Types Of Gypsum Research Articles

Effect of different forms of calcium sulfate on the properties of cement

Abstract In our conditions, mainly flue gas desulfurization gypsum (FGD gypsum) is used as a cement setting regulator. When cement is ground, it decomposes into hemihydrate or even anhydrite as the temperature rises. The ground cement is placed in a storage silo where the increased temperature is compounded by increased pressure and the cement properties are affected by the moisture released and by the change in the phase composition of the setting regulator. Under laboratory conditions, hemihydrate and anhydrite II and III were prepared from one type of FGD gypsum. Their purity was monitored by X-ray diffraction analysis and differential thermal analysis. The prepared calcium sulfates were used in different proportions as setting regulators in the laboratory preparation of Portland cements. Technological properties such as strength and solidification were then determined for cements. The hydration process was monitored by the calorimetric method.

Gypsum-Enhanced Red Mud Composites: A Study on Strength, Durability, and Leaching Characteristics

The strong alkalinity of red mud and the heavy metals it contains pose a serious threat to the environment. This study investigated the possibility of applying red mud as a solid waste material in road construction to mitigate the problem of red mud accumulation. Red mud was modified using titanium gypsum and phosphogypsum as curing agents. The effects of varying gypsum types and mixing ratios on the mechanical properties and heavy metal leaching of the resulting red mud-based materials were assessed using percussion tests, unconfined compressive strength measurements, scanning electron microscopy (SEM), and continuous heavy metal leaching tests. The results showed that the optimal moisture content for titanium gypsum–cement-stabilized red mud (RTC) exceeds that of phosphogypsum–cement-stabilized red mud (RPC), with RTC exhibiting a lower maximum dry density compared to RPC. When the gypsum admixture was within 10%, the strength of the RPC was higher than that of the RTC at the same and curing time. The reticulation in RPC-10 was denser. The cumulative heavy metal releases from both RTC and RPC were within the permissible limits for Class III groundwater discharge standards. Based on the comprehensive test results, RPC is identified as the superior modified red mud material, with an optimal mix ratio of red mud/phosphogypsum/cement of 87:5:8.

Isolation And Diagnosis Of Skin Fungi That Causes Tinea Capitis In The Children

One hundred clinical samples of hair and scalp flakes were collected for children with tinea capitis aged from 1 year to 12 years from the dermatology consultant affiliated with Tikrit Teaching Hospital and outpatient clinics, with the aim of isolating the pathogenic fungi that cause tinea capitis and diagnosing them in children. Out of the total, 77 samples were found in the laboratory culture, while the findings of the direct microscopic examination indicated the presence of 55 samples. Several dermatophyte species from the genera Trichophyton and Microsporum were identified. T. mentagrophytes was the most prevalent with 18 isolates (23%), followed by T. violaceum and T. rubrum, each with 12 isolates (15%). Next, there were 10 isolates of the fungus T. schoenleinii (13%), compared to 4 isolates (10%) of each of the two species of fungus, T. tonsurans and T. verrucosum. While fungi belonging to the genus Microsporum were isolated at a rate of 10 isolates (13%) of the type M. canis, while 7 isolates of the M. gypsum type were isolated (9%). The incidence of tinea capitis among was greater in men than in women., as the number of infected males was 62 (62%), and females were 38 (38%) infected out of the total number. Regarding age groupings, 20% of children between the ages of one and four have head ringworm. The infection rate for children aged 5-8 was 32%, and the highest risk of infection was for those aged 9-12, who were at risk for 48%. It was also found that the rate of infection with the fungi that cause tinea capitis in the children from whom the samples were taken was high among patients coming from rural areas, at 80%, compared to patients coming from urban areas, at 20%.

Comparison between Conventional and Digital Impressions for Determining Axes and Distances of Three Implants in Straight and Curved Lines: An In Vitro Study.

