General analysis on factors effecting color of White Fused Alumina & Analysis Methods on its particle distribution
White fused alumina taking industrial alumina powders as raw material, is smelted in electric arc furnace over 2000℃and cooled down, being smashed, magnetic separation to iron, screened to various particle sizes. Due to compact character, high hardness and sharp edges, white fused alumina has been widely used to produce ceramic and resign bonded abrasives tools, grinding, polishing, sandblasting and precision casting, etc. Besides, it is applied to produce superior fireproof materials.
However, it can be seen that the color of white fused alumina sometimes appears to be white with red, white with yellow or white with dark green, which affects the appearance of white fused alumina. At the same time, the content of WFA contains certain amount of Na2O, a little amount of Na2O consumes a great amount of Al2O3(Aluminum Oxide), which equals to 18.10 times of Na2O, and then comes into being NaAlO2. Since there is strict regulation to the content of Al2O3 in chemical content of WFA as well as the content of Na2O. There are some other contents, besides a large part of Al2O3 and a little Na2O in alumina powders.
After theoretical analysis and many experiments, we draw the conclusion as follows:
- The change of luster for white fused alumina abrasives tools mainly depends on the amount of mixture in cement and smelting environment. If in oxidizing atmosphere, WFA doesn’t appear to be red or orange, when the content of cement ( TiO2 and Fe2O3) is less than 0.55%. WFA abrasives tools have a greater chance to show deep red or orange in white color, with the increase content of TiO2 and Fe2O3. Therefore, WFA abrasive tools are not suitable for oxidizing atmosphere if the content is over 0.55%, the neutral condition or weak oxidizing atmosphere is much better.
- When ceramic cement and WFA abrasive tools cement contain these materials, such as talcum powders, quartz powders and magnesium oxide, WFA won’t appear to be red. However, it has negative effects on the strength of abrasive tools.
One the other hand, there are no international regulations to the content of Fe203 for alumina abrasive tools. The reason is that content of Fe203 has more effects on the sense of magnetic for WFA than luster. National standard limits strictly the content of magnetic material in the standard for the content of magnetic material to abrasive tools, which regulates a more strict content of Fe203 indirectly and improve the luster of WFA effectively.
White fused alumina abrasive is a kind of artificial abrasive, it is produced by a special smelting of calcined alumina with a complicated processing method, smashed, magnetic separation to iron, screened to various particle sizes. So how to detect the particle size of WFA? The followings sum up certain use methods.
Pros: simple, more directly understanding, low cost of equipment, which is often used for samples over 40um.
Cons: Human factors and sieve mesh out of shape have great impacts on results.
- Graphic process
Pros: simple, more directly understanding, we can analyze WFA by appearance, it is suitable for samples with narrow distribution.
Cons: It has weak representativeness and causes trouble to analyze wide distribution samples. And it is impossible to analyze samples less than 1um.
Pros: It needs simple processing crafts, the equipment runs continuously, with low cost, high accuracy, good iterancy and wide range of test.
Cons: It takes a long time to detect WFA, and needs complex processing.
- Electric-resistivity method
Pros: It is simple, rapid and accurate. We can detect amounts particles.
Cons: It is not suitable for samples less than 0.1um, it is troublesome to change small sieve pores for wide distributed samples.
Pros: It is simple and rapid for test, high accuracy, good iterancy and wide range of test. We can take on-line measurement and drying measure.
Cons: The distribution model has great impact on Results. The equipment is costly with low Resolution.
- By electron microscope
Pros: It is good for new particle, even nanoparticle, with high resolution. we can analyze WFA by appearance and structure.
Cons: There are a few samples with weak representativeness and cheap equipment. The human factors affect the test easily.
- Light blockage method
Pros: It is rapid for particles in liquid or gas with a high resolution.
Cons: It is bad for samples less than 1um and needs much care for systematic comparison. It is just suitable for dust, pollutant and dilute drug. It is seldom for usual powders.
- Ventilation method
Pros: The equipment is cheap and we need not disperse Samples.
Cons: The result just shows average grain size, particle distribution can’t be measured.
- Scattering method in X-rays
It is for nanoparticle.
- Scattering method in dynamic light.
It is for nanoparticle.
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