In this work an epitaxial layer of Indium Phosphide (InP) has been grown on top of a silicon substrate using the Corrugated Epitaxial Lateral Overgrowth (CELOG) technique. The grown InP CELOG top layer typically has a poor surface roughness and planarity. Before this surface can be used for any processing it has to be smooth and planarized. For this purpose a two-step Chemical Mechanical Polishing (CMP) technique has been investigated and developed. In the first step commercially available Chemlox has been used to planarize the sample. In the second step Citric Acid (CA) and sodium hypochlorite (NaClO) has been mixed together to form abrasive-free polishing slurry. The second step has been developed to remove defects introduced by the first step. This surface is prepared to demonstrate that a photonic device such as a quantum well can be realized in a Photonic Integrated Circuit (PIC). A quantum well was grown on the polished CELOG InP/Si sample and measured with Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Photoluminescence (PL). The roughness was improved with CMP from 33.2 nm to 12.4 nm. However the quantum well did not give any response in the PL measurements. / I detta arbete har ett epitaxiellt lager indiumfosfid (InP) blivit växt på ett kiselsubstrat med hjälp av en korrugerad epitaxial lateral överväxt (CELOG) teknik. Det översta lagret av den CELOG växta ytan har ofta en väldigt ojämn yta. Innan denna yta kan användas till någon fortsatt utveckling måste den vara slät och plan. Det översta lagret har polerats med hjälp av en två-stegs kemisk mekanisk polerings (CMP) teknik. I det första steget har komersiellt tillgänglig Chemlox använts för att planarisera ytan. I det andra steget har citronsyra (CA) och natrium hypoklorit (NaClO) blandats samman för att bilda ett partikelfritt polermedel. Det andra steget har tagits fram för att ta bort defekter introducerade I det första steget. Ytan är preparerad för att demonstrera att en fotonisk enhet, t.ex. en kvantbrunn kan realiseras I en fotonisk integrerad krets (PIC). En kvantbrunn växtes fram på det polerade CELOG InP/Si provet och mattes med hjälp av atomkraftsmikroskop (AFM), scanning electron mikroskopi (SEM), röntgendiffraktion (XRD) och fotoluminisens (PL). Ytojämnheten förbättrades med hjälp av CMP från 33.2 nm till 12.4 nm. Dock så gav ej kvantbrunnen någon respons I PL-mätningarna.

Bioplastic research has become more diverse and different types of research on bioplastic production have been conducted from fruits and vegetable waste, for example, orange waste. The wastes that come from oranges contain more than just vitamins, it has soluble sugars, starch, hemicellulose, cellulose, and pectin. The intention of this project was to study the possibility to produce bio-composite films from orange waste, after removing the soluble sugars. It was also to analyze the properties of the material by tensile strength, visual observation, and to find a methodology that suits this study. An ultrafine grinder was used to mechanically separate the cellulose fibres, with the intention to compare the fibrillation cycles on the properties of the bio-composite films. A total of 30fibrillation cycle was performed. In addition, different film casting strategies were performed and evaluated. The primary plan was to produce a biofilm without the use of chemicals. After the observing the results three new routes for the methodology was developed where the usage of chemicals was be included. The citric acid was used as a solvent for pectin and glycerol was used as a plasticizer. In the first method, different concentration of citric acid and glycerol were added and observed. The combination which gave uniformed films that contained 0.3 g of citric and 0.375 g of glycerol for a 75 ml hydrogel. The second method was to infuse citric acid before grinding the orange waste suspension. Lastly, the third method was to bleach the orange waste before grinding. The films that were produced gave interesting results and from the tensile testing implied that an impact was made on the strength by every fibrillation. The amount of glycerol was consistent throughout the project, but by adding different amount of citric acid gave the films differentIIproperties. The same happened when changing the mould of the film. The best values of the films were from the 30th fibrillation, gave the mean value of 31.6 MPa in tensile strength, and had a strain in elongation at 6.1 %. The tensile strength and elongation had increased drastically compared the fifth fibrillation which had 9.8 MPa and 7.6%.

