143 results about "Relative density" patented technology

The invention discloses a preparation method of low-temperature rapid densification silicon nitride ceramic based on an aluminum oxide-yttrium oxide composite sintering aid, and aims to solve the problems of high temperature, high energy consumption, difficult densification and the like in the existing Si3N4 ceramic preparation. The preparation method comprises the following steps: 1, mixing alpha-Si3N4 powder, Y2O3 powder and Al2O3 powder, and carrying out ball milling dispersion to obtain mixed powder; 2, carrying out rotary evaporation drying on the mixed powder under a vacuum condition; 3, carrying out heat preservation treatment under the conditions of 1600-1700 DEG C and 40-60 MPa through a spark plasma sintering process; and 4, demolding after cooling. Under the action of the Al2O3-Y2O3 composite sintering aid, phase transformation from alpha-Si3N4 to beta-Si3N4 is remarkably promoted, the relative density of the ceramic reaches 97%-99%, the fracture toughness of the ceramic is 5.21 MPa.m < 1 / 2 >, and the bending strength of the ceramic is 924.99 MPa.

The invention provides a method for preparing a high-performance silicon nitride ceramic ball based on a pressure modulation sintering technology, and relates to the field of functional ceramic material preparation, and the method comprises the following steps: 1, preparing a green body; 2, PMS sintering is carried out; step 3, cooling; traditional high-performance silicon nitride ceramic balls (the relative density is required to be larger than 99%, the Vickers hardness is required to be larger than or equal to 1500 kgf / mm, the bending strength is required to be larger than or equal to 920 MPa, and the fracture toughness is required to be larger than or equal to 6.0 MPa.m / ) are mainly prepared through a two-step process of normal pressure / air pressure sintering (GPS) and hot isostatic pressing (HIP). Although high densification of the material can be realized, the method has the problems of complicated process flow, high energy consumption, long production period, high equipment occupancy rate and the like.

The present disclosure addresses the problem of providing: a high-density V2O3 sintered compact; a method for producing a high-density V2O3 sintered compact; and a high-density V2O3 sputtering target. The V2O3 sintered compact has a relative density of 95% or more. The method for producing a V2O3 sintered compact comprises subjecting a V2O3 powder to hot press sintering at 1350-1450°C under vacuum or in an inert atmosphere gas.

The invention belongs to the technical field of refractory materials. The invention provides a graphene ceramic composite material and a preparation method and application thereof, the preparation method comprises the following steps: adding zirconium boride particles, silicon carbide particles, yttrium oxide and lanthanum-doped cerium oxide into a graphene oxide dispersion liquid, and carrying out ball milling and drying to obtain raw material powder; the raw material powder is put into a graphite mold to be sintered, and the graphene ceramic composite material is obtained. The raw material powder is prepared from the following components in parts by volume: 5.6 to 6 parts of graphene oxide, 70 to 72 parts of zirconium boride particles, 20 to 21 parts of silicon carbide particles, 1.5 to 2 parts of yttrium oxide and 1 to 1.3 parts of lanthanum-doped cerium oxide. By increasing the content of graphene oxide, the bending strength of the composite material is further improved while the relative density of the prepared composite material is increased.

The invention discloses a preparation method of a high-strength and high-toughness 17-4ph material. The preparation method comprises the steps of powder treatment, mixing, injection molding, degreasing, sintering and heat treatment. The preparation method comprises the following steps: pretreating fine powder in nitrogen to obtain nitrogen-containing fine powder, mixing the nitrogen-containing fine powder with coarse powder, then carrying out mixing, injection molding and degreasing, and finally carrying out high-temperature sintering and solid solution aging treatment in a nitrogen atmosphere. The prepared 17-4ph material has the excellent comprehensive performance that the relative density is larger than or equal to 97%, the hardness is larger than or equal to 40 Hrc, the tensile strength is larger than or equal to 1200 MPa, the yield strength is larger than or equal to 1000 MPa, and the ductility is larger than or equal to 20%, and the 17-4ph material is suitable for being applied to high-end medical instruments such as surgical robots.

