A method for preparing soft and brittle crystals with high thermal expansion coefficient

Abstract

The present invention provides a method for preparing soft and brittle crystals with a high thermal expansion coefficient, comprising a blank shaping step; placing the ingot after exiting the furnace in a dry and clean room for 3 to 5 days; waiting for the crystal temperature to align with the processing environment temperature before commencing rough processing of the crystal; the equipment used for rough processing includes a diamond wire saw, a surface grinder, an internal circle slicer, a band saw, and a chamfering machine; a wafer cleaning step; and an optical-grade polishing step. This invention addresses the unique physical and chemical properties of calcium fluoride crystals and improves existing optical processing techniques on the market, increasing the processing yield of calcium fluoride crystals and reducing processing risks, thereby lowering production costs and improving production efficiency.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry and relates to soft and brittle crystals, specifically a preparation method of soft and brittle crystals with a high thermal expansion coefficient. Background Art

[0002] Soft and brittle crystals are crystalline materials with low hardness and poor impact resistance (typically less than 5 on the Mohs scale). They are widely used in the optical field. However, due to their unique physical properties, the processing of these crystals differs significantly from that of conventional optical glass, making them prone to cracking, edge and corner chipping, and other issues during gluing and processing. This invention uses the optical cold processing of calcium fluoride crystals, a typical soft and brittle material, as an example to address these processing challenges.

[0003] Calcium fluoride crystal material has the chemical formula CaF2 and belongs to the cubic crystal system. It is an optical crystal material with a light transmission band of 0.13~10µm. It is an excellent ultraviolet and infrared window material and is often processed into special lenses. It is one of the indispensable materials in the future optical field.

[0004] At present, the prices of products made of this type of material are generally high in the market, and processing costs account for a large part of the reason. The existing processing technology mostly applies the processing technology of optical glass, ignoring the special physical properties of this material, thus generating a large amount of waste in actual operation.

[0005] Existing processing techniques for calcium fluoride crystals often mirror the quartz glass processing process: blank shaping, followed by precision grinding and optical-grade polishing. While the process flow is essentially the same, the parameters within each process should not be mechanically applied. The physical and chemical properties of calcium fluoride crystals and quartz glass differ significantly (see parameter table 1 for details), leading to numerous processing challenges:

[0006] 1. The crystal cracks and breaks during processing;

[0007] 2. The crystal cracks during heating;

[0008] 3. The crystal surface is scratched or corroded, etc.

[0009] Calcium fluoride crystal-quartz physical property comparison table

[0010]

[0011] The coefficient of thermal expansion refers to the expansion and contraction of an object due to changes in temperature. This change is expressed as the change in length per unit temperature change under constant pressure (p). The coefficient of thermal expansion varies from object to object, but is generally measured in degrees Celsius for metals. Summary of the Invention

[0012] The present invention provides a method for preparing soft and brittle crystals with a high thermal expansion coefficient. The method aims to solve the technical problems in the prior art that soft and brittle crystals with a high thermal expansion coefficient are prone to cracking and breaking during processing; and the crystal surface is easily scratched and corroded.

[0013] The present invention provides a method for preparing soft and brittle crystals with a high thermal expansion coefficient, comprising the following steps:

[0014] (1) a step of blank shaping;

[0015] 1) Place the ingot in a dry and clean room for 3 to 5 days after it is taken out of the furnace;

[0016] 2) Wait until the crystal temperature is consistent with the processing environment temperature before starting the crystal rough processing;

[0017] 3) The equipment used for crystal rough processing includes a diamond wire cutting machine, a surface grinder, an internal circle slicer, a band saw machine, and a chamfering machine; the roughness of the grinding wheels or blades of the diamond wire cutting machine, surface grinder, internal circle slicer, band saw machine, and chamfering machine used is between 400 and 800 mesh; the cutting speed of the diamond wire cutting machine is 2.5 mm / min, the grinding speed of the surface grinder is 0.02 mm / round trip, and the round trip speed is 1 / 3 of the peak value; the cutting speed of the internal circle slicer is 1.8 mm / min, the cutting speed of the band saw machine is 2 mm / min, and the grinding shaft speed of the chamfering machine is 800 rpm;