Background: In this study, we aimed to compare the effects of conventional and digital impressions on several parameters (inter-implant distance, intra-implant distance, inter-implant axis, and intra-implant axis) of three implants in curved lines and straight lines by using a laboratory scanner (LBS) versus an intra-oral scanner (IOS). Methods: Two 3D models were fabricated using a printer, each model with three internal hex implants analogues at the positions of 15#,16#,17# (straight line) and 12#,13#,14# (curved line). Standard intra-oral scan bodies (ISBs) were used, and the two models were scanned using 7 Series dental wings (LBS, reference model), followed by ten scans with Primescan (digital method). Standard Tessellation Language (STL) files were created. Five polyether impressions were taken from each model (straight and curved), and gypsum type 4 models were poured; each model was scanned five times to create a total of 25 STL files for each group (conventional method). The comparison between all the STL files (conventional and digital) was made by superimposition of the STL files on the STL reference model laboratory file using a 3D analyzing software. A Kolmogorov-Smirnov test was performed, followed by Mann-Whitney tests and Wilcoxon signed-rank tests. (p < 0.05). Results: For the conventional method, the mean errors were significantly higher for the curved line model (12-14) compared to the straight line model (15-17) for most parameters (p < 0.05). For the digital method, the mean errors were significantly higher for the curved-line model (12-14) compared to the straight line model (15-17) in half of the parameters (p < 0.05). Within the curved line model (12-14) and the straight line model (15-17), the mean errors between the conventional method and the digital method were not significant for most variables. Conclusions: The difference between curved lines and straight lines has an impact on the mean error of the conventional method. Both methods are reliable for straight and curved lines in partially dentate situations.

Damage Mechanics Challenge: Predictions based on the phase field fracture model

In this work, we describe our contribution to the Purdue-SANDIA-LLNL Damage Mechanics Challenge. The phase field fracture model is adopted to blindly estimate the failure characteristics of the challenge test, an unconventional three-point bending experiment on an additively manufactured rock resembling a type of gypsum. The model is formulated in a variationally consistent fashion, incorporating a volumetric–deviatoric strain energy decomposition, and the numerical implementation adopts a monolithic unconditionally stable solution scheme. Our focus is on providing an efficient and simple yet rigorous approach capable of delivering accurate predictions based solely on physical parameters. Model inputs are Young’s modulus E, Poisson’s ratio ν, toughness Gc and strength σc (as determined by the choice of phase field length scale ℓ). We show that a single mode I three-point bending test is sufficient to calibrate the model, and that the calibrated model can then reliably predict the force versus displacement responses, crack paths and surface crack morphologies of more intricate three-point bending experiments that are inherently mixed-mode. Importantly, our peak load, crack trajectory and crack surface morphology predictions for the challenge test, submitted before the experimental data was released, show a remarkable agreement with experiments. The characteristics of the challenge, and how changes in these can impact the predictive abilities of phase field fracture models, are also discussed.

Dominant species and functional complexes of phytoplankton in some unique karst lakes of the Middle Volga basin

The characteristics of the composition, ecological-geographical, and functional structure of the phytoplankton dominant complexes of three different types of lakes in the Nizhny Novgorod Volga region (Klyuchik, Svetloyar, and Svyatoye Dedovskoye) are given. Lake Klyuchik is a rare type of gypsum, highly mineralized “blue” lake; unique in terms of its supply source, the role of which is played by the underground river with high water consumption, and has a weakly expressed stratification. Lakes Svyatoye Dedovskoye and Svetloyar are dimixic, light-water, low-mineralized, of hydrocarbonate class, and with neutral pH values that are fed by rainwater. All lakes belong to specially protected natural areas. Analysis of the algal flora of the studied lakes showed the taxonomic significance of the divisions of Cyanobacteria, Chlorophyta, Bacillariophyta, Ochrophyta, and Euglenophyta, constituting more than 70% of the total species richness. The composition of the dominant species contained 114 taxa of algae (26.38% of the total composition): in Lake Svyatoye Dedovskoye, greens and diatoms predominated (50%), in Lake Svetloyar, euglenids predominated (25%), in Lake Klyuchik, diatoms predominated (more than 40%). Among 13 dominants (from 5 divisions) with high values of DF&gt;10, Dt&gt;10, and pF&gt;20, dinoflagellates from the functional group L0 (Ceratium hirundinella, Peridinium cinctum) were noted in all lakes, with maximum development in the summer stratification. In the group of diatoms, representatives of centric diatoms of codon B (species of the genus Cyclotella) predominated in each water body, reaching maximum development rates under conditions of water mixing. The composition of the remaining dominant groups in each reservoir was determined by its limnological features. Using the method of multivariate analysis of variance (PERMANOVA), a statistically significant (P-value=0,001) low degree of similarity of the dominant and functional phytoplankton complexes was shown, which may indicate the uniqueness of algae cenogenesis in each of the studied lakes due to the influence of a certain combination of factors.

