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The use of heat in inventing a new method of changing the color

Comment

this method is inspired by the effect of natural atmospheric processes (such as heat and sunlight over long periods of time) on building and decorative stones. For this purpose, building stones were studied and studied in terms of mineralogy and physical, mechanical and chemical properties. Considering the effective elements and factors, a number of decorative stones were selected as a sample and heat tests were performed under certain conditions. The obtained samples were subjected to physical, mechanical and chemical tests, and after the study, the success of the discolored stones in terms of color appearance, color stability and standard properties was determined.

Introduction:

In general, Iranian decorative stones have a lot of variety in terms of color, which is mostly due to the presence of iron impurities in these stones. As we know, among building and decorative stones, we can name stones that are aired due to weather conditions, including physical factors (heat and light) or chemical factors (acid rain) and then change the appearance of the stone. Among these, we can name the red marble of Sanandaj, which tends to be white due to weathering, as well as the gray marble of Lashtar or some granites that fade over time. This point led us to study the factors of discoloration of decorative stones in the form of simulations of these factors in the laboratory to be able to achieve a new way to change the color of the stone in much less time by controlling the weathering factors.

In this regard, only in some countries, such as China, it has been possible to change the color of the stone with the use of dyes, which has defects such as color instability. In this study, by studying the behavior of the effect of atmospheric factors such as heat and light over time, we were able to change the color of decorative and building stones by controlling, calculating and controlling the heat applied to the stone at the calculated times.

Heat effect study:

Rocks are poorly conductive and have a conductivity ranging from 0.1 to 7 j / msc, and are weaker in this respect than metals because the conductivity in metals is electron while in rocks it is phononic. For this reason, minerals such as magnetite, hematite and limonite have high conductivity (10-30 j / msc). Increasing the temperature increases the amplitude of the atomic vibration of the minerals and also with increasing the application of heat on the rocks we see a decrease in density and an increase in the porosity of the rock as well as a sharp decrease in the Young's modulus.

Fe is one of the main color factors in rocks and minerals; In other words, it has impurities of hematite, limonite and sometimes chlorite. In the case of precious stones, we can also use the element Cr, which causes red color in ruby and green color in emerald, and mineral color in smoky quartz, which is affected by the presence of Al3 + impurity.

Regarding the effect of heat on the color of minerals, experiments have been performed so far, for example, smoky quartz electrons are displaced after heating and smoky quartz is discolored after electron pairing. An example is the white Spodumene mineral, which turns purple when heated to 250 ° C and becomes completely colorless when heated further to 500 ° C. In a sample of siderite, after applying heat, the color of the mineral darkened, which can be related to the oxidation of Fe2 +. Due to the fact that color is one of the most striking characteristics of precious stones, the study of the effect of heat on their color also shows its position more.

Heat in the case of decorative stones and facades in different samples has a different effect on the color of the stones, which in some cases is appropriate and in others is inappropriate because sometimes the original color is more attractive. This article goes on to describe the effect of heat on the color of decorative stone and the control of this factor as a way to prepare new stone.

Study and study of stones:

First, a comprehensive study was performed on all decorative and building stones in Iran that had undergone discoloration due to weathering. Most of these rocks had colored impurities such as iron compounds. As previously described, the minerals magnetite, hematite and limonite are at a high level in terms of thermal conductivity. After studying the mineralogical and mechanical properties of this group of building stones, some of them Selected for thermal tests. The aim was to accelerate the effect of atmospheric factors such as heat in the laboratory, which changes the color of the rock over long periods of time.

Sample selection:

After the final study of the effect of atmospheric factors such as temperature over a long period of time, a number of Iranian decorative stones were selected which, according to their mineralogical characteristics, were predicted to reach the desired and appropriate color in a shorter time after applying heat. In order to have variety in the type of stone, a suitable sample was selected from each family of decorative stones, which include limestone travertine, green gabbro igneous stone, yellow limestone and pale yellow-yellow limestone.

