Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1–xLaxFe12–xCoxO19 (x=0–0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetizationMs, magnetic anisotropy fieldHa, intrinsic coercivityHci, and Curie temperatureTC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amountx did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such asα-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved theMs (>62 emu/g),Ha (>1400 kA/m), andHci (>320 kA/m) for the ferrites withx varying from 0.1 to 0.3, but theTC decreased with increasing substitution amount. More-over, the microwave sintered ferrites could provide largerHci and similarMs compared with the conventional sintered ferrites.

Refined microstructure and enhanced mechanical properties in Mo-Y_(2)O_(3)alloys prepared by freeze-drying method and subsequent low temperature sintering

The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying method.Consequently,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an average grain size of 54 nm.After low temperature sintering at 1600°C,the Mo-Y_(2)O_(3)alloys maintaining a high density(99.6%)have the finest grain size(620 nm)comparing with available literature about oxide dispersion strengthened molybdenum alloy(ODS-Mo).The oxide particles remain their small size(mainly<50 nm)within Mo grains and at Mo grain boundaries.Furthermore,the Y_(5)MO_(2)O_(12)particles were firstly observed within Mo matrix,and its formation can absorb nearby oxygen impurities,which involves the purification of Mo matrix.The mechanical properties show that Mo-Y_(2)O_(3)alloy possess a high hardness of 487±28 HV_(0.2),a high yield strength of 902 MPa,a high compressive strength of1110 MPa,respectively.Our work suggests that freeze-drying and subsequent low temperature sintering can shed light on the preparation of ultrafine ODS-Mo alloys with high performance.

Sintering of WC-Co powder with nanocrystalline WC by spark plasma sintering

A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering （SPS） at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.

The Properties of YSZ Electrolyte Sintering at 1300 ℃

The properties of yttria stabilized zirconia（YSZ） related to the sintering process were discussed.YSZ nano-powders about 40-100 nm as raw material,the sub-micrometer grain sizes such as 0.4-3 μm in YSZ were gotten by sintering process at 1300 ℃,which was performed at 1000 ℃ for 2 h,then raised the temperature at the rate of 50 ℃ / h to 1400 ℃,then decreased directly to 1300 ℃ in 30 minutes,finally at 1300 ℃ for 5-20 hours.The ratio of bigger grain size becomes larger as the holding time increasing at 1300 ℃.The grains less than 1 μm are about 50%,eg,43.2%,52.2% and 51.1% related to 1300 ℃ holding 5 hours,8 hours and 10 hours,respectively.As YSZ grain size became small,the electrical conductivities did not decrease,even increased,about 0.20 s/cm at 1000 ℃.The reduced sintering temperature and time were benefited to co-fire with the electrodes in electrode-supported SOFCs.

Sintering characteristics, phase transitions, and microwave dielectric properties of low-firing [(Na_(0.5)Bi_(0.5))_(x)Bi_(1-x)](W_(x)V_(1-x))O_(4) solid solutionceramics

A series of high-k[(Na_(0.5)Bi_(0.5))_(x)Bi_(1-x)](W_(x)V_(1-x))O_(4)(abbreviated as NBWV(x value))solid solution ceramics with a scheelite-like structure are synthesized by a modified solid-state reaction method at the temperature range of 680-760 C.A monoclinic(0≤x<0.09)to tetragonal scheelite(0.09≤x≤1.0)structural phase transition is confirmed by X-ray difraction(XRD),Raman,and infrared(IR)analyses.The effect of structural deformation and order-disorder caused by Na^(+)/Bi^(3+)/W^(6+) complex substitution on microwave dielectric properties is investigated in deail.The compositional series possess a wide range of variable relative permittivity(er=24.8-80)and temperature coefficient of resonant frequency(TCF value,-271.9-188.9 ppm/℃).The maximum permittivity of 80 and a high Qxf value of~10,000 GHz are obtained near the phase boundary at x=0.09.Furthermore,the temperature-stable dielectric ceramics sintered at 680 C with excellent microwave dielectric properties of ε_(r)=80.7,Qxf=9400 GHz(at 4.1 GHz),and TCF value=-3.8 ppm/℃ are designed by mixing the components of x=0.07 and 0.08.In summary,similar sinterability and structural compatibility of scheelite-like solid solution systems make it potential for low-temperature co-fired ceramic(LTCC)applications.