Application of the Min-Max Stock Method in the Inventory Control of the Raw Materials for the Cement Production at PT XYZ

PT XYZ is the largest cement manufacturer in Indonesia that produces cement with different types of cement, namely OPC, PCC, and PPC. The implementation of its production process, starts with the mixing of raw materials, processing, and packaging to the finished product, namely cement. PT XYZ has a problem in the form of raw material inventory that has not been well controlled because the raw materials are often placed outside the storage area provided by the company due to overloading, thus taking up space that should not be used as a raw material storage area. In this study, the minimum-maximum method is applied to 4 types of raw materials, silica sand, gypsum, trass, and fly ash. By determining the amount of safety stock, minimum stock, maximum stock, reorder point and order quantity, companies can effectively determine the raw material inventory policy to avoid overstock or stockout. The study uses a 99% service level with a 1% risk of out-of-stock products. The results of the study obtained the safety stock value of silica sand 3,854 tons; gypsum 4,405 tons; trass 10,456 tons; and Fly Ash 511 tons. Then, the minimum inventory calculation is carried out, it is known that the minimum inventory results are in Fly ash raw material of 776 tons while the results for maximum inventory are in Trass of 34,613 tons. After the min-max calculation, the ordering policy for each material can be obtained, silica sand 5,255 tons, gypsum 9,111 tons, trass 22,534 tons, fly ash 776 tons.

Durability study and mechanism analysis of red mud-coal metakaolin geopolymer concrete under a sulfate environment

The durability of construction materials in sulfate environments is extremely important for their service life. Geopolymer concrete, as a new type of construction material, has been subjected to very little research in sulfate environments and lacks real-time nondestructive testing methods. For this reason, in this study, the physical and mechanical properties of geopolymer concrete synthesized from red mud and coal metakaolin were tested and compared with ordinary silicate cement concrete. The physical phase composition, micro-morphology, porosity and functional group composition of the red mud-coal metakaolin geopolymer concrete were further analyzed using XRD, SEM-EDS, FT-IR and NMR. In addition, the electrochemical properties of the geopolymer were tested by electrochemical impedance spectroscopy and correlated with the diffusion coefficient of the material. The results show that the stability and compressive strength of geopolymer concrete is significantly better than that of ordinary silicate cement concrete in sulfate environment. Ettringite and gypsum type expansion damage were present in ordinary silicate cement concrete. In contrast, only sodium sulfate crystals were found in geopolymer concrete and no expansion products were found. This nearly indicates that the inert interaction between sulfate and hydration products is the main reason for its superior sulfate resistance. There is a significant correlation between the diffusion coefficient of red mud-coal metakaolin polymer concrete and the electrochemical parameter RCP/t and RDCP/t. Therefore, electrochemical impedance spectroscopy testing can be used as a real-time, non-destructive means of monitoring the performance of geopolymer concrete in sulfate environments.

