Metal powders, water determination

Beryllium in tap water, dialysis fluids and alkali-metal salts was determined with Chrome Azurol S after preconcentration of the complex on a column packed with polyethylene powder [1]. Sorption preconcentration of Be on a fibrous sorbent (poly(acrylonitrile)-carboxylated polyethylene-polyamine) prior to the determination of metal with Arsenazo I in sea water was described [2]. 

The X-ray phase analysis confirmed that the synthesis products are TiC, ZrC, NbC and TaC carbides, which do not contain free carbon. Fineness of the carbides is determined by the grain size of the metal powder. The synthesis time depends on the diffusion rate of carbon into the volume of the grain or the crystallite. We used oxides of refractory metals as the starting materials for production of fine (1-5 pm) carbides. In this case the mass of the metallic calcium was increased taking into account its consumption for the calcium thermal reduction of the oxides. The presence of a higher amount of the calcium oxide in the salt melt did not incur large difficulties in the synthesis of the carbides and their washing with water to remove salts, because the calcium oxide easily dissolves in acidified water. This method of the carbide synthesis has been covered by a Russian Federation patent [6]. 

Cerium was included in a list of 14 elements determined by Lee et al. [627] in seawater using neutron activation analysis. The metals were first precon-centraed on a mixture of Chelex 100 and glass powder. The elements were desorbed from the column by 4 M nitric acid, and aqueous solution was irradiated for 3 days and subjected to y-ray spectrometry method with a Ge(Ii) detector coupled to a 4000-channel analyser. Cerium was found to be present to the extent of 16.7 xg/l in water taken from the Kwangyang Bay (South Korea). 

Nevertheless, the main parameter that affects the course of hydrolysis reaction is the molar ratio of reactants (i.e., the water to metal alkoxide ratio h = [H2OJ [M(OR)J). This h value determines the composition and the properties of the hydroxides and oxides formed on hydrolysis and thus allows them to be obtained in different forms of powders, films, glasses, and fibers. 

---