A new challenge: grain boundary engineering for advanced materials by magnetic field application

This paper gives an overview of “Grain boundary engineering (GBE) for advanced materials by magnetic field application” based on recent experimental work performed on different kinds of structural and functional materials. It is shown that magnetic field application has a great potential and unique advantage as “non-contact processing” for microstructure control, irreplaceable by any other existing processing methods. The control of grain growth and texture by magnetic fields has been found to be generally applicable to many metallic materials, irrespective of whether they are ferromagnetic or not. Grain growth which is controlled by grain boundary migration was found to be strongly affected by magnetic field application. Recent attempts at the grain boundary engineering by magnetic field application through phase transformation have revealed that magnetic phase transformation can provide us a new approach to grain boundary engineering for iron alloys and steels, as well as a new nanocrystalline material produced by magnetic crystallization from the amorphous state. The possibility of engineering applications of enhanced densification using magnetic sintering and magnetic rejuvenation has been discussed for iron powder compacts and deformation-damaged iron alloys, respectively.     

Proprietes electriques de l'oxyde V6O11 pur et dope au titane ou au fer

Electrical conductivity and thermopower have been investigated on V₆O₁₁ single crystals from room temperature down to 50 K.The metal-insulator transition is confirmed, but the behavior of the Seebeek coefficient disagrees with previous results. Discrepancies from sample to sample can be explained by a hopping model taking into account localized V³⁺ and V⁴⁺ levels and a small oxygen non-stoichiometry. Results obtained by Ti⁴⁺ and Fe³⁺ doping are consistent with this hypothesis.     

Structure of colloidal particles in water-oil mixtures stabilized by polymeric emulsifiers: 2. Small angle neutron scattering investigation

Small-angle neutron coherent scattering techniques have been used to characterize the conformation of amphiphilic macromolecules in polymeric microemulsions. The radius of gyration, the molecular weight and the aggregation number of the macromolecules within the micelles have been measured using a dilution procedure in conjunction with an adjustment of the contrast factor between polymer and solvents. Additional information on the internal structure of the micelles has been obtained from the asymptotic behaviour of the scattering form factor P(q). From considerations of the respective affinities between the two copolymer sequences and the solvent mixture, plausible models are proposed for the micellar structure.     

Electro-optical and viscometric behaviour of sodium polystyrene sulphonate in formamide

Unusual electro-optical signals have been recorded on sodium polystyrene sulphonate in formamide. It was shown that such signals largely arise from the positive birefringence of the solvent being superimposed on the negative birefringence of the polyion. On the basis of conductimetric experiments, the residual content of ammonium formate caused by hydrolysis of formamide was estimated. Commercial formamide of analytical grade was shown to contain rather large amounts (0.02 M) of ammonium formate, sufficient to very strongly decrease the polyelectrolyte effect. The persistence length in these conditions is equal to 80Å, quite similar to that determined in 2 × 10^?2 M NcCl aqueous solution. At a lower ammonium formate content (7 × 10^?4 M), the degree of extension of the polyion at infinite dilution, calculated from the relaxation time of the birefringence, is identical to that measured in 6 × 10^?4 M NaCl. The influence of the nature of the solvent and the ionic strength on the electric polarizability and the optical anisotropy factor was also analysed and compared with the results obtained in water. The latter parameter was discussed in terms of the so-called form anisotropy of the solvent and the intrinsic optical anisotropy of the polyion.     

Photochemistry of polymeric systems. III. Photocrosslinking of polymers and copolymers including cyanocinnamylydene–pyridinium groups

Photocrosslinkable polymers were obtained by reacting esters of cinnamic acid or cyanocinnamylideneacetic acid onto pyridine units of a homopolymer or onto a suitable copolymer. These photosensitive polymers were characterized by conventional analysis and spectrometry. The photocrosslinking was studied on thin films measuring the threshold of insolubilization together with UV and IR spectrometry.     

The optically pumped ozone laser

We report here the CW observation and the assignment of 7 lines of¹⁶O₃ pumped by a CO₂ laser. The frequency measurement of one line of¹⁸O₃ has also been obtained.