Study on the Mechanism of Solid-Phase Oxidant Action in Tribochemical Mechanical Polishing of SiC Single Crystal Substrate

Na2CO3—1.5 H2O2, KClO3, KMnO4, KIO3, and NaOH were selected for dry polishing tests with a 6H-SiC single crystal substrate on a polyurethane polishing pad. The research results showed that all the solid-phase oxidants, except NaOH, could decompose to produce oxygen under the frictional action. After polishing with the five solid-phase oxidants, oxygen was found on the surface of SiC, indicating that all five solid-phase oxidants can have complex tribochemical reactions with SiC. Their reaction products are mainly SiO2 and (SiO2)x. Under the action of friction, due to the high flash point temperature of the polishing interface, the oxygen generated by the decomposition of the solid-phase oxidant could oxidize the surface of SiC and generate a SiO2 oxide layer on the surface of SiC. On the other hand, SiC reacted with H2O and generated a SiO2 oxide layer on the surface of SiC. After polishing with NaOH, the SiO2 oxide layer and soluble Na2SiO3 could be generated on the SiC surface; therefore, the surface material removal rate (MRR) was the highest, and the surface roughness was the largest, after polishing. The lowest MRR was achieved after the dry polishing of SiC with KClO3.


Introduction
As a third-generation semiconductor material, SiC has excellent chemical and physical properties [1,2] and widely used in satellite communications, integrated circuits and consumer electronics [3][4][5]. However, SiC is characterized by high hardness, high brittleness, and good physical and chemical stability, therefore, it is typically a difficult material to machine [6].
At present, the common method for ultra-smooth processing of SiC is free abrasive chemical mechanical polishing (CMP), which achieves the ultra-smooth, damage-free, and ultra-flat surface processing of the workpiece through acombination of chemical etching of polishing solution and mechanical action of abrasive, and is one of the more effective global flattening processing methods for semiconductor materials [7,8]. However, CMP has the following disadvantages, low processing efficiency, poor environmental friendliness, poor surface consistency, and poor process engineering controllability [9]. Fixed abrasive chemical machining can effectively avoid the above disadvantages of free abrasive machining and has become one of the emerging technologies in the field of ultra-precision machining [10][11][12]. Fixed abrasive tribochemical mechanical polishing is a fixed abrasive chemical-mechanical processing technology, which can use the abrasive and chemical additives in the polishing pad and the surface of the workpiece in a tribochemical reaction to change the surface of the workpiece material and chemical organization. This mechanism achieves the efficient removal of its material; therefore, is the process increasingly gaining the attention of researchers [13].

Factors
Speed of Polishing Tool n1 (r/min)

Speed of Polishing Head n2 (r/min) Polishing Pressure P (psi) Time t (h)
Parameters 60 45 2 1.5 Table 2. Solid-phase oxidant and its composition used in the test.
The solid-phase oxidant was spread evenly on the polishing pad, as shown in Figure 2a, and the dry polishing process had a dosing rate of 20g/h. Figure 2b,c show the beginning of the dry polishing process, during the dry polishing process, and after the completion of dry polishing, respectively. The single-factor method was used for the experiments and analysis to explore the oxygen production mechanisms of different solid-phase oxidant polishing. The mass of each sample was measured using a precision electronic balance.Before and after its processing, the difference was calculated, and the material removal rate (MRR, nm/min) for polishing was calculated using Equation (1). The surface roughness and 3D morphology of the sample before and after polishing were measured on a ContourGTk-1 3D profile inspection system (Bruker, Billerica, MA, USA).

Factors
Speed of Polishing Tool n 1 (r/min)