[pt] A celulose é um biopolímero abundante, renovável e altamente biodegradável com produção no Brasil de aproximadamente 20 milhões de toneladas em 2017. A obtenção de nanocelulose a partir de diversas fontes e sua utilização em uma variedade de aplicações tem sido objeto de uma grande quantidade de pesquisas, visto suas propriedades diferenciadas e possibilidade de modificações, a partir de reações com outras substâncias orgânicas e inorgânicas. Entre as potenciais aplicações que a nanocelulose apresenta está o tratamento de água e efluentes, por processos como separação por membranas, troca iônica e adsorção. O principal processo de obtenção de nano cristais de celulose é a hidrólise ácida da região amorfa, restando em sua maior parte as regiões cristalinas. Os procedimentos mais aplicados para a produção de nano cristais de celulose consistem na reação de material celulósico puro com ácidos fortes com temperatura, agitação e tempo controlados. A nanocelulose cristalina (CNC) foi obtida através de hidrólise ácida com ácido sulfúrico (40 por cento) e então modificada com ácido cítrico (1,2M), CNC-Mod, para posterior caracterização e ensaio de adsorção de cátions metálicos. As amostras produzidas foram caracterizadas por técnicas como MEV-EDS, AFM, DRX, FTIR e TGA. Soluções de nitrato de cobalto (Co(NO3)2), cloreto de sódio (NaCl) e cloreto de mercúrio (HgCl2) foram colocadas em contato com amostras de celulose, CNC e CNC-Mod por um tempo máximo de 3h sendo o sólido e o sobrenadante separados. As amostras sólidas obtidas no processo de adsorção foram então submetidas a análises como DRX, MEV-EDS e TGA. Enquanto os sobrenadantes foram analisados por ICP-OES, os resultados indicam a ocorrência de adsorção para todas as amostras e cátions metálicos. / [en] Cellulose is an abundant, renewable and highly biodegradable biopolymer with production in Brazil of approximately 20 million tons in 2017. Obtaining nano-cellulose from different sources and using it in a variety of applications has been the subject of a great amount of research, given its differentiated properties and the possibility of modifications, based on reactions with other organic and inorganic substances. Among the potential applications that nanocellulose presents is the water and wastewater treatment, by processes such as membrane separation, ion exchange and adsorption. The main process for obtaining cellulose nanocrystals is the acid hydrolysis of the amorphous region, remaining more crystalline regions. The most applied production procedures for cellulose nanocrystals consist of the reaction of pure cellulosic material with strong acids with controlled temperature, stirring and time. The crystalline nano-cellulose (CNC) was obtained through acid hydrolysis with sulfuric acid (40 percent) and then modified with citric acid (1.2M), CNC-Mod, for further characterization and adsorption test of metal cations. The samples produced were characterized by techniques such as STEM-EDS, AFM, XRD, FTIR and TGA. Cobalt nitrate (Co(NO3)2), Sodium chloride (NaCl) and mercury chloride (HgCl2) solutions were placed in contact with cellulose, CNC and CNC-Mod samples for a maximum of 3 hours, then having the solid and supernatant separated. The solid samples obtained in the adsorption process were then subjected to analyzes such as XRD, STEM-EDS and TGA. While the supernatants were analyzed by ICP-OES and the results indicates the occurrence of adsorption for all samples and metallic cations.

Integrating ultrafiltration (UF) membranes in lieu of traditional media filters within conventional surface water coagulation-flocculation-sedimentation processes is growing in popularity. UF systems are able to produce low turbidity filtered water that meets newer drinking water standards. For typical drinking water applications, UF membranes require periodic chemically enhanced backwashes (CEBs) to maintain production; and citric acid is a common chemical used for this purpose. Problems may arise when the backwash recycle stream from a citric acid CEB is blended with raw water entering the coagulation basin, a common practice for conventional surface water plants. Citric acid is a chelating agent capable of forming complexes that interfere with alum or ferric chloride coagulation. Interference with coagulation negatively affects settled water quality. Acetic acid was investigated as a potential substitute for citric acid in CEB applications. A jar testing study was conducted to compare the impacts of both citric acid and acetic acid on the effectiveness of aluminum sulfate (alum) and ferric chloride coagulants. Citric acid was found to adversely affect coagulation at lower acid to coagulant (A/C) molar ratios than acetic acid, and a coagulation interference threshold was identified for both acids based on settled water turbidity goals recommended by the U.S. Environmental Protection Agency (EPA). Pilot testing was conducted to assess the viability of acetic acid as a UF CEB chemical. Acetic acid CEBs maintained pilot performance in combination with sodium hypochlorite CEBs for filtering a raw California surface water. It is believed that this is the first ultrafiltration membrane process application of acetic acid CEBs for municipal potable water production in the United States.

