High temperature of the refractory substitute mate

2022-08-15
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Test of high temperature compressive strength and fire resistance of fire-resistant substitutes for titanium alloy powder coated bottom crown

Abstract Objective: to test the high temperature compressive strength and fire resistance of the self-developed fire-resistant substitutes for powder coated bottom crown. Methods: three cylindrical specimens were made of refractory substitute materials, and their compressive strength was measured at 1000 ℃. Truncated triangular cone specimens were made, and the treatment temperature was reduced in the order of 1420 ℃, 1400 ℃, 1350 ℃, 1100 ℃, so as to determine the practical refractoriness of refractory materials. Results: the compressive strength of the refractory substitute at 1000 ℃ was 17.81mpa, and the practical refractoriness was higher than 1100 ℃. Conclusion: the main high temperature properties of the self-developed fire-resistant substitute material (basic type) for titanium alloy powder coated bottom crown can meet the application requirements of titanium alloy powder coated bottom crown

powder metallurgy is similar to ceramic production, which is called metalceramic method [1]. There are few reports on the research of titanium alloy powder metallurgy in the field of Prosthodontics, which is still a blank in China. The plastic coating and sintering of titanium alloy slurry must be carried out on the fire-resistant type. The sintering temperature is about 1000 ℃, so the high-temperature strength of the type material is required. In this paper, the high temperature compressive strength and practical refractoriness of the self-developed refractory substitute material are tested, which provides a basis for clinical application

1 materials and methods

1.1 materials, instruments and equipment

self developed fire-resistant substitute materials [2], WD-10 electronic universal testing machine, cjs-53 high temperature and high vacuum compression furnace (Changchun)

1.2 specimen mold

the metal mold of the high temperature compressive strength test specimen is a cylinder with a diameter of 10mm and a height of 15mm; The plexiglass male mold for fire resistance test is trihedral cone shape (the upper triangle side is 2mm long, the lower triangle side is 8mm long, and the height is 20 mm. The oil pipe with higher strength needs to be replaced)

1.3 high temperature compressive strength test

sample preparation, turn the metal mold into a female mold with agar, mix the refractory according to the powder liquid ratio of 7.5:1, pour the mold, take it out after solidification, and dry it naturally for 24 hours. After trimming, the sample is heated to 700 ℃ in an ordinary oven and vented to prevent the volatilized gas from polluting the high-temperature compression furnace. It is naturally cooled to room temperature. Measure the outer diameter of each sample with a vernier caliper. It is carried out in the high-temperature vacuum compression furnace of WD-10 electronic universal testing machine, and the force sensor is 20K. It is worth mentioning that n × 5. Before the test, add preload to the sample. The preload value must be greater than the atmospheric pressure, then install the temperature measuring thermal electric coupling device, and then vacuum until the vacuum reaches 5 × PA, the temperature shall be increased at the rate of 7 ℃/min, and the pressure on the sample shall be continuously reduced to the preload value during the heating process. After the test temperature reaches 1000 ℃, the temperature shall be maintained for 15 minutes, and then the load shall be carried out at the rate of 0.05mm/min. During the insulation period, the temperature gradient of the sample is not greater than 3 ± 1 ℃, and the force value is output by the sensor and displayed by X-Y function recorder and hg1965 a digital voltmeter. Measure 3 samples and take the average value

1.4 fire resistance test

use trihedral cone-shaped plexiglass male mold to make samples, and the method is the same as that of making high-temperature compressive strength samples. Trim the specimen with fine sandpaper. Place the sample in the central area of the high-temperature furnace to heat up and vacuum to protect the heating element from being damaged by oxidation. The heating rate is 10 ℃/min, rise to 1420 ℃, store for 2 hours, then slowly drop to room temperature, take out the material and observe the shape. Medical membrane materials such as blood purification membrane and separation membrane, gas selective permeation membrane, corneal contact lens, tissue adhesive and suture materials. If the contour shape of the material has changed, indicating that the material is molten, take another sample to repeat the previous step, reduce the maximum temperature, and then take it out for observation after holding for 2 hours until the contour does not change. The temperature at this time is the practical fire resistance of this substitute material

2 results

2.1 high temperature compressive strength

1000 ℃, the ultimate pressure and compressive strength of this generation of molding materials are shown in Table 1, with an average value of 17.81mpa

Table 1 ultimate pressure and compressive strength of self-made fire-resistant substitute materials at 1000 ℃

measurement item sample 1 sample 2 sample 3 average value

ultimate pressure (KN) 1.5381.3911.4361.455

compressive strength (MPA) 18.8317.0317.5817.81

2.2 fire resistance

when the temperature rises to 1420 ℃ for the first time, take it out after storage for 2 hours. It is observed that the sharp edge of the triangular cone has no obvious passivation, There is obvious expansion on each smooth plane, including the upper and lower bottom surfaces and three sides, and the amount of expansion is basically the same. It shows that the practical fire resistance of this generation of molding material is lower than 1420 ℃. The second and third times are heated to 1400 ℃ and 1350 ℃ respectively, and then taken out after 2 hours of storage. The observation results are the same as the first time, indicating that the practical fire resistance of this generation of molding material is lower than 1350 ℃. After the fourth temperature rise to 1100 ℃ and storage for 2 hours, it was taken out. It was observed that there was no change in the triangular cone, so the practical fire resistance of the substitute was higher than 1100 ℃

3 discussion

3.1 high temperature compressive strength

high temperature compressive strength refers to the ultimate pressure value that a material can bear per unit section at high temperature [3]. It is an important mechanical property of refractory materials. It can reflect the change of bonding state of materials at high temperature, especially for materials with a certain bond. When the bonding state changes due to the increase of temperature, the determination of high-temperature compressive strength is more useful. This generation of material is a supporting platform for powder metallurgy sintering. According to the literature report [4], the sintering temperature of powder coated titanium alloy powder is 1000 ℃, so 1000 ℃ is selected as the test temperature in this test. There is no unified regulation on the testing method of refractory materials in industry [5]. Ohno et al. [6,7] and Chen Guifeng et al. [6,7] used samples with a diameter of 10mm and a height of 15mm when testing the high-temperature compressive strength of phosphate embedments and refractory substitutes for porcelain veneers. For reference, this sample size is also used in this test. Morey et al. [8] used a specimen with a diameter of 20mm and a height of 30mm when testing the high-temperature compressive strength of the embedding material for full crown. It can be seen that there is also a lack of unified standards for the high-temperature compressive strength test methods of dental materials

ohno et al. [6] found when studying the influence of the transformation of crystal structure of quartz and cristobalite in the embedded material on the compressive strength when heated: Crystal α、β The phase transformation has no great effect on the compressive strength of the material. However, according to the research of Chen Guifeng and others, the high-temperature compressive strength of refractories, which are mainly quartz and have formulated correct and reasonable solutions to the problem, is significantly higher than its normal temperature compressive strength, up to twice [3,7]. The results of this study show that the high-temperature compressive strength of refractories is slightly higher than that of normal temperature drying for 24 hours

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