Dental metallurgy, for the use of dental students and practitioners

Preface

In this manual on the subject of dental metallurgy I have endeavored to emphasize those properties of the various metallic elements which are of particular interest to the dentist.

As in every other science, there are branches which border on kindred sciences. Such operations as involve prosthesis are treated only in such detail as to emphasize the metallurgical principle involved.

The chemical properties of the metals are dealt with very superficially, as this knowledge should have been acquired by the student before any attempt is made to study metallurgy.

The chemical test for the metals, both in the dry and wet way, is placed in the back of the book. The object of this is twofold : in the first place it tends to condense the chapters on the individual metals, and secondly, the theme of analysis may be used in the study of qualitative analysis, and being condensed in one chapter is in more convenient form.

The course in metallurgy, as I have been conducting it for a number of years, is given at the same time as the course on qualitative analysis. The advantage of such an arrangement is that the chemical properties of the metals are thoroughly studied in conjunction with metallurgy, in which the physical properties are of the greatest importance.

vi PREFACE

In the preparation of this volume I have made frequent references to the following valuable works on Metallurgy : Fenchel, Schnabel, and Essig and Koenig; on Chemistry: Oswald, Newth, Smith, and Remsen; Qualitative Analysis: Prescott and Johnson; Mineralogy: Moses and Parson, and Dana; Prosthetic Dentistry: Prothero; Assaying: Brown; Physics: Ganot; and the various scientific journals.

I wish to express my appreciation to the following for their kindness in allowing me the privilege of using their illustrations: Central Scientific Co., E. H. Sargent & Co., Chicago; F. L. Schmidt & Co., New York City, and the Bureau of Mines, State of Colorado.

E. P. B.

St. Louis, 1917.

CONTENTS,

Chapter I. Metallurgy

Historical. — The history of prehistoric ages depends upon relics for the study of the people living in the remote past. Depending upon the nature of these relics, it is possible to determine the state of civilization, habits and also peculiarities of the race under consideration. The lower savages of the present day correspond to the oldest traces of man. In order to leave traces, it was necessary for primitive man to make something, not subject to quick decay or easily destroyed.

The age known as the " paleolythic" or "old stone age" is designated as that period in which man had advanced to that degree, which enabled him to work rocks into some useful form so as to serve in his daily life. Arrow-heads and various other flint implements, in their crudest form, are among the relics found corresponding to this age. The "neolythic," "new stone age," following this era, shows culture has advanced, and the stone implements in this period assume a higher degree of workmanship.

The "neolythic" period varied in length of time in different localities; however, long ages must have passed before metals were made use of by mankind. Copper in its native state (too soft to be of material value to primitive man) , when hardened by the admixture of tin, forming bronze, was brought into use later. That this occurred in countries beyond the Mediterranean, before any people in Europe found the- metals secreted in their ores, appears to be more 2

18 METALLURGY

than probable, and formerly it was assumed that the use of copper and bronze, followed later by the use of iron, came into Europe from the East. Now there is a growing opinion that primitive metallurgy in some parts of Europe was an art independently acquired. 1 The more advanced of the native races were acquainted with copper and bronze, tin, lead, gold, and silver.

Sacred history teaches us that the metals were made use of at a very early age. One of Adam's grandsons was a worker in metals and frequent mention of gold, silver, bronze, etc., is made in the Bible.

The development of chemical science has been divided into several stages, and as the early history of metallurgy is identical with that of chemistry, it may be permissible to quote the history of the two sciences as if they were one and the same.

1. Ignorant Observation. — In this period experimentation was carried on in a haphazard manner, as no set laws had been formulated. The observer was simply following, as we may say, his own initiative. Rarely were records kept, and humanity or science was rarely benefited as the result of the efforts expended.

2. Isolated Observation. — This period is so called because the investigators guarded very zealously their efforts: and, as a rule, worked in hidden places, and science was not benefited, due to the fact that there was no cooperation between the investigators of this period.