The application discloses a carburized nanoscale yttrium oxide shell and a preparation method thereof. The preparation method comprises the following steps: preparing a nanoscale yttrium oxide shell embryo by using a grouting method; and placing the shell embryo after high-temperature sintering in a vacuum induction melting furnace filled with high-concentration active carbon to perform carburization treatment. The nanoscale yttrium oxide shell treated by using the carburization technology has excellent high-temperature resistance and chemical inertness, can reduce the pollution of yttrium oxide particles to a TiAl alloy melt, hinder the occurrence of a TiAl alloy melt-shell interface reaction, and make the surface of the TiAl alloy after melting more smooth, so that columnar grains on the surface of an alloy ingot can be clearly observed. Moreover, the shell has high bending strength and Vickers hardness, and the relative density is increased, so that the problem of the cracking of the yttrium oxide shell after the melting of the TiAl alloy is solved. The bending strength of the yttrium oxide shell prepared by the application can reach 24.3 MPa, and the Vickers hardness can reach 152 HV.

This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a TEOS-coated silicon nitride ceramic powder, its preparation method, and its application. The TEOS-coated silicon nitride ceramic powder comprises a core layer and a coating layer; the core layer comprises silicon nitride; the coating layer is mainly prepared from tetraethoxysilane; based on the mass of SiO2, the mass of the coating layer is 0.5–15 wt% of the mass of the core layer. The TEOS-coated silicon nitride ceramic powder prepared by this invention can achieve a better refractive index match with photosensitive resin and a more uniform interface in photocurable ceramic forming processes, reducing light scattering and absorption unevenness problems, and significantly increasing the curing depth under the same exposure conditions. When used as a sintering aid, the TEOS-coated silicon nitride ceramic powder prepared by this invention can lower the densification temperature of silicon nitride ceramics while improving relative density and mechanical properties.

This application provides a filler for an encapsulation material and its preparation method, a magnetic molding compound, and an encapsulation device. The filler for the encapsulation material includes ferrite particles, wherein the ferrite particles include nickel-copper-zinc ferrite (Ni... a Zn b Cu c Fe d The O4 material has the following properties: a ranges from 0.3 to 0.55, b ranges from 0.45 to 0.55, c ranges from 0 to 0.2, and d ranges from 1.8 to 2. The ferrite particles have a particle size of 2-11 μm, accounting for 50-70% of the total. This filler has advantages such as low relative density, wide absorption bandwidth, and good high and low temperature performance, thereby reducing the overall weight of the packaged device and improving its electromagnetic interference resistance and applicable temperature range.

The invention discloses a preparation method of a nitrogen-reinforced high-hardness corrosion-resistant 17-4ph material. The preparation method comprises the steps of mixing, injection molding, degreasing, nitrogen sintering and heat treatment. Through in-situ nitrogen solid solution strengthening, a strengthened martensite matrix structure is obtained. The relative density of the obtained material is larger than or equal to 97%, the Hrc hardness is larger than or equal to 46, the tensile strength is larger than or equal to 1500 MPa, the yield strength is larger than or equal to 1200 MPa, the ductility is larger than or equal to 5%, the neutral salt spray test corrosion resistance time is larger than or equal to 48 h, and the material is suitable for surgical robots and other high-end medical instruments.

The invention relates to a lattice structure performance characterization and optimization design method based on laser powder bed melting, and belongs to the technical field of additive manufacturing and structural design. The method aims at improving the mechanical property of a traditional BCC lattice structure under complex loads. The equivalent Young modulus of the lattice structure can be effectively represented by providing a lattice performance characterization method based on large unit cell hypothesis and establishing an analytic relationship between the equivalent Young modulus and the relative density of the lattice. In addition, topological optimization design of the BCC dot matrix is carried out by adopting an SIMP method, and redundant struts are removed and the structural shape is optimized by taking maximization of the equivalent Young modulus of the dot matrix as an optimization target. Finally, compared with a traditional BCC dot matrix, the T-BCC dot matrix structure manufactured through the LPBF process shows higher rigidity and strength. According to the optimization design method, the compression resistance of the lattice structure can be improved on the premise that the light weight of the lattice structure is kept, and the method has wide application prospects in the field of high-end equipment such as aerospace and automobiles.