Speed of Polishing Head n 2 (r/min) Polishing Pressure P (psi) Time t (h)
Parameters 60 45 2 1.5 The solid-phase oxidant was spread evenly on the polishing pad, as shown in Figure 2a, and the dry polishing process had a dosing rate of 20g/h. Figure 2b,c show the beginning of the dry polishing process, during the dry polishing process, and after the completion of dry polishing, respectively. The single-factor method was used for the experiments and analysis to explore the oxygen production mechanisms of different solid-phase oxidant polishing.
Micromachines 2021, 12, x FOR PEER REVIEW 3 o using the ZYP230 rotary oscillating gravity lapping and polishing machine (Kem Shenyang, China). The processing principle is shown in Figure 1, and the polish process parameters are shown in Table 1. The polishing pad used for the test wa  polyurethane polishing pad, and the polishing medium was five typesof solid-ph  oxidant. The specific compositions are shown in Table 2.
The solid-phase oxidant was spread evenly on the polishing pad, as shown Figure 2a, and the dry polishing process had a dosing rate of 20g/h. Figure 2b,c show beginning of the dry polishing process, during the dry polishing process, and after completion of dry polishing, respectively. The single-factor method was used for experiments and analysis to explore the oxygen production mechanisms of differ solid-phase oxidant polishing. The mass of each sample was measured using a precision electronic balance.Bef and after its processing, the difference was calculated, and the material removal (MRR, nm/min) for polishing was calculated using Equation (1). The surface roughn and 3D morphology of the sample before and after polishing were measured o ContourGTk-1 3D profile inspection system (Bruker, Billerica, MA, USA). The mass of each sample was measured using a precision electronic balance.Before and after its processing, the difference was calculated, and the material removal rate (MRR, nm/min) for polishing was calculated using Equation (1). The surface roughness and 3D morphology of the sample before and after polishing were measured on a ContourGTk-1 3D profile inspection system (Bruker, Billerica, MA, USA). where, ∆m is the mass difference before and after polishing, g, t is the processing time, min, ρ is the density of SiC, g/cm 3 , which is taken as 3.2 g/cm 3 , r is the radius of the test sample, mm.

Workpiece Surface Composition Testing
In order to explore the solid-phase chemical reaction between different solid-phase oxidants and SiC and their oxygen production mechanism, the chemical elemental composition of the sample surface before and after polishing was examined by Quanta 200 SEM and the accompanying OXFORDINCA250 energy spectrometer system (FEI, Hillsboro, OR, USA). In addition, the chemical structure composition of the sample surface before and after polishing was examined by Bruker D8 Advance A25 XRD (Bruker, Billerica, MA, USA).

Elements and Content of SiC Surface after Polishing
The percentage of surface oxygen element content on the surface of SiC before and after dry polishing with five solid-phase oxidants was detected by SEM, and the results showed that the initial surface of SiC didnot contain oxygen before polishing. The atomic percentages of surface C and Si are shown in Table 3. After testing, oxygen appeared on the surface of SiC after dry polishing with five solid-phase oxidants.The percentage of oxygen atoms is shown in Figure 3.  where, Δm is the mass difference before and after polishing, g, t is the processing time min, ρ is the density of SiC, g/cm 3 , which is taken as 3.2 g/cm 3 , r is the radius of the tes sample, mm.

Workpiece Surface Composition Testing
In order to explore the solid-phase chemical reaction between different solid-phase oxidants and SiC and their oxygen production mechanism, the chemical elementa composition of the sample surface before and after polishing was examined by Quanta 200 SEM and the accompanying OXFORDINCA250 energy spectrometer system (FEI Hillsboro, OR, USA). In addition, the chemical structure composition of the sample surface before and after polishing was examined by Bruker D8 Advance A25 XRD (Bruker, Billerica, MA, USA).

Elements and Content of SiC Surface after Polishing
The percentage of surface oxygen element content on the surface of SiC before and after dry polishing with five solid-phase oxidants was detected by SEM, and the results showed that the initial surface of SiC didnot contain oxygen before polishing. The atomic percentages of surface C and Si are shown in Table 3. After testing, oxygen appeared on the surface of SiC after dry polishing with five solid-phase oxidants.The percentage of oxygen atoms is shown in Figure 3.  The occurrence of the tribochemical reaction of SiC can be reflected by the change o the atomic percentage on its surface, as shown in Figure 3. After polishing with five solid-phase oxidants, although oxygen was produced on the surface, the oxygen atomic percentage content varied, indicating that different degrees and mechanisms o tribochemical reactions occur between the five solid-phase oxidants and SiC. The highes percentage of oxygen atomson the surface reaction layer was observed after the dry polishing of SiC with the solid-phase oxidant Na2CO3-1.5 H2O2, and the lowes The occurrence of the tribochemical reaction of SiC can be reflected by the change of the atomic percentage on its surface, as shown in Figure 3. After polishing with five solid-phase oxidants, although oxygen was produced on the surface, the oxygen atomic percentage content varied, indicating that different degrees and mechanisms of tribochemical reactions occur between the five solid-phase oxidants and SiC. The highest percentage of oxygen atomson the surface reaction layer was observed after the dry polishing of SiC with the solid-phase oxidant Na 2 CO 3 -1.5 H 2 O 2 , and the lowest percentage of oxygen atoms in the surface of SiC was observed after dry polishing with the solid-phase oxidant KClO 3 .
According to the SEM analysis, the appearance of oxygen on the surface of SiC indicated that the solid-phase oxidant could generate oxygen to oxidize the SiC surface under the action of frictional heat to produce an oxidation reaction film on the SiC surface. Therefore, it has been shown that SiC can generate a more shearable reaction film by tribochemical reaction at room temperature [20,21].

