Graphite

“ Graphite, both in the natural and artificial form, contains impurities such as silica, iron oxide and alumina, but the natural form has a much greater percentage of these foreign materials, in some cases as high as 40%. Graphite is usually mixed with other pigments, such as red lead and sublimed blue lead, thus serving better as a paint coating. The difference in physical appearance of the various carbon pigments is interesting, as each pigment has characteristics of its own. In graphite we find a great tendency toward agglomeration or massing of particles. ”

“ Graphite is produced in several grades which are adapted to different purposes. Amorphous graphite is a trade term applied to non-crystalline or very fine-grained graphite of varying degrees of purity. ”

“ All of this graphite occurs in extremely old Precambrian graphite schist rocks that we now see at the surface in this part of Texas. It is believed that the schists were once ancient sedimentary rocks, such as shales, which contained organic matter. Long ago, great forces below the earth’s surface altered these rocks. When this happened, the organic material that they contained changed into the mineral we know as graphite.
Graphite has a number of uses. It is mixed with clay to make the pencil lead that we use for writing. ”

“ Artificial graphite is now made from any amorphous carbon which contains an admixture of some carbide forming substance and though other carbonaceous substances are used anthracite coal has been found to be the most satisfactory and economical carbonaceous material from which to make graphite. ”

“ Origin of Archæan Graphite.—In a paper at the British Association on the origin of graphite in the archæan rocks, the Rev. A. Irving points out that the occurrence of carbon in late rocks as the result of plant-life is no argument to prove that the graphite of the archæan is of similar origin. Indeed, conditions were then so different that this mode of origin is extremely unlikely. Elementary carbon is produced in three ways: in pig-iron, by reduction of carbonic acid by alkali metals, and by contact action of heated surfaces on hydrocarbons. ”

“ The fact that graphite may dissolve in the iron as austenite, and that when this latter again breaks up it is more likely to yield cementite than graphite, is only an apparent and not a real exception to this law of the greater stability of graphite than of cementite.
Slow cooling, slow solidification, the presence of an abundance of carbon, and the presence of silicon, all favour the formation of graphite; rapid cooling, the presence of sulphur, and in most cases that of manganese, favour the formation of cementite. ”

“ If there were no growth of vegetation at this far-away period to give rise to these deposits of graphite, we are compelled to ask ourselves whether, perchance, there did not then exist conditions of which we are not now cognisant on the earth, and which allowed graphite to be formed without assistance from the vegetable kingdom. ”

“ Here, also, pure phosphorus and the phosphates are made in large quantities; and here is made carborundum—gem-crystals as hard as the diamond and as beautiful as the ruby.
An extensive plant has also been built to produce the heat necessary to make graphite such as is used in your lead-pencils, and for lubricants, stove-blacking, and so on. Graphite has been mined from the earth for thousands of years; it is pure carbon, first cousin to the diamond. ”

“ Amorphous graphite may occur wherever coal or other carbonaceous beds have undergone regional or igneous metamorphism. Crystalline graphite has two principal geologic occurrences, as flakes in schists and as larger crystals in veins. Flake graphite in schists is usually associated with granitic intrusions which appear to have aided recrystallization of original carbonaceous material in the sediments. Vein graphite in commercial quantities is rather rare. ”

“ It is usually spoken of as pure carbon, but from a very large number of carefully conducted analyses, it would appear that native graphite is never quite pure, even the finest grades of the mineral containing 96·8% of carbon at the most. The accompanying substances—which in some cases186 form nearly 50% of the whole—are of divergent composition and consist of iron, silica, lime, magnesia and alkalis. Even the combustible constituent of graphite is not pure carbon, but always contains a certain—though small—proportion of volatile substances. ”