The invention discloses a rare earth AB2 type hydrogen storage alloy and a preparation method thereof, and relates to the field of hydrogen storage alloys, and the rare earth AB2 type hydrogen storage alloy comprises the following components in percentage by mass: 50% of titanium, 45% of manganese, 2.5-3.5% of lanthanum and 1.5-2.5% of cerium. By adjusting the adding proportion of rare earth elements, the lattice stress of the alloy is optimized, the hydrogen storage performance is improved, and the raw material cost is reduced; a proper amount of additive is added to improve the performance of the alloy; in the preparation process, the processes of crushing and ball-milling after raw material sintering are added, the alloy particle granularity is refined, the hardness and relative density of the alloy are improved, and the service life is prolonged.

This invention discloses a method for simulating and testing ceramic sintering stress and a method for reducing ceramic sintering stress. The simulation and testing method includes: 1. Measuring the grain size, relative density, and geometric dimensions before and after sintering; 2. Using Abaqus to establish the ceramic geometry and construct a transient heat conduction model; 3. Establishing the viscoelastic constitutive equation for the sintering shrinkage deformation of zirconia ceramics and constructing a sintering shrinkage model; 4. Sequentially coupling the transient heat conduction model and the sintering shrinkage model to perform joint simulation of solid-state sintering, obtaining the simulation results of ceramic sintering stress. The method for reducing ceramic sintering stress includes: 5. Establishing a finite element model of ceramic sintering shrinkage with proportionally distributed grain sizes and calculating the average sintering stress distribution of the grain size proportional distribution model; 6. Comparing the average sintering stress of sintering shrinkage models with different grain size proportions to determine the method for reducing sintering stress. This invention improves ceramic sintering quality and production efficiency.

This invention discloses a two-step oscillating hot-pressing sintering method for WC-Co cemented carbide. Specifically, the method involves: loading WC-Co cemented carbide mixed powder into a mold and pre-pressing it; firstly, holding the powder at 800°C in a vacuum environment to degas and pre-sinter the billet; then applying unidirectional oscillating pressure to the billet through the mold and raising the temperature to 1100°C for solid-state sintering. Dynamic pressure causes WC particles to rearrange, and Co particles undergo severe plastic deformation under the pressure of the WC particles, further increasing the relative density of the billet; finally, the temperature is raised to 1300-1350°C to form a WC-Co eutectic liquid phase. Dynamic pressure drives further particle rearrangement, and the eutectic liquid phase uniformly fills the gaps between WC particles, completing the sintering process. This invention improves the three-dimensional spatial distribution uniformity of the Co phase, eliminates residual porosity, effectively inhibits abnormal growth of WC grains, and produces cemented carbide with excellent strength and toughness.

The application relates to a preparation method of a low-oxygen heterogeneous structure tungsten-based composite material, and relates to the technical field of tungsten-based composite material preparation. W powder, Ti powder, TiB2 powder and WC hard alloy balls are loaded into a ball mill tank for ball milling; then a two-step sintering method is adopted to prepare W-Ti-TiB2 tungsten-based composite material with high hardness and low oxygen content. The relative density of the prepared W-Ti-TiB2 tungsten-based composite material reaches 92.0% or more, and the microhardness value is 425-530 HV, which is superior to that of pure tungsten material (microhardness 360-420 HV). The oxygen content (20-80 ppm) of the prepared new heterogeneous structure W-Ti-TiB2 tungsten-based composite material is lower than that of pure tungsten (70-180 ppm) prepared by the same process and W-Ti-TiB2 tungsten-based composite material (150-380 ppm) prepared by the same process but with different powder loading sequences.

The invention belongs to the technical field of ceramic material preparation, and discloses a ceramic material sintering process optimization method and system based on a grain growth dynamic model, and the method comprises the following steps: quantitatively describing a deformation mechanism of a ceramic material in a sintering process based on continuum mechanics; constructing a grain growth kinetic model according to the quantitatively described deformation mechanism of the ceramic material and the grain size estimation model at the final stage of sintering; determining grain growth parameters in the final stage of sintering, and predicting the grain size by using a grain growth kinetic model; calculating the relationship between the grain size and the relative density and the sintering temperature, and verifying the calculation result of the grain growth kinetic model according to the experimental result of the grain size and the relative density; the change from low temperature to high temperature behavior is simulated through a Sigmodal function, the slope (derivative) of the function is calculated, and the temperature transition point of grain growth is obtained. And the temperature transition point of the grain boundary mobility from high to low can be accurately determined.