Continued increase in CO2 emissions has unquestionably led to rising global temperatures. To aid in themitigation of climate change new Negative Emission Technologies (NETs) have been proposed. CO2-sequestration by bio-enhanced silicate weathering is one such proposed NET that seeks to captureatmospheric CO2 by weathering silicate rocks. The research focuses on investigating whether the naturalprocess of weathering can be enhanced using biology. Previous studies have shown promising resultswhere microbes have increased the weathering rates of silicates.As such, this project aimed to investigate how the presence of citric acid affects the weathering rateof dunite. Furthermore, the study aimed to investigate how the process is affected by biological growth.The setup consisted of 50 g of dunite powder mixed with 1 M citric acid that was incubated for aboutthree months. Due to this extensive time-period, most of the analyses made were performed on anexperiment started in December of 2023. The following analyses consisted of Scanning ElectronMicroscopy (SEM) imaging, geochemical analyses such as pH, anions, organic carbon content, specificsurface area analyses (BET) and X-ray diffraction spectroscopy (XRD). The second part of this studyconsisted of starting up a new more extensive setup similar to the original one. Furthermore, the studyalso investigated the biological growth that could be seen on the original setup and how the weatheringrate was affected.The setup demonstrated a substantial increase in weathering rate in the presence of citric acid. Theanalyses also showed that the alkalinity had significantly increased during incubation, demonstratingthe method’s possible use in mitigating acidification as well as the CO2 emissions. Although the initialpH of the citric acid solution was low (pH 2), fungal growth became evident after a few weeks. Thisobservation holds promise for an efficient bio-enhanced silicate weathering experimental setup, as lowerpH levels are associated with an increased weathering rate. This report concludes that citric acid cansignificantly enhance silicate weathering, thus proving to be a promising NET to mitigate climatechange. However, earlier research has shown that weathering of olivine risks accumulation of heavymetals. As such, further studies are needed to fully understand how the combination of organic acid andmicrobes affect the weathering rate of dunite and other silicate minerals and the net accumulation ofheavy metals in leachate and cells. / Med de ökande koldioxidutsläppen ökar även de globala temperaturerna såväl som andraklimatförändringar. För att på ett snabbt men även rimligt sätt sänka CO2-utsläppen har så kalladeNegative Emission Technologies (NETs) lagts fram som en möjlig lösning. En sådan teknik ärkoldioxidinfångst med hjälp av accelererad silikatvittring, som bygger på att använda biologi för attpåskynda vittringsprocessen som naturligt tar upp CO2 från atmosfären. Tidigare studier har visat på attmikrober kan förbättra vittringen av silikater.Detta arbete hade som syfte att undersöka hur vittringen av dunitpulver påverkas av citronsyra.Utöver detta undersöktes även hur vittringen påverkas av mikrobiologisk tillväxt inom reaktorerna.Reaktorerna bestod av 50 g dunitpulver och 1 M citronsyra som fick inkuberas under ungefär tremånaders tid. På grund av denna tidsperiod utfördes majoriteten av analyserna på experiment somstartades i december 2023. Analyser som utfördes var bland annat svepelektronmikroskopering (SEM),geokemiska analyser såsom pH, anjoner, organiska syror, organiskt kol samt analys av specifik ytarea(BET) och röntgendiffraktion (XRD). Förutom analyser av det originella experimentet, startades ävenett nytt, utökat experiment liknande det första. En tredje del av denna studie bestod av att undersöka denbiologiska tillväxten inom reaktorerna och hur den har påverkat vittringen.Experimentet visade på en betydande ökning i vittringshastighet med citronsyra närvarande.Analyser visade också på en markant ökning i alkalinitet, vilket pekar på en möjlig användning avaccelererad silikatvittring för att motverka försurning så väl som CO2-utsläppen. Trots de låga pHnivåerna i början av experimentet (pH 2), fanns ingen antydan om att citronsyran påverkademöjligheterna för tillväxt av liv, vilket öppnar för möjligheten att påskynda vittringen ännu mer iexperiment för bio-accelererad silikatvittring. Slutsatsen för projektet blir att citronsyra kan användasför att accelerera silikatvittring, och därmed användas för att motverka de stigande koldioxidutsläppen.Dock har tidigare forskning visat att vittring av olivin kan leda till en ackumulation av tungmetaller,vilket har gjort att andra silikater såsom basalt har blivit populära. Därför behövs mer undersökning föratt fullt förstå hur kombinationen av organisk syra och mikrober påverkar vittring av dunit och andrasilikatmineral samt ackumulation av tungmetaller i lakvatten och celler.

