphology of sPP in the extruded layered films. An approach of isothermal melt recrystallization of sPP nanolayers revealed the formation of oriented lamellae under the rigid confinement of hard glassy PC layers. X-ray scattering data showed that sPP crystallized as stacks of single crystal lamellae oriented parallel to the layers at high crystallization temperatures. As the crystallization temperature decreased, on-edge lamellar orientation was preferred. Formation of in-plane lamellae was attributed to heterogeneous bulk nucleation, while nucleation of on-edge lamellae was initiated at substrate interface. It was observed that as the layers thickness reduced, the orientations of both in-plane and on-edge lamellae became sharper.Detailed analysis of crystal orientations in 30 and 120 nm sPP layers was carried out. Melt recrystallization of 30 nm layers revealed formation of in-plane lamellae above 90 °C and mainly on-edge lamellae below 70 °C. At intermediate temperatures, formation of mixed crystals was reported. In 120 nm layers, crystallization temperature of 100 °C was required to form in-plane crystals, while on-edge lamellae were formed below 90 °C.We also investigated crystallization onset for on-edge and in-plane lamellar nucleation. Although, the two crystal fractions were significantly affected as a function of crystallization temperature, it was noticeable that both crystal habits were initiated at the same time. The results suggested that the relative growth rates of in-plane and on-edge crystal orientations was responsible for different fractions of the two crystal orientations at a given crystallization temperature.Oxygen transport properties of melt recrystallized sPP layers were measured. When the melt recrystallization temperature increased from 85 to 105 °C in 120 nm sPP layers, at least one order of magnitude enhancement in the barrier properties was observed. It was evident from the X-ray data that the amount of in-plane crystal fraction increased with increasing crystallization temperature. In-plane crystals acted as impermeable platelets to oxygen flux resulting in improved gas barrier properties. A similar effect was observed in 30 nm sPP layers over a temperature range of 60-105 °C. A correlation between in-plane crystal fraction and the oxygen permeability was obtained from X-ray and oxygen transport data analysis. It was shown that the permeability decreased exponentially with increasing in-plane crystal fraction.     

Study of morphology and crystal growth behaviour of nanoclay-containing biodegradable polymer blend thin films using atomic force microscopy

Thin films of unmodified and nanoclay-modified polylactide/poly(butylene succinate) (PLA/PBS) blends were prepared on a glass substrate with a spin coater. The morphology and crystal growth behaviours for the films, crystallized at different temperatures, were visualized with atomic force microscope (AFM). AFM images showed that the size of the dispersed PBS phase was reduced on the addition of 2 wt% clay to the PLA/PBS blend, and the size of the dispersed phase increases with the further addition of clay. Transmission electron microscopy studies indicated that this behaviour was due to the preferential location of silicates in the PBS phase than in the PLA phase. A similar effect of clay to the blend thin films on the dispersed phase and the crystalline morphology were observed when annealed at 60 °C and 120 °C. However, at 60 °C the addition of clay to the blend quenched the growth of edge-on lamellae. The crystalline morphologies at 120 °C were dominated by edge-on lamellae grown around the PBS phase to form spherulites. Morphologies of thin films crystallized at 120 °C from melt were dominated by the flat-on lamellae, while the ones crystallized at 70 °C from melt were dominated by the edge-on lamellae. The degree of clay silicate dispersion in the blend matrix was characterized by X-ray diffraction. These results show how the crystallization temperatures and the addition of the clay particles influence the morphology of the thin films.     

Polymorphic behavior of some fully hydrogenated oils and their mixtures with liquid oil

Fully hydrogenated soybean oil, beef fat, rapeseed oil, a rapeseed, palm and soybean oil blend, cottonseed oil and palm oil were characterized by fatty acid composition, glyceride carbon number and partial glyceride content, as well as melting and crystallization properties. The latter were established by differential scanning calorimetry. Polymorphic behavior was analyzed by X-ray diffraction of the products in the flake or granulated form and when freshly crystallized from a melt. The hard fats were dissolved in canola oil at levels of 20, 50 and 80% and crystallized from the melt. Palm oil had the lowest crystallization temperature and the lowest melting temperature; rapessed had the highest crystallization temperature and soybean the highest melting temperature. All of the hard fats crystallized initially in the =00 form. When diluted with canola oil, only palm oil was able to maintain β′ stability.     

Effect of temperature on recrystallization behavior of cocoa butter

Crystallization of cocoa butter in the β phase directly from the melt is only possible by employing the memory effect of cocoa butter. Cocoa butter crystallized in the β phase, heated to the so-called maximal temperature (just above its melting end point), recrystallizes in the β phase after cooling to a crystallization temperature. The influence of the maximal and crystallization temperatures on the recrystallization behavior has been investigated for two cocoa butters. Rapid-starting recrystallization into the β(VI) phase and slow-starting recrystallization into the β(V) have been observed. It is concluded that rapid-starting recrystallization is induced by high-melting 1,3-distearoyl-2-oleoyl-glycerol (SOS)-rich crystals. The two β phases were identified by X-ray powder diffraction and melting ranges. However, the X-ray powder diffraction patterns for the β phases depended on the composition of the cocoa butter and on the crystallization method used. Therefore, it was not possible to take any particular β(VI) X-ray powder diffraction pattern as a standard for the β(VI) phase of all cocoa butters.