Physical Phase Analysis of SiC Surface after Polishing
The XRD results of SiC after dry polishing were compared with those of SiC before dry polishing, as shown in Figure 4. After importing the XRD data before and after dry polishing into Jade software, it wasfound that the same peaks appeared between 30 • and 40 • and between 70 • and 80 • . The peak at 32 • may be SiO 2 after software comparison analysis, and the intensity of the detected peak on the surface of the initial SiC was small. No oxygen appears, indicating that the content on the surface of SiC is small and not easy to detect. The intensity of the peak increased after dry polishing, indicating that silicon oxides were generated on the surface.
percentage of oxygen atoms in the surface of SiC was observed after dry polishing with the solid-phase oxidant KClO3.
According to the SEM analysis, the appearance of oxygen on the surface of SiC indicated that the solid-phase oxidant could generate oxygen to oxidize the SiC surface under the action of frictional heat to produce an oxidation reaction film on the SiC surface. Therefore, it has been shown that SiC can generate a more shearable reaction film by tribochemical reaction at room temperature [20,21].

Physical Phase Analysis of SiC Surface after Polishing
The XRD results of SiC after dry polishing were compared with those of SiC before dry polishing, as shown in Figure 4. After importing the XRD data before and after dry polishing into Jade software, it wasfound that the same peaks appeared between 30° and 40° and between 70° and 80°. The peak at 32° may be SiO2 after software comparison analysis, and the intensity of the detected peak on the surface of the initial SiC was small. No oxygen appears, indicating that the content on the surface of SiC is small and not easy to detect. The intensity of the peak increased after dry polishing, indicating that silicon oxides were generated on the surface. The appearance and change of some micropeaks in the detection results may be (SiO2)x, a class of microporous silicate inclusion compounds with a (4,2)-3D structure [22]. In the dry polishing test, a surface tribochemical reaction generated a layered structure.This layered structure may be due to oxidation during the solid-phase oxidant and SiC test period under the thermal effect of tribochemical reaction transformation of oxidation substances.This layered structure includes a multi-functional layer useful for redox, friction reduction, and anti-wear functions [23,24]. Figure 5 show the material removal rates of SiC after dry polishing with five different solid-phase oxidants. The results showed that the five different solid-phase oxidants used for the tribochemical mechanical polishing tests all produce material removal from the SiC, indicating that the five solid-phase oxidants used in the tests may have experienced tribochemical reactions with the workpiece material. Among them, the highest material removal rate was achieved with the solid-phase oxidant NaOH and the lowest with the solid-phase oxidant KClO3. The appearance and change of some micropeaks in the detection results may be (SiO 2 ) x , a class of microporous silicate inclusion compounds with a (4,2)-3D structure [22]. In the dry polishing test, a surface tribochemical reaction generated a layered structure.This layered structure may be due to oxidation during the solid-phase oxidant and SiC test period under the thermal effect of tribochemical reaction transformation of oxidation substances.This layered structure includes a multi-functional layer useful for redox, friction reduction, and anti-wear functions [23,24]. Figure 5 show the material removal rates of SiC after dry polishing with five different solid-phase oxidants. The results showed that the five different solid-phase oxidants used for the tribochemical mechanical polishing tests all produce material removal from the SiC, indicating that the five solid-phase oxidants used in the tests may have experienced tribochemical reactions with the workpiece material. Among them, the highest material removal rate was achieved with the solid-phase oxidant NaOH and the lowest with the solid-phase oxidant KClO 3 .

