1. 1 experimental materials and equipment
1. 1. 1 experimental materials
The materials used in this experiment are: carbon fiber (3 K, Dalian Xinke Carbon Fiber Co., Ltd.); Hydroxyapatite powder (60 nm, Nanjing Aipu Nano Materials Co., Ltd.); Organic monomer acrylamide (am, analytically pure, produced by Mitsui Dongjin Chemical Company of Japan); Crosslinking agent N, N "-methylene bisacrylamide (MBAM, chemically pure, Beijing Hongxing Biochemical Products Factory); Dispersant sodium hexametaphosphate (analytically pure, Beijing Chemical Reagent Company); Initiator ammonium persulfate ((NH4) 2S2O3, analytically pure, Beijing Third Chemical Reagent Factory); Catalyst N, N, N ",N"-tetramethylethylenediamine (TEMED, chemical purity, Beijing Xingfu Institute of Fine Chemistry); Ammonia (chemically pure, Tianjin Yongsheng Fine Chemical Co., Ltd.); Anhydrous ethanol (CH 3CH 2OH, Tianjin Yongsheng Fine Chemical Co., Ltd.); Phosphorus pentoxide (P 2O 5, Tianjin Shengmiao Fine Chemical Co., Ltd.); Calcium nitrate (Ca (NO3) 2 4h2o, Tianjin Yongsheng Fine Chemical Co., Ltd.).
1. 1.2 experimental equipment
See table 2- 1 for the experimental equipment used.
Table 2- 1 experimental equipment
Serial number 1 2 3 4 5 6 7 8 9 10
Equipment name: ball mill, rotary viscometer, water bath furnace, electric heating constant temperature blast drying box.
Centrifugal box resistance furnace vacuum tube furnace scanning electron microscope microhardness tester electronic universal testing machine
Model C062-7NDJ-1DKW-4DL-10180Sx3-4-10GSL-1600X S-4800HVS-1000.
manufacturer
Changsha Qinghe General Machinery Equipment Co., Ltd. Shanghai Pingxuan Scientific Instrument Co., Ltd. Beijing Zhongxing Ye Wei Instrument Co., Ltd. Tianjin Zhonghuan Experimental Electric Furnace Co., Ltd. Shanghai Pudong Physical Optical Instrument Factory Longkou Electric Furnace Factory Hefei Jing Ke Material Technology Co., Ltd.
Hitachi Japan Corp.
Shanghai Wan Heng Precision Optical Instrument Factory Ji 'nan Dongfang Test Instrument Co., Ltd.
1.2 experimental process
This experiment mainly includes surface modification of carbon fiber, preparation of carbon fiber /HA slurry, centrifugal gel injection molding, blank drying, demoulding and sintering. The process flow chart is shown in Figure 2- 1.
The specific process of this experiment is as follows: 1, carbon fiber modification (1) low temperature oxidation treatment.
Put the carbon fiber into a box resistance furnace at 400℃ for 30 minutes and then take it out for later use. (2) preparing hydroxyapatite sol
50 ml of Ca(NO3) 2 alcohol solution with a concentration of 2 mol/L and 58.5 ml of P 2O 5 alcohol solution with a concentration of 4 mol/L were prepared to ensure the Ca/P ratio of 65,438+0.67. The alcohol solution of P 2O 5 was slowly dropped into the alcohol solution of Ca(NO3) 2, and stirred by magnetic force for 2 h. After the reaction, the solution became a transparent and viscous sol.
(3) Surface stretching of carbon fiber
Soak the carbon fiber oxidized at low temperature on the surface in HA sol and pull it up. The stretched carbon fiber was dried in an oven at 80℃ for 30 minutes to convert the sol into gel. Then soak the carbon fiber in HA sol before pulling. Repeat the above process for 5 times to form a well-bonded film on the surface of carbon fiber.
2. Preparation of carbon fiber/hydroxyapatite slurry
At room temperature, 50 ml of deionized water was put into a beaker, and organic monomer acrylamide and cross-linking agent methylene bisacrylamide (cross-linking agent mass: organic monomer mass = 1: 10) were added to prepare premixes (monomer mass: 5 wt%, 10 wt%, 15 wt% and 20 wt% respectively). Then adding sodium hexametaphosphate with different dispersant contents (dispersant contents are 3 wt%, 4 wt%, 5 wt% and 6 wt% respectively), stirring and mixing uniformly, adjusting pH with ammonia water, then adding hydroxyapatite powder (mass fraction is 30 wt%, 35 wt%, 40 wt%, 45 wt% and 50 wt% respectively), stirring uniformly, ball milling for 2 hours, and then adding pretreatment.