[0018] (2) a step of cleaning the wafer;

[0019] 1) When cleaning the wafer, use ultrasonic cleaning, the power of the ultrasonic wave is less than or equal to 600w; the temperature difference between the cleaning liquid and the wafer is less than or equal to 5℃;

[0020] (III) Steps of an optical-grade polishing process:

[0021] 1) The cleaned blank wafer is attached to the grinding wheel for finishing. The adhesive is quick-drying glue. During the attachment process, the wafer is heated. The temperature is increased in a step-by-step manner from (10-20℃) -40℃ -60℃ -80℃ -90℃ -100℃ -110℃. Each step temperature must be kept warm for at least 3 minutes.

[0022] 2) After the wafers are pasted into discs, they are polished using diamond powder;

[0023] 3) The polished surface needs to be evenly coated with optical protective paint for protection. Optical protective paint is a neutral protective paint.

[0024] Specifically, the high thermal expansion coefficient soft brittle crystal is calcium fluoride crystal, and the thermal expansion coefficient of calcium fluoride crystal is as high as 18.85×10 -6 / ℃; Kerr hardness is 158.3kg / mm 2 .

[0025] The present invention aims at the special physical and chemical properties of calcium fluoride crystals, improves the inherent optical processing technology on the market, increases the processing yield rate of calcium fluoride crystals, reduces processing risks, thereby reducing enterprise production costs and improving production efficiency.

[0026] Compared with the prior art, the technical effects of the present invention are positive and obvious.

[0027] 1. Temperature control: Before starting each process, the crystal must be kept at a constant temperature for 2-6 hours; processes involving heating require step-by-step heating, generally from room temperature (about 10-20°C) - 40°C - 60°C - 80°C - 90°C - 100°C - 110°C. Each step temperature must be kept warm for at least 3 minutes to ensure uniform temperature distribution inside the crystal. The heating rate should be 2°C / min.

[0028] 2. Selection of equipment abrasive roughness: relevant abrasives need to be specially customized, and the roughness of the abrasive should not be lower than 400 mesh and not higher than 800 mesh; diamond micropowder should be used as abrasive.

[0029] 3. Adjustment of equipment processing speed: The cutting and grinding speed of rough processing equipment needs to be slowed down appropriately (compared to quartz glass).

[0030] 4. The processing scrap rate is significantly reduced; the processing efficiency is significantly improved; the production cost is reduced, which is conducive to the application and promotion of calcium fluoride materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a process flow chart for preparing soft and brittle crystals with high thermal expansion coefficient according to the present invention. DETAILED DESCRIPTION

[0032] Example 1

[0033] like Figure 1 As shown, the present invention provides a method for preparing calcium fluoride crystals, comprising the following steps:

[0034] (1) A step of rough shaping (rough machining);

[0035] 1) Place the ingot in a dry and clean room for 3 to 5 days to release the residual thermal stress inside the ingot and prevent it from cracking during processing;

[0036] 2) During the rough processing of crystals, it is necessary to wait until the crystal temperature is roughly consistent with the processing environment temperature before starting processing. Especially when the temperature difference between indoor and outdoor exceeds 10 degrees Celsius, the crystal to be processed needs to be kept at a constant temperature in the environment for at least 6 hours in advance. In normal environments, a constant temperature of 1-2 hours is sufficient. Excessive temperature differences can cause the crystal to crack. However, during the processing of quartz glass, there is basically no need to pay special attention to the problem of constant temperature.

[0037] 3) The ingot is processed using rough shaping equipment including emery wire cutting machines, surface grinders, internal circle slicers, band saws, and chamfering machines. All processing equipment must be slowed down (see the parameter table for details). The grinding wheels or blades used in emery wire cutting machines, surface grinders, internal circle slicers, band saws, and chamfering machines must have a roughness of no less than 400 mesh and no greater than 800 mesh. Excessively coarse grinding wheels or blades can cause edge chipping of the crystal. The blade roughness used for quartz glass is typically around 180 mesh, and the grinding wheel roughness generally does not exceed 200 mesh.