The invention discloses a method for preparing silver-tungsten-nickel graphite through an infiltration method. The preparation method specifically comprises the steps that S1, raw materials are prepared and mixed, and mixed raw material powder and nickel graphite powder are mixed; s2, the mixed powder is subjected to pressing, dewaxing sintering and sintering infiltration, and a product is formed; s3, cleaning and drying the product; the nickel is added into the silver-tungsten graphite, the silver-tungsten-nickel graphite powder raw material is mixed and granulated, and dewaxing, sintering and infiltration are performed in the protective atmosphere, so that the wettability problem of liquid silver and solid substances at the infiltration temperature, particularly the wettability problem of silver and graphite, is solved, and the sintering and infiltration can be smoothly completed; the relative density of the prepared AgWNi / C reaches 97% or above, the electric conductivity IACS% can be improved by about 5%-40%, the tensile strength is improved by 80 Mpa-300 Mpa, and the use amount of AgW / C electric contact silver is reduced by 5%-50%.

This invention discloses a beryllium-titanium alloy microsphere for neutron multiplication materials and its preparation method, belonging to the field of beryllium-titanium alloy technology. The preparation method includes: Step S1, ball milling and mixing beryllium powder and titanium powder at a predetermined mass ratio, followed by a first dry particle composite process to obtain beryllium-titanium spherical powder. Step S2, adding a polyvinyl alcohol binder to the beryllium-titanium spherical powder, followed by a second dry particle composite process to obtain beryllium-titanium granulated powder. Step S3, filling the beryllium-titanium granulated powder into multiple flexible spherical molds, then placing the multiple flexible spherical molds into a sleeve and performing cold isostatic pressing to obtain beryllium-titanium powder blank microspheres. Step S4, degreasing the beryllium-titanium powder blank microspheres under inert gas protection. Step S5, sintering the degreased beryllium-titanium powder blank microspheres to obtain beryllium-titanium alloy microspheres with a diameter of not less than 5 mm and a relative density ≥ 98%.

The invention relates to the technical field of powder metallurgy, and discloses metal powder vacuum hot pressing sintering forming equipment which comprises a relative density processing module, a feedforward prediction evaluation module, a state feedback evaluation module, a signal credibility evaluation module and a dwell pressure regulation and control module. The relative density, the sintering temperature, the upper pressure head displacement, the mold-powder system temperature difference, the vacuum degree and the hydraulic system oil temperature are monitored in real time, the densification driving force index, the relative density index, the pressure trend factor, the system rigidity factor and the signal credibility are calculated respectively, and the target dwell pressure is dynamically adjusted based on the densification driving force index, the relative density index, the pressure trend factor, the system rigidity factor and the signal credibility. According to the equipment, self-adaptive adjustment of pressure maintaining pressure in the sintering process is achieved, the problems of traditional control lag and pressure fluctuation are effectively solved, and the product density and quality consistency are improved.

The present invention provides zirconia media, zirconia bearing balls, and methods for manufacturing the same, with improved wear resistance and durability. [Solution] (a) Made of a sintered body of ZrO2-Y2O3 zirconia, with a Y2O3 / ZrO2 molar ratio in the range of 2.5 / 97.5 to 3.2 / 96.8, (b) Al2O3 content in the range of 0.1% by mass to 30.0% by mass, (c) Contains 90% by volume or more of tetragonal zirconia, (d) Relative density of 95% or more, (e) Average crystal grain size in the range of 0.25 μm to 0.50 μm, (f) Minimum crushing load value Pmin(N) > 600 × D 2.0 (D is the average media diameter), (g) the Weibull coefficient of the crushing load is 10 or greater, and (h) the coefficient of variation of the media diameter is less than 6%. This is a zirconia-based media.

