The Spectral Sensitization of Silver Bromide Emulsions on Different Crystallographic Faces

Experiments concerning spectral sensitization of cubic and octahedral silver bromide crystals, contained in the same emulsion have been carried out. Different types of sensitizing dyes were employed. Significant differences in sensitization and desensitization on the (1,1,1) and (1,0,0) faces, related to the type of the dye, were found. Greater tendency to form the J-band on the cubic crystals and of the H-band as well as desensitization on the octahedral crystals was observed.     

The Adsorption of Gelatin to Developed Silver and the Role of Gelatin in Development

The adsorption of gelatin to developed silver is demonstrated and semi-log isotherms are constructed at two temperatures in the presence and absence of developer components. Analysis of the isotherms suggests that the adsorption is weak (physicol) but this is contradicted by its observed irreversibility. The induction period and apparent energy of activation of development in the liquid system studied are shown to increase with gelatin concentration.The effect of a cationic wetting agent on adsorption and development is described. The specific gravity of silver developed under various conditions is recorded.The possibility is suggested that the firmly bound layer of gelatin on emulsion groins, creates a "thermal" barrier as a result of a difference (not proven) in the heat of adsorptions to silver hol1de and silver. Loosely bound gelatin is believed to form a conventional negative charge barrier.     

Starch consolidation of M3/2 high speed steel powder – influence of microstructure on mechanical properties

Abstract

The influence of microstructure on the mechanical properties of starch consolidated super solidus liquid phase sintered AISI type M3/2 high speed steel powder has been evaluated. Hardness measurements, Rockwell C indentation and scratch testing were used to evaluate the mechanical properties and light optical microscopy and scanning electron microscopy were used for post-test characterisation. The results show that it is possible to starch consolidate and sinter large particle size high speed steel powder to obtain microstructures with high mechanical strength. However, the results show a strong correlation between the as sintered microstructure and the resulting mechanical properties and illuminate the importance of having a dense and isotropic microstructure in order to meet engineering requirements in demanding applications. Consequently, the failure mechanisms observed during indentation and scratch testing can be related to residual pores, present in the low temperature sintered samples, and a coarse microstructure with eutectic carbides, present in the high temperature sintered samples.     

Technical note Stress corrosion cracking of ammonia receiver tank

Abstract

A 900 t/day capacity installation, used for recycling of ammonia to a urea plant, with two ammonia streams and four receiver tanks, failed after 3 years in service. The vessels were of the cylindrical bullet type, made of SA 516 grade 70 carbon steel. Of the four receiver tanks, only one suffered stress corrosion cracking, caused by incomplete mixing of the 0·2% water required by the process parameters. The vessel was operated at ambient temperature and a pressure of 1·765 x 10⁶ Pa; the design pressure of the vessel was 2·256 × 10⁶ Pa.     

Stray grain formation,thermomechanical stress and solidification cracking in single crystal nickel base superalloy welds

Abstract

In the present study, the effects of stray grain formation and thermomechanical stresses on solidification cracking in welds of single crystal Ni-base superalloys have been investigated. Welds were made in an asymmetric crystallographic orientation under three different processing conditions. As welding speed and power increased, stray grain formation became extensive, but only on one side of the weld. Solidification cracking also became more extensive and occurred mostly along the stray grain boundaries. The three welding processes have been simulated using the finite element method (FEM). The calculation results showed that thermomechanical stresses increase with welding speed and power, leading to increased susceptibility to cracking. These results agree well with experimental observations.     

Effect of spiral shape on grain selection during casting of single crystal turbine blades

Abstract

In the development of turbine blades, solidification structures have progressed from equiaxed to directionally solidified (DS) and then to single crystal (SX). The transition from DS to SX was achieved by introducing a grain selector which consists of two parts: a starter block referring to the grain orientation optimisation and a spiral part to ensure that only one grain can eventually survive and grow into the blade. With emphasis on the spiral selector, the microstructure evolution and grain competitive growth is visualised using a coupled macroscale ProCAST and mesoscale cellular automaton finite element (CAFE) model in this study. To improve the efficiency of the spiral grain selector and to save cost in casting, the effects of spiral geometries on the grain selection are investigated. Simulation results reveal that the spiral becomes more efficient in grain number selection with a smaller spiral thickness (d _T) and a larger spiral diameter (d _S).     

Development of heat conductor technique for single crystal components of superalloys

Abstract

A new heat conductor (HC) technique was developed to minimise stray grain formation arising from the geometrical effect during single crystal solidification of superalloys. Graphite is recommended as HC material because of its excellent thermophysical properties. Computer simulation and temperature measurements have shown that this technique is able to produce a clear improvement of thermal condition in the critical region of the components. Both the extent and the period of undercooling at the platform extremity significantly decreased. Structural investigation revealed a notable reduction in stray grain quota, providing evidence for the effectiveness of the HC technique for improving the quality of single crystal components.     

An illumination and highlights invariant colour model for image matching

Abstract

Colour can provide critical information for a variety of computer vision tasks such as image matching, object recognition and image retrieval. However, for it to be useful in practice, the colour model used to represent the intrinsic properties of the imaged objects must be insensitive of imaging conditions such as lighting geometry, illumination colour and highlights. In this paper, we present a colour model for image matching and object recognition that is invariant for illumination and highlights. The colour model is defined as the ratios of the colour differences between neighbouring pixels for each colour component. Based on the dichromatic reflection colour model, it is shown that the proposed colour model is invariant to lighting geometry, illumination colour, highlights and diffuse lighting. Experimental results show robust image matching using the proposed colour model on objects that are illuminated under different illumination colours and lighting geometry. The proposed colour model can be used as a prepossessing step for applications where limited or no constraints on the imaging process can be imposed.     

Photofabricated Focussing Diffracting Optics

Optical components such as zone plates which operate by diffraction can be formed from a recording, in a photosensitive layer, of the intensity distribution created by the interaction of two coherent wavefronts.

This paper describes some examples of such components and discusses the practical aspects of photofabrication. Examples of wavefront aberration introduced by a wavelength change and two methods of aberration correction are shown.