Alumina silicate fibre, also known as ceramic fibre, is a type of fireproof composite material. It is made of mullite

(Al2SiO5), melted and blown into fibre by resistance or electric arc furnace. It has the advantages of high temperature

resistance, good thermal stability and low heat conductivity. It is a new material instead of asbestos, widely used in

metallurgy, electric power, machinery and chemical industry and other thermal insulation on thermal equipment.

3 different techniques will be introduced in the proposal to characterization alumina silicate fibre, shown in Table 1.

Introduction

To investigate the chemical composition and proportion of aluminum silicate fibers, X-ray fluorescence diffraction (XRF) was used to characterize the material. XRF is a commonly used emission spectrum method in element analysis, to characterize the constituent elements and their contents of samples.

Principle

The characterization principle of XRF technology is under the irradiation of incident X rays, the sample to be tested absorbs X rays and is stimulated. In this process, electrons in the K layer of element atoms are excited to generate transition, and electrons in the outer L layer and M layer immediately replenish their vacancies, and generate K series characteristic X-rays.[1] By using analytical crystal, the characteristic X rays produced by each element can be separated to detect and record the X-ray intensity of its element characteristics, to achieve the purpose of qualitative analysis and quantitative analysis of various elements in the sample.

Precisity and accuraty   

Generally, more uniform sample, smaller particle size, and longer detection time can get higher accuracy and precision of XRF. XRF can represent elements with a content of more than 5/10000, and its sensitivity to light elements is low.The result is easy to be affected by the interference of mutual elements and superimposed peaks. Thus, XRF technology is suitable for qualitative and semi-quantitative analysis.

 Example data

As the content of main constituent elements Al and Si in material are large, while the content of other impurity elements is low. In order to obtain as high counting strength as possible for low-content elements, ensure the sensitivity of measurement, and prevent high content elements from leaking due to too high counting strength, the element analysis conditions for XRF are made as Table 1. The experiment using vacuum optical path, with 25mm gold cover for sample analysis.

In order to further reduce the absorption-enhancement effect of the matrix, during establishing the Calibration curve, Philips mathematical model theory α coefficient was used to calibrate the matrix. The obtained analysis results are shown in Table 2:

Results

According to the characterization data, Si and Al constitute the main body of material elements in the sample(about 96％), while Fe, Ti and other elements constitute impurities in the sample. The accuracy and precision of characterization is further guaranteed by adopting the improved experimental operation method.

Introduction and Principle

XRD, or X-ray diffraction can be used to characterization the microstructure of the alumina silicate fibres. X-ray diffraction (XRD) is a kind of structural analysis method which uses the X-ray diffraction of crystal formation to analyse the spatial distribution of internal atoms in matter. When the X-ray with certain wavelength is irradiated on the crystalline material, the X-ray will scatter due to the regular arrangement of atoms or ions in the crystal, and the phase of the scattered X-ray will be strengthened in some directions, thus showing the unique diffraction phenomenon corresponding to the crystal structure. X-ray diffraction method has the advantages of no damage to the sample, no pollution, fast, high measurement accuracy, and large amount of information about crystal integrity [4].

Precisity and accuraty

In the diffraction measurement, the specimen rotates around the centre axis of the goniometer, constantly changing the angle Ɵ counter between the incoming ray and the specimen surface to rotate along the goniometer circle, receiving the diffraction intensity corresponding to each diffraction angle 2Ɵ. Scanning range of goniometer: up to 165 ° in positive direction and 100 ° in negative direction. The absolute accuracy of 2Ɵ angle measurement is 0.02 ° and the repetition accuracy is 0.001 °.

Example data

Figure 1 shows an example data of XRD spectrum of the fibre in different temperatures. According to the figure 1, When the heat treatment temperature rises to more than 800 ℃, the structure of alumina silicate changes from non-qualitative structure to regular crystal structure [4], shown as figure 2. And the particle size is very small. The peaks in the figure are consistent with the composition of alumina silicate.[5] It shows that alumina silicate can absorb the heat of the outside world and has good heat resistance. The crystallinity is better at high temperature, and the crystal structure is regular and not easy to be destroyed, which is also good for its high temperature work.

