414 



NATURE 



[July 19, 1917 



Johns, the furnace manager of Vickers, Ltd., and, 

 took the form of a compact statement of the properties 

 of the refractories in general use and the urgent need 

 tor systematic research work along certain hnes. 



In any giyen metallurgical process the ideal refrac- 

 tory must be infusible and non-volatile ; its volume 

 must not vary during the temperature fluctuations 

 that occur ; it must be chemically inert ; it must have 

 sufficient structural strength and be a non-conductor 

 of heat. No such substance is known. Whether any 

 such material can be prepared only the future will 

 show. Up to the present the refractories actually 

 used are simply the best approximations to the above 

 ideal, which have been reached almost entirely by 

 experience gained by empirical trials spread over a 

 century or more. As Mr. Johns observes: — "The 

 methods employed to-day represent the survival of the 

 fittest by the searching test of commercial success, 

 but it by no means follows that they represent the 

 best obtainable"; and, further: — "The art has been 

 so long in front of the science of the refractory indus- 

 try that the most urgent need at the present is for an 

 expression in terms of scientific precision of the most 

 successful practice in manufacturing the refractory 

 product and of the physico-chemical changes which 

 take place when they are used." 



As regards the materials available, leaving aside 

 carbon and its compounds with silicon, which have 

 only a limited application, they are chiefly the oxides, 

 silica, alumina, lime, magnesia, and chromium oxide, 

 or compounds of these with oxides of iron, sodium and 

 potassium, and traces of other substances, regarded 

 as impurities, some of which may act as catalysts. 

 The raw materials for coke-oven bricks, blast-furnace 

 bricks, and casting ladle nozzles are the fireclays, 

 most of which were obtained from home sources before 

 the war. Again, quartzite, the raw material of silica 

 bricks, used in acii open-hearth furnace construction, 

 is entirely derived from home supplies. On the other 

 hand, magnesite, the raw material of basic refrac- 

 tories used in basic open-hearth and electric furnace 

 construction, is nearly all imported, either in 

 the raw or calcined state. Chromite, the raw 

 material of bricks used where a neutral refractory is 

 required, which will not have a reducing action such 

 as the carbon refractories exert, has also to be obtained 

 from abroad. The materials available are therefore 

 strictly limited, and they never occur in a state of 

 purity in Nature. Their manufacture into finished re- 

 fractories involves a succession of processes which vary 

 according to the purpose for which they are intended, 

 and the final product is always a mineral aggregate, 

 often of great complexity. In consequence of this 

 the refractory does not possess a melting point, but 

 rather a softening range spread over a considerable 

 temperature interval, which results finally in the mate- 

 rial failing to perform its functions. It is essential 

 that any refractory should be "burnt" at a tempera- 

 ture somewhat higher than it will be called upon to 

 endure in practice ; otherwise serious difficulties arising 

 from volume changes, especially shrinkages, will be 

 encountered. 



Texture and porosity determine very largely the 

 suitability or otherwise of refractories for particular 

 purp>oses. The relative size of the grains, and the extent 

 of the surface exposed by the more resistant constitu- 

 ents to the others used as a bond or matrix, are most 

 important factors in contributing to the ability of the 

 material to perform useful service. Another point of 

 importance is the influence of mass in promoting or 

 retarding inversions. Some inversions occur almost 

 instantaneously once the critical temperature has been 

 reached, but with others marked hysteresis occurs. 

 Porosity must always occur when the refractory is 



NO. 2490, VOL. 99] 



composed of more than one constituent, and where 

 their chief volume changes are dissimilar, or occur at 

 different temperatures. Little is known of the effect 

 of porosity on properties, but it is obvious that it per- 

 mits the deposition of extraneous material in the inte- 

 rior of the bricks and renders them permeable to 

 gases. 



Both tenacity and compressive strength are impor- 

 tant properties of refractories at high temperatures. 

 Abrasion is caused by the movement of solid substances 

 while in contact with their heated surfaces ; erosion is 

 due to the passage of dust-laden gases at high veloci- 

 ties. Almost nothing ?s known as to the conditions 

 which may be expected to retard abrasion and erosion, 

 and in what way they are related to the mechanical 

 properties of the materials. There is accordingly 

 urgent need for the accurate determination of tenacity 

 and compressive strength, over wide ranges of tem- 

 perature, of the chief refractories under both oxidising 

 and reducing conditions. Not less important is the 

 property of resistance to corrosion caused either by 

 slags or gases. The effects of acid slags on basic 

 refractories, and of basic slags on acid refractories, are 

 well known. Less familiar, except to experts, are the 

 instances of gas corrosion of the silica bricks in the 

 gas ports and uptakes of open-hearth furnaces due 

 to the alternating passage of oxidising and reducing 

 gases with the resulting formation of fusible silicates. 



It is satisfactory to be able to record that the 

 Geological Survey is preparing a memoir of the 

 mineral resources of this country, and is dealing 

 specially with refractories. Mr. Johns points out that 

 the concentration and purification of these, their 

 proximate and ultimate analysis, their mineralogical 

 description, and their thermal analysis are all matters 

 requiring scientific investigation. Pioneer work has 

 already been carried out under Dr. Mellor at the 

 Pottery Laboratory. Stoke-on-Trent. Researches are 

 also in contemplation, or have been initiated, at 

 various universities and technical institutions in the 

 countrv. H. C. H. C. 



THE COMPLEXITY OF THE CHEMICAL 

 ELEMENTS.'^ 



'X'HE elements of the chemist are now known to be 

 -*■ complex in three different senses. In the first 

 sense the complexity is one that concerns the general 

 nature of matter, and therefore of all the elements in 

 common to a greater or less degree. It follows from 

 the relations between matter and electricity which have 

 developed gradually during the past century as the 

 result of experiments made and theories born within 

 the four walls of this institution. Associated initially 

 with the names of Davy and Faraday, they have only 

 in these days come to full fruition as the result of the 

 very brilliant elucidation of the real nature of electricity 

 by your distinguished professor of physics, Sir Joseph 

 Thomson. Such an advance, developing slowly and 

 fitfully with long intervals of apparent stagnation, 

 needs to be reviewed from generation to generation, 

 disentangled from the undergrowth that obscures it, 

 and its clear conclusions driven home. This com- 

 plexity of the chemical elements is a consequence of 

 the condition that neither free electricity nor free 

 matter can be studied alone, except in very special 

 phenomena. ^ Our experimental knowledge of matter 

 in quantity is necessarily confined to the complex of 

 matter and electricity, which constitutes the material 

 world. This applies even to the "free" elements of 

 the chemist, which in reality are no more free then 

 than they are in their compounds. The difference is 



1 Discourse delivered at the Royal Institution on Friday, May i8, by 

 Prof. Frederick Sortdy, F.R.S. 



