Synthesis mechanochemical powder

Mechanochemical processing (MCP) represents a compelling method for the production of nanostructured HA, during which the reaction is activated by mechanical milling. Mechanochemical powder synthesis is a solid-state synthesis method that takes advantage of the perturbation of surface-bonded species by pressure or mechanical forces to enhance the thermodynamic and kinetic reactions between solids [77]. Pressure can be applied via conventional milling 

Whilst the main advantages of the mechanochemical synthesis of ceramic powders are simplicity and low cost, the main disadvantages are the low crystallinity and calcium-deficient nonstoichiometry (Ca/P molar ratio 1.50-1.64) of the HA powders, as this results in their partial or total transformation into ft-TCP during calcination. 

---

Suchanek, L.W., Shuk, P., Byrappa, K., Riman, R.E., TenHuisen, K.S. and Janas, V.F. (2002) Mechanochemical-hydrothermal synthesis of carbonated apatite powders at room temperature. Eiomaterials, 23, 699-710. 

In a variant of the second method described earlier the premixed metallic powders (or pulverized ingots) are milled under hydrogen atmosphere to directly form an intermetallic hydride. It can be also viewed as hydrogen alloying of metal powders and powder mixtures in hydrogen alloying mills. This method is called a reactive mechanical alloying (RMA) or mechanochemical synthesis (MCS). 

Mechanochemical synthesis (MCS) by reactive milling of metal powders or intermetaUics in hydrogen gas... 

Fig. 7 Comparison between the experimental powder XRD pattern of a material prepared by mechanochemical synthesis and the simulated powder XRD pattern of a potential candidate known structure prepared previously by a solvothermal route. Visual comparison (top part) might tend to suggest that the two materials are very similar. However, detailed comparison (bottom part) reveals important differences between the powder XRD patterns. In particular, the peak at 26 29° is present for the material prepared by mechanochemical synthesis but is absent...

Fig. 11 Crystal structure of a metal-organic framework material Zn2(fina)2(bipy) prepared by mechanochemical synthesis, with the structure determined directly from powder XRD data. The structure is viewed (a) along the c-axis and (b) along the b-axis. The two (identical) interpenetrated frameworks are indicated by yellow and purple shading. For comparison, (c) and (d) show the corresponding views of the stmcture of a DMF solvate material Zn2(fma)2(bipy)(DMF)o.5 prepared by a solvothermal route. Although there is some similarity between these structures, there are nevertheless important stmctural differences between them...

The solid-phase reactions starting from metal powders in conditions of friction (Examples 8 and 9) are described in two recent monographs [201,202] (see the scheme of the mechanochemical reactor in Ref. 202). In this respect, we note the possibility of a solid-state synthesis with the use of metal salts. In particular, mechanochemical syntheses are widely used for obtaining acetylacetonates [698-70Id] by the method of ligand exchange, for example (3.277) [701a] ... 

P. G. McCormick, Synthesis of Ultrafme Gadolinium Powder by Mechanochemical Processing,... 

I.V. Uvarova, M.P. Savyak, I.M. Zabrodsky, D.P. Ziatkewych, L.P. Isaewa, 1.1. Timofeewa. Mechanical milling and mechanochemical synthesis of refractory compounds. Nanostructure materials. Physical chemical foundations of powder metallurgy technology. Kyiv 2003. 

Similar investigations of the mechanochemical synthesis of zircon using anhydrous and sol-gel powders of zirconium and silicon oxides as initial reagents were reported in [43,44]. 

Mi G., Saito F., Hanada M. Mechanochemical synthesis of tobermorite by wet grinding in a planetary ball mill. Powder Technology 1997 93 77-81. 

Complex oxides with perovskite structure are prepared by means of mechanochemical synthesis. A mixture of initial oxides, hydroxides or carbonates are subjected to mechanical activation, then the powder is calcined at 600-800°C for 2-4 h. The specific surface area of thus prepared perovskites is 10-20mVg [35-37]. 

The use of mechanical milling is also a suitable method for powder preparation. The feature of this procedure is to obtain powders of small crystallite size of a few nanometers with a high concentration of lattice defects. There are many mechanochemical studies on the synthesis of alloys, solid solutions, nanophasc materials, and intermetallic compounds. Of course, the mechanical alloying also has been applied to prepare mixed oxides containing cerium oxide to enhance catalysis, such as CeOj-TbO, CeOj-HfOj, Ce02 Zr02-Mn0, and CeOt ... 

Mechanochemical processing has been used to manufacture nanocrystalline powders of nitride and carbide ceramics. The majority of systems involve milling of the metal precursor with a source of carbon or nitrogen. The source of carbon or nitrogen has typically taken the form of the element itself. However, a variety of other reagents have also been used. For example, Zhang et al. reported the synthesis of titanium nitride by milling titanium metal with pyrazine in a benzene solution. 

Summary of Some Representative Examples of Mechanochemical Reaction Systems Developed for the Synthesis of Ultrafine Ceramic Powders... 

Dodd, A.C., Raviprasad, K., and McCormick, P.G., Synthesis of ultrafine zirconia powders by mechanochemical processing, Scripta Mater, 44, 689, 2001. 

Recently [13, 16] we have shown the possibility of efficient promotion of VPO precursor with bismuth compounds. The present paper reports new results on promotion of VPBiO precursor with lanthanum compounds (previously a similar catalyst was shown to be active in tetrahydrofuran formation [17]). Table 5 compares the properties of traditionally prepared VPBiLaO sample (by simultaneous introduction of bismuth and lanthanum additives in the course of the synthesis of VPO precursor) with that (VPBiO-La-M) produced by the mechanochemical treatment of VPBiO precursor and lanthanum oxide powders. The treatment in the latter case was carried out for 10 min. in ethanol medium. 

---