Influence of different types and contents of gypsum on mechanical properties and porosity of sulphate activated binder

Fly ash (FA) is pozzolanic, while blast furnace slag (GGBS) is latent hydraulic. These two materials react slowly in the presence of water to harden. Adding an alkali activator such as strong hydroxide could boost the hardening process, but the safe handling of highly corrosive materials is the primary concern. Therefore, the present work prescribed various types of gypsum to activate FA and GGBS as a binder phase for making mortar. It aimed to investigate the influence of different types and contents of gypsum on the mechanical properties and porosity of sulphate-activated binder. Gypsum is a less corrosive material to provide calcium and sulphate ions for activating GGBS and FA. The main component of gypsum was calcium sulphate. Gypsum provides calcium sources that promote more C-S-H to be formed. A few types of gypsum were studied with their effect on FA/GGBS blended mortar. Furthermore, the mechanical strength and porosity of gypsum-activated GGBS/FA blended mortar were assessed. The mortar containing white gypsum exhibited the best mechanical performance among all types of gypsum. On the other hand, red gypsum and dental gypsum were established to be more effective in pore refinements, lowering the mortar’s total porosity. In conclusion, white gypsum is the most suitable material for activating the FA/GGBS blend among the various types of gypsum examined.

Pendampingan Renovasi Plafond dan Pembuatan Tirai Pembatas Posyandu Mekar Kuntum Bau Semerbak Kelurahan Kampung Baru Kota Pekanbaru

&lt;p&gt;&lt;em&gt;Kampung Baru Village is one of the villages in Senapelan District, Pekanbaru City&lt;/em&gt;&lt;em&gt;. Has a Posyandu Mekar Kuntum Smell Fragrant. Posyandu functions are explained by partners for continuous monitoring of public health. Currently, posyandu still has simple facilities and infrastructure. To encourage people to feel comfortable when they are there, it is necessary to add facilities and infrastructure, namely by installing ceilings and dividing curtains.&lt;/em&gt; &lt;em&gt;The purpose of this community service is to assist partners in making planning designs and cost budget plans (RAB) for ceiling renovations and curtain installation. The method used is the counseling method. The output of this activity is a planning drawing and the type of ceiling and curtain used and the RAB for installing the ceiling and curtain. The installed ceiling is a type of gypsum with a volume of 45 m&lt;sup&gt;2&lt;/sup&gt;. For blinds that are installed made of soft and not transparent. Assisting with the installation of the posyandu ceiling and curtain.&lt;/em&gt;&lt;/p&gt;&lt;br /&gt;&lt;em&gt;&lt;/em&gt;

Accuracy of 2D numerical models towards the prediction of the fire resistance on LSF partition walls

Lightweight steel framing (LSF) walls are commonly used in modern buildings due to their high strength-to-weight ratio and readiness for installation. However, empty cavities within these walls can pose a fire risk if not properly addressed. In order to ensure the fire resistance and performance of LSF walls with empty cavities, various modelling techniques can be employed. Two-dimensional thermal models can also be used to simulate the behaviour of LSF walls with empty cavities in a fire scenario. These models can predict the spread of heat through the empty cavity, allowing designers to identify potential fire hazards and make adjustments to the design to mitigate those risks.Three different computational solution methods were used to compare the fire performance of LSF walls with void cavities. Solution method 1 considers the air-structure interaction in the cavity region. Solution method 2 considers the existence of interface elements for the radiation heat transfer in the cavity region allowing the cavity temperature prediction. Solution method 3 considers the convection and radiation in the cavity region with a prescribed cavity temperature from experiments (hybrid). Solution methods 1 and 3 give a small root mean square error (RMSE), when compared with solution method 2. Solution method 3 gives a better approximation because can capture the main fire events during the fire, such as the cracks and fall off. Based on the parametric study, a new proposal is presented to predict the fire resistance by insulation, depending on the gypsum type and thickness.

