Effect of graphite powder absorbing agent on gypsum plaster properties
Objective With the increasing use of radio,television,mobile phones,computers,artificial intelligence,and 5G technology,our lives have become more convenient,but it has also inevitably resulted in indoor electromagnetic radiation pollution.The increase in electromagnetic density has changed our indoor electromagnetic environment,potentially leading to serious electro-magnetic interference,damage to buildings,harm to electrical equipment,and even health risks posed to humans.Therefore,it is necessary to develop building materials to reduce electromagnetic radiation and improve indoor electromagnetic environment.Generally,electromagnetic shielding and absorbing materials are used.Shielding materials only reflect electromagnetic waves without weakening or eliminate them,while electromagnetic wave-absorbing materials convert the energy from electromagnetic waves into other forms such as heat during internal transmission,thereby attenuating the waves and improving building safety.For civil constructions,the requirements for effective electromagnetic wave-absorbing materials should be inexpensive and easy for construction.Graphite,abundant in nature,inexpensive,and exhibiting good electrical and thermal properties,emerges as the main candidate as a wave absorbing agent in construction.Plaster,which is neither load-bearing like concrete nor decorative like architectural paint,is particularly well-suited as a substrate due to its thick application,large surface area coverage,and ease of construction.Methods To prepare cost-effective wave-absorbing materials for civil buildings,different types of graphite powders,including natural flake graphite,graphite microchips,and homemade expanded crushed graphite,were mixed into gypsum plaster.Their effects on physical properties,strength,and wave absorption were compared.The structure of the graphite-gypsum plaster com-posites was characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),and vector network analysis.Results and Discussion XRD analysis showed that the characteristic diffraction peaks of the graphite powder were at 26.5°and 54.7°,corresponding to the(002)and(004)crystal planes,respectively,but with variations in peak strengths and widths.Natural flake graphite exhibited strong and sharp diffraction peaks,indicating large grain size and complete crystallization.SEM images confirmed its morphology of thick flakes around 100 um in size,made up of closely stacked layers resembling fish scales.XDR patterns of graphite microchips showed irregular,thin,curled,and fragmented particles with weak,broad diffraction peaks,indicating incomplete crystallization.Expanded crushed graphite,consisting of granular particles with fragmented lamel-lae,demonstrated intermediate properties between the other two types of graphite.Incorporating graphite powder increased the standard water consumption for gypsum plaster diffusivity.However,the extent of the increase varied depending on the type of graphite powder used.The difference was caused by variations in the specific surface area,particle size,and morphology.Also,their hydrophilicity differences caused by the varying number of surface oxides on the particles contributed to this varia-tion.Natural flake graphite,with its large grain size and compact structure,showed a slow increase in water consumption,while expanded crushed graphite,with smaller particles and a loose lamellae structure,showed a rapid increase due to higher specific surface area and surface oxides after chemical treatment and physical expansion.Graphite powder also accelerated the setting time of gypsum plaster,shortening both the initial and final setting times,which would be disadvantageous for mortar construc-tion.To mitigate this,a retarder must be added to extend the setting time to meet the required standards.For instance,gypsum plaster mixed with 8％expanded crushed graphite powder had an initial setting time of only 20 minutes.However,after adding 0.1％wt citrate retarder,the initial setting time was extended to 115 minutes,and the final setting time to 240.5 minutes,meet-ing the GB/T 28627-2023 standards.The addition of graphite powder reduced the bulk density of gypsum plaster.When 10wt.％natural flake graphite,10％microchips with particle sizes of 30-50 μm,or 5％expanded crushed graphite was added,the bulk density of the gypsum plaster fell below 1 000 kg/m3,meeting the density requirements for lightweight base-layer gyp-sum plaster.Expanded crushed graphite demonstrated advantages as a lightweight filler due to its loose graphite lamella struc-ture and low grain density,which was a result the high-temperature expansion.However,the addition of graphite powder nega-tively impacted the mechanical properties of the gypsum plaster.The reduction in strength was attributed to increased porosity from higher water consumption and the poor bonding between graphite particles and calcium sulfate crystals.When less than 5wt.％natural flake graphite or graphite microchips was added,the resulting gypsum plasterboards met the GB/T 28627-2023 standards for heavyweight based-layer gypsum plaster,with flexural strengths above 2 MPa and compressive strengths above 4 MPa.When 5wt.％expanded crushed graphite was added,the resulting gypsum plasterboards almost reached the GB/T 28627-2023 standards for lightweight gypsum plaster with more than 2.5 MPa in compressive strengths and more than 1 MPa in flexural strengths,but not yet.It iwas a good attempt to strengthen the mechanical properties of the expanded crushed graphite/plaster by the wire mesh.Graphite powder significantly improved the wave-absorbing properties of gypsum plasterboards.Compared to natural flake graphite and graphite microchips,adding 8％expanded crushed graphite to the plaster yielded the best wave-absorbing performance,achieving a bandwidth of 10.8 GHz with Rt＜-5 dB in 2-18 GHz frequency range,with at least 68.38％of electromagnetic waves absorbed.Conclusion Homemade expanded crushed graphite powder is the most suitable,cost-effective wave absorber among the studied graphite powder for civil construction materials.
万方数据
维普