The invention discloses an IWCO composite target material and a preparation method thereof, and belongs to the technical field of transparent conductive oxide target materials. The method comprises the following steps: providing In2O3 powder, WO3 powder and CeO2 powder according to an atomic ratio of In: W: Ce of 1: (0.03-0.07): (0.02-0.04); carrying out plasma activation treatment on the WO3 and CeO2 powder to obtain active composite powder; dissolving In2O3, mixing with the active composite powder, generating a ternary coprecipitate through a coprecipitation reaction, washing, drying, calcining and converting into IWCO precursor powder, and grinding and granulating to obtain IWCO particles; carrying out gradient pressure forming to obtain a biscuit; and finally, the IWCO composite target material is prepared through a step-by-step sintering process including air degreasing, inert atmosphere presintering, reducing atmosphere hot-pressing densification sintering and air annealing. According to the method, Ce element atomic-level uniform solid solution is achieved through activation, coprecipitation and calcination, and the segregation degree is smaller than or equal to 0.4 at%; the sintering temperature is reduced by 120-180 DEG C in combination with step-by-step sintering, and the W volatilization rate is smaller than or equal to 0.7 The relative density of the obtained target material is greater than or equal to 99.2%, the resistivity is less than or equal to 1.9 * 10 <-4 > omega.cm, and the target material is suitable for photoelectric devices such as HJT solar cells and flexible OLEDs.

A method for producing a dense perovskite ceramic shaped body containing an alkaline earth metal element, at least one element selected from Ti, Zr and Hf, and oxygen, and having a relative density of 60% or more, the method comprising a contact reaction step in which a precursor shaped body containing a gel containing at least one oxide selected from Ti, Zr and Hf and water alone, and a liquid containing a hydroxide of an alkaline earth metal element are brought into contact. The obtained shaped body is a collection of crystal domains (2) of a perovskite ceramic crystal (1), the crystal domains (2) being connected to each other.

To provide a copper alloy powder for additive manufacturing capable of obtaining an additive manufactured article having excellent conductivity and high relative density.MEANS: A copper alloy powder for additive manufacturing, comprising Cr, the balance being Cu and inevitable impurities, wherein A f represents an X-ray absorption spectrum derived from Cr having a face-centered cubic structure in a spectrum obtained by X-ray absorption near edge structure (XANES) analysis of the copper alloy powder, and A b represents an X-ray absorption spectrum derived from Cr having a body-centered cubic structure in the XANES analysis of the copper alloy powder, wherein A b and A f are obtained by decomposing the obtained spectrum into a linear combination of an X-ray absorption spectrum derived from Cr2O3, an X-ray absorption spectrum derived from Cr having a face-centered cubic structure, and an X-ray absorption spectrum derived from Cr having a body-centered cubic structure based on a spectrum of a standard sample. In the copper alloy powder for additive manufacturing, the ratio R is 0.1 to 10.SELECTED DRAWING: None

The present application relates to the technical field of target material manufacturing, and in particular to a ruthenium target material and a preparation method thereof. The method comprises: high-pressure cold die forming of ruthenium powder to obtain a ruthenium blank; placing the ruthenium blank in a metal sheath made of stainless steel or low-carbon steel, high-temperature vacuum pumping and exhaust, and welding to obtain a metal sheath containing the ruthenium blank; two-stage hot isostatic pressing sintering of the metal sheath containing the ruthenium blank; the pressure of the first-stage sintering is 130-150 MPa, and the temperature is greater than or equal to 1000 DEG C; the pressure of the second-stage sintering is 160-180 MPa, and the temperature of the second-stage sintering is higher than the temperature of the first-stage sintering by more than 150 DEG C. The ruthenium target material prepared by the present application has an average grain size of less than 5 mu m, a relative density of more than 99.5%, and the ruthenium target material and the metal sheath skin are easy to separate and not to adhere, and the target material yield is more than 98%, thereby reducing the manufacturing cost of the noble metal ruthenium target material and meeting the application requirements of advanced process integrated circuit chips.

The present application belongs to the technical field of engineering structure optimization design, and discloses a kind of topological optimization method and equipment of three-dimensional curved surface composite material thin shell structure, steps are as follows: S1, using conformal geometric mapping algorithm three-dimensional curved surface grid is mapped to the parameterization coordinate of two-dimensional plane parameter domain angle-preserving, obtain the mapping relationship of three-dimensional curved surface composite material thin shell structure from three-dimensional curved surface to two-dimensional plane;S2, construct shell element stiffness matrix of finite element grid;S3, in two-dimensional plane parameter domain, with the relative density of shell element and the direction of element as design variable, establish the topological optimization model of finite element grid based on conformal mapping;S4, based on moving asymptote method and topological optimization model to update design variable;S5, based on the design variable and mapping relationship of updated inversion mapping back original three-dimensional curved surface, thus obtain the three-dimensional configuration of optimal material distribution of three-dimensional curved surface composite material thin shell structure.The present application improves optimization efficiency.

