THE COLLIERY GUARDIAN

'AND '

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CXIII.

FRIDAY, FEBRUARY 2, 1917.

No. 2927.

Physical Properties of the Materials of Coke Oven Bricks.*

By Prof. W. G. FEARNSIDES, M.A.

Prof. Fearnsides, in opening his lecture,, said he
wished to talk about'the 'anatomy of the constituent
materials of coke oven-bricks.* He thought that,.if they
could understand how-these several materials behaved
separately, this would teach them what to expect when
these materials had been manufactured into the state at
which they became of interest to those who were con-
nected with the coke oven industry. ■ During the last-
two years it had -been his war work to go as deeply as
possible into the difficulties which had been , brought to
him by those connected with the refractory industry.-He
had heard it said by consumers ,of refractory- materials
that'it was very evident that those who were making
them into'a condition ready for sale were just following
the steps of 'their fathers, grandfathers, and perhaps
great-grandfathers—that they had learnt very little, and
forgotten very 'little of what their grandfathers knew.

His experience had taught him that the difficulties .
were, in point of fact, very real. Most of the opera-
tions (at any rate, in the case'of those who were at the
top of their profession) were controlled with a nicety that
would (Surprise some people who controlled the distilla-
tion of benzol with a thermometer. It was rule of
thumb of a sort that they used, but it was rule of thumo
which gave a control exactly analogous to the. control.
which coke oven managers obtained when they used a
pyrometer. He had seen people making mixtures,.
apparently very casual mixtures; he had seen foremen,
and very often labourers, getting hold of a material, feel-
ing at it, and recognising at once that it was just right.
He had had handfuls, of material passed by the foreman
who was feeling to ascertain if his ‘ labourers had pro-
duced the right materia], and he had found that from
one. year’s end to the next the results agreed within-
a quarter of 1 per. cent. That had surprised him .very
much. There was a real control, and it was one.that
he had had to learn about. He did not think that the
manufacturers of refractory materials were really as
behindhand as many people had thought, and tee was
rather favourably impressed with the scientific manner
in which their practices were controlled.

Expansion in Baking.

On the other hand, if it so happened that a maker of
one sort of material was turned on to another, he carried
with him all the processes that controlled the one, and
expected them to control the other. For coke oven bricks
to be satisfactory at all, there must be two physically
different materials, which were more different than most-
people had any idea of until they went into the .matter.
Bricks in an ordinary way were made in a mould which
was a great deal bigger than the finished brick. An
inch to a foot, 1| in., 1| in., up to 2 in. to the foot, was
the ordinary allowance between the moulded and the
finished brick. In the silica brick trade, on the other hand,
the moulds were very much smaller than the finished
brick. In bulk, the difference was as much as between
222 and 266. Now, if a man had learnt brickmaking
under conditions in which the materials came down, in
process of manufacture, from 131-in. to 1ft., and was
turned on to another material, which, when moulded a
foot long, finished half an inch longer, it was not likely
that he would get a real success by applying the- methods
that controlled the one sort of material to the either.

One of the questions frequently asked him by the
friends whom he saw -at coke ovens and in colliery
directors’ offices was : “ Can you tell us how to put in a
specification to which we can expect the makers of coke
oven bricks to work? What is the. specification?” He
could not give an exact specification. He did not think
anyone could. He had known cases, of people who had
been.building coke ovens of German bricks—bricks made
to a definite specification—handing over that specifica-
tion to an English firm working with another set of
materials. .The English firm.had complied accurately,
to the best of its ability, with the German specification,.
but the result had not been the same. The German
material had one behaviour, and apparently the English
material had another. In our present knowledge, there
was no specification that would stand. It had therefore
occurred to him to raise a discussion upon the question
.at that meeting of the Coke Oven Managers’ Associa-
tion. In opening the discussion, he would lay stress
upon the influence which the physical properties of the
more important mineral constituents of the raw materials
used in making coke oven bricks exerted upon the
behaviour of the brick during manufacture, and after-
wards when it took its place in the walls of the oven.

