Coprecipitation synthesis

K. Osseo-Asare, F. J. Arriagada, and J. H. Adair, "Solubility Relationships in the Coprecipitation Synthesis of Barium Titanate Heterogeneous Equihbria in the Ba—Ti—C2O4—H2O System," in G. L. Messing, E. R. Fuller, Jr., and Hans Hausin, eds.. Ceramic Powder Science Vol. 2,1987, pp. 47-53. 

Coprecipitation Synthesis with Template (Method-D) In the preparation of sample lOD, Ni(N03)2 8H2O, ZrOCl2 8H2O, and YCl3(2) were dissolved in distilled water to get a clear solution. CTABr template was then added and the resulting solution was stirred for 30 min. Then, ammonia (70% 10 mL diluted to 105 mL with distilled water) was added to get a white gelatinous precipitate. The pH was maintained at around 9. The contents were stirred for 1 h and the precipitate was aged for 16.5 h, then filtered and calcined at 773 K for 1 h in a static air oven. 

Precipitation and coprecipitation Synthesis of defect-rich materials, easy to perform Homogeneity difficult to achieve... 

Scientists have fabricated scaffolds in a two-step approach that combines an in situ coprecipitation synthesis route with the electrospinning process to prepare a novel type of biomimetic nanocomposite nanofibres of HA/CHT. The electrospun composite nanofibres of HA/CHT, with compositional and structural features close to the natural mineralised nanofibril counterparts, are of potential interest for bone TE. The results of HA/CHT indicate that although an initial inhibition occurs, the nanofibrous scaffolds which contained HA, as compared to scaffolds of CHT alone, appeared to have significantly stimulated the bone forming ability as shown by the cell proliferation, mineral deposition, and morphological observations, due to the excellent osteoconductivity of HA [19, 34, 56, 70]. 

Coprecipitation synthesis method enables the use of a wide range of cations and anions for their incorporation in the layers and interlayers of LDHs. Large quantities of synthesized materials can be obtained using this synthesis method. As previously mentioned, the pH value of coprecipitation is of great importance and may affect the nature and properties of the synthesized material. In general, the pH ranges from 8 to 10 and is considered to be the optimal for the preparation of LDHs [2]. 

This method allows the incorporation of a wide range of anions in the interlayer. Considering that it is important to provide simultaneous coprecipitation of precursors, this synthesis method must be carried out in oversaturated conditions, while controlling and regulating the pH value of the solution that must be higher or equal to the pH value for the precipitation the most soluble hydroxide [20]. Two coprecipitation synthesis methods are most commonly used for LDH synthesis coprecipitation at low supersaturation (LS) and coprecipitation at high supersaturation (HS) methods. The LS synthesis method is performed by slow addition of mixed aqueous solutions of M" and M " ions in the selected ratio with simultaneous addition of alkaline solution at such a rate to maintain constant pH. On the contrary, the HS synthesis method is carried out by the instant addition of the mixed M VM " solution to the alkaline solution containing the desired interlayer anion [20]. 

Ion exchange synthesis method is suitable when the coprecipitation synthesis method cannot be applied, in cases in which the divalent and trivalent metal cations or anions, which participate in the synthesis, are unstable in alkaline environment or have greater affinity to guest ions. Therefore, this synthesis method is used for preparing LDH materials with interlayer anions that are different from CO " due to the higher affinity of these anions to be incorporated into the LDH interlayer [20]. Earlier studies made an observation that the treatment of LDH with diluted HCl did not obstruct its structure, but lead to the formation of new LDHs with different crystal lattice parameters and to the substitution of anions with CL ions [2]. Recent studies claim that for the COj anion substitution in the interlayer the most suitable anions are chlorides, nitrates, sulfates, and bromides [20]. 

In Figure 20.13, the occurrence of the memory effect for HS-MgAl mixed oxide sample (HS coprecipitation synthesis, x=0.3) is presented by XRD spectra. It can be observed that after thermal activation at 500 °C the characteristic LDH XRD peaks disappeared (designated as 0) and peaks of mixed oxides (designated as are formed. After only two weeks of contact with air, partial reconstruction of the layered structure is achieved, whereas after 10 months the layered structure is completely reconstructed, as can be seen from the characteristic XRD peaks. 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

The GdAlgB O QiCe ", Tb " is synthesized by a soHd-state firing of the rare-earth coprecipitated oxide plus boric acid and MgCO at 900° C in a slightly reducing atmosphere. As in the case of the lanthanum phosphate phosphor, a flux is usually used. The synthesis of this phosphor is further comphcated, however, by the fact that it is a ternary system and secondary phases such as gadolinium borate form and must then react to give the final phosphor. 

Besides supported (transition) metal catalysts, structure sensitivity can also be observed with bare (oxidic) support materials, too. In 2003, Hinrichsen et al. [39] investigated methanol synthesis at 30 bar and 300 °C over differently prepared zinc oxides, namely by precipitation, coprecipitation with alumina, and thermolysis of zinc siloxide precursor. Particle sizes, as determined by N2 physisorpt-ion and XRD, varied from 261 nm for a commercial material to 7.0 nm for the thermolytically obtained material. Plotting the areal rates against BET surface areas (Figure 3) reveals enhanced activity for the low surface area zinc... 

Bhandarkar, S. and Bose, A. (1990) Synthesis of nanocomposite particles by intravesicular coprecipitation. Journal of Colloid and Interface Science, 139, 541-550. 

The NiO phase could be reduced to metallic Ni by hydrogen treatment (723 K, 1 h). The crystallite size of Ni metal (estimated from XRD pattern of the reduced sample) is similar to that of the NiO in the unreduced sample (e.g., for 7B, the Ni metal crystallite size is 8.2 nm). The textural characterization studies reveal that for the samples prepared by coprecipitation + digestion and hydrothermal synthesis (methods B and C) the pore sizes are in the mesopore range (2.9 to 6.8 nm) (Table 11.2). 

Some fimctionalized materials have also been prepared by coprecipitation at low supersaturation. A perylene chromophore, for example, has been intercalated into LDH in an attempt to prepare stabihzed pigments [40]. Catalyt-ically active species have also been introduced into the interlayers of LDHs by direct synthesis, e.g. the intercalation of (PWi204o) or (SiWi204o) gives catalysts or catalyst precursors containing interlayer polyoxometalate anions [41]. Vein et al. reported the synthesis of Zr-containing LDH-Hke... 

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