AN IN VITRO COMPARISON OF OVERALL FIT OF COBALT-CHROMIUM COPINGS CASTED CONVENTIONALLY FROM INLAY CASTING WAX, PATTERN RESIN &amp; 3D PRINTED RESIN EVALUATED BEFORE &amp; AFTER CERAMIC FIRING CYCLES

Aim: To compare the overall fit of cobalt-chromium copings casted conventionally from inlay casting wax, auto polymerizing pattern resin &amp; 3D printed resin evaluated before &amp; after ceramic firing cycles. Method: A stainless-steel master die assembly was fabricated which was used to fabricate the working models. 60 working dies (Group A Inlay Casting Wax n=20, Group B Pattern Resin n=20, Group C 3D Printed Resin n=20) simulating full crown preparations werestudied. The stainless-steel master die was duplicated using polyvinyl siloxane (PVS) elastomeric impression and poured in gypsum type IV die stone. Dieswere scanned using a digital scanner. 60 cobalt-chromium (Co-Cr) metal copings were fabricated using three different techniques: inlay casting wax, autopolymerising pattern resin&amp; 3D printed resin. Each die was fired with conventional PFM ceramic. A standardized weightwas used to exert uniform pressure on the elastomeric impression material while recording the intaglio surface of the crowns (copings) fabricated before and after ceramic firings. It was thenscanned aiding in STL File. The STL files were later overlapped and evaluated on their respective working die STL file using the software. The overall fit was measured by colour surface mapping software viz before &amp; after ceramic firing cycles. Results: The copings obtained by 3D printed resin technique revealed the best overall fit before and after ceramic firing cycles amongst the three fabrication techniques. Conclusion: 3D printed resin technique had the best overall fit before and after ceramic firing cycles followed by inlay casting wax technique and pattern resin technique.

The effect of sodium borate addition to dimentional stability in type 3 of gypsum

Background: The removable dentures or fixed dentures can be used as a replacement for missing teeth and restore the aesthetics and functional condition of the patien. Dentures with good adaptation can be obtained from accurate impressions. Dimensional accuracy and adequate mechanical properties are one of the main requirements of working model making materials. The addition of sodium borate can help gypsum type III achieve balance dimentional stability. The purpose of this study was to determine the difference in dimensional stability of gypsum type III with aquades with the addition of sodium borate and aquades without the addition of sodium borate.Method: Post test only control group design was used as the research design method. This study consisted of 2 groups with a total sample of 32 samples, experimental group with gypsum type III given distilled water with added sodium borate 0.4% and control group with gypsum type III given distilled water without added sodium borate 0.4%. The change of gypsum dimentional stability is measured using digital sliding caliper. Statistical tests were carried out using the Mann Whitney test and the results of the Mann Whitney test were P &lt; 0.05 which means a significant difference between the two groups. Result: The lowest average dimensional change was found in gypsum type III mixed with 0.4% sodium borate.Conclusion: The conclusion of the research is the addition of 0,4% sodium borate solution can help gypsum type III achieve balance dimentional stability.

Rheological and Strength Properties of Steel-Slag Cemented Paste Backfill: Link to Gypsum Type and Dosage

This paper aims to study the effects of gypsum type and dosage on the rheological and strength properties of steel-slag cemented paste backfill (SSB-CPB) using fluorogypsum (FG), phosphogypsum (PG), and desulfurization gypsum (DG). Experimental results indicate that the yield stress and the viscosity of fresh SSB-CPB are the smallest when using FG, followed by PG, and the highest when using DG. The strength of hardened SSB-CPB is the lowest when using PG, regardless of curing time, and is the highest when using DG after 3 and 7 days of curing or FG after 14 and 28 days of curing. With the increase of DG dosage, yield stress and viscosity of fresh CPB increase, while the strength of hardened CPB first increases and then decreases. For the rheological properties, the zeta potential changes the yield stress of fresh SSB-CPB, while the internal particle size and pH affect its viscosity. For the strength property, regardless of the effect of gypsum type or dosage, the changes in the results of microscopic experiments for hardened paste and SSB-CPB are critical indicators that the strength of SSB-CPB varies. When steel slag dosage is 35%, the best gypsum dosage is 24% and gypsum type is DG in the SSB for backfill. The findings of this study contribute to an enhanced understanding of the backfill binder material, which has beneficials of lower greenhouse gas emission, avoidance of natural raw materials excavation, saving environmental taxes, and reducing backfill costs.