As a geologist, he did not happen to have the arts
of the physicist and the chemist at his fingers’ ends,
and in his department of the university he was entirely ;
by himself at present. The result was that the bulk

* From a paper read before the Coke Oven Managers’
Association, Midland branch. \

c-f the information which he could give them was not
exactly first-hand, though perhaps the assembling of it
was. He should like to refer his hearers to two sources
of information which had been very useful to him. One
was the work of the Geo-Physical Laboratory at Wash-
ington. Mr.. Carnegie and some -of the other American,
millionaires had put at the disposal cf this laboratory a
capital sum of nearly Id,000,000, and an income of
more than £10,000 per. annum. The.research carried on
was on subjects of pure science, and one very large
department had- taken , f up the investigation of the
physical and''chemical .-properties of materials. The
American. Journal of Science had from time to time con-
tained a large series of papers on what was effectively
the applications of. the phase.rule.to substances such as
silica, alumina, lime, iron oxide, magnesium oxide,
sodium oxide,-potassium oxide,- and a certain amount
of water.

Beginning with the definite knowledge that most
materials which were in any way alike would, at some
temperature or other, each dissolve the,other and make
solutions., they had investigated these materials, and
bad ascertained the physical behaviour of mixtures of
these various oxides—which were rather out-of-the-way
materials for the ordinary chemical laboratory—when
they had been dissolved one in the other. It -was pro-
bably well known to his hearers that if- they mixed a
little common salt (which had a melting point of-about
800 degs. Cent.) with water (melting point 0 deg. Cent.),
they brought down the melting point of the water; and
that if they mixed a little water-'with their salt, they
brought down the melting point of the latter. At every
percentage, between pure water and pure salt, there was
a definite point at which solids would separate. That
was a matter of the greatest importance, when it came
to any refractory material. Any pure body, used as. a
refractory material, mixed with a small quantity of any
other of the refractory class of bodies, lost its refractory
qualities to a greater or less extent. Most people said,
on first principles, that if they had a. mixture there was
a sort of swallow-up, but experience showed that that
was not the case in any of the bodies, but that all the
constituents of coke oven bricks were spoiled to some
extent—not -as refractory bricks, but . as refractory
extent by admixture.

American Research.

The Americans had investigated the ordinary consti-
tuents of rocks, taking every one with every other, and
had ascertained the eutectic curves. In the American
Journal of Science could be found the melting point of'
practically every mixture of any two of these bodies.
That was the most important bank from which to draw
information as to the behaviour of the raw materials of
coke .oven bricks. The Americans had gone even
further, and taken the-materials three at a time-. Some
very important results had been obtained. For example,
the melting point of silica by itself was 1,625 degs. Cent.,
of, lime by itself 2,500degs. Cent., .and of alumina
2,050 degs. Cent. But a mixture of these three gave at-
one point (which the-lecturer illustrated by a curve on
the blackboard) a melting point 'of 1,280 degs. Cent., and
at another point, which they had in every brick that was
made, of 1,325 degs. Cent.’ As a matter of fact, there
came into their coke oven practice an area-round about
silica,, and .going, on somewhere towards alumina. It
was -a distinctly interesting matter that, although the
lowest melting point of any one of the three materials
was 1,625 degs. Cent., they found a mixture of those
three, in every set of bricks which they handled, that
came down to 1,280 degs. Cent. That .was: a high
temperature for a coke oven,-and a mixture., that con-
tained only those three substances, would give them such .
a..margin that they would never, find, bricks -failing by ■
reason of melting., But there ;was always some iron,:
some, magnesia,, some alkalies,. whatever -mixture. they
began with,-and 1,280 degs. Cent, was not-the limit.-
The limit of the most refractory fireclay that he had any -
knowledge of at all—the Lea Moor-kaolin—was at least-
as low as 800 degs. Cent. When they had got any clay
in the furnace, and had raised its temperature to 800
degs. Cent., some of it—-it might be only a thousandth
of the whole bulk—had become a liquid at that lowest
eutectic point.	>

. The next source of information was the work that had
been done at the Potteries laboratories by Dr. Mellor, of .
Stoke-, and his assistants.- Tn this country the work, of
Mellor Stood absolutely alone.’ Unfortunately, it was
recorded in publications which until recently had. been
very difficult'to obtain, but he was told that They were
before long to have the advantage of a fairly adequate
publication. If his hearers did hot know it, he should
like to call their attention to a book called “ Clay and
Potteries Industries,” edited by Dr. Mellor., Dr. Mellor
thought that refractory materials should,'in consequence

cf the w-ork that was being done, be studied principally
at Stoke, and that Sheffield was a sort of rival affair.
He (the speaker) hoped that he did not take that limited
point of view’ very strongly. Certainly, he did say that
Dr. Mellor had . done very valuable pioneer work.