Appearance characteristics of samples:

For each type of stone, 40 polished cube samples with suitable dimensions were prepared ("This number was considered due to the study of color change process and less error in the final selection"). The samples were selected in a polished manner in order to study the effect of heat on the color of the stone and the effect of heat on the quality of stone polishing as a very important factor in decorative stone.

Test environment specifications:

For heat treatment, an advanced ceramic furnace was selected with the appropriate inlet size and also with the ability to apply heat at different time rates, at low and high temperatures. Each individual sample was placed in a furnace at a different temperature and time and was heated by applying heat and a suitable temperature increase rate, and at different times after cooling with a specific temperature return rate, they were removed from the furnace. The range of tested temperatures was considered to be 25-25 ° C.

Description of experiments: The first sample

The first example is lemon-colored travertine. A total of 40 prepared samples of this stone were placed separately in the furnace at different temperatures and at different times and then removed from the furnace at different times. The rate of increase in temperature and its apparent color, which tended from lemon to red, were studied.

Over time, as the temperature increased, the color of the stone shifted from a lime color to a bright red color. Among the 40 samples of stone tested, the samples had a good red color to check the physical and chemical properties (according to the stone standard). After studying the laboratory results of heated samples and comparing their results with the original samples and also comparing with the standards of decorative stone, a successful sample was selected in terms of color appearance, color stability and physical and mechanical properties.

It is worth noting that if the heat factor and the characteristics of the environment are not under control, although the stone may have a suitable color in appearance, but over time there is a possibility of loss of properties and its disintegration, and this requires careful process Displays the operation.

Second example:

The second stone is a type of green gabbro, which is called granite in the term of decorative stone market. As in the first stone, 40 polished cube samples were prepared from this stone. Each sample was heated separately at specific temperatures and at specific times, and the process of changing the color of the rock from green to brown was quite evident.

Finally, those samples that had a suitable brown color in terms of appearance were sent to the laboratory to check the physical and chemical properties, and among them, a successful sample that had a suitable color in terms of both appearance and standard characteristics was selected and recorded. Took.

Third example:

This is a type of yellow limestone that turns brown when heated. A total of 40 polished cube samples were prepared and separately exposed to heat at different temperatures and at different times. It is worth noting that in determining the range of heat tested for each type of rock, their thermal resistance must be considered.

After performing tests and examining the samples in terms of color and quality of polishing, a number of samples were sent to the laboratory for physical and chemical tests. After studying the test results, a successful sample was identified.

Fourth example:

The fourth example is from the family of limestone, the main color of which is yellow with brown veins. This stone has a beautiful color in appearance, but after applying heat, it changes color to an eye-catching color. As in the previous experiments, 40 polished cube samples were prepared from this stone and thermal tests were performed on it at different times and at certain temperatures.

After examining the color change process of different samples that had led to bold and beautiful browns, a number of suitable samples were sent to the laboratory and the necessary tests were performed on them, and finally a successful sample was selected.

Conclusion:

In this study, all necessary tests including physical and mechanical tests, section studies as well as XRD and XRF tests of samples, before and after heat application and color stability test of samples after heat application and color change were performed, the results of which will be presented in a future article. Is presented.

The results of this research and its application can be listed as follows:

1- Success in presenting a new method in order to create a deep color change of some decorative stones using the control of heat and time factors.

2 - Many decorative stones in Iran, due to the presence of iron impurities, have the ability to change color due to heat at calculated times.

3- The proposed method makes it possible to have a stone with one texture but in two different colors, which this phenomenon can be used effectively in the principles of building architecture and stone decorations.

4- Unstable minerals and colored impurities change the color of decorative stones, which can be studied by petrography before selecting facade stones.

5 - In cases of decorative stones that have suffered from surface weathering or have a mixture of colors with this method can achieve a consistent color in the surface and depth of the stone, which is an important issue in the decorative stone industry.

6- Due to the limited reserves of decorative stone in terms of color variety and limited use of natural stone color, this method can open a window to produce a new generation of decorative stones and facades.

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