[0038] Attached parameter comparison table:

[0039]

[0040] (2) a step of cleaning the wafer;

[0041] 1) When cleaning the wafer, ultrasonic cleaning can be used with a power not higher than 600W. When cleaning quartz glass, the power can reach 800-1000W. The temperature difference between the cleaning liquid and the wafer should not exceed 5 degrees Celsius. Excessive power and temperature difference will damage the wafer. When cleaning quartz glass, a temperature difference of 15-20℃ will not damage the lens.

[0042] (III) Steps of an optical-grade polishing (finishing):

[0043] 1) Cleaned blanks are typically bonded to a grinding wheel for finishing. Due to the high thermal expansion coefficient of calcium fluoride crystals, adhesives that do not require heating to melt should be selected, with quick-drying adhesive being a common choice. During the bonding process, the wafer is heated in a stepwise manner, typically from room temperature (approximately 10-20°C) to 40°C, 60°C, 80°C, 90°C, 100°C, and 110°C. Each step should be maintained for at least 3 minutes to ensure uniform temperature distribution within the crystal. Avoid violent airflow disturbances during heating. Quartz glass lenses, on the other hand, only require normal heating and bonding.

[0044] 2) After pasting into a disc, the wafer can be polished normally. Cerium oxide powder is often used for quartz glass, but cerium ions will cause absorption in the ultraviolet band, so calcium fluoride crystals need to be polished with diamond powder.

[0045] 3) The polished surface should be evenly coated with an optical protective varnish. The protective varnish used on calcium fluoride crystals must be neutral; acidic or alkaline varnishes will corrode the lens surface. Quartz glass lenses can use either acidic or alkaline varnishes; there is no need to pay special attention to the pH value.

[0046] The present invention aims at the special physical and chemical properties of calcium fluoride crystals, improves the inherent optical processing technology on the market, increases the processing yield rate of calcium fluoride crystals, reduces processing risks, thereby reducing enterprise production costs and improving production efficiency.

[0047] .

Claims

1. A method for preparing a soft and brittle crystal with a high thermal expansion coefficient, wherein the soft and brittle crystal with a high thermal expansion coefficient is a calcium fluoride crystal, characterized in that The steps include: (1) A step of shaping a blank; (1) Place the ingot in a dry and clean room for 3 to 5 days after it is taken out of the furnace; (2) Wait until the crystal temperature is consistent with the processing environment temperature before starting the crystal rough processing; (3) The equipment used for rough processing of crystals includes a diamond wire cutting machine, a surface grinder, an internal circle slicer, a band saw machine, and a chamfering machine; the roughness of the grinding wheels or blades of the diamond wire cutting machine, the surface grinder, the internal circle slicer, the band saw machine, and the chamfering machine is between 400 and 800 mesh; the cutting speed of the diamond wire cutting machine is 2.5 mm / min, the grinding speed of the surface grinder is 0.02 mm / round trip, the cutting speed of the internal circle slicer is 1.8 mm / min, the cutting speed of the band saw machine is 2 mm / min, and the grinding shaft speed of the chamfering machine is 800 rpm; (2) a step of cleaning the wafer; (1) When cleaning the wafer, ultrasonic cleaning is used, and the power of the ultrasonic wave is less than or equal to 600w; the temperature difference between the cleaning liquid and the wafer is less than or equal to 5℃; (III) Steps of an optical grade polishing: (1) The cleaned blank wafer is pasted on the grinding wheel for finishing. The adhesive is quick-drying glue. During the pasting process, the wafer is heated. The temperature is increased in a step-by-step manner. The temperature increase method is (10-20℃) -40℃ -60℃ -80℃ -90℃ -100℃ -110℃. Each step temperature needs to be kept warm for more than 3 minutes. (2) After pasting into a disc, the wafer is polished using diamond powder; (3) The polished surface needs to be evenly coated with optical protective paint for protection. Optical protective paint is a neutral protective paint.

2. The method for preparing a soft and brittle crystal with a high thermal expansion coefficient according to claim 1, characterized in that: The thermal expansion coefficient of calcium fluoride crystal is 18.85×10 -6 / ℃; Kerr hardness is 158.3kgf / mm 2 .

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