Mechanical and thermophysical characterization of gypsum composites reinforced by different wastes for green building applications

This paper presents three types of gypsum reinforced with different waste materials, such as paper, polystyrene, and polyester. Several investigations were performed through a set of multiphysics tests, including mechanical (flexural and compression strengths), physical (density and water absorption coefficient), microscopic (SEM), thermophysical, and ultrasonic measurement techniques. The results revealed that the gypsum elaborated with the use of the three wastes generates a good balance for the optimization of mechanical and physical properties, with a good interaction between residues and the gypsum matrix. In comparison with the neat gypsum sample, the results show a clear increase in flexural strength (up to 5.75 MPa) and water absorption coefficient (up to 96%). The drop in density to 0.718 g/cm3 makes this new material both light and insulating, with a reduction of thermal conductivity and sound propagation velocity of 40.5% and 34%, respectively. This paper provides a solution to recycle waste materials and transform them into useful interior insulation materials for building applications.

Alteração dimensional linear de modelos edêntulos fabricados com silicones laboratoriais de alta densidade em diferentes tempos de armazenagem

ABSTRACT Objective: To evaluate the dimensional change of edentulous models made of high density laboratory silicones at different storagetimes. Methods: A metallic master model simulating an edentulous maxilla was used. The model had projections of 1.8 cm located in the regions of canines (A and B) and molars (C and D) allowing the linear measurement of distances AB, BC, CD, DA, AC and BD. A laboratory silicone mold was made for duplication of master model in the following materials (n = 10): G1: Zetalabor 85, G2: Titanium 95, G3: Platinum 95 and G4: Gypsum type III (control). The samples were photographed and measured using a software (Image J) at times T1 (baseline) and T2 (after one week of models fabrication). The data were statistically analyzed using Kruskal- Wallis and Dun non-parametric tests (α = 0.05). Results: The storage time influenced the behavior of the materials evaluated. All groups presented dimensional changes in both times and the group Tit95 presented the best results. Only Zet85 group showed a different behavior related to the region of the model. Conclusions: The high density laboratory silicones showed satisfactory results when compared to the gypsum group. Tit95 was the most stable material and it can be recommended as an edentulous model for total protheses.

Industrial Waste Management: Economical Benefits of the Resource Utilization of Phosphogypsum

There are many publications in the literature on the reuse of waste gypsum in material production. In this study, in which the analysis of these existing publications is made through the determinations, the data examined are limited to the article and these are not included. However, to understand the general framework of the research in this field better, a few of these in the related literature are given below as examples. It is seen that industrial waste gypsum, which is a type of waste gypsum, has been examined more. Phosphogypsum, which is included in this waste group, reduces the water requirement for adjusting the cement consistency by adding phosphogypsum in cement production. As a result of the addition of phosphogypsum in wall element production, it was determined that the addition of phosphogypsum caused a decrease in mechanical strength, a decrease in unit weight and an increase in water requirement. It has been concluded that the addition of 15% phosphogypsum in soil stabilization of phosphogypsum, which is in the chemical waste class, causes an increase in water demand and pressure strength. In addition, 5.4% gypsum board waste with recycling potential is generated in the production of building elements made with waste gypsum boards formed at a construction site.

Environmental risk assessment of industrial byproduct gypsum utilized for filling abandoned mines

