How to distinguish titanium from stainless steel and aluminum?
Distinguishing titanium from austenitic stainless steel or aluminum is quite difficult. Especially if you have one sample and there is nothing to compare with. All three metals are paramagnetic and do not react to a magnet, have a silvery color and similar specific gravity. But there are some simple and proven ways to distinguish titanium from alloy steel and aluminum at home without special equipment.
An affordable and easy way is to scratch glass with metal.
In short
- Titanium won’t scratch glass, but it will leave a streak
- Stainless steel will scratch, but will not leave a dark mark
- Aluminum leave no trace
Explanation
The method is based on the ability of titanium to leave characteristic dark marks on the surface of glass and tiles. At the same time, the metal does not scratch the glass, but rather draws on its surface. Such a trace can only be washed off with a solution of hydrofluoric acid (HF). And stainless steel can scratch the glass, but will not leave a dark mark. Aluminum doesn’t do any damage at all.
Distinguish titanium by spark
In short
- Titanium: will give a lot of bright white sparks
- Stainless: less yellow or red sparks, or no sparks at all
- Aluminum: will not spark
Explanation
During the processing of titanium on a grinding machine or with sharp longitudinal friction along the abrasive surface of a grindstone, metal contact is accompanied by a scattering of bright white sparks. In the absence of an abrasive, a fine file or even plain concrete can be used, although the effect will be less.
Sparks from stainless steel have a yellow and red tint. They fly out much less, and on concrete and a file there will be none at all. Some grades of stainless steel have been developed to be fire resistant. Sparking during the processing of such metals is technologically impossible. When aluminum is rubbed against an abrasive surface, sparks are not emitted, but characteristic silvery traces may remain on the surface.
Such a test for the possibility of sparks is the most popular and simple, since the color really differs very much, and their complete absence immediately indicates that this metal is not titanium.
Galvanic reaction test
To perform this test, you will need a DC source of about 12 V. This can be a car battery or a conversion transformer. Connect the battery plus to the test sample through a wire, and the minus to a metal rod, at the end of which cotton wool, gauze or a piece of cotton cloth is wound.
If it is titanium, then when touching the metal, its surface will be painted as a result of the formation of an oxide film. The color shade depends on the magnitude of the voltage, the concentration of the acid in the solution and the time of exposure. Stainless alloys and aluminum are not subject to this reaction.
Specific Gravity Comparison - A Method Requiring Accurate Measurements
Everyone knows that aluminum is the lightest of the three metals, and steel is the heaviest. But how to determine if you have one sample and there is nothing to compare with? This can be done by measuring and calculating the density or specific gravity of the material, which is approximately:
- 7 g/cm3 for aluminium;
- 5 g/cm3 for titanium;
- 8 g/cm3 for stainless steel.
This method of determination requires an accurate balance and a container for immersing the sample in water.
After weighing the metal, it is necessary to determine its volume. The easiest way to do this is to use the Archimedes law, known from school, by immersing the sample in a liquid. The change in water level will show the desired value.
This is a more complex and lengthy version of the definition and therefore it is used very rarely. But it also produces results and should be considered.
Specific ways to identify titanium
In some cases, the definition of metal can be made in simple and very original ways:
- Set the metal
on fire. Titanium shavings are fairly easy to ignite and burn. - Heat the metal
This metal is a good thermal insulator and when one edge of the sample is heated, the rest of the sample will be cold - Hold it in your hands
Low thermal conductivity makes the object feel warm in your hands, unlike cold steel and aluminum - Hit with a hammer
Finally, hit the sample with a hammer, as a result there will be no marks on the steel, a small dent on the titanium, and the aluminum will suffer the most.
How reliable are these methods?
- Set the metal
on fire. Titanium shavings are fairly easy to ignite and burn. - Heat the metal
This metal is a good thermal insulator and when one edge of the sample is heated, the rest of the sample will be cold - Hold it in your hands
Low thermal conductivity makes the object feel warm in your hands, unlike cold steel and aluminum - Hit with a hammer
Finally, hit the sample with a hammer, as a result there will be no marks on the steel, a small dent on the titanium, and the aluminum will suffer the most.
The above methods are quite reliable and are often used by scrap metal collectors. However, it should be borne in mind that an accurate determination of the chemical composition of the alloy, especially in the presence of impurities, can only be performed using special equipment.
Metal identification is an intermediate step in which raw materials are sorted for subsequent transportation and/or processing. Dozens of alloys have similar physical, chemical characteristics, but can differ significantly in cost and method of remelting.
For example, titanium – and alloys based on it: a silvery metal, relatively light and ductile, belonging to the austenite group. Aluminum, alloyed steels with high nickel content have similar properties.
How to distinguish titanium from metals (iron, aluminum with the addition of carbon and other additives)?
The best and most reliable way is to study the sample in a laboratory equipped with modern research analyzers:
- optical, which, with the help of spark discharges, capture light chemical elements – sulfur, phosphorus, carbon;
- stationary, portable X-ray installations, the principle of which is based on the study of photons emitted by certain chemical elements;
- laser, capable of simultaneously identifying up to 90 components in a sample.