M. Tech. (Chemical Engineering, Faculty of Engineering and Technology), Vaal University of Technology| / The co-existence of organic acids and toxic heavy metals in natural water creates harmful effects on human, plants and animals. Therefore, it is necessary to treat organic acids and toxic heavy metal contaminated wastewater prior to its discharge to the environment. The aim of this study was to apply co-treatment of industrial wastewater containing citric acid and toxic heavy metals in single and binary systems using photocatalysis process. The hydrothermal method was used to synthesise dandelion-like TiO2 structures. Modifications of the dandelion-like TiO2 by deposition of gold nanoparticles and immobilisation on calcium alginate were done using deposition precipitation and one-step encapsulation methods, respectively. Dandelion-like TiO2 and dandelion-like TiO2 immobilised on calcium alginate (Alg/TiO2) were used as photocatalysts for Cr(VI), Hg(II) and citric acid removal from water. The results showed that the production of dandelion-like TiO2 structures strongly depends on the reaction time and synthesis temperature as key process parameters. The characterisation of the dandelion-like TiO2 by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and Brunauer-Emmett-Teller (BET) revealed the crystal structure, morphology, chemical composition and surface area. It was found that the efficiency of photocatalytic process depends on the type of pollutants, initial pH of the solution, photocatalyst dosage, contact time, substrate initial concentration, UV wavelength and light intensity. The reduction efficiency of Cr(VI) ion and citric acid increased with decreasing the initial pH values and initial concentration. On the other hand, Hg(II) reduction efficiency increased with increasing the initial pH values and initial concentration. In a binary system, the reduction of Cr(VI) and Hg(II) was found to be faster than in the single and ternary systems. The relationship of the chemical reaction rate of Cr(VI), Hg(II) and citric acid were expressed by the pseudo-first-order kinetic equation. Addition of ferric ions to Cr(VI)-citric acid complex and Hg(II)-citric acid complex enhanced the reduction of Cr(VI) and Hg(II), a complete reduction was accomplished within 30 and 60 minutes (min) of irradiation time, respectively. The reduction efficiency of both Cr(VI) and Hg(II) in the presence of citric acid in a solution was still significant after four times of Alg/TiO2 reuse. These results indicated that the UV/TiO2 photocatalysis process can be considered as a suitable method to reach a complete reduction of Cr(VI) and Hg(II) in the presence of citric acid in a solution.

L’objectif de notre travail était d’étudier les bascules métaboliques chez Yarrowia li-polytica d’un métabolisme purement oxydatif vers l’accumulation de lipides puis à l’excretion d’acide citrique.Le développement d’un procédé D-stat et d’un mode de conduite fed-batch nous a permis, dans un premier temps, de quantifier les ratios N/C caractéristiques pour chacune des bascules étudiées. Nos résultats montrent que les ratios rN/rC critiques aux bascules métaboliques sont de 0,085 molN.Cmol-1 et de 0,018-0,022 molN.Cmol-1 pour l’accumulation de lipides et production de citrate, respectivement.L’analyse systémique des cultures réalisées nous a permis de mettre en évidence des mécanismes de co-régulation de certaines enzymes du métabolisme lipidique ainsi qu’une prépondérance de mécanismes post-transcriptionnels dans l’établissement des bascules étudiées.Enfin, l’utilisation de souches génétiquement modifiées au niveau de l’ATP citrate lyase, la malate déshydrogénase et de la glycérol-3-phosphate déshydogénase a permis d’évaluer l’impact de ces enzymes sur le métabolisme lipidique / This thesis aimed at studying the metabolic shifts in Yarrowia lipolytica from the pure oxidative metabolism to lipid accumulation and citric acid excretion.The development of a D-stat culture and of a monitoring fed-batch strategy allowed us to determine the N/C ratio characteristic for each of metabolic shifts. rN/rC ratio were determined equal to 0,085 molN.Cmol-1 and 0,018-0,022 molN.Cmol-1 for the lipid accumu-lation and the citric acid production, respectively.Systemic analysis of the cultivations showed coregulation phenomena among some enzymes of the lipidic metabolism and post-transcriptional modifications in the onset of the metabolic shifts.Finally, the impact of enzymes (ATP citrate lyase, malate dehydrogenase and gly-cérol-3-phosphate dehydrogenase) on the lipidic metabolism was evaluated through systemic analysis of 3 genetically modified strains