Material Removal Rate after Polishing
The highest material removal rate after dry polishing of SiC with NaOH is due to the tribochemical reaction between SiC and NaOH during the dry polishing process to generate CO and CO 2 released in the air. On the other hand, because silicon oxides and water-soluble silicates are easily removed by mechanical action, they are also generated on the surface of SiC. The highest material removal rate after dry polishing of SiC with NaOH is due to the tribochemical reaction between SiC and NaOH during the dry polishing process to generate CO and CO2 released in the air. On the other hand, because silicon oxides and water-soluble silicates are easily removed by mechanical action, they are also generated on the surface of SiC. Figure 6 show the changes in surface roughness before and after the dry polishing of SiC using five different solid-phase oxidants. The results showed that th tribochemical polishing tests using five different solid-phase oxidants all affect th surface roughness of the SiC, indicating that the tribochemical interaction between the five solid-phase oxidants used in the tests and the workpiece material all cause the removal of some material from the workpiece surface, thus changing its surfac roughness. Among them, the surface roughness of SiC after the action of NaOH increased significantly, while the surface roughness of SiC after the action of othe solid-phase oxidants increased slightly but not significantly. The comparison of SEM before and after the dry polishing of SiC with solid-phas oxidant is shown in Figure 7. The surface of SiC after dry polishing with NaOH showed a significant change in pits and scratches compared to the initial morphology.   Figure 6 show the changes in surface roughness before and after the dry polishing of SiC using five different solid-phase oxidants. The results showed that the tribochemical polishing tests using five different solid-phase oxidants all affect the surface roughness of the SiC, indicating that the tribochemical interaction between the five solid-phase oxidants used in the tests and the workpiece material all cause the removal of some material from the workpiece surface, thus changing its surface roughness. Among them, the surface roughness of SiC after the action of NaOH increased significantly, while the surface roughness of SiC after the action of other solid-phase oxidants increased slightly but not significantly. The highest material removal rate after dry polishing of SiC with NaOH is due to the tribochemical reaction between SiC and NaOH during the dry polishing process to generate CO and CO2 released in the air. On the other hand, because silicon oxides and water-soluble silicates are easily removed by mechanical action, they are also generated on the surface of SiC. Figure 6 show the changes in surface roughness before and after the dry polishing of SiC using five different solid-phase oxidants. The results showed that the tribochemical polishing tests using five different solid-phase oxidants all affect the surface roughness of the SiC, indicating that the tribochemical interaction between the five solid-phase oxidants used in the tests and the workpiece material all cause the removal of some material from the workpiece surface, thus changing its surface roughness. Among them, the surface roughness of SiC after the action of NaOH increased significantly, while the surface roughness of SiC after the action of other solid-phase oxidants increased slightly but not significantly. The comparison of SEM before and after the dry polishing of SiC with solid-phase oxidant is shown in Figure 7. The surface of SiC after dry polishing with NaOH showed a significant change in pits and scratches compared to the initial morphology.  The comparison of SEM before and after the dry polishing of SiC with solid-phase oxidant is shown in Figure 7. The surface of SiC after dry polishing with NaOH showed a significant change in pits and scratches compared to the initial morphology.

Solid-Phase Oxidant Tribochemical Reaction Oxygen Generation Mechanism
From Figure 2, it can be seen that the solid-phase oxidant fills between the SiC a the polishing pad during the polishing process, but under the polishing pressure, t SiC specimen and the polishing pad or solid-phase oxidant can be in contact at t micro-convex body [25]. Friction, local compression, or micro-collisions may occur the micro-convex body at the polishing interface, which will generate concentrated lo stresses at the point of contact (several gigapascals [26])and high flash po temperatures(up to 1000 degrees Celsius [27,28]). Then, under the action of friction a high flash point temperatures, etc., the solid-phase oxidant decomposes oxygen a oxidizes SiC or reacts with SiC by friction chemistry with other media [25,[29][30][31].
Sodium percarbonate (Na2CO3-1.5 H2O2) is an inorganic substance and wh granular solid commonly known as solid H2O2; it is a strong oxidant. It is easy separate out oxygen when exposed to moisture to obtain Na2CO3, H2O, and O2 addition, sodium percarbonate is a heat-sensitive substance, dry Na2CO3-1.5 H2O2 120 °C decomposition. However, in the presence of water, heat, or if mixed with hea metal and organic material, it is very easy to decompose into Na2CO3, H2O, and O2, a its stability decreases with the rise of temperature [32,33]. See Equation (2). Na2CO3-1.5 H2O2(2Na2CO3-3 H2O2)→4Na2CO3 + 6H2O + 3O2↑ (120 °C) Studies have shown that the decomposition of sodium percarbonate is autocatalytic mechanism. In the decomposition of sodium percarbonate, H2O is the ma catalyst [34]. The product of sodium percarbonate decomposition diffuses to the reacti