The laboratory set-up requires special isolated rooms and one or more analyzers, the lower cost of which starts from 20,000 US dollars.
There are also simpler, slightly inferior in efficiency methods for determining materials, available in a workshop, workshop or garage. Roughly speaking, in terms of physical and mechanical properties, titanium occupies an intermediate position between similar stainless steel and aluminum: less hard and elastic than steel, slightly less ductile than aluminum alloys.
Titanium is heavier, stronger than aluminum, thanks to the film formed. It is resistant to corrosion, with low thermal conductivity. The simplest and more or less reliable methods of identification are based on its characteristics:
- on glass;
- by spark;
- electroplating;
- by specific weight.
Metal scratch glass
The graphical method is considered the most accessible: it will require a piece of scrap metal with a pointed edge, ordinary silicate glass or ceramic tile. A titanium sample, when trying to scratch a smooth surface, leaves a mark that is remotely similar to the drawing of a slate pencil.
The sharp edge does not leave any damage on glass or tile, and the left strip is not washed off with plain water. Steel alloy is highly likely to leave a scratch; aluminum scrap is not capable of either damaging the material being tested or “drawing” a line.
Titanium scrap is resistant to many aggressive substances, but its minimum amount on a glass surface can be washed off with a cotton swab moistened with a solution of hydrofluoric or phosphoric acid.
Reference: Hydrofluoric acid is an aqueous solution of hydrogen fluoride HF, which is produced by the chemical industry in concentrations of 40%, 50% and 72%. For its production, a mineral is used – fluorspar (fluorite).
The optical method has a lot of advantages: simplicity, accessibility, the possibility of carrying out in any conditions. Before conducting the experiment, the glass does not need to be washed or degreased; hydrofluoric acid is used in dentistry and can be bought in 5 ml tubes.
How to identify titanium by a spark?
The second most popular method due to the high degree of accuracy is in determining the type of material. How is titanium different from stainless steel or scrap aluminum?
You will need a grinder, angle grinder or a regular file. When in contact with a rotating abrasive wheel, the Ti metal produces a large sheaf of bright white sparks.
Stainless steel sparks less yellow, red; aluminum due to its high viscosity does not spark at all. Some types of steel alloys are designed to work in flammable environments, so sparking may not occur at all.
The same effect can be achieved with less clarity by rubbing the edges of the sample under study with a file, there will be fewer sparks, and the aluminum alloy will leave many silvery traces on the ribbed surface. The method allows fairly accurate identification of Ti due to the nature and color of the sparks, since other alloys do not have such properties.
Galvanic reaction
To determine the material in a galvanic way, you will need minimal knowledge in the field of chemistry and a few improvised tools: a 12 V car battery (or several “crown” batteries), a pair of wires, a metal rod, one end of which is wrapped with a piece of cloth.
The method is based on the electrochemical coloration of metals – anodizing, when the oxide film (in this case, titanium oxide TiO2) changes color under the influence of an electric current.
If the object under study is titanium, then if a rod is drawn over its surface, a clearly distinguishable trace remains. Stainless and alloy steels, aluminum alloys are not anodized.
Advantages of the method:
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Advantages of the method:
- a sufficiently high probability of identification;
- does not require laboratory conditions;
- Available components for research.
Among the shortcomings – it takes time to prepare and conduct the experiment, it is impossible to conduct at home.
Specific Gravity Comparison
The method is also called mathematical, because according to the results of the research, it is necessary to calculate the density of the workpiece. For titanium, stainless steel and aluminum, such indicators are known: 4.5 g / cc, 7.8 g / cc, 2.7 g / cc, respectively. To determine the chemical composition, you will need:
- knowledge of the law of Archimedes;
- fragment of scrap metal;
- calibrated scales;
- Capacity.
The density of water is 1 kg / cubic dm, therefore, in each gram of the displaced liquid, there is 1 cubic centimeter of the volume of the rod or plate placed in it.
The metal sample is weighed on a balance. Water is poured into the container installed in the bath to the brim, and then a piece of scrap is placed in the liquid. Displaced water is measured with a measuring cup or other measuring device. The volume of displaced water will be equal to the volume of the fragment under study.
Other ways to distinguish titanium from other metals
Before distinguishing titanium alloys from other materials with a spark or glass, you can try other more or less effective methods based on the thermal conductivity, density and chemical composition of the materials.
Thermal conductivity Ti – 21.9 W / (m K) at 20 ° C, i.e. if you take a plate or rod in your hand, the surface will feel warm to the touch. True, stainless steel has a similar property, so the method is only suitable for initial assessment. The same effect is achieved if the object under study is heated on one side with a lighter or other heat source: the temperature of the opposite edge of the plate will remain unchanged.
Due to their different Ti densities, aluminum and stainless steel have different effects when hit with a hammer with roughly the same force:
- a small dent will remain on the titanium surface;
- the steel will not have any defects, except for the impact mark;
- A decent, clearly visible dent will remain on a duralumin or aluminum sample.
Several experiments can be carried out with shavings: titanium shavings immediately ignite and burn with white fire, steel shavings do not burn, and aluminum shavings melt. Duralumin shavings in an alkaline solution give a violent reaction due to the release of a large amount of hydrogen.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.