Microstructure refinement and second phase particle regulation of Mo-Y_(2)O_(3) alloys by minor TiC additive

The oxide dispersion strengthened Mo alloys(ODS-Mo)prepared by traditional ball milling and subsequent sintering technique generally possess comparatively coarse Mo grains and large oxide particles at Mo grain boundaries(GBs),which obviously suppress the corresponding strengthening effect of oxide addition.In this work,the Y_(2)O_(3) and TiC particles were simultaneously doped into Mo alloys using ball-milling and subsequent low temperature sintering.Accompanied by TiC addition,the Mo-Y_(2)O_(3) grains are sharply refined from 3.12 to 1.36μm.In particular,Y_(2)O_(3) and TiC can form smaller Y-Ti-O-C quaternary phase particles(~230 nm)at Mo GBs compared to single Y_(2)O_(3) particles(~420 nm),so as to these new formed Y-Ti-O-C particles can more effectively pin and hinder GBs movement.In addition to Y-Ti-O-C particles at GBs,Y_(2)O_(3),TiOx,and TiCx nanoparticles(<100 nm)also exist within Mo grains,which is significantly different from traditional ODS-Mo.The appearance of TiOx phase indicates that some active Ti within TiC can adsorb oxygen impurities of Mo matrix to form a new strengthening phase,thus strengthening and purifying Mo matrix.Furthermore,the pure Mo,Mo-Y_(2)O_(3),and Mo-Y_(2)O_(3)-TiC alloys have similar relative densities(97.4%-98.0%).More importantly,the Mo-Y_(2)O_(3)-TiC alloys exhibit higher hardness(HV0.2(425±25))compared to Mo-Y_(2)O_(3) alloys(HV0.2(370±25)).This work could provide a relevant strategy for the preparation of ultrafine Mo alloys by facile ball-milling.

Effect of LiF on Densification and Mechanical Properties of Dy-α-Sialon Ceramics

The effect of LiF on the densification and mechanical properties of hot-pressed Dy-a-sialon ceramics was studied. Comparatively, without LiF as sintering additive, the pure Dy-a-sialon ceramic should be sintered at 1750℃. When LiF is used, the sintering temperature of the Dy-a-sialon is greatly lowered to 1500 ~ 1650℃. Obviously, the addition of LiF has a strong effect on the improvement in densification. Meanwhile, the resultant Dy-a-sialon has no significant changes in the mechanical properties.