Alchemy, with its prime object to find the philosopher's stone, may be classed in this period; and one may indeed excuse this set of men, when we consider the object of their endeavors was to find a substance which would change base metals into gold or silver. Their laboratories were sacred to them, no one was permitted to view their operations; mystic signs were used, and their favorite deity called upon to assist in their work. Up to this period the chief impetus to the development of chemistry was through the metallic

1 Larned.

TRUE SCIENTIFIC INVESTIGATION 19

elements, and without a doubt this period may be considered the forerunner of the development of our present-day science of metallurgy.

The phylogiston theory was the common belief of the alchemists; according to this theory a substance undergoing rapid oxidation or combustion burned, losing phylogiston. Combustible substances possessed phylogiston, noncombustible substances did not. This peculiar substance when combined with other substances made them weigh less, after burning, which was described as the act of a substance losing its phylogiston, the calx or ash resulting weighed more or possessed the original weight of the substance devoid of phylogiston.

The elements were four, namely, earth, warm and moist; water, cold and moist; air, cold and dry; fire, hot and dry. With these four elements and the phylogiston theory, attempts were made to explain the various phenomena that were met with.

3. True Scientific Investigation. — We may date this period with the introduction of the chemical balance by Lavoisier and the thorough understanding of the chemical phenomenon of oxidation about the year 1776. From this time we have the setting aside of the older theories such as have been mentioned, and the introduction by degrees of our present-day views upon the science of chemistry.

One factor which has done more to further the progress of science than any other fact which may be brought to bear is that of cooperation of the investigators. By the combined efforts and setting of professional narrow-mindedness we have all gained knowledge from one another.

It may be readily seen by reviewing the past that metallurgy has played its part in the rise of mankind from the primitive. As industry increased the needs for metals and alloys has increased correspondingly, and one has only to look to our own profession to see that at the present time there is a crying need for advancement and research investigation to provide for emergencies which have developed in the metallurgical side of dentistry.

Chapter II. Metals

Metallurgy is a very extensive science and, like others, must depend upon its kindred sciences for its development. Geology, mineralogy, physics and chemistry, all have a direct bearing upon this science. A knowledge of chemistry and physics is absolutely necessary for the proper understanding of metallurgy.

Metallurgy may be defined as the science which treats of the physical and chemical properties, mode of occurrence, reduction from their ores, and application to useful purposes of the metallic elements.

Chemistry teaches us that the universe is made up of matter and energy. Matter being composed of simple substances called elements, and also a combination of these elements known as chemical compounds. The number of elements is constantly subject to change, and at the present time there are about eighty substances classed as elements. These are again divided into metals and non-metals. The names of the metallic elements and their principal valency so far known with certainty are as follows:

International Atomic Weights. = 16. 1913. Symbol.

Aluminum Al

Antimony Sb

Arsenic 1 As

Barium Ba

Bismuth Bi

Cadmium . Cd

Caesium Cs

Calcium Ca

Cerium Ce

1 Metalloid.

Valency.

At, Wt.

Ill

27.1

III or V

120.2

III or V

74.96

II 137.37

III or V

II

112.4

I

II

40.07

III or IV

140.25

International Atomic Weights.

Symbol.

Chromium Cr

Cobalt Co

Copper Cu

Erbium Er

Gadelinium Gd

Gallium Ga

Germanium Ge

Gold Au

Indium In

Iridium Ir

Iron Fe

Lanthanum La

Lead Pb

Lithium Li

Magnesium Mg

Manganese Mn

Mercury Hg

Molybdenum Mo

Nickel Ni

Niobium \ Nb

Osmium Os

Palladium Pd

Platinum Pt

Potassium - K

Radium Ra

Rhodium Rh

Rubidium Rb

Ruthenium Ru

Samarium Sm

Scandium Sc

Selenium 1 Se

Silver Ag

Sodium Na

Strontium Sr

Tantalum Ta

Tellurium Te

Terbium Tr

Thallium Tl

Thorium Th

Tin Sn

Titanium Ti

Tungsten W

Uranium U

Vanadium V

Ytterbium Yb

Yttrium Y

Zinc Zn

Zirconium Zr

II,

Valency, II or II or I or III III III II or I or III III or II or III II or I

II II, III or I or

II, III, IV or

II or

III or II or II or II or I II

III I

II, III or

III

III II or I I II V II or

III I or

III or II or

IV II, IV, V or

III, IV, V or

II or III III

II IV

III III II

IV III

IV III

IV IV

II

V

III

IV IV IV IV

IV

IV

VI III

IV IV

VI

VIII IV

Considered a non-metal.