Dans ce travail de thèse, nous nous sommes intéressés au mélange de la farine de blé et du poly(acide lactique). La farine de blé, qui est composée principalement d'amidon, a été thermoplastifiée en extrudeur bivis par l'effet conjugué de la chaleur et du cisaillement en présence de plastifiants. Le poly(acide lactique) est, quant à lui, le polyester biodégradable le plus répandu à l'heure actuelle. Le mélange de ces deux phases est thermodynamiquement immiscible et peu compatible, différents leviers sont testés afin d'améliorer la qualité du mélange. Une première partie de ce travail repose sur la recherche de conditions optimales pour la transformation et le mélange des matières premières. L'extrusion bivis est utilisée à la fois pour plastifier l'amidon et pour assurer un bon mélange entre les phases. Le profil de vis et les différents équipements sont donc choisis en conséquence. Différents paramètres classiques de l'extrusion bivis sont étudiés : le profil de vis, le profil de température, le taux de remplissage… L'étude de la formulation, notamment des plastifiants utilisés pour la plastification de l'amidon mais également l'utilisation de compatibilisants pour améliorer l'interface amidon/PLA est traitée en deuxième partie. L'acide citrique est testé à la fois comme plastifiant et comme compatibilisant. Ces investigations nous ont permis de mettre au point différents grades intéressants répondant à des applications industrielles distinctes : injectabilité, souplesse, rigidité… / In this work, we have been interested in blending wheat flour and poly(lactic acid). Wheat flour, which is mainly constituted of starch, has been transformed with plasticizers in a twin-screw extruder with the effect of heat and shear. Poly(lactic acid) is the main biodegradable polyester in the world nowadays. These two phases are thermodynamically immiscible and not very compatible, different ways are tried to improve the blend quality. A first part of this work lies on the search of optimal conditions to transform and blend the raw materials. Twin-screw extrusion is used to pasticize starch and to ensure a good blending between the two phases. Screw design and different equipments have been chosen for this purpose. Classical twin-screw parameters have been studied: screw design, temperature profile, filling ratio… The study of the formulation, more particularly of plasticizers for starch plasticization but also of compatibilizers to improve starch/PLA interphase is tackled in a second part. Citric acid is tested as a plasticizer but also as a compatibilizer. These researches have allowed to develop interesting formulations for industrial applications: possibility of processing by injection-molding, flexibility, rigidity…

Neste trabalho, os sistemas de eletrocatalisadores platina-rutênio (PtRu/C) e platina-estanho (PtSn/C) suportados em carbono de alta área superficial XC72R (Cabot) foram preparados pela redução química de precursores metálicos em solução usando o ácido cítrico como agente redutor. Os eletrocatalisadores foram preparados em diferentes valores de pH, com o objetivo de obter as condições de sínteses mais otimizadas para cada um dos sistemas preparados. O método otimizado mostrou-se eficiente na redução e ancoragem de todos os metais presente em solução, sendo possível preparar tanto catalisadores com baixos teores de segundo metal (razão atômica entre Pt:M = 90:10) quanto catalisadores com altos teores de segundo metal (Pt:M = 50:50). Os eletrocatalisadores obtidos foram caracterizados por espectroscopia de energia dispersiva de raios X, difração de raios X e microscopia eletrônica de transmissão. A atividade frente a eletro-oxidação de metanol e etanol foi avaliada através de voltametria cíclica e cronoamperometria em célula eletroquímica. Para os catalisadores com melhores desempenhos eletroquímicos foram realizados experimentos em célula a combustível unitária alimentada diretamente por metanol ou etanol. O desempenho dos eletrocatalisadores preparados foi comparado com o desempenho dos eletrocatalisadores comerciais Pt50Ru50/C e Pt75Sn25/C da linha HP (High Performance) fornecidos pela E-TEK, considerados como referência nos estudos frente a eletro-oxidação de alcoóis. Para eletro-oxidação do metanol foram obtidos eletrocatalisadores com desempenho comparável ao E-TEK e para eletro-oxidação de etanol foram obtidos eletrocalisadores com desempenho superior aos catalisadores E-TEK. / In this work, platinum ruthenium (PtRu/C) and platinum tin (PtSn/C) electrocatalysts were prepared by a chemical reduction process using citric acid as reducing agent and high surface area Vulcan Carbon XC72R (Cabot) as supports. The PtRu/C and PtSn/C catalysts were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction and transmission electron microscopy. The electro-oxidation of methanol and ethanol were studied at room temperature by cyclic voltammetry and chronoamperometry. Single fuel cell experiments were carried at 90 °C and the performance of the homemade electrocatalysts prepared by citric acid method in optimized conditions were compared with commercial Pt50Ru50/C and Pt75Sn25/C E-TEK HP (High Performance) catalysts. For methanols electro-oxidation electrocatalysts with comparable E-TEKs catalysts performance were obtained and for ethanols electro-oxidation electrocatalysts with superior performance than E-TEKs electrocatalysts were obtained.