In response to the basic policy of green and low-carbon circular development to solve resource, environmental and ecological problems, gypsum is considered to be a filling material for mine backfilling. To explore the potential risks of gypsum to the groundwater environment due to the backfilling of abandoned mines, a sequential batch leaching experiment was carried out in this paper, which used three types of industrial waste gypsum, namely, phosphorus gypsum (PG), titanium gypsum (TG) and flue gas desulfurization gypsum (FGDG). COMSOL Multiphysics 5.4 software was used to simulate and solve the migration process of the leached metal elements in the mine floor when these three gypsum types were used as filling materials to observe the concentration distributions and diffusion distances of the metal elements from these three gypsum types in the mine floor. The results show that (1) during repeated contact of the three types of industrial waste gypsum with the leaching medium, the pH levels changed, and the changes in pH affected the leaching patterns for the heavy metal elements in the gypsum. (2) Based on the concentrations of the metal elements that were leached from the three types of gypsum, it can be determined that these three types of gypsum are not classified as hazardous solid wastes, but they cannot be ruled out with regard to their risk to the groundwater environment when they are used as mine filling materials. (3) When the three types of gypsum are used as filling materials, the concentration distributions of the metal elements and their migration distances all exhibit significant changes over time. The concentration distributions, diffusion rates and migration distances of the metal elements from the different gypsum types are affected by their initial concentrations in the leachate. The maximum migration distances of Zn in the floor from the PG, FGDG and TG are 8.2, 8.1 and 7.5 m, respectively.

DIMENSIONAL ACCURACY OF DIGITAL IMPRESSION AND DOUBLE IMPRESSION MOLDING MODELS IN THE MANUFACTURING OF BRIDGE DENTAL

Dimensional accuracy of the impression model is very important in determining the success of denture treatment. The choice of printing technique is a factor that has a big influence on the printout. Digital impression and double impression techniques have good dimensional stability and provide accurate print details on the working model. The purpose of this study was to determine the level of dimensional accuracy of the digital impression and double impression models in the manufacture of bridge dentures. The research materials used were polyvinyl siloxanes elastomeric impression materials, stone gypsum type IV and aquades. The tools used are the master model, physiological printing spoon, glass stirrer, lekron, bowl spatula, calipers and 3D laser scanner. This research method used a laboratory experimental study design, and the master model was imprinted on the simulation of two abutments using digital impression and double impression techniques. The results showed that the digital impression technique showed a significant difference measured from the mesiodistal distance with the smallest value -0.004, the largest 0.011, the average difference 0.0369, at the occlusogingival distance the smallest value -0.003, the largest 0.009, the average difference 0.0375 , and the smallest value of interbutment distance is -0.001 and the largest is 0.000, and the average difference is -0.00031. The double impression technique showed a significant difference measured from the mesiodistal distance, the smallest value was -0.004, the largest was 0.011, the average difference was 0.00663, at the occlusogingival distance the smallest value was -0.014, the largest was 0.003, the average difference was 0.00300, and the interabutment distance was the smallest -0.001, the largest 0.003, and the average difference 0.00044. The conclusion of this study is that the digital impression technique is more accurate than the double impression technique in making denture bridges.

Study of Fabrication on Sponge Aluminum by Investment Casting

Sponge aluminum ranged from 10 to 40 PPI was fabricated by investment casting combined with vacuum infiltration, the effects of infiltration temperature, pressure and size of infiltration channel on the infiltration length were systematically studied theoretically and experimentally. The results show that the infiltration temperature difference has little effect on the infiltration length of aluminum foam with the same pore grades. With the increase of infiltration pressure and the decrease of infiltration channel size, the infiltration length increases. By increasing the infiltration pressure to 2 MPa and the infiltration temperature to 700 °C, aluminum sponge with high pore grades can be prepared. Under the same infiltration channel, the porosity of aluminum foam is the same. At this point, the applied infiltration pressure increases and the infiltration length increases. In order to ensure that the infiltration length of sponge aluminum with large pore grades is the same as that of sponge aluminum with small pore grades, the infiltration pressure should be increased. When the size of the infiltration channel, namely the pore grades, remains unchanged, and the infiltration temperature of the metal fluid is increased, the infiltration length will increase. However, it is necessary to consider the gypsum temperature. If the infiltration temperature is too high, the gypsum temperature will be too high, resulting in cracks in the gypsum type and defects in the sponge aluminum. When preparing sponge aluminum with high pore grades, it is necessary to raise the infiltration temperature of the metal liquid in order to obtain the same infiltration length.