The metals vary in their degree of usefulness; some are met with in e very-day life, while others are mere curiosities.

The following seventeen metals are used to a greater or less extent in the metallic condition. These are:

Antimony, Mercury,

Aluminum, Nickel,

Bismuth, Platinum,

Copper, Tantalum,

Gold, Tungsten,

Iridium, Silver,

Iron, Tin,

Lead, Zinc.

Manganese,

For dental purposes, the following metals are of the most importance, namely:

Antimony, Mercury,

Aluminum, Nickel,

Bismuth, Platinum,

Copper, Silver,

Gold, Tin,

Iridium, Tantalum,

Iron, Tungsten,

Lead, Zinc.

Eighteen are more or less extensively used in medicine and in the arts as coloring pigments and for alloying purposes. These are:

Antimony, Lithium,

Arsenic, Manganese.

Barium, Mercury,

Bismuth, Potassium,

Cadmium, Sodium,

Calcium, Tungsten,

Chromium, Titanium,

Cobalt, Uranium,

Copper, Zinc.

The remaining metals are of very little or no practical use in the metallic state.

The metallurgist classifies the metals into two classes — the noble and base metals. A noble metal is one that forms unstable oxides, and is reduced from their oxides by simply

Platinum group heating to redness. Base metals, on the other hand, form stable oxides, and it requires the presence of certain substances, known as "reducing agents," before they may be freed from combination with oxygen, when heated to redness. The noble metals consist of the platinum group, together with gold, silver, and mercury.

Symbols. At. Wt.

Platinum Pt 195.2

Osmium Os 190.9

Iridium Ir 193.1

Palladium Pd 106.7

Rhodium Rh 102.95

Ruthenium Ru 101.7

Silver Ag 107.88

Mercury Hg 200.6

The elements are also classified into families or groups, according to their atomic weights; this forms a basis for the "periodic classification" or the so-called "law of Octavos." According to this classification we have the "alkali metals" (sodium, potassium, lithium, etc.); "alkali earth metals" (calcium, barium, strontium, etc.) ; zinc, copper, aluminum, iron, tin, antimony and gold-platinum groups.

Finally, metals may be classified according to their behavior in solution toward certain reagents, as in the five or six groups of qualitative analysis. We mention the various ways in which the metals may be classified to show how indefinite the question often asked, "How are metals classified?" seems to a person who has made a study of this subject.

The metals occur in nature widely distributed, and may be found in the metallic condition, "native state," in combination and as impurities in other metallic substances.

The native metals generally contain admixtures of other metals — rarely are they found in the pure condition. The natural occurring compounds of the metals are known as minerals. A mineral may be defined as " a natural occurring compound of a metal formed by inorganic nature, generally possessing a definite crystalline form." The native metals and also minerals are often associated with earthy impurities. These impurities are known as gangue, vein-stuff, or chat.

An ore is a material containing one or more metals in the free or combined state. This term is generally restricted to a material bearing some metal in paying quantities. The difference between an ore and a mineral is that the latter is a chemical compound, while the former may be composed of two or more minerals or the elementary metal as a complex mixture.

The third source of metals which in some instances is very important is the presence of a metal in an ore in which some other metal predominates. Gold as an impurity in iron and lead ores, silver in lead ore, and cadmium in zinc ores, illustrates this mode of occurrence.

It has been estimated that 99 per cent, of the earth's crust consists of nine elements in the following proportions:

Oxygen .

. . 49.98

Calcium .

. 3.51

Silicon

. . 25.30

Magnesium .

. 2.50

. . 7.26

. 2.28

Iron ...

5.08

. 2.23

Hydrogen

. 0.94

Practically none of these exist in the free state, but combined for the most part as silicates and oxides and, with rarer elements, as carbonates, haloids, and sulphates. The unoxidized substances, such as sulphides, are comparatively rare.