The present invention relates to an alpha alumina having a high purity, a high density and a low surface area and particularly, to a method to produce such an alpha alumina as well as to the use of the alpha alumina in sapphire production or the production of composite and ceramic bodies.

This invention discloses a zirconium boride dispersion-reinforced fine-grained tungsten sintered billet. The billet consists of a tungsten matrix and zirconium boride particles dispersed within the tungsten matrix, exhibiting a dual distribution state of intragranular and grain boundary dispersion. The average grain size of the tungsten matrix is ​​no greater than 40 μm, the average grain size of the zirconium boride particles is no greater than 2 μm, and the relative density of the sintered billet is no less than 94%. A semi-coherent metallurgical bonding transition layer with a thickness of no less than 1.5 nm is formed between the zirconium boride particles and the tungsten matrix. This invention also provides a method for preparing this sintered billet, which involves long-time wet ball milling, short-time dry ball milling, combined with cold isostatic pressing and pressureless sintering. The doped tungsten prepared by this invention achieves uniform dispersion of zirconium boride particles and grain refinement of the tungsten matrix. The process is controllable, the interfacial bonding is excellent, and the prepared sintered billet has a fine microstructure and uniform dispersion of the dispersed phase, overcoming the defects of uneven dispersion of the traditional tungsten reinforcing phase, coarsening of grains, and weak interfacial bonding.

A sintered body, a method of fabricating the sintered body, a semiconductor fabricating device, and a method of fabricating the semiconductor fabricating device, the sintered body including 50 mass % or more of Y5O4F7, wherein the sintered body has a relative density of 97.0% or more and a Vickers hardness of 2.4 GPa or more.

This sintered oxide contains an In element, a Ga element, and a Zn element, contains an In2Ga2ZnO7 crystal phase and a Ga2ZnO4 crystal phase, has a relative density of more than 100.0%, and has a Zr content of 100 ppm by mass or less.

The invention discloses small-particle-size low-oxygen ZrB-SiC complex-phase powder, a one-step controllable synthesis method thereof and application of the powder in high-performance ceramics, and belongs to the technical field of ultra-high-temperature ceramic materials. According to the method, ZrO, BC, elemental Si and activated carbon are used as raw materials, and the ZrB-SiC complex-phase powder is prepared through an optimized boron-carbon thermal reduction method. The core innovation point is that the specific raw material ratio design is as follows: n (ZrO): n (BC): n (Si): n (C) = 3: (1.65-1.95): (0.5-1.0): (4.95-6.05), the most preferable ratio is 3: 1.8: 1: 5.5, and heat preservation is performed for 60 minutes at 1500 DEG C in an inert atmosphere. The design effectively compensates volatilization of intermediate phase BO, and ensures complete reaction. The prepared multiphase powder has the prominent advantages of small particle size (D100lt, 0.71 [mu] m), low oxygen content, high purity and accurate regulation and control of the ratio of two phases, and ZrB and SiC two-phase interfaces in the powder are in semi-coherent combination. The high-performance ZrB-SiC composite ceramic can be prepared by using the self-made powder as a raw material and adopting spark plasma sintering (SPS), and the relative density of the high-performance ZrB-SiC composite ceramic is up to 99.24% or above.

The application relates to the technical field of target materials, and provides a CrCuAg alloy target material for antibacterial plating and a preparation method thereof, wherein the preparation method comprises the following steps: mixing Cr powder, Cu powder and Ag powder under the protection of inert gas to obtain mixed powder through mechanical ball milling; filling the mixed powder into a can, and the relative density of the filled can is greater than or equal to 55 %; performing vacuum thermal degassing on the filled can; performing hot isostatic pressing liquid phase sintering on the can after the vacuum thermal degassing is completed to obtain a CrCuAg alloy target material blank; and removing the can from the CrCuAg alloy target material blank to obtain the CrCuAg alloy target material. Through the synergistic design of the specific particle size grading and the hot isostatic pressing liquid phase sintering process, the densification problem caused by the large melting point difference of Cr, Cu and Ag is solved, the high-performance antibacterial alloy target material with a relative density greater than 99 % can be prepared, and the Cr substrate has high hardness and wear resistance and the Cu and Ag have the synergistic antibacterial function.