Solid-Phase Oxidant Tribochemical Reaction Oxygen Generation Mechanism
From Figure 2, it can be seen that the solid-phase oxidant fills between the SiC and the polishing pad during the polishing process, but under the polishing pressure, the SiC specimen and the polishing pad or solid-phase oxidant can be in contact at the micro-convex body [25]. Friction, local compression, or micro-collisions may occur on the micro-convex body at the polishing interface, which will generate concentrated local stresses at the point of contact (several gigapascals [26])and high flash point temperatures(up to 1000 degrees Celsius [27,28]). Then, under the action of friction and high flash point temperatures, etc., the solid-phase oxidant decomposes oxygen and oxidizes SiC or reacts with SiC by friction chemistry with other media [25,[29][30][31].
Sodium percarbonate (Na 2 CO 3 -1.5 H 2 O 2 ) is an inorganic substance and white granular solid commonly known as solid H 2 O 2 ; it is a strong oxidant. It is easy to separate out oxygen when exposed to moisture to obtain Na 2 CO 3 , H 2 O, and O 2 .In addition, sodium percarbonate is a heat-sensitive substance, dry Na 2 CO 3 -1.5 H 2 O 2 at 120 • C decomposition. However, in the presence of water, heat, or if mixed with heavy metal and organic material, it is very easy to decompose into Na 2 CO 3 , H 2 O, and O 2 , and its stability decreases with the rise of temperature [32,33]. See Equation (2).
Studies have shown that the decomposition of sodium percarbonate is an autocatalytic mechanism. In the decomposition of sodium percarbonate, H 2 O is the main catalyst [34]. The product of sodium percarbonate decomposition diffuses to the reaction interface to form intermediates with the reactants, which reduces the activation energy of the reaction and accelerates the reaction. It can be considered that the autocatalytic decomposition of sodium percarbonate proceeds in the following steps.  (4) and (5) proceed more rapidly and reach an equilibrium quickly [33].
Sodium hydroxide (melting point is 318.4 • C, the boiling point is 1390 • C) powder will turn into molten sodium hydroxide under the action of frictional heat. In addition, the oxidant sodium hydroxide is easily deliquesced in air and reacts with CO 2 to form Na 2 CO 3 and H 2 O [35]. See Equation (6).
Potassium chlorate (KClO 3 ) is an inorganic compound, a colorless or white crystalline powder, that is a strong oxidantandis stable at room temperature. When heated to approximately 360 • C (the melting point of potassium chlorate), oxygen is released, and the reaction mechanism can be expressed in Equation (7). At continuous heating to 610 • C, the rate of oxygen release becomes slower, and the viscosity of the system thickens. At this point, the reaction is as in Equation (8); that is, potassium chlorate is oxidized to potassium perchlorate (KClO 4 ) by self-disproportionation. Equations (7) and (8) occur objectively at the same time, and when further heating to 800 • C is conducted, oxygen is released again until the system is completely changed to potassium chloride, such as Equation (9) [36].
In addition, light has a catalytic effect on the decomposition of potassium permanganate, KMnO 4 is not very stable in sunlight, and KMnO 4 can spontaneously undergo redox reactions with H 2 O [40].
Potassium iodate (KIO 3 ) is an inorganic substance. It is a colorless crystal, and its melting point is 560 • C (decomposition). It can be decomposed into KI by heat; KI reacts with O 2 and H 2 O in moist air to form KOH [41,42].

Mechanism of Tribochemical Oxidation Reaction on the Surface of SiC
(1) Solid-phase oxidant NaOH See Equation (6), the solid-phase oxidant NaOH readily deliquesces in air and reacts with CO 2 to form Na 2 CO 3 and H 2 O [35]. In addition, under the action of friction, the suspended silicon bond in SiC will also undergo the following tribochemical reaction. The main chemical equation is as follows [42,43]: The Na 2 SiO 3 produced by the reaction is soluble and can be easily removed from the SiC surface by mechanical action.
(2) Other solid-phase oxidants From Section 3.1, Na 2 CO 3 -1.5 H 2 O 2 , KIO 3 , KClO 3 , and KMnO 4 can produce O 2 by decomposition under the action of friction heat, then the surface of the SiC undergoes a tribochemical oxidation reaction under the action of frictional heat and other media [20,21]. (