Resultados de pesquisas prévias tem encontrado potencial aumentado para a consolidação de enxertos ósseos mediante desmineralização do material enxertado e/ou das superfícies de consolidação. Entretanto há carência de embasamento apoiado em evidências biológicas do benefício de tal procedimento. Para testar esta hipótese, o tecido ósseo da calvária de cobaias (Cavia porcellus) foi exposto ao condicionamento por ácido cítrico durante 15, 30, 90 e 180 segundos (grupos teste). Quarenta e cinco discos ósseos de três milímetros de diâmetro foram removidos dos animais, dos quais 36 foram condicionados com ácido cítrico pH 1 a 50% e nove não receberam condicionamento (grupo controle). Sobre nove discos de cada grupo foram cultivados pré-osteoblastos MC3T3-E1 durante 24, 48 e 72 horas (três discos de cada grupo em cada tempo). Análises da morfologia celular, do número de células aderidas sobre as superfícies e da área de cobertura destas superfícies por préosteoblastos foram realizadas à microscopia eletrônica de varredura. Observou-se aumento do número de células aderidas às superfícies com o tempo, independentemente de haver condicionamento ou de seu tempo de aplicação. Entretanto, essa diferença só foi estatisticamente significante intragrupos (p<0,05) e quando comparados os períodos de 24 e 72 horas de incubação. A área de cobertura das superfícies por células aumentou significantemente com o tempo somente nos grupos teste, também entre os períodos de incubação de 24 e 72 horas (p<0,01). O grupo controle apresentou-se com 50% ou menos de área de cobertura superficial em relação aos demais. A duração de aplicação do ácido não interferiu significantemente nesse parâmetro de avaliação, mas nos grupos 15 e 30, a área de recobrimento ósseo mais do que triplicou às 72 horas em relação às 24 horas (p<0,01), com cerca de 70% das superfícies cobertas por células, contra 30% no grupo controle. Conclui-se que a desmineralização óssea nos tempos de condicionamento estudados propicia um substrato sobre o qual as células pré-osteoblásticas adquirem morfologia compatível com estágio de diferenciação mais avançado, promovendo maior cobertura de área, o que aumenta o potencial para deposição de novo osso sobre essas superfícies em comparação ao tecido não condicionado. / Results of previous research has found increased potential for the consolidation of bone grafts by demineralization of the graft material and / or areas of consolidation. However there is a lack of foundation supported by biological evidence of benefits from such procedures. To test this hypothesis, the bone tissue of the calvaria of guinea pigs (Cavia porcellus) were exposed to conditioning by citric acid for 15, 30, 90 and 180 seconds (test group). Forty-five bone disks measuring three millimeters in diameter were removed from the animals, of which 36 were conditioned with citric acid pH 1 to 50% and nine did not receive conditioning (control group). About nine disks in each group were pre-cultured with MC3T3- E1 osteoblasts for 24, 48 and 72 hours (three discs of each group at each time point). Analysis of cell morphology, number of cells attached on the surface and the coverage area of these surfaces by pre-osteoblasts were performed on scanning electron microscopy. There was na increase in the number of cells attached to surfaces over time, regardless of conditioning or application time. However, this difference was not statistically significant intra-group (p <0.05) when comparing the periods of 24 and 72 hours of incubation. The coverage area of the surfaces of cells increased significantly with time only in the test groups, also among the incubation periods of 24 and 72 hours (p <0.01). The control group presented with 50% or less of surface area coverage compared to the other. The duration of application of the acid did not affect significantly this parameter of evaluation, but in groups 15 and 30, the bonearea covered more than tripled from 24 to 72 hours (p <0.01), with about 70 % of the area covered by cells, versus 30% in the control group. It was concluded that bone demineralization in the studied conditioning times provides a substrate on which cells acquire pre-osteoblastic morphology compatible with more advanced stage of differentiation, promoting greater coverage area, which increases the potential for deposition of new bone on these surfaces compared to the tissue-air basis.