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Porous structures have been widely used in filtration, medical implants and aerospace field. In the filtration field, the study of permeability of the porous structures is of great importance. This paper aims to study the influence of selective laser sintering/melting (SLS/SLM) process parameters on porosity and permeability of stainless steels filters with gradient porosity (FGM).

AISI 316L stainless steel powder was used to manufacture FGM filters by varying the hatch distance while other process parameters were fixed. The relationship between porosity and permeability of such FGM filters was investigated by means of Archimedes’ and Forchheimer’s laws. The gradient of porosity was also analyzed by means of micro-computed tomography.

The results have confirmed the ability of SLS/SLM in controlling porosity of the final product by varying the hatch distance. Further, the results allow to assume that FGM filters will have particle retention capacity related to lowest porosity value (which in turn is associated with the lowest hatch distance value used), while it will work at lower pressure drops – or at higher flow rates for equal pressure drop – when compared to a filter without gradient porosity.

Some research found in recent literature has showed the relationship between SLS/SLM process parameters and permeability of stainless steel porous structures. However, this paper fulfils the need to understand the relationship between SLS/SLM process parameters, porosity and permeability behavior of functionally graded porous structures (FGM filters).

A new range of stainless‐steel bonded filter elements (Fig. 1) has been introduced by Marston Palmer Ltd of Wolverhampton WV10 6QJ, England. The patented design combines the low pressure‐drop properties of woven‐metal filter media with the fine filtration and dirt‐holding capacity of felted metal fibres. Filtration levels from 3 to 40 micrometres absolute are achieved with the new Microclene™ bonded filter.

THE previous articles in this series, concerning the titanium, magnesium and aluminium alloys, followed a very similar form, in that in each case consideration of the aircraft engineering applications was preceded by a metallurgical appreciation of the alloy systems under review. In the case of steels, a comprehensive article on similar lines would be nothing less than a monograph, and if steels are to be discussed within the space of a single article, then a quite different approach must be adopted. This review will not, then, examine steels generally in any great metallurgical detail, but will rather consider their special merits in aircraft engineering, particularly in the context of supersonic aircraft.

The coolant systems of pressurised, water‐cooled, nuclear reactors become radioactively contaminated. Since reactors, like other process equipment, require personnel for operation and maintenance, this coolant system contamination and associated radiation may pose difficult operating problems. Inefficiencies in personnel utilisation result as the radiation levels increase. Generally the radiation levels tend to increase with time. Decontamination is then required to lower radiation levels and to improve personnel utilisation. During a reactor's lifetime, the coolant systems may be decontaminated a number of times to keep radiation levels within acceptable limits. Since this decontamination operation involves chemical cleaning of the reactors' coolant system it has a certain corrosive effect upon the components of the system. To determine these corrosive characteristics, a procedure simulating the cyclic filming and defilming in the pressurised water system is employed in the USA. Special equipment is needed to simulate reactor conditions and to allow evaluation of decontamination methods. Although this article is focused on nuclear reactor systems, the technique of cyclic filming and defilming could be used readily to determine long‐term corrosion effects in other industrial systems where chemical cleaning is frequently employed, such as in boilers, heat exchangers, evaporators, reactors, condensers, and process vessels. Equipment designs and operating procedures would be formulated so as to simulate process and chemical cleaning conditions for the particular system of interest.

This article, the first part of which was published in the September issue of ANTI‐CORROSION, is based on a lecture given by the author to the North‐ Eastern Branch of the Institution of Corrosion Technology on 14 February 1967. Mr. Banfield, who is Corrosion and Materials officer in the Laporte Group of companies, concluded the first part of his article with the example of a stainless steel dished end which was suffering from inter‐granular corrosion. The function of titanium stabiliser in austenitic steel was then discussed ; this discussion now being concluded in the opening paragraphs of this second part of the article.

Audio Thickness Gauge. Thickness of sprayed zinc and aluminium coatings can be rapidly checked with the new Metallisation Ltd. audio thickness gauge. The instrument has an exploring head which may be moved quickly over the coated surface and, having been set to indicate a minimum thickness, it gives an audible warning of areas which are below the required thickness. Accurate test specimens are used to set the gauge to any desired thickness between 0.002 to 0.012 in. The set is completely portable, fully transistorised and is unaffected by magnetic fields or stray magnetism. CT 1200

Reducing Level of Alcohol in Inks ‐ A medium‐sized US ink manufacturer recently needed to reduce the level of alcohol in its bases for water‐based inks. Ciba Geigy Pigments Division's Inks Technical Centre developed an improved formulation, containing half the alcohol of the previous one and 40 per cent more pigment to allow the ink producer to meet VOC limits and increase production efficiency, at no additional cost.

The effects of a number of metals and alloys on the thermal stability of Avtur 50 have been evaluated from ASTM‐CRC and high temperature coker tests. The materials tested are used in current aircraft fuel systems or are possible alternatives for fuel systems of supersonic aircraft where they will be in contact with hot fuel. The alloys currently used in aircraft fuel systems have been classified and their probable effects on the stability of hot fuel listed. A number of the materials affected stability adversely, particularly alloys containing significant amounts of copper, and the use of these should be avoided. The pick‐up of copper by Avtur 50 at ambient temperature from alloys such as brass and gun‐metal has also been investigated. The results indicated that sufficient copper to affect thermal stability adversely is readily picked up from these alloys.

Perkin‐Elmer Ltd., Post Office Lane, Beaconsfield, Bucks., has introduced a new range of analytical LC Columns. There are eight columns available in the range which will satisfy the needs of most users.