Research on Diamond Enhanced Tungsten Carbide Composite Button

At the present, the cutters used in button bits and rock bits are mainly cobalt tungsten carbide in our country. Because of its low abrasive resistance, the bit service life and drilling efficiency was very low when the hard and extremely hard formations were being drilled. Owing to its high abrasive resistance, the diamond composite material is widely used in drilling operations. However, its toughness against impact is too low to be used in percussion drilling, only can it be used in rotary drilling. In order to solve the problems encountered by DTH hammer in hard rock drilling, make bit life longer, increase rate of penetration and decrease drilling cost, a new type diamond enhanced tungsten carbide composite button with high abrasive resistance and high toughness against impact, which may be used in percussion drilling, has been developed. The key problems to make the button are to improve the thermal stability of diamond, to increase the welding strength between diamond and cemented tungsten carbide, and to lower the sintering temperature of tungsten carbide. All these problems have been solved effectively by pretreatment of diamond, low temperature activation hot-press sintering and high sintering pressure. (1) To plate tungsten on the surface of diamond. Diamond suffers easily from erosion in the environment of high temperature containing oxygen and iron family elements. There is very high energy between the interface of diamond and bonding metal and so the metallurgical bond can’t form at the interface between diamond and bond metal. This will lower greatly the bending strength and the toughness against impact of diamond enhanced tungsten carbide composite button. In order to improve thermal stability of diamond and increase the bonding strength of the interface between diamond and bond metal, to plate tungsten on the surface of diamond by vacuum vapor deposit is adopted. (2) To lower the sintering temperature by adding nickel, phosphorus and boron etc into conventional mixed powder. In general, the sintering temperature of cemented tungsten carbide is more than 1 350 ℃ in which diamond will suffer from serious heat erosion, so the sintering temperature must be lowered. To add nickel, phosphorus and boron etc into cobalt-base bond whose melting point is more than 1 350 ℃ will lower the sintering temperature to about 1 050 ℃. To add phosphorus can lower the temperature of liquid phase occurring and promote the densification of matrix alloy in advance because the co-crystallization temperature of Ni-P and Co-P is 880 ℃ and 1 020 ℃ respectively. The proper adding amount of nickel, phosphorus and boron etc is a key problem. To substitute nickel for partial cobalt can improve the toughness against impact of diamond enhanced tungsten carbide composite button and lower the sintering temperature. To add boron is helpful for sintering and improving the toughness against impact of diamond enhanced tungsten carbide composite button. (3) To increase the sintering press. Under the same sintering temperature, to improve the sintering press can improve the density and strength of sintering products. In this study to increase the sintering press 35 MPa in the usual conditions to 50～60 MPa in sintering diamond enhanced tungsten carbide button by adopting ceramic material as pressing rod has improved the sintering quality effectively. The properties of the button have been measured under lab conditions. The testing results show that its hardness is more than HRA86 and that its abrasiveness resistance is 100 times more than conventional cemented tungsten carbide, and its toughness against impact is more than 100J. All these data theoretically show that the button has very good mechanical properties that can meet the need of percussion drilling, and can solve the problems encountered with button bit of conventional cemented tungsten carbide.

Crystal structure and enhanced microwave dielectric properties of the Ce_(2)[Zr_(1−x)(Al_(1/2)Ta_(1/2))_(x)]_(3)(MoO_(4))_(9) ceramics at microwave frequency

Dense microwave dielectric ceramics of Ce_(2)[Zr_(1−x)(Al_(1/2)Ta_(1/2))_(x)]_(3)(MoO_(4))_(9)(CZMAT) (x = 0.02–0.10) were prepared by the conventional solid-state route. The effects of (Al1/2Ta1/2)^(4+) on their microstructures, sintering behaviors, and microwave dielectric properties were systematically investigated. On the basis of the X-ray diffraction (XRD) results, all the samples were matched well with Pr_(2)Zr_(3)(MoO_(4))_(9) structures, which belonged to the space group R3¯c. The lattice parameters were obtained using the Rietveld refinement method. The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by using the Phillips—Van Vechten—Levine (P—V—L) theory. Excellent dielectric properties of Ce_(2)[Zr_(0.94)(Al_(1/2)Ta_(1/2))_(0.06)]_(3)(MoO_(4))_(9) with a relative permittivity (ε_(r)) of 10.46, quality factor (Q × f) of 83,796 GHz, and temperature coefficient of resonant frequency (τ_(f)) of −11.50 ppm/℃ were achieved at 850 ℃.

Sintered Ore Sprayed by Acid and Alkaline Waste Water Resulted From Cold Rolling

In order to prevent the powdering of a sintered ore from influencing the smooth operation of a blast furnace,the conventional way to deal with it is that the CaCl2 solution is prepared by tap water,and then the solution is sprayed onto the sintered ore for improving its RDI（low temperature reduction degradation index）.The CaCl2 solution prepared by adding acid and alkaline waste water resulted from cold rolling is sprayed onto the sintered ore to improve its RDI.The values of RDI＋6.3 and RDI＋3.15 of the sintered ore which is sprayed by the CaCl2 solution with the CaCl2 concentration of 3.5%（mass percent） are increased by 17.5% and 11.63%,but the index of RDI-0.5 is decreased by 3.1% when the spraying amount of the solution is making up 0.5% of the total sintered ore sprayed in comparison with those of the sintered ore which is not sprayed by using the CaCl2 solution.Experimental results show that after the CaCl2 solutions prepared by adding the acid and alkaline waste water are sprayed on the sintered ore,RDI of the ore can be remarkably improved and therefore another way for recycling acid and alkaline waste water can be available,by which both cost for treating waste water and cost for producing a sintered ore can be decreased and environment is free of pollution by harmful substances in the waste water.