3) Tribochemical hydration reaction on SiC surface
During the polishing process, due to the high flash point temperature at the polishing interface, SiC reacts with H 2 O to produce SiO 2 on the SiC surface. The main chemical reactions are as follows [44][45][46][47]: SiC +4H 2 O→SiO 2 + CO 2 + 4H 2 ↑ SiC +O 2 + H 2 O→SiO 2 + CO↑+H 2 ↑ The flash point temperature during polishing excites the oxidation reaction in Equations (18)- (20). Therefore, the temperature of the test environment is so low that it does not affect the occurrence of thetribochemical reaction and has little effect on friction behavior [48,49].
Thus, as described above, the surface of SiC transforms into SiO 2, Na 2 SiO 3, or a surface film composed of SiO 2 and Na 2 SiO 3 [26,42,43]. The resulting product, regardless of the state in which the generated product exists, is less hard than SiC. This oxide layer is easily removed using abrasive.

Material Removal Mechanism of Solid-Phase Oxidant
From Figures 3 and 4, after polishing SiC with five solid-phase oxidants, it was found that the surface of SiC contained oxygen, and the surface products of SiC are SiO 2 and silicon oxides. This illustrates the complex tribochemical reactions generated at the polishing interface during the polishing process, see Equations (2)- (20).Moreover, SiO 2 on the surface of SiC is obtained by the tribochemical reaction shown in Equations (17) (18)- (20).The CO and CO 2 generated by the reaction escape into the air, and the generated C is removed by friction; the SiO 2 generated is attached to the SiC surface. Figures 8 and 9 show the surface morphology of SiC after dry polishing with NaOH. (2) Under the action of friction, the suspended silicon bonds of SiC also undergo a tribochemical reaction with NaOH, see Equation (16). The reaction produces soluble Na 2 SiO 3 , which is removed from the SiC surface. As can be seen from the SEM inspection of the enlarged Figures 7c and 9b, after polishing, more small pits appear on the SiC surface with a smoother edge, not just brittle fracture removal. It can be shown that the Na 2 SiO 3 produced by the reaction is removed by dissolution.
Micromachines 2021, 12, x FOR PEER REVIEW 10 inspection of the enlarged Figures 7c and 9b, after polishing, more small pits ap on the SiC surface with a smoother edge, not just brittle fracture removal. It ca shown that the Na2SiO3 produced by the reaction is removed by dissolution. The solid-phase oxidant Na2CO3-1.5 H2O2 decomposes into Na2CO3, H2O, an under the action of friction, see Equation (2), and the products, in turn, produ tribochemical reaction with SiC, as shown in Equations (17)- (20).The generated adheres to the surface of SiC, the generated CO and CO2 escape into the air, and generated C is removed by friction.The material removal rate consists of the produc CO, and CO2; however, the Si atoms in the SiC are not lost, but partly oxidize SiO2.Therefore, the removal rate is lower than that of the solid-phase oxidant NaOH Figure 5.  Figures 7c and 9b, after polishing, more small pits app on the SiC surface with a smoother edge, not just brittle fracture removal. It can shown that the Na2SiO3 produced by the reaction is removed by dissolution. The solid-phase oxidant Na2CO3-1.5 H2O2 decomposes into Na2CO3, H2O, and under the action of friction, see Equation (2), and the products, in turn, produc tribochemical reaction with SiC, as shown in Equations (17)- (20).The generated S adheres to the surface of SiC, the generated CO and CO2 escape into the air, and generated C is removed by friction.The material removal rate consists of the product CO, and CO2; however, the Si atoms in the SiC are not lost, but partly oxidized SiO2.Therefore, the removal rate is lower than that of the solid-phase oxidant NaOH, Figure 5. The solid-phase oxidant Na 2 CO 3 -1.5 H 2 O 2 decomposes into Na 2 CO 3 , H 2 O, and O 2 under the action of friction, see Equation (2), and the products, in turn, produce a tribochemical reaction with SiC, as shown in Equations (17)- (20).The generated SiO 2 adheres to the surface of SiC, the generated CO and CO 2 escape into the air, and the generated C is removed by friction.The material removal rate consists of the products C, CO, and CO 2 ; however, the Si atoms in the SiC are not lost, but partly oxidized to SiO 2 .Therefore, the removal rate is lower than that of the solid-phase oxidant NaOH, see Figure 5 Under frictional heat, KIO 3 produces O 2 and generates KI, see Equation (14), which in turn reacts with the SiC surface in an oxidation reaction, see Equation (17). Furthermore, KOH is generated from the reaction of KI with O 2 and H 2 O in the air, which can also provide an alkaline environment to induce the SiC to react with O 2 , see Equation (15). Since there is no H 2 O in the KIO 3 decomposition reaction equation, SiC may also react with H 2 O in the air by frictional chemistry under the action of frictional heat, see Equations (18)- (20). However, the Si atoms in SiC are also not lost but partially oxidized to SiO 2 .
The SiO 2 generated by the tribochemical reaction adheres to the SiC surface, and the generated gas escapes into the air, thus creating a material removal rate.