Introduduction

Scanning electron microscopy (SEM) is used to detect 3 properties below:

1. The Diameter of AS fiber.
2. The distribution area of the AS fiber.
3. The defect and fracture of AS fiber.

The thermal conductivity or adiabatic property of the material is obtained through the above three results.[1]

Principle

Scanning electron microscopy (SEM) is a microscopic morphological characterization method with advantages of large field of view, high resolution and so on.[2] Scanning electron microscope (SEM) is a kind of observation means between transmission electron microscope and light microscope. It uses a narrow focused high-energy electron beam to scan the sample, and stimulates various physical information through the interaction between the beam and the material, which is collected, amplified and photographed to achieve the purpose of characterization of the material's microscopic morphology.

Precise and Accuraty

New scanning electron microscopes have a resolution of 1nm, and the depth of field is large, the field of vision is large, the imaging stereo effect is good. [2] Generally, the permissible error is ±5% of the magnification. Under the same working conditions, the magnification usually does not drift and the accuracy is reliable. But with the change of temperature and humidity, with the change of electromagnetic environment, there may be drift. The SEM can’t give quantitative or qualitative information alone. But the combination of scanning electron microscope and other analytical instruments can observe the microscopic morphology and analyze the composition of the material microregion.

New scanning electron microscopes have a resolution of 1nm; The magnification can reach 300000 times or above continuously adjustable; And the depth of field is large, the field of vision is large, the imaging stereo effect is good.[7]Generally, the permissible error is ±5% of the magnification. Under the same working conditions, the magnification usually does not drift, and the accuracy is reliable. But with the change of temperature and humidity, with the change of electromagnetic environment, there may be drift. The SEM can’t give quantitative or qualitative information alone. But the combination of scanning electron microscope and other analytical instruments can observe the microscopic morphology and analyse the composition of the material microregion.

Example picture and data

From the fig.1 A, it shows the diameter of the AS fiber. The fiber diameter is 3-8 microns with an average diameter of 5 microns.

From the fig.1 B, it shows the distribution area of the AS fiber which can be used to determine whether the fibers are evenly distributed.

From the fig.1 C, it shows the defect and fracture of the AS fiber in high identify.

There are also some other techniques that play an important role in the characterization of alumina silicate fibre. Based on the thermal analysis, the macro-properties of alumina silicate fiber including the basic mechanical properties and other physical properties, such as thermal properties, electrical properties and magnetic properties can be detected.

 Different properties are detected by different techniques. For instance, the electrical properties can be detected by thermoelectrometry and magnetic properties can be detected by thermomagnetometry. In addition, the infrared spectroscopy analysis can be used to identify the structural composition of alumina silicate fiber or to determine its chemical groups. Because the position and strength of the infrared absorption peak reflect the characteristics of the molecular structure. The absorption intensity of the absorption band is related to the content of chemical groups, so it also can be used for quantitative analysis and purity identification.

The properties of fiber products, especially at high temperature, are related to their chemical composition. Alumina silicate fiber is made from calcined materials of natural minerals such as kaolin or clay.^[3] The content of both  and  are about 96% and  accounts for about 44.7%. Sorting is an important process step to improve the purity of raw materials by removing  and other impurities. At the same time, as ,  and  are added, the refractory temperature of alumina silicate fiber can be increased to 1350-1450. The addition of and  can improve the microstructure of fiber, increase fiber density and reduce high temperature shrinkage rate.^[4]

Liquid displacement method on the determination of fiber density is at present the most commonly used method, its principle is to put the knot of fibrin in normal weighing, and then completely submerged in the known density is less than the fiber density of the liquid, will weigh again fiber, and fiber in the buoyancy, the liquid so as to deduce the volume of fiber, fiber density are obtained.

Ρ -- the density of the fiber, unit ;V -- volume of fiber, unit ; -- Sample weight under normal condition, unit ; -- weight in sample infiltration, unit; -- the density of the infiltrate in . [5]

In the operation, the appropriate length of continuous and complete fibre is first taken to make it into a knot. After being cleaned with acetone and desized, the fiber is placed in the oven for drying for 2 hours. After being taken out, is accurately weighed. Take a certain amount of liquid whose known density is less than the fiber density, immerse the fiber in the infiltration fluid through the suspension wire, remove the bubbles adhering to the fiber surface, and then weigh it again.