光學玻璃晶體的化學拋光是利用氫氟酸破壞玻璃表面，使原有的表層矽氧膜破壞，生產(chǎn)新的表面矽氧膜，使得玻璃得到很高的透過率且表面很光潔。目前，平板玻璃的拋光大多用化學拋光和機械拋光相結(jié)合的方法，也即化學機械拋光。
采用化學侵蝕拋光玻璃時，除使用氫氟酸外，還要加入能使侵蝕生成物（矽氟化物）溶解的添加物。一般采用硫酸，硫酸具有酸性強，沸點高、不易揮發(fā)、室溫下比較穩(wěn)定等特點，故通常將硫酸加入氫氟酸中配成拋光液。另外，因氫氟酸易揮發(fā)。侵蝕性強，故需要在密閉條件下進行拋光，同時要對拋光過程中產(chǎn)生的廢氣、廢水進行嚴格的處理。
影響化學拋光的因素如下：
1、玻璃的成分 一般情況下鈉鈣矽玻璃拋光比較困難，效果較差，含鉛玻璃化學拋光效果較好；
2、拋光液的成分 特別是拋光液中氫氟酸和硫酸的比例構(gòu)成，要根據(jù)玻璃的成分進行調(diào)整。一般的鉛晶質(zhì)玻璃配方中：7%~10.5%的氫氟酸和58%~65%的硫酸。對鈉鈣矽玻璃來說，水、氫氟酸、硫酸的體積比比例為1：（1.62~2）：（2.76~3）。
3、拋光溫度 溫度過低則反應(yīng)慢，溫度過高反應(yīng)劇烈，一般以40~50℃為宜。
4、處理時間 處理時間短，拋光作用不完全，處理時間長則玻璃表面會有鹽類沉積物，因此具體的拋光時間，應(yīng)依據(jù)拋光液的培比、處理溫度等來決定。一般情況下采用短時間多次拋光的方法來處理，每次處理時間在6~15s左右，處理次數(shù)不超過10次，若處理次數(shù)過多易在表面形成波紋等缺陷，每次酸處理完后都應(yīng)將玻璃表面用水沖洗以去掉沉淀的鹽類。
Chemical Polishing of Optical Glass Crystals
Chemical polishing of optical glass crystals involves using
hydrofluoric acid (HF) to erode the glass surface. This process breaks down the
original silicon-oxygen layer on the surface and generates a new silicon-oxygen
layer, resulting in a glass surface with high transmittance and excellent
smoothness.
Currently, the polishing of flat glass often employs a
combination of chemical polishing and mechanical polishing, commonly referred
to as chemical-mechanical polishing (CMP).
Process of
Chemical Polishing
When using chemical etching to polish glass, hydrofluoric
acid is the primary agent. Additives are also required to dissolve the etching
byproducts (such as silicon fluorides). Sulfuric acid is commonly used due to
its strong acidity, high boiling point, low volatility, and relative stability
at room temperature. Therefore, a polishing solution is typically prepared by
mixing sulfuric acid with hydrofluoric acid.
Due to hydrofluoric acid's volatility and strong
corrosiveness, the polishing process must be conducted under sealed conditions.
Additionally, strict treatment is required for waste gases and wastewater
generated during the polishing process.
Factors
Affecting Chemical Polishing
Glass Composition
? Sodium-Calcium-Silicate Glass: Polishing is more challenging, with less effective results.
? Lead-Containing Glass: Shows better results in chemical polishing due to its composition.
? Polishing Solution Composition
? The ratio of hydrofluoric acid (HF) to sulfuric acid (H?SO?) in the polishing solution must be adjusted based on the glass composition.
? For lead crystal glass: The solution typically contains 7%–10.5% HF and 58%–65% H?SO?.
? For sodium-calcium-silicate glass: A volume ratio of water: HF: H?SO? = 1 : (1.62–2) : (2.76–3) is recommended.
? Polishing Temperature
? Low Temperature: Leads to slower reactions.
? High Temperature: Results in overly aggressive reactions.
? The optimal temperature is usually 40–50°C.
? Polishing Time
? Short Time: Results in incomplete polishing.
? Long Time: May cause salt deposits on the glass surface.
? The specific polishing time should depend on the composition of the polishing solution and the processing temperature.
? Generally, short multiple polishing sessions are recommended:
Each session lasts about 6–15 seconds.
Total sessions should not exceed 10, as excessive processing may create surface defects like ripples.
After each acid treatment, the glass surface must be rinsed with water to remove deposited salts.