Solid-Phase Oxidant Sodium Chlorate (KClO 3 )
Under frictional heat, KClO 3 decomposes to produce O 2 and generates KCl, see Equations (7)- (9).The resulting O 2 reacts with the SiC surface in an oxidation reaction, see Equation (17). The SiO 2 generated by the tribochemical reaction adheres to the SiC surface, and the generated CO 2 escapes into the air, thus creating a material removal rate.
Since there is no H 2 O in the KCIO 3 decomposition reaction equation, SiC may also react with H 2 O in the air by frictional chemistry under the effect of frictional heat, see Equations (18)- (20). However, the Si atoms in the SiC are not lost, but partially oxidized to SiO 2 .

Solid-Phase Oxidant Sodium Permanganate (KMnO 4 )
Under the action of frictional heat, KMnO 4 decomposes to produce O 2 and generates KCI, see Equations (10)- (12). In turn, this reacts with the SiC surface in an oxidation reaction, see Equation (17). At the same time, KMnO 4 can spontaneously react with H 2 O in the air to produce O 2 via a redox reaction.
The SiO 2 generated by the tribochemical reaction adheres to the SiC surface, and the generated CO 2 escapes into the air, thus creating a material removal rate.
Since there is no H 2 O in the KMnO 4 decomposition reaction equation, SiC may also produce a tribochemical reaction with H 2 O in the air under the effect of friction heat, see Equations (18)- (20). However, Si atoms in SiC are not lost, but partly oxidized to SiO 2 .
To sum up, under the action of friction, a more complex tribochemical reaction was produced between the solid-phase oxidant NaOH and SiC and air medium, not only the removal of C atoms, but also Si atoms. Comparatively, in the other reactions, only the C atoms were removed. Therefore, the largest removal rate wasproduced when polishing with the solid-phase oxidant NaOH, see Figure 5. In addition, since Na 2 SiO 3 was produced when the solid-phase oxidant NaOH was used for polishing, and Na 2 SiO 3 was easily removed by dissolution, more small pits with a depth of 1400 nm were produced on the surface, see Figure 9. As a result, the polishing surface roughness was also at a maximum when the solid-phase oxidant NaOH was used, see Figure 6.

Conclusions
(1) After dry polishing SiC with all five solid-phase oxidants, oxygen was detected on the surface, but the percentage of oxygen atoms on the surface after polishing varied. The highest percentage of oxygen atoms was observed after dry polishing SiC with Na 2 CO 3 -1.5 H 2 O 2 and the lowest percentage of oxygen atoms was observed on the surface after dry polishing with KClO 3 . (2) From the XRD results, it couldbe seen that the appearance of surface oxygen was due to the tribochemical reaction between the five solid-phase oxidants and the SiC in the polishing process. The reaction product was known to be silicon oxides, and the main substance was SiO 2 . In addition, under the action of friction, due to the high flash point temperature at the polishing interface, SiC reacted with H 2 O and generated a SiO 2 oxide layer on the SiC surface. (3) The material removal rate was calculated by measuring the mass before and after polishing, and the highest material removal rate couldbe obtained after dry polishing of SiC with NaOH and the lowest material removal rate could be obtained after dry polishing with KClO 3 . (4) After polishing SiC with oxidant NaOH, soluble Na 2 SiO 3 was generated. Therefore, more obvious scratches and pits appeared on the surface of SiC, and the roughness hada substantial increase.The surface roughness of the remaining four solid-phase oxidants didnot change significantly after polishing.