“ Graphite and diamond pass insensibly into one another. Hard graphite and soft diamond are near the same specific gravity. The difference appears to be one of pressure at the time of formation.
Some forms of graphite exhibit the remarkable property by which it is possible [84] to ascertain approximately the temperature at which they were formed, or to which they have subsequently been exposed. Sprouting graphite is a form, frequently met with in nature, which on moderate heating swells up to a bulky, very light mass of amorphous carbon. Moissan has found it in blue ground from Kimberley ”

“ A junction covered only by a thin tube of molybdenum quickly attains the temperature of its surroundings.
4. Graphite and Graphite Compositions.—Carbon has the highest melting point of all known substances, and in the form of artificial or Acheson graphite may be easily machined to any desired shape. Graphite sheaths are sometimes used for immersion in molten metals, but at 1000° C. and higher Acheson graphite oxidises easily and becomes friable. It is a good conductor of heat, but is easily broken. ”

“ To fix our ideas let us assume that the iron contains 4% of carbon. If this carbon is all present as graphite, so that in cooling the graphite-austenite diagram has been followed strictly (§ 26) , the constitution is extremely simple; clearly the mass consists first of a metallic matrix, the carbonless iron itself with whatever silicon, manganese, phosphorus and sulphur happen to be present, in short an impure ferrite, encased in which as a wholly distinct foreign body is the graphite. ”

“ After exposure under a negative finely-ground colour—for instance, graphite—is carefully dusted over the surface of the plate by means of a camel-hair brush, and the powder will adhere in exact proportion to the protection afforded by the negative. A picture is thus produced in graphite powder possessing all the gradations of the original. From a negative a second negative is produced, while from an exposure under a positive a positive will result, each, however, reversed as regards left and right when compared with the original. ”

“ Finally, it is deserving of notice that, if Laurentian graphite indicates vegetable life, it indicates this in vast profusion. That incalculable quantities of vegetable matter have been oxidized and have disappeared we may believe on the evidence of the vast beds of iron-ore; and, in regard to that preserved as graphite, it is certain that every inch of that mineral must indicate many feet of crude vegetable matter.
It is remarkable that, in ascending from the Laurentian, we do not at first appear to advance in evidences of plant-life. ”

“ The graphite of cast iron is obtained in scales of a metallic aspect, whereas the combined carbon is obtained in a fine powder. When the white cast iron has been roasted, and become gray, and is as malleable as the softest gray cast iron, it still affords no graphite as the latter does, though in appearance both are alike. ”

“ Fire-proof ink for writing or printing on incombustible paper is made according to the following recipe: Graphite, finely ground, 22 drams; copal or other resinous gum, 12 grains; sulphate of iron, 2 drams; tincture of nutgalls, 2 drams; and sulphate of indigo, 8 drams. These substances are thoroughly mixed and boiled in water, and the ink thus obtained is said to be both fire- proof and insoluble in water. When any other color but black is desired, the graphite is replaced by an earthly mineral pigment of the desired color. ”

“ Although we cannot convert graphite into diamond, we can change the diamond into graphite. A clear crystal of diamond is placed between two carbon poles, and the poles with intervening diamond are brought together and an arc formed between. The temperature of the diamond rapidly rises, and when it approaches 3600° C., the vaporising point of carbon, it breaks down, swells, and changes into black and valueless graphite. ”

“ Analysis has never detected a trace of carbon unaltered or of graphite in white cast iron, if it did not proceed from small quantities of the gray mixed with it; while perfect gray cast iron affords always a much smaller quantity of carbon altered by combination, and a much greater quantity of graphite. Neither kind of cast iron, however, betrays the presence of any oxygen. Steel affords merely altered carbon, without graphite; the same thing holds true of malleable iron; while the iron obtained by fusion with 25 per cent. of scales of iron contains no carbon at all. ”

“ For instance, though in cast iron, which is rich in carbon, that carbon passes comparatively easily into the state of graphite, yet in steel, which contains much less carbon, but little graphite forms under most conditions. Indeed, in the common structural steels which contain only very little carbon, hardly any of that carbon exists as graphite. ”