In general, the raw material from which coke oven
bricks were made up v-as either a fireclay, or a fireclay
mixed with a greater or less proportion of some crushed
siliceous, rock of such a texture ; that . the fireclay was
able to hold it -together.- Fireclays-were distinguished
from other clays by being ■“ refractory,” but it should
be pointed out that the refractory qualities required of
bricks used in coke oven construction were not at all the
same as those required by the steel maker, whose fur-
naces in general w’-orked at temperatures several hundred
degrees higher than those attained even when , the coke
ovens were-at top heat. High melting temperature
(above about 1,400 degs. Cent.) was not a quality worth
paying for in materials for coke oven lining, physical
stability of the body, and chemical inertness of the
mineral constituents of the bricks in the - presence of
certain • fluxes at temperatures round about 1,000 to
1,100 degs. Cent., being the criteria of longevity.

Sources of Supply.

As regards the source of supply of satisfactory fire-
clays and the mode of their occurrence, the most (abun-
dant supply yet exploited in this country was from the
under-clays associated with the thin coal seams in the
lower part of the coal measures and the millstone grit
series of. the carboniferous. The lecturer had recently
expressed''his'views upon the possibilities cf extending
the supply when the properties of other clay beds inter-
stratified among other parts of the coal measures of
Yorkshire should have been examined, and that was
equally true of the other midland and northern coal
fields of England, as-also of the central valley of Scot-
land. Other clay beds slowly accumulated along'with
lacustrine or' terrestrial plant deposits, occurring among
rocks newer than the carboniferous, e.g., the middle
jurassic estuarine series of North-East Yorkshire and of
South Lincolnshire and Northamptonshire, the upper
jurassic and lower cretaceous series of Dorset and the
Central Weald, the tertiary rocks ' of Bovey Tracey,
Poole, and other places in Devon and' Dorset, and the
white sand and clay beds which filled certain hollows in
the limestone of the High Peak district of Derbyshire
and Staffordshire, could also be manufactured into bricks
sufficiently fire-resisting to stand any temperature met
with in coke oven construction; and las they had close
similarity with clays which in pre-war days were made
up in Belgium and Germany, they surely should be tried.

All fireclays were sedimentary deposits, fine-grained in
texture, and of a highly specialised type, in which the
chief characteristic wras that the hydration and general
chemical breakdown of the various mineral constituents
of igneous rocks (to which ultimate source all minerals
contained in sedimentary deposits ow’ed their origin)
had gone as far as it wmuld, under ordinary conditions
of atmospheric temperature and humidity’, and from
which, by long continued soaking in fresh water with
frequent renewal of the water, all soluble materials had
been removed.. Examined microscopically, the-mass of
those fireclays was generally too fine-grained to yield
much information, and when, after washing awiay the
fine material, a sample of the larger fragments was
selected for examination, it would appear that, in good
class fireclays, nine-tenths of. the fragments of finite
size were' angular chips of quartz. From the results of
chemical analysis, and by comparison of these, with
analyses of well recognised mineral materials, it was
generally agreed that the clay base of fireclay was chemi-
cally not dissimilar from the kaolinite of china clay,
for which the empirical formula, Al203, 2SiO2, 2H2O,
was generally accepted. When a parcel of fireclay was
offered to an intelligent buyer, he would generally
appraise its value as a refractory material mainly upon
the closeness with. which its composition approximated
to that of the" mineral kaolinite, with'39’5 per cent, of
alumina, 46’5.per cent.' of Si02,’ and about 14 per cent,
of .H20, . while any other ’bases, .' more .especially the
alkalies and alkaline earths, were considered -as- detri-
mental to the quality of the material.- -Apart from the
kaolinite and the’quartz, the balance of the composition
could • usually ' be expressed in .terms ’ of felspathic
material, the hydrates .of iron and of'aluminium', and the
carbonates of iron, calcium, and magnesium.

Effect of Heating on Kaolin.

With rejgard to the behaviour of kaolin when heated,
by' heating small crucibles containing air-dried kaolin in
which a thermo-couple was embedded, Mellor and
his co-workers at the Stoke Ceramic Laboratory dis-
and his co-w’orkers at the Stoke Ceramic Laboratory dis-
covered that ’ the heating of the purest obtainable Lea
Moor kaolin ’was not a simple process. Mechanically
entangled water was given off at temperatures just above
100 degs. Cent., but the combined water did not come
aw^ay until 500 degs. Cent, was passed, and the heat
absorption which took place when this dissociation was
in progress delayed the rise of temperature considerably.
When the water of combination had been got rid of, the