Identification of Metals in their Ores. — The physical properties of the mineral is examined, such as the crystal form, hardness, and lines of cleavage. A blow-pipe analysis is next made; this consists of bead tests, charcoal block reactions, and flame tests. The wet methods of qualitative analysis is generally used to confirm the findings of the blow-pipe. As a rule the dry methods of analysis is used by the prospector, and are sometimes spoken of as field tests, because they are made at the site w T here the ore is discovered. The chemical laboratory is an absolute necessity for the performance of the wet tests.

TREATMENT OF ORES

Quantitative Methods. — These are also classified into wet and dry methods.

Assaying is that science which enables ns to find out of what a substance is composed, and the proportions, by means of dry reagents and heat.

The wet methods are divided into two classes:

(a) Volumetric analysis, using solutions of definite strength, known as standard or normal solutions.

(b) Gravimetric analysis, precipitating the element and calculating the quantity present from the weighed precipitate.

UNDHARD [ftTEHTED] KOMINUTER.

Fig. 1

Treatment of Ores. — The ore is crushed to reduce it to a suitable size. A ball-mill may be used, or some other form of machine which accomplishes the same purpose. The ball-mill (Fig. 1) consists of an iron drum which is caused to revolve. On the inner side there are step-like projections, and iron balls; in some cases Iceland pebbles are placed inside the drum, and when the drum revolves the pebbles or balls crush the ore against the projections. The ground ore sifts through screens located between each projection and is collected below the mill.

The next treatment is to concentrate the ore, and for this purpose the crushed ore is treated with water and run over gravity tables (gig tables) , the earthy material of less specific gravity passes to one side, and the heavier metal-bearing ore to another side of the table. The concentrates are then subjected to some of the following processes in order to further remove impurities or aid in the reduction.

Calcination. — The object of this process is to remove organic impurities and water; by heating to a low red heat it renders the ore more porous.

Roasting. — Roasting consists in heating to a higher temperature, expelling substances which can be volatilized, such as arsenic, sulphur, carbon dioxide, etc. The metals, as a rule, are reduced to their oxides as the result of this process.

Sublimation. — Sublimation is the process of heating a substance until it volatilizes and the vapor is collected as a solid. Arsenic, arsenious oxide, ammonium chloride are substances which may be sublimed.

Distillation. — Distillation is a similar process of boiling, but the vapor collects as a liquid. Mercury, zinc, cadmium may be distilled.

Smelting. — Smelting is a process of refining a metal-bearing substance by fusing. It is necessary at times to remove foreign material present in an ore by chemical means. During the smelting process these materials become oxidized, and the nature of these oxides determine the material which must be added to remove them. If the oxides are of an acid nature, such as silica, it will be necessary to add a substance of a basic nature, such as lime-stone. At the temperature of the furnace, the calcium oxide formed combines with the silica, forming calcium silicate.

CaCOs + Si0 2 = CaSiOs + C0 2 .

The calcium silicate is a fusible glass, and rises to the top of the crucible, and is spoken of as a fusible slag. If, on the other hand, the impurities present are basic oxides, then an acid material like silica or the silicates are added.

A substance which possesses the property of combining with the impurities present in an ore, thus forming a fusible

REGULUS 27

slag, is called a flux. There are two varieties of fluxes: acid and basic fluxes.

In soldering we use a flux, the object being to remove any oxide which may be formed, due to the heating of the metallic surface. (See Soldering.)

Lixiviation. — Lixiviation is a process of washing an ore to remove soluble compounds. Low-grade copper ores are roasted with sodium chloride, then washed or lixiviated, and the soluble copper chloride is recovered from the water by a precipitation method.

Desiccation. — Desiccation is simply heating an ore to a temperature slightly above the boiling point of water in order to dry the ore.

Regulus. — Regulus is a term applied to certain sulphides formed during the process of smelting in the presence of sulphur. Iron, copper, or silver ores when smelted in the presence of sulphur form a regulus. Speiss is the arsenides of certain metals formed during fusion, while Matte is a term embracing both of these and includes sulphides, arsenides, and antimonides of the metals formed during fusion.