“ Austria, Chosen, Mexico, Italy and the United States are the principal producers of amorphous graphite; Chosen and Mexico supply most of the pencil graphite of the world.
The development of the electric furnace will no doubt decrease the demand for crucibles in steel making.
Great Britain, through sovereignty over Ceylon and Canada, and France, through sovereignty over Madagascar, control politically the world’s most important deposits of crystalline graphite. Japan controls the deposits of Chosen. ”

“ Thus it is extremely probable that the primary graphite, which forms large sheets, is much more weakening and embrittling than the eutectic and other forms, and therefore that, if either strength or ductility is sought, the metal should be free from primary graphite, i.e. ”

“ The mining and manufacture of graphite into articles of commerce give employment to thousands of people. The mines of Ceylon alone, when working to their full capacity, employ about twenty-four thousand men, women, and children. The rapid increase in the use of graphite has led to considerable discussion in recent years regarding the possibility of its commercial manufacture. ”

“ Black.—There is really only one member of this class, which, however, is frequently used, viz. that form of carbon occurring as hexagonal crystals and known as graphite. Another natural black natural product, occasionally used as a painters’ colour is the so-called black chalk. However, since black pigments can be produced very cheaply by artificial means, the natural colours find only a limited application; and only in one instance is graphite used alone, viz. for making blacklead pencils. ”

“ The film is after increased by the usual means. Knight's expeditious process consists in dusting fine iron filings on the wet graphite surface of the wax mould, and then pouring upon it a solution of sulphate of copper. Stirring with a brush expedites the contact, and a decomposition takes place; the acid leaves the copper and forms with the iron sulphate a solution which floats off, while the copper is freed and deposited in a pure metallic form upon the graphite. The black surface takes on a muddy tinge with marvelous rapidity. ”

“ In correspondence with this, while in some Laurentian graphitic rocks, as, for instance, in the compact graphite of Clarendon, the carbon presents a curdled appearance due to segregation, and precisely similar to that of the bitumen in more modern bituminous rocks, I can detect in the graphitic limestones occasional fibrous structures which may be remains of plants, and in some specimens vermicular lines, which I believe to be tubes of Eozoon penetrated by matter once bituminous, but now in the state of graphite. ”

“ Very rich graphite seams have been found during recent decades, both at the mouth of the Yenisej (Sidoroff's graphite quarry) and at a spur of the Sayan mountains in the southern part of Siberia (Alibert's graphite quarry) , and these discoveries have played a certain rôle in the recent history of the exploration of the country.
[349] Nephrite is a light green, sometimes grass-green, very hard and compact species of amphibolite, which occurs in High Asia, Mexico, and New Zealand. At all these places it has been employed for stone implements, vases, pipes, &c. ”

“ Amongst others, we may adduce the different states in which we know carbon to exist. We have the diamond with its beautiful light-refracting property, its hardness and high specific gravity, capable of being converted into graphite and coke. [29] Charcoal, graphite, and the diamond, are totally unlike each other, yet we know they are each composed of the same atoms. Charcoal is a black irregular substance, light, and readily inflammable; graphite is crystallizable; but the forms of its crystals cannot be referred to those of the diamond, and it burns with difficulty. ”

“ Compositions of [36] natural graphite and refractory earths, such as Morgan’s “Salamander,” are inferior to pure graphite in conductivity, but are stronger and not readily oxidised, and may be used to form sheaths for temperatures up to 1400° C. or possibly higher, when penetration of furnace gases to the junction is not of moment. ”

“ Already the output exceeds that of any other country, though the deposits have been developed but recently. France has a small local production of amorphous graphite, and obtains some from Italy.
Germany is now chiefly dependent on Bavarian flake graphite for crucibles. The efforts made during the war to get Ceylon graphite in through Holland and Switzerland indicate that the Bavarian supply is not wholly satisfactory. Amorphous graphite is supplied from Austria. Overproduction has made it possible at times to sell the products in America below cost.
Japan produces some flake graphite. ”