3. Centrifugal gel injection molding
After carbon fiber /HA slurry was prepared, different contents of catalyst and initiator were added (the contents of catalyst were 0.3 wt%, 0.6 wt%, 0.9 wt%,1.2 wt% respectively; The content of initiator was 0.3 wt%, 0.6 wt%, 0.9 wt% and 1.2 wt% respectively. Sludges with different solid contents were put into a centrifugal tube mold and centrifugally molded at 500 r/min, 1000 r/min and 1500 r/min.
Cut into three pieces to measure the density of the green body, and then determine the best centrifugal process parameters. The dried samples were sintered according to the sintering process shown in Figure 2-2, the sintering temperature was 1 100℃ and the holding time was 2 h. The sintered products were used for microstructure observation and mechanical properties test.
Fig. 2- 1 experimental flow chart of preparing gradient carbon fiber /HA composites
Time/hour
Figure 2-2 Sintering Process Curve
1.3 performance test
1.3. 1 carbon fiber/hectare slurry viscosity measurement
The viscosity of carbon fiber /HA slurry was measured by rotary viscometer (NDJ-1). The No.2 rotor was pre-stirred at 60 r/min for 30 s, and the slurry viscosity was measured in the range of 500 MPa·s, and the experimental temperature was 20℃. The calculation formula is as follows:
η=k α (2. 1)
Where: η-absolute viscosity;
K- coefficient, k = 5；;
α-Reading indicated by pointer (deflection angle).
1.3.2 determination of stability of carbon fiber /HA slurry
In order to study the stability of slurry with high solid content, the slurry ground for 24 h was poured into a small beaker with scale, and the initial height of the slurry was recorded. After standing for a period of time, the slurry will be layered, with the upper layer clear and the lower layer turbid. Measure the height of the lower suspension every 12 hours. The sedimentation percentage (RSH) of the slurry is the height of the lower suspension divided by the initial height of the slurry.
1.3.3 determination of green density
Cut the green body into three pieces from top to bottom, measure the mass of each piece, then measure the volume of each piece by Archimedes drainage method, calculate the actual density of each piece, and then compare the actual density with the theoretical density of the sample to get the green body density (relative density D). The formula is as follows:
Actual value of rho =
(2.2)
d =
(2.3)
Where: m-mass of each green body, g;
V—— the volume of each green body, cm3；; ; Rho actual-actual density, g/cm3;
ρ theory-theoretical density, g/cm3;
m
V
ρ reality
? 10%0 ρ theory
D- green density (relative density),%.
Microstructure observation of 1.3.4
The morphology of carbon fiber before and after surface modification was observed by scanning electron microscope (Hitachi S-4800). At the same time, the microstructure of different parts of sintered samples and the microstructure of bending fracture were observed.
1.3.5 bending performance test
The bending properties of gradient carbon fiber /HA ceramics were tested on a bending machine. The sample size is 465,438+0 mm× 65,438+00 mm× 65,438+00 mm, the span is 25 mm in three-point bending, and the loading rate is 65,438+0 mm/min. Calculate the bending strength of the specimen according to formula (2.4) [36]. σf =(2.4)
Where: σ f-bending strength, MPa.
P- failure load, n;
3P？ L
2
2b？ h
L- span, mm; B—— sample width, mm;
H—— sample thickness, mm
1.3.6 fracture toughness test
The sample size is 10 mm× 10 mm×5 mm (length× width× height), the experimental surface of the sample is ground flat, and then a load is applied to the experimental surface of the sample to press out the indentation, and the load holding time is 15 s. The A, C and D data of the indentation are measured by IBAS -2 image analyzer.
? k？ h？
IC 1/2
? Huh? e？
(2.5)
Where: k IC- fracture toughness, MPa m1/2; E- Young's modulus, GPa, about118 GPA; H- microhardness, GPa, (H=0. 189 1
P
); d 2
2/5
? c？
=0.0 18 ?
? Answer?
- 1/2
D—— average length of diagonal line of indentation, mm; A—— half the diagonal length of indentation, mm;
C-half of the surface crack length, mm;
P load, n.